Parametric Study and Computational Two-Phase Flow Simulation of the Refrigerant Distributor in a Spray Type Evaporator

2006 ◽  
Author(s):  
Liang-Han Chien ◽  
Shih-Ming Wang ◽  
Shu-Che Lee
Keyword(s):  
Fluid Model ◽  
Perforated Plate ◽  
Flow Simulation ◽  
Flow Distribution ◽  
Surface Force ◽  
Full Scale ◽  
Fluid Distribution ◽  
Force Model ◽  
Vapor Flow ◽  
Two Phase

This manuscript presents a simplified model for the simulation of liquid-vapor flow in a spray type evaporator of a chiller unit. In the present study, the liquid and vapor phases are considered as two separate fluids and simulated by the commercial code, FLUENT. Two types of distributors were investigated: (1) a miniature tubular distributor, and (2) a full scale distributor. The tubular distributors consists of two tubes, the pore size (1.0 mm or 1.5 mm) of the inner tube and the gap size (1.0, 2.0 or 3.0 mm) of the outer tube were varied for comparisons of the velocity and pressure distributions. Three different flow rates: 1.6, 3.2 and 6.4 g/s, were set in the simulations of miniature distributor. The full scale distributor consists of a 30 mm diameter tube having 4.0 mm pores in 18 mm pitch, and a 2400 mm × 226 mm perforated plate having 3.0 mm pores. The Volume of Fluid model and the Continuum Surface Force model were used in the two-phase simulation of the full scale distributor. From the present study, we found that the 3.0 mm gap width yields the most uniform flow distribution for 1.6 ∼ 6.4 kg/s for the miniature distributor. Based on the simulation of the miniature distributor, a falling film evaporation test apparatus is designed, and uniform fluid distribution in the evaporator is found. The fluid distribution observed in the test of an 80 ton chiller is more uniform than that shown in the preliminary result of the full scale simulation.

Cavitating Flow Simulation in a Closed Pump Sump by Two-Fluid Model and Its PIV Verification

2003 ◽  
Author(s):  
Yu Xu ◽  
Yulin Wu ◽  
Shuhong Liu ◽  
Yong Li
Keyword(s):  
Fluid Model ◽  
Flow Simulation ◽  
Cavitating Flow ◽  
Governing Equations ◽  
Two Phase ◽  
Averaged Equations ◽  
Flow Through ◽  
Pump Sump ◽  
Two Fluid Model ◽  
Two Fluid

In this paper, the two-fluid model was adopted to analyze the cavitating flow. Based on Boltzmann equation, governing equations for two-phase cavitating flow were obtained by using the microscopic kinetic theory, in which the equation terms for mass and momentum transportations can be obtained directly. Then the RNG k–ε–kg turbulence model, that is RNG k–ε model for the liquid phase and kg model for the cavity phase, was used to close the Reynolds time-averaged equations. According to the governing equations above, the simulation of the two-phase cavitating flow through a closed pump sump has been carried out. The calculated results have been compared with a PIV experiment. Good agreement exhibited.

Pressure Drop Analysis for Liquid-Liquid Downflow Through Vertical Pipe

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
S. Ghosh ◽  
G. Das ◽  
P. K. Das
Keyword(s):  
Pressure Drop ◽  
Fluid Model ◽  
Flow Distribution ◽  
Separated Flow ◽  
High Viscosity ◽  
Flow Patterns ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Low Viscosity ◽  
Two Fluid Model

In the present paper, the pressure drop characteristics and flow patterns during downward vertical flow of lube oil-water as well as kerosene-water through a circular glass conduit have been studied. Core-annular flow has been observed to be the dominant flow pattern and it gives rise to slug flow with increase of water and/or decrease of oil velocity. However, there are subtle differences in the flow distribution observed for high viscosity and low viscosity oils. The two-phase frictional pressure drop for separated flow patterns of both the liquid pairs is predicted using two-fluid model. Since the model predictions have a large mismatch with experimental data, an empirical correlation is also proposed for improved predictions. The homogeneous and drift flux models are used for slug and dispersed flow patterns.

scholarly journals Numerical Demonstration of In-Tube Liquid-Column Migration Driven by Photoisomerization

2018 ◽  
Author(s):  
Kei Nitta ◽  
Takahiro Tsukahara
Keyword(s):  
Control Method ◽  
Surface Force ◽  
Liquid Column ◽  
Light Irradiation ◽  
Experimental Result ◽  
Force Model ◽  
Two Phase ◽  
Isomer Distribution ◽  
Fluid Properties ◽  
Transfer Method

Liquid manipulation by photoisomerization attracts recent attentions as a new active droplet control method for micro-chemical analysis. Such a non-inverse manipulation can be realized by a use of solution liquid of surfactant that exhibits the \emph{cis}-\emph{trans} isomerization triggered by light irradiation with a specific wavelength such as ultraviolet light. Since the isomerization is accompanied by changes in fluid properties, a light irradiation on one of liquid-air interfaces of a liquid column in a tube would generate differences in the wettability accompanied between the both sides of the finite liquid column. Although this technique has been demonstrated experimentally by Muto et al. (\emph{Euro.~Phys.~J.~Special Topics}, {\bf 226}, 2016, 1199--1205), its dynamics and developments of each isomer distribution are not understood. In order to reveal the liquid-column migration phenomenon, we have performed numerical simulations of air-liquid two-phase flows and its scalar transport of the isomer, using the Volume-of-Fluid method in conjunction with the Continuum-Surface-Force model and Continuous-Species-Transfer method. We validated present results by comparison with experimental result in terms of the migration distance of the liquid column. We confirmed a termination of the liquid-column migration occurs when the \emph{cis} isomer distribution reaches the non-irradiated region. The migration speed was less dependent on the liquid-column length and was proportional to the tube diameter.

Addressing Two-Phase Flow Maldistribution in Microchannel Heat and Mass Exchangers

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Dhruv C. Hoysall ◽  
Khoudor Keniar ◽  
Srinivas Garimella
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Distribution ◽  
Interfacial Area ◽  
Fluid Distribution ◽  
High Speed Photography ◽  
Phase Flow ◽  
Water Mixture ◽  
Two Phase ◽  
Microchannel Array

Multiphase flow phenomena in single micro and minichannels have been widely studied. Characteristics of two-phase flow through a large array of microchannels are investigated here. An air–water mixture is used to represent the two phases flowing through a microchannel array representative of those employed in practical applications. Flow distribution of the air and water flow across 52 parallel microchannels of 0.4 mm hydraulic diameter is visually investigated using high-speed photography. Two microchannel configurations are studied and compared, with mixing features incorporated into the second configuration. Slug and annular flow regimes are observed in the channels. Void fractions and interfacial areas are calculated for each channel from these observations. The flow distribution is tracked at various lengths along the microchannel array sheets. Statistical distributions of void fraction and interfacial area along the microchannel array are measured. The design with mixing features yields improved flow distribution. Void fraction and interfacial area change along the length of the second configuration, indicating a change in fluid distribution among the channels. The void fraction and interfacial area results are used to predict the performance of different microchannel array configurations for heat and mass transfer applications. Results from this study can help inform the design of compact thermal-fluid energy systems.

Control of Adiabatic Liquid/Vapor Flow Utilizing EHD Conduction Pumping Mechanism

2004 ◽  
Author(s):  
Yinshan Feng ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Finite Thickness ◽  
Flow Distribution ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Phase Liquid ◽  
Liquid Vapor

Unlike the electrohydrodynamic (EHD) induction and iondrag pumping, the conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes which are based on the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The conduction term here represents a mechanism for electric current flow in which charged carriers are produced not by injection from electrodes, but by dissociation of molecules within the fluid. This paper presents the control of adiabatic two-phase (liquid/vapor) flow distribution with EHD conduction pumping mechanism at two mass flux levels, Gtotal = 50 kg/m2s and Gtotal = 100 kg/m2s. The effects of the vapor quality, ranging from 0 to 26%, on the EHD conduction pumping have also been experimentally investigated. The measured pressure data show that the EHD conduction pumping can significantly decrease the pressure drop of the two-phase flow. It is also found that the performances of the EHD conduction pump are related to the mass flux and quality of two-phase flow.

Analysis on the Transient-State of the Gas-Condensate Pipeline

2017 ◽  
Author(s):  
Guoyun Shi ◽  
Xiaoping Li ◽  
Zhi Wang ◽  
Dan Wang ◽  
Jing Gong
Keyword(s):  
Multiphase Flow ◽  
Energy Equation ◽  
Fluid Model ◽  
Flow Simulation ◽  
Transient State ◽  
Gas Condensate ◽  
Transient Condition ◽  
Two Phase ◽  
Two Fluid Model ◽  
Two Fluid

The mixture energy equation of the pipeline is developed. By introducing the mass transfer between the two phases, the two-fluid model is extended to two phase flow simulation in pipeline. Taking the space limit of the pipe in pipeline multiphase flow into account, the combined continuity equation is established to represent the interaction between phases, and a segregated solution method is promoted and adopted in this study. A numerical method coupled with phase behavior, flow pattern and hydro-thermodynamic is presented through combing mixture energy equation and two-fluid model developed in transient condition, and is used to simulate the transient-state two-phase in gas-condensate pipeline. In discretization, high-resolution scheme is adopted for conquering nonphysical oscillation caused by step distribution of air void fraction on premise of at least second accuracy. Simulation results have a good performance on the fluctuation of the pipeline multiphase flow and on depressing the dispersion and dissipation. Compared with the OLGA (a commercial software), the maximum difference of the liquid phase fraction is 0.075, the pressure is 0.08MPa and the temperature is 0.6°C.

Modeling the Characteristics of Thermally Governed Transient Flow Surges in Multitube Two-Phase Condensing Flow Systems With Compressibility and Thermal and Flow Distribution Asymmetry

1997 ◽  
Vol 119 (3) ◽  
pp. 534-543 ◽  
Author(s):  
G. L. Wedekind ◽  
C. J. Kobus ◽  
B. L Bhatt
Keyword(s):  
Flow Rate ◽  
Transient Flow ◽  
Flow Distribution ◽  
Vapor Flow ◽  
Complex Flow ◽  
Two Phase ◽  
Physical Mechanisms ◽  
Tube Type ◽  
Design Perspective ◽  
Spreadsheet Software

In a tube-type condenser involving complete condensation, small changes in the inlet vapor flow rate momentarily cause very large transient surges in the outlet mass flow rate. An Equivalent Single-Tube Model (ESTM), based on the System Mean Void Fraction Model, is developed that predicts these transient flow surges for a multitube system; including the effects of compressibility as well as thermal and flow distribution asymmetry. The model is verified theoretical and experimentally. From a design perspective, the significant value of the ESTM is that it includes the primary physical mechanisms involved in such complex flow transients, yet is simple enough to be solved on typical “spreadsheet” software.

Prediction of Flow Distribution in Gas-Liquid Two-Phase Annular Flows in a Rod Bundle Under Hydraulically Equilibrium Condition

2003 ◽  
Author(s):  
Akimaro Kawahara ◽  
Michio Sadatomi ◽  
Nobutaka Aoyama ◽  
Satoru Tanoue
Keyword(s):  
Equilibrium Condition ◽  
Fluid Model ◽  
Vertical Channel ◽  
Flow Distribution ◽  
Two Phase ◽  
Rod Bundle ◽  
Liquid Phases ◽  
Closure Equation ◽  
Annular Flows ◽  
Two Fluid Model

Subchannel flow distributions of both gas and liquid phases under a hydraulically equilibrium condition have been investigated experimentally and analytically for two-phase annular flows in a vertical channel simulating a BWR fuel rod bundle. In the experiment, data on two-phase flow rates in subchannels were obtained for several equilibrium annular flows. In the analysis, a simple, one dimensional, one pressure, two-fluid model has been applied to calculate the flow distributions. In addition, an equation of identical-wall-shear-stress between subchannels was incorporated as a closure equation for the analysis. From a comparison between the calculation and the experiment, the present analysis was found to be promising.

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