Thermo-Fluid Effects Associated with Modelling Subscale Automotive Heat Exchangers

摘要

Automotive components are tested extensively in wind tunnels by automotive manufacturersand race teams. This is usually achieved using an accurate scale modelrepresentation of the component within the wind tunnel.Automotive heat exchangers, however, are comprised of numerous intricate geometriesand are therefore impractical to produce at model scale. Instead they aresimply modelled as pressure drops, achieved using a thin mesh or honeycomb ofknown porosity. Most commercial computational fluid dynamics solvers ignore thegeometry of the heat exchanger and instead model it as a discontinuity with a knownpressure drop and heat transfer.The pressure drop across an automotive heat exchanger, however, was found tovary with both the coolant temperature and the angle of inclination of the heatexchanger. This thesis initially presents a relationship between the pressure dropcoefficient and the inclination angle for varying media porosities. Mathematicalrelationships for inclination angles of 0°, 15°, 30° and 45°. were derived relatingthis pressure drop coefficient to the porosity of the media. Weighted least squaresis proposed over ordinary least squares when obtaining the Forchheimer equationcoefficients from experimental measurements.Investigation extends into the thermo-fluid effects on a full scale automotive heatexchanger when inclined at 0 °, 15°, 30° and 45°. It was found, depending on theangle, that there was a difference in the pressure drop of up to 10% between theunheated and heated (100 C) heat exchanger. Based on the proposed mathematicalrelationship, this correlated to a 4% decrease in porosity in order to accurately modelthe automotive heat exchanger at subscale.The thesis concludes with experimental and numerical investigation into the heattransfer on a hydrodynamically and thermally developing ow within a radiatorchannel. Laser doppler anemometry measurements recorded a 1.5% increase in thecentreline velocity compared to 0.8% obtained from numerical simulation.