Experimental Investigation of Heat Transfer to Tightly Packed Cylinder Arrays

With the increased emphasis on the development of hybrid electric aircraft and other electric driven vehicles, the thermal demand on batteries is increasing. Unique to the aviation sector is the combined need of high battery thermal loads and a light-weight thermal management system. A proposed configuration is an array of batteries directly cooled with a dielectric coolant. The knowledge of heat transfer characteristics of battery cooling is becoming an ever pressing issue due to the need to optimize volume and mass in a safe manner. Tighter spacings between batteries provide higher pack densities, however, at the cost of increased cooling power and decreased cooling efficiency. The tightly packed array of typical battery packs poses a unique challenge to effective cooling during demanding phases of aircraft flight and relies on a geometric configuration not characterized in the literature. Greater knowledge of these battery configurations can reduce overall cooling component weight and increase overall vehicle efficiency. An optimum battery spacing can minimize power and inert mass dedicated to coolant pumping while maximizing overall battery system efficiency. A tightly packed (S/D = 1.25) conducting pin array with internal volumetric heat generation is considered and the heat transfer characteristics of these pins are analyzed. Average pin surface Nusselt numbers are determined at various Reynolds numbers and show strong agreement with previous literature on short pin arrays. Data gathered show high dependence on the flow structures developed on pin-wall interfaces. A new correlation is presented for the average array Nusselt number for tightly-packed short pins.