This study presents a control strategy for electronic cooling systems incorporating microchannel evaporators that experience unanticipated variations in heat loads. The overall objective of this study is to maintain a fixed evaporator temperature, enable high system efficiency, and avoid critical heat flux (CHF) despite the presence of transient heat loads. We developed a moving boundary model to account for the presence of single-phase and two-phase flow in the evaporator and account for their respective pressure drops and heat transfer. We use this model to identify optimum operating conditions for different evaporator heat loads that correspond to high COP and avoid CHF. Since the changes in the heat loads are unanticipated, we design a disturbance observer are designed based on the optimum operating conditions for estimating the unanticipated evaporator heat load, which could serve as the feedforward control signal for system inputs (pump-speed and valve settings) while the feedback control could further adjust the input values to achieve desired evaporator wall temperature. Results show that system with controller and disturbance observer can ensure the evaporator wall temperature and high heat performance under large variation of heat loads. Furthermore, disturbance observer-based control is applied to cooling system with two-evaporators. With the estimated values of evaporator heat loads, the pump-speed and valve settings can be adjusted properly to ensure the safe operation and reduce the wall temperatures difference.
Applied Thermal Engineering, Vol. 183, Part 2, Jan, 2021.