Research On The Performance Of Parallel Flow Small Channel Phase Changer

Parallel-flow small channel heat exchanger is a device to transmits heat via phasechange of the refrigerant,which is driven by the temperature differences of the cold fluid and warm fluid.Through the heat exchanger test platform established in the environmental control laboratory,the factors that influence the thremal performance of the heat exchanger were studied.The external temperature distribution of the evaporator and the condenser was measured by the thermal imager and the flow and phase-change characteristics of the regrigerant were further investigated.Based on incremental model,we propose a physical model for calculating the boiling heat transfer coefficient in small channels.The theory of entransy dissipation was applied to optimize the small channel phase change heat exchanger.The main works are as follows:1.The tests on the parallel-flow small channel heat exchanger with phase change were carried out.With the inlet warm air and cold air temperature difference expanding from 3?to 21?,the heat transfer rate of heat exchanger increases from 0.11 k W to 1.12 k W.The optimum liquid filling rate is about 36% to achive the best heat exchange proformance when we change the liquid filling rare from 16% to 61%.When the heat exchanger deviates from the vertical direction ±25°,the heat reansfer rate reduces in the range from 0.04 k W to0.27 k W.When keeping constant area of the evaporator,the approach air velocity of the condenser was increases from 4.4m/s to 11.1m/s by reducing the area of the windward area.And the heat transfer rate in the unit area of heat exchanger increases from 4.24 k W to38.9k W.2.According to the image taken by the thermal imager,the surface temperature distribution of the evaporator of the parallel flow small-channel phase change heat exchanger is uniform,which conforms to the heat transfer characteristics of the slug flow in the tube.It is similar to the phenomenon of the formation of randomly distributed bubble column and liquid plug in the tube under the action of the surface tension in the oscillating heat pipe,and there appears the gas-liquid stratification in the condenser.Under the optimal liquid filling rate and temperature difference of 12?,there is a liquid pool with a height of 7.4cm at the lower part of the tube.3.By comparing the experimental data with the predicted results of the boiling heat transfer coefficient calculation model in similar literature,it is found that the existing correlation formula is not applicable to the heat exchanger.A new model suitable for predicting the boiling heat transfer coefficient of working medium in small channel heat pipe with parallel flow was established.The experimental results were verified by using the model.The results show that 88% of the calculated values falls in the error band of ±15%,and the mean absolute error is 7.92%.The calculated error of the total heat transfer coefficient with the experimental value is 3.6%.4.The analytical diagram was established based on the coordinates of heat transfer temperature difference and heat transfer rate.The optimization analysis of the heat exchanger was carried out based on the entransy dissipation theory.We put forward an analytical formula for optimization of the small-channel phase change heat exchangers,in which the minimum entransy dissipation rate can be taken as the optimization objective and operation parameters can be optimized when the maximum heat transfer is ensured.