Control of boiling instabilities in a two-phase pumpless loop using water-alcohol mixtures

2021 ◽  
pp. 1-23
Author(s):  
Ankit Bhagat ◽  
Gautam Ghaisas ◽  
John Mathew ◽  
Shankar Krishnan
Keyword(s):  
Two Phase Flow ◽  
Complex Geometry ◽  
Pure Water ◽  
Electronic Devices ◽  
Phase Flow ◽  
Power Electronic ◽  
Two Phase ◽  
Split Flow ◽  
Alcohol Mixtures ◽  
Water Alcohol

Abstract The mitigation of boiling instabilities by employing water-alcohol mixtures as coolants in a two-phase pumpless loop is experimentally investigated. Water-miscible alcohol, namely 2-propanol, is added to water in quantities of 0.05, 0.1, and 0.2 mole fractions to reduce the bubble departure diameters. Boiling experiments are carried out in the pumpless loop involving a copper-based split-flow microchannel evaporator. Two-phase flow stability and heat transfer performance are compared between pure water and 2-propanol-water mixtures. Temperature measurements at the evaporator inlet, evaporator outlet, and condenser inlet show a considerable reduction in fluctuations when the binary mixtures are used as coolants. Therefore, the addition of a small amount of alcohol to water is proposed as a simple technique to control two-phase flow instabilities as against complex geometry modification to the evaporator, often studied in the literature. The pumpless loop with water-alcohol mixtures is a viable thermal management solution for power electronic devices that involve time-varying workloads.

scholarly journals Numerical analysis of pressure fluctuation in a multiphase rotodynamic pump with air–water two-phase flow

2019 ◽  
Vol 74 ◽  
pp. 18 ◽  
Author(s):  
Wenwu Zhang ◽  
Zhiyi Yu ◽  
Yongjiang Li ◽  
Jianxin Yang ◽  
Qing Ye
Keyword(s):  
Pressure Fluctuation ◽  
Two Phase Flow ◽  
Guide Vane ◽  
Fluid Model ◽  
Pure Water ◽  
Maximum Amplitude ◽  
Phase Flow ◽  
Two Phase ◽  
Rotor Stator Interaction ◽  
Two Fluid Model

Pressure fluctuation in single-phase pumps has been studied widely, while less attention has been paid to research on multiphase pumps that are commonly used in the petroleum chemical industry. Therefore, this study investigates the pressure fluctuation for a multiphase rotodynamic pump handling air–water two-phase flow. Simulations based on the Euler two-fluid model were carried out using ANSYS_CFX16.0 at different Inlet Gas Void Fractions (IGVFs) and various flow rate values. Under conditions of IGVF = 0% (pure water) and IGVF = 15%, the accuracy of the numerical method was tested by comparing the experimental data. The results showed that the rotor–stator interaction was still the main generation driver of pressure fluctuation in gas–liquid two-phase pumps. However, the fluctuation near the impeller outlet ascribe to the rotor–stator interaction was weakened by the complex gas–liquid flow. For the different IGVF, the variation trend of fluctuation was similar along the streamwise direction. That is, the fluctuation in the impeller increased before decreasing, while in the guide vane it decreased gradually. Also, the fluctuation in the guide vane was generally greater than for the impeller and the maximum amplitude appeared in the vicinity of guide vane inlet.

scholarly journals NUMERICAL MODELING OF THE DISTRIBUTION OF SNOW LOAD ON A HYPERBOLIC PARABOLOID. THEORETICAL BASIS

2021 ◽  
pp. 43-51
Author(s):  
M.G. Surianinov ◽  
◽  
S. Jgalli ◽  
Al Echcheikh El Alaoui Douaa ◽  
◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Mixture Model ◽  
Two Phase Flow ◽  
Complex Geometry ◽  
Computational Cost ◽  
Phase Flow ◽  
Hyperbolic Paraboloid ◽  
Two Phase ◽  
Ansys Fluent ◽  
Euler Model

Abstract. The paper discusses the choice of a method for studying the distribution of snow loads on a biconcave roof of a hyperbolic paraboloid and its theoretical justification. It is noted that the numerical modeling of the aerodynamic characteristics of buildings and structures is a difficult and resource-intensive task due to the design features of building objects, which, as a rule, have a complex geometric shape, as well as due to a complex unsteady flow resulting from their flow around them. In addition, the task becomes more complicated due to the interference of vortex structures between different objects. Overcoming these objective difficulties became possible with the advent of modern specialized software systems, primarily ANSYS Fluent. Opportunities have appeared for accurate modeling with verification of the results obtained, which implies the use of an effective, well-tested mathematical apparatus. To implement the theory of two-phase flow, two methods based on numerical modeling are mainly used: the Euler-Lagrange method and the Euler-Euler method. The second method is used in the work. Comparative analysis, which investigates two-phase flow around different structures using different turbulence models (including RSM model, SST k-ω model, k-ε model and k-kl-ω model), shows that the k-kl-ω model is the best fit with experiment. ANSYS Fluent supports four multiphase models, i.e. VOF model, Mixture model, Wet Steam and Euler model. Compared to the other three models, the Mixture model provides better stability and lower computational costs, while the Euler model provides better accuracy, but at a higher computational cost . With a rather complex geometry and flow conditions, the use of the RANS approach does not lead to reliable simulation results. Moreover, unsteady turbulent flows cannot be reproduced. In real situations, landslides, saltations, and the suspended state of snow particles are closely related to the real effects of microbursts and bursts present at the surface of the boundary layer. Therefore, in further research, it is advisable to apply alternative approaches to RANS, which include Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), and the hybrid RANS-LES approach to turbulence modeling, which combine efficiency LES techniques in tear-off free zones and the cost-effectiveness of RANS in near-wall areas.

Two-Phase Flow through Corrugated U-Tube

2010 ◽  
Vol 224 (11) ◽  
pp. 2408-2417 ◽  
Author(s):  
B Shannak ◽  
R Damseh ◽  
M Al-Odat ◽  
M Al-Shannag ◽  
A Azzi
Keyword(s):  
Pressure Drop ◽  
Friction Factor ◽  
Two Phase Flow ◽  
Complex Geometry ◽  
Geometrical Parameters ◽  
Phase Flow ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
System Pressure ◽  
Inner Diameter

New measurements of the frictional pressure drop of air—water two-phase flow in a flexible corrugated U-tube have been carried out. Experiments were performed under the following conditions of two-phase parameters: mass flux of 300—800 kg/m2 s, gas quality of 1—60 per cent, and system pressure of 3—7 bar. The inner diameter of the U-tubes tested was 40 mm, with a ratio of curvature radius to inner diameter varying from 3 to 7.5. The results demonstrate that the two-phase flow resistance, energy dissipation, friction losses, and interaction of the two phases in flexible corrugated U-tubes are perceptible about two to five times greater than those in smooth U-tubes. Hence, the two-phase friction factor of such tubes increases from 0.65 to 1.4, depending on the influencing flow and geometrical parameters. The available correlations in the open literature present a similar trend and behaviour. However, they predict the data presented poorly because of the complex geometry of the flexible corrugated U-tube. Based on the energy balance and the presented experimental results, a new model has been developed to calculate the frictional two-phase pressure drop and hence the friction factor of the flexible U-tube. The model includes the relevant primary parameter, fits the experimental data well, and is sufficiently accurate for engineering purposes. The standard deviation of the data is less than 7 per cent. The reported results enable a practical design with standard products and optimization of the geometry of the flexible corrugated U-tube for specific conditions.

Experimental Study on the Effect of Surface Tension on Void Fraction and Frictional Pressure Drop of an Air-Liquid Two-Phase Flow in a Horizontal Flat Narrow Rectangular Channel

2003 ◽  
Author(s):  
Hideo Ide ◽  
Tohru Fukano
Keyword(s):  
Surface Tension ◽  
Pressure Drop ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Pure Water ◽  
Rectangular Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Effect Of Surface

Air-liquid two-phase flow in a horizontal flat capillary rectangular channel has been studied to clarify the effects of surface tension on the flow phenomena, such as flow patterns, holdup and frictional pressure drop and so on. The concentrations of surfactant solution were 0, 10, 50 and 100 ppm and the surface tension of each solution was reduced to about 34mN/m from that of pure water of about 72mN/m. The dimension of the channel used was 10.0 mm×1.0 mm. The drag reduction by mixing the surfactant was examined in both the single phase flow and the two-phase flow. The experimental data of void fraction and two-phase frictional pressure drop were compared with the respective correlations which were previously proposed by the other researchers. Finally, we proposed new correlations of two-phase frictional pressure drop in which the effect of surface tension and the aspect ratio of cross section of channel were taken into account.

TWO-PHASE FLOW OF AN OIL-WATER SYSTEM IN POROUS MEDIA WITH COMPLEX GEOMETRY INCLUDING WATER FLOODING: MODELING AND SIMULATION

2011 ◽  
Vol 14 (7) ◽  
pp. 579-592 ◽  
Author(s):  
Francisco Alves Batista ◽  
Brauner Gongalves Coutinho ◽  
Francisco Marcondes ◽  
Severino Rodrigues de Farias Neto ◽  
Antonio Gilson Barbosa de Lima
Keyword(s):  
Porous Media ◽  
Modeling And Simulation ◽  
Two Phase Flow ◽  
Complex Geometry ◽  
Water System ◽  
Water Flooding ◽  
Phase Flow ◽  
Two Phase ◽  
Oil Water

Two Phase Computational Study of Flow Behaviour in a Region Within an Aeroengine Gearbox

2014 ◽  
Author(s):  
A. Turner ◽  
H. P. Morvan ◽  
K. Simmons
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Complex Geometry ◽  
Computational Study ◽  
Flow Behaviour ◽  
Phase Flow ◽  
Two Phase ◽  
Validation Data ◽  
Air Jet ◽  
Vof Model

Within large civil aeroengines a significant contributor to parasitic power loss (manifest as increased heat-to-oil) is the internal gearbox (IGB). An IGB typically contains high speed shafts, a spiral bevel gear pair, bearings and seals as well as the complex geometry of the stationary components. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems (UTC) has conducted experimental and computational projects to enhance understanding of two phase flow behaviour. Validated single phase modelling capability for an unmeshed shrouded crown gear has been established [1–3] and discrete phase modelling [3] has been applied to investigate the oil path under the shroud. Experimental work on shroud configurations [5] and two-phase flow [6] has also been conducted at the UTC using a rig with representative but simplified geometry relative to an aeroengine. Recent modelling activity has focussed on the region behind the gear. In an aeroengine this region includes a large shaft location bearing that sheds oil into the rear chamber. This oil, combined with the high speed and complex airflows generated by proximity to the gear, makes this region particularly challenging to model. In the experimental test rig at the UTC this zone does not contain a bearing and so as yet no validation data exists. In this paper an axisymmetric sector model of the rig back chamber is presented. Two phase flow behaviour was modelled using the Volume of Fluid (VOF) and Eulerian models within the CFD software ANSYS-Fluent. A comparison between these two multiphase models is made and their suitability to model the oil behaviour in the back chamber is discussed. Oil flow behaviour in this region is also reported. The CFD results show that the VOF model is insufficient for predicting oil flows in this environment. Although there is a significant amount of liquid present as wall film, the liquid not on the walls appears important and is not adequately modelled by VOF, which is well-known as being most suitable where there is a definite interface between liquid and gaseous phases. The Eulerian model shows significantly more likely flow behaviour with results indicating a non-uniform distribution of oil across the axial length of the rear chamber with a bias towards the rear (bearing side). The air jet entering in the rear chamber from between the gear and shroud strongly influences flow behaviour in the rear chamber. The computed flow field is such that a full 360° model is recommended for future work of this nature.

scholarly journals Calibration of Mineralization Degree for Dynamic Pure-water Measurement in Horizontal Oil-water Two-phase Flow

2016 ◽  
Vol 16 (4) ◽  
pp. 218-227 ◽  
Author(s):  
Weihang Kong ◽  
Lei Li ◽  
Lingfu Kong ◽  
Xingbin Liu
Keyword(s):  
Electrical Conductivity ◽  
Two Phase Flow ◽  
Pure Water ◽  
Conductivity Measurement ◽  
Stratified Flow ◽  
Phase Flow ◽  
Electrical Conductivity Measurement ◽  
Two Phase ◽  
Conductance Probe ◽  
Oil Water

Abstract In order to solve the problem of dynamic pure-water electrical conductivity measurement in the process of calculating water content of oil-water two-phase flow of production profile logging in horizontal wells, a six-group local-conductance probe (SGLCP) is proposed to measure dynamic pure-water electrical conductivity in horizontal oil-water two-phase flow. The structures of conductance sensors which include the SGLCP and ring-shaped conductance probe (RSCP) are analyzed by using the finite-element method (FEM). In the process of simulation, the electric field distribution generated by the SGLCP and RSCP are investigated, and the responses of the measuring electrodes are calculated under the different values of the water resistivity. The static experiments of the SGLCP and RSCP under different mineralization degrees in horizontal oil-water two-phase flow are carried out. Results of simulation and experiments demonstrate a nice linearity between the SGLCP and RSCP under different mineralization degrees. The SGLCP has also a good adaptability to stratified flow, stratified flow with mixing at the interface and dispersion of oil in water and water flow. The validity and feasibility of pure-water electrical conductivity measurement with the designed SGLCP under different mineralization degrees are verified by experimental results.

Applicability of Modified Drift Flux Model for Bubbly Flow in 2-D/3-D Rectangular Box With Various Kinds of Obstacles

2002 ◽  
Author(s):  
Tatsuya Matsumoto ◽  
Akihiro Uchibori ◽  
Ryo Akasaka ◽  
Toshinori Seki ◽  
Shyuji Kaminishi ◽  
...  
Keyword(s):  
Mass Flow ◽  
Two Phase Flow ◽  
Complex Geometry ◽  
Perforated Plate ◽  
Phase Flow ◽  
Nitrogen Gas ◽  
Two Phase ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Flux Model

In order to develop analytical tools for the analyses of multi dimensional two-phase flow in channels with obstacles, the modified drift flux model has been applied. Numerical simulations of multi dimensional gas-liquid two-phase flow in a channel, with some kinds of obstacles inserted to simulate a simple sub-channel in the fuel bundle, were carried out. Analytical results were compared with experiments, to show the validity of the modified drift flux model. Experiments were carried out with using an apparatus of 2-D/3-D rectangular box with a perforated plate or a horizontal plate with slit hole or a vertical rod inserted. Nitrogen gas-water adiabatic two phase flow was circulated in the box. The apparatus was made of acrylic resin plates and be able to make the flow inside visualized. Two-phase flow pattern were recorded with a high-speed video camera and the mass flow rate of nitrogen gas was measured with a digital gas-mass flow meter. Comparisons between the experimental results and the numerical ones showed good agreements, thus it was verified the model would be applied for predicting flows in more complex geometry with obstacles.

scholarly journals Startup Characteristics of a Centrifugal Pump Delivering Gas-Liquid Two-Phase Flow

2014 ◽  
Vol 6 ◽  
pp. 782619 ◽  
Author(s):  
Yu-Liang Zhang ◽  
Jun-Jian Xiao ◽  
Jian-Ping Yu ◽  
Ying-Yu Ji
Keyword(s):  
Centrifugal Pump ◽  
Two Phase Flow ◽  
Pure Water ◽  
Internal Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Transient Flows ◽  
The Difference ◽  
Startup Period

The transient performance of centrifugal pumps during the startup period has drawn more and more attention in recent years due to urgent engineering needs. In order to make certain the transient startup characteristics of a high specific-speed prototype centrifugal pump delivering the gas-liquid two-phase flow, the transient flows inside the pump are numerically simulated during the startup period using the dynamic slip region method in this paper. The results show that the difference in heads mainly focuses on the later stage of the startup period when the pump is used to transmit the pure water and the gas-liquid two-phase flow, respectively. The existence of the gas phase makes the head less than that of delivering pure water. The nondimensional head coefficient is very high at the very beginning of the startup period and then quickly drops to a stable value. The continuous variation of the attack angle at the leading edges of blades is the main reason for evolution of the internal flow field during the startup period.

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