CFD simulation of multiphase flow in evaporators

Inside evaporators of air-conditioning systems, uneven mass flow distribution of refrigerant leads to a loss of efficiency and finally a reduction of comfort in passenger compartments. The distribution is influenced by the flow field and two-phase distribution (flow pattern) in various elements, comprising developing and developed two-phase flow in straight and angled ducts, headers, flat tubes and the connection between these.
This talk presents on-going efforts to predict this type of flow with CFD.
In a first step, extensive experimental investigations on generic geometries are done using advanced measurement techniques. This data are then used to develop and validate numerical models capable of reproducing the relevant physics.
Important two-phase phenomena are: multiple regimes (continuous-disperse + separated flow), wall films, stripping/impingement, particle size distribution, two-phase heat transfer, boiling/condensation. In a final step, the developed modeling strategy is applied to real evaporators.
In comparing simulation results to experimental data, we find both good agreement as well as discrepancies which confirm that there is still more work on developing appropriate models to do.