| The relative humidity of air is an important parameter in living and production environments.In recent years,membrane contactors have been widely used for liquid dehumidification due to their advantages in solvent absorption and membrane separation.The contactors exchange heat and water vapor indirectly through semi-permeable membranes.This technology not only effectively solves the serious shortcomings of liquid droplet entrainment in traditional dehumidifiers,but also can use low-grade energy,so it has the advantages of high efficiency,low energy consumption and environmental protection.In the process of dehumidification,the solution absorbs the water vapor in the air and releases a lot of latent heat which can not be taken away.The increase of solution temperature leads to the decrease of its moisture absorption performance.Internal cooling membrane liquid dehumidification technology has been proposed to effectively improve the dehumidification performance of the solution.This technology uses cooling water to cool the solution in the process of dehumidification,so as to maintain the efficient dehumidification performance of the solution.At present,the internal cooling membrane liquid dehumidification technology and its economic value are nearly feasible in practical application,but there are still some limitations.This article will study the heat and mass transfer characteristics of internally cooled membrane contactors and their dehumidification systems in dehumidification applications.The thesis mainly carried out the following three aspects of work:For the internally cooled hexagonal quasi-countercurrent flat membrane contactor,the partial differential equations for fluid flow and heat and mass transfer are established.Using the numerical solution method,the effect of the air Reynolds number,solution Reynolds number and outer diameter of inner cooling tubes on the basic criterion number of heat and mass transfer are investigated under the coupling condition.It shows that the number and the outer diameter of the tubes have a large influence on the Nusselt number and Sherwood number on the solution side,but have little effect on the air side.The resistance coefficient and Nusselt number on the water side are basically independent of the distribution of the inner cooling tube in the solution channel.For internally-cooled cross-flow flat membrane contactors,the physical and mathematical model of heat and mass transfer of the membrane contactor is established and solved by the finite difference method in this paper.The influence of important structural parameters and operating conditions on the dehumidification performance of the membrane contactor is analyzed.An entropy production model is proposed to calculate the entropy change and entropy production of each part of the membrane contactor,and the relationship between the entropy production and performance of each part of the contactor is determined.For a new type of internal cooling flat membrane liquid dehumidification system,this paper designs and builds a liquid dehumidification system device based on an internally-cooled flat-plate film dehumidifier and makes an experimental investigation.The experimental results show that the theoretical model is in good agreement with the experimental results.Adjusting the inlet flow of the solution to 360 Lh-1is a better choice.Reducing the inlet temperature of cold water can significantly improve the dehumidification performance of the dehumidifier,and the COP of the system almost unchanged.Finally,it provides guidance and suggestions on the operation and optimization design of the system.This article makes an in-depth study on the characteristics of the internally cooled membrane contactor and its dehumidification system,provides parameter research and optimization methods for membrane contactors of different structures,and the experimental results of the dehumidification system are used to optimize its design and operation. |
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