Simulation of removal of humidity in a factory using various rotary honeycomb dehumidifiers

Abstract

In this thesis a simple dynamic model for the rotary honeycomb lithium chloride coated absorption-type dehumidifier consisting of ordinary differential equations has been modified and extended to the case of silica gel and zeolite-13X coated adsorption-type dehumidifiers. Dubinin-Astakhov equation is employed to correlate the equilibrium adsorption isotherm for water vapor on both silica gel and zeolite-13X coated ceramic fiber sheet. The reliability of the model is validated against detailed experimental data published by Kodama, A. et al. (1993, 1994). The present model is shown to accurately predict the dehumidification performance and the local phenomena of simultaneous heat and mass transfer inside honeycomb of the dehumidifier. The air temperature and humidity profiles inside the rotary dehumidifier are compared and found to agre well with the experimental results. Next five factors, i.e. the rotational speed of the rotor, regenerative air temperature, mass velocity of humid room air, mass velocity of hot regenerative air and length of the rotor are investigated. The results show that the optimal regenerative air temperatures are 393 K and 453 K for silica gel and zeolite-13X coated dehumidifiers, respectively. Meantime, the optimal rotational speed is approximately 6-14 rph which depends on the length of the rotor and the mass velocity of humid room air. At the optimal condition, increasing the mass velocity of the humid room air from 4.05x10 -3 to 1.62x10-2 kgw/(m2s) decreases the dehumidification efficiency from 95% to 70% and from nearly 100% to 95% for the cases of silica gel and zeolite-13X, respectively. Furthermore, both of silica gel and zeolite-13X coated rotary dehumidifiers are simulated in conjunction with a closed process room with wet floor in a modern beverage factory in Thailand in order to investigate and predict the dehumidification performance and the dynamic process of the water evaporation at various conditions as well as to compare the results with the case of lithium chloride absorbent (Prawarnpit, 1997). The results show that the lithium chloride, silica gel and zeolite-13X sorbents can dry out water on the wet floor within 10 hr, 6 hr and 3 hr, respectively.