Computational analysis of spray type counter flow liquid desiccant dehumidifier

Abstract

The liquid desiccant air conditioning system (LDAC) is considered as the substitute for the conventional air conditioning system mainly because of its energy-saving characteristics. The dehumidifier is one of the most important components in LDAC, therefore, it is chosen as the system for analysis. A 3D computational model of the spray type dehumidifier with counter flow configuration was created and analysed its mass transfer characteristics for two different cases. 2D CFD models studied by various researchers failed to elaborate on the actual flow process. In order to fill this gap 3D model was created and the analysis was conducted to investigate the influence of flow rate of air and desiccant on the mass transfer performance of the dehumidifier. Air and desiccant flow rate have direct influence on the mass transfer performance of the dehumidifier. In this study, the dehumidification performance is evaluated through the simulation by increasing the desiccant flow rate and simultaneously reducing the airflow rate and the results are observed. ANSYS-FLUENT® software is used for the current analysis. The increase in desiccant flow rate and decrease in air flow rate tends to improve the change in humidity ratio (specific moisture removal) from 4.2 to 6.3 g/kg of dry air. The temperature variation of solution keeps increasing as the moisture transfer increases. The rise in temperature of the solution is higher than the air during moisture transfer due to exothermic process. Similarly the equilibrium humidity ratio of solution increased due to moisture absorption during dehumidification, which indicates the decrease in solution concentration during dehumidification. The heating of solution and air during dehumidification will affect the moisture transfer rate, which can be avoided by adding a cooling unit to the liquid desiccant system.