scholarly journals Dryout-type critical heat flux in vertical upward annular flow: effects of entrainment rate, initial entrained fraction and diameter

2017 ◽  
Vol 54 (1) ◽  
pp. 81-90 ◽  
Author(s):  
Zan Wu ◽  
Vishwas Wadekar ◽  
Chenglong Wang ◽  
Bengt Sunden
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Entrainment Rate ◽  
Flow Effects

An Investigation of Flow, Heat Transfer Characteristic of Annular Flow and Critical Heat Flux in Vertical Upward Round Tube

2006 ◽  
Author(s):  
Fan Pu ◽  
Suizheng Qiu ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Heat Transfer Characteristic ◽  
Annular Flow ◽  
Transfer Characteristic ◽  
Round Tube

The term annular flow is used to describe the configuration of vapor-liquid flow in which part of the liquid travels as a film on the wall and the rest is entrained as drops by the vapor core in the center of the channel. The objective of this paper is to develop a hydrodynamic model for vertical upward annular flow. A separated flow model is developed and the conservations of Mass, Momentum, Energy, entrainment rate correlation in wide range of conditions and interfacial frictional correlation are used to research the flow and heat transfer characteristic of annular flow. The liquid film thickness, liquid film mass flow rate, two-phase heat transfer coefficient pressure along axial position, local velocity profiles along radial position are predicted theoretically. The influence of the mass flux, heat flux on liquid film thickness, heat transfer coefficient etc. are investigated in detail. The critical heat flux are also predicted in vertical upward round tube according to the theory that the dryout in vertical annular flow emerges at the point where the film is depleted due to the integrating result of entrainment, deposition and evaporation. The influence of mass flux, inlet mass quality and tube diameter on critical heat flux is also predicted in this paper. Finally the predicted result of critical heat flux is compared with experimental data, and the theoretical CHF values are higher than that of experimental data, with error within 30%.

Application of Film Dryout Model in Liquid Metal CHF Prediction

2014 ◽  
Author(s):  
Zaiyong Ma ◽  
Yue Nina ◽  
Suizheng Qiu ◽  
Wenxi Tian ◽  
Guanghui Su
Keyword(s):  
Heat Flux ◽  
Liquid Metal ◽  
Deposition Rate ◽  
Annular Flow ◽  
Nuclear Reactors ◽  
Liquid Metals ◽  
Large Error ◽  
Entrainment Rate ◽  
Large Heat ◽  
Sodium And Potassium

Liquid metals have been used as coolants of several kinds of nuclear reactors, and the prediction of critical heat flux (CHF) is rather important for the design, safety and economy of these reactors. A film dryout model considering the deposition and entrainment of droplets was established to obtain the CHF of liquid metal in annular flow flowing in tubes. The correlations of deposition rate, entrainment rate and so on for conventional fluids were used, and the initial entrainment fraction was determined according to experimental data. Results showed that the correlations for conventional fluids could be used for liquid metals approximately, but relatively large error might occur for large heat flux. The accuracy of this model for sodium and potassium was similar for small heat flux, but had some differences for large heat flux. Special correlations of deposition rate, entrainment rate and so on should be developed to predict the CHF of liquid metals more accurately.

Flow Behavior and Flow Boiling Heat Transfer in Thin-Rectangular Mini-Channels

2008 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Tomonari Yamada
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Liquid Slug ◽  
Flux Condition

Boiling heat transfer of thin-rectangular channels of the width of 10 mm has been examined. The height of the flow channel was in a range from 0.6 mm to 0.4 mm. Experimental fluid was water. Bubbly flow, slug flow, semi annular flow and annular flow were observed. The flow pattern transition agreed well with the Baker flow pattern map for the usual sized flow path. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments. At the critical heat flux condition, the heat transfer surface was covered by liquid slug, a large bubble pushed away the liquid slug, a dry area was formed on the heat transfer surface and then liquid slug came around to cover the heat transfer surface again. This process repeated rapidly. Following this observation, a heat transfer surface temperature calculation model at the critical heat flux condition was proposed. The calculated result re produced the experimental result.

Prediction of Critical Heat Flux in Annular Flow Using a Film Flow Model

2003 ◽  
Vol 40 (6) ◽  
pp. 388-396 ◽  
Author(s):  
Tomio OKAWA ◽  
Akio KOTANI ◽  
Isao KATAOKA ◽  
Masanori NAITO
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Flow Model ◽  
Film Flow

A Lower Bound for the Dryout Quality in Annular Flow

2014 ◽  
Author(s):  
J. P. Manning ◽  
S. P. Walker ◽  
G. F. Hewitt
Keyword(s):  
Heat Flux ◽  
Lower Bound ◽  
Liquid Film ◽  
Phenomenological Models ◽  
Flow Regime ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Large Fraction

The mechanism responsible for Critical Heat Flux (CHF) depends on the flow regime. In the annular flow regime it is normally assumed that CHF occurs when the liquid film dries out. The quality at the onset of annular flow varies, but is generally a few percent, and phenomenological models to predict CHF are routinely applied at qualities above this value. In this paper we will demonstrate that annular flow film dryout cannot occur until a quality significantly greater than this. This finding means that for a large fraction of the annular flow regime the film dryout mechanism cannot be responsible for CHF. This finding provides guidance as to under what circumstances such phenomenological models may properly be used.

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