Study On Performance Of Spiral Elliptical Tube Heat Exchanger In Waste Heat Recovery System For Internal Combustion Engine

The waste heat recovery system of internal combustion engine can effectively recover part of the energy in the exhaust and transform this part of low quality heat into high quality effective work,which improves the efficiency of energy utilization,and is of great significance for energy saving and emission reduction.Heat waste heat recovery system is mainly composed of heat exchanger(evaporator and condenser),pump and expander.The heat transfer efficiency of heat exchanger will directly affect the efficiency of waste heat recovery system.In this paper,the heat exchanger in the waste heat recovery system of gasoline engine is studied.In order to further improve the efficiency of spiral tube heat exchanger and combine with the principle of enhanced heat transfer of elliptical twisted tube,a spiral elliptical tube heat exchanger is proposed in this paper.The heat transfer law and flow law of spiral tube heat exchanger in tube and shell side are studied.With the help of ANSYS Fluent software,this paper establishes a numerical model of spiral elliptical tube heat exchanger,studies the heat transfer performance and flow performance of tube and shell side,and evaluates the performance of heat exchanger,so as to optimize the structural parameters and improve the efficiency of heat exchanger.The main conclusions are as follows:(1)The secondary flow intensity in spiral elliptical tube is higher than that in spiral tube.Increasing the entrance angle?and the ratio of long axis to short axis of elliptical section a/b can improve the heat transfer performance in spiral elliptical tube.The heat transfer correlation and flow correlation in spiral elliptical tube are fitted.Within the scope of study,the comprehensive heat transfer performance in spiral elliptical tube is improved by 9%-53%.(2)Reynolds number Re,the ratio of long axis to short axis a/b,the ratio of equivalent diameter to helical diameter d_e/D,the ratio of pitch to helical diameter P/D are the main factors affecting the performance of helical elliptical tube shell side.Through single factor analysis and multi-factor collaborative analysis,heat transfer and flow correlations of shell side are obtained.The structure of helical elliptical tube is optimized when Reynolds number Re=10000.The comprehensive heat transfer performance of rear shell side has been improved by 56.3%.(3)Compared with spiral tube heat exchanger,the exhaust heat utilization efficiency of spiral elliptical tube heat exchanger is increased by 4%-6%,the Rankine cycle efficiency is increased by 1%-2%,and the total efficiency of waste heat recovery system is increased by 2%-3%under the same working conditions.