Cooling Heat Transfer Research Articles

Effect of Crossflow-to-Jet Temperature Ratio on Heat Transfer and Flow of Impingement Cooling

Effect of Crossflow-to-Jet Temperature Ratio on Heat Transfer and Flow of Impingement Cooling

Neural network prediction of cooling heat transfer characteristics of supercritical R1234ze(E) in horizontal tube

<sec>The prediction of heat transfer coefficients or wall temperatures of heat exchanger tubes is an important research topic in supercritical heat transfer, which is extremely significant for the application of supercritical fluids in industrial production and the design of the entire thermal system. At present, the empirical correlation method is the most widely adopted prediction method, but its predicted heat transfer coefficient still has significant difference from the actual data near the pseudo-critical temperature. Therefore, some scholars proposed using artificial neural networks to predict the heat transfer performance of supercritical fluids in tubes. On the basis of previous researches, this work further explores the effectiveness of artificial neural network in predicting supercritical heat transfer, focusing on the influence of input parameters on neural network prediction results and the influence of genetic algorithm optimization on the prediction results.</sec><sec>In this research, a neural network prediction model for supercritical R1234ze(E) cooled in horizontal straight tubes is established and compared with the modified D-B heat transfer correlation. The result shows that the input parameter has great influence on the prediction accuracy of BPNN, and not all BPNN input parameter combinations can bring better prediction results than heat transfer correlation. The combination of <inline-formula><tex-math id="M7">\begin{document}$ {{Re} _{\text{b}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M7.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M7.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M8">\begin{document}$ {Pr _{\text{b}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M8.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M8.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M9">\begin{document}$ {{{\rho _{\text{b}}}} \mathord{\left/ {\vphantom {{{\rho _{\text{b}}}} {{\rho _{\text{w}}}}}} \right. } {{\rho _{\text{w}}}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M9.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M9.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M10">\begin{document}$ {{{{\overline C }_{\text{p}}}} \mathord{\left/ {\vphantom {{{{\overline C }_{\text{p}}}} {{C_{{\text{pw}}}}}}} \right. } {{C_{{\text{pw}}}}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M10.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M10.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M11">\begin{document}$ {{{\lambda _{\text{b}}}} \mathord{\left/ {\vphantom {{{\lambda _{\text{b}}}} {{\lambda _{\text{w}}}}}} \right. } {{\lambda _{\text{w}}}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M11.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M11.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M12">\begin{document}$ {{{\mu _{\text{b}}}} \mathord{\left/ {\vphantom {{{\mu _{\text{b}}}} {{\mu _{\text{w}}}}}} \right. } {{\mu _{\text{w}}}}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M12.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240283_M12.png"/></alternatives></inline-formula> features the best prediction performance. The AAD and Error<sub>max</sub> of the prediction result for the trial set are only 2.02% and 9.34%, which are far lower than the prediction deviation of the heat transfer correlation, and the predictions of the trend of <i>h</i> in the high temperature region, the maximum value of <i>h</i> and the position of the peak value of <i>h</i> are more precise than heat transfer correlation. Moreover, this research compares GA-BP model with BP model under two different fitness value calculation methods to reveal the effectiveness of GA-BP in enhancing the prediction accuracy of supercritical heat transfer, concluding that when the same dataset is adopted for network training and fitness value calculation, over-fitting will occur and the GA-BP cannot further improve the prediction accuracy; when different datasets are used to train the network and calculate the fitness value, the generalization ability of the network will be strengthened, and the root mean square deviation and the maximum deviation of the prediction result can be further reduced.</sec><sec>This work will provide a practical tool for predicting the cooling convection heat transfer of supercritical R1234ze(E) in horizontal tubes, laying the foundation for its application in trans-critical heat pump systems, and providing inspiration for potential research directions of ANN in supercritical heat transfer prediction.</sec>

Thermal Modeling With Surrogate Model-Based Optimization of Direct Oil Cooling Heat Transfer Coefficient for HEV Motor

Thermal Modeling With Surrogate Model-Based Optimization of Direct Oil Cooling Heat Transfer Coefficient for HEV Motor

Effects of PEMFC cooling channel insulation coating on heat transfer and electrical discharge characteristics of nanofluid coolants

Nanofluids have high thermal conductivity and electrical conductivity, and there is a problem of electrical discharge when used as a coolant in proton exchange membrane fuel cell (PEMFC). In this study, the compact Al2O3 insulating coating was prepared by supersonic plasma spray processing technology and evenly coated in the cooling channel. The electrical discharge effect and heat transfer enhancement ability of three coolants, namely deionized water, Al2O3 nanofluid and graphene nanofluid, were studied when applied in the electrically active atmosphere of PEMFC. The results show that, the graphene nanofluid has the best heat transfer performance before insulation coating integration, but the dispersion of solid nanoparticles in the base fluid leads to a higher pressure drop, with an increase of 6.7%. When the voltage is 200 V, the leakage current of Al2O3 nanofluid and graphene nanofluid is up to 16 mA and 33 mA respectively. After insulation coating integration, the index of uniform temperature (IUT) and maximum temperature of graphene nanofluids further decrease, while the pressure drop increases by 7.0%. The leakage current of all three coolants at different voltages and Re numbers decrease to 0, indicating a significant improvement in the insulation performance of PEMFC cooling channel. In addition, dimensionless evaluation parameter ε for the applicability of heat transfer fluids were proposed from the perspectives of work and energy. Within the pump power range of 0.0065 W ∼ 0.0325 W, the ε of graphene nanofluids with insulating coating is always lower than Al2O3 nanofluid. At the pump power of 0.014 W, the ε of graphene nanofluids with insulating coating is 0.76, which has the best coolant applicability when applied in the electrically active atmosphere of PEMFC.

Effects of Phosphorus Treatment on Cooling Behavior, Heat Transfer, Microstructure, and Mechanical Properties of Hypereutectic Al-23%Si Alloy

Effects of Phosphorus Treatment on Cooling Behavior, Heat Transfer, Microstructure, and Mechanical Properties of Hypereutectic Al-23%Si Alloy

Statement of Retraction: The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate

Statement of Retraction: The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate

Evaluation and optimization of a new condensation dehumidification system with fan-coil units using low-cost cold source for greenhouses

Dehumidification is crucial on winter nights in closed greenhouses. To address disadvantages such as the high cooling power consumption of traditional condensation-dehumidification systems, this study proposes a condensation dehumidification system with fan-coil units (CDSFU) for greenhouses that utilizes outdoor cold air as the cooling source, thereby significantly reducing power consumption. The study integrated predictive methods for air treatment in fan-coil units under dry and wet conditions, it established a heat transfer model suitable for CDSFU, and verified the accuracy of the model experimentally. The impact of controllable factors on the performance of the system was also investigated, and the parameters for maximizing the dehumidifying and cooling capabilities of the system were determined using multi-objective optimization methods. At the optimal point, the moisture removal rate, heat removal ratio, cooling heat transfer rate and cooling COP were 10.96 kg h−1, 61.2%, 9.27 kW, and 24.1, respectively. The system consumed only 0.11 kW h of electrical energy to remove 1 kg of moisture, implying energy savings by 52.2%–84.7%. Therefore, the CDSFU is a promising dehumidification technology for overwinter crop production in closed greenhouses.

Numerical Study on Heat Transfer and Pressure Loss Characteristics of Swirl Cooling in Elliptical Tubes With Tangential Jet Inlets

Abstract The paper presents a numerical study of the heat transfer, pressure loss, and flow characteristics of swirl cooling in elliptical tubes, which are compared to the counterpart of swirl cooling in a circular tube with a diameter of D = 50.0 mm under equal passage Reynolds numbers and equal jet Reynolds numbers. The swirl tubes with two kinds of fixed tube length of 12D and 20D are compared, where there are sequentially arranged three tangential jet inlets over the leading tube length of 12D. The numerical results show that the swirl tubes with the tube length of 12D has a much better heat transfer performance. Under equal passage Reynolds numbers, the elliptical swirl tubes with the tube length of 12D show appreciably higher Nusselt numbers by up to 22.8% and lower pressure loss coefficients by up to 69.0% than the circular tube. Under equal jet Reynolds numbers, the elliptical tubes can reduce the global heat transfer performance modestly by up to 25.6%, but reduce the pressure loss much significantly by up to 70.6%. Mostly due to much less pressure loss, the elliptical tubes have remarkably higher thermal performance in terms of the obtained heat transfer coefficient per unit pumping power for both L1 = 12D and L2 = 20D. The numerical simulations indicate that the suppression of elliptical tubes on the swirling flow development reduces the heat transfer on the wall between the jet inlets, and decreases the wall shear force and the pressure loss in the tube.

Numerical investigation of the effect of vibration on spray cooling heat transfer in the non-boiling region

Vibrations profoundly influence the liquid film formed by spray droplets in spray cooling applications. However, understanding heat transfer mechanisms in the non-boiling region under vibrating conditions is limited in the existing literature. This study aims to bridge this gap by numerically investigating the heat transfer performance of spray cooling in non-boiling regions under vibration using the Lagrange-Euler method. To validate the computational fluid dynamics (CFD) model, experimental measurements of spray heat transfer were conducted on a heated vibrating surface test rig. The results demonstrate that the average film thickness (AFT) and average film velocity (AFV) increase at lower frequencies, leading to a decrease in the heat transfer coefficient. Conversely, the AFT decreases at higher frequencies while the AFV remains relatively constant. This reduction in AFT enhances the heat transfer coefficient, resulting in an up to 12% improvement in heat transfer performance. When a larger vibration amplitude is introduced, a higher inertial force acts on the liquid film, causing it to converge towards the centre. Generally, the heat transfer coefficient of spray cooling in the non-boiling region decreases as the vibration amplitude increases.

Heat transfer of single-phase spray cooling on heated vibrating surfaces

Effective vibration control has potential to enhance convective heat transfer. However, the precise heat transfer mechanism of single-phase spray cooling under vibration remains elusive. This study aims to elucidate this mechanism by establishing a closed-loop system for vibrating surface spray cooling. Various vibration parameters, including vibration Reynolds number (Rev), dimensionless acceleration number (Ac), amplitude, and frequency, were investigated experimentally to determine their impact on heat transfer. The research findings demonstrate that the heat flux, heat transfer coefficient, cooling efficiency, and vibration enhancement factor all decrease with an increase in Rev and amplitude. At a heating power of 200 W and Rev of 4947, the spray cooling performance on the vibrating surface is inhibited by 22%. However, as the heating power increases, the inhibitory effects of Rev and amplitude on the spray cooling heat transfer performance are weakened. Conversely, the amplitude and frequency enhance the heat flux, heat transfer coefficient, cooling efficiency, and vibration enhancement factor. At a heating power of 200 W and an Ac of 3.6, the spray cooling heat transfer performance on the vibrating surface is enhanced by 17%. Finally, a dimensionless correlation equation and a Nusselt number (Nu) prediction model for single-phase spray cooling under vibrating conditions are derived and fitted with an error of ±13.2%.

Effect of the acoustic manipulation on single phase immersion cooling performance of discretely heated vertical plate

In the cooling of high heat capacity systems, immersion cooling systems are increasing importance due to the insufficient heat dissipation rates of conventional cooling systems. In this study, the effects of ultrasonic sound waves on cooling performance in single-phase immersion cooling systems were investigated. Experimental study was carried out with ultrasonic sound waves for 9.6 kHz, 14.4 kHz, 19.2 kHz, 24 kHz and silent conditions. In addition, the effects of discrete heat sources on thermal performance were investigated by changing the surface (embedded, 2 mm protruding, 4 mm protruding) and location configurations. According to the results obtained, the highest heat transfer coefficient was calculated as 1703.36 W/m2 °C for the embedded heat source closest to the tank bottom for at 24 kHz frequency. The lowest heat transfer coefficient was calculated as 373.28 W/m2 °C for the maximum protrusion amont heat source closest to the tank upper and when ultrasound manipulation was not applied. In addition, the immersion cooling heat transfer coefficient was increased by 107.49% with ultrasonic sound wave. The heat transfer coefficient increased with increasing ultrasound frequency and decreased with increasing protrusion thickness.

Multi-effect evaluation of cooling heat transfer performance for supercritical CO2 flowing in micro-channel

Multi-effect evaluation of cooling heat transfer performance for supercritical CO2 flowing in micro-channel

Experimental investigation into the thermal performance of a solar steam generator based on spray cooling heat transfer and porous silicon carbide ceramic

Experimental investigation into the thermal performance of a solar steam generator based on spray cooling heat transfer and porous silicon carbide ceramic

Beyond traditional boundaries: Exergo-economic and thermo-mechanical optimization of segmented thermoelectric generators with varied cross-sections

In this work, we present a comprehensive optimization study of a concentrating solar segmented thermoelectric generator (CSSTEG) with variable area leg geometry. We consider not just geometrical parameters but also concentrated solar heat flux and convective cooling film coefficients, pushing the boundaries of traditional studies. Performance is evaluated on multiple fronts: power output, exergy efficiency, entropy generation, CO2 savings, dollar per watt, and thermal stress. Uniquely, we establish that an optimal skutterudite content of 6.17% provides maximum power output (47.47 W) and exergy efficiency (10.95%) at a solar heat flux of 50 kWm−2. This optimized configuration also delivers maximal annual CO2 savings (22.5 kgyr−1). Additionally, we pinpoint that a semiconductor height of 0.2 mm minimizes the dollar per watt (0.0048 $W−1) at 100 kWm−2 solar irradiances and reduces thermal stress (0.25 GPa) at a cooling heat transfer coefficient of 4 kWm−2 K−1. Our research is pioneering in its holistic approach to CSSTEG optimization, providing valuable insights for creating efficient, sustainable energy systems.

Experimental study on cooling heat transfer performance of supercritical CO2 in zigzag printed circuit heat exchanger

The zigzag printed circuit heat exchanger (PCHE) is promising as the precooler in the application of supercritical CO2 (S-CO2) Brayton cycle. In this study, the experimental investigation is conducted to explore the heat transfer performance of supercritical CO2 in the mini channels of zigzag PCHE. The experimental range of pressure, temperature and mass flux is 7.5–9.0MPa, 50–90°C and 300–600kg/(m2·s), respectively. The structural parameters of diameter, pitch, and bend angle are D=2.0mm, Lp = 7.24mm and θ = 40°, respectively. The effects of system pressure, inlet temperature, and mass flux on the heat transfer performance of supercritical CO2 are investigated by measuring multiple temperature points along the zigzag channel. The results show that the heat transfer coefficient exhibits a higher level near the pseudocritical region due to the dramatic thermophysical properties variation of supercritical CO2. Meanwhile, both the change of mass flux and pressure have a significant influence on the S-CO2 heat transfer coefficient, while the effect of inlet temperature is relatively small. Furthermore, the comparison is conducted between the existing heat transfer correlations and the experimental results. Four new cooling heat transfer correlations are proposed and compared by considering the effect of velocity change and cross-sectional thermophysical property variation on heat transfer performance. It is found that adding variates to the correlation can improve the prediction accuracy of the results while iterative calculation becomes more difficult. In order to improve the robustness and prediction accuracy, it is determined to choose the correlation without the density form, which predict 91.5% of the experimental data within ±25% error band.

Mathematical formulation of Al2O3-Cu/water hybrid nanofluid performance in jet impingement cooling

Liquid coolant is an important substance often used to lower the temperature of an object. To increase the heat transfer performance of a coolant, metal nanoparticles are introduced into a base fluid such as water, which is then called a nanofluid. A further development is the hybrid nanofluid, in which researchers try to mix two types of metal nanoparticles with high thermal conductivity to further increase the heat transfer performance. In this work, the heat transfer performance of a hybrid nanofluid in delivering heat from a target surface is investigated using a cylindrical single-jet impingement method. A three-dimensional numerical analysis is performed using Ansys FLUENT to investigate the effects of different types of coolants on the heat transfer performance. The coolants used in the simulation were pure water, Al2O3-Cu/water hybrid nanofluid, Al2O3/water nanofluid, and Cu/water nanofluid with 0.5% volume concentration. The effects of Reynolds number on the heat transfer performance of hybrid nanofluid were presented and discussed in detail. The results showed that hybrid nanofluid has the highest heat transfer performance compared to pure water and single particle nanofluids. At the end of the study, mathematical formulation was developed to describe the correlation between Reynolds number and volume concentration on the average heat transfer coefficient. This will enable the assumption of hybrid nanofluid jet impingement cooling heat transfer performance for future development.

Experimental Study of the Heat Flow and Energy Consumption during Liquid Cooling Due to Radiative Heat Transfer in Winter

Radiation cooling is a passive energy saving cooling technology. The process of cooling heat transfer liquid due to the combined effect of night radiative cooling and convection of air at negative temperatures (in winter) is studied. The radiator used for cooling was built into the roof of the building. Its radiating plate was made of a steel sheet coated with zinc oxide. In it, heat dissipation was carried out both from the upper and lower sides of the radiating plate. The experimental values of the heat flux ranged from 20 to 80 W·m−2 at a temperature difference between heat transfer liquid and air from 5 to 15 °C and ambient air temperature from −17 to +5 °C. The correctness of the model for calculating the heat flux in winter conditions was confirmed. A theoretical calculation showed that, in winter, the heat flux removed by the radiator will be 15% less than the heat flux in summer. The amount of heat transferred per watt of electrical power of the refrigeration unit reached 8 W·W−1. To keep the refrigeration unit with radiative heat transfer more efficient than in a conventional vapor compression chiller, the heat transfer liquid temperature should be 6 °C above the atmospheric temperature air. The results of the study show that radiative cooling can be used in winter and may be useful for the development of energy-efficient cooling systems for various purposes (air conditioning, industrial cooling systems and fruit storage chambers).

Heat Transfer and Flow Structure Characteristics of Regenerative Cooling in a Rectangular Channel Using Supercritical CO2

At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO2 is regarded as an effective coolant in severe heating environments due to its excellent properties of heat and mass transportation. In this paper, the heat transfer and flow structure characteristics of regenerative cooling in a rectangular channel using supercritical CO2 are analyzed numerically using a validated model. The effect of heat flux magnitude, nonuniform heat flux, acceleration and buoyancy and flow pattern are considered to reveal the regenerative cooling mechanism of supercritical CO2 in the engine condition of a scramjet. The results indicate that the heat transfer deterioration phenomenon becomes obvious in the cooling channel loaded with relatively high heat flux. Compared with the cooling channels loaded with increased heat flux distribution, the maximum temperature increased for the channel loaded with decreased heat flux distributions. When larger acceleration is applied, a relatively lower wall temperature distribution and higher heat transfer coefficients are obtained. The wall temperature distribution becomes more uniform and the high-temperature region is weakened when the coolants in adjacent channels are arranged as a reversed flow pattern. Overall, the paper provides some references for the utilization of supercritical CO2 in regenerative cooling at an extremely high Mach number in a scramjet.

Experimental Study on the Thermal Performance of Flat Loop Heat Pipe Applied in Data Center Cooling

The cooling system is the auxiliary equipment that consumes the most energy in a data center, accounting for about 30 to 50% of the total energy consumption. In order to effectively reduce the energy consumption of a data center, it is very important to improve the heat exchange efficiency at the chip level. Compared with air cooling, single-phase cold plate liquid cooling, and immersion liquid cooling, the flat loop heat pipe (FLHP) is considered to be a better chip-level cooling solution for data centers. It has extremely high heat transfer efficiency and heat flux variability, and it can avoid the operation risk caused by liquid entering the server. In this paper, a FLHP with an evaporator designed with a “Tesla valve” flow channel configuration is developed. Experiments on the FLHP are carried out, focusing on the installation angles and cooling condition factors. The results show that an inclination angle of 20° is the critical point of the influence of gravity on the performance of the FLHP; to ensure good operation of the FLHP, the installation angle should be greater than 20°. The equivalent heat transfer coefficients of the FLHP condenser under different cooling conditions are calculated. It is found that water cooling can provide higher cooling heat transfer coefficients with lower energy consumption and operating noise. Additionally, the heat transfer limit, operating temperature uniformity, and start-up stability of the FLHP are significantly improved under water cooling conditions. The maximum heat load of the FLHP is up to 230 W, and the temperature difference of the evaporator surface can be controlled within 0.5 °C, under 20 °C water cooling. Finally, using the FLHP for thermal management of the chip, its heat transfer efficiency is 166 and 41% higher than that of air cooling and water cooling, respectively.

Effect of Rib Blockage Ratio and Arrangements on Impingement Heat Transfer in Double-Wall Cooling

Abstract A numerical study was conducted on the multiple jet impingement heat transfer of the double-wall cooling with high blockage ratio ribs of various configurations. Three different blockage ratios (BR = 0.2, 0.3, and 0.5) and two rib arrangements relative to the effusion holes (l/Sx = 0.25 and 0.75) were thoroughly examined using the RANS method with the SST–KIC turbulence model, considering the Kato–Launder modification (K), intermittency (I), and crossflow (C) transition effects. The ratio of jet-to-target plate spacing to jet diameter (H/d) was fixed to be 1, and Reynolds numbers varied in the range of 4000–16,000. Furthermore, the computed data on the rib roughed wall were also compared with those on a flat plate for the double-wall cooling. The results demonstrate that the installation of the high blockage ribs significantly decreases the detrimental crossflow effect due to the blockage effect of the ribs and intensively disturbs the jet flow in flow passing over the ribs, thereby enhancing the heat transfer performance. For the impingement/effusion cooling, the arrangement of the rib downstream of the effusion holes (l/Sx = 0.25) shows more advantages, and the heat transfer level rises quickly as BR increases. The best thermal-hydraulic performance and heat transfer uniformity on the rib roughed target plate is both obtained at BR = 0.3, which can be increased by up to 10% and 8%, respectively, compared to those on the flat plate.