Identification of boiling regimes by force measurements
The onset and end of transition from film to nucleate boiling can be identified with force measurements. The apparatus used to investigate the transition consisted of a quartz tube filled with water balanced on a piezoelectric crystal. A thermocouple-instrumented silver sphere (0.356 in-diameter, 99% pure) was injected into the column of water. The output of the piezoelectric crystal was used to indicate the change in force level. It was found that the beginning of transition is characterized by a definite increase in force level, while at the end of transition there is a definite decrease in force level. The effect of subcooling on the temperature at the onset of transition and the temperature at the end of transition was investigated. It was found that these temperatures decreased for higher temperature water, and that they were independent of sphere initial temperature if the sphere were inserted at a temperature sufficient to insure film boiling. Also, with less subcooling, transition occurs over a longer period of time. The heat-transfer data obtained in this study, for a highly transient case, agrees relatively well with the classical boiling curve.