Transition boiling has, for 50 years, held its place as the least understood of the several boiling mechanisms. Consequently it has been virtually impossible to design heat transfer films to operate in this regime. Indeed, the threat of thermohydraulic nuclear accidents - the possibility of uncovering a nuclear core and then having to rewet it - has done more to demand an understanding of transition boiling than the more positive problems of process design. The Berenson Experiment. For years, our best knowledge of the regime was that given us by Berenson (1960) in his pioneering study. Berenson used a copper block, heated from below by the condensation of high-pressure steam, and cooled on top by the boiling of a low-boiling-point fluid. He then measured the heat flux q as a function of the almost independently specifiable temperature difference between the
top of the copper block and the saturated liquid: (Tw — TsM) = AT. He was thus able to obtain nearly complete "boiling curves"(specifications of the q(AT) relationship) for the boiled liquid. The following are among Berenson's more important experimental findings:
The nucleate boiling heat flux is extremely dependent on
The peak (or "burnout") heat flux qmix in pool boiling is
only slightly dependent upon the surface condition of the
heater. He obtained about a 15 percent total variation of qmax
over the full range of surface finishes, with the roughest surfaces giving the highest values.
The film boiling heat flux is independent of the surface
condition of the heater.
The minimum film boiling heat fluxes were fairly consistent with one another if the surface chemistry was such as to give a relatively large contact angle (3. If the surfaces were polished with a lapping compound as well, the minimum heat flux qmili reached its lowest value which Berenson correlated using a modified Zuber (1959) theory as follows:
iPf + Po)1 (1)
Manuscript received by the Heat Transfer Division January 17, 1986.
was exceedingly high, and the transition heat fluxes were also very high.
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