R600a, isobutane, transient simulation, cooling cycle simulation, numerical simulation
Generally, domestic refrigerators and freezers are running in non-continuous operation mode most of the time, which is a necessity to match cooling capacity to thermal loads. In currently available domestic appliances this matching is realized either by on/off or variable frequency control of the hermetic compressor, leading to a repetitive and transient change of the system state. On the other hand, if the runtimes of the compressor are longer because cooling capacity demand is high (e.g. pull down cycles, initial operation), steady state operating conditions might be reached. The cycling transients cause losses in system efficiency thus they should be reduced or avoided. To understand the complex transient physical processes and to optimize the cooling system efficiency, it turned out that the use of numerical methods is a promising approach. For this reason, a 1D heat exchanger model, which has been successfully implemented in a domestic cooling cycle simulation tool, is presented in this work. The heat exchanger model is a further development of the model being presented in Berger et al. (2012). The same mathematical framework is used for modelling the evaporator and condenser. In order to compute the void fraction, the pressure drop and the heat transfer special empirical models for evaporation and condensation, which are proposed in literature, have been implemented. Finally, the numerical predictions are compared to experimental data gained from a purpose-built test rig.