Numerical Analysis of Condensation and Frost in Rotary Heat Exchangers

Abstract

In this thesis, a three-dimensional mathematical model is developed and implemented using COMSOL Multiphysics - a platform for physics-based modeling and simulation. The numerical model solves a conjugated heat transfer problem for the air stream and heat exchange media with only wheel data and inlet flow properties needed as input. The model was validated using previously established effectiveness correlations for a comparable regenerative heat exchanger but needs further validation. Proper scaling analysis was performed to establish the simultaneously developing Nusselt numbers in the entrance region from incomplete tabular data sources, and a new local peripheral Nusselt number function was defined from the flow geometry to take into account the variable local heat flux around the periphery. Results indicate that the local properties at any cross-section may differ significantly from the bulk properties, suggesting that condensation may be present locally in pockets of near-stagnant regions for a considerable length of the wheel.