Study On Flow Distribution Characteristics In Head Of Plate Fin Heat Exchanger And Structural Optimization

Plate fin heat exchanger,as a kind of efficient and compact heat exchange equipment,is the core component of the cold box,and flow maldistribution leads to the decrease of the heat exchanger performance,which limits its application.The irrational inlet design is the main factor of flow maldistribution in heat exchanger.In this paper,the distribution characteristics of the fluid in the head of the heat exchanger are studied by means of numerical simulation and experimental test.The effects of different factors on the fluid distribution are studied.On this basis,the structural optimization is carried out to improve the plate-fin heat exchanger work performance and guide its design and manufacture process.The main contents of this paper are as follows:(1)The numerical model of plate-fin heat exchanger is established,and the correction of the main vector of porous media is considered.The simulation results show that,in general,the flow nonuniformity in the transverse direction of the head is more serious than that in the longitudinal direction,and the flow in the middle channel is larger than that on both sides.The distribution characteristics of two-phase flow in the heat exchanger were studied by using the fluid distribution test system.The results show that the two phases of the liquid-phase distribution are not uniform and the liquid phase is concentrated in the middle.In contrast,the liquid flow in the channel is high,the gas flow rate is low,the liquid flow rate is low,the gas flow rate is higher(2)The factors influencing the distribution of fluid in the plate-fin heat exchanger were studied from the working conditions and the head structure.In terms of operating conditions:For the same medium,the degree of fluid uneven distribution is only related to the inlet Reynolds number,and the pressure drop is related to the physical properties of the medium.Head structure:to reduce the length of the head,to improve the height of the head,increase the channel spacing can improve the distribution of uniformity,diversion fin angle is best at 30°?35°.(3)According to the distribution characteristics of fluid in the plate-fin heat exchanger head,an improved head structure with cross baffle is designed,its main optimization parameters are determined,and the structure is optimized by orthogonal method.The results show that the improved head can reduce the unevenness of fluid distribution and cause the pressure drop of the heat exchanger to rise slightly for the two-phase flow with liquid content of 5%?11%.(4)The influence of fluid distribution on the heat transfer and energy consumption of the heat exchanger is analyzed,and the improvement of heat transfer and energy consumption of the heat exchanger is analyzed.It is found that the heat exchanger efficiency of improved head is higher than that of the prototype head,and the increase of pressure drop caused by uneven distribution of fluid increases with the increase of Reynolds number.Finally,the significance of improving the head structure to the cold box is explained,which can save the gas-liquid separation tank before the heat exchanger and reduce the margin of the heat transfer area,thus reducing the volume and weight of the cold box.