Microprocessor cooling based on an intermittent multijet spray system

The power dissipation of electronic devices is reaching the limit of the cooling capacity of current heatsinks, demanding new developments in cooling technologies. Moreover, the dissipated power varies with time, reducing the efficiency of the cooling system, unless an Intelligent Thermal Management is applied. In this paper, a control strategy is devised based on the Intermittent Spray Cooling concept. A multijet atomization defined by the simultaneous impact of two jets, together with an electromechanical valve, produce an intermittent spray made of small and slow droplets, which are likely to deposit on the surface for cooling purposes. The multijet spray cooling is characterized in the transition region between non-boiling and boiling regimes. The experiments consider a maximum imposed heat dissipation of 100 W in a 6.25 cm2 copper plate. While the Duty Cycle (the percentage of liquid injection within the cycle time) is known as the key parameter for controlling heat transfer in Intermittent Spray Cooling, optimal cooling conditions are obtained for high injection frequencies, up to 20 Hz in the present work. Also, the boiling curves presented evidence how an Intermittent Spray Cooling is able to benefit from phase-change in the non-boiling regime enhancing the evaporation in the non-injection time between consecutive cycles. The transient behaviour of the cooling process is studied through the assessment of the response time to an overshoot situation. Finally, the Intermittent Spray Cooling control strategy devised is applied to a typical processor power profile with constant and variable injection conditions, for a maximum and controllable project temperature. The results presented demonstrate how the control of the cooling process through the spray intermittency leads to an increase of the efficiency and liquid savings, demonstrating the feasibility and advantage of implementing Intermittent Spray Cooling for developing Intelligent Thermal Management.