Dynamic modelling and experimental validation of the cyclic operation and loaded pull-down of a conventional domestic refrigerator

Abstract

A dynamic model of a top mounted, conventional, serial system domestic refrigerator is created in this thesis using the TIL library in Dymola. The compressor is modelled semi-empirically using loss parameters obtained by model fitting simulation results and data from calorimeter experiments, while the capillary tube is modelled by incorporating both friction and momentum pressure drop. Heat exchangers (condenser and evaporator) are modelled as tubes divided into finite volume cells. The capillary tube-suction line heat exchanger is treated by connecting part of the capillary tube to the suction line via a heat resistor. As for the cabinet, the walls, air and items present inside the cabinet are connected to each other in a network, such that heat gained by the surroundings is transmitted to each component. All the components are then arranged in a cycle, and several simulations are carried out. The cyclic operation is validated at 32 °C and 25 °C using a fixed speed compressor. To test the sensitivity of the model to a different compressor and different compressor speeds, simulations are carried out at 32 °C using a different compressor operated at three different speeds. As the second part of this thesis, the model is modified to include the effect of placing a warm load of water in the refrigerator and simulating the subsequent pull down. This model is also validated using an experiment in which 20 L of water at 27 °C is placed inside the Fresh Food compartment. Results show that the power consumption value is captured well, with the average power consumption deviating less than 10 % for all tests except for the loaded pull-down case. The energy consumption yielded even better results, with deviation lying within ±5% for all tests. For the loaded pull down, the deviation in water temperature was a maximum of 1.2 °C for the whole cooling period.