A Comparative Study of Cooling of High Power Density Electronics Using Sprays and Microjets

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Abstract
Direct cooling by means of jets and sprays has been considered as a solution to the problem of cooling of high power density electronic devices. Although both methods are capable of very high heat removal rates no criterion exists that helps one decide as to which one is preferable, when designing a cooling system for electronic applications. In this work, the results of an investigation of the performances of sprays and arrays of micro jets are reported. Experiments have been conducted using HAGO nozzles and orifice plates to create droplet sprays and arrays of micro jets, respectively. The liquid jets had diameters ranging from 69 to 250 μm and the pitches between the jets were 1, 2, and 3 mm. The test fluid was deionized water and the jet Reynolds number ranged between 43 and 3813. A comparison of heat transfer and pressure drop results obtained employing both sprays and jets has been carried out. The microjet arrays proved superior to the sprays since they required less pumping power per unit of power removed. A cooling module employing impinging jets was tested. Such a module would require three primary components: an orifice plate for forming jets or a nozzle to form the spray; a container to hold the nozzle, the heat source and the cooling liquid, which also serves as a heat exchanger to the ambient; and a pump which recirculates the coolant. A fan could be used to improve the heat transfer to the ambient, and it would allow the use of a smaller container. An impinging jets cooling module has been designed and tested. Heat fluxes as high as 300 W/cm2 at 80°C surface temperature could be removed using a system which includes a 4×6 array of microjets of water of 140 μm diameter impinging on a diode 5.0×8.7 mm2.