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The heat transfer and hydraulic performance of the following coolants was examined in five automobile radiators in a wind tunnel: 100% Water 100% Propylene Glycol 70/30 Propylene Glycol/Water (Volume) 50/50 Propylene Glycol/Water (Volume) 70/30 Ethylene Glycol/Water (Volume) 50/50 Ethylene Glycol Water (Volume) The results of these studies are presented to demonstrate the relative performance of these coolant mixtures in terms of heat transfer, coolant pressure drop and radiator effectiveness for a range of coolant flowrates and air flowrates. It is concluded that the most effective of the coolants in transferring heat in the test radiators was water, followed by 50/50 ethylene glycol/water, 50/50 propylene glycol/water, 70/30 ethylene glycol/water, 70/30 propylene glycol and, finally, 100% propylene glycol.

The performance of 50/50 (vol) propylene glycol/water and ethylene glycol/water mixtures in the convective and forced flow boiling regimes has been evaluated and compared with water and previously published data for ethylene glycol/water mixtures. The fluid velocities examined ranged from 0.1 to 0.5 m/s at heat fluxes between 50,000 and 750,000 W/m2. The results indicate that the heat transfer of 50/50 (vol) propylene glycol/water coolants is slightly less effective in the convective regime compared to 50/50 (vol) ethylene glycol/water mixtures, but superior once nucleate boiling is the dominant mechanism. The experimental data showed good agreement with the predictions of the Chen correlation for boiling heat transfer to saturated fluids in convective flow. It is concluded that a 50/50 (vol) propylene glycol/water mixture will be at least as effective in providing cooling within an automobile engine as a 50/50 (vol) ethylene glycol/water mixture.