INITIAL VAPOR BUBBLE GROWTH ON A HEATED WALL DURING NUCLEATE BOILING

An experimental investigation of the initial vapor bubble growth on a horizontal, heated wall during saturated pool boiling is reported. Streak photography has been adapted for the first time to the observation of bubble growth rates. When combined with high-speed framing photography this has proven to be an effective technique for the observation of the initial growth of a bubble because the uncertainty in the zero time datum can be reduced to about 10μs. This compares with a correspondingly uncertainty of at least 100μs in previously reported works which used high-speed framing photography alone. Hemispherical bubbles were measured during the first 500μs following nucleation. The growth curves showed the liquid momentum effects were not significant beyond the first 50μs. For the time period between 50 and 500μs following nucleation, the data fitted very closely the one half power, R = mt 1 2, where R is the bubble radius, m the growth constant and t the time. The measured growth constant was compared with those predicted from five different analytical models, and was found to correspond closely to a model which postulated a thick" microlayer of constant thickness underlying the bubble. "Thick" implied a sufficient thickness to delay the arrival of the temperature wave at the microlayer liquid-heated-surface interface until some time later than 500μs. © 1969."