Numerical simulation of multiphase heat transfer and evaporation of liquid films in rectangular heat exchanger channels

Multiphase heat transfer offers a substantial improvement compared to conventional single-phase by leveraging the latent heat of the liquid–gas phase change process. Therefore, adding liquid water at the air side surface of heat exchangers can provide significant improvements with regard to the heat transfer effectiveness by wetting and forming a thin liquid film. The present study investigates multiphase heat transfer phenomena considering a single passage of a plate heat exchanger. A simplified 2D channel geometry is considered with a stationary liquid film initialized on a heated wall at the bottom of the channel, where a constant temperature is specified. The governing equations are solved using an Eulerian framework with the volume-of-fluid method to resolve the liquid–gas interface. To verify the method, a closed channel with evaporation is simulated and compared with an analytical solution of Fick’s law. Simulations with air flow are conducted to study the influence of parameters such as wall temperature, inlet air temperature, and relative humidity as well as air flow rates onto the local heat and mass transfer behavior. The range of values chosen for the study are particularly relevant for, but not exclusive to, thermal management systems of fuel cells in the context of aviation applications. Based on the results the global heat transfer and latent heat transfer as a function of the input parameters are discussed and compared with correlations from literature.