An experimental characterization of cross-flow cooling of air via an in-line elliptical tube array

Flows of hot air at 41.5 ± 1.5 °C across an array of elliptical tubes carrying cold water were experimentally investigated in the range of waterside and airside Reynolds numbers of 1.0×103<Rew<3.7×103 and 1.0×104<Rea<3.3×104 respectively. The waterside Reynolds number was based on the inner hydraulic diameter and that of the airside, on the major axis length of the tube. Cold water at 6.5 ± 1.0 °C entered and jig jagged through a single passage tube array, and exited at a temperature dictated by the total heat transferred. The array consisting of 18 elliptical tubes each 30 cm long, with minor to major outside axis ratio of 0.30, and equally spaced by 0.61 cm gap, was oriented at zero angle of attack in a 30 cm by 30 cm test section with the major axis parallel to the air flow. The results showed that the heat transfer rate (q) increased with the increase of both water and air flows. The pressure coefficient (Cp), across a single tube in the array was found to remain at approximately 0.16 for Rea>2×104. Both q and Nusselt number (Nu) were found to vary in power law relationship with Re. The Nu–Re correlation obtained from the idealized test bench was found to be in the form Nua=0.26Rea0.66.