Study of heat transfer with surface treatment in pre-coolers for aeroengine applications

Abstract

The effect of surface roughness on convective heat transfer and pressure drop is assessed for a simplified pre-cooler system for application in high-speed airbreathing engines. The pre-cooler system comprises of four circular cylinders in cross-flow inside a square duct. The cylindrical wires of 1 mm diameter were textured using an economical method of surface treatment, via sand-blasting with 100 µm (diameter) particles. Experiments were conducted at Reynolds numbers ranging from 600 to 8000. The Nusselt number was observed to decrease for the rough wires, indicating decreased convective heat transfer rates. Moreover, roughness was found to have no appreciable effect on pressure drop for these conditions. This is attributed to a fully developed turbulent duct flow upstream of the wires, which was confirmed by observing the Nusselt-Reynolds number correlation for treated and untreated cases. Surface roughness strategy in pre-coolers for an ascent trajectory of a high-speed airbreathing engine is also discussed. Keywords: Convective heat transfer, Surface roughness, Heat exchangers, High-speed airbreathing engines