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Proceedings of Symposium on Energy Engineering in the 21<sup>st</sup> Century (SEE2000) Volume I-IV

ISSN:
1-56700-132-7 (Print)

TRANSIENT BOILING HEAT TRANSFER ON SMALL FINNED SURFACES

Satoshi Kumagai
Department of Machine Intelligence and Systems Engineering Tohoku University

Jun Fushimi
Department of Machine Intelligence and Systems Engineering Tohoku University

Masaaki Izumi
Department of Applied Chemistry and Molecular Science Iwate University

Abstract

Many types of structured surface have been studied on their boiling heat transfer performance because of their high potential in removing generated heat. Most of them, however, concerned with only a steady state. But a rapid change in heat generation frequently occursln many practical cases. In this study, transient pool boiling heat transfer from surfaces with stud fins or groove fins was investigated under atmospheric pressure. Tested surfaces were 0.5 − 1.5 mm in the fin thickness, 0.5 − 3.0 mm in the spacing and 0.5 − 2.0 mm in the height. Stepwise heat input that exceeds CHF of all surfaces was supplied by a steam impingement (158 °C, 0.6 MPa) to the opposite end surface of a small copper finned column and the time constant of heating was about 1.5 sec, that should be a rather slow change as a transient phenomenon. Those surface can achieve high heat transfer perfor¬mance in a steady state. Comparisons of transient and steady state boiling characteristics are presented for those surfaces, showing not a small effect of fin configuration on the transient boiling performance. The CHF in transient heating was almost the same value as that in steady state for groove finned surfaces. On the other hand, the CHF of stud finned surfaces was mostly smaller in transient heating than in steady state. The nucleate boiling period that was defined as the duration from the moment when a temperature rise was recorded at the base surface to the moment of CHF, was longer in the groove finned surfaces than the stud ones.