Counter Flow Adiabatic Regenerator and Comparative Study

Abstract

Liquid desiccant air conditioning systems have recently been attracting attention due to their capability of handling the latent load without super-cooling and then reheating the air, as happens in a conventional compression-type air conditioning system. This paper presents the results from a performance study of the simultaneous heat and mass transfer between air and liquid desiccant in an adiabatic, counter flow, structured packed regenerator. A heat and mass transfer numerical model has been developed, based on the Runge-Kutta non-stiff fixed step method, to predict the performance of the device under various operating conditions. Good agreement was found between the theoretical model and experimental tests from previous studies, with the deviation range being ±6.2% in air outlet temperature, ±8.1% in air outlet humidity ratio and ±1.4% in solution outlet temperature. Important design variables are also defined. The effects of air and desiccant flow rates, air humidity ratio, desiccant temperature and concentration have been reported on the regeneration rate and regeneration effectiveness. A detailed sensitivity analysis has been implemented to indicate which input variables mostly affect the output conditions. The three most commonly used liquid desiccant solutions, namely LiCl, LiBr and CaCl2 were evaluated against each other. The results show that high regeneration efficiency could be achieved under high desiccant mass flow rates, high air mass flow rate, high desiccant inlet temperature, low desiccant inlet concentration and CaCl2 as the desiccant solution.