Modeling and control of single and multiple evaporator vapor compression cycles for electronics cooling

This paper presents a dynamic model and feedback control strategies for vapor compression cycles (VCC) in electronics cooling applications. A notable difference between traditional VCC and VCC for electronics cooling is that two-phase flow is required at the evaporator outlet in order to avoid burnout. Therefore, the control objective is to avoid critical heat flux during transient heating conditions. An emphasis is placed on the heated accumulator, which is a necessary component to guarantee superheated flow in the compressor suction-line. Addition of heat in the accumulator provides control actuation that may be used to avoid the critical heat flux via the effect on system pressure. In contrast to previous work, we present more detailed evaporator and accumulator models, implement the heated accumulator as a control actuator, and consider both single and multiple evaporator systems. For single evaporator VCC, we use frequency-domain techniques to design a dual-input, proportional-integral controller using accumulator heat and compressor speed. Both simulation and experiment show this design to be superior to strategies that do not actuate accumulator heat. We then use similar design strategies to develop a controller for the much more challenging two-evaporator VCC.