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Advanced Course in Heat Exchangers: Theory and Practice. ICHMT Symposium.
1981, Dubrovnik, Croatia

DOI: 10.1615/ICHMT.1981.AdvCourseHeatExch


ISBN Print: 978-0-07062-806-9

Saturated Flow Boiling—Effect of Non-uniform Heat Transfer along the Tube Perimeter

pages 143-156
DOI: 10.1615/ICHMT.1981.AdvCourseHeatExch.120
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摘要

In this work the heat transfer for forced convection boiling in a horizontal tube with constant heat flux is investigated. In the case of stratified and wavy flow the measured temperature distribution along the tube perimeter looks like a cosine function with a maximum at the top and a minimum at the bottom of the tube. Due to this temperature distribution the main part of the heat supplied at the top is conducted to the bottom.
A model which takes into account the tangential heat conduction was developed to calculate local heat transfer coefficients along the perimeter based on the measured temperature distribution. The results show two regions with different heat transfer behavior along the perimeter. In the upper part of the tube, which is in contact with the vapor, the heat transfer coefficient is very low and may be neclected. The heat transfer coefficient in the wet part can be described as a function of the local temperature difference. With this information it was possible to calculate the temperature distribution for tubes with different wall thickness.
The calculations predict an increase of the perimeter averaged heat transfer coefficient as well as of the critical heat flux with increasing heat conductivity and thickness of the tube wall. Therefore attention must be paid to the influence of tangential heat conduction when experimental data obtained with test sections of different materials, different wall thickness and different kinds of heat supply are compared.

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