Critical Impact of Fin Thermal Conductivity in the Modeling of Evaporator Under Frost Conditions

Refrigeration systems such as heat pumps may be subject to frost formation. This phenomenon plays a major role in the heat pump overall performance drop due to the presence of an additional thermal resistance and an increase of the airside pressure drop. Deep experimental investigations show a typical pattern in frost distribution through the heat exchanger, in various operating conditions. A tube-by-tube simulation model is proposed. The dynamic model accounts for two-phase and overheated zones on the refrigerant side. On the air side, the frost may evolve independently on each tube and their corresponding fins, giving a non-uniform frost layer throughout the device. However, in a first time, important discrepancies are noticed between the distribution of frost predicted by the model and the obtained experimental data. The aforementioned model is then improved by taking the fin thermal conductivity into account. Unlike the first version of the model, the results from the new one match more closely with the experimental observations. This model is successfully validated by means of the empirical data. Such model can pave the way toward future designs of evaporator that requires accurate frost accretion prediction.