Moving boundary model for dynamic control of multi-evaporator cooling systems facing variable heat loads

Abstract

Two-phase systems comprising of a single pump or compressor, a condenser, and multiple microchannel evaporators can provide the unique advantage of handling multiple heat sources while being compact and lightweight. Such systems also present challenges with regards to handling asynchronous transient heat loads, maintaining fixed evaporator temperatures, enabling high system efficiencies, and avoiding the critical heat flux. The overall objective of this study is to dynamically control the performance of a two-phase system comprising of two evaporators experiencing transient heat loads. This study simulates a pumped liquid cycle comprising of two microchannel evaporators using the moving boundary model, which considers phase-change heat transfer and pressure drop occurring in the evaporators. The moving boundary model predicts the overall performance corresponding to different system settings and evaporator heat loads to determine the optimum operating conditions. By knowing these conditions in advance, the study presents a strategy combining feedforward and feedback control to ensure system operation close to the optimum operating condition. The approach discussed in this study is generally applicable and allows maintaining the desired evaporator temperatures and high system efficiency in the presence of transient heat loads.