ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Crisis in Pool Boiling: Alternative to Hydrodynamic Approach
要約
The hydrodynamic approach to pool boiling crisis remains a mainstream, in spite of many theoretical inconsistences and experimental facts being revealed, which contradict to this theory. The Kutateladze equation for CHF was obtained on basis of dimensions analysis. This factually predetermines that any crisis model, which considers only hydrodynamic effects and ignores influence of liquid viscosity and heat transfer at the heated surface, inevitably leads to this equation with small corrections on liquid/vapor densities ratio. Now it is convincingly established that the limiting vapor velocity does not determine the crisis origin in the real boiling process; at low reduced pressures the actual vapor velocity can exceed multiply the critical one. As for the theoretical studies, assumptions are often found, which contradict to either experimental measurements or to some scientific fundamentals. In the model developed by the present author the crisis is considered as a result of enlarging area of dry spots which existence is an intrinsic feature of nucleate boiling. Great difference of vapor specific volume at high and low reduced pressures makes it reasonable to derive separately the equations for CHF for these two cases. A simple interpolating formula allows calculating CHF at arbitrary pressure. The equation for high reduced pressures predicts the CHF values close to those computed according to the hydrodynamic theory. As the most part of the experimental data are obtained at moderate and high reduced pressures, this coincidence gives a possible explanation of agreement of the Kutateladze-Zuber formula with the data.