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With the continuous integration and miniaturization of electronic devices, the heat transfer of the electronic devices continues to surge. This means that thermal management equipment with higher heat flux cooling capacity is required to maintain its normal operation. This paper systematically reviews the progress of spray cooling. In the first part, the thermal dissipation mechanism of spray cooling in the non-boiling regime and boiling regime are summarized, and the correlation formula of heat transfer is summarized. In the second part, the influencing factors of various parameters of the nozzle are summarized, the experimental research and numerical simulation research are summarized separately, and some means and methods to strengthen heat transfer are listed. In the third part, we summarize the current application research of spray cooling in some hot new fields, including electronic technology, aerospace, biomedicine, battery safety, etc. The research prospects and challenges in these fields are highlighted. This research provides a timely and necessary study of spray cooling. [ABSTRACT FROM AUTHOR]

Kingfishers during rain remain dry even standing still on a branch, because of converting normally vertical impacting to horizontal droplets transport, and bioinspired applications with the mixed-wettability surface exhibit the maximum horizontal transport distance by up to 6.2 D 0. [Display omitted] Kingfishers stand on a branch, and raindrops tumble translationally from feathers during raining, enlightening functional surfaces design and liquid transport control. Far-ranging studies on oriented transportation are confined to vertical impacting, which is, to date, in-depth philosophy of horizontal droplets transport on motionless surface deems to be rather serviceable. This study, employed mixed-wettability surface inspired by kingfishers' feather, occurs on directional transportation issues, such as the synergies of wettability-controlled, driving force and transportation capability. Here we conduct both experimental testing and CFD-aided numerical modelling to reproduce the asymmetric bouncing and directional transport phenomena. We found that the anisotropic surface manipulates to convert normally vertical impacting to horizontal droplets transport. Law of the thrown droplet, on the other hand, is predominated by the wettability-controlled surface, while the coexistence of contact angle difference and surface offset location cooperatively dictates the intensity and patterns of the thrown droplet. Of all these factors, the post-optimized surfaces are designed first and then the regime map of transportation pattern is elaborated. Results manifest that the elements induce the maximum horizontal transport distance by up to 6.2 D 0 , and first desorption time is only 7.8 ms. The findings shed light on engineering design principles that can pave the way for novel applications in anti-icing, lubrication, and spray cooling. [ABSTRACT FROM AUTHOR]

Micro-structured surfaces can affect heat transfer mechanisms because of enlarged specific surface areas. However, employing the Leidenfrost effect during liquid nitrogen (LN2) droplet cooling of a heated micro-structured surface possessing a fin with a spacing much smaller than the diameter of the droplet has not yet been explored. In the present work, a direct numerical simulation (DNS) is carried out to investigate heat transfer mechanisms of the LN2 droplet, whose diameter is sufficiently larger than the structured spacing of fin, impinging on a micro-structured surface with variable velocities. For a comparative study, a smooth surface is also employed in numerical simulations. The spreading mechanisms and vaporization behavior of the droplet along with liquid film morphology at various conditions are investigated. Results show that a smaller fin size inhibits LN2 in entering into the grooves between the fins and left the surface untouched by the droplet completely, and eventually, a thinner liquid film is spread out in contrast to the smooth surface. Notably, at a low Weber number, the droplet can be shrunk or even rebounded away from the wall after impinging on the wall. The fastest vaporization behavior for both surfaces, namely smooth and micro-structured, is obtained at a Weber number of 180. Additionally, an effective heat transfer upon the micro-structured surface is observed at a low impinging velocity of the droplet. [ABSTRACT FROM AUTHOR]

As one of the most promising thermal management solutions, spray cooling has the advantages of high heat-transfer coefficient and maintaining a low temperature of the cooling surface. By summarizing the influential factors and practical applications of spray cooling, the current challenges and bottlenecks were indicated so as to prompt its potential applications in the future. Firstly, this paper reviewed the heat-transfer mechanism of spray cooling and found that spray cooling is more advantageous for heat dissipation in high-power electronic devices by comparing it with other cooling techniques. Secondly, the latest experimental studies on spray cooling were reviewed in detail, especially the effects of spray parameters, types of working fluid, surface modification, and environmental parameters on the performance of cooling system. Afterwards, the configuration and design of the spray cooling system, as well as its applications in the actual industry (data centers, hybrid electric vehicles, and so on) were enumerated and summarized. Finally, the scientific challenges and technical bottlenecks encountered in the theoretical research and industrial application of spray cooling technology were discussed, and the direction of future efforts were reasonably speculated. [ABSTRACT FROM AUTHOR]

Functional surfaces with controllable droplet spreading and breakup dynamics have received widespread attention in self-cleaning, spraying cooling, 3D printing, etc. The arrangement of a microstructure is of great value for the design of functional surfaces. Here, we numerically investigated the droplet impact dynamics on the sparse hydrophobic pillar surface with OpenFOAM. We investigated the effect of Weber number, impact locations, and pillar spacing. Outcomes are most strongly influenced by impact locations, pillar pitch, Weber number, and eight spreading patterns were registered, including circle, square, cross-shaped, Chinese knot, octopus, ellipse, dumbbell, and hexagram. Furthermore, a set of theoretical models were developed for the spreading pattern transition to predict the critical Weber number for different droplet spreading patterns. The breakup dynamics of droplets strongly depend on the spreading patterns and the impact location, which can emit secondary droplets in specific directions. The cross pattern significantly reduces the threshold for secondary droplet generation. The results obtained some essential characteristics for droplet impinging sparse hydrophobic pillar surface, which could provide valuable insights into functional surface design, fluidic-based systems and applications. [ABSTRACT FROM AUTHOR]

In recent years, global automotive industries are going through a significant revolution from traditional internal combustion engine vehicles (ICEVs) to electric vehicles (EVs) for CO2 emission reduction. Very similarly, the aviation industry is developing towards more electric aircraft (MEA) in response to the reduction in global CO2 emission. To promote this technology revolution and performance advancement, plenty of electronic devices with high heat flux are implemented on board automobiles and aircraft. To cope with the thermal challenges of electronics, in addition to developing wide bandgap (WBG) semiconductors with satisfactory electric and thermal performance, providing proper thermal management solutions may be a much more cost-effective way at present. This paper provides an overview of the thermal management technologies for electronics used in automobiles and aircraft. Meanwhile, the active methods include forced air cooling, indirect contact cold plate cooling, direct contact baseplate cooling, jet impingement, spray cooling, and so on. The passive methods include the use of various heat pipes and PCMs. The features, thermal performance, and development tendency of these active and passive thermal management technologies are reviewed in detail. Moreover, the environmental influences introduced by vibrations, shock, acceleration, and so on, on the thermal performance and reliability of the TMS are specially emphasized and discussed in detail, which are usually neglected in normal operating conditions. Eventually, the possible future directions are discussed, aiming to serve as a reference guide for engineers and promote the advancement of the next-generation electronics TMS in automobile and aircraft applications. [ABSTRACT FROM AUTHOR]

Summary: Spray cooling has a wide application prospect in the heat dissipation of high‐power devices due to its excellent heat transfer performance and low demand for working medium. In this work, an experimental setup was built to investigate the heat transfer characteristics of the deionized water spray cooling in the non‐boiling zone. Copper surfaces with different roughness conditions, as well as superhydrophilic/hydrophobic surfaces, were introduced to study the influence of surface property on cooling performance. Results show that no prominent change in heat transfer coefficient occurs due to the variation of roughness in the working conditions discussed. Furthermore, the superhydrophilic/hydrophobic surfaces experience a maximum reduction of 9.6% and 9.2% in heat transfer coefficient, respectively, compared with that of a smooth surface. [ABSTRACT FROM AUTHOR]

The production of electricity from photovoltaic panels has experienced significant developments. To manage the energy flows introduced into the electricity grid, it is necessary to estimate the productivity of PV panels under the climatic conditions. In this study, a photovoltaic panel is modelled from thermal and electrical points of view to evaluate electrical performance and identify the temperature distribution in the layers. The analysis performed is time dependent and the problem is solved using the finite difference technique. A methodology is introduced to estimate the cloudiness of the sky, which affects radiative heat exchange. The calculation method is validated using experimental data recorded in a laboratory of the University of Calabria. Temperature and electrical power are predicted with RMSE of 1.5–2.0 °C and NRMSE of 1.2–2.1%, respectively. The evaluation of the temperature profile inside the panel is essential to understand how heat is dissipated. The results show that the top surface (glass) is almost always colder than the back of the panel, despite being exposed to radiation. In addition, the upper surface dissipates more heat power than the lower one. Cooling systems, such as spray cooling, work better if they are installed on the back of the panel. [ABSTRACT FROM AUTHOR]

Droplet impact on a hot substrate under an electric field is fundamental and crucial for electrospray cooling. However, the involved thermal–electric coupling impact electrohydrodynamic has not been well understood. In this study, the effects of an electric field on the droplet impact behavior in different thermal regimes and the subsequent dynamic mechanisms were experimentally investigated. The results showed that the vertical electric field would result in an upward liquid ejection in the film evaporation regime. In the nucleate boiling regime, the liquid pinch-off phenomenon was observed. In addition, the droplet evaporation rate was increased by approximately 23% with an electric field of 6 kV/cm. In the film boiling regime, both the residence time and bounce-off droplet height were significantly increased. The various impact phenomena were mainly explained by the competition between electrostatic and capillary pressures. The comprehensive effects of surface free charges and temperature variation on the droplet surface tension coefficient were discussed. Moreover, according to the thermal analysis, the heat transfer in the film boiling regime with an electric field was enhanced by approximately 137%. This work contributed to the development of the droplet impact dynamics under the coupling temperature and electric fields and demonstrated great promise for the electric field for thermal-fluid manipulation. [ABSTRACT FROM AUTHOR]

This article presents improvements to bio-oil production systems by using a spray condenser, which was developed from previous work. Napier grasses (NG), sugarcane leaves (SL), and rubber leaves (RL) were used as raw materials in order to produce bio-oil. The indirect contact heat exchanger called conventional condenser and direct contact heat exchanger called spray condenser were employed while the bio-oil and the ethanol were also applied as an absorber in the spray condenser. The circulating fluidized bed reactor was employed to produce the bio-oil by using a fast pyrolysis process. The condition generating the highest yield of the bio-oil production whether the conventional condenser or the spray condenser was 60 kg/h of feed rate and 480 °C of bed temperature. From the result of the bio-oil production, it was found that the highest yields of bio-oil production from NG, SL, and RL using conventional condenser were 43.73%wt, 49.47%wt, and 37.00%wt, respectively. The highest yield of bio-oil production from NG, SL, and RL performing on spray condenser and the use of ethanol as absorber were 55.67%wt, 62.53%wt, and 44.60%wt, respectively. The use of the spray condenser and use of the ethanol as absorber can improve the properties of bio-oil such as heating value and can also increase the yield of bio-oil, but the viscosity of bio-oil was increased. Furthermore, the use of spray condenser can increase the efficiency of energy conversion and can decrease the cost production of bio-oil production; it can also solve problems of dirt from volatiles or droplets in the bio-oil which were adhesive in the recirculating blower in case the system returned non-condensable gas (NGC) to the bio-oil production process. [ABSTRACT FROM AUTHOR]

In this study, influence factors of liquid nitrogen spray cooling, including the parameters of the nozzle, the area of the heat sink, and the flow rate of liquid nitrogen, were investigated experimentally. On the basis of experimental data, experimental dimensionless correlations were obtained. It was shown that the error of correlation with only the Reynolds number (Re) and Prandtl number (Pr) was too low to predict the Nusselt number (Nu). With Re, Pr, the boiling number (Bg), and the Jacob number (Ja), while the error of correlation decreased, the experimental data deviated considerably from the fitting line by the correlation, which was still not suitable for prediction. The reasons for the experimental data's deviation were that the uniformity of the droplet distribution varied with the nozzle aperture, a change in the heat exchange area resulted in the formation of a local gas film, the droplet splash caused by a change in the flow rate influenced the heat exchange. The correlation obtained with Re, Pr, Bg, Ja, and the effective of spray mass flow flux η which was determined as the ratio of the liquid nitrogen mass flow rate involved in heat transfer to the uniform mass flow on the heat surface could be used to accurately predict Nu. [ABSTRACT FROM AUTHOR]

The heat transfer characteristics of air-atomized water spray cooling on the hot metallic surface are presented and discussed in this paper. The controlling parameters mainly investigated are air pressure and spray height. The effects of these parameters on the important thermal characteristics such as interfacial heat transfer coefficient, cooling rate, and wetting layer evolution attained by experiment and inverse heat conduction method. The value of interfacial heat transfer coefficient is proportional to the air pressure and inversely proportional to the spray height. As the air pressure is 0.2 MPa, and the spray height is 40 mm, the maximum cooling rate is 85.08 ℃/s. There is no film boiling stage under this condition. At the spray height is 80 mm, and air pressure is 0.3 MPa, the maximum cooling rate is 62.6 ℃/s. In addition, transition boiling and nucleate boiling always exist, but their retention time is different under different conditions. The temperature-dependent interfacial heat transfer mechanism of air-atomized water spray cooling is explored according to the thermal characteristics and photographs taken by the high-speed camera. The results show that air pressure and spray height both have an influence on the interfacial heat transfer. [ABSTRACT FROM AUTHOR]

The feasibility of coupled computational fluid dynamics (CFD) and finite element (FE) simulations to aid the planning of fire intervention tactics and the effectiveness of structural cooling during firefighting were investigated. Water sprays, generated using fire monitors, were characterized using bucket tests and the results were used for calibrating the CFD spray model. The cooling ability of the sprays was measured experimentally by applying them onto a fire exposed steel beam. The experimental results showed that water application produces a sudden drop in steel temperatures and after 10–15 s, no significant further reduction in temperature was observed. The CFD-FE coupling was performed using the adiabatic surface temperature method, extended here to include the cooling by water droplets. The coupled CFD-FE model was validated using the experimental data and applied to simulate the intervention to a developing warehouse fire, showing how an attempt to cool the structure reduces the temperatures but does not stall the fire-spread. In fact, the intervention -induced vapor generation was found to enhance the flow of hot gases and accelerate the fire-spread if the water resources are inadequate. Thermal and stress analyses of the cooled and uncooled truss beams were performed, showing how the spray cooling halted the truss mid-span deformation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oil-covered dielectrowetting substrate is used to study impact dynamics of a water droplet. • Retraction dynamics of droplet are analyzed based on force balance. • Thickness of silicone oil film can affect friction loss between water droplet and substrate. • The retraction rate of droplet decreases with a decrease in the wettability of substrate. Droplet impacting on solid or liquid film is a ubiquitous phenomenon in relevant processes such as spray cooling and inkjet printing on primer layers. In this study, the dynamics of water droplets impacting a solid substrate covered by a silicon oil film is investigated under the influences of the surface wettability of the dielectrowetting substrate (69.3°-117.4°) and the thickness of the silicon oil film (7.79–21.8 μm) at We = 6.81. A phase diagram is established, which reflects the relationships between the impact dynamic behavior, equilibrium contact angle, and the oil film thickness. The maximum spreading factor β max and maximum out-of-plane height H max / D 0 for rebound of sub-droplet behaviors was smaller than 13 % and greater than 3 times than those droplet deposition behaviors, respectively. Finally, the retraction dynamics of the droplet after reaching its maximum spreading diameter is analyzed and discussed based on retraction rate γ w = v r / D max = σ w (c o s θ rmin - c o s θ eq) / f k D max through the force balance at the three-phase contact line. Results of the study indicate that the surface wettability of the dielectrowetting substrate and thickness of the silicon oil film significantly affect the impact dynamics of water droplets on a solid substrate covered by the silicone oil film, especially in the retraction stage. This study sheds new light on controlling the dynamic impact of the droplets on silicon oil films, which is of importance to the control or optimization of processes such as inkjet printing on a primer layer. [ABSTRACT FROM AUTHOR]

• Condensable Particulate Matter (CPM) can be removed in flue gas scrubbing process. • Part of CPM is removed through converting into particles during flue gas scrubbing. • Dissolution and condensation of CPM precursors contribute to its removal. • Some components in spray droplets can become CPM through evaporation. • A demister installed at the outlet of a scrubber contribute to the removal of CPM. Condensable particulate matter (CPM) is a kind of pollutant that is gaseous in stack and granular after being discharged into atmosphere. Existing studies have shown that CPM can be removed by wet flue gas desulfurization (WFGD) synergistically, but the mechanism is unclear. In this paper, a simulated WFGD experimental system was established, and the transformation and removal mechanism of CPM in the process of flue gas spray cooling was explored by adjusting experimental parameters. The research shows that the process can realize removal of CPM, which is reflected in two aspects: part of CPM is converted into filterable particulate matter (FPM), and part of CPM is absorbed and deposited by spraying liquid. The mechanism involved is condensation and dissolution, and dissolution plays a major role. There may be two ways to convert CPM into FPM in scrubber: one is FPM formed by homogeneous or heterogeneous condensation of CPM gaseous precursors; the other is that after the spray droplets absorb CPM, FPM formed by those very small droplets of spraying liquid. The demister at the outlet of the scrubber can reduce the discharge concentration of CPM and FPM. [ABSTRACT FROM AUTHOR]

This study introduces a methodology to compute spray cooling in the nucleate boiling regime. It examines the cooling of a horizontal circular tube, although the approach is not restricted to this geometry. While numerous investigations have considered nucleate boiling in the past, these are usually restricted to spray impingement onto a flat plate and not onto more complex surfaces. Furthermore, most prior studies are highly empirical in nature. The present study circumvents both of these restrictions. On the one hand, with more complex surfaces additional factors must be considered, in particular the influence of the local impingement angle on the number flux of impinging drops. On the other hand, the heat transfer for single droplets is first computed using existing theoretical solutions and then the principle of superposition is used to compute the global heat transfer from the surface over which the spray impinges. Accompanying this computation, a drop size distribution is specified in order to also investigate the influence of not only one representative drop size, but also the variance of drop size distribution on the heat transfer, an influence seldom reported on. Furthermore, the probability of drop-drop interaction on the surface has been estimated and the heat transfer correspondingly adjusted. This approach of computing total net heat transfer on a surface is first validated using available measurements in which the heat transfer in the nucleate boiling regime from a flat plate were used for comparison. The heat transfer from a circular tube was then computed as a function of mass flow rate, drop size distribution (expectation and variance) and wall temperature. Conditions for maximum heat transfer, corresponding to the critical heat flux, were identified. In all cases the net heat transfer was limited by the onset of drop-drop interaction on the substrate, i.e. the net coverage of liquid on the surface. The results of these parametric studies indicate clearly how the mass flow rate can be adjusted to maximize heat transfer while avoiding excess fluid consumption. Furthermore, the Sauter mean diameter is shown to be an appropriate drop size to use, if no further information is available concerning the size distribution. • A non-empirical methodology to computing heat transfer in the nucleate boiling regime. • Spray cooling computation taking into account explicitly the size distribution of drops. • Insight into spray conditions, which maximizes heat transfer while minimizing liquid consumption. • Consideration of highly varying number density of drops when cooling a surface of complex geometry. [ABSTRACT FROM AUTHOR]

Spray cooling is an efficient cooling technology with high heat dissipation, and has been extensively utilized in various industry areas. The interaction mechanism between the spray droplet and environmental space with high pressure and temperature is extremely complex, especially with non-condensable gas. In this paper, a pseudopotential multicomponent multiphase lattice Boltzmann model for droplet migration with non-condensable gas in high temperature and pressure was proposed. The mechanism of transfer characteristics for droplet in steam were studied. It is found that the mass transfer of droplet is controlled by density and condensation, droplet growth is mainly impacted by density at initial stage, and in later period, the growth is greatly weakened by the condensation suppression of non-condensable gas. The calculated results show that when Fo > 0.4, mass transfer is significantly decreased. Heat transfer is also affected by non-condensable gas, and 2% gas declines the droplet heat transfer rate by about 10%. It is also found that the mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content inside and outside the droplet. The results can be used for development of spray cooling model, and have positive guiding significance for optimizing spray cooling system. • A heat and mass transfer model of droplet and steam with non-condensable is established. • The mechanism of transfer characteristics for droplet in steam were studied. • The mass transfer of droplet is controlled by density and condensation in different stage. • The mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content. [ABSTRACT FROM AUTHOR]

Cooling systems often rely on numerical calculations with precise heat transfer boundary conditions (HTBC), usually expressed as average values. The value of the average HTBC depends on the area in which they are determined. The paper presents a new approach showing the influence of the choice of the method of supplying liquid onto the surface on the non-uniformity of energy transfer from the cooled surface, which is important in the selection of the determination domain on the HTBC. The tests were carried out for two full-cone nozzles with different spray angles and two materials with different thermal properties. The local and average heat fluxes were determined for various distances of the nozzles from the surface and various liquid supply pressures. Cooling capacity, unevenness of energy transfer from the surface and quenching characteristics were evaluated and assessed using cooling curves. The study concludes that adopting HTBC based on average heat flux variation does not cause a significant error in the assessment of energy transfer during cooling with a nozzle with spray angle of 60° for EN 1.4845 steel. However, for Inconel and a nozzle with spray angle of 45°, the noticeable non-uniformity requires the application of a local HTBC. • Unevenness the spray cooling process. • Possibilities of using the average heat transfer boundary condition. • Recommendations for the use of local heat transfer boundary condition. [ABSTRACT FROM AUTHOR]

• Nano-droplets impinging on cylindrical wall is investigated. • Four modes of droplets impacting the cylindrical wall are reported. • Effects of droplet size, initial velocity, impact position and wall wettability on droplet dynamics are analyzed. • Physical mechanism of droplet impacting the cylindrical wall is revealed. The impact of droplets on solid walls is the primary behavior in spray cooling, seawater desalination, self-cleaning, and other technological processes. Based on the molecular dynamics (MD) method, the morphological evolution characteristics of nanodroplets impinging on the copper cylinder wall are studied. The effects of droplet size, initial velocity, impact position, and wall wettability on nanodroplet dynamics are analyzed. The results indicate that a single nanodroplet impacting on a nanocylinder exhibits four distinct impact modes: spread-partially wrapped-deposition (SPD), spread-completely wrapped-deposition (SCD), spread-completely wrapped-splitting-deposition (SCSD), and spreading-partially wrapped-splitting-deposition (SPSD). The trend of the influence of initial velocity and droplet size on the impact mode is similar. As the initial velocity and droplet size increase, the droplet's kinetic energy and inertia force increase, successively exhibiting the SPD, SCD, and SCSD modes. The trend of the influence of impact position and wall wettability on the droplet impact mode is similar. When the impact eccentricity distance is small, and the wall is highly hydrophilic, it exhibits the SCD mode. With increasing impact eccentricity and enhanced wall hydrophobicity, the adhesion force between the droplet and the cylinder wall decreases, making the droplet less likely to be captured and more prone to splitting, exhibiting the SPSD mode. The change in droplet centroid height and mean square displacement could predict whether the droplet undergoes a splitting mode, and its influence is most significant at the impact position. Constrained by the cylindrical wall, the droplet impacts radially and spreads primarily in that direction. With the enhancement of wall hydrophilicity, the migration region of the three-phase contact line expands, and the droplet spreading transforms into synchronous development along the radial and axial directions. The research results can enrich the dynamic mechanism of micro-nano scale droplet impact and provide potential guidance for optimizing relevant technologies. [ABSTRACT FROM AUTHOR]

• The high temperature cylindrical surface cooled by spray was simulated. • The axial tilt spray can effectively solve the hot spot problem and improve the cooling uniformity. • The temperature and wall heat flux distribution of the cooling area under different spray angles were analyzed. • Only when the spray boundary is tangent to the cylindrical surface (H = 70 mm), the circumferential tilt Angle has a positive effect on the wall heat flux. In the hot-rolled seamless steel tube production process, quenching is a crucial process. Spray cooling technology can achieve uniform and high-intensity cooling during the steel tube production process, which is expected to improve production efficiency and product quality. This study performs numerical simulations to explore the effects of spray cooling on a heated cylindrical surface. The influence of spray angles is focused on the cooling efficiency, while the spray height is also found to be another crucial variable. In the simulation, the axial tilt angle and circumferential tilt angle vary between 0 ∼ 30°, and the spray height changes within 50 ∼ 150 mm. A high-temperature steel tube is selected as the test object. The detailed analysis is discussed on the variations in the cooling area and wall heat flux under different spray angles. The results indicate that the axial tilt angle can effectively solve the hot spot. With an increase in axial tilt angle and spray height, the cooling area expands gradually. Meanwhile, the wall heat flux decreases with an increasing axial tilt angle and spray height. However, when the spray height is too high (H > 100 mm), the excessive axial tilt angle will have a negative influence on the wetting region. Although the circumferential tilt angle greatly changes the shape of the cooling area, it has a smaller effect on the size. It is worth noting that the spray boundary is just tangent to the cylindrical surface at H = 70 mm. Only at this moment does the circumferential inclined spraying exhibit a positive influence on the wall heat flux. [ABSTRACT FROM AUTHOR]

• A new model established to simulate the entire electrospray cooling process. • MPCMS can significantly improve cooling characteristics at low wall temperatures. • Increasing applied voltage can improve heat transfer characteristics. • Cooling performance is the best when inlet temperature is close to phase change peak. Electrospray cooling (ESC) technology is increasingly emphasized due to its efficient heat removal capacity, minor coolant consumption and accurate thermal control. Previous articles had focused on either experimental exploration on ESC performance or numerical methods on solitary electrospray such as Volume of Fluid [1] , Boundary Element Method [2] and Lagrangian model [3]. However, there is no comprehensive model characterizing the whole ESC process. Moreover, there was barely investigation on ESC enhancement using phase change materials (PCM). Herein, this study has bridged this gap by developing a new comprehensive model to explore the ESC enhancement with microencapsulated phase change material slurry (MPCMS), and conducted experiment to verify it. The influences of applied voltage, mass concentration and inlet temperature of MPCMS on the ESC were discussed. Results revealed that MPCMS offered superior cooling performance during melting process due to latent heat absorption compared to deionized water. Nevertheless, as wall temperatures increased, the deposition, higher viscosity and lower thermal conductivity of MPCMS would compromise cooling efficiency. Moreover, higher applied voltage enhanced cooling performance by increasing droplet velocity, and reducing the possibility of droplet rebound. When the inlet temperature approached the peak melting temperature, the convective heat transfer coefficient reached its maximum. [ABSTRACT FROM AUTHOR]

Background: In contrast to traditional impact-based testing, the Dynamic Tensile Tear Test (DT3) has shown great potential to characterise high-grade pipeline steels as it mimics the in-field pipeline conditions. However, material characterisation using the DT3 method has only been performed at room temperature and lower-shelf characterisation has not yet been investigated.This study investigates a solution to perform low-temperature characterisation and analyse dynamic brittle fracture behaviour using the DT3 setup.A large-surface spray cooling system using liquid nitrogen was constructed and implemented onto the DT3 system. Cooling performance and temperature uniformity were assessed using thermocouples across a large surface area up to 412 cm2 (2 × 206 cm2). Numerical validation was performed through Finite Element (FE) analysis using the Modified Bai-Wierzbicki (MBW) material model. A combined stress–strain criterion was used to take into account cleavage failure.Temperatures down to -125 °C were reached using the spray cooling system and a fracture tests was performed at -80 °C. The obtained data and resulting fracture surface indicated clear brittle fracture behaviour. An average crack velocity of 152 m/s was measured, which is in the same order of magnitude associated with crack velocities observed in large-scale testing.The constructed spray cooling system proved to be capable of cooling a large volume down to cryogenic temperatures while achieving acceptable temperature uniformity. Lower-shelf characterisation of X70 grade pipeline steel was achieved using the DT3 method and a good correlation was obtained between numerical data and experimental observations.Objective: In contrast to traditional impact-based testing, the Dynamic Tensile Tear Test (DT3) has shown great potential to characterise high-grade pipeline steels as it mimics the in-field pipeline conditions. However, material characterisation using the DT3 method has only been performed at room temperature and lower-shelf characterisation has not yet been investigated.This study investigates a solution to perform low-temperature characterisation and analyse dynamic brittle fracture behaviour using the DT3 setup.A large-surface spray cooling system using liquid nitrogen was constructed and implemented onto the DT3 system. Cooling performance and temperature uniformity were assessed using thermocouples across a large surface area up to 412 cm2 (2 × 206 cm2). Numerical validation was performed through Finite Element (FE) analysis using the Modified Bai-Wierzbicki (MBW) material model. A combined stress–strain criterion was used to take into account cleavage failure.Temperatures down to -125 °C were reached using the spray cooling system and a fracture tests was performed at -80 °C. The obtained data and resulting fracture surface indicated clear brittle fracture behaviour. An average crack velocity of 152 m/s was measured, which is in the same order of magnitude associated with crack velocities observed in large-scale testing.The constructed spray cooling system proved to be capable of cooling a large volume down to cryogenic temperatures while achieving acceptable temperature uniformity. Lower-shelf characterisation of X70 grade pipeline steel was achieved using the DT3 method and a good correlation was obtained between numerical data and experimental observations.Methods: In contrast to traditional impact-based testing, the Dynamic Tensile Tear Test (DT3) has shown great potential to characterise high-grade pipeline steels as it mimics the in-field pipeline conditions. However, material characterisation using the DT3 method has only been performed at room temperature and lower-shelf characterisation has not yet been investigated.This study investigates a solution to perform low-temperature characterisation and analyse dynamic brittle fracture behaviour using the DT3 setup.A large-surface spray cooling system using liquid nitrogen was constructed and implemented onto the DT3 system. Cooling performance and temperature uniformity were assessed using thermocouples across a large surface area up to 412 cm2 (2 × 206 cm2). Numerical validation was performed through Finite Element (FE) analysis using the Modified Bai-Wierzbicki (MBW) material model. A combined stress–strain criterion was used to take into account cleavage failure.Temperatures down to -125 °C were reached using the spray cooling system and a fracture tests was performed at -80 °C. The obtained data and resulting fracture surface indicated clear brittle fracture behaviour. An average crack velocity of 152 m/s was measured, which is in the same order of magnitude associated with crack velocities observed in large-scale testing.The constructed spray cooling system proved to be capable of cooling a large volume down to cryogenic temperatures while achieving acceptable temperature uniformity. Lower-shelf characterisation of X70 grade pipeline steel was achieved using the DT3 method and a good correlation was obtained between numerical data and experimental observations.Results: In contrast to traditional impact-based testing, the Dynamic Tensile Tear Test (DT3) has shown great potential to characterise high-grade pipeline steels as it mimics the in-field pipeline conditions. However, material characterisation using the DT3 method has only been performed at room temperature and lower-shelf characterisation has not yet been investigated.This study investigates a solution to perform low-temperature characterisation and analyse dynamic brittle fracture behaviour using the DT3 setup.A large-surface spray cooling system using liquid nitrogen was constructed and implemented onto the DT3 system. Cooling performance and temperature uniformity were assessed using thermocouples across a large surface area up to 412 cm2 (2 × 206 cm2). Numerical validation was performed through Finite Element (FE) analysis using the Modified Bai-Wierzbicki (MBW) material model. A combined stress–strain criterion was used to take into account cleavage failure.Temperatures down to -125 °C were reached using the spray cooling system and a fracture tests was performed at -80 °C. The obtained data and resulting fracture surface indicated clear brittle fracture behaviour. An average crack velocity of 152 m/s was measured, which is in the same order of magnitude associated with crack velocities observed in large-scale testing.The constructed spray cooling system proved to be capable of cooling a large volume down to cryogenic temperatures while achieving acceptable temperature uniformity. Lower-shelf characterisation of X70 grade pipeline steel was achieved using the DT3 method and a good correlation was obtained between numerical data and experimental observations.Conclusions: In contrast to traditional impact-based testing, the Dynamic Tensile Tear Test (DT3) has shown great potential to characterise high-grade pipeline steels as it mimics the in-field pipeline conditions. However, material characterisation using the DT3 method has only been performed at room temperature and lower-shelf characterisation has not yet been investigated.This study investigates a solution to perform low-temperature characterisation and analyse dynamic brittle fracture behaviour using the DT3 setup.A large-surface spray cooling system using liquid nitrogen was constructed and implemented onto the DT3 system. Cooling performance and temperature uniformity were assessed using thermocouples across a large surface area up to 412 cm2 (2 × 206 cm2). Numerical validation was performed through Finite Element (FE) analysis using the Modified Bai-Wierzbicki (MBW) material model. A combined stress–strain criterion was used to take into account cleavage failure.Temperatures down to -125 °C were reached using the spray cooling system and a fracture tests was performed at -80 °C. The obtained data and resulting fracture surface indicated clear brittle fracture behaviour. An average crack velocity of 152 m/s was measured, which is in the same order of magnitude associated with crack velocities observed in large-scale testing.The constructed spray cooling system proved to be capable of cooling a large volume down to cryogenic temperatures while achieving acceptable temperature uniformity. Lower-shelf characterisation of X70 grade pipeline steel was achieved using the DT3 method and a good correlation was obtained between numerical data and experimental observations. [ABSTRACT FROM AUTHOR]

Heat exchangers are very crucial and easily available devices in chemical industries. Shell and tube heat exchanger are the most common amongst them. Mild steel, on other hand, is used as the basic structural material for manufacturing heat exchangers. Water is also considered as a very important environmental resource of current date. The present study focuses on synthesis of electroless Ni–P–Cu-coated mild steel utilizing the wastewater for heat transfer analysis. An inbuild laboratory-scale technique of spray cooling has been utilized for analysing the heat transfer study. The surface morphology and phase structure analysis has been carried forward using SEM and XRD results. The microhardness study of the sample has been analysed and reported. The material corrosion behaviour has also been reported stating the temperature 400 °C ideal for heat treatment maintaining corrosion resistance of the composite coating at the given scenario. Finally, the heat transfer coefficient study reveals a result of 3.69 KW/m2/ K for the optimized sample of Ni–P–Cu–1. The process aims to reutilize and retreat the wastewater in the most productive way following the concept of sustainability respectively. [ABSTRACT FROM AUTHOR]

• The transient liquid film deposition of cryogen spray cooling was investigated. • The CAJ enhanced the CAJ-to-spray mixing and mitigated the film thickness. • The CAJ-to-spray interaction induced CRVP that caused asymmetric film coverage. • The CRVP permitted fast evaporation with dominant CAJ at the spray-periphery while permitting fast evaporation with dominant spray at the spray-core. • The experimental film intensity and simulated film thickness were linearly correlated and significantly influenced the surface temperature. Cryogen spray cooling (CSC) has become a promising auxiliary-cooling technique for laser dermatology, which recently enhanced by cold air jet (CSC-CAJ). However, the CAJ-to-spray interactions could worsen the CSC performance and associated liquid film behavior. In this study, the transient behavior of liquid film deposition and surface heat transfer of CSC-CAJ was investigated. A high-speed camera was used to capture the film intensity through Mie-scattering technique. Fast-response TFTC thermocouple was used to measure the transient surface temperature. The large eddy simulation (LES) was used to extract the vortical structure, while the discrete-phase model (DPM) and Eulerian wall film (EWF) were coupled for the spray process and the transient film modeling. The results showed that the CAJ significantly enhanced CAJ-to-spray mixing and mitigated the film thickness (i.e., 32 % reduction). The CSC-CAJ had asymmetric film coverage due to induced counter-rotating vortex-pairs (CRVP) from the CAJ-to-spray interaction, which laterally clustered the spray. It permitted fast evaporation with dominant CAJ at the spray-periphery while permitting fast evaporation with dominant spray at the spray-core. Consequently, the CSC-CAJ showed 75 % temperature increment at the windward side and 15 % temperature reduction with 60 % heat transfer coefficient enhancement at the impingement point. The experimental film intensity and simulated film thickness were linearly correlated and significantly influenced the surface temperature. The combined results affirmed the significant impact of the CAJ on the transient film deposition, which potentially helps promote advanced cooling technology. [ABSTRACT FROM AUTHOR]

• The heat transfer enhancement and surface temperature non-uniformity are numerically studied. • The radial groove surface has a stronger heat transfer capability than the straight groove surface. • There is an optimal groove width and optimal groove number on the radial groove surface. • A novel enhanced surface achieves maximum heat flux with a small heat transfer area. • The design of the enhanced surfaces should focus on the flow and distribution of the liquid film more. A numerical model of spray cooling for enhanced surfaces in the non-boiling regime is created with deionized water as cooling medium. This model is validated by contrasting the simulated data with the corresponding experimental data, and the relative deviation is within 12 %. Compared with a smooth surface, the area of the enhanced surface is expanded, the cooling performance is significantly improved, but the surface temperature distribution is less uniform. Compared to the straight groove surface with the same area, the heat flux of the radial groove surface is higher because its surface structure is more conducive to the spreading and leaving of the liquid film. Studies of the effects of the structure parameters (groove width and groove number) of the radial groove surface on the heat transfer show that there is an optimal groove width (0.2 mm) and groove number (45) for the strongest cooling capacity, and both the velocity and thickness of the liquid film are significant factors in cooling performance. The faster the liquid film velocity, the thinner the liquid film and, thus, the better the heat transfer. Motivated by these findings, three novel enhanced surfaces are machined to increase liquid film fluidity and heat transfer area even further. The cooling performance of the three novel enhanced surfaces is further improved, and the slope groove surface acquires the strongest cooling capacity due to the acceleration of liquid film flow by gravity, although its heat transfer area is not the largest. Research on all enhanced surfaces indicates that thinner liquid film and faster liquid film flow should be the primary design goals of the enhanced surface, followed by an increase in heat transfer area. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the residual bond behaviour between rebar and recycled aggregate concrete (RAC) using granite natural coarse aggregates and different recycled coarse aggregate (RCA) replacement levels (δ = 0%, 30%, 50%, and 100%) for both pull-out and cubic specimens. After high-temperature exposure (T = 200, 400, and 600 ℃) followed by water spray cooling, the results revealed a consistent decline in bond strength and compression strength with increasing temperature. Compared to ambient conditions, bond strength and compression strength decreased by 65.2% ∼ 77.8% and 53.2% ∼ 58.4%, respectively, after exposure to 600 ℃. The reduction rate of residual bond strength changed significantly at about 400 ℃. There was a linear relationship between RAC compression strength and rebar–RAC bond strength after high temperature exposure followed by water spray cooling. With increasing RCA replacement levels, the relative bond strength gradually improved at the same temperature. Based on the regression analysis, empirical formula for the rebar–RAC bond strength and bond–slip relationship models were proposed, all taking into account RCA replacement levels and temperature. • HTWSC is high-temperature exposure followed by water spray cooling. • Compressive strength of RAC with 100% RCA replacement level is approximately 70% of that of NAC after HTWSC. • Relative bond strength increases with an increase in RCA replacement level after HTWSC. • Prediction model for bond strength between rebar and RAC after HTWSC is developed. • Bond–slip relation between rebar and RAC after HTWSC is suggested. [ABSTRACT FROM AUTHOR]

In the nuclear energy utilization, the passive containment cooling system (PCCS) holds paramount importance, with its heat transfer performance standing as a critical aspect of nuclear safety. This study simulated the flow and heat transfer behaviors of PCCS with equal height difference by APROS software under a broad range of steady state operating conditions. At first, the flow pattern of natural circulation is categorized by phase state of flow through operational parameters. A criterion model of boundary of phase change is proposed with prediction deviation of less than ±25 %. Furthermore, the influence of various operation parameters such as temperature, non-condensable gas content, and pressure on the heat transfer behaviors of natural circulation was also revealed. A new heat transfer coefficient correlation for both single-phase and two-phase conditions is proposed with prediction deviation of ±15 %. Finally, the thermal stratification phenomenon in the containment vessel with non-condensable gas was investigated, indicating that local heat transfer characteristics in the upper region surpass those in the lower section on account of deposition of the non-condensable gas at bottom of the vessel. [ABSTRACT FROM AUTHOR]

We propose the high-performance evaporative spray cooling strategy by combining the hierarchical flake formation and the intermittent spraying. A simple, scalable, and cost-effective method was introduced to fabricate hierarchical flakes with multi-scale wicks where the size of the pores varies along the direction normal to the wick plane, which provides substantially improved wicking capability for capillary pumping. In addition, the intermittent spray methods allowed for more efficient evaporative cooling by enabling the reduction in spraying volume. Through the thermal management experiments, the hierarchical flake heat exchanger could provide up to ∼32.1% reduced amount of sprayed water and ∼ 1.8 times higher energy efficiency compared to the untreated aluminum heat exchanger during intermittent spraying. Using the quantitative analysis on the single-droplet evaporation and water retention ability, we systematically demonstrate the effects of the combination of hierarchical flake and intermittent spray scheme on the efficient thermal management. We believe that our outcomes of this work show the potential of the spray cooling method for the heat exchangers and present the scalable evaporative surfaces applicable to various evaporative cooling applications. • Hierarchical flake fin is fabricated via a scalable dipping method. • Wicking capability is quantified by a single-drop evaporation test. • Water retention ability is systematically evaluated during intermittent spraying. • Water savings and energy efficiency are demonstrated by a heat exchanger test. • Hierarchical flake with intermittent spray facilitates efficient thermal management. [ABSTRACT FROM AUTHOR]

• The high temperature cylindrical surface cooled by spray was simulated. • The effect of spray spacing on cooling was simulated, and the best spray spacing range was obtained. • The temperature and wall heat flux distribution of the cooling area under different nozzle array forms were analyzed. • It is pointed out that the unidirectional inclined array spray can obtain better cooling effect. Spray cooling technology is an efficient cooling method. In the industrial application, the large area cooling requires the multi-nozzle spray design. Reasonable selection of nozzle array form is particularly important. Therefore, the simulation is applied in this study to investigate the effect of the nozzle array on the spray cooling of steel pipes after the model is validated. A steel pipe with a diameter of 140 mm, a wall thickness of 20 mm, and a length of 350 mm is employed as the research object, with an initial temperature of 900 °C. The scheme has four options for double spray spacing: OLR = −15 %, 0 %, 15 %, and 30 %. The results show that when the OLR grows, the cooling area gradually diminishes, and the cooling area's average temperature and average surface heat flux fall and subsequently increase. When OLR=30 %, the best cooling zone shape is obtained. The minimum average temperature, 231 °C, is obtained when OLR = 15 %. After comprehensive analysis, the ideal spray spacing range is found at OLR = 15 %∼30 %. In order to study the nozzle array, spray nozzles are arranged in multiple rows according to OLR = 30 %. This study also explores the strategies of unidirectional inclined spray and opposite inclined spray for lessening the area of the hot spot. There are six nozzle array arrangements in total. By comparing the results, it is discovered that the inclined spray increases the cooling area and accelerates the surface cooling of steel pipes. Under the side-by-side unidirectional inclined spray and the staggered unidirectional inclined spray, the cooling areas are 146,868 mm2 and 142,914 mm2 respectively, the average temperatures are 157.09 °C and 154.28 °C respectively. It is indicated that side-by-side inclined spray and staggered inclined spray are the better nozzle array arrangement to obtain the maximum cooling efficiency. [ABSTRACT FROM AUTHOR]

Summary: To balance the temperature uniformity and the compactness of the battery module, the heat transfer performance of spray cooling technology is theoretically analyzed in this article. The main factors affecting the heat transfer performance of spray cooling are discussed. Through the experiments, the influence of spray cooling on the thermal management of the battery thermal management system under high discharge rate is studied. The results show that, in spray‐cooling 4 + 2.5 m/s cooling mode, the total heat transfer coefficient K reaches 201.0 W/(m2 K), which is 409.3% higher than the heat transfer coefficient of the forced air cooling. In addition, the difference between the spray concentration of the heat source surface and the spray concentration of the mainstream area during steady‐state heat dissipation is an important factor affecting the heat transfer performance of spray cooling. Moreover, spray cooling can provide a lower temperature rise and a more uniform temperature distribution for the battery module. For the spray‐cooling 4 + 4 m/s case, the maximum temperature rise is only 10.3°C, and the temperature difference among the battery module is stably maintained within 5°C. Therefore, the proposed spray cooling battery thermal management system shows to be efficient approach in handling the heat accumulation of battery module. [ABSTRACT FROM AUTHOR]

Summary: The thermal management system has essential effects on the performance, life, and consistency of lithium‐ion batteries. Compared with commonly used cooling methods, spray cooling has excellent performance and is now widely used in electronic equipment, metal processing, laser surgery, and other fields. However, there are few applications of spray cooling in the battery thermal management systems (BTMSs). With the increase of the charge and discharge speed and people's rising attention to the thermal runaway accidents of electric vehicles, it is urgent to intensively investigate the performance of spray cooling in the BTMS and discuss its design method. In this research, a BTMS using spray cooling was designed with pouch‐type lithium‐ion cells and injectors. A synthetic lubricant was used as the spray medium. The electrical–thermal coupled model was adopted to obtain the heat production and temperature distribution of the cell. Numerical calculation and analysis of the spray cooling process were performed based on the discrete phase model. It was found that spray cooling could reduce the maximum temperature (MAT) on the cell from 53.6°C to 39.7°C during the 3 C discharge process and the maximum temperature difference (MATD) from 9.1°C to 6.0°C. And the temperatures of the tabs were also reduced. The effects of the spray speed, the mass flow rate, the specific heat capacity, and the droplet size on the performance of the BTMS using spray cooling were further investigated. The results showed that within a certain range, increasing the mass flow rate and specific heat of the spray, or decreasing the average diameter of the droplets could reduce both the MAT and the MATD on the cell. But their effects on the latter were not significant. When the spray speed was increased, the MATD demonstrated a monotonous decreasing trend and could be reduced to below 5°C. [ABSTRACT FROM AUTHOR]

The electrospray (ES) cooling technique, which is a combination of spray cooling and high-voltage electrostatic technology, has attracted considerable interest because of its simple unit structure and low power consumption. To overcome the low flow rate and high boiling point problems of current working fluids, a mixture of R141b and ethanol was used as the working fluid to experimentally investigate the break-up modes at a high flow rate. Furthermore, the effects of break-up modes and ethanol concentration on spray characteristics, cooling performance, and impingement characteristics were examined. The experimental results indicated that ES at a high flow rate exhibited four break-up modes: dropwise, varicose, whipping, and ramified. As the spray mode transitioned from the dropwise to the ramified mode, the droplet size decreased, and the droplet splash phenomenon on the hot surface was suppressed. The cooling performance was considerably enhanced with the evolution of the break-up mode, and the critical heat flux (CHF) was increased by 27.3 % when the break-up mode was transformed into the ramified mode from the dropwise mode. Under certain conditions, an ES cooling efficiency of 92.6 % was achieved. Furthermore, the volume fraction of ethanol (corresponding to the best cooling performance) increased with the wall temperature. In this study, considering the actual requirements of the chip for the cooling capacity, the optimal volume fraction of ethanol in the whole temperature region was determined to be 30 %. These findings can provide theoretical guidance for thermal management of high-power electronic devices. [ABSTRACT FROM AUTHOR]

Spray cooling experiments on the hot metallic surfaces with different initial temperatures were performed. This paper adopts a self-developing program which is based on the inverse heat transfer algorithm to solve the interfacial heat transfer coefficient and heat flux. The temperature-dependent interfacial heat transfer mechanism of water-air spray cooling is explored according to the wetting layer evolution taken by a high speed camera and the surface cooling curves attained by the inverse heat transfer algorithm. Film boiling, transition boiling, and nucleate boiling stages can be noticed during spray cooling process of hot metallic surface. When the cooled surface's temperature drops to approximately 369-424 °C. the cooling process transfers into the transition boiling stage from the film boiling stage. The wetting regime begins to appear on the cooled surface, the interfacial heat transfer coefficient and heat flux begin to increase significantly. When the cooled surface's temperature drops to approximately 217-280°C, the cooling process transfers into the nucleate boiling stage. The cooled surface was covered by a liquid film, and the heat flux begins to decrease significantly. [ABSTRACT FROM AUTHOR]

Multirow film cooling is an advanced cooling method to provide effective surface cooling for gas turbine components exposed to high temperature. In this paper, the performance of multirow film cooling under different configurations is investigated numerically. The geometrical parameters, including the hole arrangement, hole orientation, and trenched hole, are considered. The numerical setup is validated before the performances of different cooling configurations are compared. The flow and heat transfer characteristics of the various cooling configurations are analyzed, and the different row-to-row interactions are revealed. For the configurations with standard holes, the staggered arrangement of simple angle holes achieves better cooling efficiency than the counterpart with inline configuration, while the inline arrangement with opposite compound angle holes provides the best cooling efficiency. For the configurations with trenched holes, the trench promotes the coolant uniform mixing, and the coolant stays more close to the effusion plate. Thus, the multirow cooling efficiency with trenched holes is better than the cooling configurations with standard holes. [ABSTRACT FROM AUTHOR]

Spray cooling characteristics of TG6.5 solid cone nozzle are studied by building a liquid nitrogen spray cooling experimental bench. The relationships between the superheat and the heat flux as well as the superheat and the heat transfer coefficient near the critical point are analyzed. Then the influence of the spray area and the spray flow rate on the heat transfer effect is discussed. Results show that, in the process of heat transfer, with the increase of the heat flux, the change of superheat can be divided into three stages: a slow increase, an obvious increase and a sharp increase. Under the influence of bubbles in nucleate boiling, the superheat at the maximum heat transfer coefficient is less than that at the critical heat flux. Increasing the spray flow can significantly improve the heat transfer effect. Increasing the heat sink area will reduce the impact frequency and intensity of droplet particles in the unit area, so that the heat transfer effect will decrease. [ABSTRACT FROM AUTHOR]

The paper presents the method and results of determination of heat transfer coefficient for air-atomized water spray cooling with consideration of infrastructural factors of industrial cooling conveyor, such as effect of accelerated air. The established values of heat transfer coefficient were implemented into a numerical model of cooling line, with special definition of sprayers and the movement of the part subjected to quenching. After quantitative validation on selected samples, the obtained coefficients were used for the solution of the technological problem by means of localized cooling rate enhancement, which forms a case study confirming reliability of the established water spray heat transfer functions and suitability of the determined models for design of thermomechanical controlled processing of complex-geometry parts. [ABSTRACT FROM AUTHOR]

Spray cooling is an effective heat transfer technique capable of handling high heat fluxes and temperatures. The study of droplet impact offers a simplified approach to understanding the fundamentals of spray cooling and elucidates the effects of droplet diameter and velocity. Experiments on a single-droplet impact on a thin liquid film with boiling bubbles are carried out in this study. Two-phase interface evolution is observed using high-speed video, and the heater surface temperature variation at the impact point following an impact is recorded and analyzed, which can be divided into the response stage, the recovery stage, the steady stage, and the slow recovery stage. Furthermore, a cooling factor based on the change in heater surface temperature is introduced to evaluate the cooling effect of droplet impact. Results show that the steady stage plays a significant role in the heater surface cooling process. Moreover, the maximum cooling factor increases appreciably with increasing droplet diameter and impact velocity. [ABSTRACT FROM AUTHOR]

Cryogen spray cooling (CSC) is widely applied in laser dermatologic surgery to minimize the risk of non-specific epidermal thermal damage caused by the competitive laser energy absorption of epidermal melanin. However, the light absorption and attenuation by cryogen film and subsequent frost formation on the skin surface during CSC are needed to be investigated by using R-134a, R-404A, and R-32. A spray system equipped with an integrating sphere-based light collection apparatus was constructed to evaluate the time-resolved laser transmittance and spectral absorption characteristics induced by R-134a, R-404A, and R-32 sprays, under the clinical-used 755-nm and 1064-nm laser irradiations. No obvious light absorption peaks exist in the wavelengths of 370–1400 nm. R-404A produces the largest average light absorbance (0.089), as compared to those of R-134a (0.066) and R-32 (0.068) in the near-infrared range (780–1400 nm). Given the lowest boiling point and highest latent heat of R-32, the evaporation of liquid film and melting of subsequent frost are promoted, leading to smallest light attenuation. R-32 spray shows great potential in clinics owing to its high light transmittance, small light absorption, and high cooling capability. For R-32 spray, the durations between spurt termination and laser irradiation are recommended to be 8–100 ms and 13–100 ms with average light transmittances of 86% and 95% under 755-nm and 1064-nm laser irradiations. [ABSTRACT FROM AUTHOR]

Increased applications of fluorochemicals have prompted development of elemental methods for detection and quantitation of these compounds. However, high-sensitivity detection of fluorine is a challenge because of difficulties in excitation and ionization of this element. Recently, a new approach has emerged to detect F as a diatomic ion (BaF+) in inductively coupled plasma mass spectrometry (ICP-MS). However, formation of this species in the high-temperature plasma is inefficient, leading to low sensitivities. Here, we introduce a post-ICP chemical ionization approach to enhance analytical performance for F detection in liquid samples. Solutions of fluorochemicals are introduced into an ICP leading to formation of HF in the afterglow. Subsequently, reagent ions from nanospray of sodium acetate and barium acetate electrolytes are utilized to ionize HF to Na2F+ and BaF+, respectively, via post-plasma ion-neutral reactions. Both ions provide substantially better sensitivities compared to that of BaF+ formed inside the plasma in conventional ICP-MS methods. Notably, post-plasma BaF+ offers a sensitivity of 280 cps ppb−1 for F, near two orders of magnitude higher than that of conventional ICP-MS methods. Compound-independent response for F from structurally diverse organofluorines is confirmed by monitoring BaF+ and a limit of detection (LOD) of 8–11 ng mL−1 F is achieved. Importantly, isobaric interferences are substantially reduced in chemical ionization, leaving F background as the main factor in LOD determination. Insights into BaF+ formation via experimental and computational investigations suggest that BaNO2+ and Ba(H2O)n2+ serve as reagent ions while nonreactive BaCH3CO2+ is the dominant ion produced by nanospray. The facile development of effective post-plasma ionization chemistries using the presented approach offers a path for further improvements in F elemental analysis. [ABSTRACT FROM AUTHOR]

Experiments have been performed to study the effect of enhanced surfaces including micro-finned, micro-/nano-coated (coating thickness of 100 µm and 200 µm) and hybrid surface on heat transfer coefficient and critical heat flux using spray cooling. Commercial HFE-649 coolant obtained from 3 M Corporation has been used to spray over copper heater of 10 mm2 cross-sectional area using a full cone pressure swirl nozzle with 0.51-mm orifice diameter. The pressure swirl nozzle squeezed the incoming fluid and dispersed into spray droplets in the volumetric flux range between 1.0 and 4.5 cm3/cm2s. Results have been obtained for various surfaces at optimum distance of nozzle-to-surface and comparison is done with the plain surface. Findings revealed that heat transfer performance improved considerably with hybrid surface, which showed at least 360% enhancement in heat transfer coefficient and 72.9% in critical heat flux in contrast to the plain surface. An improvement of 7.1% in critical heat flux is observed for hybrid surface in comparison with other enhanced surfaces. Furthermore, experiments were conducted to examine the effect of inclination angle (0°, 15°, 30°, and 45°) on heat transfer performance. The heat transfer coefficient, critical heat flux, and cooling efficiency all improved dramatically at 15°C inclination angle. In comparison with horizontal spray, an improvement of 18.9% and 20.1% in heat transfer coefficient and critical heat flux, respectively, have been observed. However, heat transfer performance degraded with the further increase of inclination angle. Other experimental parameters remain constant, such as the volumetric flux, spray height, and spray pressure. [ABSTRACT FROM AUTHOR]

This study was performed to better understand the laser–tissue interaction mechanism and optimize the laser wavelength and pulse duration for the laser treatment of Ota's nevus, thereby providing the precise theoretical guidance for clinician to improve the therapeutic effect. A non-equilibrium bio-tissue heat transfer model coupled with thermo-mechanical effect for the explosive vaporization of melanin granule induced by laser heating was developed to investigate the temperature and thermal damage distribution using alexandrite (755 nm) and Nd:YAG (1064 nm) lasers with the pulse width of 10–120 ns. Cryogen spray cooling (CSC) was introduced to prevent the epidermal thermal damage due to competitive laser absorption between epidermal and dermal melanin. Thermal injury of the epidermis with temperature in the melanin zone reaching 132.3 °C was induced by alexandrite laser. The optimal pulse durations were 50 and 30 ns, and the corresponding incident laser fluence thresholds were 6.45 and 19.5 J·cm−2 for alexandrite and Nd:YAG laser, respectively, with the pre-cooling of R32 spray. Using R32 spray cooling, the 1064-nm laser fluence threshold of melanin can be increased by 56.0%, resulting in an indirect increase (80.4%) of injury thickness. Nd:YAG laser (1064 nm) was highly suitable for the removal of melanin in the deep tissue owing to its deep penetration. Too short pulse duration should be avoided to prevent the epidermal thermal damage. The improvement of therapeutic effect by CSC demonstrates its high clinical application potential. [ABSTRACT FROM AUTHOR]

The heat transfer characteristics of the microwave heating coupled with atomization feeding were investigated using ethanol as the spray medium on a pressure swirl nozzle. The effects of spray height, flow rate and temperature on the sauter mean diameter of atomized droplets were examined. The results showed that the droplet sauter mean diameter was 12-130 μm, which increased with the spray height and decreased with the flow rate and temperature of spray medium. Through the fitting of the experimental data, the dimensionless correlation of the droplet sauter mean diameter which was based on orifice diameter, Reynolds and Ohnesorge numbers was obtained. The calculated results were basically consistent with the experimental data within 15% error. The heat transfer characteristics of atomized droplets on high temperature surface of SiC bed heated by microwave were then investigated. The effects of spray flow rate, spray height, and spray temperature on the heat transfer characteristics were examined. The power of spray heat transfer decreased with the temperature and increased with the spray flow rate and spray height. The dimensionless correlation to describe the heat transfer characteristics of atomized droplets on the high temperature SiC surface under the microwave heating was obtained which included thermophysical properties of spray medium, spray parameters, and temperatures of the high temperature bed surface and spray medium, with the error of ±20%. These correlations can be used to predict the sauter mean diameter of the atomized droplets and the power of spray heat transfer in the microwave heating process. [ABSTRACT FROM AUTHOR]

In DC plasma spray torches, anode erosion is a common concern. It mainly depends on the heat flux brought by the arc and on the dimensions and residence time of the arc attachment to a given location on the anode wall. The latter depend, to a great extent, on the attachment mode of the arc on the anode wall. This paper compares the anode arc attachment modes predicted by an LTE (Local Thermodynamic Equilibrium) and 2-T (two-temperature) arc models that include the electrodes in the computational domain. It deals with a commercial cascaded-anode plasma torch operated at high current (500 A) and low gas flow rate (60 NLPM of argon). It shows that the LTE model predicted a constricted anode arc attachment that moves on the anode ring, while the 2-T model predicted a diffuse and steady arc attachment. The comparison between the predicted and measured arc voltage showed that the 2-T prediction is closer to the actual voltage. Also, the post-mortem observation of a new anode ring of the actual plasma torch operated under the same conditions for a short time confirmed a diffuse arc attachment on a new anode. [ABSTRACT FROM AUTHOR]

The spray cooling is investigated for very high mass‐flux coolants at different temperatures. First, the intended spray is characterized for its role in the cooling enhancement, which reveals that droplet detachment frequency, droplet residence time, liquid film, and vapor film wavelength influence heat‐transfer performance for high‐temperature very‐high mass‐flux spray. After that, the furnace heated 6‐mm thick steel plate at 1030°C is quenched using spray possessing average impingement density (231 kg/m2s) and coolant temperatures (30°C, 40°C, and 50°C). The heat transfer performance is analyzed using inverse heat conduction analysis, wherein temperature‐dependent steel thermophysical properties are considered. The heat transfer performance assessment through parameters such as cooling rate, surface heat flux, and heat transfer coefficient curves shows improvement in cooling performance. For 50°C coolant temperature, we observed the maximum improvement in cooling rate, 141°C/s, and critical heat flux, 3.64 MW/m2. The efficiency analysis reveals that coolant at the highest temperature is the most efficient. Also, an approximate cost assessment suggests enhanced coolant temperature as an economical alternative for heat transfer enhancement than additives‐based coolant. [ABSTRACT FROM AUTHOR]

In this article, a low-loss RF coaxial through-silicon vias (TSVs) (C-TSVs) configuration in the silicon interposer with the embedded cooling cavity is proposed. For the single C-TSV array passing through the embedded cooling cavity, the transmission losses with different coolants were compared. The insertion loss immersed in FC770 is 0.14 dB at 40 GHz, which is closed to the typical C-TSV interposer (0.2 dB). It is much smaller than the deionized water (6.49 dB) one. The optimal spacing of multiple C-TSV arrays filled with FC770 coolant is $600~\mu \text{m}$ (vertical transmission of 0.16 dB at 40 GHz). When the cooling cavity is embedded in the interposer with FC770 coolant, the maximum surface temperature of the power devices can be less than 56.8 °C at 250 W/cm2 heat flux. Compared with the solid silicon interposer, the maximum von Mises thermal stress of the C-TSV interposer with the embedded cooling cavity can be reduced by 44.8%. [ABSTRACT FROM AUTHOR]

• Experimental study on spray cooling with microencapsulated phase change suspension. • Latent heat of suspension improves spray cooling by up to 33.9 % relative to water. • Excessive suspension concentration results in the deterioration of spray cooling. • Optimal spray rate or height exists when liquid-film exactly covers heat surface. • Optimal inlet temperature is 10 °C lower than melting peak temperature of particle. This paper reveals the spray cooling heat transfer mechanism with the microencapsulated phase change suspension as the working fluid based on an experimental investigation. The heat transfer performances between the spray cooling and jet impinging with suspension are compared. A series of key parameters affecting the heat transfer are analyzed, including suspension concentration, nozzle diameter, spray height, inlet temperature, and spray inclined angle. It concludes that the spray cooling of suspension has a stronger heat transfer capability relative to the jet impinging, but the pressure loss is correspondingly larger. Compared with the water, the spray cooling heat transfer of phase change suspension is superior owing to the latent heat ability of particle core, and the maximum improvement in the current tests is 33.9 %. However, excessive suspension concentration can result in the deterioration of heat transfer because of the larger viscosity. There is an optimal volumetric flow rate and an optimal spray height for the spray cooling, where a suitable spray cone angle is present so that the heating surface may be exactly covered by the liquid-film. The latent heat absorption characteristic of phase change core leads to the existence of an optimal spray inlet temperature, which is about 10 °C lower than the melting peak temperature of the particle core. For the cases of incomplete-coverage, the decrease of the spray inclined angle may enlarge the liquid-film covering area and thence improve the heat transfer. A theoretical analysis indicates that the suspension in current tests has a high complete-melting rate (σ ≥ 93.7 %) when using in the spray cooling. The results may provide the beneficial support for the potential application of spray with phase change suspension for the cooling of electronic devices. [ABSTRACT FROM AUTHOR]

An experimental study on multi-nozzle spray cooling of a downward-facing heater surface has been carried out in the SPAYCOR facility at KTH, to provide data assessing the feasibility of spray cooling for in-vessel melt retention (IVR) in light water reactors. To help understand the characteristics and influential factors of the liquid film formed on the heater surface in spray, a numerical study on the dynamics of an isothermal liquid film on the heater surface has also been performed by adopting the OpenFOAM platform, and Eulerian and Lagrangian methods for liquid film and droplets, respectively. The present study is an extension of the previous modeling from hydrodynamics to thermal-hydraulics of the spray cooling problem, via adding heat flux of the heater and two convective heat transfer models between the heater wall and the liquid film. Moreover, droplets-film interaction model is modified. The SPAYCOR experiment is simulated by the numerical models, and the simulation results show a good agreement between the numerical and experimental data, in particular when the modified droplets-film interaction model is applied. After the validation of the numerical models against the SPAYCOR experiment, the numerical models are employed to investigate influential factors on heat transfer, such as mass flux, nozzle-to-surface distance, and nozzle matrix layout. The results indicate that heat transfer is enhanced by increasing mass flux and decreasing nozzle-to-surface distance, and the change of nozzle matrix from inline to staggered layout has little impact on heat removal capacity or temperature distribution of the multi-nozzle spray cooling. [ABSTRACT FROM AUTHOR]

• Three sequential processes occur, including coalescence, spreading, retraction. • Spreading diameter and time are normalized by impact and stationary droplets. • Effects of Weber number, droplet volume ratio, surface wettability are clarified. • Maximum spreading coefficient elevates at larger Weber number or drop volume ratio. • An accurate theoretical model of the maximum spreading diameter is proposed. In numerous applications related to droplet impact, impacting droplets often interact with solid surfaces with adhesive droplets rather than dry surfaces, but the former is significantly less studied than the latter. Here, for the fundamental process of droplet impact on a stationary droplet on the surface, we investigate droplet dynamics and maximum spreading under various conditions. The spreading diameter and time are reasonably nondimensionalized as the spreading coefficient and dimensionless time by considering both the impacting and stationary droplets, and the complex influence of diameters of two droplets is reduced to the effect of a single droplet volume ratio. The proposed dimensionless framework provides a method to simplify influencing factors and facilitates the study of droplet dynamics under different Weber numbers, surface wettabilities, and droplet volume ratios. The maximum spreading coefficient increases with the increase of the Weber number or the droplet volume ratio, while it is nearly independent of surface wettability. A theoretical model of the maximum spreading diameter is established through energy analysis. By considering the coupled effects of various factors and modifying the viscous dissipation, the model has the merits of high prediction accuracy and broad applicability. Our findings can not only advance the basic understanding of the ubiquitous droplet impact phenomena, but also provide useful guidance for applications such as spraying cooling and inkjet printing. [Display omitted] [ABSTRACT FROM AUTHOR]

This work presents the experimental investigation of droplet boiling characteristics on superhydrophilic surfaces. These surfaces are prepared on a copper substrate, and the boiling characteristics are studied and compared with the bare copper surface. Two types of superhydrophilic surfaces exhibiting needle-like (CuO-1) and sheet-like (CuO-2) nanostructures are prepared by the chemical etching oxidation technique. The hierarchical surface structures are characterized by carrying out SEM and XRD analysis. We employ high-speed imaging along with temperature measurement to characterize the heat transfer phenomenon. The surface temperature varies from 100 °C to 190 °C, and the Weber number is maintained constant at 2.78, corresponding to the gentle droplet impact regime. The effectiveness in the heat transfer performance of the different surfaces is characterized by measuring the critical heat flux (CHF) and the Leidenfrost point (LFP), and it is correlated with the surface properties viz. roughness, wettability, and porosity. The superhydrophilic surface alteration reduces the contact angle by about 99.7% compared to the bare surface. This reduction in contact angle corresponds to an increase in Critical Heat Flux (CHF) by 69.95% for CuO-1 and 47.17% for CuO-2, respectively, compared to bare copper. It is also seen that the LFP is delayed on the superhydrophilic surfaces, with an increase in the LFP temperature by 16.67% and 14.28% for CuO-1 and CuO-2 coatings, respectively. The effect of structures on the atomization and formation of secondary droplets is also presented. We report the contact coefficient (k w) for superhydrophilic surfaces for the first time, which is helpful in the theoretical prediction of CHF. These results show that significant improvement in heat transfer can be obtained in spray cooling and hot spot cooling applications without resorting to sophisticated microfabrication techniques. • Significant enhancement in droplet boiling by cost-effective wet etching technique. • 70% increase in CHF and 17% increase in the Leidenfrost temperature. • Atomization is strongly dependent on surface microstructure. • Contact coefficient is reported for the first time for superhydrophilic surfaces. [ABSTRACT FROM AUTHOR]