Modeling and measurements of Soret and Dufour effects on the water vapor transfer in membrane-based desiccant solution dehumidification dual-chamber system

Abstract

In order to study the mutual influences of temperature gradient and concentration gradient in the coupled heat and mass transfer process of membrane-based desiccant solution dehumidification, an air-solution dual-chamber system was built. The reduced heat of transfer without concentration gradient is defined, qm2∗=-rmmrmq, to derive thermal diffusivity DSr, and then derive the corresponding Onsager coefficients rqm2(rmq2) and rmm2. The expression of the total entropy production with respect to temperature gradient and chemical potential varying with concentration is given as σ=-λ2Jm2∙T2∙dTdx3+[λJm12∙(dlnT)2+∂μ/∂cT∙Dm]∙Jm1∙Jm1+Jm2. There should be a certain temperature gradient to enable the thermal diffusion process to occur by qualitative analysis. The hydrophilic-hydrophobic alumina porous ceramic membrane grafted with fluoroalkylsilane (FAS) was prepared. The improved time lag method was applied in air-solution compartments to obtain the water vapor diffusivity in large temperature difference. The thermal conductivities of the membrane under different temperature gradients were measured. The Soret number and the Dufour number are calculated by the discretization method. A transient two-dimensional mathematical model was established to describe the Soret term affecting the mass transfer process and the Dufour term affecting the heat transfer process. In model validation section, the deviation in the latter part is explained from the perspective of the intrinsic resistance of the membrane material influenced by air inlet temperature. The phenomenon of the occurrence of additional mass flux caused by the temperature gradient in the coupled heat and mass transfer process was revealed by the simulation results of water vapor concentration and temperature distribution.