Study on the Performance of a Fluidized Air Dehumidifier

Transient adsorption/desorption characteristics of solid desiccant particles in fluidized bed have been presented. The system operates in batch mode and the atmospheric air with controlled inlet humidity and temperature is dehumidified by the applied desiccant. Also, heated air is used for regeneration purposes. A simplified analytical solution, with isothermal adsorption assumption, is demonstrated. In the experimental study, spherical particles of silica gel about 3 mm in diameter are used as the working desiccant in the fluidized bed. The experimental system is equipped with the necessary control valves to facilitate operation in adsorption and desorption modes, respectively. To control the humidity of inlet air, a humidifier is designed and fitted in a proper location in the system. Also, the system is well instrumented to measure the inlet and outlet air parameters as well as bed temperatures during the operation modes. Transient values of the mass of adsorbed water in the bed, rate of adsorption and water content in silica gel particles are evaluated from the experimental measurements. Also, numerical values of the volumetric mass transfer coefficient are plotted and discussed for different operating conditions. Model output, which shows the dependence of the dimensionless value of water content in the bed [(w*_i − w)/(w*_i − w_o)] on the dimensionless time, is compared with the experimental results. Good agreement is found at the first period of adsorption, when the adsorption is nearly isothermal. Successive increase in bed temperature, due to the heat of adsorption, results in increase in discrepancy between the model and the experimental data. Accordingly, the isothermal model could be applied with reasonable degree of reality for systems with shorter adsorption/desorption cycles. The effect of air inlet humidity on the system operation has been highlighted. The drop in air humidity is highly affected by its inlet value. It is found that, the maximum decrease in air humidity occurs at the beginning of adsorption for the different inlet values. Also, the rate of water vapor adsorption increases with the increase in the inlet humidity.