From lumped to full scale modeling approach: on the use of computational fluid dynamics to model heat and mass transfer processes in water cooled evaporator.

This paper reports on an extensive numerical investigation of a water cooled evaporator following a full scale modeling approach. A 3D CFD model of a water cooled evaporator was constructed to simulate the hydrodynamics and thermal fields of humid air and refrigerant (water) flow streams. The problem involves a conjugate heat transfer turbulent multi-phase flow situation where condensation on the outer surface of the evaporator coil was modeled following Fick’s law. The pressure and velocity coupling was resolved by the segregated SIMPLE-Consistent algorithm. Solutions were generated via a hybrid collocated unstructured finite volume method for wet and dry coil assumptions. Complex turbulent flow fields were obtained at different regions of the evaporator coil. Numerical predictions were then compared with available experimental data of similar coil construction for validation purposes. On the other hand, a lumped analytical model for dry heat transfer phenomena was developed and simulated for dry coil assumptions. The purpose of the lumped model is to show its limited predictive capabilities in capturing the detailed physics of the problem in contrast to the full CFD approach. Results have shown the need to tune the lumped model to fit with the more realistic situation modeled by the full scale approach. This paper concludes the fortuitous need to shift towards full scale modeling approaches in simulating industrial applications where lumped models, if not properly tuned, lack the ability to capture the physics of the defined problem.