ABSTRACT
Theoretical and experimental studies have been carried out to investigate the effect of the wall heat flux conditions on upward cross flow film boiling heat transfer from a horizontal cylinder. The Extreme condition of uniform wall heat flux was first considered and theoretically investigated. The predicted overall average Nusselt number was concluded to be higher than that reported in the literature for the uniform wall temperature condition. Besides, the results showed that a minimum limit of the wall heat flux is required to sustain the vapor film and that the separation angle is always encountered at an angle θ ≈ π/2 regardless of liquid subcooling or wall superheat.
Experimental investigation followed to check the angular distribution of local wall heat flux and local wall temperature around a horizontal cylinder. Both of the uniform input heat flux and the uniform wall temperature conditions were applied. The measured distributions were utilized to estimate the heat transfer contribution of the back side surface down stream the separation points which is neglected by the theory.
Theoretical study was finally performed to develop a mathematical model for the uniform input heat flux condition, the nearest condition to the actual applications in which electrically heated surfaces are used. The model aimed at studying the effect of the heat transfer by conduction through the heated wall on the heat transfer characteristics. Results of the model showed a good agreement with the present experimental data.
