(159e) Membrane Processes Utilizing Coupled Heat and Moisture Transfer

This presentation will review fundamentals and recent research on thermally-driven membrane processes, which involve coupled heat and mass transfer. These processes often include a vapor/liquid phase change, where this fluid is removed from (or added to) a liquid or gas stream. Understanding the coupled heat and mass transfer is important for modeling, designing, and/or selecting devices and systems for thermally driven processes. Applications that use coupled heat and mass transfer include traditional separation processes, like liquid purification (e.g., membrane/osmotic distillation, pervaporation), but also processes relevant to the heating, ventilation, and air conditioning industry, such as dehumidification of air streams (e.g., liquid-desiccant air drying), and processes where heat is the desired output (e.g., absorption heat pumps).

Membrane and osmotic distillation use a vapor-pressure differences to drive a vapor (often water) from one liquid to another. Pervaporation is a similar process, but relies on a vapor-pressure gradient between a liquid and gas stream, often set up by reducing the pressure of the gas.

Liquid desiccant air drying has received considerable attention in recent years as an efficient method for dehumidifying air. It relies on a liquid-to-air membrane contactor, where the liquid desiccant is a low-vapor-pressure solution that absorbs moisture from the air. Heating the desiccant in a liquid-to-air membrane contactor drives vapor out of the desiccant, regenerating it so it can be used for drying again.

Absorption heat pumps traditionally use a closed system with ammonia-water or LiBr-water working fluids. These closed systems operate under pressures either much higher or lower than ambient. Alternative systems using membranes allow for semi-open or fully-open heat pump processes, which can be advantageous in certain cases.

The presentation will review these processes, their key modeling aspects, recent research, and future research needs.