Nucleate and Film Boiling of Engine Coolants Flowing in a Uniformly Heated Duct of Small Cross Section

Measurements of heat transfer to water/ethylene glycol mixtures are reported for a range of coolant velocities (0.1 to 5.5 m/s) and heat fluxes (up to 140 W/cm²). At the highest velocities (3 and 5.5 m/s) forced convection was the dominant mode of heat transfer. At lower velocities, however, strong nucleate boiling occurred and at the lowest velocities dryout or vapour blanketing of the test section was detected. For most of the tests reported the pressure drop across the test section was held constant and the coolant flowrate adjusted accordingly. A number of tests are, however, reported for conditions of constant flowrate.

The heat-transfer data obtained are shown to be in good agreement with a heat-transfer model that allows for forced convection and nucleate boiling.