A Predictive Model for Condensation in Small Hydraulic Diameter Tubes Having Axial Micro-Fins

1997 ◽  
Vol 119 (4) ◽  
pp. 776-782 ◽  
Author(s):  
C.-Y. Yang ◽  
R. L. Webb
Keyword(s):  
Surface Tension ◽  
Mass Velocity ◽  
Surface Tension Force ◽  
Hydraulic Diameter ◽  
High Mass ◽  
Semiempirical Model ◽  
Condensation Coefficient ◽  
Asymptotic Equation ◽  
Cross Sectional ◽  
R 134A

A semiempirical model is proposed to predict the condensation coefficient inside small hydraulic diameter extruded aluminum tubes having microgrooves. The model accounts for the effects of vapor shear and surface tension forces. Surface tension force is effective in enhancing the condensation coefficient as long as the fin tips are not flooded by condensate. This enhancement increases as mass velocity is reduced. At high mass velocity the flow is vapor shear controlled and the surface tension contribution is very small. The surface tension effect is strongly affected by the fin geometry. A smaller fin tip radius provides a higher surface tension drainage force. A large cross sectional area in the interfin region will allow the surface tension enhancement to occur at lower vapor quality. Separate models are developed for the surface tension and vapor shear controlled regimes and the models are combined in the form of an asymptotic equation. The vapor shear model is based on use of an equivalent mass velocity and the heat-momentum transfer analogy. The surface tension model is analytically based. The model is validated by predicting the authors data for two tube geometries using R-12 and R-134a, and the model predicts 95 percent of the condensation data within ±16 percent.

Prediction of the Condensation Coefficient on Horizontal Integral-Fin Tubes

1985 ◽  
Vol 107 (2) ◽  
pp. 369-376 ◽  
Author(s):  
R. L. Webb ◽  
T. M. Rudy ◽  
M. A. Kedzierski
Keyword(s):  
Surface Tension ◽  
Theoretical Model ◽  
Surface Tension Force ◽  
Tension Force ◽  
Condensation Coefficient ◽  
Film Drainage ◽  
Predicted Values ◽  
Experimental Values ◽  
Fin Tubes

A theoretical model is developed for prediction of the condensation coefficient on horizontal integral-fin tubes for both high and low surface tension fluids. The model includes the effects of surface tension on film drainage and on condensate retention between the fins. First, the fraction of the tube circumference that is flooded with condensate is calculated. Typically, the condensation coefficient in the flooded region is negligible compared to that of the unflooded region. Then the condensation coefficient on the unflooded portion is calculated, assuming that surface tension force drains the condensate from the fins. The model is used to predict the R-11 condensation coefficient on horizontal, integral-fin tubes having 748, 1024, and 1378 fpm. The predicted values are within ±20 percent of the experimental values.

scholarly journals Comparison of Surface Tension Models for the Volume of Fluid Method

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 542 ◽  
Author(s):  
Kurian J. Vachaparambil ◽  
Kristian Etienne Einarsrud
Keyword(s):  
Surface Tension ◽  
Multiphase Flow ◽  
Capillary Rise ◽  
Surface Tension Force ◽  
Surface Force ◽  
Parallel Plates ◽  
Time Step ◽  
Mesh Resolution ◽  
Active Research ◽  
Spurious Currents

With the increasing use of Computational Fluid Dynamics to investigate multiphase flow scenarios, modelling surface tension effects has been a topic of active research. A well known associated problem is the generation of spurious velocities (or currents), arising due to inaccuracies in calculations of the surface tension force. These spurious currents cause nonphysical flows which can adversely affect the predictive capability of these simulations. In this paper, we implement the Continuum Surface Force (CSF), Smoothed CSF and Sharp Surface Force (SSF) models in OpenFOAM. The models were validated for various multiphase flow scenarios for Capillary numbers of 10 − 3 –10. All the surface tension models provide reasonable agreement with benchmarking data for rising bubble simulations. Both CSF and SSF models successfully predicted the capillary rise between two parallel plates, but Smoothed CSF could not provide reliable results. The evolution of spurious current were studied for millimetre-sized stationary bubbles. The results shows that SSF and CSF models generate the least and most spurious currents, respectively. We also show that maximum time step, mesh resolution and the under-relaxation factor used in the simulations affect the magnitude of spurious currents.

An Experimental Investigation of Flow Boiling Characteristics in a Single Transparent Heated Microtube

2009 ◽  
Author(s):  
Osamu Kawanami ◽  
Shih-Che Huang ◽  
Kazunari Kawakami ◽  
Itsuro Honda ◽  
Yousuke Kawashima ◽  
...  
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Mass Velocity ◽  
Tube Wall ◽  
Flow Boiling ◽  
High Mass ◽  
Test Fluid ◽  
High Heat Flux ◽  
Gold Plating ◽  
Heated Tube

In the present study, flow boiling in a transparent heated microtube having a diameter of 1 mm was investigated in detail. The transparent heated tube was manufactured by the electroless gold plating method. The enclosed gas-liquid interface could be clearly recognized through the tube wall, and the inner wall temperature measurement and direct heating of the film were simultaneously conducted by using the tube. Deaerated and deionized water that was subcooled temperature of 15 K was used as a test fluid, and constant and stable mass velocities of 50, 100, and 200 kg/m2s were provided by using a twin plunger pump. Among our experimental results, a vapor bubble grew up in a direction opposite the flow at a low heat flux and low mass velocities; however, this flow pattern was not observed at a high mass velocity of 200 kg/m2s. Under the conditions of G = 50 kg/m2s and high heat flux, the liquid film surrounding an elongated bubble near the heated tube wall occasionally thickened partially. The inner wall temperature exhibited large random oscillations in this regime; however, the visual observation revealed that dry-patches did not occur. The mass velocity had a negligible effect on the boiling heat transfer except in the counter-growth bubble flow regime.

Effects of surface tension and intraluminal fluid on mechanics of small airways

1997 ◽  
Vol 82 (1) ◽  
pp. 233-239 ◽  
Author(s):  
Mark J. Hill ◽  
Theodore A. Wilson ◽  
Rodney K. Lambert
Keyword(s):  
Surface Tension ◽  
Bending Stiffness ◽  
Liquid Interface ◽  
Cross Sectional Area ◽  
Pressure Curve ◽  
Small Airways ◽  
Sectional Area ◽  
Cross Sectional ◽  
Inner Surface ◽  
Air Liquid Interface

Hill, Mark J., Theodore A. Wilson, and Rodney K. Lambert.Effects of surface tension and intraluminal fluid on the mechanics of small airways. J. Appl. Physiol.82(1): 233–239, 1997.—Airway constriction is accompanied by folding of the mucosa to form ridges that run axially along the inner surface of the airways. The muscosa has been modeled (R. K. Lambert. J. Appl. Physiol. 71: 666–673, 1991) as a thin elastic layer with a finite bending stiffness, and the contribution of its bending stiffness to airway elastance has been computed. In this study, we extend that work by including surface tension and intraluminal fluid in the model. With surface tension, the pressure on the inner surface of the elastic mucosa is modified by the pressure difference across the air-liquid interface. As folds form in the mucosa, intraluminal fluid collects in pools in the depressions formed by the folds, and the curvature of the air-liquid interface becomes nonuniform. If the amount of intraluminal fluid is small, <2% of luminal volume, the pools of intraluminal fluid are small, the air-liquid interface nearly coincides with the surface of the mucosa, and the area of the air-liquid interface remains constant as airway cross-sectional area decreases. In that case, surface energy is independent of airway area, and surface tension has no effect on airway mechanics. If the amount of intraluminal fluid is >2%, the area of the air-liquid interface decreases as airway cross-sectional area decreases, and surface tension contributes to airway compression. The model predicts that surface tension plus intraluminal fluid can cause an instability in the area-pressure curve of small airways. This instability provides a mechanism for abrupt airway closure and abrupt reopening at a higher opening pressure.

Inward Flow of Micro-Particles in an Evaporating Di-Dispersed Colloid Droplet on Hydrophilic Surface

2009 ◽  
Author(s):  
Jung-Yeul Jung ◽  
Young Won Kim ◽  
Jung Yul Yoo
Keyword(s):  
Surface Tension ◽  
Contact Line ◽  
Surface Tension Force ◽  
Nano Particles ◽  
Tension Force ◽  
Hydrophilic Surface ◽  
Micro Particles

It is well known that the liquid and the nanoparticles in an evaporating colloid droplet on the hydrophilic surface move radially outward for the contact line to maintain its position. However, the motion of micro-/nano-particles in an evaporating di-dispersed colloid droplet has not been reported to date. In this study, an experiment on an evaporating di-dispersed colloid droplet on the hydrophilic surface is carried out. It is found that nano-particles move radially outward and remain at the contact line while micro-particles move inward toward the center of the droplet. Further the mechanism of the micro-particles moving toward the center of the droplet is found to be due to the surface tension force of the liquid.

scholarly journals How do galaxies build up their spin in the cosmic web?

2014 ◽  
Vol 11 (S308) ◽  
pp. 433-436
Author(s):  
Charlotte Welker ◽  
Yohan Dubois ◽  
Christophe Pichon ◽  
Julien Devriendt ◽  
Sebastien Peirani
Keyword(s):  
Mass Velocity ◽  
Velocity Dispersion ◽  
High Mass ◽  
Spin Orientation ◽  
Star Forming ◽  
Blue Star ◽  
Physical Mechanisms ◽  
Low Mass ◽  
Mass Dependent

AbstractUsing the Horizon-AGN simulation we find a mass dependent spin orientation trend for galaxies: the spin of low-mass, rotation-dominated, blue, star-forming galaxies are preferentially aligned with their closest filament, whereas high-mass, velocity dispersion- supported, red quiescent galaxies tend to possess a spin perpendicular to these filaments. We explore the physical mechanisms driving galactic spin swings and quantify how much mergers and smooth accretion re-orient them relative to their host filaments.

Cavitation of a viscous fluid in narrow passages

1963 ◽  
Vol 16 (4) ◽  
pp. 595-619 ◽  
Author(s):  
G. I. Taylor
Keyword(s):  
Surface Tension ◽  
Viscous Fluid ◽  
Hydrodynamic Lubrication ◽  
Surface Tension Force ◽  
Physical Description ◽  
Bubble Cavitation ◽  
Oil Flow ◽  
Hydrodynamic Separation ◽  
Flow Through ◽  
Air Column

The conditions which determine the existence and position of cavitation in the narrow passages of hydrodynamically lubricated bearings have been assumed to be the same as those which produce cavitation bubbles, namely a lowering of pressure below that at which gas separates out of fluid. This assumption enables certain predictions to be made which in some cases are verified, but it does not provide a physical description of the interface between oil and air. Theoretical analysis of the situation seems to be beyond our present capacity, and in none of the experiments so far published has it been possible to measure both the most important relevant data, namely the minimum clearance and the oil flow through it.A method is described here which enables this to be done. It turns out that two physically different kinds of cavitation can occur. One of these is well described by the existing theory and assumption. Surface tension plays no part in it, and in most text books on hydrodynamic lubrication is not even mentioned. The other kind, which is akin to hydrodynamic separation rather than bubble cavitation, depends essentially on surface tension. Both kinds appear clearly in published photographs taken through transparent bearings, but the experimenters do not seem to have distinguished between them.The reason why surface tension, which is only able to supply stresses that are exceedingly small compared with the pressure variation in the fluid itself, may have a large effect on the flow can be understood by considering the flow of a viscous fluid in a tube when blown out by air pressure applied at one end. For any given length of fluid the rate of outflow depends almost entirely on the pressure applied, the surface tension force being negligible; but the amount of fluid left in the tube after the air column has reached the end depends essentially on surface tension.

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