Thermodynamics of Void Fraction in Saturated Flow Boiling

2005 ◽  
Vol 128 (6) ◽  
pp. 611-615 ◽  
Author(s):  
Francisco J. Collado ◽  
Carlos Monné ◽  
Antonio Pascau ◽  
Daniel Fuster ◽  
Andrés Medrano
Keyword(s):  
Void Fraction ◽  
Heat Balance ◽  
Flow Boiling ◽  
Essential Element ◽  
Saturated Flow ◽  
Two Phase ◽  
Slip Ratio ◽  
Flow Quality ◽  
The 1960S ◽  
Thermodynamic Quality

Recently, Collado (Proc, IMECE 2001, Symposium on Fluid Physics and Heat Transfer for Macro- and Micro-Scale Gas-Liquid and Phase Change Flows) suggested calculating void fraction, an essential element in thermal-hydraulics, working with the “thermodynamic” quality instead of the usual “flow” quality. The “thermodynamic” quality is a state variable, which has a direct relation with the actual vapor volumetric fraction, or void fraction, through phase densities. This approach provides a procedure for predicting void fraction, if values of “thermodynamic” quality are available. However, the standard heat balance is usually stated as a function of the “flow” quality. Therefore, we should search for a new heat balance between the mixture enthalpy, based on “thermodynamic” quality, and the absorbed heat. This paper presents the results of such analysis based on the accurate measurements of the outlet void fraction measured during the Cambridge project by Knights (1960, “A Study of Two-Phase Pressure Drop and Density Determination in a High-Pressure Steam-Water Circuit,” Ph.D. thesis, Cambridge University Engineering Lab, Cambridge, UK) in the 1960s for saturated flow boiling. In the 286 tests analyzed, the pressure and mass fluxes range from 1.72 MPa to 14.48 MPa and from 561.4 to 1833.33 kgm−2s−1, respectively. As the main result, we find that the slip ratio would close this new thermodynamic heat balance. This has allowed the accurate calculation of void fraction from this balance, provided we can predict the slip ratio. Finally, the strong connection of this new thermodynamic heat balance with the standard one through the slip ratio is highlighted.

INVESTIGATION ON VOID FRACTION FOR TWO-PHASE FLOW PRESSURE DROP OF EVAPORATIVE R-290 IN HORIZONTAL TUBE

2016 ◽  
Vol 78 (8-4) ◽  
Author(s):  
Agus Sunjarianto Pamitran ◽  
Sentot Novianto ◽  
Normah Mohd-Ghazali ◽  
Nasruddin Nasruddin ◽  
Raldi Koestoer
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Homogeneous Model ◽  
Saturation Temperature ◽  
Horizontal Tube ◽  
Phase Flow ◽  
Two Phase ◽  
Experimental Conditions

Two-phase flow boiling pressure drop experiment was conducted to observe its characteristics and to develop a new correlation of void fraction based on the separated model. Investigation is completed on the natural refrigerant R-290 (propane) in a horizontal circular tube with a 7.6 mm inner diameter under experimental conditions of 3.7 to 9.6 °C saturation temperature, 10 to 25 kW/m2 heat flux, and 185 to 445 kg/m2s mass flux. The present experimental data was used to obtain the calculated void fraction which then was compared to the predicted void fraction with 31 existing correlations. A new void fraction correlation for predicting two-phase flow boiling pressure drop, as a function of Reynolds numbers, was proposed. The measured pressure drop was compared to the predicted pressure drop with some existing pressure drop models that use the newly developed void fraction model. The homogeneous model of void fraction showed the best prediction with 2% deviation

Two-Phase Flow Modeling in a Pipe Related to Flow-Induced Vibration

2005 ◽  
Author(s):  
W. G. Sim ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Void Fraction ◽  
Power Law ◽  
Slug Flow ◽  
Momentum Flux ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Fluid Dynamic ◽  
Phase Flow ◽  
Two Phase ◽  
Slip Ratio

To understand the fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. The distributions of flow parameters across a pipe, such as gas velocity, liquid velocity and void fraction, may be assumed to follow a power law (Cheng 1998, Serizawa et al. 1975). The void fraction profile is, for example, uniform for bubbly flow while it is more or less parabolic for slug flow. In the present work, the average values of momentum flux, slip ratio, etc. are derived by integral analysis, based on approximate power law distributions. A parametric study with various distributions was performed. The existing empirical formulations for average void fraction, proposed by Wallis (1969), Zuber et al. (1967) and Ishii (1970), are considered to obtain the present results. In particular, the unsteady momentum flux for slug flow is approximated.

Experimental Investigation of Two Phase Flow in Micro-Sized Circular Tubes

2012 ◽  
Author(s):  
Y. S. Lim ◽  
Simon C. M. Yu
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Transitional Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Slip Ratio ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Glass Tubes ◽  
Flux Model

Single phase and two phase flow characteristics in micro-sized glass tubes with i.d. (inner diameter) of 300 and 500 μm have been examined experimentally. Single phase pressure drop measurements are found generally in good agreement with Poiseulle flow theory. Transitional flow is found to start earlier at Reynolds number about 1600 as compared to the onset of transitional flow at Reynolds number of 2300 for macro-scale tubes. In addition, these glass tubes are employed for the investigation of adiabatic two phase flow characteristic by introducing gas phase via a stainless steel tube inserted at the center of the glass tube. Real time flow visualization obtained under the same flow condition are analyzed by both cross sectional void fraction (one dimensional drift flux model) and volumetric void fraction (image processing method). The analysis shows that the void fraction estimated by drift flux model (DFM) agrees with homogeneous correlation (α = β) and Armand correlation (α = 0.833β). However image processing method seems to reveal that the slip ratio for the two phase flow is more significant and that the void fraction results are clustering between slip ratio of 3 and 7. Additionally, two phase frictional pressure losses are compared with the convention correlation for macro-sized tube (Lockhart-Martinelli model). It is found that measurements of the two phase frictional pressure drop can serve as a flow map to predict the flow patterns when the flow in the channel is not transparent.

Calibration of a Fast Neutron Scattering Technique for Measurement of Void Fraction in Rod Bundles

1979 ◽  
Vol 101 (2) ◽  
pp. 295-299 ◽  
Author(s):  
S. Banerjee ◽  
P. Yuen ◽  
M. A. Vandenbroek
Keyword(s):  
Neutron Flux ◽  
Fast Neutron ◽  
Void Fraction ◽  
Transient Flow ◽  
Phase Distribution ◽  
Flow Boiling ◽  
Rod Bundles ◽  
Two Phase ◽  
Scattering Technique ◽  
Flow Through

A technique based on scattering and transmission of fast neutron beams has been developed for measuring void fraction in two-phase flow through rod bundles. Experiments indicate that the scattered neutron flux varies linearly with void fraction and is largely independent of phase distribution. Measurements of the transmitted neutron flux have been used to determine phase distribution (or flow regime). The technique gives good sensitivity and count rates and appears suitable for void fraction and phase distribution measurements in transient flow boiling.

An Appraisal of System Mean Void Fraction and Its Application for the Moving Boundary Simulation of Phase-Change Heat Exchangers

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
S. P. Datta ◽  
R. K. Chandra ◽  
P. K. Das
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Void Fraction ◽  
Heat Exchangers ◽  
Moving Boundary ◽  
Transport Processes ◽  
Closed Form Expression ◽  
Two Phase ◽  
Slip Ratio ◽  
Wide Range

In gas–liquid two-phase flow, void fraction is the most unique parameter which influences all the transport processes. In the most general case, though the void fraction varies nonlinearly with the channel length, many practical simulations make use of the “system mean void fraction.” The present investigation makes a critical assessment of different system mean void fraction models for a wide range of slip velocity and density difference between the phases. To this end, different correlations for slip ratio have been considered and, for all the cases, closed form expression for the system mean void fraction has been presented. The local as well as the system mean void fractions have also been estimated numerically from a heat transfer based model. Predictions from the heat transfer based model and the slip ratio based model have been compared. As an application, the slip ratio based system mean void fraction is used in to build the moving boundary model for phase-change heat exchangers. The prediction of startup transients for both an evaporator and a condenser of an automotive air conditioning system (AACS) agrees well with the experimental results.

TWO-PHASE PRESSURE DROP AND VOID FRACTION DURING FLOW BOILING OF ISO-OCTANE

2007 ◽  
Vol 19 (3) ◽  
pp. 211-223 ◽  
Author(s):  
Vishwas V. Wadekar ◽  
K. M. Miller ◽  
M. E. D. Urso
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Boiling ◽  
Two Phase ◽  
Phase Pressure
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