Theoretical Analysis Of Heat&Mass Transfer Relation Of Fluids And NTU_m-based Optimization In Liquid Desiccant Dehumidification Systems

Liquid desiccant(LD)is an innovative method to dehumidify humid air,where LD solution is used to directly contact with humid air and thus complete the dehumidification or regeneration process.Compared with some traditional methods,such as condensation dehumidification and solid desiccant dehumidification,LD dehumidification has many advantages and many research results about it have been used in practical projects.The LD dehumidification system is analyzed in this work with theoretical analysis and numerical simulation methods.The research objective of this paper includes two parts:one is to deeply analyze the heat&mass transfer relation between the components and flowing liquids(humid air and LD solution),and the other is to optimize the system based on NTU_m distribution between parking towers.The mathematical models of the heat and mass transfer processes between the humid air and solution are first built.Then the experimental results in literature are used to validate the models.In the basic LD dehumidification system regenerated by return air,which consists of a dehumidifier,a regenerator and two heat exchangers,the analytical solution of the models is used to theoretically deduce the one-to-one relation between the air states,solution circulation and temperatures of the heating and cooling sources.Certain air states(fresh air,return air,supply air and exhaust air)can determine one certain solution circulation,which can only be completed by one certain pairs of temperatures of heating and cooling sources.Accordingly,the mutual influence between air states and temperatures of heating and cooling sources is numerically demonstrated.Results show that the temperature of cooling source has a greater effect on supply air than that of heating source.The temperatures of heating and cooling resources are more affected by the humidity ratio of fresh air than its temperature.In the basic system regenerated by fresh air,when the heat required by the system or the work consumed by the heat pump is taken as the index,under a fixed total NTU_m,the NTU_m distribution between the dehumidifier and regenerator is theoretically optimized.Results show that the optimum NTU_m of dehumidifier is a little larger than that of regenerator because of the nonlinear iso-relative humidity lines and the different process ranges of the two parking towers.For the system regenerated by return air with a total heat recovery module and a dehumidification module,the optimum NTU_m of the dehumidification module takes up about 70%of the total NTU_m.The optimization of required heat can be the typical criterion for the NTU_m-based optimization of the LD dehumidification systems.