Influence of Altitude on the Behavior of Solid Desiccant Dehumidification System

Abstract

A study is described regarding the influence of the altitude, from 0 to 4,217 m (corresponding to atmospheric pressure from 101,325 to 60,000 Pa), on the behavior of a simple solid desiccant system used for air dehumidification purposes. The heating coil and the desiccant wheel are the main components investigated. The effectiveness method is used to evaluate the global behavior of the heating coil, and a detailed numerical model developed by the authors is used to predict the behavior of the desiccant wheel. Fixed-mass and fixed-volume airflow rate operations are considered in the comparison of the results at different altitudes. Two modes of specifying the inlet states of both airflows in the system are taken into account: (1) temperature and water vapor content and (2) temperature and relative humidity. As the atmospheric pressure decreases, the heat and mass transfer rates increase or decrease, depending on the mode of fixing the airflow rates and the inlet states of both airflows. Correction factors are determined for fixed-volume and fixed-mass airflow rate operations. The results show that these correction factors are also affected by the rotation speed of the desiccant wheel. Sea level data can be adopted for sizing the system without the need of correction when fixed-mass airflow rate and specifying the inlet states by the temperature and water vapor content.