Fin analysis, Analytical model, Dehumidification, Conduction, CFD
Numerical microchannel heat exchanger (MCHX) models are favored in recent research and development process due to their cost effectiveness as opposed to prototype development and testing. One of the challenges in using MCHX in the stationary heating, ventilating, air-conditioning and refrigeration (HVAC&R) applications is the evaporator design. A literature survey suggests that there lacks a unified air-to-surface heat transfer modeling approach for MCHX, especially under dehumidifying condition with tube-to-tube heat conduction. In this research, we present a fin heat transfer model under dry, wet and partial wet conditions for MCHX applications. Typically, there are two boundary conditions for the fins in MCHX. The adiabatic fin tip boundary condition is applied to the extended fins on top and bottom of the heat exchanger. The proposed model also accounts for tube-to-tube conduction wherein the surface temperatures of the two tubes bounding the fin are prescribed. The modeling approach is capable of locating the boundary between dry and wet surface if partial-wet condition appears. A finite volume approach is adopted in the proposed model where the fin is separated into segments in the air-flow direction. The model is verified against simulation results obtained using a commercially available Computational Fluid Dynamics (CFD) package. The changing air-side heat transfer coefficient along the air flow direction is calculated from CFD. These coefficients are then plugged into each segment in the fin analysis model. The prediction of two-dimensional temperature field along the fin surface using the proposed finite volume approach agrees very well with the CFD predictions. It is also expected that using the proposed wet-fin and partially-wet fin model, the latent load prediction in evaporators will be improved. The proposed model can serve as the foundation for further air-to-refrigerant heat transfer modeling in MCHX design and simulation tools.