A Mathematical Model for Predicting the Performance of Liquid Desiccant Wheel

Abstract

The liquid desiccant cooling system is found to be a good alternative of conventional air conditioning system for better control of both latent and sensible loads. The major component of a liquid desiccant cooling system is desiccant dehumidifier which controls the latent cooling load. In this paper a mathematical model for rotary type liquid desiccant dehumidifier commonly known as desiccant wheel has been presented. The desiccant wheel has a cylindrical shape with a number of identical narrow circular slots distributed uniformly over the rotor cross section. The slots are filled with a porous medium carrying the solution of liquid desiccant, to make the absorbing surface. The absorption and regeneration performance of the desiccant dehumidifier is discussed in this paper for different operating conditions. The wheel performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of wheel thickness (0.06-0.6m), air mass flux (1-8 kg/m2 .s), and regeneration temperature (60- 85o C). A reduction of about 30% in outlet humidity ratio is observed with an increase in the wheel thickness from 0.06 to 0.2m. The computed results show that better supply air conditions can be obtained to provide human thermal comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel thickness and humidity ratio of process air.