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International Heat Transfer Conference 16

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

EXPERIMENTAL EVALUATION OF THE FLOW BOILING HEAT TRANSFER COEFFICIENT OF DI-WATER INSIDE MINICHANNELS UNDER CONDITIONS CLOSE TO THE CRITICAL HEAT FLUX

Tiago A. Moreira
University of Sao Paulo, Sao Carlos School of Engineering, Department of Mechanical Engineering, Av. Trabalhador Sancarlense, 400, Pq. Arnold Schimidt, Sao Carlos, SP, Brazil

Francisco J. do Nascimento
University of Sao Paulo, Sao Carlos School of Engineering, Department of Mechanical Engineering, Av. Trabalhador Sancarlense, 400, Pq. Arnold Schimidt, Sao Carlos, SP, Brazil

Gherhardt Ribatski
Heat Transfer Research Group, University of Sao Paulo, Sao Carlos School of Engineering, Department of Mechanical Engineering, Av. Trabalhador Sancarlense, 400, Pq. Arnold Schimidt, Sao Carlos, SP, Brazil

DOI: 10.1615/IHTC16.bae.021908
pages 647-652


KEY WORDS: Boiling and evaporation, Convection, Heat transfer coefficient

Abstract

This work concerns an experimental evaluation of the flow boiling heat transfer coefficient of DI-water inside minichannels. Experiments were performed for mass velocities, G, from 133 to 600 kg/m2s, vapor qualities, x, up to 0.85 and heat fluxes, q, up to 2.5 MW/m2. For G<500 kg/m2s, the heat transfer coefficient initially decreases with increasing vapor quality, until achieves a minimum value. Then, its trend is shifted and the heat transfer coefficient increases as the vapor quality rises. Such behavior is explained based on the superposition of convective and nucleate boiling effects. For vapor qualities lower than the one corresponding to the minimum heat transfer coefficient (xmin), the heat transfer coefficient increases with increasing q and G. On the other hand, for q close to the CHF condition at the ending region of the test section and the heat transfer coefficient evaluated upstream to the CHF region decreases with increasing vapor quality. Comparisons among eight predictive methods and the experimental data were performed, none of the methods provided reasonable predictions of the present data. Therefore, taken into account this fact and considering that the methods for prediction of the heat transfer coefficient based on data for DI-water does not include in their database results for conditions close to the CHF, the empirical constants of the method of Kanizawa et al. [2] were modified based on the present database. The modified version of the method predicted more than 91% of its database within an error band of ±30% and provided a mean absolute error of only 12.1%.

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