年間 4 号発行
ISSN 印刷: 2169-2785
ISSN オンライン: 2167-857X
Indexed in
ON THE RELATION BETWEEN CHURN FLOW AND CRITICAL HEAT FLUX PREDICTION
要約
Boiling crisis commonly occurs in many industrial systems, which is a threat to the security of the arrangements. Therefore, effective thermal management and accurate prediction of heat transfer are of utmost importance in the safety of heat transfer equipment. Although previous predictions of the critical heat flux (CHF) in heated annular two-phase flow had worked sufficiently well, the general assumption of the entrained fraction at the onset of annular flow is in contradiction to the reality, i.e., the discrepancies between the required and theoretical values become quite large, especially for higher mass flow rates. According to the discussions on the defects of the traditional liquid film flow model, the dryout mechanism relates more closely to churn flow. With great momentum, the entrained droplets in the churn flow travel along the pipe into the annular flow and inevitably affect the downstream flow field. Thus, it is more reasonable to start the calculation from the transition of the slug to the churn flow rather than the annular flow. The usual practice was to assume the entrained fraction at the onset of the churn flow. However, no published correlations have been successful in accounting for it. To address this deficiency, we discuss the transition of slug flow to churn flow and investigate the entrainment mechanisms and characteristics of droplets in the churn flow. Accordingly, we propose an empirical correlation to predict the entrained fraction at the onset of the churn flow. Using the newly developed model, the prediction of CHF in tubes yields good results. More importantly, the defects of the original model are solved with the help of reasonable physical interpretations, and the present model provides better understanding of the effect of flow pattern on CHF predictions.
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Ahmad, M., Peng, D.J., Hale, C.P., Walker, S.P., and Hewitt, G.F., Droplet Entrainment in Churn Flow, in Proc. of 7th Int. Conf. on Multiphase Flow, 2010.
-
Barbosa, J.R., Govan, A.H., and Hewitt, G.F., Visualization and Modelling Studies of Churn Flow in a Vertical Pipe, Int. J. Multiphase Flow, vol. 27, no. 12, pp. 2105-2127, 2001.
-
Barbosa, J.R., Hewitt, G.F., Konig, G., and Richardson, S.M., Liquid Entrainment, Droplet Concentration and Pressure Gradient at the Onset of Annular Flow in a Vertical Pipe, Int. J. Multiphase Flow, vol. 28, no. 6, pp. 943-961, 2002.
-
Brauner, N. and Barnea, D., Slug/Churn Transition in Upward Gas-Liquid Flow, Chem. Eng. Sci., vol. 41, no. 1, pp. 159-163, 1986.
-
Collier, J.G., Convective Boiling and Condensation, New York: McGraw-Hill, pp. 18-19, 1972.
-
Govan, A.H., Phenomenological Prediction of Critical Heat Flux, in Proc. of 2nd UK National Heat Transfer Conf., London, UK, pp. 315-326, 1988.
-
Govan, A.H., Hewitt, G.F., Owen, D.G., and Bott, T.R., An Improve CHF Modelling Code, in Proc. of 2nd UK National Heat Transfer Conf., London, UK, pp. 33-48, 1988.
-
Govan, A.H., Hewitt, G.F., Richter, H.J., and Scott, A., Flooding and Churn Flow in Vertical Pipes, Int. J. Multiphase Flow, vol. 17, no. 1, pp. 27-44, 1991.
-
Groeneveld, D.C., Shan, J.Q., Vasic, A.Z., Leung, L.K.H., Durmayaz, A., Yang, J., Cheng, S.C., and Tanase, A., The 2006 CHF Look-Up Table, Nucl. Eng. Des., vol. 237, nos. 15-17, pp. 1909-1922, 2007.
-
Hewitt, G.F. and Govan, A.H., Phenomenological Modelling of Non-Equilibrium Flows with Phase Change, Int. J. Heat Mass Transf., vol. 33, no. 2, pp. 229-242, 1990.
-
Hibiki, T. and Ishii, M., One-Dimensional Drift-Flux Model and Constitutive Equations for Relative Motion between Phases in Various Two-Phase Flow Regimes, Int. J. Heat Mass Transf., vol. 46, no. 25, pp. 4935-4948, 2003.
-
Inoue, A. and Lee, S.R., Influence of Two-Phase Flow Characteristics on Critical Heat Flux in Low Pressure, Exp. Therm. Fluid Sci., vol. 19, no. 3, pp. 172-181, 1999.
-
Ishii, M. and Denten, J.P., Two-Phase Flow Characteristic of Inverted Bubbly, Slug and Annular Flow in Post-Critical Heat Flux Region, Nucl. Eng. Des., vol. 121, no. 3, pp. 349-366, 1990.
-
Jayanti, S. and Hewitt, G.F., Prediction of the Slug-to-Churn Flow Transition in Vertical Two-Phase Flow, Int. J. Multiphase Flow, vol. 18, no. 6, pp. 847-860, 1992.
-
Kaichiro, M. and Ishii, M., Flow Regime Transition Criteria for Upward Two-Phase Flow in Vertical Tubes, Int. J. Heat Mass Transf., vol. 27, no. 5, pp. 723-737, 1984.
-
Leung, A., Benejee, S., and Groeneveld, D.C., Investigation of Heater Characteristics on CHF Performance of a Long Vertical Annulus in High Pressure Water, in Proc. of 7th Int. Heat Transfer Conf., Munchen, German, pp. 303-308, 1982.
-
McQuillan, K.W. and Whalley, P.B., A Comparison between Flooding Correlations and Experimental Flooding Data for Gas-Liquid Flow in Vertical Circular Tubes, Chem. Eng. Sci., vol. 40, no. 8, pp. 1425-1439, 1985.
-
Oh, C.H. and Englert, S.B., Critical Heat Flux for Low Flow Boiling in Vertical Uniformly Heated Thin Rectangular Channels, Int. J. Heat Mass Transf., vol. 36, no. 2, pp. 325-335, 1993.
-
Okawa, T., Kotani, A., Kataoka, I., and Naito, M., Prediction of Critical Heat Flux in Annular Flow Using a Film Flow Model, J. Nucl. Sci. Technol., vol. 40, no. 6, pp. 388-396, 2003.
-
Okawa, T., Kotani, A., Kataoka, I., and Naito, M., Prediction of the Critical Heat Flux in Annular Regime in Various Vertical Channels, Nucl. Eng. Des., vol. 229, nos. 2-3, pp. 223-236, 2004.
-
Saito, T., Hugher, E.D., and Carbon, M.W., Multi-Fluid Modelling of Annular Two-Phase Flow, Nucl. Eng. Des., vol. 50, no. 2, pp. 225-271, 1978.
-
Taitel, Y. and Dukler, A.E., A Model for Slug Frequency During Gas-Liquid Flow in Horizontal and near Horizontal Pipes, Int. J. Multiphase Flow, vol. 3, no. 6, pp. 585-596, 1977.
-
Tong, L.S. and Tang, Y.S., Boiling Heat Transfer and Two-Phase Flow, Washington, DC: Taylor and Francis, pp. 231-232, 1997.
-
Wang, K., Bai, B.F., and Ma, W.M., Huge Wave and Drop Entrainment Mechanism in Gas-Liquid Churn Flow, Chem. Eng. Sci., vol. 104, pp. 638-646, 2013.
-
Wang, K., Bai, B.F., and Ma, W.M., An Improved Liquid Film Model to Predict the CHF based on the Influence of Churn Flow, Appl. Therm. Eng., vol. 64, nos. 1-2, pp. 422-429, 2014.
-
Wang, K., Ye, J., and Bai, B.F., Entrained Droplets in Two-Phase Churn Flow, Chem. Eng. Sci., vol. 164, pp. 270-278, 2017.
-
Whalley, P., Hutchinson, P., and Hewitt, G.F., Calculation of Critical Heat Flux in Force Convection Boiling, in Proc. of 5th Int. Heat Transfer Conf., Tokyo, Japan, vol. 4, 1974.
-
Zuber, N. and Staub, F.W., Stability of Dry Patches Forming in Liquid Films Flowing over Heated Surfaces, Int. J. Heat Mass Transf., vol. 9, no. 9, pp. 897-905, 1966.