Frosting on porous membranes in energy exchangers.

Abstract

A liquid-to-air membrane energy exchanger (LAMEE) is a device that uses a semi-permeable membrane to transfer heat and moisture between an air stream and a liquid stream. In cold climates, they can be used to dehumidify an air stream and reduce or even prevent frost formation inside the exchanger. Understanding the mechanisms of frosting and the frost limits on membranes is essential for advancing the applications of LAMEEs in cold conditions. This paper combines a review of previously published research on the growth of frost on a membrane surface, compared to an impermeable surface, along with new experimental results that extend the applications of the frost research to cover more air temperature and relative humidity (RH) conditions. Frost limit maps are created for various operating conditions using an analytical model and verified with experimental results. These maps indicate the liquid temperature and air RH values that will result in frost conditions on the membrane surface. It was found that when the air temperature is 23°C, the liquid temperature could be lowered by 2°C-3°C at a constant RH level without frost appearing on the surface as compared to an impermeable surface, and when the air temperature is 0°C, the liquid temperature could be lowered by approximately 5°C compared to the impermeable surface. The results show that a porous membrane has great potential to create frost-free energy exchangers.This article is part of the theme issue 'Heat and mass transfer in frost and ice'.