Experimental Study On Heat Transfer And Pressure Drop Characteristics Of Flow Boiling In Mini-channels Heat Sink

Along with the miniaturization of microprocessor design in modern high performance electronic devices,the chip will generate greater power density due to high density packaged electronic devices.According to the ITRS?International Technology Roadmap for Semiconductors?,the power density of integrated circuits will reach 100 W·cm^-22 by 2020.Many high performance electric devices can dissipate more power than the ITRS predicted.There are more challenges in thermal management of electronics devices for traditional heat dissipation methods such as air cooling and heat pipe.Because of its high efficiency and compactness,microchannel heat transfer has become one of the most promising heat dissipation technologies for high-power electronic equipment in the future.Especially in microchannel,the flow boiling heat transfer using refrigerant has become a research hotspot at home and abroad because of its strong heat transfer capacity and uniform heat transfer effect.At present,although researchers at home and abroad have done a lot of research on flow boiling in microchannels,due to the complexity of two-phase heat transfer in microchannels,there is no general consensus on the dominant heat transfer mechanism and pressure drop in microchannels.Therefore,the study of flow boiling heat transfer in microchannels can deepen the understanding of the mechanism of flow boiling heat transfer and pressure drop in microchannels,provide theoretical guidance for practical engineering applications,which has important academic value and engineering application value.In this paper,the experimental study of flow boiling heat transfer in microchannel heat exchanger was carried out with R141b as working fluid.The characteristics of flow boiling heat transfer and pressure drop in microchannel heat exchanger were experimentally studied by setting up an experimental platform.The effects of heat flux,mass flow rate and saturated pressure on heat transfer and pressure drop are analyzed.The main contents and conclusions are as follows:1)An experimental platform for flow boiling heat transfer of pump-driven micro-channel heat exchanger was designed and built aiming at the heat dissipation requirement of high-power electronic chips.Some works were completed including the verification and calibration of various measuring equipment in the experimental system,the sealing inspection,refrigerant filling and system debugging of the experimental system.2)Based on the experimental platform of flow boiling heat transfer of micro-channel heat sink driven by pump,the verification experiment of single-phase flow was completed.The Nu-Re_l and f-Re_l variations were obtained through single-phase flow heat transfer experiments,and the predicted results were compared with the classical correlation of single-phase flow.The validity and repeatability of the experimental platform were verified.The results show that the classical single-phase flow and heat transfer prediction model can predict the experimental results well,which verifies the effectiveness and repeatability of the experimental device.3)Based on the experimental platform of flow boiling heat transfer of micro-channel heat sink driven by pump,the heat transfer characteristics and pressure drop characteristics of heat exchanger under different working conditions were obtained with heat flux of2.2 to 20W·cm^-2,mass flux of 9.8 to 16.3 kg·m^-2·s^-1,cooling water temperature of 30 to 50?,and outlet dryness of-0.1 to 1.The results show that at low dryness(x_out<0.1⁰.4),the two-phase heat transfer coefficient increases with the increase of heat flux,but less affected by mass flux.When x_out=0.1⁰.4,the heat transfer coefficient reaches its peak value,while at high dryness(x_out>0.1⁰.4),the two-phase heat transfer coefficient decreases slowly with the increase of heat flux.At this time,the effect of mass flow on heat transfer coefficient is obvious,the higher the mass flow rate is,the lower the heat transfer coefficient is.And the heat transfer coefficient increases with the increase of saturation pressure.however,when x_out>0.2⁰.3,the corresponding heat transfer coefficient under the condition of larger saturation pressure is lower than that under the smaller saturation pressure.In the process of flow boiling heat transfer,the two-phase friction pressure drop is the main part of the pressure drop,which occupied about 63%of the total pressure drop.The friction pressure drop increases with the increase of heat flux and mass flux,and decreases with the increase of saturation pressure.4)The experimental results were compared with the predicted results of the more classical and quoted predicted correlations.The experimental results of heat transfer coefficient were compared with the predicted results of 15 heat transfer correlations in the classical literature.The experimental results of friction pressure drop were compared with the predicted results of pressure drop prediction models including homogeneous model and separated model.The results show that the prediction deviation of the existing heat transfer correlations is large on the whole,Cooper,Bertsch,Gungor-Winterton and Tran formulas have good prediction results.The average absolute errors are 37.7%,39.4%,39.9%and 39.1%respectively,but they are still in a high error range.The pressure drop homogeneous model?Cicchitti?can predict the experimental results well for friction pressure drop,The average absolute error is about 17.23%.