Evaluation of rotary dehumidifier performance with and without heated purge ☆ Mihajlo N. Golubovic, H.D. Madhawa Hettiarachchi, William M. Worek ⁎ Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607, United States Available online 4 May 2007 Abstract In this paper we evaluate the potential benefits from separating process air stream at the exit of rotary dehumidifier into two streams. One air stream, hot and humid, is called purge air stream and other is remaining process air stream. The remaining process air stream has a lower temperature and humidity ratio as result of separation of initial hot process air stream. It is found that as the purge angle increases the exit humidity ratio of remaining process air stream decreases up to a point where it reaches a minimum. The purge angle for which this occurs is named “effective purge angle”. The effective purge angles for different splits between adsorption and desorption side of the rotary dehumidifier, various regeneration temperatures, non-dimensional lengths and their corresponding optimum non-dimensional times are determined. An existing finite-difference model, developed by the authors of this paper, for simulation of desiccant wheel performance is extended to account for the separation of the process air stream at the exit of rotary dehumidifier and later mixing of purge air stream and outside air to form the regeneration air stream. The performance of desiccant wheel with heated “effective purge angle” is evaluated and compared with performance of the same wheel without purge angle at all. It is found, for all cases considered in this study, that having heated “effective purge angle” has overall positive effect on the performance of the rotary dehumidifier. © 2007 Elsevier Ltd. All rights reserved. Keywords: Desiccant wheel; Dehumidification; Heated purge angle 1. Introduction Rotary dehumidifiers are used to dry moist ventilation ambient air in many air conditioning systems. In numerous applications, rotary dehumidifiers are used when the latent load is large in comparison with the sensible load and when cost of energy to regenerate desiccant wheel is low as compared to the cost of energy to dehumidify the air by chilling it below its dew point in a vapor compression air conditioning system. The dehumidification of outside air within rotary dehumidifier takes place as result of a difference between the water vapor pressure at the desiccant surface and surrounding air. When the water vapor pressure at the desiccant surface is lower than that of the air, the desiccant adsorbs moisture. When the surface water vapor pressure is higher than that of the surrounding air, the desiccant releases the moisture, which is termed desorption. International Communications in Heat and Mass Transfer 34 (2007) 785 – 795 www.elsevier.com/locate/ichmt ☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: wworek@uic.edu (W.M. Worek). 0735-1933/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.icheatmasstransfer.2007.03.011