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.

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.

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.

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.

High Heat Flux Subcooled Flow Boiling of Methanol in Microtubes

2015 ◽  
Author(s):  
Farzad Houshmand ◽  
Hyoungsoon Lee ◽  
Mehdi Asheghi ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Inner Diameter ◽  
Phase Pressure

As the proper cooling of the electronic devices leads to significant increase in the performance, two-phase heat transfer to dielectric liquids can be of an interest especially for thermal management solutions for high power density devices with extremely high heat fluxes. In this paper, the pressure drop and critical heat flux (CHF) for subcooled flow boiling of methanol at high heat fluxes exceeding 1 kW/cm2 is investigated. Methanol was propelled into microtubes (ID = 265 and 150 μm) at flow rates up to 40 ml/min (mass fluxes approaching 10000 kg/m2-s), boiled in a portion of the microtube by passing DC current through the walls, and the two-phase pressure drop and CHF were measured for a range of operating parameters. The two-phase pressure drop for subcooled flow boiling was found to be significantly lower than the saturated flow boiling case, which can lead to lower pumping powers and more stability in the cooling systems. CHF was found to be increasing almost linearly with Re and inverse of inner diameter (1/ID), while for a given inner diameter, it decreases with increasing heated length.

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.

scholarly journals Simulation of Stratified Two-phase Flow Regime using Air-Water Model in ANSYS Fluent ®

2019 ◽  
Vol 1355 ◽  
pp. 012014
Author(s):  
Binet Monachan ◽  
Rijo J. Thomas ◽  
Deepak Steaphen ◽  
Mathew Skaria ◽  
K.A. Shafi
Keyword(s):  
Flow Regime ◽  
Two Phase Flow ◽  
Water Model ◽  
Phase Flow ◽  
Two Phase ◽  
Ansys Fluent

Variations of Buoyancy-Induced Mass Flux From Single-Phase to Two-Phase Flow in a Vertical Porous Tube With Constant Heat Flux

1999 ◽  
Vol 121 (3) ◽  
pp. 646-652 ◽  
Author(s):  
T. S. Zhao ◽  
Q. Liao ◽  
P. Cheng
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
Single Phase ◽  
Two Phase Flow ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Constant Heat ◽  
Two Phase ◽  
Porous Tube

This paper presents an experimental study of a buoyancy-induced flow of water with phase-change heat transfer in a vertical porous tube heated at a constant heat flux. Experiments were carried out from subcooled liquid flow to connective boiling by varying the imposed heat fluxes. At a prescribed heat flux the steady-state mass flux of water, as well as the temperatures along the tube wall and along the centerline of the packed tube, were measured. It is shown that for both single-phase flow and the two-phase flow with a rather low vapor fraction, the induced mass flux increased as the heat flux was increased. However, as the imposed heat flux was increased further, the induced mass flux dropped drastically, and remained relatively constant afterwards. The influences of various parameters such as the porous tube diameter, the particle sizes, and the hydrostatic head on the induced mass flux are also examined.

scholarly journals Numerical Simulation of Evaporating Two-Phase Flow in a High-Aspect-Ratio Microchannel with Bends

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Adam Girard ◽  
Seung M. You ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Flow Boiling ◽  
Vertical Component ◽  
Hydrophobic Surface ◽  
Surface Tension Force ◽  
Heat Fluxes ◽  
Vertical Force ◽  
Two Phase ◽  
Hydrophobic Contact

Flow boiling was investigated on a hydrophobic surface by coating Teflon® onto a 1×1 cm2 copper surface, resulting in contact angle of 118°. The images depicted were taken using distilled water flowing at 299 kg/m2s with 3°C subcooling. In the first series, the number of active nucleation sites increased as heat flux increased. For lower values of heat flux (< 80 kW/m2), vapor bubbles remained almost stationary on the surface. The hydrophobic contact angle makes the horizontal component of surface tension force act radially outward, causing the bubble interface to grow. This leads to increased triple contact line and increased vertical component surface force. The buoyancy force due to the vapor bubble volume appears to be insufficient to overcome this vertical force for liftoff. This explains the stationary bubbles observed at the lower heat fluxes. The bubbles show an increase in size and number with heat flux. After this increasing trend, the bubble continues to grow larger when heat flux is higher than 80 kW/m2, eventually leading to the dryout at 117.5 kW/m2. The later bubble growth at high heat fluxes is caused primarily by the coalescences of neighboring bubbles. These larger bubbles are more affected by flow induced drag forces and move downstream. This can be seen in the lower sequential series at 100 kW/m2. The larger vapor masses slide across the surface, continue to absorb smaller bubbles as they move downstream, and are swept off the surface.

A Review of Two-Phase Forced Cooling in Three-Dimensional Stacked Electronics: Technology Integration

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Craig Green ◽  
Peter Kottke ◽  
Xuefei Han ◽  
Casey Woodrum ◽  
Thomas Sarvey ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Three Dimensional ◽  
High Heat ◽  
Heat Fluxes ◽  
Thermal Design ◽  
High Heat Flux ◽  
Two Phase ◽  
Forced Cooling ◽  
Fluidic Routing

Three-dimensional (3D) stacked electronics present significant advantages from an electrical design perspective, ranging from shorter interconnect lengths to enabling heterogeneous integration. However, multitier stacking exacerbates an already difficult thermal problem. Localized hotspots within individual tiers can provide an additional challenge when the high heat flux region is buried within the stack. Numerous investigations have been launched in the previous decade seeking to develop cooling solutions that can be integrated within the 3D stack, allowing the cooling to scale with the number of tiers in the system. Two-phase cooling is of particular interest, because the associated reduced flow rates may allow reduction in pumping power, and the saturated temperature condition of the coolant may offer enhanced device temperature uniformity. This paper presents a review of the advances in two-phase forced cooling in the past decade, with a focus on the challenges of integrating the technology in high heat flux 3D systems. A holistic approach is applied, considering not only the thermal performance of standalone cooling strategies but also coolant selection, fluidic routing, packaging, and system reliability. Finally, a cohesive approach to thermal design of an evaporative cooling based heat sink developed by the authors is presented, taking into account all of the integration considerations discussed previously. The thermal design seeks to achieve the dissipation of very large (in excess of 500 W/cm2) background heat fluxes over a large 1 cm × 1 cm chip area, as well as extreme (in excess of 2 kW/cm2) hotspot heat fluxes over small 200 μm × 200 μm areas, employing a hybrid design strategy that combines a micropin–fin heat sink for background cooling as well as localized, ultrathin microgaps for hotspot cooling.

Analysis of Two-Phase Pressure Drop Fluctuation Characteristics in a Single Mini-Channel

2016 ◽  
Vol 366 ◽  
pp. 151-156
Author(s):  
Bei Chen Zhang ◽  
Qing Lian Li ◽  
Yuan Wang ◽  
Jian Qiang Zhang
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Boiling ◽  
Circular Cross Section ◽  
Low Frequency ◽  
Amplitude Fluctuation ◽  
Heat Fluxes ◽  
Two Phase ◽  
Phase Pressure

Two-phase pressure drop fluctuations during flow boiling in a single mini-channel were experimentally investigated. Degassed water was tested in circular cross section mini-channels with the hydraulic diameter of 1.0 mm at liquid mass fluxes range of 21.19-84.77 kg m-2 s-1 and heat fluxes of 0~155.75 kW m-2. Effects of heat flux and mass flux on pressure drop fluctuations were discussed based on the time and frequency domain analysis of the measured pressure drop. Two types of fluctuations were identified, which are the incipient boiling fluctuation (IBF) and the explosive boiling fluctuation (EBF) respectively. The IBF is a low frequency low amplitude fluctuation, which relates to the bubble dynamics when incipient boiling occurs. It is sensitive to the thermal and flow conditions. With the increase of heat flux and mass flux, the IBF is suppressed. The EBF is a low frequency high amplitude fluctuation, which occurs near the critical heat flux.

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