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International Heat Transfer Conference 10

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

POOL BOILING HEAT TRANSFER OF PROPANE/N-BUTANE MIXTURES AT A SINGLE TUBE WITH SUPERIMPOSED CONVECTIVE FLOW OF BUBBLES OR LIQUID

Martin Buschmeier
Laboratorium fur Warme- und Kaltetechnik, Universitat (GH) Paderborn

Admilson Dultra Pinto
Laboratorium fur Warme- und Kaltetechnik, Universitat (GH) Paderborn

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

Peter Sokol
BEB Erdgas und Erdol GmbH, Hannover; Laboratorium fur Warme-und Kaltetechnik Universitat (GH), D-4790 Paderborn, Pohlweg 55

Abstract

Pool boiling heat transfer at a single horizontal tube with large diameter (88.4 mm) and superimposed convective flow of bubbles or liquid from below has been investigated experimentally simulating the convective effects caused by bubbles and liquid streaming upwards within a shell-and-tube evaporator. The boiling liquids are propane, n-butane, n-hexane and propane/n-butane mixtures with three different compositions.
The additional convection of the vapour bubbles produced at a supplementary heater, or the liquid distributed by a tUbe, both arranged below the test tube, increase the heat transfer coefficients at low heat fluxes drastically, if the saturation pressures are not very high. This holds above all for the boiling of mixtures, for which the well known deterioration of heat transfer below the molar average of the heat transfer coefficients of the pure components may be compensated or even overcompensated.
At low heat fluxes, heat transfer is dominated by convective effects, and the increase of a with heat flux and pressure characteristic for nucleate pool boiling does not exist, instead, the a-values are independent of heat flux and decrease slightly (pure components) or significantly (mixtures) with increasing pressure. The data at low pressures agree well with a modified version of a calculation method in the literature.
Local measurements of the wall temperature reveal that the minima occurring at the flanks of the tube without additional flow are shifted to the bottom within the convective domain.

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