LIQUID FILM BEHAVIOUR IN ANNULAR DISPERSED FLOW AT CRITICAL HEAT FLUX

1970 ◽  
Author(s):  
E. O. Moeck ◽  
Jules W. Stachiewicz
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Dispersed Flow

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%.

scholarly journals Термокапиллярные структуры и разрыв нагреваемой пленки жидкости

2019 ◽  
Vol 45 (14) ◽  
pp. 44
Author(s):  
Е.А. Чиннов
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Type A ◽  
Vertical Surface ◽  
Film Rupture ◽  
Interaction Of Waves

The data of thermocapillary structures formation and breakdown of the heated liquid film flowing down on a vertical surface with the Reynolds number varied from 0.1 up to 500 are analyzed. It is shown that the interaction of waves with thermocapillary structures type A leads to an increase in critical heat flux, corresponding to the liquid film rupture, compared with literature data (regime B).

H222 Critical Heat Flux of Counter-Current Two-Phase Flow : Effect of Subcooled Liquid Film

2011 ◽  
Vol 2011 (0) ◽  
pp. 371-372
Author(s):  
Ayaka Fujiwara ◽  
Takuya Suzuki ◽  
Takeyuki Ami ◽  
Hisashi Umekawa ◽  
Mamoru Ozawa
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Flow Effect ◽  
Counter Current

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.

Measurement of Vapor Superheat in Post-Critical-Heat-Flux Boiling

1980 ◽  
Vol 102 (3) ◽  
pp. 465-470 ◽  
Author(s):  
S. Nijhawan ◽  
J. C. Chen ◽  
R. K. Sundaram ◽  
E. J. London
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flow ◽  
Flow Boiling ◽  
Experimental Results ◽  
Flow Rates ◽  
Dispersed Flow ◽  
Mass Flow Rates ◽  
Non Equilibrium

A differentially-aspirated superheat probe was developed to measure vapor temperatures in post-critical-heat-flux, dispersed-flow boiling. Measurements obtained for water, at low-to-moderate pressures and mass flow rates in a tube, indicated very significant non-equilibrium, with vapor superheats of several hundred degrees (°C). Predictions of published correlations showed unsatisfactory agreement with the experimental results.

Experimental Study on Liquid Film Dryout Under Oscillatory Flow Conditions

2009 ◽  
Author(s):  
Yosuke Yamagoe ◽  
Taisuke Goto ◽  
Tomio Okawa
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Power Density ◽  
Critical Heat Flux ◽  
Boiling Water ◽  
Boiling Water Reactors ◽  
Flow Oscillation ◽  
Two Phase ◽  
Water Reactors ◽  
Liquid Film Dryout

The use of high power density core is one of the promising ways to improve economic efficiency of advanced boiling water reactors. It is however known that in boiling two-phase flows, an increase in power density commonly reduces the margin to the onset of unanticipated flow instability. Hence, in the development of a boiling water reactor of high power density core, ability to predict the occurrence of boiling transition is considered indispensable even when the coolant flow rate is not in the steady state. In the present work, sinusoidal oscillation was applied to the inlet mass flux and the experimental measurement of the critical heat flux was carried out under flow oscillation conditions. It was shown that the critical heat flux decreases monotonically with increased values of oscillation amplitude and oscillation period. These results are consistent with experimental data reported by previous investigators. A simple theory was then proposed to estimate the critical heat flux in oscillatory flow condition. Considering the application to the advanced boiling water reactors, the triggering mechanism of the critical heat flux condition is supposed to be the liquid film dryout in annular two-phase flow regime of high vapor quality. Under the flow oscillation condition, it is expected that long waves are formed on a liquid film due to the time variation of inlet mass flux. Assuming that the wave evolution within a boiling channel is influential in the occurrence of the local dryout of a liquid film, an available nonlinear wave theory was applied to the estimation of critical heat flux under the flow oscillation condition. It was demonstrated that the critical heat fluxes measured under the oscillatory conditions agree with the proposed theory fairly well.

Theoretical Model of Electric Field Effects on the Enhancement of Critical Heat Flux

2004 ◽  
Author(s):  
Takeshi Yajima ◽  
Akira Yabe ◽  
Hiroshi Maki
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Film Thickness ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Applied Voltage ◽  
Liquid Film Thickness ◽  
Flux Enhancement ◽  
The Relationship ◽  
Lines Of Force

Critical heat flux enhancement by the electrohydrodynamic (EHD) effect has been analyzed quantitatively based on the increased frequency of liquid-vapor interface oscillations around the edge of the bubble. The majority of heat transfer occurs when the liquid film thickness becomes less than 50 μ m, which only occurs once per period. The main mechanism of heat flux enhancement induced by the EHD effect would be a result of an increase in surface tension due to the effect of electric lines of force. By representing the terms of the forces for a change in curvature and the surface tension resulting from the electric lines of force, the equation of the liquid-vapor instability was obtained and analyzed. Experimentally it has been shown that as the applied voltage increased, the periodic time interval of the thickness change was shortened. This effect reduces the potential for dryout of the liquid film by making the minimum thickness time period shorter. By measuring the pressure oscillation on the boiling surface, the change of the thin liquid film thickness and the dynamic shape of bubbles, the relationship among the pressure, the liquid film thickness and the bubble shape was clarified. Consequently, this model successfully explains the relationship between the applied voltage and the enhancement of the critical heat flux.

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