2,273 research outputs found
A mechanistic critical heat flux model for wide range of subcooled and low quality flow boiling
No full textA mechanistic model to predict a critical heat Aux (CHF) over a wide operating range in the subcooled and low quality flow boiling has been proposed based on a concept of the bubble coalescence in the wall bubbly layer. The conservation equations of mass, energy and momentum, together with appropriate constitutive relations, are solved analytically to derive the CHF formula. The model is characterized by an introduction of the drag force due to wall-attached bubbles roughness in the momentum balance, which determines the limiting transverse interchange of mass flux crossing the interface of the wall bubbly layer and core. Comparison between the predictions by the proposed model and the experimental CHF data shows good agreement over a wide range of parameters for both light water and fusion reactors operating conditions. The model correctly accounts for the effects of flow variables such as pressure, mass Aux and inlet subcooling as well as geometry parameters. (C) 1999 Published by Elsevier Science S.A. All rights reserved
A procedure to predict subcooled-water-flow-boiling CHF in uniformly heated tubes for high-heat-flux applications
No full textA model to predict critical heat flux (CHF) for high-heat-flux subcooled flow boiling in uniformly heated tubes is proposed. The present CHF model is based on the mechanism of wall-attached bubble coalescence. To take into account the enhanced condensation due to high subcooling and high mass velocity in small-diameter tubes, a mechanistic approach is adopted to evaluate the non-equilibrium flow quality and void fraction in the subcooled water flow boiling. Comparison of the model predictions against similar to 3100 subcooled water CHF data shows relatively good agreement over a wide range of parameters that covers the operating conditions of fusion reactor components. The operating ranges of the present database cover 0.33 less than or equal to D less than or equal to 37.5 mm, 0.002 less than or equal to L less than or equal to 4 m, 0.1 less than or equal to P less than or equal to 20 MPa, 0.37 less than or equal to G less than or equal to 134 Mg/m(2) . s, 49 less than or equal to Delta h(sub, in) less than or equal to 1659 kJ/kg, -1.25 less than or equal to x(em) < 0 and 1.05 less than or equal to q(CHF) less than or equal to 276 MW/m(2)
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