ISSN Online: 2377-424X
ISBN Print: 0-85295-345-3
International Heat Transfer Conference 10
POOL BOILING HEAT TRANSFER OF PROPANE/N-BUTANE MIXTURES AT A SINGLE TUBE WITH SUPERIMPOSED CONVECTIVE FLOW OF BUBBLES OR LIQUID
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.
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.