| Plate-fin heat exchanger(PFHE)has the advantages of compact structure,high heat exchange efficiency and simultaneous heat transfer of multi working medium.It is widely used in aerospace,petrochemical,natural gas processing,air separation and other industries,and it's one of the important parts of these industries.With the development of large-scale,low-energy consumption and high-precision equipment in these industries,there are higher requirements for the design of PFHE.In this paper,the method of structural optimization and performance coordination design for the header and fin of PFHE is proposed.Through the research on the header structure,fin structure,header and fin structure coordination design,the internal flow uniformity and multi condition adaptability of the heat exchanger are improved,and then the overall heat exchange performance of the PFHE is improved.This paper mainly includes the following three aspects.(1)Aiming at the problem of maldistribution of flow in the inlet section of PFHE,a regional split header structure is proposed.By adding several baffles with different inclination angles at the inlet of the header shell,the fluid entering the header is dispersed in the length direction of the header,and the nonuniformity of the fluid mass flow rate at each outlet of the header is reduced.Through Fluent simulation analysis,the number of baffles,the angle of the outermost baffles,the height of baffles,the spacing of baffles and the height of header are optimized,and the optimal size parameters of the regional split header are obtained.Compared with the traditional header,the distribution uniformity of the regional split header is improved by 84%.(2)In order to reduce the influence of the fluid thermal boundary layer on the heat transfer performance in the fin channel,a plow-type micro-convex fin structure is proposed with reference to the working characteristics of the agricultural tool "plow",which is characterized by periodic addition of plow-convex structure on the wall of straight fin.The total heat transfer rate and pressure drop of the fins under different plow-convex size are obtained by simulation,and their approximate models with plowconvex structural parameters are generated,after that the NLPQL gradient optimization algorithm is used to obtain the optimal size of plow-convex structure.In addition,the effects of arrangement and spacing of plow-convex structure on heat transfer performance are also studied.Based on the analysis of temperature field,pressure field and velocity field,the mechanism of improving fin performance by plow-convex structure is explained.(3)Existing PFHE often need to operate in 80%~110% variable working conditions,and they need to have certain adaptability to avoid the decline of production efficiency and safety accidents.By comparing the distribution performance of the traditional header and the regional split header at different inlet velocity,the adaptability of the regional split header is verified.The velocities of header outlet under different working conditions are obtained by simulation,and 6,8,11,14m/s are selected as the inlet multi-condition of the fin area.The heat transfer performance of fins under multiple operating conditions is evaluated by the heat flux(37)of air,the Kriging Model approximation technique is used to generate the approximate model with the average value of(37)and ?P as the output variable and the plow-convex structure parameter as the input variable,the gradient optimization algorithm is used to optimize the model.By comparing the prediction results with the simulation results,the accuracy of the method is verified,and the optimal structural parameters of the plow-type microconvex fins under multiple working conditions are obtained.Through the improvement and optimization research of the header and fin structure,the overall heat transfer performance of the PFHE is improved,and the research results have certain guiding significance for the actual production and manufacturing. |
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