A STUDY OF HEAT TRANSFER FROM A SPHERE TO WATER FOR INVESTIGATING THE VAPOR FILMS BOILING AROUND IT DURING FREE CONVECTION

This report describes an experimental investigation of Rapid quenching of hot metal. An apparatus was used to study the destabilization of the vapor film boiling around 3/4 in diameter silver-plated Copper sphere. The results show an increase in heat Flux in the film boiling regime caused by bubble induced oscillation. Data were obtained in distilled water for bubble rates of 3 and 5 bubbles/ sec, and initial sphere temperature range of 800 to 1100 F. Data also were taken for different Sizes of nozzles which were 1/2 and 1/4 mm inside diameter, and water temperature range. From 60 to 140F were investigated. The nature of bubble disturbances and Transient vapor film behavior was investigated with a highspeed movie Camera during quenching. All experiments were done at atmospheric pressure. It was found that a transition which was named a PSEUDOTRANSITION will appear before the regular transition boiling. This pseudotransition is characterized by nucleate like bubbles covering the Front portion of the sphere. The effect of subcooled water upon the onset of transition temperature was investigated. It was found that decreasing sub cooling results in Lower heat Flux. It was Found the higher sphere temperature tends to increase the transition temperature. Higher bubbles rates tend to increase the heat Flux in the Film boiling regime.

کلیدواژه ها:

pseudo Transition ، bubble-induced oscillation ، bubble Rates ، heat Flux