Two-Phase Frictional Pressure Loss in Horizontal Bubbly Flow with 90-Degree Bend

2006 ◽  
Author(s):  
Seungjin Kim ◽  
Jung Han Park ◽  
Gunol Kojasoy ◽  
Joseph Kelly
Keyword(s):  
Pressure Drop ◽  
Pressure Loss ◽  
Two Phase Flow ◽  
Bubbly Flow ◽  
Glass Tube ◽  
Axial Direction ◽  
Phase Flow ◽  
Local Pressure ◽  
Two Phase ◽  
Phase Pressure

The two-phase pressure drop due to the minor loss in horizontal bubbly two-phase flow is studied. In particular, geometric effects of a 90-degree elbow is of interest in the present study. Experiments are performed in air-water two-phase flow near atmospheric pressure condition in round glass tube with inner diameter of 50.3mm. Along the test section, 90-degee elbow is installed at L/D = 206.6 from the two-phase mixture inlet. Experiments are performed in 15 different flow conditions and the local static pressures are measured at five axial locations. Characteristic pressure drop due to the elbow is clearly demonstrated in the profiles of local pressure data along the axial direction. It is also found that the elbow effect propagates and is more significant further downstream than immediate downstream of the elbow. The overall two-phase frictional pressure loss between L/D = 0 and 329 can be predicted well with the Lockhart-Martinelli correlation with parameter C = 25, which is higher than the generally accepted value of C = 20. A correlation for the two-phase pressure loss, including the minor loss due to the 90-degree elbow is developed by employing the approach analogous to that of Lockhart-Martinelli’s. The newly developed correlation suggests that the modified parameter, C = 65 fits best with the experimental data. In addition, the two-phase minor loss factor for the 90-degree elbow is found to be k = 0.58, 50% higher than that recommended for single-phase flow.

Experimental Study on Resistance Characteristics in a 3 × 3 Rod Bundle

2014 ◽  
Author(s):  
Chaoxing Yan ◽  
Changqi Yan ◽  
Licheng Sun ◽  
Yang Wang
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Local Resistance ◽  
Local Pressure ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Rod Bundle

Experimental study on resistance of air-water two-phase flow in a vertical 3 × 3 rod bundle was carried out under normal temperature and pressure. The rod diameter and pitch were 8 mm and 11 mm, respectively. The ranges of gas and liquid superficial velocity were 0.013∼3.763 m/s and 0.076∼1.792 m/s, respectively. The result indicated that the existing correlations for calculating frictional coefficient in the rod bundle and local resistance coefficient could not give favorable predictions on the single-phase experimental data. For the case of two-phase flow, eight correlations for calculating two-phase equivalent viscosity poorly predicted the frictional pressure drop, with the mean absolute errors around 60%. Meanwhile, the eight classical two-phase viscosity formulae were evaluated against the local pressure drop at spacer grid. It is shown that Dukler model predicted the experimental data well in the range of Rel<9000 while McAdams correlation was the best for Rel⩾9000. For all the experimental data, Dukler model provided the best prediction with MRE of 29.03%. Furthermore, approaches to calculate two-phase frictional pressure drop and local resistance were proposed by considering mass quality, two-phase Reynolds number and densities in homogenous flow model, resulting in a good agreement with the experimental data.

Pressure Drop in a Capillary Tube in Boiling Two-Phase Flow

2003 ◽  
Author(s):  
Fumito Kaminaga ◽  
Baduge Sumith ◽  
Kunihito Matsumura
Keyword(s):  
Pressure Drop ◽  
Vapor Phase ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Capillary Tube ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
System Pressure ◽  
Phase Pressure

Two-phase pressure drop is experimentally examined in a flow boiling condition in a tube of diameter 1.45 mm using water in ranges of pressure from 10 to 100 kPa, mass flux from 18 to 152 kg/m2s, heat flux from 13 to 646 kW/m2, and exit quality from 0.02 to 0.77. Also, pressure drop in an adiabatic air-water two-phase flow is measured at atmospheric pressure using the same test section and mass flux ranges of liquid and gas as those in the flow boiling. Decreasing system pressure the pressure drop significantly increases at a given mass flux. Influence of vapor phase on the pressure drop is found to be large both in the adiabatic and the diabatic conditions. The frictional pressure drop correlation for the adiabatic two-phase flow is developed and applied to predict pressure drop in the flow boiling. But it cannot give satisfactory predictions. The Chisholm correlation calculating a two-phase pressure drop multiplier is modified to account the influence of vapor phase in a capillary tube and the modified correlation can predict the pressure drop in the flow boiling within an error of 20%.

scholarly journals Slug Regime Transitions in a Two-Phase Flow in Horizontal Round Pipe. CFD Simulations

2020 ◽  
Vol 10 (23) ◽  
pp. 8739
Author(s):  
Vitaly Sergeev ◽  
Nikolai Vatin ◽  
Evgeny Kotov ◽  
Darya Nemova ◽  
Svyatoslav Khorobrov
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Two Phase Flow ◽  
Stokes Equations ◽  
Bubbly Flow ◽  
Fluid Motion ◽  
Navier Stokes ◽  
Technical Solution ◽  
Phase Flow ◽  
Two Phase

The main objective of the study is to propose a technical solution integrated into the pipeline for the transition of the flow regime from slug to bubbly two-phase flow. The object of research is isothermal two-phase gas–Newtonian-liquid flow in a horizontal circular pipeline. There is local resistance in the pipe in the form of a streamlined transverse mesh partition. The mesh partition ensures the transition of the flow from the slug regime to the bubbly regime. The purpose of the study is to propose a technical solution integrated into the pipeline for changing the flow regime of a two-phase flow from slug to bubbly flow. The method of research is a simulation using computational fluid dynamics (CFD) numerical simulation. The Navier–Stokes equations averaged by Reynolds describes the fluid motion. The k-ε models were used to close the Reynolds-averaged Navier–Stokes (RANS) equations. The computing cluster «Polytechnic—RSK Tornado» was used to solve the tasks. The results of simulation show that pressure drop on the grid did not exceed 10% of the pressure drop along the length of the pipeline. The mesh partition transits the flow regime from slug to layered one, which will help to increase the service life and operational safety of a real pipeline at insignificant energy costs to overcome the additional resistance integrated into the pipeline.

scholarly journals A New Method to Experimentally Investigate Local Pressure Loss of Oil-Water Two-Phase Flow through Pore Throats

2020 ◽  
Vol 185 ◽  
pp. 01091
Author(s):  
Dongxu Liu ◽  
Na Huang ◽  
Lei Liu
Keyword(s):  
Pressure Loss ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Pore Throat ◽  
Local Pressure ◽  
Two Phase ◽  
Local Loss ◽  
Flow Through ◽  
Oil Water ◽  
Phase Water

To investigate the resistance performance of pore throats in porous media, a new method was used to conduct experiments to indirectly measure the local pressure loss of single-phase water and oil- water two-phase flow through pore-throat structures. Four microchannels were designed and manufactured with MEMS technology. One of the four microchannels is a straight duct with no throat and each of the other three has one throat within the passage. By comparison of total pressure drops between the straight duct with no throat and the channel with a throat at the same flow rate, the local pressure loss over a pore- throat structure can be determined. In this paper, the pore-throat structure is defined as a combination of a contraction, an expansion and a throat to stimulate the pore throat in porous media. Experimental results show that local pressure loss, nonlinear with the flow rate, grows up with the decrease of throat size and the increase of oil volume fraction. Local loss coefficient, characterizing the local resistance performance of pore-throat structure, diminishes with the increase of Reynolds number. Reynolds number (in throat part) is in the range of 100-1100. A new empirical correlation of local loss coefficient is proposed for single-phase water and oil-water two-phase flow through pore-throat structure.

Numerical Simulation on Pressure Drops for Air-Water Two-Phase Flow in Micro-Channels

2008 ◽  
Author(s):  
Hao Peng ◽  
Xiang Ling
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Vof Method ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Pressure Drops ◽  
Micro Channels ◽  
Phase Pressure

Rigorous two-phase flow modeling is one of the great challenges in the thermal sciences. A two-dimensional computational fluid dynamics (CFD) simulation of air-water two-phase pressure drop characteristics in micro-channels by using volume of fluid (VOF) method was carried out in this paper. The simulations were performed in a horizontal micro-channel with a diameter of 1.1 mm and a length of 200 mm. Firstly, a variety of air-water two-phase flow patterns (including bubbly, slug, slug-annular and annular flow) were simulated in order to validate the feasibility and reliability of the VOF method. Next to that, the two-phase pressure drops in micro-channel were analyzed numerically by using the same CFD method. Also the comparison of pressure drop among the numerical simulations, experimental data and the results calculated by homogeneous equilibrium model was presented. The agreement between numerical results and the existing experimental data was found to be satisfactory. Based on this good agreement, it is finally found that the numerical analysis procedure proposed in this paper can be used to achieve a better prediction for micro-channel air-water flow characteristics.

Two-Phase Flow in a Gas Flow Channel of Polymer Electrolyte Fuel Cells

2011 ◽  
Author(s):  
Sung Chan Cho ◽  
Yun Wang
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Water Droplet ◽  
Two Phase Flow ◽  
Rectangular Channel ◽  
Aluminum Surface ◽  
Carbon Paper ◽  
Phase Flow ◽  
Two Phase ◽  
Phase Pressure

Two-phase flow behavior in a mini channel is studied by both experimental and numerical methods. Various surface conditions are considered to capture the fundamental characteristics of water droplet behavior in a PEMFC gas channel. In the considered rectangular channel with 1 mm height, critical velocity for annular flow type is measured as 1∼2 m/s of superficial air velocity. Two-phase flow pattern shows some uncertainty near transition zone with aluminum surface. With carbon paper GDL, two-phase flow pattern is stabilized. Measured two-phase pressure drop data explains the relation between two-phase flow pattern and two-phase pressure drop. Numerical simulation using VOF technique successfully mimicked the development of water droplet and corner flow as well as formation of a slug. It also explains the possibility of random slug formation with aluminum surface and stabilized two-phase flow pattern with carbon paper GDLs.

Verification, Validation and Uncertainty Quantification of a Nuclear Thermal Hydraulics Code

2013 ◽  
Author(s):  
Fatih Aydogan
Keyword(s):  
Pressure Drop ◽  
Power Distribution ◽  
Two Phase Flow ◽  
Numerical Technique ◽  
Nuclear Safety ◽  
Phase Flow ◽  
Thermal Hydraulics ◽  
Two Phase ◽  
Two Fluid ◽  
Phase Pressure

Nuclear thermal hydraulics codes are used in designing next generation systems and analyzing existing designs. Since most of the nuclear safety analyses employ nuclear thermal hydraulics codes, every step of the development in these codes are carefully verified and validated (V&V). This study shows the V&V steps of uncertainty equations implemented into the nuclear safety code of Coolant Boiling in Rod Arrays Code-Two-Fluid (COBRA-TF). COBRA-TF, designed by Pacific Northwest Laboratory, represents a two-fluid, three-field (continuous liquid, continuous vapor and entrained liquid drop) representation of two-phase flow. For heat transfer from and within the solid structures in contact with the fluid, a finite difference and semi-implicit numerical technique on an Eulerian mesh is used to solve conservation equations for each of the three fields. Even though the code is capable of predicting two-phase flow response of a system, it only predicts deterministic results without uncertainty bounds. Therefore, uncertainty equations based on Aydogan’s sampling uncertainty method are implemented into COBRA-TF to obtain uncertainty bounds of code predictions. The V&V steps of US-NRC’s Regulatory Guide 1.203 (Rg 1.203) are followed as a guideline after the code updates. Several code-to-data comparisons are done in the process of V&V: single phase pressure drop, two phase pressure drop, void distribution, critical power and dry-out location. Uncertainty bounds of code predictions are calculated and compared with the experimental uncertainty bounds. An experimental database which covers various two phase flow experiments, boundary conditions (mass flow rate, pressure and inlet enthalpies), 1/1 scale nuclear fuel bundles, axial and radial power distribution is selected for the purpose of this study. The uncertainty results of new uncertainty equations coded in COBRA-TF are satisfying.

Two-Phase Pressure Drop Characteristics During Low Temperature Transients in PEMFCs

2014 ◽  
Author(s):  
Rupak Banerjee ◽  
Satish G. Kandlikar
Keyword(s):  
Fuel Cells ◽  
Steady State ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Transient Behavior ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Four Levels ◽  
Phase Pressure

Proton Exchange Membrane fuel cells are being considered as the powertrain of choice for automotive applications. Automotive fuel cells experience transients during start-up, shut-down and changing load conditions, which constitute a significant part of the drive cycle. Transient behavior of PEMFCs can be classified into three categories: electrochemical, thermal and two-phase flow. Two-phase transients require a longer time to return to steady state than the electrochemical transient (which typically requires less than 1 second). Experiments have shown two-phase transients to be more prominent at the lower temperatures due to the increased presence of liquid water. Overshoot / undershoot behavior of current and voltage has been observed during investigations of electrochemical transients. This study investigates similar overshoot / undershoot behavior in the two-phase pressure drop in the reactant channels. An increase in the current drawn from the PEMFC is accompanied by larger air flow rates and greater water generation. An in situ setup is utilized to measure the pressure drop in the reactant channels across the length of the channel, when the electrical load drawn from the PEMFC is changed. This pressure drop measurement along the length of the reactant channels is used to characterize the overshoot / undershoot behavior. A parametric study is conducted to identify the factors which influence the overshoot / undershoot in two-phase flow pressure drop. The transient behavior is explored at the temperatures of 40, 60 and 80°C. Transient behavior is more pronounced at the lower temperature. Five different ramp rates have been used to show that faster ramp rates results in larger overshoot. The effect of magnitude of current change is investigated using four levels of load change. It was observed that increased magnitude of change results in increased overshoot behavior. However, no direct relationship has been observed between the magnitude of overshoot and the time required to return to steady state.

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