scholarly journals Determination of dryout localization using a five-equation model of annular flow for boiling in minichannels

2017 ◽  
Vol 38 (1) ◽  
pp. 123-139 ◽  
Author(s):  
Jan Wajs ◽  
Dariusz Mikielewicz
Keyword(s):  
Liquid Film ◽  
Mass Balance ◽  
Gas Phase ◽  
Annular Flow ◽  
Film Flow ◽  
Equation Model ◽  
Two Phase ◽  
Model Predictions ◽  
Cross Correlations

AbstractDetailed studies have suggested that the critical heat flux in the form of dryout in minichannels occurs when the combined effects of entrainment, deposition, and evaporation of the film make the film flow rate go gradually and smoothly to zero. Most approaches so far used the mass balance equation for the liquid film with appropriate formulations for the rate of deposition and entrainment respectively. It must be acknowledged that any discrepancy in determination of deposition and entrainment rates, together with cross-correlations between them, leads to the loss of accuracy of model predictions. Conservation equations relating the primary parameters are established for the liquid film and vapor core. The model consists of three mass balance equations, for liquid in the film as well as two-phase core and the gas phase itself. These equations are supplemented by the corresponding momentum equations for liquid in the film and the two-phase core. Applicability of the model has been tested on some experimental data.

scholarly journals Experimental and theoretical study of dryout in annular flow in small diameter channels

2011 ◽  
Vol 32 (1) ◽  
pp. 89-108 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Michał Gliński ◽  
Jan Wajs
Keyword(s):  
Experimental Data ◽  
Liquid Film ◽  
Annular Flow ◽  
Theoretical Study ◽  
Small Diameter ◽  
Infrared Camera ◽  
Equation Model ◽  
Internal Diameter ◽  
Two Phase ◽  
Liquid Film Dryout

Experimental and theoretical study of dryout in annular flow in small diameter channels In the paper the experimental analysis of dryout in small diameter channels is presented. The investigations were carried out in vertical pipes of internal diameter equal to 1.15 mm and 2.3 mm. Low-boiling point fluids such as SES36 and R123 were examined. The modern experimental techniques were applied to record liquid film dryout on the wall, among the others the infrared camera. On the basis of experimental data an empirical correlation for predictions of critical heat flux was proposed. It shows a good agreement with experimental data within the error band of 30%. Additionally, a unique approach to liquid film dryout modeling in annular flow was presented. It led to the development of the three-equation model based on consideration of liquid mass balance in the film, a two-phase mixture in the core and gas. The results of experimental validation of the model exhibit improvement in comparison to other models from literature.

Studies on Gas-Phase Turbulence Modification in Vertical Upward Annular Flow

2003 ◽  
Author(s):  
Kenji Yoshida ◽  
Hidenobu Tanaka ◽  
Keizo Matsuura ◽  
Isao Kataoka
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Gas Phase ◽  
Annular Flow ◽  
Film Flow ◽  
Velocity Profiles ◽  
Fluctuation Velocity ◽  
Turbulence Modification ◽  
Liquid Film Flow ◽  
Wavy Interface

Experimental and numerical studies were made to investigate the effects of wavy interface on the liquid film to gas-phase turbulence modification of air-water annular flow in a vertically arranged round tube. By using the constant temperature hotwire anemometer, time-averaged axial velocity profiles, turbulence fluctuation profiles, energy spectrum and auto-correlation coefficient for fluctuation velocity component of gas-phase axial velocity were precisely measured. The liquid film thickness was also measured by using point-electrode resistivity probe to make clear the time-averaged liquid film thickness and wave height moving on the liquid film. Direct observations using high speed video camera were also added to make clear the dynamic behavior and propergating velocity of ripple or disturbance waves on liquid film flow. Numerical simulations for gas-phase turbulence in annular flow considering the effect of wavy interface of liquid film flow were also carried out. Liquid film flow was modeled to be the wall surface roughness of interfacial wave height moving with the interfacial velocity. The roughness and moving velocity of the modeled liquid film for computational condition were provided by the present experimental results. Time-averaged velocity profiles and fluctuation velocity profiles were calculated with standard k-ε model. Numerical results were generally consistent with the experimental results obtained in the present study.

Towards the Understanding of Transformation of Annular to Droplet-Annular Gas-Liquid Flow

2016 ◽  
Author(s):  
Parmod Kumar ◽  
Sushanta K. Mitra ◽  
Arup Kumar Das
Keyword(s):  
Liquid Film ◽  
Gas Phase ◽  
Gaseous Phase ◽  
Annular Flow ◽  
Clear Understanding ◽  
Gravitational Acceleration ◽  
Liquid Droplets ◽  
Two Phase ◽  
Phase Velocities ◽  
Gas Liquid Flow

Annular flow and its deviations due to change of phase velocities in parallel and counter flows are very common in many adiabatic and non-adiabatic applications of two phase flow. The transformation from annular flow to its counterpart droplet-annular flow is often poorly understood as it needs to handle multi scale interfaces experimentally or numerically. In the present work, attempts have been made to capture both wavy annular interface and dynamics of tiny droplets throughout its life cycle using grid based volume of fluid framework. 3-D simulation domain with length (L)/diameter (D) ratio as 6 is considered under the effect of gravitational acceleration and phase inertial field. Wavy interface is observed numerically between the phases using phase fraction contours along with the occurrence of three very interesting phenomena, which include rolling, undercutting and orificing. At low liquid and gas velocities orificing has been observed which restricts the path of gaseous phase. Departure from the orificing phenomenon has been seen at higher gas phase velocities which transforms to other phenomenon called rolling. Rolling is the folding of liquid film by the high velocity gaseous phase towards the radially outward direction. Further, increase in liquid phase velocities above gaseous phase velocities results in undercutting of liquid film by the gas phase. Moreover the liquid droplets can be seen in the entire phenomenon through the gas phase in the core of the tube. We presented a regime map of gas liquid velocities to segregate clear understanding of annular to droplet-annular flow due to orificing, rolling and undercutting. The present study will enrich the knowledge of multiphase flow transportation in process plants, chemical reactors, nuclear reactors and refineries where gas-liquid annular flow is most widely used flow pattern.

scholarly journals Liquid Film Flow Phenomena in Upwards Two-Phase Annular Flow

1973 ◽  
Vol 39 (317) ◽  
pp. 313-323 ◽  
Author(s):  
Kotohiko SEKOGUCHI ◽  
Kaneyasu NISHIKAWA ◽  
Masao NAKASATOMI ◽  
Hidetoshi NISHI ◽  
Akira KANEUZI
Keyword(s):  
Liquid Film ◽  
Annular Flow ◽  
Film Flow ◽  
Two Phase ◽  
Flow Phenomena ◽  
Liquid Film Flow

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.

Experimental Determination of Statistical Properties of Two-Phase Turbulent Motion

1960 ◽  
Vol 82 (3) ◽  
pp. 609-621 ◽  
Author(s):  
S. L. Soo ◽  
H. K. Ihrig ◽  
A. F. El Kouh
Keyword(s):  
Gas Phase ◽  
Tracer Diffusion ◽  
Statistical Properties ◽  
Solid Particles ◽  
Turbulent Motion ◽  
Two Phase ◽  
Gaseous State ◽  
Diffusion Technique ◽  
And Diffusion

Experimental methods for the determination of certain statistical properties of turbulent conveyance and diffusion of solid particles in a gaseous state are presented. Methods include a tracer-diffusion technique for the determination of gas-phase turbulent motion and a photo-optical technique for the determination of motion of solid particles. Results are discussed and compared with previous analytical results.

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