Frost prediction based on a 3D CFD model of heat and mass transfer in a counter-cross-flow parallel-plate liquid-to-air membrane energy exchanger

The frosting is a critical phenomenon in building systems because it decreases the performance of exchangers and damages them. In this article, heat and mass transfer in a specified liquid-to-air membrane energy exchanger (LAMEE) and their effects on condensation and frost formation are simulated numerically using the 3D computational fluid dynamics (CFD) technique. The CFD model has been validated with experimental results for different design parameters, and the agreement is within ±2%. The developed CFD model provides the distribution of temperature and humidity ratio and MgCl₂ concentration along the LAMEE. In the present study, effects of exchanger structure on producing viscosity and heat and mass transfer are studied. The selected LAMEE is a counter cross structure, therefore vortices appear in the inlet and outlet solution channel, and their influence can be seen on heat transfer in these parts. In addition, the diffusion of heat and mass transfer are studied on distributions of temperature and humidity ratio. Results show that the permeable membrane and moisture transfer make more regular temperature distribution along airflow direction in energy exchangers. This study provides an extended vision of heat and mass transfer. A 3-dimensional CFD model is developed to predict frost formation based on obtained temperature and humidity ratio. The CFD model is validated with an experimental study by calculating the frost limit. The developed model distinguishes condensed and frosted areas, and a new parameter is defined for this purpose namely as the frosted humidity ratio. Results show that frost and condensation distributions depend significantly on temperature and humidity ratio distributions. Adjusting temperature and humidity ratio to avoid air vapor to reach to saturation conditions is the better way to combat frosting.