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.

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.

A Mechanistic Model for Predicting Subcooled Boiling Flow

2003 ◽  
Author(s):  
G. H. Yeoh ◽  
J. Y. Tu
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Group Model ◽  
Subcooled Boiling ◽  
Boiling Flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.

scholarly journals CFD parametric investigation for two-phase flow of ammonia-water mixing in bubble pump tube

2019 ◽  
pp. 324-324
Author(s):  
Ali Benhmidene ◽  
Kozhikkatil Arjun ◽  
Bechir Chaouachi
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Liquid Velocity ◽  
Turbulent Viscosity ◽  
Heat Fluxes ◽  
Two Phase ◽  
Ansys Fluent ◽  
Ammonia Water ◽  
Hydrodynamic Parameters ◽  
Bubble Pump

Two-dimensional numerical simulation of two-phase ammonia/water flowing under uniformly heated tube is used. ANSYS Fluent is used to predict the time evolution of thermal and hydrodynamic parameters of the bubble pump. Phase-dependent turbulent models are used to calculate the turbulent viscosity of each phase. Through User-Defined Functions, different interfacial force models and the wall boiling model are implemented in the code. The simulation results show a slow oscillation of hydrodynamic parameters such as pressure, mass flux, vapour velocity and liquid velocity during the initial stage of operation; however, a vigorous oscillation is detected for the temperature behaviour. The amplitude and period of oscillation decrease with the heat input increasing. By using the void fraction contour, it is possible to predict the flow regime along the bubble pump at different times of the operation. The domination of flow regime is the function of heat flux too. It is bubbly to slug for heat fluxes less than 5kW/m? and transits from churn to annular for 15 and 50kW/m? of heat flux.

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.

Numerical Simulation of Forced Convective Boiling in a Microchannel

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Yun Whan Na ◽  
J. N. Chung
Keyword(s):  
Numerical Simulation ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Simulation Method ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling

Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation method to investigate bubble dynamics, two-phase flow patterns, and boiling heat transfer. The momentum and energy equations were solved using a finite volume (FV) numerical method, while the liquid–vapor interface of a bubble is captured using the volume of fluid (VOF) technique. The effects of different constant wall heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were also analyzed. The predicted bubble shapes and distribution profiles together with two-phase flow patterns are also provided.

Critical Heat Fluxes and Flow Patterns in High-Pressure Boiling Water Flows

1964 ◽  
Vol 86 (1) ◽  
pp. 12-22 ◽  
Author(s):  
F. E. Tippets
Keyword(s):  
Heat Flux ◽  
High Pressure ◽  
Critical Heat Flux ◽  
Rectangular Channel ◽  
Motion Pictures ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Boiling Water ◽  
Forced Flow ◽  
Flux Level

High-speed motion pictures (4300 pictures/sec) of boiling water flow patterns in conditions of forced flow at 1000 psia pressure in a vertical heated rectangular channel were taken over the range of mass velocities from 50 to 400 lb/sec-ft2, fluid states from bulk subcooled liquid flow to bulk boiling flow at 0.66 steam quality, and heat fluxes up to and including the critical heat flux level. Eighty critical heat flux determinations were made in the course of the experiment at 1000 psia in conditions of bulk boiling. The motion pictures provide photographic evidence of the general arrangement of the flow in conditions of bulk boiling at high pressure with heat fluxes near and including the critical heat flux level.

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.

Subcooled Flow Boiling in Mini and Micro Channel: Contribution Toward High Heat Flux Cooling Technology for Electronics

2009 ◽  
Author(s):  
Tomoyuki Nomura ◽  
Michael V. Shustov ◽  
Koichi Suzuki ◽  
Chungpyo Hong ◽  
Yury A. Kuzma-Kichta
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Heating Surface ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Subcooled Flow Boiling ◽  
Maximum Heat ◽  
Subcooled Flow ◽  
Micro Channels

Subcooled flow boiling has been investigated for horizontal mini and micro channels of which hydraulic diameters are 1mm and 150μm, respectively for high heat flux cooling in electronics. The heating surface is 1mm in width and 10mm in length for the mini channel. Eleven micro grooving are made on the copper heating block of 5.25mm×5.25mm. Aqueous solutions of ethanol, 10% and 50% in mass concentration, are used as boiling liquid for the micro channel. Microbubble emission boiling (MEB) of water is generated at liquid subcooling of 40K in the mini channel as same cases of conventional macro channels and the maximum heat flux obtained is a 10MW/m2 at liquid velocity of 1m/s (1000kg/m2s). However, the boiling turns to film boiling at low liquid velocity, 0.3m/s (300kg/m2s) for an example. In subcooled boiling of aqueous solutions, the heat flux becomes small for the lower ethanol concentration. The critical heat fluxes are well agreed with the existing theories and the maximum heat fluxes are higher than CHF. However, no micro bubble emission boiling is observed in subcooled flow boiling of mini channels and the CHF is considerably smaller than the existing theories. It is difficult to generate MEB for micro channels with heating surface of large thermal capacity because the coalescing bubbles formed on the heating surface are filled up in the channel and the liquid vapor exchange is disturbed.

Critical Heat Flux in Helically Coiled Tubes

1981 ◽  
Vol 103 (4) ◽  
pp. 660-666 ◽  
Author(s):  
M. K. Jensen ◽  
A. E. Bergles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
High Heat ◽  
Heat Fluxes ◽  
Tube Diameter ◽  
Coiled Tube ◽  
Coil Diameter ◽  
The Difference

A study of boiling R-113 in electrically heated coils of various diameters is reported. Subcooled critical heat flux (CHF) is lower with coils than with straight tubes. The difference increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases. On the contrary, quality CHF is enhanced and increases with d/D; CHF initially increases with increasing mass velocity, but decreases after a maximum is reached. Operational problems, in particular upstream dryouts, can occur if a coiled tube is operated with low to moderate subcooling near the inlet and with moderately high heat fluxes.

Orientation Effects on Critical Heat Flux From Discrete, In-Line Heat Sources in a Flow Channel

1993 ◽  
Vol 115 (4) ◽  
pp. 973-985 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Velocity ◽  
Heat Fluxes ◽  
Heat Sources ◽  
Low Velocity ◽  
Two Phase ◽  
Chip Surface ◽  
Horizontal Orientation ◽  
Limited Success

The effects of flow orientation on critical heat flux (CHF) were investigated on a series of nine in-line simulated microelectronic chips in Fluorinert FC-72. The chips were subjected to coolant in upflow, downflow, or horizontal flow with the chips on the top or bottom walls of the channel with respect to gravity. Changes in angle of orientation affected CHF for velocities below 200 cm/s, with some chips reaching CHF at heat fluxes below the pool boiling and flooding-induced CHF values. Increased subcooling was found to dampen this adverse effect of orientation slightly. Critical heat flux was overwhelmingly caused by localized dryout of the chip surface. However, during the low velocity downflow tests, low CHF values were measured because of liquid blockage by vapor counterflow and vapor stagnation in the channel. At the horizontal orientation with downward-facing chips, vapor/liquid stratification also yielded low CHF values. Previously derived correlations for water and long, continuous heaters had limited success in predicting CHF for the present discontinuous heater configuration. Because orientation has a profound effect on the hydrodynamics of two-phase flow and, consequently, on CHF for small inlet velocities, downflow angles should be avoided, or when other constraints force the usage of downflow angles, the inlet liquid velocity should be sufficiently large.

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