scholarly journals Effect of operating conditions on the performance of the bubble pump of absorption-diffusion refrigeration cycles

2011 ◽  
Vol 15 (3) ◽  
pp. 793-806 ◽  
Author(s):  
Ali Benhmidene ◽  
Bechir Chaouachi ◽  
Slimane Gabsi
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Constant Heat Flux ◽  
Operating Conditions ◽  
Tube Diameter ◽  
Pump Design ◽  
Refrigeration Unit ◽  
Two Fluid Model ◽  
Bubble Pump

The mathematical model will be able to predict the operated condition (required tube diameters, heat input and submergence ratio?.). That will result in a successful bubble pump design and hence a refrigeration unit. In the present work a one-dimensional two-fluid model of boiling mixing ammonia-water under constant heat flux is developed. The present model is used to predict the outlet liquid and vapor velocities and pumping ratio for different heat flux input to pump. The influence of operated conditions such as: ammonia fraction in inlet solution and tube diameter on the functioning of the bubble pump is presented and discussed. It was found that, the liquid velocity and pumping ratio increase with increasing heat flux, and then it decreases. Optimal heat flux depends namely on tube diameter variations. Vapour velocity increases linearly with increasing heat flux under designed conditions.

Numerical Prediction of Flow Patterns in Bubble Pumps

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Ali Benhmidene ◽  
Bechir Chaouachi ◽  
Mahmoud Bourouis ◽  
Slimane Gabsi
Keyword(s):  
Heat Flux ◽  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Tube Diameter ◽  
Tube Length ◽  
Velocity Versus ◽  
Bubble Pump

In the present study, the ammonia-water mixing flow in a bubble pump is numerically simulated. The flow patterns of a two-phase flow in a bubble pump were studied under different conditions of heat flux and tube diameter. A one-dimensional two-fluid model was developed under constant heat flux. This model was used to predict the variations in void fraction and liquid and vapor velocities throughout the tube. Then, the void fraction profile and the curve of liquid velocity versus vapor velocity were used to predict the flow patterns along the tube length. It was found that at heat fluxes below 15 kW m−2, bubbly, slug, and churn flows are the dominating regimes, and the length of these flow regimes depends on the tube diameter. For heat fluxes higher than 15 kW m−2, the bubble pump operates under the churn and annular regimes, and the bubble pump performance is improved when the tube diameter increases.

Experimental Measurements and CFD Evaluation of the Onset Flow Boiling at Low Pressure and High Subcooling Flow of R-11 Within Vertical Annulus

2014 ◽  
Author(s):  
Y. Bouaichaoui ◽  
R. Kibboua ◽  
M. Matkovič
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fluid Model ◽  
Computer Code ◽  
Computational Method ◽  
Subcooled Boiling ◽  
Two Phase ◽  
Local Flow ◽  
Wide Range

The knowledge of the onset of subcooled boiling in forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. A computational method based on theoretical studies of steady state two phase forced convection along a test section loop was released. The calculation model covers a wide range of two phase flow conditions. It predicts the heat transfer rates and transitions points such as the Onset of Critical Heat Flux.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

Simulation Study of Gas-Solid Macro-Mixing Characterization in Small Fixed-Fluidized Bed Reactor

2011 ◽  
Vol 236-238 ◽  
pp. 1537-1545
Author(s):  
Wen Jing Liu ◽  
Hui Zhao ◽  
Chao He Yang ◽  
Hong Hong Shan
Keyword(s):  
Fluidized Bed ◽  
Raw Materials ◽  
Fluid Model ◽  
Structural Parameters ◽  
Flow Behavior ◽  
Fluidized Bed Reactor ◽  
Operating Conditions ◽  
Laboratory Evaluation ◽  
Two Fluid Model ◽  
Two Fluid

In fixed-fluidized bed reactor, laboratory evaluation of different catalyst, raw materials and process parameters can be implemented, so it has wide applications in the refining process. In this study, we focused on small fixed-fluidized bed reactor, using Eulerian-Eulerian two-fluid model, simulated the gas-solid flow behavior in it. Gas residence time distribution was measured in order to characterize macro-mixing. At the same time, by changing the reactor structure and operating conditions, we studied their effects on gas-solid macro-mixing characterization. The results show that the effects of structural parameters are larger than operating conditions, and different parameters have different effects. Different parameters can be adjusted to change the gas-solid macro-mixing characterization in small fixed-fluidized bed reactor. Therefore, the small fixed-fluidized bed reactor can provide better results in more application areas.

Performance Analysis of Electric Submersible Pumps (ESP) Handling Two-Phase Mixtures

2002 ◽  
Author(s):  
Jose´ Caridad ◽  
Frank Kenyery
Keyword(s):  
Liquid Velocity ◽  
Fluid Model ◽  
Bubble Diameter ◽  
Petroleum Industry ◽  
Primary Concern ◽  
Cfd Simulations ◽  
Two Phase ◽  
Impeller Blade ◽  
Two Fluid Model ◽  
Complex Phenomena

Behavior of Electric Submersible Pumps (ESP) handling two-phase flow is a subject of primary concern, especially in the petroleum industry, where significant amounts of free gas may be found in oil wells production. Several attempts have been made in order to predict the performance of such kind of pumps, nevertheless, limited success has been achieved due to the complexity of the flow dynamics inside the impeller. Geometry, gas void fraction (GVF) and suction pressure seem to be the main parameters affecting ESP performance. Furthermore, the higher the GVF of the mixture is, the higher the degradation of head that it is experimented by the pump. This complex phenomena is not well understood so far. In this work, a two fluid model is used in 3D CFD simulations carried out in order to obtain the pressure, liquid velocity and gas velocity fields as well as the GVF distribution in an ESP impeller of known geometry; using flow rates, bubble diameter and GVF at the suction as independent variables and an incompressible fluid hypothesis. The gas pocket in the impeller blade reported from other researchers is obtained and comparison with experimental results has shown good agreement. The obtained variables from the simulations are the cornerstone that allows the prediction of the performance curve of the pump for different GVF and in this way, estimate the head degradation of the pump.

CFD Analysis on Wall Boiling Model During Subcooled Boiling in Vertical Narrow Rectangular Channel

2018 ◽  
Author(s):  
Tingting Ren ◽  
Changqi Yan ◽  
Meiyue Yan ◽  
Shengzhi Yu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Model ◽  
Rectangular Channel ◽  
Subcooled Boiling ◽  
Site Density ◽  
Rectangular Channels ◽  
Two Fluid Model ◽  
Nucleate Site ◽  
Two Fluid

Two-fluid model is a common method to simulate the subcooled flow boiling heat transfer, in which the wall boiling model is mainly used for the partition of wall heat flux and the mass transfer between two phases on the wall. The model determines the amount of vapor phase and predicts the cross-sectional void fraction in the channel, nucleate site density and bubble departure diameter play an important role in the accurate prediction of wall boiling model. Eulerian two-fluid model coupled with Rensselaer Polytechnic Institute (RPI) wall boiling model is employed to simulate the heat transfer characteristics and boiling phenomena in vertical narrow rectangular channels by using FLUENT code. Based on the experimental data of subcooled boiling in vertical narrow rectangular channel, different combinations of nucleate site density and bubble departure diameter correlations are used to calculate under different conditions of heat flux and inlet subcooling. Comparing the calculated heat transfer coefficients along the vertical height with experimental results, it can be found that these two parameters have a significant effect on the subcooled boiling heat transfer in narrow rectangular channels. Different parameter combinations lead to differences in wall heat flux distribution, different heat flux and inlet subcooling also have different effects on these models, which eventually lead to different evaporative heat flux, thus affecting the prediction of void fraction.

Characterizing Effects of the Shape of Screw Conveyors in Gas–Solid Fluidized Beds Using Advanced Numerical Models

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Qingang Xiong ◽  
Soroush Aramideh ◽  
Alberto Passalacqua ◽  
Song-Charng Kong
Keyword(s):  
Numerical Study ◽  
Numerical Models ◽  
Fluid Model ◽  
Operating Conditions ◽  
Screw Conveyor ◽  
Blade Thickness ◽  
Computational Mesh ◽  
Computational Fluid Dynamics Cfd ◽  
Two Fluid Model ◽  
Screw Pitch

A numerical study of the effects of the shape of an enclosed screw conveyor on the mixing and heat transfer in a horizontal gas–solid fluidized bed was conducted using computational fluid dynamics (CFD). A two-fluid model (TFM) was employed to model the gas and solid phases as continua through mass, momentum, and energy conservations. The motion of the screw conveyor was simulated by using a rotating reference frame (RRF) such that the computational mesh was free from dynamic reconstruction. The diameters of the screw flight and shaft, the pitch, and the blade thickness were varied in the parametric study. Under the operating conditions studied, it was found that the increase in the diameter of the screw flight results in the enhancement of the solid mixing and conveyance. The increase in the diameters of the screw shaft and the screw blade thickness lead to the enhanced solid mixing but reduced conveyance. The variation in the screw pitch gives rise to rather complex behaviors in the solid mixing and conveyance. As the screw pitch is decreased, the solid mixing increases initially but then decreases before it increases eventually. The solid conveyance capability was found to first increase and then decrease. Explanations to the effects of the shape of the screw conveyor were discussed in this work.

The Effect of Swirl, Inlet Conditions, Flow Direction, and Tube Diameter on the Heat Transfer to Fluids at Supercritical Pressure

1970 ◽  
Vol 92 (3) ◽  
pp. 465-471 ◽  
Author(s):  
B. Shiralkar ◽  
P. Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Tube Diameter ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

An investigation has been made of the factors governing the heat transfer coefficient to supercritical pressure fluids, particularly at high heat fluxes. The deterioration in heat transfer to supercritical carbon dioxide has been experimentally studied with reference to the operating conditions of mass velocity and heat flux, tube diameter, orientation, tape induced swirl, inlet temperature, and pressure. A detailed comparison has been made with the apparently contradictory results of other investigators, and operating regions, in which the heat transfer coefficient behaves differently, have been defined. The terms used to describe these regions are the Reynolds number, a heat-flux parameter, and a free-convection parameter.

scholarly journals Edge turbulence and divertor heat flux width simulations of Alcator C-Mod discharges using an electromagnetic two-fluid model

2017 ◽  
Vol 57 (11) ◽  
pp. 116025 ◽  
Author(s):  
B. Chen ◽  
X.Q. Xu ◽  
T.Y. Xia ◽  
M. Porkolab ◽  
E. Edlund ◽  
...  
Keyword(s):  
Heat Flux ◽  
Fluid Model ◽  
Two Fluid Model ◽  
Two Fluid

Heat Transfer to Blood Flow in a Small Tube

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
C. Y. Wang
Keyword(s):  
Heat Transfer ◽  
Blood Flow ◽  
Transfer Problem ◽  
Fluid Model ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Axial Temperature ◽  
Small Tube ◽  
Two Fluid Model ◽  
Two Fluid

Blood flow in a small tube (30–1000μm) can be successfully modeled by the two-fluid model. The fully developed, constant heat flux convective heat transfer problem is studied. The velocity and temperature profiles are determined in closed form. Formulas for friction-factor-Reynolds number product, axial temperature gradient, and Nusselt number are found.

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