Charge Management for Large Transient Loads in a Multi-Evaporator Vapor Compression System with Recuperator

Two-phase cooling of electronics using vapor compression systems (VCS) is a promising approach for high heat flux removal. A challenge for multi-evaporator VCS is charge management during highly transient or peak/off-peak loads. We present a VCS architecture for direct cooling of multiple, high transient heat loads. This system utilizes a secondary-evaporator (recuperator) with an electronic bypass valve and a suction-line accumulator to enable evaporator overfeed and active charge management. An existing lumped-parameter, low-order nonlinear model is augmented to include the recuperator and bypass control valve. The cycle performance and efficiency is improved with the inclusion of the recuperator, but is susceptible to instability. A proportional-integral (PI) bypass valve control is tuned for evaporator pressure tracking, stabilizing the cycle. The improved circulating charge-management capability of the VCS with recuperator is demonstrated with multi-evaporator experiments, and the improvement in coefficient of performance (COP) over the accumulator-heated cycle is calculated.