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International Heat Transfer Conference 13
Graham de Vahl Davis (open in a new tab) School of Mechanical and Manufacturing Engineering, University of New South Wales, Kensington, NSW, Australia
Eddie Leonardi (open in a new tab) Computational Fluid Dynamics Research Laboratory, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia 2052

ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

CONVECTIVE BOILING HEAT TRANSFER OF WATER IN A CAPILLARY TUBE UNDER A LOW FLOW RATE CONDITION

page 12
DOI: 10.1615/IHTC13.p28.340
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ABSTRACT

The characteristics of saturated flow boiling heat transfer of water in a heated capillary tube with a 1.45 mm diameter are experimentally studied in a pressure range of 10 to 100 kPa. Wall temperature on the tube and pressure drop are measured in ranges of mass fluxes from 23 to 153 kg/m2s and heat fluxes from boiling inception to CHF. The two-phase flow patterns in the tube are correlated using an adiabatic two-phase flow pattern map. The dominant flow patterns in the tube are found to be wavy-annular and annular flow. This fact is not so affected by the system pressure. Local heat transfer coefficients along the tube are discussed since the pressure drop is large enough. The coefficients are similar along the heated tube as long as the flow pattern is the wavy-annular or annular flow. The effects of mass flux and quality on the heat transfer coefficient are examined. Large heat transfer enhancement is observed and existing flow boiling correlations largely underpredict the heat transfer coefficient especially for a low heat flux condition. The underprediction gradually decreases with increasing heat flux. A heat transfer model based on a liquid film evaporation, which was confirmed for heat transfer coefficients at an atmospheric pressure, is applied to the present data on a lower pressure and is modified to obtain a better prediction within 30% error. The CHF can be consistently evaluated by Katto's correlation but is overpredicted by about 30% below a mass flux of about 60 kg/m2s.

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