Pressure Drop During Condensation in Microchannels

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Hua Sheng Wang ◽  
Jie Sun ◽  
John W. Rose
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Void Fraction ◽  
Annular Flow ◽  
Gradient Methods ◽  
Pressure Gradients ◽  
High Quality ◽  
Friction Pressure ◽  
Flow Condensation ◽  
Approximate Equations

The paper reports calculations of friction pressure gradient for the special case of laminar annular flow condensation in microchannels. This is the only flow regime permitting theoretical solution without having recourse to experimental data. Comparisons are made with correlations based on experimental data for R134a. The correlations differ somewhat among themselves with the ratio of highest to lowest predicted friction pressure gradient typically around 1.4 and nearer to unity at high quality. The friction pressure gradients given by the laminar annular flow solutions are in fair agreement with the correlations at high quality and lower than the correlations at lower quality. Attention is drawn to the fact that the friction pressure gradient cannot be directly observed and its evaluation from measurements requires estimation of the nondissipative momentum or acceleration pressure gradient. Methods used to estimate the nondissipative pressure gradient require quality and void fraction together with equations which relate these and whose accuracy is difficult to quantify. Quality and void fraction can be readily found from the laminar annular flow solutions. Significant differences are found between these and values from approximate equations.

Pressure Drop During Condensation in Microchannels

2012 ◽  
Author(s):  
H. S. Wang ◽  
J. W. Rose
Keyword(s):  
Pressure Drop ◽  
Pressure Gradient ◽  
Void Fraction ◽  
Annular Flow ◽  
Pressure Gradients ◽  
Flow Solution ◽  
Approximate Models ◽  
Significant Difference ◽  
Friction Pressure ◽  
Flow Pressure

The paper examines the special case of annular laminar flow pressure drop, or more precisely pressure gradient, during condensation in microchannels. This is the only flow regime permitting wholly theoretical solution without having recourse to experimental data. Solutions are obtained and comparisons made with empirical formulae for void fraction (needed to calculate the momentum pressure gradient) when obtaining the friction pressure gradient from experimentally measured or “total” pressure gradient. To date calculations and comparisons are restricted to one fluid (R134a), one channel section and one flow condition. For the case considered it is found that earlier approximate models for estimating void fraction agree quite well with the theoretical annular flow solutions. There is, however, significant difference between momentum pressure gradients obtained from approximate models used in the earlier investigations and that given by the theoretical annular flow solution which is (numerically) higher than all of them. The annular flow solution indicates that the momentum pressure gradient is not small in comparison with the friction pressure gradient. The friction pressure gradient in the annular flow case is appreciably smaller than given by the earlier correlations.

Velocity and Temperature Profiles in Turbulent Boundary Layer Flows Experiencing Streamwise Pressure Gradients

1997 ◽  
Vol 119 (3) ◽  
pp. 433-439 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Velocity Profiles ◽  
Temperature Profiles ◽  
Pressure Gradients ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Prandtl Numbers ◽  
Energy Equations ◽  
Near Wall

The standard turbulent law of the wall, devised for zero pressure gradient flows, has been previously shown to be inadequate for accelerating and decelerating turbulent boundary layers. In this paper, formulations for mean velocity profiles from the literature are applied and formulations for the temperature profiles are developed using a mixing length model. These formulations capture the effects of pressure gradients by including the convective and pressure gradient terms in the momentum and energy equations. The profiles which include these terms deviate considerably from the standard law of the wall; the temperature profiles more so than the velocity profiles. The new profiles agree well with experimental data. By looking at the various terms separately, it is shown why the velocity law of the wall is more robust to streamwise pressure gradients than is the thermal law of the wall. The modification to the velocity profile is useful for evaluation of more accurate skin friction coefficients from experimental data by the near-wall fitting technique. The temperature profile modification improves the accuracy with which one may extract turbulent Prandtl numbers from near-wall mean temperature data when they cannot be determined directly.

Effect of Drag-Reducing Agents in Multiphase Flow Pipelines

1998 ◽  
Vol 120 (1) ◽  
pp. 15-19 ◽  
Author(s):  
C. Kang ◽  
R. M. Vancko ◽  
A. S. Green ◽  
H. Kerr ◽  
W. P. Jepson
Keyword(s):  
Multiphase Flow ◽  
Pressure Gradient ◽  
Slug Flow ◽  
Annular Flow ◽  
Flow Regimes ◽  
Reducing Agents ◽  
Pressure Gradients ◽  
Horizontal Pipes ◽  
Flow Pressure ◽  
Inclined Pipes

The effect of drag-reducing agents (DRA) on pressure gradient and flow regime has been studied in horizontal and 2-deg upward inclined pipes. Experiments were conducted for different flow regimes in a 10-cm i.d., 18-m long plexiglass system. The effectiveness of DRA was examined for concentrations ranging from 0 to 75 ppm. Studies were done for superficial liquid velocities between 0.03 and 1.5 m/s and superficial gas velocities between 1 and 14 m/s. The results indicate that DRA was effective in reducing the pressure gradients in single and multiphase flow. The DRA was more effective for lower superficial liquid and gas velocities for both single and multiphase flow. Pressure gradient reductions of up to 42 percent for full pipe flow, 81 percent for stratified flow, and 35 percent for annular flow were achieved in horizontal pipes. In 2 deg upward inclination, the pressure gradient reduction for slug flow, with a concentration of 50 ppm DRA, was found to be 28 and 38 percent at superficial gas velocities of 2 and 6 m/s, respectively. Flow regimes maps with DRA were constructed in horizontal pipes. Transition to slug flow with addition of DRA was observed to occur at higher superficial liquid velocities.

Modeling of Interfacial Component for Two-Phase Frictional Pressure Gradient in Microchannels and Minichannels

2011 ◽  
Author(s):  
M. M. Awad ◽  
Y. S. Muzychka
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Single Phase ◽  
Simple Approach ◽  
Phase Flow ◽  
Pressure Gradients ◽  
Two Phase ◽  
Interfacial Pressure ◽  
Proposed Model ◽  
Phase Liquid

A simple approach for calculating the interfacial component of frictional pressure gradient in two-phase flow in microchannels and minichannels is presented. This approach is developed using superposition of three pressure gradients: single-phase liquid, single-phase gas, and interfacial pressure gradient. The proposed model can be transformed in two different ways. First, two-phase interfacial multiplier for liquid flowing alone (φl,i2) as a function of two-phase frictional multiplier for liquid flowing alone (φl2) and the Lockhart-Martinelli parameter, X. Second, two-phase interfacial multiplier for gas flowing alone (φg,i2) as a function of two-phase frictional multiplier for gas flowing alone (φg2) and the Lockhart-Martinelli parameter, X. This proposed model allows for the interfacial pressure gradient to be easily modeled. Comparisons of the proposed model with experimental data for microchannels and minichannels and existing correlations for both φl and φg versus X are presented.

Prediction of Annulus Pressure Gradients in Pumping Wells

1980 ◽  
Vol 102 (4) ◽  
pp. 181-183 ◽  
Author(s):  
Zˇ. Schmidt ◽  
J. P. Brill ◽  
H. D. Beggs
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Physical Model ◽  
Physical Property ◽  
Pressure Gradients ◽  
Concentric Annulus ◽  
Pumping Wells ◽  
Adequate Representation ◽  
Gas Bubbling ◽  
S Curve

Experimental data on pressure gradients were obtained for gas bubbling through static liquids in various concentric annulus configurations with eight different liquids. Although a definite liquid physical property effect exists, the Gilbert “S” curve gave an adequate representation of the data. A more accurate correlation was developed, together with a physical model that separates hydrostatic and friction components of the pressure gradient.

Paper 35: The Influence of Mass Velocity on Friction Pressure Gradients during Steam-Water Flow

1967 ◽  
Vol 182 (8) ◽  
pp. 336-341 ◽  
Author(s):  
D. Chisholm
Keyword(s):  
Pressure Gradient ◽  
Critical Point ◽  
Water Flow ◽  
Mass Velocity ◽  
Pressure Gradients ◽  
Friction Pressure ◽  
Velocity Effect

From analysis of data for the flow of steam-water mixtures in tubes at pressures between 3 MN/m2 [435 lb/in2 (abs.)] and 17·5 MN/m2 [2540 lb/in2 (abs.)] equations for friction pressure gradient are developed. These equations allow for the influence of the ‘mass velocity effect’, not previously allowed for in accepted correlations. The equations are in a form making them applicable at the critical point, and are compared with the data of Miropolskii, Isbin, and Berkowitz for steam-water flow.

A General Heat Transfer Correlation for Annular Flow Condensation

1968 ◽  
Vol 90 (2) ◽  
pp. 267-274 ◽  
Author(s):  
M. Soliman ◽  
J. R. Schuster ◽  
P. J. Berenson
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Annular Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Transfer Process ◽  
Heat Transfer Correlation ◽  
Wide Range ◽  
Prandtl Numbers ◽  
Flow Condensation

The interaction between friction, momentum, and gravity, as they affect the heat transfer process during annular flow condensation inside tubes, is studied. Analytical forms for each of these forces are derived and incorporated in a correlation that predicts the local heat transfer coefficient. The predictions agree well with the available experimental data over a wide range of vapor velocities and over a range of Prandtl numbers from 1 to 10. The analysis also yields a means for predicting the onset of liquid run-back in the presence of an adverse gravitational field.

A Numerical Investigation on the Development of an Embedded Streamwise Vortex in a Turbulent Boundary Layer With Spanwise Pressure Gradient

2001 ◽  
Vol 123 (3) ◽  
pp. 551-558 ◽  
Author(s):  
InSub Lee ◽  
Hong Sun Ryou ◽  
Seong Hyuk Lee ◽  
Ki Bae Hong ◽  
Soo Chae
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Three Dimensional ◽  
Simple Algorithm ◽  
Streamwise Vortex ◽  
Pressure Gradients ◽  
Reynolds Stresses ◽  
Turbulent Structures

It is the aim of this article to investigate numerically the effects of spanwise pressure gradient on an embedded streamwise vortex in a turbulent boundary layer. The governing equations were discretized by the finite volume method and SIMPLE algorithm was used to couple between pressure and velocity. The LRR model for Reynolds stresses was utilized to predict the anisotropy of turbulence effectively. The validation was done for two cases: one is the development of a streamwise vortex embedded in a pressure-driven, three-dimensional turbulent boundary layer. The other involves streamwise vortex pairs embedded in a turbulent boundary layer without the spanwise pressure gradient. In the case of the former, the predicted results were compared with Shizawa and Eaton’s experimental data. In the latter case, the calculated results were compared against the experimental data of Pauley and Eaton. We performed numerical simulations for three cases with different values of spanwise pressure gradient. As a result, the primary streamwise vortex with spanwise pressure gradients decays more rapidly than the case with no pressure gradients, as the spanwise pressure gradient increases. This indicates that the spanwise pressure gradient may play an important role on mean and turbulent structures. In particular, it can be seen that the increase of pressure gradient enhances a level of turbulent normal stresses.

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