DYNAMIC MODELING OF A TWO-PHASE ON-CHIP COOLING SYSTEM APPLIED ON PARALLEL HIGH PERFORMANCE MICROPROCESSORS

Transient modeling and control of two-phase on-chip microevaporator cold plates of a liquid pump cooling cycle is studied. The purpose is to cool down multiple micro-processors in parallel and their auxiliary electronics (memories, DC/DC converters, etc.) in series. The cooling system is composed of multiple on-chip microevaporators in parallel, a condenser, a liquid accumulator, a liquid pump and all piping joining these components. In order to achieve high heat transfer and chip temperature uniformity, two-phase flow of HFC134a is considered for the coolant. The dynamics of the system are relevant aspects to be studied since the heat dissipated by the microprocessors is changing continuously. Thus, a new simulation code has been developed here to emulate the operation during transients. Such transient simulations allow us to verify whether critical heat flux (CHF) conditions are reached during heat load disturbances and to track the available heat at the condenser for energy recovery purposes. Presently, a case study with four microprocessors cooled in parallel flow is simulated considering different levels of uniform heat flux (36, 30, 25 and 10 Wcm(-2)), which showed the robustness of the predictive-corrective solver used. For a desired exit mixing vapor quality of 30%, at an inlet pressure and subcooling of respectively 16 bar (saturation temperature of 57.9 degrees C) and 2 K, the resulting distribution of the mass flow rates in the microevaporators were 3.6, 4.0, 4.5 and 7.4 kg/h (largest flow rate for lowest heat load) and the total pressure drop over the entire section was 0.6 kPa. The CHF and maximum chip temperature remained below of the critical limits. Preliminary comparisons with experimental tests showed errors in the predictions of mean chip temperature and mixing vapor quality to be within +/- 10%.