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The heat and momentum transfer of crop pulp fibre suspensions were studied in a single pipe heat exchanger test loop. The data were produced at the pre-selected temperature, concentrations, and a range of flow rates. It was found that at the low fibre concentrations, the magnitude of heat transfer coefficient was higher than those of water data at the corresponding experimental conditions. However, the values progressively decreased below the water data at higher concentrations. The heat transfer data were affected by the variation of fibre characteristics, such as fibre flexibility, fibre length, fibre mechanical and chemical treatment, and the pulping methods used to liberate the fibres. The reduction of heat transfer coefficient was obtained with the enhancement of fibre flexibility observed by previous researchers for wood pulp fibres. In the present study, the characteristics of fibres and paper are correlated with heat and momentum transfer of suspensions of the fibres. Deviations in fibre properties can be monitored from the measurement of heat transfer coefficient or frictional pressure loss, and they can be adjusted by altering the degree of fibre refining treatment. Thus, the papers made from the fibre suspensions via in-situ monitoring could be uniform, consistent, and remain within the product specification. This could curb the rejected papers and ultimately reduce production costs and energy consumption. [ABSTRACT FROM AUTHOR]

During the actual operation of the power plant, the steam turbine will appear to operate under low load conditions. This paper proposes a novel water spray arrangement for the exhaust channel. Spraying ports are evenly arranged on the cone wall so that the direction of water spraying is opposite to that of the exhaust steam flow (reverse spraying). The feasibility of the nozzle was verified by simulation calculations of existing wind tunnel experiments. The results show that evaporation increases with decreasing load. And the evaporation volume is greater in the reverse spraying than in the down spraying (the direction of water spraying is the same as the direction of steam flow), with a maximum difference of 0.42 kg/s. The deterioration of the aerodynamic performance in the exhaust passage after water spraying can be attributed to the combined effect of the evaporation of water droplets and droplet interference with the flow field. The maximum reduction of 8.17% in the static pressure recovery coefficient in the reverse spray mode increased the total pressure drop by 377.4 Pa. After the water spraying, the temperature dropped significantly compared to before the water spraying. In reverse spraying, the vortex scale in the exhaust passage becomes larger, the return vortex flow increases, the volume absorption ability is stronger, the water droplets and steam contact time is long, good temperature reduction is achieved, and the temperature of the leaf root high-temperature zone is reduced. The maximum difference in temperature drop between the two spraying methods is 56.87 K. The results of this paper provide a reference for the cooling of the exhaust passage when the turbine is operated under low flow conditions for a long time. [ABSTRACT FROM AUTHOR]

Electric vehicles are gradually replacing some of the traditional fuel vehicles because of their characteristics in low pollution, energy-saving and environmental protection. In recent years, concerns over the explosion and combustion of batteries in electric vehicles are rising, and effective battery thermal management has become key point research. Phase change materials (PCM) can absorb or release a large amount of latent heat during the phase change process while maintaining a constant temperature (phase change temperature). In this paper, STAR-CCM+ software is used to carry out three-dimensional simulation of single cell and battery packs with PCM to investigate changing characteristics of battery temperature rise and temperature difference during the cooling and heat preservation process. At the same time, temperature rise and temperature difference of battery are analyzed under different ambient temperatures, convection heat transfer coefficients and phase change latent heats of PCMs. In summer, at an ambient temperature of 30 °C, when using PCM, the battery cell temperature can be reduced by 4 °C in 1800 s, which is about 8.6% lower than that without PCM. In winter, at an ambient temperature of −5 °C, the PCM with a melting point about 20 °C can keep the battery cell temperature drop of no more than 28% within 6700 s at a higher convection coefficient of 5 W/m2·K. Comparing the temperature of the battery pack with that of the battery cell, in the summer with an ambient temperature of 30 °C, the temperature of the battery pack decreased by 13.3 °C in 3600 s, while in the winter with an ambient temperature of −30 °C, the temperature of the battery pack increased by 14.3 °C in 5700 s. The use of phase change materials is conducive for batteries in electric vehicles to dissipate heat in summer and preserve heat in winter. [ABSTRACT FROM AUTHOR]

Through the analysis of hot oil carrying theory, the problem of oil film heat accumulation in hydrostatic bearing can be revealed, so as to avoid serious lubrication failure caused by heat accumulation. In this paper, the hot oil carrying factor is defined and the mathematical model of the thermal oil carrying characteristics of the oil film is established by taking the beveled double rectangular oil pad hydrostatic bearing as the object, and the hot oil carrying law under different working conditions is obtained by changing the inclination angle of the beveled oil pad at 0.0230°, 0.0250° and 0.0280°, respectively. Theoretical calculations and simulation studies show that within the range of the circumferential inclination of the oil pad with better dynamic pressure effect of the bearing, the inclination has little effect on the oil film hot oil carrying. When the speed of the workbench is lower than 10r/min, no oil film hot oil carrying phenomenon occurs. When the speed is in the range of 10r/min-100r/min, a part of the load will cause the phenomenon of oil film hot oil carrying. And when the speed exceeds 100r/min, the heat accumulation of the oil film is the most serious at this time. There are many reasons for the lubrication failure of hydrostatic bearings, and hot oil carrying is a new research direction, this paper starts from the oil film heating mechanism of beveled oil pads hydrostatic bearings, and describes the phenomenon of hot oil carrying. [ABSTRACT FROM AUTHOR]

Pulsating Heat Pipe (PHP) is an emerging efficient heat transfer device, that transfers heat passively through oscillating motions of liquid slugs and vapor plugs within the device. PHP is of high effective thermal conductivity with great potential in heat transfer management for various applications. The objective of this review paper is to summarize and analyse the applications of PHP in various fields that have been reported in the open literature, emphasizing on studies reported in past half decade. The thermo-hydraulic behaviour of PHP is influenced by numerous geometric and operational parameters, which are discussed in detail in the first part of the paper. The thermal performance of the PHP under rotation condition, which is seldom discussed in previous review articles, is also discussed. These parameters act individually and in tandem to alter the performance of PHP, which makes its prediction extremely difficult. However, the benefit of numerous influencing parameters is that they can be altered to make PHP suitable for various applications. These highly variable configurations make PHP suitable for applications such as the transfer of absorbed solar energy to the location of interest, waste heat recovery, thermal management of electric vehicle batteries, fuel cells, cooling of electronic components etc. PHPs are recently being studied for applications in cryogenics and cooling of cutting tools in the machining process also. In addition, novel applications of PHP such as high-performance fins for heat exchangers, cooling of building roofs etc. are also being reported. All these applications of PHP reported in the open literature are reviewed and summarized in the present article. [ABSTRACT FROM AUTHOR]

The current paper experimentally studied the performance of solar-driven internally cooled liquid desiccant system for hot and humid climates using CaCl2 as a liquid desiccant. The system is designed to investigate the input conditions of the room by adjusting various air and solution variables. This internally cooled liquid desiccant system consists of the dehumidifier and regenerator in a single module and the regeneration of the solution is done by solar energy. The present study analyzes the effect of solution concentration, air mass flow rate and solution volume flow rate using different performance indices such as humidity reduction, moisture effectiveness, enthalpy effectiveness, and COP. The results demonstrate that the maximum moisture reduction of 4.2 g/kg d.a. is found at an airflow rate of 0.03195 kg/s, a solution volume flow rate of 12.5 LPM, and a solution concentration of 37%, while the maximum COP of 0.274 is obtained at an airflow rate of 0.0715 kg/s, a solution volume flow rate of 12.5 LPM, and a solution concentration of 37%. The maximum moisture and enthalpy effectiveness are obtained as 24.1% and 26.2%, respectively. The paper also presents the correlations for moisture and enthalpy effectiveness based on findings from experiments. [ABSTRACT FROM AUTHOR]

This document is a summary of the 14th Heat Exchanger Fouling and Cleaning Conference held in Wagrain, Austria in June 2022. The conference aimed to provide a platform for researchers in the field of heat exchanger fouling to exchange ideas and research results. The special issue includes a selection of nearly 50 papers that were preselected and peer-reviewed prior to the conference. The papers cover a wide range of topics related to fouling of heat exchangers and reflect current interests in Heat and Mass Transfer. The document also acknowledges the guest editorial and expresses gratitude to the authors and reviewers for their contributions. [Extracted from the article]

This paper introduces a novel a CO2 mechanical subcooling heat pump water heater (MSHPWH) to improve the heating performance in low temperatures. By utilizing a mechanical subcooling (MS) cycle, additional heat is supplied to cooling water, improving system efficiency. The study evaluates the heating COP (COPh), power consumption and temperature of hot water under various steady-state operating conditions. Results indicate that the COPh of the MSHPWH increases by 44% to 57% compared to conventional HPWH as ambient temperatures range from -25 ℃ to -5 ℃. The MS cycle proves beneficial, with a subcooling range of 4 ℃ to 20 ℃. Adjusting the refrigerant mass flow rate ratio enhances heating output and hot water temperature. Changes in the mass flow rate ratio impact COPh and the temperature of hot water concurrently. This research highlights the innovative MS cycle's significant role in enhancing CO2 heat pump water heater performance in cold climates, showcasing its potential as an eco-friendly and efficient heating solution. [ABSTRACT FROM AUTHOR]

In the context of dual-carbon strategy, the insulation performance of the gathering and transportation pipeline affects the safety gathering and energy saving management in the oilfield production process. PCM has the characteristics of phase change energy storage and heat release, combining it with the gathering and transmission pipeline not only improves the insulation performance of collecting and transporting pipes, but also extends the safe shut time during the shutdown. Proposed a thermal model of a PCM-based composite energy storage pipeline combining the character of phase transformation between PCM and crude oil has been established. The heat preservation performance of the combined energy storage pipeline was evaluated by numerical simulation.This paper analyses the heat transfer performance of complex energy storage pipes, and considers the influence of natural convection and variable temperature zone on insulation performance.On this basis, the structure design of cascade phase transition was proposed, the optimized cascading composite pipe was presented, and the performance of different insulation structures was compared. [ABSTRACT FROM AUTHOR]

This research examines the water and energy performance in wet cooling towers and identifies methods for enhancing efficiency and minimizing water and energy consumption by exploring methods to enhance system performance. A three-dimensional transient model, developed using MATLAB's open-source code software, was utilized to simulate the cooling tower's behaviour under various operating conditions. This research focuses on precise simulation of cooling tower behavior and demand modeling aided by regression. The model's accuracy was validated through experimental measurements in diverse environmental conditions. The key parameter and performance that is investigated in this paper is the temperature profile of the cooling tower, in which the performance algorithm and proposed methodologies are anchored in the operational temperature. The experimental results led to operational solutions for enhancing cooling tower performance. For winter conditions, the recommended action involves closing the upper part of the cooling tower and activating the two side fans. Specific approaches are suggested for mid-season and summer scenarios, focusing on make-up water consumption and ambient air temperature control, respectively. In addition, results indicated a close alignment between the model and the actual system, with discrepancies of less than 2% in energy consumption and 5% in water consumption. Analysis of proposed productivity enhancements and changes in supply policies indicated significant potential for energy and water conservation in wet cooling towers. Implementing these solutions could lead to an estimated annual reduction of 44% in water consumption and 4.2% in energy consumption. [ABSTRACT FROM AUTHOR]

Microchannel heat sinks are widely used in the era of electronic equipment heat dissipation. This paper builds a numerical model of the heat sink with the interrupted rectangular microchannel and uses the experimental platform for validation. Two interrupted models including in-lined and staggered types are simulated to enhance the performance of the heat sink. The results show that the staggered type microchannels exhibit the lowest thermal resistance but the highest frictional resistance coefficient while the continuous microchannels have the opposite performance. However, the effect of heat transfer enhancement is decreasing with the increment of the interruption spacing for both of the in-lined and staggered interrupted microchannels as the overall heat transfer area is decreasing. Using the performance evaluation criterion (PEC) to evaluate the global heat transfer and flow characteristics of the heat sinks shows that the PEC of the in-lined interrupted microchannel is approximately 1.10 times higher, while the PEC of the staggered type is about 1.23 times higher compared to the continuous microchannel. This improvement is due to the interruption of the boundary layer by the cavity and the flow doping. Besides, when the Reynolds number is lower than 150, the temperature uniformity increases to roughly 1.14 times its original value. It provides a good guidance for the microchannel sink to obtain the better heat dissipation efficiency. [ABSTRACT FROM AUTHOR]

The technological development in measuring devices is massive due to the need for accurate flow measurements in various industries. However, the problem is choice of the flow meter for the complex and harsh environmental industrial applications. Due to the varied characteristic of gas and liquids, the mass flow meter provides an inaccurate result. Hence, this paper introduces the advancements in volumetric flow meters that provide highly accurate flow measurements. The various volumetric flow meter investigated in the paper are used for measurement of liquid, gas, and multi-phase flow. The study shows that electromagnetic is more suitable for complex environments of chemical and petroleum industries. The ultrasonic flow meter is a better alternative than the electromagnetic meter when the price is not a major concern. The ultrasonic flow meter also provides higher accuracy than other measurement techniques in multiple-phase-flow condition. However, electromagnetic measurements are only suitable for conducting liquids. [ABSTRACT FROM AUTHOR]

There is a rapid movement towards miniaturization in the field of micro-electronics, medical, defence, and space applications as well as an increase in thermal load density in the field of solar power. This has resulted in the requirement for technologies to be developed which enable the rapid removal of high thermal load from the components for effective and safe operation. Microchannel cooling has been one of the areas which has been investigated to provide the solution as required. This paper aims to looks at the different types of microchannels being developed, review the performance of microchannels being developed with different working fluids, explore the various structures utilized of microchannels and explore the use of microchannel in the various applications with regards to field of thermal management. Finally, future needs are proposed for extending the research and enlarging its application fields. This review paper serves as guidance for researchers to design and predict the performance of microchannel heat sinks (MCHS). [ABSTRACT FROM AUTHOR]

This article is a special edition of the Heat and Mass Transfer Journal dedicated to the 14th Heat Exchanger Fouling and Cleaning Conference. The conference took place in Wagrain, Austria from June 5-10, 2022, and brought together researchers and engineers from various industries and academic institutions worldwide to discuss the importance of heat exchanger fouling research. The conference covered a wide range of topics, including fouling in hydrocarbon systems, food processing fouling, biofouling, fouling mitigation, CFD modeling, and industrial cleaning methods. This special edition of the journal includes fifteen papers focusing on fundamental research. The next conference is scheduled to be held in Portugal in April 2024. [Extracted from the article]

Predicting the cleaning time required to remove a thin layer of soil is a challenging task and subject of current research. One approach to tackle this problem is the decomposition into physical sub-problems which are modelled separately and the subsequent synthesis of these models. In this paper, an existing model for adhesive detachment is extended for the prediction of the cleaning time of cohesively separating soil layers. The extension is based on measurements of the pull-off forces and their correlation to the local water mass fraction. The resulting new model is validated using cleaning experiments with starch in a fully developed channel flow. Furthermore, an inhomogeneous soil distribution and its effect on cleaning results like cleaning time and removal rate is investigated. It is shown that accounting for the local soil distribution in the model leads to a significant improvement of the prediction of the cleaning behaviour. [ABSTRACT FROM AUTHOR]

Oil jet impingement cooling is the standard approach to cool high-speed high-power gears. The heat transfer between oil jets and gears is experimentally investigated in this paper. The three established methods of oil jet impingement cooling -into-mesh, out-of-mesh and inclined impingement on one of the gears- are studied. Heat transfer coefficients for these methods are experimentally determined. A loss correction approach is implemented for the evaluation of measurements. For the inclined impingement method, heat transfer on the non-impinged gear and the influence of meshing on the heat transfer coefficient are investigated. Gear meshing has an insignificant effect on the average heat transfer coefficient over the gear tooth. However, the spatial distribution of the heat transfer coefficient depends on the meshing configuration. Significant cooling on the non-impinged gear is observed with the inclined impingement method. The inclined impingement method is superior to the into-mesh and out-of-mesh methods at all measured operating points. [ABSTRACT FROM AUTHOR]

The process of heat transfer is one of the most important issues in the food industry and plays a crucial role in the storage of frozen foods. The main objective in this field is to extend the storage time, which can be achieved by limiting the heat transfer between the ambient air and the frozen food product. In this paper, the authors applied a numerical model of the phase change process to simulate the freezing and thawing process of a package wrapped with compressible multilayer polymer thermal insulation. The model was solved in COMSOL Multiphysics program and verified with experimental results with satisfactory agreement. Based on the performed simulations and experiments, it was proved that the freezing time of the tylose package is almost the same regardless of the applied film, while the thawing time of the package strongly depends on the type of film—transparent, opaque or metallized. The use of transparent film allows to extend the maximum thawing time of food products by 2 times, the use of opaque film—by about 3.7 times, and the use of metallized film—by about 4.1 times. [ABSTRACT FROM AUTHOR]

The direct emission of coal mine methane caused serious environmental pollution and resource waste. To improve the methane utilization, the porous media burner was regarded as an efficient method. In this paper, the bluff body was proposed to combine with porous media to optimize the combustion characteristics. The effects of bluff body position, size and shape on the temperature distribution and gas emission were studied at different operating conditions. The results indicated that the position of the bluff body greatly influenced the combustion characteristics, and the maximum temperature of 1295 K was obtained at the position of 62 mm. The increase of the bluff body diameter promoted the flame moving to the burner outlet. And the combustion temperature increased first and then decreased when the bluff body height increased. Moreover, the CO and NOx emissions at the height of 20 mm reached 31 and 16.8 ppm respectively. The combustion temperature was significantly improved by increasing the equivalence ratio and velocity. Compared with the single porous media, the addition of the bluff body increased the combustion temperature and reduced the CO emission by 11%. [ABSTRACT FROM AUTHOR]

In the traditional tobacco drying process, there is often a problem of uneven drying, which is closely related to drying conditions such as air velocity and temperature. To better understand the drying characteristics of tobacco, its drying kinetic performance were experimentally studied and predicted in this paper. In the drying experiment, the range of air temperature and velocity is 20–60℃ and 0.95–4.93 m/s, respectively. The results show that the effective diffusion coefficient increases with the increase of air temperature and decreases with the increase of air velocity. The effective moisture diffusivity( D eff ) ranges from 2.077 × 10–7 to 9.136 × 10–7 m2/s. Additionally, the activation energy (Ea) is between 14.292 and 21.032 kJ/mol according to Arrhenius law. Among the six commonly used empirical correlations, the logarithmic model has higher prediction accuracy, but it has a prediction deviation of more than 20% in the later stage of drying. Based on the logarithmic model and the two models, a new prediction model of tobacco drying characteristics was proposed with a maximum relative deviation error of less than 1%. [ABSTRACT FROM AUTHOR]

This paper studies the combined heating and cooling thermal performance of a CO2 heat pump system considering the subcooling effect. For such a system without cold thermal energy storage (CTES), the gas cooler outlet temperature normally needs to be controlled to match the cooling load required. However, the integration of CTES would enable the system to be operated under its optimal conditions depending on the ambient temperatures, i.e. a considerable amount of cooling capacity can be generated and stored for later use. A configuration of a CO2 heat pump integrated with CTES is described in this paper. A thermodynamic cycle and a simulation model considering the subcooling effect have been developed. The mathematical model for the pinch point analysis has been newly validated against published experimental data with acceptable agreements. In the case study, the impacts of the subcooling temperature on the optimal combined performance under four ambient temperatures (5 °C, 15 °C, 25 °C, and 32 °C) have been studied. The highest optimal combined COP of 5.38 can be achieved when the ambient temperature is 5 °C. The detailed profiles of CO2 temperatures, heating and cooling loads, and the COPs when the CTES is in operation have been revealed for the first time. It is found when the ambient temperature is higher than the water inlet temperature (plus the pinch point temperature), the optimal cooling COPs can even have a surge without the subcooling effect, due to a lower sCO2 temperature leaving the heat exchanger compared to the ambient temperature. Additionally, performance analysis for the CO2 heat pump system with or without CTES is compared, and it is concluded that all optimal heating, cooling, and combined COPs integrated with CTES surpass those without CTES. [ABSTRACT FROM AUTHOR]

The freezing point of offshore saline sand is required to evaluate the formation of frozen walls during artificial freezing construction in coastal areas, which strongly depends on solute species and concentrations. In this study, 33 groundwater samples from Tianjin Binhai New Area were collected for salinity analysis, with Na+, Cl− and SO42− being the predominant ionic components. After salt leaching of the field collected sand, saturated samples with single solute (NaCl, KCl, CaCl2, MgCl2, NaHCO3 and Na2SO4) and multiple solutes (original salt and CaCl2) were prepared. The freezing points of soil samples were determined by the cooling curve method, while the suction by the filter paper method. The results reveal that the freezing point depresses with greater salt content. The effect of cations on freezing point can be ranked as Mg2+ > Ca2+ > Na+ > K+ for certain Cl− concentrations, which is linked to ion hydration capacity. Soil suction is dominated by osmotic suction, with matric suction as a minor component. A cationic impact resembling the freezing point was also noted. The greater the osmotic suction, the lower the freezing point. Based on the extended UNIQUAC model, the freezing points of aqueous solutions with single and multiple solutes were calculated, and the discrepancies with test data for offshore saline sands were discussed from the perspectives of osmotic suction and colloidal double electrical layer. A model for the freezing point of offshore saline sand was developed by incorporating the osmotic coefficient and solute concentration, and its rationality was verified by test data. [ABSTRACT FROM AUTHOR]

Natural ester insulating oil has the advantages of environmental protection and high ignition point. FR3 is a natural ester insulating oil that can be used in high voltage transformers above 110 kV. In order to provide theoretical guidance for the application of FR3 insulating oil in transformer. The heat transfer performance of transformer with FR3 insulating oil is evaluated by means of experiment and numerical simulation. In this paper, a heat transfer model of large oil immersed transformer winding is established and verified. The experimental results show that the accuracy of the established heat transfer model can reach 98.5%. The heat transfer performance of FR3 and traditional mineral oil are compared and analyzed by using the established heat transfer model. Research results show that: In ODAF cooling mode, the heat transfer performance of natural ester insulating oil is stronger than that of mineral oil;When the inlet temperature or low rate of the model is increased, the heat transfer advantage of natural ester insulating oil will be reduced; With the increase of coil heat load, natural ester insulating oil shows a better cooling performance; Especially in the area close to the guide plate, the heat transfer advantage of natural ester insulating oil become more obvious. [ABSTRACT FROM AUTHOR]

Miniaturization and enhanced performance of microchips has resulted in powerful electronic devices with high heat flux components. For these advanced electronics, the current heat transfer method of single-phase forced convection is reaching its thermal limit and more effective cooling solutions are needed. A pumped two-phase loop, in which a pump circulates a working fluid that evaporates to absorb heat, can offer a solution. In this paper the cooling performance of a pumped two-phase loop is discussed and validated. A numerical tool has been developed to aid in designing a fit-for-purpose pumped two-phase loop and to predict its behaviour to changing system parameters and heat inputs. Results from the numerical model are compared with temperature, pressure and flow velocity measurements obtained from a prototype setup. The effects of applying varying heat loads on both a single evaporator and on multiple evaporators simultaneously either in series or in parallel have been investigated. Heat transfer coefficients between 7 and 10 kW/m2K were obtained during the experiments. Model predictions correspond well to the measured performances and findings on the two-phase boiling behaviour are presented. The model is particularly useful for the rapid assessment of the layout of a pumped two-phase loop for high heat flux electronics cooling. [ABSTRACT FROM AUTHOR]

In this paper, a multilayer perceptron (MLP)-type artificial neural network model with a back-propagation training algorithm is utilized to model the bubble growth and bubble dynamics parameters in nucleate boiling with a non-uniform electric field. The influences of the electric field on different parameters that describe bubble's behaviors including bubble waiting time, bubble departure frequency, bubble growth time, and bubble departure diameter are considered. This study models single bubble dynamic behaviors of R113 created on a heater in an inconsistent electric field by utilizing a MLP neural network optimized by four different swarm-based optimization algorithms, namely: Salp Swarm Algorithm (SSA), Grey Wolf Optimizer (GWO), Artificial Bee Colony (ABC) algorithm, and Particle Swarm Optimization (PSO). For evaluating the model effectiveness, the MSE value (Mean-Square Error) of the artificial neural network model with various optimization algorithms is measured and compared. The results suggest that the optimal networks in the two-hidden layer and three-hidden layer models for the bubble departure diameter improve MSE by 33.85% and 35.27%, respectively, when compared with the best response in the one-hidden layer model. Additionally, for bubble growth time, the networks with two hidden layers and three hidden layers have the 44.51% and 45.85% reduction in error, when compared with the network with one hidden layer, respectively. For the departure frequency, the error reduction in the two-layer and three-layer networks is 46.85% and 62.32%, respectively. For bubble waiting time, the best networks in the two hidden-layer and three hidden-layer models improve MSE by 52.44% and 62.27% compared with the best 1HL model response, respectively. Also, the two algorithms of SSA and GWO are able to compete well (comparable MSE) with the PSO and ABC algorithms. [ABSTRACT FROM AUTHOR]

Ultrasonic field and rib surfaces are very important factors that affect the thermal performance in pool boiling. The paper has investigated the significance testing of thermal performance of the rib arrangement, the distance of ultrasonic field and the ultrasonic power in pool boiling with ultrasonic field and ribs surfaces by the orthogonal experiment. The deionized water is used as the working coolant. Then, the synergistic heat transfers and bubble motion characteristics in pool boiling are carried out at different rib arrangement, distance of ultrasonic field and the ultrasonic power by the single factor experiment. It is obtained that, compared with the single heat transfer technology of rib surface or ultrasonic field in the pool boiling, the thermal performance of compound heat transfer enhancement can be improved more significantly by combining the rib surfaces and ultrasonic field as a result of the expanded areas of heat exchange surface of rib and the cavitation effect and acoustic streaming effect of the ultrasonic field. The most significant affecting factor on the thermal performance is the rib arrangement, followed by ultrasonic power and distance of ultrasonic field. The increasing rate of heat transfer coefficient (HTC) of the best optimal scheme combination A3B3C1 with the rib arrangement of Rib II, the distance of ultrasonic field of 50 mm and the ultrasonic power of 528 W is 29.9%, which is higher than those of all the other schemes. The research results can effectively optimize the pool boiling performance of the heat transfer enhancement and provide useful support for the development of heat dissipation in related fields. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids with superior thermal characteristics can be a new choice of working fluid in enhancing the heat dissipation rate of microchannels heat sink. Therefore, this paper deals with the hydrothermal characteristics of a microchannel heat sink utilizing MWCNT-Al2O3/water hybrid nanofluids. The thermal conductivity and viscosity of mono and hybrid nanofluids were measured and new experiential correlations were derived. The convective tests were carried out in three different composition ratios as well as two volume fractions of hybrid nanofluids at different Reynolds numbers. The results showed that MWCNT-Al2O3/water hybrid nanofluid at composition ratio of (80:20) and 0.05% vol. had the highest performance evaluation criteria value. [ABSTRACT FROM AUTHOR]

Horizontal tube falling film evaporation technology has outstanding advantages such as high energy efficiency and easy operation. The purpose of this paper is to investigate the impact of cross airflow on the falling film thickness distribution outside the horizontal tube. The axial and circumferential film thickness distributions under inter-tube column flow mode are measured using the air-water system and the conductance probe method, and the mechanism of cross airflow on the falling film thickness distribution is analyzed. The results show that the axial film thickness between the two adjacent liquid columns has a wave crest region and is symmetric distributed, and the circumferential film thickness at the wave crest section does not symmetry about horizontal axis with a minimum value within the circumferential angle range of 100°~120° in the quiescent surroundings. When the cross airflow exists, the circumferential film thickness on the windward surface increases in the circumferential angle of 30°~90° and decreases in the circumferential angle of 90°~150°, while those on the leeward surface increases and becomes more uniform. The axial wave crest region and spreading region of the liquid film on the windward surface also increase, but those on the leeward surface change little. [ABSTRACT FROM AUTHOR]

The measurement data of single droplet evaporation experiments are often biased due to the extra heat input through the fiber suspension and the presence of thermal radiation in hot environments. This encumbers model validation for heat and mass transfer simulations of liquid droplets. In this paper, a thermal analysis of this measurement layout is presented with a coupled lumped parameter model, considering heat conduction through the suspension. The model was validated by experimental data from the literature and good agreements were found. The thermal analysis focused on fiber material and geometry, and thermal radiation properties. Calculations were performed on a broad range of ambient conditions for liquids with different volatility characteristics. Temporal squared droplet diameter- and temperature-profiles, furthermore, droplet stationary evaporation rate were used to characterize vaporization phenomena. The thermal balance of the droplet is dominated by the convective heat rate from the environment in the early stage of evaporation. The effect of heat conduction through the fiber becomes important at the end of the droplet lifetime when the droplet size is decreased. Temperature sensor suspension may seriously bias droplet temperature due to the larger thermal conductivity compared to quartz fiber. Large droplets in high-temperature environments show significant sensitivity to thermal radiation properties, which should be considered in measurements and model validation. [ABSTRACT FROM AUTHOR]

For the outside cabin heat exchanger of wind power generation, the overall numerical simulation plays an important role in its design and optimization. The periodic iterative simulation method proposed in this paper makes up for the deficiency of analogy research using the local model in the previous research of plate-fin heat exchanger so that the research conclusions can be directly applied to practical engineering. The effectiveness of this method is verified by comparing 10 groups of simulation results with experimental results. It is concluded that the maximum relative error of the periodic iterative simulation method is 0.9%, which meets the requirements of engineering calculation. The number of iterations can be reduced to two when only the outlet average temperature is involved, which is more convenient than the dozens of iterations. Furthermore, the effects of altitude, air velocity, air temperature, wave fin structure parameters, and generator power on the performance of heat exchanger are comprehensively analyzed. The results show that larger naturally captured air volume, lower ambient temperature, and lower altitude can effectively reduce the outlet temperature of ethylene glycol solution. When the amplitude and wavelength of the corrugated fin on the airside of the heat exchanger are 0.6 mm and 20 mm respectively, the naturally captured air volume is effectively increased, the overall heat exchange performance of the heat exchanger is further improved. [ABSTRACT FROM AUTHOR]

Boiling of liquids upon impact of the spray on heated surfaces is common in many practical applications. However, a comprehensive modelling approach for these phenomena is still not available in commercial software, despite decades of experimental, theoretical, and numerical research efforts. The motivation of this paper is to clarify the state of the art on the three-dimensional (3D) simulation of the boiling of liquid films and spray droplets during their contact with hot substrates. Based on recent experimental and theoretical research, this paper proposes a set of heat transfer models for 3D simulation of spray cooling considering conjugate heat transfer (CHT). These updated models and correlations were implemented in a computational fluid dynamics (CFD) solver, which already included a classical two-phase Lagrangian–Eulerian approach and CHT modelling functionality. A detailed validation of the improved modelling proposals is performed using a unique and novel database including wall surface temperature and heat flux measurements for different flow rates and spray impact velocities. Excellent agreement with experiments was obtained for all boiling regimes using a Leidenfrost-like temperature to manage the prompt heat flux change between the film boiling regime and the transition boiling regime. Most notable are the great results produced by the recent film boiling model summarized in this article. [ABSTRACT FROM AUTHOR]

Visualization of the two-phase flow in micro-scale helps to reveal the thermophysical behavior of the fluids. This paper presents and discusses the flow patterns of two-phase R1234yf, R1233zd(E), and R1336mzz(Z) in a 0.643 mm microchannel tube. The condition covers mass flux from about 25 to 250 kg-m−2 s−1. The inlet saturation temperature is 30 °C for R1234yf and R1233zd(E), and 40–60 °C for R1336mzz(Z). As vapor quality increases, the flow is firstly in plug/slug flow, then transitional flow, and finally annular flow at high quality. When mass flux is 50 kg-m−2 s−1, no transitional flow is observed. The annular flow starts at high quality. The transitional flow in the low mass flux was absent. When mass flux is 100 kg-m−2 s−1, the transitional flow covers quality from 0.8 to 0.9. The superficial velocities follow a power function for flow pattern transitioning. The velocity is measured by a video processing method proposed in this paper. The vapor plug velocity is calculated by measuring the velocity of the vapor plug head in the frames and corrected by the video information (frame per second and meter per pixel). The velocity is slightly higher than the velocity calculated based on the homogeneous assumption when it is higher than 1 m-s−1. A new correlation for predicting the vapor plug velocity is proposed. The new correlation has a small MAE (5.42%) compared to the results and can be used for Capillary number less than 0.14. [ABSTRACT FROM AUTHOR]

The present study investigates the behaviour of thermal streaks on a heated foil which is cooled with turbulent flow in a square duct channel. Real-time infrared thermography is used to visualize and measure the spacing between the thermal streaks. A stainless-steel foil with a thickness of 25 microns is cooled by water. The experiments were performed in a range of Reynolds numbers from 5000 to 20000 and Prandtl numbers from 3 to 7. The mean temperature, root-mean-square of temperature and autocorrelation function have been calculated and used to measure the average thermal streak spacing and power spectra in the spanwise and streamwise directions. The root mean square temperature was 0.3 °C to 0.5 °C which corresponds to roughly 10% of the mean temperature difference between foil and water. The uncertainty in mean temperature difference and root mean square temperature was around 5% and 10%, respectively. The measured thermal streak spacing was 100 wall unit to 180 wall unit under the present experimental range. The uncertainty in measured thermal streak spacing was around 2.5%. The effects of Reynolds number, Prandtl number and heat flux on the thermal streak spacing and also on the statistics of the temperature field have been presented and discussed in this paper. A new correlation has been proposed to predict the dimensionless thermal streak spacing. The error in the prediction is estimated within ± 15 %. [ABSTRACT FROM AUTHOR]

In this paper, a simple but detailed new theoretical model is developed for a thin loop heat pipe (LHP) to predict: the overall thermal resistance, the temperature distribution, the heat transfer rate, the heat leakage by conduction and the length of single and two-phase working fluid flows within the condenser. The theoretical results were confronted with experimental data of a mini flat LHP, manufactured using sintering and diffusion bonding processes. The working fluid used was water. A workbench, capable of simulating the actual operating conditions of a modern chip processor, with 1 cm2 of heat dissipating area, as found in smartphones and other electronic gadgets, was used to evaluate the LHP thermal performance. The tested LHP had dimensions of 76 x 60 x 1.6 mm3. The cold source was natural air convection to the surroundings. The device operated successfully in the orientations: horizontal, gravity-assisted, and against gravity. Tests were conducted until the evaporator reached 100°C, the limit temperature of electronics, resulting in overall thermal resistances of 0.37 °C/W, 0.47 °C/W and 0.44 °C/W, respectively. The model could successfully predict all steady-state operational parameters of the LHP with small deviations, proving to be suitable for designing new LHPs and other thin devices. The difference between predicted and measured resistances were within 5.64%, while between predicted and measured temperatures were within 3.30%. Lastly, the heat leak from the evaporator to the liquid line had a deviation of 16.62%. The LHP, although very thin, showed to be a good solution for cooling small electronic gadgets, such as mobile smartphones. [ABSTRACT FROM AUTHOR]

Super saturation of inversely soluble salts in the phosphoric acid concentration process, like calcium sulfate, promotes fouling on the heat exchanger walls. This phenomenon leads to reduce the efficiency of such equipment and their continuous operation and increase energy losses. The present work aimed at studying the effect of the deposit of calcium sulfate on the fouling resistance on a heated walls. The fouling resistance was determined based on the operating data collected from the phosphoric acid concentration loop of a cross flow heat exchanger. X-ray diffraction analysis method was used to determine the crystal form of calcium sulfate. In addition, this paper aimed at modeling the fouling resistance with experimental data under various operating conditions using response surface methodology (RSM) in order to studying the interactive effects of operating parameters on fouling. Results show that the anhydrite (CaSO4) is the main crystal form of fouling formed on heat exchanger walls indicating that the crystallization fouling dominates the fouling process. The volume flow affects the fouling resistance especially at high wall temperature by increasing the fouling resistance with decreasing volume flow. The fluid temperatures are found to enhance significantly the fouling resistance on the surface. The determination coefficient of the proposed RSM model in the studied case was found to be 99.54%, which is considered to be satisfactory. [ABSTRACT FROM AUTHOR]

Compared to other energy conversion devices, the efficiency of thermoelectric generators (TEGs) is relatively low. Thus, several papers have sought to improve device performance by investigating the effects of Thomson effect on thermoelectric efficiency. However, the synergistic relationship between the temperature dependent Seebeck coefficient (SC) and Thomson effect (TE) is yet to be explored. Thus, in this paper, four possible cases of modelling a thermoelectric generator (TEG) are presented. Case 1 models equal hot and cold junction Seebeck coefficient ignoring Thomson effect, case 2 adopts equal hot and cold junction SC including TE, case 3 defines unequal hot and cold junction SC neglecting TE while case 4 represents unequal hot and cold junction SC with TE. The theoretical model used is thoroughly validated by comparing the values obtained with experimental data provided by previous similar studies. Results show that including TE in the analysis of the TEG for temperature gradients less than 300 K reduced the system performance. However, including TE in the modelling of the TEG for temperature gradients higher than 400 K increased the system performance. Also, accounting for TE in the geometric optimization of the TEG, resulted in an inverse correlation between the TEG maximum power generation and efficiency. Thus, not just the TE, but also the SC configuration needs to be considered in maximising TEG performance. [ABSTRACT FROM AUTHOR]

To investigate the nozzle geometry influence on vortex cooling performance in the actual leading edge region, an improved vortex cooling configuration with a coolant chamber is established based on the middle cross section of stage 1 vane blade of GE-E3 high pressure gas turbine. Numerical simulations are conducted to research the effects of nozzle position, nozzle number and nozzle aspect ratio on the flow and heat transfer behavior. Results show that with the introduction of the coolant chamber, the mass flow of nozzles increases gradually from the upstream to the downstream instead of a uniform mass flow distribution. Configurations with nozzles placed at the sides (the vortex cooling) have better cooling performance than with nozzles placed in the middle (the impingement cooling). What's more, the configuration with nozzles placed along the pressure side has the best comprehensive cooling performance. Due to the irregular blade line, a flow entrainment that is not found in simplified circular configurations is observed on the pressure side weakening the local heat transfer performance. The cooling performance is most sensitive to the nozzle number. As the nozzle number increases, the friction coefficient and heat transfer intensity both decrease. Moreover, as the nozzle aspect ratio increases, the friction coefficient and heat transfer intensity both increases first and then decrease. Results indicate a certain vortex cooling configuration may have the optimal nozzle number and nozzle aspect ratio. For this paper's configuration, the best nozzle number is 5 and the best nozzle aspect ratio is 4. [ABSTRACT FROM AUTHOR]

The loop thermosyphons has advantages of high heat transmission efficiency and needing no additional power. It can quickly draw out the heat in the motorized spindle with no coolant getting into the shaft, and has a good application prospect in the field of motorized spindle cooling. However, the evaporation and condensation sections of a loop thermosyphon will be in the same pipe and at the same height under the heat conduction of the shaft. These structural changes will directly affect the flow characteristecs and heat transfer performance of the loop thermosyphon. This paper experimental studied the vapor-liquid two phase flow characteristics in a pentane loop thermosyphon. The effects of the heat input power and fill ratio on the flow characteristics were analyzed. Results show that the two-phase flow pattern transitions from stratified flow to wavy flow and finally to plug flow as fill ratio increases. The velocity of the liquid flow in the upper adiabatic section of the loop thermosyphon is on the order of 0.1 m·s-1, and it decreases with increasing heat input when the fill ratio is between 30 and 70 %. [ABSTRACT FROM AUTHOR]

Flow boiling in micro pin fin arrays is an effective way to solve the heat dissipation problem. However, studies on the flow boiling performance of pin fin arrays with different structural parameters are still insufficient, especially for the application of long channels for practical evaporators in aircraft environmental control systems. In this paper, the flow boiling performance of R134a was experimentally investigated in a 300 mm long mini channel with micro pin fin arrays. The mass fluxes, heat fluxes, inlet saturation pressures and vapor qualities were in ranges of 200 -500 kg/(m2s), 15–30 kW/m2, 500–700 kPa and 0.05–0.90, respectively. The local heat transfer coefficient and pressure drop of staggered diamond pin fin arrays with different channel widths of 1.0, 1.2 and 1.4 mm were comprehensively studied. Subsequently, the performance analysis of the above channels was carried out. Results indicate that the nucleate boiling and convective boiling together govern the two-phase flow boiling heat transfer in the pin fin array. In particular, the increase in channel width delays the transition to convective boiling dominated flow. The local heat transfer coefficient increases with mass flux. However, in the high vapor quality region, the flow disturbance caused by a large mass flux may suppress the heat transfer, as high-speed gas destroys the continuous thin liquid film on the walls. Furthermore, the influence of saturation pressure on the heat transfer coefficient is reversed with the increase in vapor quality. Additionally, the performance analysis indicated better performance of the pin fin array at low vapor quality regions and small mass flux. Significantly, the best performance was obtained in pin fin array with a channel width of 1.4 mm, due to a drastic increase in two-phase pressure drop compared to heat transfer. Finally, a new correlation with the consideration of pin fin array structure parameters was proposed with an overall mean absolute deviation of 16.2%. This new correlation is proved to have an obvious accuracy improvement in predicting the flow boiling local heat transfer coefficient of R134a in a mini channel with pin fin arrays. The present work can provide critical information for the design optimization of a mini channel two-phase heat exchanger with pin fin arrays. [ABSTRACT FROM AUTHOR]

Experimental studies on heat transfer enhancement and friction factor characteristics of water flowing in Laminar flow regime through a square duct, fitted with full-length helical inserts of varying twist ratio have been reported in the present paper. The test liquid flows in the laminar flow through a square duct and in counter current manner a hot water at very high flow rate is directed though the annulus to ensure a constant wall temperature conditions. A plain duct fitted with helical inserts provides higher friction factor and Nusselt number than that of empty duct. The heat transfer and pressure loss were observed to be higher at minimum twist ratio. The thermo hydraulic performance ratio on constant pumping power of the duct induced by helical inserts at different twist of 1.44, 2.55, 3.66, 4.66 were found to be 5.20, 4.44, 4.01, and 3.50 times higher than the plain duct. [ABSTRACT FROM AUTHOR]

The paper deals with the classification and the design features of direct contact heat exchangers used in various technological processes. It describes the existing two-phase flow regimes and the methods for heat and mass transfer prediction in heat exchangers with the direct contact of fluids in a vertical tube. The authors carried out the measurements of heat and mass transfer coefficients during the liquid film flow under the action of gravity towards the air flow in a vertical tube. The range of experimental variables is set to be the following: air mass flow rate is 1·10-3-4·10-3 kg/s, air inlet temperature is 26-28 °C, air inlet humidity is 38-50 %, water mass flow rate is 1.5·10-2 -4·10-2 kg/s, and water inlet temperature is 55-58 °C. It is shown that an increase in the fluid flow rate leads to the heat and mass transfer intensification due to an increase of waves on the film surface. The authors obtained new empirical correlations for calculating convective heat and mass transfer coefficients. These equations consider the influence of the water flow rate for the film Reynolds number. The described methods are recommended to be used in the range of air Reynolds numbers from 2300 to 6700 and film Reynolds numbers from 600 to 1300. [ABSTRACT FROM AUTHOR]

In this paper, thermal to electrical using waste heat recovery from a refrigeration system is utilized to generate electricity through a closed-loop heat sink thermoelectric generator (TEG) is presented. The concentric tube heat exchanger is used to take the waste heat from a refrigeration system to produce hot fluid for TEGs. The cold fluid is produced by a refrigeration system used for cooling the cold side. The hot and cold sides of the TEGs are coupled with heat sinks where hot and cold fluids flow through the heat sink channel to generate electricity. The effects of the fluid flow, and on/off modes of the refrigeration system, are investigated. It was found that the output voltage depends on the operating behavior of the refrigeration system, and operating time when on mode and off mode directly affects a hot fluid temperature fabrication. Applying fluid mass flow rate on the hot side and the cold side is very important that may cause the output voltage to be enhanced. The maximum temperature difference was obtained for the long-running refrigeration test mode. For on mode and off mode, the operating time of 10 minutes is the greatest to obtain the minimum and maximum temperature difference of 19.80°C and 13.10°C to get the maximum and the minimum output voltage of 9.80 V and 5.67 V. Besides, the cooling efficiency of the refrigeration system was increased and reduced power consumption by approximately 23% as integrated with the TEG system. Cooling capacity (Qc) and COP of the refrigeration system equipped with TEG increased by approximately 40% over traditional refrigeration system. Excess heat from the cooling system is recovered and converted into electricity. This is an energy-saving alternative that may help reduce the global warming crisis. [ABSTRACT FROM AUTHOR]

Sarcheshmeh lime rotary kiln in the south of Iran consumes a lot of thermal energy compared with other rotary kilns. As a result, Sarcheshmeh lime kiln is being investigated for the potential to improve energy consumption. Experimental data and CFD simulation are both used in this paper. The numerical simulation has been performed for three modes to investigate the problems and solutions of energy consumption in the lime kiln: design mode, operation mode, and effect of operating condition changes. In the last mode, five parameters including the percentage of excess air, the ratio of primary to secondary air flow, primary air flow, moisture, and particle size of limestone are studied and discussed. To consider different factors of lime kiln operation, the numerical simulation takes into account all three major phenomena of fuel combustion in the burner, limestone calcination, and particle movement. Operating conditions measurements with mass and energy balances show that there is insufficient suction air from the secondary air inlet to the burner head. This is due to multiple leaks from the kiln's initial length part, resulting in incomplete combustion and fuel waste eventually. According to CFD simulation, lowering the size of the intake limestone particles enhances the calciantion of limestone. Also, if quicklime's maximum temperature is limited, a higher ratio of primary to secondary airflow can be used, in which case the degree of conversion of limestone to quicklime at the kiln exit remains constant. [ABSTRACT FROM AUTHOR]

In this paper, two types of nanoparticles were used to manufacture nanoenhanced PEG 400 fluids. Both types of nanofluids (i.e. Al2O3 and ZnO with PEG 400) were experimentally studied in regard to their morphology, thermal stability, porosity and thermophysical properties. This research presents an analysis of possible behavior at heat transfer for these new fluids, based on several properties previously determined. Specifically, Prandtl number, thermal diffusivity, Mouromtseff number and pumping power were discussed for all fluids. Results demonstrated an increase up to 4% in thermal diffusivity for suspensions with ZnO, while Pr number remains the same or even decreases, proving a better heat transfer of ZnO – PEG 400 in comparison with the base fluid. For Al2O3 it was noticed an increase in pumping power of up to 8.1% in laminar flow, while in turbulent regime the increase or decrease in relative Mo number is not significant. As a general outcome, it can be concluded that the best results were noticed for low concentrations of ZnO – PEG 400 nanofluids, making them a good option to increase the convection heat transfer. [ABSTRACT FROM AUTHOR]

The leakage of molten salt tanks has attracted great attention in molten salt tower concentrating solar power plants. The current research on the leakage characteristics of molten salt mainly focuses on Solar Salt, and there is no report on the leakage characteristics of molten salt with great application potential, which is crucial to the design of molten salt tanks and their foundations in the future. In addition, there is no unified explanation for the morphological characteristics of the agglomerates formed after the molten salt leakage. In this paper, the migration and heat transfer characteristics of three potential molten salts (60–10-20–20 wt% KNO3-NaNO3-LiNO3-Ca(NO3)2.4H2O, 7.5–23.9–68.6 wt% NaCl–KCl-ZnCl2, 32.1–33.4–34.5 wt% Li2CO3–Na2CO3–K2CO3) leaking into the thermal tank foundation material are experimentally studied and compared with Solar Salt. The results indicate that both the operating temperature and molten salt type significantly affect the temperature rising rate of tank foundation and migration characteristics of molten salt. Increasing the operating temperature, the average temperature rising rate, maximum migration depth, maximum migration width and migration speed respectively increase, increase, decrease and increase. Compared with Solar Salt, the maximum migration depths of the three potential molten salts increase 56.3%, -11.6%, and -50.2%, and the maximum migration widths increase -22.7%, -16.7% and -2.7%, respectively. In addition, a model explaining the solidification and agglomeration of the molten salt is proposed and well verified by the experimental results. [ABSTRACT FROM AUTHOR]

Improving the thermal performance of cooling systems is crucial for energy and raw material savings, increasing the thermal ratings, and extending the work life of various equipment. This paper aims to provide a comprehensive review of experimental and numerical research on natural convection heat transfer and fluid flow in heat sinks. This review presents the characteristics and capabilities of various feasible cooling strategies, including new methods and advanced solutions. The many research that have paid attention to the parametric study of the geometry of the heat sink are extensively discussed Key parameters with a significant impact on the heat sink's design and performance are thoroughly discussed, including the effects of operating conditions and geometric parameters of working fluids (i.e., effect of magnetic field, use of nanofluids, etc.), and the use of phase change materials. Correlations for estimating natural convection heat transfer rates as a relation of key parameters (spacing, height, orientations) are provided and detailed. Finally, the study highlights the important points and research gaps to provide better insight and valuable guidance for researchers who intend to study, improve, or optimize any type of heat sink for different applications. [ABSTRACT FROM AUTHOR]

Inorganic hydrated salt calcium chloride hexahydrate (CaCl2·6H2O) has a broad application prospect in the field of phase change energy storage due to its own characteristics. However, it has some problems such as large supercooling and serious phase separation, which limit its practical application. In this paper, boron nitride nanosheets (BNNSs) were applied in the CaCl2·6H2O system. It was found that the heterogeneous nucleation of CaCl2·6H2O can take place on the surface of BNNS. BNNS can solve the supercooling and heat transfer problems of CaCl2·6H2O effectively. At the same time, the addition of an appropriate amount of BNNSs can improve the stability of phase change composites. Compared with pure CaCl2·6H2O (supercooling was 22.06 °C and thermal conductivity was 0.382 W·m−1·K−1), the supercooling of CaCl2·6H2O/1 wt% BNNS composite was only 3.89 °C and the thermal conductivity was 3.918 W·m−1·K−1. CaCl2·6H2O/0.5 wt% BNNS composite has good cycling stability. This study has scientific significance for the development and application of BNNSs in the field of phase change energy storage. [ABSTRACT FROM AUTHOR]

This paper focuses on the enhancement of flow boiling heat transfer and improvement of flow instability due to the porous surface modification and channel section expansion, which is a hot research issue. The two-phase cooling system offers a potential solution for dissipating a large amount of heat at a very small area. There are too many articles on enhancing flow boiling heat transfer on smooth (non-coating) straight and divergent heat exchangers, however, all of them ignored the effect of the surface characterizations such as micro porous coating which is very significant parameter when presented and discussed the flow boiling results. Therefore, the major novelty of the current work is to improve the heat transfer performance of the heat exchanger by applying micro porous coatings on the linear and divergent heat exchangers as well as it aims at further understanding the effect of micro porous coatings under low and high heat flux conditions. The micro porous coatings were fabricated by spraying method with average particle size of 25 µm and having optimum thickness of 150 µm using FC-72 as a working fluid. The test results show that the micro porous coatings increase the active cavities, decrease the required vapour superheat, enhance the liquid replenishment to the heating surface, delay the dry-out phenomena, and decrease the vapour release resistance, and therefore, better enhancement in the performance of the system and critical heat flux up to 20% and 61% respectively. It was also observed that applying micro porous coating led to decrease thermal resistance by 35%. Moreover, the results depict that for the straight channel micro-micro-heat exchanger, the geometry of the flow path is very simple, and therefore, the pressure drop is very small compared to the divergent heat exchanger. For the divergent micro-heat exchanger, the pressure drops are higher than that of the straight channel micro-heat exchanger at varies vapor qualities since the fluid is distributed in the different flow channels, and this leads to higher pressure drops loss compared with the straight flow channels. In addition, the test results show that the flow boiling HTC and CHF are affected by the geometric configurations, i.e. the ability of increasing the heat transfer area, the ability to release the bubbles to the outlet of the channels, reducing the back flow, and delaying the dryness phenomena (CHF). For linear flow-channel surface, a stratified flow state of vapour in the upper layer and the liquid in the lower layer under low and high heat fluxes conditions dominates. For the divergent flow-channel surface, the results show that under low heat flux condition, the bubbles generated are easy to move downstream of the flow channel, and there is no bubbles backflow phenomenon, but under high heat flux condition, the backflow phenomena occurs on the uncoated divergent-flow channel surface. However, attributing to the capillary action on the micro porous layer surface, the liquid can rewet the surface, and this enhances the flow boiling HTC as well as this delay the CHF. [ABSTRACT FROM AUTHOR]

A CFD model based on the Reynolds Averaged Navier–Stokes (RANS) approach combined with a detailed chemical kinetic mechanism to investigate a turbulent CH4/H2/N2 jet diffusion flame is developed. The CFD governing equations of momentum, mass, and energy in the turbulent field were solved in conjunction with the standard k − ε turbulence model. The laminar flamelet concept that views the turbulent diffusion flame as an ensemble of laminar diffusion flamelets is adopted. The coupling between turbulence and chemistry is achieved by the statistical description of three parameters namely (1) mixture fraction (Z), (2) variance of mixture fraction (Z"2) and (3) scalar dissipation rate (χ). The flamelet model consists of two steps namely (a) the generation of a set of laminar flamelet solutions and (b) the integration of the laminar flamelet solutions with presumed-shape Probability Density Function (PDF). The GRI Mech-3.0 mechanism that involves 53 species and 325 reactions is adopted. The effect of various parameters such as C1ε constant in the turbulent dissipation transport equation on the numerical solution is highlighted. Also, the comparison between the CFD model results and the experimental data of velocity, temperature and mass fractions of species (CH4, H2, N2, H2O, CO2, O2 and CO) along the centreline as well as on the radial position of x/D = 5, 40 are presented. Generally, the CFD results show a good agreement with the experimental data, and the presented approach in this paper is an accurate promising alternative to LES and DNS approaches for the modelling of non-premixed turbulent configurations. [ABSTRACT FROM AUTHOR]

Nanofluids are important heat transfer mediums with great potential in industry applications because of its high thermal conductivity when adding metal or metalloid nanoparticles, which has better heat transfer characteristics and controllability than the base liquid. However, there are great uncertainties, deviations and anomalies in the computational model, experimental results and theoretical analysis when conducting research on the thermal physical properties, convective heat transfer performance and heat transfer mechanism of nanofluids. This poses a great challenge to the precise and active controllability of nanofluids when considering their own parameters and external excitation. Also, these inevitable problems may cause certain confusions on the follow-up study of nanofluids. Based on these phenomena, this paper systematically reviews the recent researches on heat transfer performance of nanofluids. The thermophysical characteristics, convective heat transfer coefficient, stability and heat transfer mechanism of suspension mixed nanofluids were summarized and compared. It is hoped that it can provide effective references and guidance for researchers to study the heat transfer performance of nanofluids, and also provide new ideas for future researches on the heat transfer performance of nanofluids. [ABSTRACT FROM AUTHOR]

In this Paper, a Flexible Pulsating Heat Pipe (FPHP) was experimentally tested to evaluate the effect of foldability on the start-up, overall thermal resistance and evaporator temperature. Evaporator and condenser sections were made of 9 turn copper capillary of 2 mm inner diameter. Adiabatic section was made of a silicon rubber tube with an inner diameter of 3 mm. Deionized water with 50% filling ratio was used as working fluid. Heating power range kept was 10–100 W. Four different structural styles (Vertical, 45-Degree, 60-Degree and 90-Degree) created by deforming adiabatic section were experimentally tested and compared. The results show that FPHP showed efficient performance in vertical style. The minimum thermal resistance found is 0.65 °C/W for vertical style when heating power is 99.88 W. Deformation of adiabatic section degrades start-up and thermal performance of FPHP which depends on the deformation extent. The highest increase in thermal resistance for 90-Degree style is 29.30% for the heating power of 99.88 W when compared with vertical style. Start-up heat input observed is 50.52 W for vertical and 45-Degree styles while it is 60.29 W for 60-Degree and 90-Degree styles. Start-up evaporator temperature increases when the structural style is changed from vertical to 90-Degree. [ABSTRACT FROM AUTHOR]