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This paper compares the performance of a vertical-finned microchannel heat exchanger (VMHX) and a 2-row fin-tube heat exchanger (FTHX) under wet and frosting conditions. The VMHX features vertically oriented fins with an extension at the windward side and parallel microchannel tubes, allowing for efficient water drainage and better performance than conventional microchannel heat exchangers with parallel serpentine fins. However, the performance of the VMHX has not been sufficiently compared to that of FTHX. After conducting experiments under specific operating conditions, the VMHX exhibits better water drainage performance than the FTHX at higher inlet air velocities, higher maximum heat flow, and time-integrating heat flow under certain operating conditions. Although the heating time is relatively shorter than the 2-row FTHX, these results suggest that the VMHX may be a more suitable option for applications requiring efficient water drainage and heat transfer. Additionally, the operating conditions significantly affect the heat exchanger's performance. The performance of VMHX is analyzed under different inlet air velocities, inlet air temperatures, and evaporation temperatures. The results indicate that frost itself had no effect on the heat exchanger performance and that the decrease of the inlet air flow rate was the main factor that decreased the heat exchanger performance. Overall, the results of this study provide valuable insights into the performance of VMHX and FTHX under wet and frosting conditions and the impact of various operating parameters on VMHX performance. These findings can inform the development of more efficient and reliable heat exchangers for various applications. [ABSTRACT FROM AUTHOR]

In heating processes using superheated steam, a practical heat transfer model for predicting the change in the material temperature taking condensation/evaporation into consideration is required. This study observed the behavior of condensed water and verified a simple but practical heat transfer model to predict the heating time of materials. The one-dimensional model, which comprehensively includes the conductive, convective, radiative, and latent heat fluxes, was utilized. For simplicity, film condensation was assumed. To conduct experiments covering a wide humidity range, the humidity of the airflow was regulated by mixing superheated steam with high-temperature air. The sample material having 50 mm of length, 50 mm of width, and 10 mm of thickness was placed under this airflow, and the change in temperature over time was measured. During the initial stages of heating via superheated steam, condensation, and subsequent evaporation were observed. The time required for the evaporation of condensed water increased with the humidity, owing to the large amount of condensed water. The ending time of evaporation was successfully estimated within about −30% error. Although some modifications will be required in the future, the model is expected to be a powerful tool in various industries where superheated steam is applied. [ABSTRACT FROM AUTHOR]

This study focuses on the development of an advanced high heating rate thermobonding process for the manufacture of preforms and the metrological characterisation of the process. The process involves passing hot air, driven by pressure differential, through a textile stack consisting of several plies of a quadraxial fabric coated with a binder. Heat is transferred into the stack and into the binder by forced convection, melting the binder. The process is used in the same way to cool the stack and binder so that the plies are bonded together. The pressure differential compacts the stack. The comprehensive methodological characterisation of the process includes first determining the air permeability of the stack and thus the volume flow of air as a function of the number of plies stacked. Further characterisation focuses on a comprehensive determination of the heating behaviour in the individual plies as a function of time, using thermocouples and thermal imaging to determine the temperatures of hot air and textiles. These are compared and related using a mathematical approach as different values have been found. The results indicate high heating rates, reducing process time by at least 85% compared to previous binder activation methods. In addition, the cantilever method assesses the flexural stiffness of the processed stacks and shows a twofold improvement in bond strength compared to uncompacted stacks. Results and discussions include orifice based volume flow determination, thermography calibration, mathematical modelling, stiffness of bonded textile plies, process comparison, process control and potential energy savings. [ABSTRACT FROM AUTHOR]

Conventional multi-cylinder drying of paper and board involves a mixture of conductive drying from steam-heated dryer cylinders and convective drying by the flow of heated air over the surface of the paper web in the pockets. Pocket ventilation is a critical component in assisting heat and mass transfer during the drying process but is the primary contributor toward removing evaporated water from the web. Air temperature, velocity, and humidity are critical parameters involved in the convective drying process. This paper covers an experimental study involving the design and development of a small lab-scale setup for convective drying of various grades of paper and board, monitoring multiple parameters like paper temperature, moisture content, air humidity, temperature, and velocity measured in situ as the drying proceeds with continuous and accurate sampling capabilities for all parameters in the sample and the system. Instantaneous drying rates, heat, and mass transfer coefficients were also deduced for every time step till the paper completely dried. Furthermore, the coefficients obtained were also reported in the form of dimensionless correlations, and the results were compared against traditional correlations used in the modeling of paper drying. This data will be useful in process development, modeling, design, and the paper drying process simulation. [ABSTRACT FROM AUTHOR]

Rapid development of the anomalous enhancement of separated turbulent Re = 6000 air flow and heat transfer in an in-line single-row package of 31 inclined grooves, 0.2 in dimensionless depth, in a singled-out longitudinal region of the wall of a narrow channel is studied. It is due to the interference of vortex wakes behind the grooves and the acceleration in the channel flow core with the formation of a zone of ultrahigh longitudinal velocity. The wave-shaped parameter characteristics are stabilized in the region of approximately 15th groove, whereupon the oscillation amplitudes are moderately reduced. The return flows in the grooves are enhanced with distance from the entry section, the minimum negative friction diminishing from −2 to −4. The total relative heat removal from the structured region increases at q = const by a factor of approximately 2.75 and by the factor of two at T = const with increase in the relative hydraulic losses by the factor of 1.7, as compared with the case of a plane–parallel channel. The relative heat removal from the surface bounded by the contour of the 20th inclined groove amounts to 3.7 (q = const) with increase in the hydraulic losses by the factor of 2.2. An increase in the local maximum of the longitudinal velocity up to a factor of 1.5, as compared with the mean-mass velocity, can be observable. [ABSTRACT FROM AUTHOR]

In cold regions, the flow of outside air into a tunnel often causes freeze–thaw damage to the surrounding rock, and insulation methods are usually adopted to avoid this damage. In this study, the heat transfer in a multilayer tunnel structure that includes a rock layer, an initial lining, an insulation layer, and a secondary lining was investigated, and convection between the tunnel air and the inner surface of the tunnel lining was considered. A mathematical model describing the heat transfer process was established, and an analytical solution for the temperature field was developed using Duhamel's principle and the separation-of-variables method. The model and the solution were verified by comparing the computational results of the analytical solution with the computational results and in situ measurements available in the literature. By treating the minimum temperature of the inner surface of the surrounding rock as a function of the insulation thickness, a procedure to determine the minimum insulation thickness that ensures no freeze–thaw damage to the surrounding rock was developed based on the analytical solution using the bisection method. Computational examples were presented, and the effects of different factors on the minimum temperature of the inner surface of the surrounding rock and minimum insulation thickness were investigated. [ABSTRACT FROM AUTHOR]

The industry is faced with the task of introducing novel products with significant added value due to the rising customer demand for ingredients derived from sustainable sources and organic processes. Lycopene, a red pigment with well-known antioxidant effects, is particularly abundant in watermelon. They are also a remarkable source of different nutrients, but because of a specific harvesting period, seasonal production in certain agro-climatic zones, watermelon fruit have a relatively short shelf life. Therefore, the fruits are processed into juice concentrates, which extends their shelf life, lowers the cost of transportation and storage, and makes the fruit available year-round, even when it is out of season. Evaporation is the typical process used for producing juice concentrates. The main drawbacks of various evaporators, however, include the increase in viscosity brought on by the concentration of the juice and the fouling of the heat transfer surface. In this study, concentration is achieved by stripping water from the juice by an unsaturated air stream, under a high centrifugal field in a rotating packed bed with wire mesh packing. The performance of the contactor is studied by varying the operating parameters (rotating speed, air flow rate, juice flow rate, and temperature). The highest concentration obtained in the study after two hours of operation is ~21.9 °Brix which is remarkable. [ABSTRACT FROM AUTHOR]

The current study uses numerical methods to evaluate the thermal and flow characteristics of air jet impingement on concave multi-protruded surfaces. A two-dimensional numerical analysis is carried out with the help of commercially available FLUENT package. The impact of different geometric parameters is studied, including protrusion shape (convex and triangle), protrusion height and central angle by protrusions (α). Multiple protrusions on a surface lead to a series of peaks and valleys in the local Nu variation, which governs the overall thermal performance of jet impingement. It is found that protrusions with lower central angle by protrusions improve the heat transfer attributes compared to smooth surface, irrespective of protrusion size and shape. A drastic improvement in thermal performance is noted by replacing convex protrusion with triangle protrusion, particularly at the larger central angle by protrusions (α). [ABSTRACT FROM AUTHOR]

This study prepares an experimental examination of thermal and hydraulic analysis of an absorber plate integrated with different arrangements of twisted turbulators, including longitudinal, transversal, and oblique orientations. These arrangements are considered for both the integral and the interrupted turbulators over Reynolds number range from 9174 to 55048. Nu ratio and f ratio range from 1.15–2.21 and 1.73–7.79, respectively. The interrupted turbulators with oblique arrangements with the attach angles of 30° and 60° come in the second and third places, respectively, and the maximum criterion value in the latter cases is 1.29 and 1.21. [ABSTRACT FROM AUTHOR]

This study investigates time-dependent free convection heat transfer and buoyancy-assisted flow over a horizontal heated plate within a vertical channel for two distinct scenarios: one stand alone and second involving tilted plates and varying plate positions. The temperature difference between the plate and air induces buoyant airflow. The study explores the impact of plate tilt angles and positions on time-dependent heat transfer coefficients due to varying buoyant airflow. The primary focus of the research for both classes of study is on the effects of the tilt angles (which control the change in flow blockage ratio) and positions of the heated plate on the time-dependent heat transfer coefficients due to the time-dependent buoyant airflow. As the blockage ratio increases and the positions of the heated plate in the vertical channel decreases, the influence of time-dependent buoyancy on the time-dependent Nusselt number weakens. The time-dependent Richardson's number varied from 7.4 to 9.6 throughout the tests. Based on the experimental data gathered from corresponding flux geometries and test conditions, the CFD model was validated. We have also developed a set of empirical correlations for predicting time-dependent Nusselt numbers for a time-dependent Rayleigh number range of 2000 < Ra < 7500, the dimensionless height of the heated plate from 0.507 ≤ ϕ ≤ 0.551, and a flow blockage ratio of 0.08 ≤ χ ≤ 0.024. At orientations where γ = π/2 and γ = π/4, it has been observed that the heat transfer at position ∅ 1 is higher, whereas at γ = 0 orientation, ∅ 1 heat transfer value is lower compared to the others. When the time required for the heated plate at all positions (∅) to reach thermal equilibrium with the ambient environment is compared with respect to orientation angles, it has been observed that the γ = π/2 orientation angle reaches thermal equilibrium in the shortest time compared to the γ = π/0 and γ = π/4 orientation angles. [ABSTRACT FROM AUTHOR]

Anomalous heat transfer enhancement in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45° to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 103 to 3 × 104. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3 × 104. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) × 103. [ABSTRACT FROM AUTHOR]

The setting machine exhaust gas contains a large number of fiber particles and micro oil droplets, which are adhesive and flammable. This leads to difficulties in waste heat recovery of the exhaust gas. In this article, numerical and experimental studies of a non-uniform plate heat exchanger with dimples/protrusions for waste heat recovery of setting machines are carried out. Based on the three-dimensional fluid-thermal-structural coupling method, the regenerative process between gas and air are investigated numerically with low Reynolds number turbulence model. The effect of the structural parameters (protrusions diameters, protrusions spacing and plate spacing) and operation parameters (air inlet temperature, gas and air flow rate) on the heat transfer performance are discussed. The multi-objective optimization of the plate regenerator is conducted by Box-Behnken Design and Nondominated Sorting Genetic Algorithm II to maximize the thermal performance coefficient and minimize entransy dissipation number. It is found that when D1, H1 S1, D2, H2, S2 are 9 mm, 7 mm, 161 mm, 9 mm, 8 mm and 153 mm respectively, the heat exchanger has the best heat transfer performance. Compared with the original model, the heat transfer rate of the optimized heat exchanger is increased by 3.9%, the thermal performance coefficient of the air side and flue gas side is increased by 5.7% and 5.9% respectively, and the entransy dissipation number is reduced by 24.6%. [ABSTRACT FROM AUTHOR]

Air-based photovoltaic thermal(PVT) solar collectors can convert solar energy into both electrical and thermal energy. However, the output efficiency was often low due to the limitation of the heat transfer capacity for air. Therefore, in this paper, an air-based PVT with the application of a novel rib was modeled and numerically simulated. The innovation of this paper was proposing a novel rib, which was based on the Venturi effect. First, the effects of the new rib control parameters on the performance of the PVT system were analyzed using orthogonal design tests. The result showed that the thermal efficiency of the best factors combination test was 51.16% when the solar radiation was 500W=m²and the air inlet rate was 0:09m=s. Second, analyzing the fluid flow characteristics and the enhanced heat transfer mechanism, this study found that the increased air velocity under the novel rib and the low-velocity vortex formed between the rib both negatively affected heat transfer. Consequently, this paper proposed a novel fin design coupled with curved fins to address the issues with the novel rib design, which achieved 55.12% thermal efficiency with the combination structure. Finally, we applied the combined structure to the PVT system, studied its thermal efficiency under real-world conditions, and compared it with the empty channel collector. The results showed significant improvement, with a 16.38% increase in thermal efficiency and the model exhibited excellent, stable performance. [ABSTRACT FROM AUTHOR]

With the increasing number of high-temperature mines, there has been a growing focus on research into thermal environment management and prediction in long-distance ventilation roadways. Mastering the principles of heat transfer in roadways is crucial for enhancing ventilation performance and achieving energy savings in mine heat hazard control. A onedimensional ventilation ultra-long roadway with high precision and low weight is presented in this study, which accurately depicts the dynamic heat transfer between the airflow and three-dimensional surrounding rock (SR) of roadway. The calculation time of the one-dimensional roadway numerical model is reduced by over 90%. The accuracy of the proposed numerical model is verified by the heat convection within roadway wall and the heat transfer in SR. In addition, the evolution of the temperature field and Nusselt (Nu) number of ultra-long roadway wall regarding ventilation time and periodic fluctuation of initial temperature of airflow (TA) are analyzed. The results indicate that the temperature of SR and Nu number of ultra-long roadway wall both periodic changes with the fluctuation of TA, and the TA and Nu number of ultra-long roadway wall fluctuate in opposite phases. When the TA temperature ranges from 15 to 25°C, the Nu number of ultralong roadway wall changes in the range 90 in a year. The Nu number of ultralong roadway wall decreases with the increase of ventilation distance. Additionally, the TA in ultra-long roadway exhibits a linear relationship with both the initial TA, the thermal conductivity of SR, and the initial temperature of SR, but it is subject to negative exponential decay in relation to ventilation speed. As the length of the roadway increases, fluctuations in the initial TA have less impact on the thermal environment within the longdistance ventilation roadway, while ventilation speed, thermal conductivity of SR, and initial temperature of SR become more influential factors. [ABSTRACT FROM AUTHOR]

The effect of the boundary conditions of the first and second kind on the predicted characteristics of anomalous heat transfer intensification in the case of turbulent low-velocity air flow over an inclined groove in the hot wall of a narrow channel is numerically investigated. It is shown that the isothermality conditions lead to a considerable underestimation of the thermal efficiency of a surface structured with narrow grooves, compared with the conditions of heat flux constancy. [ABSTRACT FROM AUTHOR]

The ambient temperature's impact on the power output of gas turbines is significantly pronounced, particularly in hot and dry climates such as Iraq. This study seeks to elucidate the potential enhancement of heat transfer and performance improvement in gas turbines through the implementation of an inlet air fogging system. By cooling and humidifying the inlet air, it is hypothesized that the air's density and mass flow rate will be augmented, thereby increasing the power output and overall cycle efficiency. A comprehensive experimental and numerical investigation was undertaken, employing the inlet fogging technique which introduces a mist of fine water droplets into the incoming airflow. The heat exchange between the water droplet surface and the hot air-up until the droplet's evaporation - was examined meticulously. The results underscored differential improvements when using 9 and 5 nozzles, which modified the air velocity flow. These improvements were attributed to the enhancement in heat exchange between the hot air and the evaporating water droplets, leading to an increase in electrical energy output. Computational fluid dynamics (CFD) was employed to analyze the thermal behavior inside the wind tunnel using the commercial software Fluent 22 R1. The model predictions and experimental observations along the duct exhibited satisfactory agreement, with the most significant discrepancies being a temperature drop of 2.5% and a heat transfer rate difference of 3.8%. [ABSTRACT FROM AUTHOR]

The article presents numerical simulations of the flow and heat transfer for beds with an ordered and shifted arrangement of elements. The numerical model applied is based on the unsteady equation of heat conduction (3D) and the Navier-Stokes equations. A high-order compact method in combination with the weighted essentially non-oscillatory scheme and predictor-corrector method is applied for the spatio-temporal discretisation. The flows of air and heat in the bed are modelled using the immersed boundary technique, which allows the use of Cartesian meshes for objects with very complex geometric shapes. The influence of the shift of elements in the bed on the temperature and velocity field was analysed. For two of the selected beds, the influence of arrangements of elements on the flow and heat exchange was analysed, which can lead, for example, to an improvement in the heating properties and to eliminating defects in the construction of reactor fillings. [ABSTRACT FROM AUTHOR]

To study the heat and mass transfer characteristics of an evaporative cooler for cooling high-temperature working fluids, an experimental device of the evaporative cooler was built, and a corresponding test system was constructed. Then, the experimental study was carried out based on an orthogonal experimental design, and the law and extent of the influence of water flow in the tube, the spray water flow rate, the inlet water temperature in the tube, and the air flow rate on the heat dissipation, cooling efficiency, and heat and mass transfer coefficients were obtained. The correlation equations of the heat and mass transfer coefficients were obtained by fitting the orthogonal experimental data, and the validity of the correlation equations was confirmed by the verification experiment. [ABSTRACT FROM AUTHOR]

The object of research is the heat transfer coefficient between pellets and air flow in industrial granulation towers. The problem lies in the difficulty of optimizing the heat transfer process. As a result of experiments and analysis, it was shown that each granulating tower for the production of mineral fertilizers has unique properties that significantly affect the efficiency of heat transfer. There are general mathematical models, but for accurate modeling and optimization of heat transfer, the unique characteristics of each production must be taken into account. The results showed that creating an accurate mathematical model for each specific fertilizer production is a difficult task due to the large number of unmeasured or difficult to reconcile factors. The method of calculating the heat transfer coefficient for the granulator tower obtained in the course of the work derives from a set of researches on the production of mineral fertilizers. This approach is based on the analysis of technical parameters and granulation composition of the product. The developed method makes it possible to reliably ensure the operating conditions of the device during modernization and changes in production volumes. These results are important for both practical and theoretical purposes. They can be used to accurately predict the operating conditions of equipment during modification and productivity growth. According to the research results, this approach allows obtaining fairly reliable data for forecasting the thermodynamic conditions of the tower equipment in the event of its modernization and transition of the granulation tower to the production of an increased amount of products. The specified method was tested in calculations of production modernization at urea production plants (Indian Farmers Fertilizer Cooperative (Iffco), India), Rustavi Azot LLC (Georgia), Grodno Azot LLC (Republic of Belarus) and others. This method has proven to be quite reliable in predicting the possible need for an additional amount of air supplied to the tower and forming requirements for the operating parameters of rotary vibrating granulators in the event of a significant increase in the load on the float in the tower and an increase in the amount of products planned for release. [ABSTRACT FROM AUTHOR]

The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0o (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000. [ABSTRACT FROM AUTHOR]

As the electronics industry gravitates towards smaller yet more powerful devices, the need to enhance traditional heat sink cooling capabilities without enlarging their footprint has become increasingly urgent. This necessity stems from the adverse effects of high temperatures on electronic performance and the limitations of traditional heat sinks' thermal transfer. This study addresses the challenge by investigating modifications to heat sink design, specifically through the strategic perforation of fins to increase their surface area, thereby improving heat dissipation without augmenting size. A series of lateral plate fins, perforated for increased surface area, were positioned on the base of a heat sink. The thermal performance of these modified heat sinks was then tested experimentally within a long, square cross-sectioned channel, facilitating forced air passage at manually controlled speeds. Three heat sink samples were compared under variable airflow rates to ascertain the cooling efficiency of the perforated fins. Three distinct rectangular heat sinks were utilized. The first featured holes of varying diameters arranged horizontally (PHS-HV), while the second had vertically varying diameters, with smaller ones at the top and larger ones at the bottom (PHS-VV). These perforated heat sinks were contrasted against a nonperforated heat sink under different thermal loads and Reynolds numbers. Results demonstrated enhanced heat dissipation, Nusselt number, and heat transfer coefficient in perforated fins compared to non-perforated ones. Notably, the use of different hole diameters in the same fin positively impacted heat dissipation, with horizontal diameter expansion (PHS-HV) outperforming vertical expansion (PHS-VV). The heat transfer improvement was 8.53% for PHS-HV and 4.36% for PHS-VV at Re 20000. Furthermore, perforation contributed to a decrease in heat sink mass compared to solid heat sinks, indicating cost and material savings. This study underscores the potential of strategic perforation in augmenting heat sink performance for next-generation electronics. [ABSTRACT FROM AUTHOR]

The thermal and flow resistance properties of wetting pads play a key role in how effective direct evaporative cooling (DEC) systems Perform. To make an informed decision, it's crucial to study the heat transfer properties and airflow resistance manifested in pressure drop for various types of wetting media. An experimental study was conducted to determine pressure drop and heat transfer correlation constants at three airflow rates for palm fruit mesocarp fibres (PFMF) wetting media. Heat transfer and pressure drop equations were fitted with generated data to obtain correlation constants. The wetting media were effective to lower the ambient temperature at an average depression of 6.6 to 8.2 °C and increase the relative humidity of the inlet air at an average value of 25.54 to 39.32%. PFMF had a low-pressure drop per unit length, ranging from 5.29 to 7.62 Pa/m, which makes it an appealing alternative to other wetting media. New correlation constants generated for pressure drop and heat transfer data fit well with high coefficient of determination (R2) values. The average cooling efficiency ranged from 56.43 to 65.27%, while the average Merkel number was 0.16 to 0.19. The Nusselt number increased with the Reynolds number and showed a laminar flow. Amaranths stored in DEC produced respiratory heat ranging from 290.86 to 336.53 mg/kg/h for all air velocities. Considering the respiratory rate within the range of cooler temperatures, it is recommended to use the DEC only for short periods or for pre-cooling of vegetable storage. [ABSTRACT FROM AUTHOR]

Steam is used to dry the milk powder in milk powder factories. When the steam used turns into condense, there is energy due to the pressure on it. This energy is generally referred to as waste heat. There are many ways to recover waste heat. Within the scope of this study, the calculations of the preheating coil will be made, and waste heat recovery will be achieved by transferring the latent heat above the condensate water to the air. In today's conditions, waste heat recovery processes are important in order to ensure energy efficiency. It is seen in the market that the sector develops projects within the scope of many savings measures and energy efficiency projects are formed as the fastest recycling. In this study, which was set out to use the competitive energy more efficiently, it was calculated how much of the heat load on the condensate could transfer to the air by verifying the air flow rate with the help of the pitot tube. The battery designed with the data obtained in line with these calculations was integrated into the system and commissioned. The temperature and pressure differences of the integrated battery were measured. The heat transfer and pressure losses obtained from the experimental results were compared with the values obtained with the CFD package program. The energy recovery obtained from the programming and training is 222.085 TL. [ABSTRACT FROM AUTHOR]

For the serrated heat transfer surface, the heat transfer and flow properties are investigated with external vibration excitation using numerical simulation method. By using the dynamic grid to realize the vibration of the fin wall, the impacts of frequency, amplitude, wind velocity and ambient temperature on vibration-strengthened heat transfer are investigated. The results show that vibration impacts the temperature distribution around the fin, interferes with the flow of air, causes the air to form a certain angle with the fin wall, thus preventing the development of the boundary layer and achieving strengthened heat transfer. The impact of amplitude on vibration-strengthened heat transfer is smaller than that of frequency, and low wind velocity is more favorable to the role of vibration-strengthened heat transfer, and the change of ambient temperature has less impact. Compared with the stationary condition, wall vibration can improve the average heat transfer coefficient by up to 66.6%. [ABSTRACT FROM AUTHOR]

In order to reduce the rain zone noise of wet cooling towers and enhance the heat transfer and ventilation, the influence of sound barriers on the thermal performance of wet cooling towers with synergistic optimization of fillers and water distribution was studied based on threedimensional numerical calculations. It is found that under the working conditions of this research, the sound barrier and the two zone synergistic efficiency scheme can uniformly distribute the temperature field, air flow velocity distribution, and water vapor mass fraction distribution inside the cooling tower;The two zone synergistic efficiency enhancement scheme can to some extent counteract the adverse effect of the noise barrier on the heat transfer performance of the cooling tower, resulting in an average increase of 0. 06℃ and 3. 8% in the circulating water temperature drop and cooling number compared to the original tower, respectively;Although the ventilation capacity of the entire tower has been reduced after the renovation, the distribution of the aerodynamic field is more reasonable, which is more conducive to the heat exchange of the cooling tower. This study can provide reference for the design of a two zone synergistic cooling tower with sound barriers. [ABSTRACT FROM AUTHOR]

In order to optimize the heat transfer characteristics of regenerative evaporative coolers under different climatic conditions and provide reference data for numerical simulation research. The dynamic coupling of heat and humidity parameters of the air flow in the regenerative evaporative cooler is the fundamental factor affecting the efficiency of evaporative heat transfer, and mastering its law can guide the structure optimization of the heat exchanger. In this paper, a simulation model is constructed based on the structure of regenerative evaporative cooler, and the variation of heat and humidity parameters in the airflow passage is studied by numerical simulation method with the application background of representative cities at home and abroad under different climate conditions. It is found that the relative humidity increases rapidly in the wet channel, and the length of 40 cm wet channel can meet the full evaporation demand under most working conditions. The evaporation cooling effect is greatly affected by the inlet air parameters, and the saturation degree of ambient air has a significant influence on the cooling effect. Keeping the latent heat exchange process in the high efficiency evaporation section and the sensible heat exchange process in the high temperature difference section of the channel can effectively improve the heat exchange efficiency of the evaporative cooler and shorten the length of the heat exchanger. [ABSTRACT FROM AUTHOR]

In this study, roughness in the form of multi-V ribs having trapezoidal slots were crafted over the surface of absorber plate for enhancing the heat transfer rate in a solar air heater. An experimental setup was designed and fabricated for demonstrating the performance of this plate with respect to smooth absorber plate. The setup has a double glazed-double pass air flow arrangement. The experiments were conducted under Indian climatic conditions (Latitude = 28.53°N and Longitude = 77.39°E) in September and October 2021 at various rates of air flow through the duct. The results of the roughened absorber plate were compared with the smooth absorber plate. It shows that the multi-V ribs with trapezoidal slots have higher efficacy as compared to smooth absorber plate in the order of 10.42% at an air flow rate of 0.078 kg/s. In addition, the present data of proposed roughness were also compared with data of various roughness available in the literature. It was found that the maximum thermo-hydraulic performance parameter of the proposed roughness texture is higher than other shapes of roughness texture. It was also found that the combination of double-glass cover and double-pass arrangement with the proposed roughness geometry increases the efficiency of the solar air heater at least by one order of the present solar air heating system. [ABSTRACT FROM AUTHOR]

An air‐cooled island can significantly alter the heat transfer performance of an air‐cooled condenser due to the reflow of hot air caused by environmental wind. This can result in a considerable deviation between the backpressure calculated by traditional air‐cooled condenser models and the actual value. To address the issue, a research study was conducted on a 600‐MW direct air‐cooled unit. Numerical simulation methods were used to obtain the corresponding air flow rates and fan inlet air temperatures for each air‐cooled heat exchanger, which were then combined to establish a backpressure calculation model. From the above model, the backpressure prediction model and unit net output of full conditions were established using a backpropagation neural network. Therefore, taking the net output as the optimization objective, a genetic algorithm was used to compute the optimal backpressure and optimal fan speed in off‐design situations. Compared with traditional calculation approaches, the model produces backpressure predictions that were closer to the actual situation under the effect of ambient wind. The results indicate that both the optimal backpressure and fan speed were positively correlated with the exhaust flow and ambient temperature. It has been observed that when a unit was affected by different wind directions, the effect of the forwarding wind on the backpressure was smaller than that of other wind directions, especially under high‐load conditions. Moreover, the fan group operates close to full capacity under high‐temperature and high‐load conditions. Therefore, considering the influence of ambient wind, the obtained optimal backpressure and fan speed under variable working conditions were more realistic. [ABSTRACT FROM AUTHOR]

The present research work aims at providing data on heat transfer by forced convection from three-dimensional bodies suspended in a free stream of air. The shapes investigated covered cubic and rectangular bodies with air flow parallel and normal to the body's axis. The experiments were carried out inside an air duct in which air flows over a model for the three-dimensional body. The results obtained were represented by power function relations between the Nusselt and Reynolds number. The results were divided into the main body axis was parallel to the direction of the air flow. The heat transfer from the whole cube could be broken to the face components. This showed that the sides and rear face were responsible for more heat transfer. Increasing the length of the rectangular body increased the heat transfer. The equation representing the increase of heat transfer with length is suggested. The present results are essential in designing air-conditioned railway coaches, heated liquid wagons, refrigerated cars, and food and fluid carriers. [ABSTRACT FROM AUTHOR]

Double-diffusive mixed convection problem had been a notable topic of research in the last decade. Lack of study is noticed under mixed convection using this double-diffusive in an enclosure specifically for roof-based ventilation systems with unsteady, partially heated conditions. This study investigates the Prandtl number effect in a double-diffusive unsteady flow in a square-shaped room where the upper channel was used for ventilation, and inside the enclosure, the walls are partially heated and mass concentrated. Galerkin residual method was implemented to get the governing equations. The Prandtl number 0.071 ≤ Pr ≤ 7.1 was chosen for the study, changing the dimensionless time 0.1 ≤ τ ≤ 1. The results have been shown in the mode of graphical representation and contour plots to observe the Prandtl number effect in such problem. The velocity streamline, isotherm, isoconcentration plots, heat and mass transfer rate, average fluid temperature and average mass concentration, etc., are shown. Results showed that heat and mass transfer rise with the growth of the Prandtl number. This research would be the guide for the design consideration in such double-diffusive systems like roof-based air ventilation systems with partial heat and mass generation. [ABSTRACT FROM AUTHOR]

The operating temperature of photovoltaic (PV) panel have significant influence on its generating efficiency and life span. To improve the performance of PV panel, we performed comparative analyses on a novel PV panel cooling strategy by integrating PV panel with phase change material (PCM) and ventilation system (PV/PCM air-based system). The heat transfer characteristics of molten PCM in an inclined cavity with constant heat flux on one side and air flow boundary on another side are numerically investigated. The thermal performance including dimensionless temperature and temperature uniformity, the heat transfer capability including local Nusselt number and average Nusselt number, are compared and analyzed. The results indicate that flow boundary has a significant effect on the PV cooling. Cavity at top-down flow direction has better temperature uniformity and at bottom-up flow direction has greater heat transfer capability. Increasing Reynolds number can enhance the heat transfer efficiency and reduce the temperature at the same time. Further, the impact of each factor on heat transfer capability are quantified based on the grey relation analyses. Grey relation grade for average Nusselt number with Ra number, Re number, AR, ϕ, and flow direction is 0.51, 0.66, 0.69, 0.62, and 0.53, respectively. This indicates that heat transfer capacity is the most sensitive to AR, followed by Re number, inclination angle, flow direction, and Ra number. [ABSTRACT FROM AUTHOR]

Mammals have presumably evolved to adapt to a diverse range of ambient environmental conditions through the optimized heat and mass exchange. One of the crucial biological structures for survivability is the nose, which efficiently transports and thermally preconditions the external air before reaching the internal body. Nasal mucosa and cavity help warm and humidify the inhaled air quickly. Despite its crucial role, the morphological features of mammal noses and their effect in modulating the momentum of the inhaled air, heat transfer dynamics, and particulate trapping remain poorly understood. Tortuosity of the nasal cavity in high-olfactory mammalian species, such as pigs and opossum, facilitates the formation of complex airflow patterns inside the nasal cavity, which leads to the screening of particulates from the inhaled air. We explored basic nasal features in anatomically realistic nasal pathways, including tortuosity, radius of curvature, and gap thickness; they show strong power-law correlations with body weight. Complementary inspection of tortuosity with idealized conduits reveals that this quantity is central in particle capture efficiency. Mechanistic insights into such nuances can serve as a tipping point to transforming nature-based designs into practical applications. In-depth characterization of the fluid–particle interactions in nasal cavities is necessary to uncover nose mechanistic functionalities. It is instrumental in developing new devices and filters in a number of engineering processes. [ABSTRACT FROM AUTHOR]

The effect of overequilibrium heating of a surface with nonuniform catalytic properties in a subsonic flow of dissociated air is experimentally studied using the VGU-4 HF-plasmatron. A temperature jump is observed on a plate of Buran orbital vehicle heat-shield material as the flow transitions from the low-catalytic area of the surface to the high-catalytic area covered with chromium-nickel spinel NiCr2O4. A temperature jump is also observed on the heat-shield tile of the Buran orbital vehicle at the transition from the low-catalytic area of its surface to the medium-catalytic area covered with niobium. The temperatures of the surfaces with uniform and nonuniform catalytic properties under the same flow regimes are compared. [ABSTRACT FROM AUTHOR]

The detailed understanding of heat transfer in the pulsating airflow in the pipe is critical to reducing heat losses in the engine exhaust stream and improving catalyst performance. In the present investigation, we have scrutinized the impact of pulsation frequencies ranging from 0-90 Hz on the flow velocity field and the consequent heat transfer through a horizontal pipe wall. The Nusselt numbers were evaluated at three distinct cross-sectional points moving from upstream to downstream, by systematically modulating the frequency. Temporal variations in the velocity field and temperature were captured utilizing particle image velocimetry (PIV) and dual-thermocouple probes, respectively. Intriguingly, while the Nusselt number for steady flow at 0 Hz closely adhered to Gnielinski's equation, the pulsating flow demonstrated a peak between 25-35 Hz, a pattern not predicted by the prevailing quasi-steady-state theory. The observed frequency response of turbulence was found to be congruous with the Nusselt number, indicating that the heightened heat transfer at frequencies of 25-35 Hz could be attributed to the enhanced turbulence and the temperature gradient between the fluid and the wall surface during the deceleration phase in the hysteresis of turbulence in the pulsating flow. The unique frequency characteristics of heat transfer that were uncovered in this study, with respect to both flow velocity and temperature, offer valuable insights for devising strategies to mitigate heat loss during ignition and idling. Furthermore, these findings provide robust benchmarks for validating numerical simulations of pulsating flows in real-life automotive engines. [ABSTRACT FROM AUTHOR]

This study presents an experimental and numerical investigation into the thermofluid characteristics of airflow over an inclined, heated plate, mimicking a solar panel. The inclination of the plate was systematically adjusted from 0° to 90°, and the heat flux was varied from 1000 to 4000 W/m², with Reynolds number ranging from 63,000 to 650,000. The study employed a second-order finite volume method for discretization and resolution of steady fluid dynamics problems, with simulations conducted using Ansys Fluent software. The k-ε RNG turbulence model was utilized for these simulations. The numerical results, validated against experimental data, were extrapolated to assess the behaviour at a wide range of attack angles and flow rates. Correlations were established between the average Nusselt number and friction coefficient, as functions of Reynolds number and attack angles. It was observed that heat transfer was optimized at lower attack angles. Conversely, higher inclination angles resulted in increased skin friction, thereby reducing airflow and negatively impacting heat convection. For larger Reynolds numbers, convective flow enhanced and the resistance of the plate was found to be lower at smaller attack angles. These findings have significant implications for the improvement of solar panel efficiency, offering valuable insights into the optimal configuration for maximizing convective heat transfer. [ABSTRACT FROM AUTHOR]

The air-based photovoltaic-thermal collector (PVTC) is a system that can generate electricity and heated air simultaneously from solar energy. This study investigates the electrical and thermal performances of an air-based single-pass double-flow photovoltaic-thermal collector (SPDFPVTC) coupled with a nonuniform cross-section rib (NUCSR) under various operating conditions. The rib is installed at the rear of the photovoltaic panel to enhance the heat transfer performance between the photovoltaic panel and the flowing air. Based on the energy balance equations, a mathematical model of the proposed SPDFPVTC is established and validated by experimental results. The solar intensity, air mass flow rate, and wind speed are selected as operating conditions. The effects of these operating conditions on the electrical and thermal performance of the SPDFPVTC have been discussed. In addition, this study evaluates the daily performance of SPDFPVTC with and without NUCSR. The average electrical, thermal, and overall efficiency were 17.59%, 43.96%, and 61.55%, respectively, for SPDFPVTC with NUCSR and 16.97%, 38.87%, and 55.83%, respectively, for SPDFPVTC without NUCSR. Consequently, installing NUCSR could enhance the daily electrical, thermal, and overall energy output of SPDFPVTC by 4.33%, 13.23%, and 10.63%, respectively. [ABSTRACT FROM AUTHOR]

In this study, the performance of the Earth air heat exchanger system for cooling applications has been investigated computationally using computational fluid dynamics (CFD) software, and the results have been compared to experimental results. According to the simulation results, the temperature of moving air drops continuously as pipe length increases. The temperature drops more slowly in larger diametric pipes than in smaller ones, and the drop in temperature reduces slightly as air velocity rises. The proposed computational fluid dynamics model has been validated by building an indoor experimental test rig with the same parameters used in the simulation for variable diameter sets. As a result, an experimental test rig was constructed and built at NIT Patna, India, for the climatic and soil conditions of Patna. This fabricated and demonstrated experimental set up may be used in any climate and soil type. This is very concise and portable for transport. In the experimental and 3D simulation results, the maximum deviation in the Nusselt number for 0.0285 m, 0.038 m, and 0.0485 m pipes varies by 9.5%, 10.9%, and 7.72%, respectively. Similarly, in experimental and 3D simulation results, the maximum deviation in friction factor for 0.0285 m, 0.038 m, and 0.0485 m pipes varies by 6.21%, 11.22%, and 9.45%, respectively. The maximum deviation in heat transfer rate and effectiveness between simulated results and experimental observations for 0.0285 m, 0.038 m, and 0.0485 m diametric pipes are 6.76%, 9.96% and 9.58% respectively. The cooling capacity (heat transfer rate) increases as the air velocity increases; however, the effectiveness reduces as the air velocity increases. [ABSTRACT FROM AUTHOR]

Multi-parameter study on the subsonic equilibrium air plasma flows in the cylindrical discharge channel of an induction RF-plasmatron IPG-3 with the maximum operating power of 1 MW is presented. Simulations are carried out by numerical solution of full Navier–Stokes equations coupled with a two-dimensional equation for high-frequency electric field; the discretization of the equations is performed on a staggered Cartesian mesh. An effective method for calculation of the transport coefficients for ionized multi-component air (including the plasma conductivity) in the temperature range 300–15000 K is applied, with the higher-order approximations by the Sonine polynomial in the Chapman–Enskog method. Simulation results are presented, including the flow fields, electric field, and thermodynamic parameters of the air plasma in the discharge channel of a high-power induction plasmatron. The results obtained reveal for the first time the structure and parameters of a plasma torch in a large-diameter (200 mm) discharge channel at powers up to 300 kW, providing the axial specific enthalpies at the channel outlet as high as 68 MJ/kg. [ABSTRACT FROM AUTHOR]

A non-tubular prototype cavity receiver absorber with extended internal surfaces (fins) is proposed to enhance heat transfer in Stirling engine-based Concentrated Solar Power systems. There is limited research on the realization of downsized absorbers in terms of their design and manufacturing. The objective of the absorber solution proposed in this paper is to address the issue of inadequate comprehension regarding the impacts of the geometric and flow parameters on thermohydraulic efficiency. These impacts are numerically investigated in a 100 mm long heat transfer channel with a 10 mm × 10 mm section. The prototype absorber is fabricated using a wire electrode-discharging manufacturing approach, and is experimentally investigated using the enthalpy method. Numerical results indicate that heat transfer to the working fluid in the novel absorber can reach 482 W at the reasonable cost of 0.391% pressure drop per 100 mm (air flow at 0.0015 kg/s and 5 bar). In the experimental investigation, the prototype realizes a 1113.033 W heat transfer rate at 8 bar and 12 kg/h. This implies that a non-tubular design with extended internal surfaces can increase the internal surface area to enhance heat transfer while downsizing the volume to reduce heat loss. [ABSTRACT FROM AUTHOR]

The paper presents the results of calculating the thermal-hydraulic heat exchange efficiency processes for direct and swirl (using an inserted twisted tape) pipe air flows at the same transferred heat fluxes and temperature conditions. The calculated energy efficiency, which characterizes the thermal-hydraulic heat exchange efficiency, demonstrated the ratio of transferred heat and energy consumption for pumping the coolant during the heat exchange for these two cases to be almost the same for coolant-flow Reynolds numbers up to 2.5 ⋅104. At large Reynolds numbers, the thermal-hydraulic efficiency of a direct flow heat exchange is higher. [ABSTRACT FROM AUTHOR]

The heat transfer and pressure drops characterization of air and CO2 through smooth and rough micro tubes are investigated experimentally. Nine smooth stainless steel micro tubes with inner diameters of 50, 80, 100, 250, 300, 400, 800, 900, and 950 μm, and six rough micro tubes with inner surface roughness are tested in the present study to characterize the friction factors, the pressure drops, the heat transfer Nusselt numbers, and evaluating the surface temperature on the wall of the micro tubes. It was observed that heat transfer Nusselt numbers on smooth micro tubes fitted well with the conventional correlations of the Gnielinski' (Gnielinski in Int J Chem Eng 16:359–368, 1976) correlation, the Dittus-Boelter' (Dittus and Boelter in Univ Cali Berkeley Publ Eng 2(13):443–461, 1930) correlation, and the Petukhov' (Petukhov and Kirillov in Teploeenergetica 4(4):63–68, 1958) correlation. Moreover, the test results of the friction factors were in a very good agreement of the Gnielinski' (Gnielinski in Int J Chem Eng 16:359–368, 1976) correlation, and Blasius' (Blasius in Forschg. Arb. Ing. -Wes, pp 131–137, 1913) equation in both laminar and turbulent regions, except for the micro tubes in the range of 50~100 μm. However, for the rough micro tubes, the test results scattered above the standard predictions of the Filonenko' (Filonenko in All Union Thermotechnical Institute, 1948) correlation. The test results showed that the heat transfer enhancement of the fabricated smooth surface micro tubes is better than that of the structural rough surface micro tubes. It was also observed that the transition regime occurred at Re of approximately 1,500~2,000 due to the increase in surface roughness. [ABSTRACT FROM AUTHOR]

• The novel two-path thermal energy storage with fin-enhanced PCM is designed and manufactured. • The thermal performance and temperature profile are experimentally investigated. • Heat transfer rate and accumulated thermal energy are fitted by test data. • Thermal environment during emergency cooling is analyzed with different inlet condition of CRAC. Emergency cooling system is necessary to guarantee high security for data center. Thermal energy storage is one of the feasible methods for emergency cooling with quick response ability to supply higher thermal safety. To simplify the traditional thermal energy storage system and improve its heat transfer efficiency, the novel two-path latent thermal energy storage unit developed for emergency cooling is experimentally studied. The effects of inlet temperature, flow rate on thermal performance of LTES, including heat transfer rate, accumulated energy, effectiveness and overall heat transfer coefficient, are investigated during both charging and discharging processes. Results from the experimental analysis show that the released energy of system could reach up to 2.9 MJ with the average heat transfer rate 1575W-2286 W. The overall heat transfer coefficient ranges from about 297–660 W/K when the flow rate of HTF varied from 12 to 16 L/min. The experimental LTES is then studied integrated with CRAC for emergency cooling. For air flow rate higher than 300 m3/h, and thermal load lower than 1800 W, the LTES meets 15 min of emergency cooling. The inlet and outlet air temperature of CRAC are successfully controlled under 40.5 °C and 23.9 °C. The newly designed LTES shows good thermal performance, and provides more flexibility and adaptability for real application in data center. [ABSTRACT FROM AUTHOR]

Air-to-air fixed plate enthalpy membrane exchanger is considered one of the equipment used in energy recovery services. Thermal performance of air-to-air energy recovery ventilator is examined numerically using a 3D CFD simulation. Air flow inside the exchanger is tested using four numerical turbulence models: Standard k-ε, k-ε renormalization group (RNG), k-ε realizable and k-ω shear-stress transport (SST) models. The adopted heat and mass exchange element within the ventilator (membrane) is a thin 98 μm porous 60 gsm Kraft paper. A user defined function (UDF) has been developed to enable the CFD model to estimate amounts of mass exchanged between the two sides of the membrane. Grid dependency study is conducted and results have shown that a perpendicular distance of 50 μm or less from the membrane surface would result in a negligible variation in the ERV thermal effectiveness. The validated CFD model and UDF code against experimental measurement resulted in a maximum difference in thermal effectiveness of 3.6%. Results have shown that the SST k-ω turbulence models under enhanced wall treatment showed more sensitivity to flow at all Re values when compared with the k-ε simulated models. [ABSTRACT FROM AUTHOR]