Numerical simulation of a refrigeration cycle for scaling towards small geometries

An approach for modelling and scaling refrigeration cycles aided by CFD software is presented. The advantages are the high resolution of the results especially for geometrical details. Furthermore parallel processing of flow mechanics and thermodynamics is done and an easy evaluation of scaling the model as well as the investigation of transport behaviour of several refrigerants are possible. The aim was setting up a model to calculate the three-dimensional refrigerant behaviour in a closed cycle tube with condenser, dryer, expansion device and evaporator which delivers all physical properties of interest like pressure, velocity, temperature, enthalpy and entropy (National Institute of Standards and Technology. Manual and Property Models for the Refprop-Database. Available from: <www.nist.gov>). Up to now, however, CFD software is not capable to model all physical features needed to create a global simulation of the refrigeration cycle simultaneously (User Manual for Fluent and Gambit. Fluent Inc. Available from: <www.fluent.com>). Especially the phase change of the refrigerant is not fully managed by CFD. Methods to tackle this problem are proposed. The result is a hybrid procedure implying CFD methods supported by analytical suppositions. Exemplary two-dimensional numerical simulations for four sample geometries that differ from each other by their overall geometric scale had been done.