Performance Optimization of Rotary Dehumidifiers

Abstract

A rotary dehumidifier consists of a rotating porous matrix made of a desiccant with mechanically supporting materials. The dehumidification performance of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. The effect of the rotational speed on the dehumidification performance of a rotary dehumidifier has been investigated by Zheng, Worek, and Novosel (1993). This paper extends that previous work and investigates the effects of desiccant sorption properties, the heat and mass transfer characteristics, and the size of the rotary dehumidifier on the dehumidification performance. The results show that the using desiccant materials in a rotary dehumidifier with different adsorption characteristics results in a wide variation in dehumidification performance. However, the maximum performance of a rotary dehumidifier occurs for a desiccant material having an isotherm shape that can be characterized to have a separation factor of 0.07. Also, as the desiccant moisture uptake increases, the dehumidifier performance also increases. However, the performance improvement for a desiccant matrix having a maximum moisture uptake of larger than 0.25 by weight is not significant. The heat and mass transfer properties and the size of a rotary dehumidifier are characterized by the number of transfer units NTU. Generally, the larger the NTU, the better dehumidification performance. However, similar to the maximum moisture uptake, when the NTU is larger than 12, the performance will not improve significantly. Also, the dehumidifier with the most favorable adsorption characteristic has a slowest rotational speed, which results in a lower power requirements to rotate the desiccant wheel and smaller carry-over losses.

A mathematical model for predicting the performance of a compound desiccant wheel (A model of compound desiccant wheel)

“…The rotation speed of the desiccant wheel is widely recognized as a crucial parameter ( [28,29]). The performance of the compound desiccant wheel has been simulated by varying the rotation speed x from 4 r/h to 40 r/h.…”

“…One-dimensional desiccant wheel models have been established by Charoensupaya and Worek [1], Zheng et al [2][3][4][5] and Zhang et al [6,7]. It was reported that the desiccant cooling system operating in the ventilation mode can yield a thermal COP as high as 1.4 [1] (the thermal COP is defined by the ratio between cooling power provided by the desiccant cooling system and the thermal energy input in regeneration heater).…”

Numerical simulation of an open sorption thermal energy storage system using composite sorbents built into a honeycomb structure

“…Mass diffusion inside the solid involves multiple mechanisms -molecular diffusion, Knudsen diffusion, and surface diffusion [20] occur in the porous material. Water molecules in the vapor phase diffuse from the surface of 12 the composite solid layer to the surface of the particles through molecular and Knudsen diffusion in the inter-particle pores. The sorbed water molecules then diffuse from the surface of the particles into the intra-particle pores through surface diffusion, and water vapor molecules in the intra-particle pores diffuse through molecular and Knudsen diffusion [21].…”

Numerical study on performance of a desiccant cooling system with indirect evaporative cooler

“…For an instance, Charoensupaya and Worek [6] developed a onedimensional heat and mass transfer model utilizing a hypothetical isotherm equation to discuss an open-cycle solid desiccant cooling system parametrically. Zheng and Worek et al [7,8] analyzed the influence of rotary speed on the performance of the desiccant wheel numerically using an implicit finite differential method.…”