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BUBBLE DENSITY ON SURFACES WITH NUCLEATE BOILING - ITS INFLUENCE ON HEAT TRANSFER AND BURNOUT HEAT FLUX AT ELEVATED SATURATION PRESSURES

Dieter Gorenflo
Laboratorium für Wärme- und Kältetechnik, Universität -GH- Paderborn, D-4790 Paderborn, Pohlweg 55, Germany

V. Knabe
BASF Aktiengesellschaft, D-6700 Ludwigshafen

Volker Bieling
Laboratorium für Wärme- und Kältetechnik, Universität -GH- Paderborn, D-4790 Paderborn, Pohlweg 55, FRG

Abstract

An approach is presented, in which burnout at elevated saturation pressures is interpreted as an event of locally coalescing bubbles, using1the transient conduction model for the heat transfer at active nucleation centers and assumptions about the distribution of the centers at high bubble density, and combining both with experimental data for the heat transfer coefficient at nucleate pool boiling. It is shown that the relative pressure dependence of the heat flux qcrit at burnout and of the heat transfer coefficient at single bubbles with heat flux controlled bubble growth are similar. Assuming that burn-out occurs always at a certain bubble density on the heated surface, the relative pressure dependence of qcrit can be described quite well by the model. The calculation of absolute values of qcrit is possible, too, but efforts in this direction should be postponed, till more reliable data about the bubble diameter and frequency at departure will be available.

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