Transient Simulation of Two-Phase On-chip Liquid Pump Cycle for Processor's Cooling
Transient modeling and regulation of a two-phase on-chip liquid pump cooling cycle is studied. The purpose is to cool down multiple micro-processors in parallel and a set of memories, DC/DC converters in series. The cycle will be incorporated in a blade/drawer of a rack as shown in Figure 1. The cooling system is composed of multiple on-chip micro-evaporators, a condenser, a liquid accumulator, a pump and all piping joining components. In order to take advantage of enhanced heat transfer and more uniform chip temperature, two-phase refrigerant R134a is used as working fluid. The dynamic of the system is relevant as the heat load of microprocessors is changing continuously with time. Transient simulations allow firstly verifying that the critical heat flux (CHF) is not reached during heat loads disturbances. Secondly, for energy recovery purpose, it allows tracking with time the available heat at the condenser. The thermal accumulation is thus taken into account in the energy balance. However, since the pressure equilibrium is a much faster phenomenon than thermal inertia, the momentum accumulation is neglected in the momentum balance. Transient two-dimensional conduction in the body of the micro-evaporators is also considered. Regulators, the roles of which are to control the mixing outlet vapor quality and the pressure drops equilibrium in the parallel branches, are also implemented in the code. Preliminary simulations with four microprocessors in parallel considering different levels of heat load (36, 30, 25 and 10 W/cm2) show the robustness of the predictive-corrective solver used. In 14 minutes of computing time, 46 seconds of real time were simulated. For a desired mixing vapor quality of 30%, at a pressure of 16 bars (saturation temperature of 58°C) and a subcooling of 2K, the mass flow rates in the micro-evaporators were respectively 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 section was 0.6 kPa.
Record created on 2013-01-14, modified on 2016-08-09