Transient 1D heat exchanger model for the simulation of domestic cooling cycles working with R600a

摘要

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. In case of longer compressor runtimes when 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, the use of numerical methods has turned out to be 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 etal. (2012). The same mathematical framework is used for modeling the evaporator and condenser. To compute the void fraction, pressure drop and heat transfer in the case of evaporation and condensation special empirical models, which are proposed in the literature, have been implemented. Finally, the numerical predictions are compared to experimental data gained from a purpose-built test rig.