Research On The Influence Of Liquid Recirculation System On The Performance Of R134a Falling Film Chiller

As a kind of high efficiency heat exchange equipment,horizontal tube falling-film heat exchanger has the advantages of small heat transfer temperature difference,high heat transfer coefficient and less refrigerant charge,an has a good application prospect Recirculation of refrigerant has great influence on the heat transfer performance of falling film.In this paper,the theoretical model of falling film heat transfer of the horizontal tube in the refrigerant recycling process is established,and the corresponding experimental device is set up.The main research contents and conclusions are as follows:In order to analyze the influence of liquid injection flow rate on the performance of R134a falling-film evaporator,a finite-difference model of horizontal tubular falling-film evaporator was established,providing an ideal model for falling-film heat transfer.Based on this model,a falling-film water chiller with injector liquid recirculation system was proposed.At the same time,Visual Basic was used to compile two kinds of falling-film evaporator simulation programs through the established physical model.On the basis of numerical simulation,a horizontal pipe falling film experimental device was built according to a series of design standards.Then,the numerical simulation results were compared with the experimental results,and the errors and causes between the simulation data and the experimental results were analyzed.The results show that when the liquid recirculation ratio increases from 1.0 to 1.21,the experimental and numerical refrigerating capacities increase by 9.5%and 6.7%respectively.The difference between experimental refrigerating capacity and numerical refrigerating capacity of evaporator is about 3.3%.With the increase of R1,the evaporation liquid flow first increased rapidly and then slightly.In addition,the results of R1 indicate that the optimal value is about 1.2,and the corresponding value of the comprehensive falling film coefficient is about 0.85.This indicates that it is not advisable to try to completely eliminate the "dry spot" outside the tube.According to the result of experimental analysis,in order to further solve the phenomenon of "dry spot" presents a two cloth liquid system,analysis the system effect the performance of the falling film evaporator,the results show that under the condition of small flow of refrigerant liquid recirculating,secondary recirculation of the structure of the falling film evaporator compared to the level of recycling of the structure of the falling film evaporator has a certain effect,but when the refrigerant recycling flow rate gradually increases,primary recirculation of the falling film evaporator refrigerant actual evaporation is significantly higher than secondary recirculation falling film evaporator.When the refrigerant circulation amount is large enough,both the primary and secondary recirculation tube bundles can be fully descended,that is,no dry spots are generated,and the evaporation capacity of both tends to be stable.