Investigation on the dynamic characteristics of the counter-current flow for liquid desiccant dehumidification

• Dynamic characteristics of the counter-current flow are investigated by CFD and VOF models.
• The effects of various parameters on the liquid film thickness, interfacial waves and pressure drop are studied.
• Typical capillary waves and roll waves are observed for the interface of unsteady air and solution flows.
• The mechanism of film waves is highly associated with the interfacial pressure and velocity fluctuations.

The dynamic characteristics of solution film flow with counter-current air flow, especially the two phase contact area, are important for the optimal design and operation of LDD (liquid desiccant dehumidifier). However, the unsteady interfacial information, including the interfacial pressure, velocity and film thickness, is hardly to be examined accurately by theoretical prediction or experimental measurement due to its complexity. In this study, CFD (computational fluid dynamic) models for the counter-current flow of the LDD were established based on the VOF (volume of fraction) and RNG (Renormalization group) k-ε turbulence model. Experimental research had been conducted to validate the liquid film thickness and typical interfacial waves obtained in simulation. With the established model, the dynamic formation process of unsteady counter-current flow is evaluated. Moreover, the effects of various parameters on the liquid film waves, pressure drop, liquid film thickness and interfacial information were obtained and analyzed by the built models. With the increase of liquid flow rate, the roll waves appear and the wave amplitudes are increased significantly, which may obviously enhance the performance in the LDD absorption and regeneration process due to the increased contact area.