Heat Transfer and Flow Analysis of a Novel Low Flow Piezoelectric Air Pump

摘要

With the propagation of ever faster and more powerful electronics, the need for active, low power cooling is becoming increasingly apparent. In particular, applications which have traditionally relied only on natural convection will soon require an active cooling solution due to continually rising heat loads. A promising solution lies in utilizing piezoelectric materials via fans or pumps. Examples of such devices include synthetic jets and piezoelectric pumps, both of which rely on an oscillating diaphragm to induce flow. The device investigated in this thesis is able to generate flow rates up to 1 L/min and overcome pressures of over 2 kPa. The focus is to experimentally characterize the cooling potential of a piezoelectric-based air pump oriented normal to a heated surface, an environment similar to jet impingement. Experimental characterizations were made through the use of a thin film heater which provided a constant heat flux while an infrared camera was used to capture the resulting temperature field of the heated surface. Full-field data of the convection coefficient was analyzed as a function of vibration amplitude of the piezoelectric diaphragm and distance from the nozzle to the heated target. The maximum heat transfer coefficient was found to always be at the stagnation point regardless of vibration amplitude or distance to the target. Correlations have been developed which account for both variables considered and can be used to predict the performance of future designs which rely on the same physical characteristics. Further, because of the piezoelectric blower’s ability to overcome large pressure drops, a theoretical analysis was conducted to assess the viability of using them in oscillating flow cooling. It was found to be a reasonable driver of reciprocating flow that can keep fluid temperature change low. Additionally it was found that reciprocating flow allows for a more uniform temperature distribution over a heated surface.