Heat and Mass Transfer Study of a High-Pressure Membrane Dehumidifier Under Nonisothermal and Humid Sweep Psychrometric Conditions

Abstract

High-pressure membrane dehumidification is of interest for aircraft environmental control system (ECS) applications. Typically, membrane dehumidifier (MD) modules are characterized by manufacturers over a range of mass flow rates, temperatures, and pressures at saturation conditions. However, to evaluate the suitability of high-pressure membrane dehumidification for aircraft applications, the performance must be characterized over the broader range of psychrometric conditions that could be encountered. Moreover, the practical integration of an MD into an environmental control system necessitates reconsideration of the traditional product sweep approach, where some of the dry air produced is removed and supplied to the other side of the membrane to enhance mass transfer. In an environmental control system, using product sweep would require excessive bleed air from the engine and cause unbalanced flow in the turbomachinery. To avoid this, alternate sources of sweep must be considered, and their effects on dehumidification must be evaluated. This work conducts an experimental investigation of an MD module using product sweep under a range of psychrometric conditions, then compares product and humid sweep modes to understand the effects of sweep conditions on dehumidification performance. Concurrently, a numerical model of an MD is implemented and validated—first against the module specification sheet, then against the empirical results that represent moderate altitude aircraft conditions. Ultimately, the feasibility of a hot and humid sweep source to maintain sufficient dehumidification performance under realistic altitude conditions is demonstrated.