Confined Jet Impingement With Boiling on a Variety of Enhanced Surfaces

Abstract

Confined jet impingement with boiling offers unique and attractive performance characteristics for thermal management of high heat flux components. Twophase operation of jet impingement has been shown to provide high heat transfer coefficients while maintaining a uniform temperature over a target surface. This can be achieved with minimal increases in pumping power compared to singlephase operation. To investigate further enhancements in heat transfer coefficients and increases in the maximum heat flux supported by twophase jet impingement, an experimental study of surface enhancements is performed using the dielectric working fluid HFE7100. The performance of a single, 3.75 mmdiameter jet orifice is compared across four distinct copper target surfaces of varying enhancement scales: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin fins), and a hybrid surface on which the pin fins are coated with the microporous layer. The heat transfer performance of each surface is compared in singleand twophase operation at three volumetric flow rates (450 ml/min, 900 ml/min, and 1800 ml/min); areaaveraged heat transfer parameters and pressure drop are reported. The mechanisms resulting in enhanced performance for the different surfaces are identified, with a special focus on the coated pin fins. This hybrid surface showed the best enhancement of all those tested, and resulted in an extension of critical heat flux (CHF) by a maximum of 2.42 times compared to the smooth flat surface at the lowest flow rate investigated; no increase in the overall pressure drop was measured.