ABSTRACT
An experimental investigation is described in which iso-octane at 1 atm, was boiled while flowing vertically up over a bundle of electrically heated in-line tubes 5 columns wide by 17 rows high. Heat transfer coefficient data is presented for the 10th and 11th rows of the column at uniform heat fluxes of 20, 40 50 and 60 kW/m2 with mass velocities and qualities in the ranges, 150 - 370 kg/m2s and 0.01 - 0.1 respectively. At q = 60 kW/m2 nucleate boiling dominates with little effect of Reynolds number or quality on heat transfer coefficient. At 20 kW/m2 there is a strong effect of both Reynolds number and quality and the heat transfer coefficient is greater than the isolated tube pool boiling value in all the tests. Transition between these phenomena was observed at the intermediate heat fluxes.
Results are compared to the Chen superposition model using the Jensen and Hsu (1988) approach modified by the addition of a heat flux dependent multiplying factor in the Chen (1966) expression for the flow factor. This model predicted the transition from convective evaporation dominated to nucleate boiling dominated vaporisation.
