Dynamic modeling of refrigeration cycle for electronics cooling

In this paper a refrigeration cycle consisting of multiple evaporators, liquid accumulator, compressor, condenser and expansion valves is analyzed. In the cycle the evaporators and condenser are treated as dynamic components while the liquid accumulator, compressor and the expansion valve are consider static components. For the dynamic components, equations for conservation of mass, energy and momentum are used to characterize the comprehensive transient behaviors. One of the differences with previous models is the use of the momentum equation which is typically neglected in traditional vapor compression refrigeration systems, but it is important in electronics cooling where microchannels are commonly used and a significant pressure drop is observed in the evaporator. This model is expected to have higher accuracy than previously used lumped parameter approximation while maintaining its simplicity to be useful for control purposes. The compressor and expansion valves are modeled using empirical relations, the accumulator is used to guarantee proper operation of the compressor. Local system stability is analyzed using a linearized model at some operating condition and an experimental testbed is developed to validate the model. The test bed consists of three electrically controlled heaters immersed in the refrigeration loop which act as the evaporators. A heated tank as an accumulator for operation at wide range of operating conditions, including low quality at the evaporator outlets. A reciprocating compressor with variable frequency drive to operate at various mass flow rates. The condenser is a flat plate heat exchanger and finally three electronically controlled expansion valves for evaporators.