Numerical Simulation And Structural Optimization Of Channel Flow Field In Plate-fin Heat Exchanger

As a highly efficient and compact heat exchanger,plate-fin heat exchangers are widely used in industrial fields.The fin as the secondary heat transfer surface is the core component of the plate-fin heat exchanger.The advantages and disadvantages of the fin structure directly affect the efficiency of the heat exchanger.In recent years,many scholars have used numerical simulation methods to analyze the flow and heat transfer characteristics of new fin structures.Based on the structure of plain fins and serrated fins,the heat transfer and flow model of single fin path was established.Simulations are carried out under constant wall temperature,constant heat flux and coupled thermal boundary conditions with CFD software,which is verified by comparison with previous experimental data from other scholars.The results were analyzed and the fin structure was optimized.The research content is as follows:(1)The simulation results of the plain fins show that the temperature difference between the fluid and the wall at the inlet of the channel is large,and the Nu number at the inlet is much higher than that in the channel.As the temperature of the fluid increases,the temperature difference from the wall surface decreases,Nu number also decreases and tends to be stable.The heat transfer factor decreases with the increase of Reynolds number.The difference of the constant wall temperature condition and the coupling condition is 5.95%,while the difference of the constant heat flow condition and the constant wall temperature condition is 16%,and the difference of the coupling condition is 11.4%.It can be seen that the Nu number is the highest under the condition of constant heat flux,while Nu number is relatively close under the condition of constant wall temperature and coupling.(2)The optimized structure of the spoiler is proposed for the plain fins,and the new structural model is established.The comparison with the simulation results of the plain fins shows that the spoiler structure can hinder the stable formation of the boundary layer of the wall and enhanced heat transfer effect.The heat transfer j-factor and the resistance f-factor of the three structures decrease with the increase of the Reynolds number.When the Reynolds number is less than 900,the j-factor of the spoiler column structure is higher than the spoiler slice structure,when the Reynolds number is greater than 900,the j-factor of the slice structure is higher than the column structure.For the f-factor,the f-factor of the slice structure is largest,and the original plain fin has the lowest f-factor.The pressure drop increases with the increase of the Reynolds number,and the pressure drop of the spoiler slice structure is the highest and plain fins have the lowest pressure drop.(3)The simulation results of serrated fins show that the boundary layer separation and the change of flow cross section cause the transition between kinetic energy and static pressure energy,which causes the pressure in the flow channel to rise.The temperature of the constant heat flow condition in the flow channel is lower than the constant wall temperature condition,and the temperature in the flow channel is the highest under the coupling wall condition.The average Nu number increases with the increase of Reynolds number under the three thermal boundary conditions,and the average Nu number under constant heat flux density is higher than the constant wall temperature condition and coupling condition when the Reynolds number is high.For the heat transfer j-factor,when the Reynolds number is less than 750,the j-factor under the constant heat flux condition is close to the experimental data in the literature.When the Reynolds number is greater than or equal to 1000,the j-factor obtained under constant wall temperature conditions is closer to the experimental data in the literature.(4)The structure of the serrated fins was optimized and improved.The cross-bending zigzag fins structure with different bending angles was proposed.The effects of different bending angles on the flow heat transfer are compared by simulation.The final result shows that when the bending angle is at 160°,the Nu Number of the flow channel is higher than other angles,the f-factor is relatively low,and the pressure drop is basically the same as the original offset fins' pressure drop.The heat transfer quality factor can reach the optimum value and the comprehensive performance of the fins is also excellent.