Structural Optimization Of Cross-Flow Hollow Fiber Membrane Dehumidification Module

Hollow fiber membrane liquid dehumidification is a unique separation technology that combines liquid and membrane dehumidification and is an efficient way to save energy,reduce emissions,and enhance environmental quality.This technology can use low-grade energy to improve dehumidification efficiency and avoid liquid droplet carryover.The hollow fiber membrane module is the core part of this technology.It has been widely employed in the chemical and energy areas due to its simple structure,low cost,and excellent heat and mass transmission performance.Currently,there is no corresponding standard for the design of hollow fiber membrane modules,especially for revealing the internal humidity field distribution characteristics of membrane dehumidification.Therefore,an in-depth and comprehensive study and understanding of the membrane dehumidification process is of great significance for the design of the hollow fiber membrane module.Based on this,this paper investigates the fluid flow,heat and mass transfer inside the membrane module using a combination of experimental and numerical means(CFD)with a staggered flow hollow fiber membrane module as the research object.The membrane dehumidification heat and mass transfer law is revealed by analyzing the flow,temperature and humidity fields of the membrane module.Specific work includes:(1)According to the background and significance of this research,the effect of changing different inlet parameters on the dehumidification and cooling effect of the membrane module was experimentally tested using a membrane dehumidification module test bench built with reasonable testing means.The results show that increasing the air flow rate is beneficial to improve the dehumidification and cooling capacity of the module,but the dehumidification efficiency and cooling efficiency will decrease.Meanwhile,increasing the solution temperature decreases the dehumidification capacity,dehumidification efficiency,cooling capacity as well as cooling efficiency.(2)The fluid flow,heat transfer and mass transfer during the membrane dehumidification process were simulated using CFD.A three-dimensional computational model was established and a user-defined program was written to simulate the heat and mass transfer process of the phase change of gas and liquid on the membrane surface.By comparing the experimental data with the simulated data,the maximum error between the simulated and experimental data is found to be 10 %,which indicates that the established model can overcome the limitation of impermeable walls of previous simulations and can reflect the actual dehumidification process of the hollow fiber membrane module well.At the same time,the findings of the cloud diagram of the moisture content and temperature distribution of the air inside the membrane module were used to analyze the heat and mass transfer mechanisms within the dehumidification membrane module.(3)The influence of geometric structure parameters(lateral spacing,longitudinal spacing and filling rate)and membrane parameters(inner diameter and thickness)on module dehumidification and cooling performance were investigated by using the control variables method with different arrangement methods(down-row and fork-row),At the same time,16 calculation conditions were designed by orthogonal tests,with cooling capacity,dehumidification capacity and air-side pressure drop resistance as evaluation indicators,combined with analysis of extreme variance and analysis of variance,to derive the primary and secondary effects of geometrical structure and membrane parameters on module performance and the optimal combination of structural parameters.It was found that the fill rate of the structural parameters was the main factor affecting the module performance.Finally,the simulation results of the effect of structural parameters on module performance were regressed to fit the correlation equation for heat and mass transfer in gas phase flow incorporating the structural parameters.The methodology used and the results obtained in this study provide a certain reference for the design of dehumidification module.