Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cr...Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.展开更多
To unravel the intricacies of two-phase gas-liquid flow characteristics and heat transfer behavior,an array mini-channel gravity plate heat pipe(AMGPHP)is proposed in this work,which allows for observing the internal ...To unravel the intricacies of two-phase gas-liquid flow characteristics and heat transfer behavior,an array mini-channel gravity plate heat pipe(AMGPHP)is proposed in this work,which allows for observing the internal changes in the state of the working fluids.The flow patterns such as pool flow,columnar flow,and slug flow,are experimentally explored and analyzed in detail.It is found that the optimal volume fill ratio is 20%by utilizing start-up time and thermal resistance as performance evaluation metrics.With this fill ratio,a medium optimization strategy by blending ethanol within R141b is proposed and evaluated.In comparison to pure working fluids,the heat transfer performance of AMGFHP in the binary fluid has been significantly augmented due to temperature and concentration shifts resulting from disparate boiling points.Under the 10%volume fraction ethanol blending condition,the equivalent thermal conductivity of the heat pipe is dramatically elevated,with a value of 3110 W/(m·℃),along with the reduction of the minimum start-up power to 4 W.In general,applying such a medium to heat pipes has considerable potential in practical applications.展开更多
Mini-channel heatsinks are one of the most effective thermal management methods for high heatflux devices due to the high performance of convective heat transfer.In recent years,various techniques have been innovated t...Mini-channel heatsinks are one of the most effective thermal management methods for high heatflux devices due to the high performance of convective heat transfer.In recent years,various techniques have been innovated to improve the thermal proficiency of the mini-channel heatsinks.Some of these are taking advantage offins’structural designs and ar-rangements of inlets and outlets.The zigzagfins and channels were considered in the previous works in heatsinks,and researchers analyzed their cooling enhancement effects.However,in the present work,a combined cooling technique,considering new-type zigzagfins’geometrical parameters(arrangement,length,and height)causes turbulenceflow and higher convective heat transfer along with different positionings offlow inlet and outlets resulting in superior temper-ature uniformity,is proposed to evaluate their impacts on the cooling proficiency of the heat sink versus different Reynolds numbers.To assess the thermal and hydraulic performance of the proposed heatsink,different parameters,including temperature contours,Nusselt numbers,thermal resistance,and entropy generation are investigated.As a result,it is observed that in the case demonstrating the best thermal performance,the Nusselt number,pressure drop,thermal resistance,and entropy generation are respectively 37.13,4586.46 Pa,0.000078 m^(2)·K/W,and 0.1078 W/K in the best header.As well,it is found that by changing the arrangements of inlets and outlets,the Nusselt number,and thermal resistance are improved by 12%and 13%,respectively.Accordingly,the proposed mini-channel heat sink could be used as a high-performance thermal management system for electronic devices in different industries,including energy,solar,and medical sectors.展开更多
An electrochemical thermal coupling model of lithium battery was established to study the heat generation characteristic in this study.The simulation results showed that the heat generation density of the battery incr...An electrochemical thermal coupling model of lithium battery was established to study the heat generation characteristic in this study.The simulation results showed that the heat generation density of the battery increased with the discharge rate.With the discharge process,the heat generation density of the battery increased continuously.With 2.5C discharge rate,the heat generation density at the end of discharge was 1.82 times of that at the beginning of discharge.The heat generation density at different areas of the battery was not uniform and 46%of the total ohmic heat was generated near the electrode tabs.A cooling plate with variable mini-channels was designed to improve the temperature non-uniformity caused by the heat generation characteristic.A cooling plate with uniform mini-channels was designed for compared experiment.The experiments were conducted with deionized water and refrigerant R141b and carried out with 1.5C,2C and 2.5C discharge rates.Experimental results showed that the cooling plate with variable mini-channels had a better cooling performance in both single-phase and two-phase cooling conditions.展开更多
Cold plate is an important component for a liquid battery thermal management system.In order to study the transient thermal performance of the cold plate under conditions with sharply increasing heat loads,the numeric...Cold plate is an important component for a liquid battery thermal management system.In order to study the transient thermal performance of the cold plate under conditions with sharply increasing heat loads,the numerical model of a battery cold plate is established.The validation experiment shows that the error between the simulation and experiment is around 2.5%to 5%.Effects of the coolant flow rate,the increase in heat flux,and the channel number are analyzed to study the transient thermal performance of the cold plate.Results show that the average temperature of the cold plate at 540 s is lowered from 28.3℃ to 26.9℃ when the coolant flow rate is raised from 0.065 kg/s to 0.165 kg/s.The temperature deviation is decreased when the coolant flow rate is increased from 0.065 kg/s to 0.115 kg/s;however,it is slightly increased if the coolant flow rate is further increased.Both average temperature and temperature deviation are raised if the final heat flux is increased from11000 W/m^(2) to 16500 W/m^(2),which are 2 and 3 times of the initial,respectively.In addition,increasing the channel number has slightly positive effect on the average temperature of the cold plate,while the temperature deviation is increased when the channel number is increased from 3 to 11 due to the non-uniform velocity distribution between each channel.The results of this study will be helpful during the design of cold plate for battery thermal management,especially for transient conditions with sudden rising heat loads like thermal runaway.展开更多
Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 ...Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 kg/(m^2·s),the inlet pressure ranged from 630 to 1080 kPa,and the heat flux ranged from 0 to 223.2 kW/m^2.Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined.Results showed that within the limited test conditions,the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance.Three heat transfer trends were identified with increasing heat flux.At low heat fluxes,the heat transfer coefficient increases first and then decreases with vapour quality.At intermediate heat fluxes,the heat transfer coefficient versus the vapour quality presents an inverted"U"shape.At high heat fluxes,a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon.The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception.The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure.A modified experimental correlation(mean absolute error(MAE)=19.3%)was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.展开更多
This paper presents a new set of experimental data of air-water flow patterns in a channel with a cross-section of 1×1 mm2. The ranges of the gas and liquid superficial velocities are 0.1-10 m/s and 0.2~7 m/s, re...This paper presents a new set of experimental data of air-water flow patterns in a channel with a cross-section of 1×1 mm2. The ranges of the gas and liquid superficial velocities are 0.1-10 m/s and 0.2~7 m/s, respectively. Bubble, bubble-slug, slug, and frothy flows are observed. The present data are compared with other data in mini-channels reported in literature, and also compared with those in normal channel at microgravity, in which the Bond number has the same order of magnitude. The slug-frothy boundary is in consistent with each other, but for the bubble-slug transition, a much smaller value for the transition quality in the drift-flux model is obtained in the present study than those predicted by the empirical relations for the case of microgravity. It’s shown that the mini-scale modeling may not be an effective way to anticipate the bubble-slug transition of two-phase flow at microgravity.展开更多
There is currently a growing demand for developing efficient techniques for cooling integrated electronic devices with ever increasing heat generation power. To better tackle the high-density heat dissipation difficul...There is currently a growing demand for developing efficient techniques for cooling integrated electronic devices with ever increasing heat generation power. To better tackle the high-density heat dissipation difficulty within the limited space, this paper is dedicated to clarify the heat transfer behaviors of the liquid metal flowing in mini-channel exchangers with different geometric configurations. A series of comparative experiments using liquid metal alloy Ga68%In20%Sn12% as coolant were conducted under prescribed mass flow rates in three kinds of heat exchangers with varied geometric sizes. Meanwhile, numerical simulations for the heat exchangers under the same working conditions were also performed which well interpreted the experimental measurements. The simulated heat sources were all cooled down by these three heat dissipation apparatuses and the exchanger with the smallest channel width was found to have the largest mean heat transfer coefficient at all conditions due to its much larger heat transfer area. Further, the present work has also developed a correlation equation for characterizing the Nusselt number depending on Peclet number, which is applicable to the low Peclet number case with constant heat flux in the hydrodynamically developed and thermally developing region in the rectangular channel. This study is expected to provide valuable reference for designing future liquid metal based mini-channel heat exchanger.展开更多
针对二氧化碳作为制冷剂在微细通道内两相流沸腾换热进行了实验与理论研究,采用红外成像观测与传热系数实验研究,定量与定性地分析了热通量2~35 k W·m-2,饱和温度-10~10℃工况时,内径为1、2、3 mm圆管内的传热系数。实验结果表明...针对二氧化碳作为制冷剂在微细通道内两相流沸腾换热进行了实验与理论研究,采用红外成像观测与传热系数实验研究,定量与定性地分析了热通量2~35 k W·m-2,饱和温度-10~10℃工况时,内径为1、2、3 mm圆管内的传热系数。实验结果表明：当质量流率增加时干涸起始干度逐渐降低,当质量流率小于临界值时,干涸现象结束之后,传热系数随着质量流率增加基本维持不变,而当质量流率大于临界值时,干涸现象结束之后,随着质量流率增加传热系数相应增加;随着管径增加,干涸发生的质量流率越小,临界热通量越大,同时管径越小传热系数越高。展开更多
文摘Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.
基金supported by Industrial Foresight Project in Yangzhou City(No.YZ2021002)Transformation of Scientific and Technical Achievements Project in Yangzhou City(No.YZ2021121)National Key Research and Development Plan of China(No.2018YFA0702300)。
文摘To unravel the intricacies of two-phase gas-liquid flow characteristics and heat transfer behavior,an array mini-channel gravity plate heat pipe(AMGPHP)is proposed in this work,which allows for observing the internal changes in the state of the working fluids.The flow patterns such as pool flow,columnar flow,and slug flow,are experimentally explored and analyzed in detail.It is found that the optimal volume fill ratio is 20%by utilizing start-up time and thermal resistance as performance evaluation metrics.With this fill ratio,a medium optimization strategy by blending ethanol within R141b is proposed and evaluated.In comparison to pure working fluids,the heat transfer performance of AMGFHP in the binary fluid has been significantly augmented due to temperature and concentration shifts resulting from disparate boiling points.Under the 10%volume fraction ethanol blending condition,the equivalent thermal conductivity of the heat pipe is dramatically elevated,with a value of 3110 W/(m·℃),along with the reduction of the minimum start-up power to 4 W.In general,applying such a medium to heat pipes has considerable potential in practical applications.
文摘Mini-channel heatsinks are one of the most effective thermal management methods for high heatflux devices due to the high performance of convective heat transfer.In recent years,various techniques have been innovated to improve the thermal proficiency of the mini-channel heatsinks.Some of these are taking advantage offins’structural designs and ar-rangements of inlets and outlets.The zigzagfins and channels were considered in the previous works in heatsinks,and researchers analyzed their cooling enhancement effects.However,in the present work,a combined cooling technique,considering new-type zigzagfins’geometrical parameters(arrangement,length,and height)causes turbulenceflow and higher convective heat transfer along with different positionings offlow inlet and outlets resulting in superior temper-ature uniformity,is proposed to evaluate their impacts on the cooling proficiency of the heat sink versus different Reynolds numbers.To assess the thermal and hydraulic performance of the proposed heatsink,different parameters,including temperature contours,Nusselt numbers,thermal resistance,and entropy generation are investigated.As a result,it is observed that in the case demonstrating the best thermal performance,the Nusselt number,pressure drop,thermal resistance,and entropy generation are respectively 37.13,4586.46 Pa,0.000078 m^(2)·K/W,and 0.1078 W/K in the best header.As well,it is found that by changing the arrangements of inlets and outlets,the Nusselt number,and thermal resistance are improved by 12%and 13%,respectively.Accordingly,the proposed mini-channel heat sink could be used as a high-performance thermal management system for electronic devices in different industries,including energy,solar,and medical sectors.
基金supported by the National Key R&D Program of China(2019YFE0104900)。
文摘An electrochemical thermal coupling model of lithium battery was established to study the heat generation characteristic in this study.The simulation results showed that the heat generation density of the battery increased with the discharge rate.With the discharge process,the heat generation density of the battery increased continuously.With 2.5C discharge rate,the heat generation density at the end of discharge was 1.82 times of that at the beginning of discharge.The heat generation density at different areas of the battery was not uniform and 46%of the total ohmic heat was generated near the electrode tabs.A cooling plate with variable mini-channels was designed to improve the temperature non-uniformity caused by the heat generation characteristic.A cooling plate with uniform mini-channels was designed for compared experiment.The experiments were conducted with deionized water and refrigerant R141b and carried out with 1.5C,2C and 2.5C discharge rates.Experimental results showed that the cooling plate with variable mini-channels had a better cooling performance in both single-phase and two-phase cooling conditions.
文摘Cold plate is an important component for a liquid battery thermal management system.In order to study the transient thermal performance of the cold plate under conditions with sharply increasing heat loads,the numerical model of a battery cold plate is established.The validation experiment shows that the error between the simulation and experiment is around 2.5%to 5%.Effects of the coolant flow rate,the increase in heat flux,and the channel number are analyzed to study the transient thermal performance of the cold plate.Results show that the average temperature of the cold plate at 540 s is lowered from 28.3℃ to 26.9℃ when the coolant flow rate is raised from 0.065 kg/s to 0.165 kg/s.The temperature deviation is decreased when the coolant flow rate is increased from 0.065 kg/s to 0.115 kg/s;however,it is slightly increased if the coolant flow rate is further increased.Both average temperature and temperature deviation are raised if the final heat flux is increased from11000 W/m^(2) to 16500 W/m^(2),which are 2 and 3 times of the initial,respectively.In addition,increasing the channel number has slightly positive effect on the average temperature of the cold plate,while the temperature deviation is increased when the channel number is increased from 3 to 11 due to the non-uniform velocity distribution between each channel.The results of this study will be helpful during the design of cold plate for battery thermal management,especially for transient conditions with sudden rising heat loads like thermal runaway.
基金the National Natural Science Foundation of China(No.11872373)。
文摘Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 kg/(m^2·s),the inlet pressure ranged from 630 to 1080 kPa,and the heat flux ranged from 0 to 223.2 kW/m^2.Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined.Results showed that within the limited test conditions,the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance.Three heat transfer trends were identified with increasing heat flux.At low heat fluxes,the heat transfer coefficient increases first and then decreases with vapour quality.At intermediate heat fluxes,the heat transfer coefficient versus the vapour quality presents an inverted"U"shape.At high heat fluxes,a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon.The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception.The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure.A modified experimental correlation(mean absolute error(MAE)=19.3%)was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.
文摘This paper presents a new set of experimental data of air-water flow patterns in a channel with a cross-section of 1×1 mm2. The ranges of the gas and liquid superficial velocities are 0.1-10 m/s and 0.2~7 m/s, respectively. Bubble, bubble-slug, slug, and frothy flows are observed. The present data are compared with other data in mini-channels reported in literature, and also compared with those in normal channel at microgravity, in which the Bond number has the same order of magnitude. The slug-frothy boundary is in consistent with each other, but for the bubble-slug transition, a much smaller value for the transition quality in the drift-flux model is obtained in the present study than those predicted by the empirical relations for the case of microgravity. It’s shown that the mini-scale modeling may not be an effective way to anticipate the bubble-slug transition of two-phase flow at microgravity.
文摘There is currently a growing demand for developing efficient techniques for cooling integrated electronic devices with ever increasing heat generation power. To better tackle the high-density heat dissipation difficulty within the limited space, this paper is dedicated to clarify the heat transfer behaviors of the liquid metal flowing in mini-channel exchangers with different geometric configurations. A series of comparative experiments using liquid metal alloy Ga68%In20%Sn12% as coolant were conducted under prescribed mass flow rates in three kinds of heat exchangers with varied geometric sizes. Meanwhile, numerical simulations for the heat exchangers under the same working conditions were also performed which well interpreted the experimental measurements. The simulated heat sources were all cooled down by these three heat dissipation apparatuses and the exchanger with the smallest channel width was found to have the largest mean heat transfer coefficient at all conditions due to its much larger heat transfer area. Further, the present work has also developed a correlation equation for characterizing the Nusselt number depending on Peclet number, which is applicable to the low Peclet number case with constant heat flux in the hydrodynamically developed and thermally developing region in the rectangular channel. This study is expected to provide valuable reference for designing future liquid metal based mini-channel heat exchanger.
文摘针对二氧化碳作为制冷剂在微细通道内两相流沸腾换热进行了实验与理论研究,采用红外成像观测与传热系数实验研究,定量与定性地分析了热通量2~35 k W·m-2,饱和温度-10~10℃工况时,内径为1、2、3 mm圆管内的传热系数。实验结果表明：当质量流率增加时干涸起始干度逐渐降低,当质量流率小于临界值时,干涸现象结束之后,传热系数随着质量流率增加基本维持不变,而当质量流率大于临界值时,干涸现象结束之后,随着质量流率增加传热系数相应增加;随着管径增加,干涸发生的质量流率越小,临界热通量越大,同时管径越小传热系数越高。
