A Physical Model for Predicting Annular Film Flow Droplet Entrainment in Heat Transfer Systems

2002 ◽  
Author(s):  
M. J. Holowach ◽  
L. E. Hochreiter ◽  
F. B. Cheung
Keyword(s):  
Heat Transfer ◽  
Film Flow ◽  
Liquid Droplet ◽  
Flow Analysis ◽  
Interfacial Instability ◽  
Force Balance ◽  
Interfacial Instabilities ◽  
Two Phase ◽  
Droplet Entrainment ◽  
Annular Film

The ability to accurately predict droplet entrainment in annular two-phase flow is required to effectively calculate the interfacial mass, momentum, and energy transfer, which characterizes nuclear reactor safety, system design, analysis, and performance. Most annular flow entrainment models in the open literature are formulated in terms of dimensionless groups, which do not directly account for interfacial instabilities. However, many researchers agree that there is a clear presence of interfacial instability phenomena having a direct impact on droplet entrainment. The present study proposes a model for droplet entrainment, based on the underlying physics of droplet entrainment from co-current upward annular film flow that is characteristic to Light Water Reactor (LWR) safety analysis. The model is developed based on force balance and a stability analysis that can be implemented into a transient three-field (continuous liquid, droplet, and vapor) two-phase heat transfer and fluid flow analysis computer code.

Convective Boiling in Vertical Channels With Different Offset Strip Fin Geometries

1989 ◽  
Vol 111 (1) ◽  
pp. 156-165 ◽  
Author(s):  
G. D. Mandrusiak ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Flow ◽  
Nucleate Boiling ◽  
Two Phase ◽  
Wall Superheat ◽  
Annular Film ◽  
Two Phase Heat Transfer ◽  
Offset Strip Fin

Newly obtained local heat transfer data are presented for flow boiling of liquids in two partially heated vertical channels with different offset strip fin geometries operating at low to moderate wall superheat levels. Experiments were conducted in special test sections that permitted direct visual observation of the boiling process while simultaneously measuring the heat transfer coefficient along the channel. Data for which nucleate boiling appeared to be completely suppressed were analyzed together with similar results for other offset fin geometries to assess the effects of channel geometry variations on the two-phase heat transfer coefficient during annular film-flow evaporation. For all geometries considered, the data for annular film-flow evaporation were found to correlate well in terms of modified versions of the F and Martinelli parameters used by Bennett and Chen (1980) to correlate similar data for round tubes. For fin matrices of similar size and configuration, the forced convective component of the two-phase heat transfer coefficient was found to be well represented by a single F-parameter correlation curve. However, F-factor correlations for matrices having significant differences in fin and channel dimensions were found to differ substantially. An approximate superposition method for including the contribution of nucleate boiling to the two-phase heat transfer coefficient at low to moderate wall superheat levels is also proposed.

Measurement of Liquid Film Thickness in Micro Tube Annular Flow

2010 ◽  
Author(s):  
Hiroshi Kanno ◽  
Youngbae Han ◽  
Yusuke Saito ◽  
Naoki Shikazono
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Two Phase ◽  
Micro Scale ◽  
Film Model ◽  
Annular Film

Heat transfer in micro scale two-phase flow attracts large attention since it can achieve large heat transfer area per density. At high quality, annular flow becomes one of the major flow regimes in micro two-phase flow. Heat is transferred by evaporation or condensation of the liquid film, which are the dominant mechanisms of micro scale heat transfer. Therefore, liquid film thickness is one of the most important parameters in modeling the phenomena. In macro tubes, large numbers of researches have been conducted to investigate the liquid film thickness. However, in micro tubes, quantitative information for the annular liquid film thickness is still limited. In the present study, annular liquid film thickness is measured using a confocal method, which is used in the previous study [1, 2]. Glass tubes with inner diameters of 0.3, 0.5 and 1.0 mm are used. Degassed water and FC40 are used as working fluids, and the total mass flux is varied from G = 100 to 500 kg/m2s. Liquid film thickness is measured by laser confocal displacement meter (LCDM), and the liquid-gas interface profile is observed by a high-speed camera. Mean liquid film thickness is then plotted against quality for different flow rates and tube diameters. Mean thickness data is compared with the smooth annular film model of Revellin et al. [3]. Annular film model predictions overestimated the experimental values especially at low quality. It is considered that this overestimation is attributed to the disturbances caused by the interface ripples.

Momentum and Heat Transfer in Laminar Flow of Gas With Liquid-Droplet Suspension Over a Circular Cylinder

1967 ◽  
Vol 89 (2) ◽  
pp. 185-193 ◽  
Author(s):  
M. E. Goldstein ◽  
Wen-Jei Yang ◽  
J. A. Clark
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Skin Friction ◽  
Gas Flow ◽  
Flow Problem ◽  
Liquid Droplet ◽  
Two Phase ◽  
Momentum And Heat Transfer ◽  
Layer Flow ◽  
Gas Liquid Flow

An analysis has been made to determine the heat transfer and friction characteristics in a two-phase (gas-liquid) flow over a circular cylinder. It is demonstrated that the resulting two-layer flow problem can be formulated exactly within the framework of laminar boundary layer theory. Two cases are studied; (1) For the parameter E greater or equal to 0.1 and the drop trajectories straight and, (2) For E less or equal to 0.1 and for any drop trajectory. Solutions obtained in power series include the local liquid-film thickness, velocity and temperature profiles, skin friction and Nusselt number. Numerical results disclose a significant increase in both heat transfer rate and skin friction over those of a pure gas flow. The theoretical prediction compares favorably with experimental results of Acrivos, et al. [1].

Modeling of Falling Film in Vertical Downward Two-Phase Pipe Flow

2012 ◽  
Author(s):  
Jose M. Lopez ◽  
Ram Mohan ◽  
Ovadia Shoham ◽  
Luis Gomez ◽  
Gene Kouba
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Liquid Droplet ◽  
Mechanistic Model ◽  
Mineral Oil ◽  
Liquid Film Thickness ◽  
Falling Film ◽  
Two Phase ◽  
Droplet Entrainment ◽  
Falling Liquid Film

Falling liquid films in vertical pipes are found in a variety of different industrial applications and industrial equipment, such as downcomers, caisson separators and reactors. The hydrodynamics of the falling film in vertical two-phase pipe flow can affect droplet entrainment, gas entrainment, and pressure drop. Therefore, a mechanistic model for prediction of falling liquid film thickness, falling liquid film velocity and a correlation for liquid droplet entrainment fraction in vertical downward liquid-gas systems has been proposed. The falling film model developed is based on applying momentum balance on the liquid film. The liquid film is assumed to be in steady-state, incompressible and free of entrained gas. The mechanistic model includes both the developing and the developed regions. The shear effect between the gas core and the falling liquid film is considered. The liquid droplet entrainment fraction traveling in the gas core is considered and a new correlation for its prediction is proposed. Detailed uncertainty analysis is performed for liquid film thickness and liquid film velocity model predictions, including Monte Carlo simulation. Predicted liquid film thickness, liquid film velocity and liquid droplet entrainment fraction are validated against experimental data for different liquid fluid properties, such as water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil).

scholarly journals HEAT TRANSFER MODELLING OF TWO-PHASE FLOW IN ISOLATED CHANNEL

2018 ◽  
Vol 14 ◽  
pp. 49
Author(s):  
Daniel Vlček ◽  
Vojtěch Caha ◽  
Martin Ševeček
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Boiling Crisis ◽  
Simple Geometry ◽  
Inverted Annular Film Boiling ◽  
Transfer Modelling ◽  
Annular Film

This paper deals with Post-CHF (critical heat flux) heat transfer with the focus on different regimes of film boiling. The new thermal-hydraulic code TUBE 2.0 is presented. This code uses the equation of energy conservation and predefined correlations to establish wall temperature, the departure of nucleate boiling ratio as well as other parameters of cooling in a simple geometry - an isolated channel. With experimental data of inverted annular film boiling from Stewart, the best-performing correlation for calculation of post-CHF heat transfer in the channel was determined. Finally, the new presented code TUBE 2.0 and subchannel code SUBCAL owned by Chemcomex a.s. are compared using results of various experiments conducted by Becker. Data from Stewart could not be used because of inability to predict the onset of boiling crisis with several correlations.

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