Dynamic control of microchannel cooling system with unanticipated evaporator heat loads

Abstract

This study presents a control strategy for electronic cooling systems incorporating microchannel evaporators that experience unanticipated and significant heat load variations. It complements prior studies that focus primarily on the steady operation of two-phase systems facing static heat loads. This study's overall objective is to maintain a fixed evaporator temperature, enable high system efficiency, and avoid critical heat flux (CHF) despite the presence of transient and unexpected variations in heat loads. In this regard, 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 flow and heat transfer characteristics. We use this model to identify optimum operating conditions for different evaporator heat loads that avoid CHF and correspond to a high COP. Since the changes in the heat loads are unanticipated, we design a disturbance observer based on the optimum operating conditions to estimate the unanticipated evaporator heat loads, which could serve as the feedforward control signal for system inputs such as pump-speed and valve settings. This study demonstrates how the system can maintain a constant evaporator temperature when it experiences a three-fold increase in the heat load. We also extend this study to two evaporators operating in parallel and experiencing unanticipated and asynchronous variations in the evaporator heat load. Our results show that the system with a disturbance observer and controller can maintain a fixed evaporator temperature even under significant heat load variations.