scholarly journals Modeling of Subcooled Flow Boiling with Nanoparticles under the Influence of a Magnetic Field

Symmetry ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1275 ◽  
Author(s):  
Mohammad Abdollahzadeh Jamalabadi ◽  
Milad Ghasemi ◽  
Rezvan Alamian ◽  
Somchai Wongwises ◽  
Masoud Afrand ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Froude Number ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Subcooled flow boiling is one of the major issues in the nuclear and power generation industries. If the fluid inlet temperature in the boiling area is less than the boiling temperature, the boiling process is called subcooled boiling. The symmetry of a physical system is a constant property of the system and is fixed by deformation. Using magnetohydrodynamic (MHD) forces and broken symmetry induced by nanosized particles, fluid and thermal systems can be more controlled. In this study, the effect of a magnetic field and nanoparticles on subcooled flow boiling in a vertical tube was investigated. For this purpose, a one-dimensional numerical code was used to simulate the flow and variations of various parameters that have been investigated and evaluated. The results showed that as the flow entered the heated area, the vapor volume fraction, Froude number, fluid cross-sectional area forces, mixture velocity, fluid velocity, bubble departure diameter, liquid and vapor Reynolds numbers, squared ratio of the Froude number to the Weber number, and fluid cross-sectional area forces coefficient increased. In the same region, the Eötvös number, root mean square (RMS) of the fluid cross-sectional area force, sound velocity, liquid superficial velocity, critical tube diameter, bubble departure frequency, and density of the active nucleation site were reduced. It was also observed that after the heated area and under the influence of the magnetic field and the nanoparticles, the values of the vapor volume fraction, Froude number, fluid cross-sectional area force, mixture velocity, fluid velocity, vapor, liquid Reynolds number, and squared ratio of the Froude number to the Weber number were decreased. Moreover, there was no significant effect on the Eötvös number, liquid superficial velocity, Taylor bubble Sauter mean diameter, bubble departure diameter, critical tube diameter, bubble departure frequency, or density of the active nucleation site.

Calcium Carbonate Scale Formation During Subcooled Flow Boiling

1997 ◽  
Vol 119 (4) ◽  
pp. 767-775 ◽  
Author(s):  
S. H. Najibi ◽  
H. Mu¨ller-Steinhagen ◽  
M. Jamialahmadi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Calcium Carbonate ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Operating Conditions ◽  
Initial Surface ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Scale deposition on the heat transfer surfaces from water containing dissolved salts considerably reduces fuel economy and performance of the heat transfer equipment. In general, this problem is more serious during nucleate boiling due to the mechanisms of bubble formation and detachment. In this study, a large number of experiments were performed to determine the effect of fluid velocity, initial surface temperature, and bulk concentration on the rate of calcium carbonate deposition on heat transfer surfaces during subcooled flow boiling. A physically sound prediction model for the deposition process under these operating conditions has been developed which predicts the experimental data with good accuracy. Two previously published models are also discussed and used to predict the experimental data.

Respiratory cross-sectional area-flux measurements of the human chest wall

1990 ◽  
Vol 68 (4) ◽  
pp. 1605-1614 ◽  
Author(s):  
R. Sartene ◽  
P. Martinot-Lagarde ◽  
M. Mathieu ◽  
A. Vincent ◽  
M. Goldman ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Tidal Volume ◽  
Chest Wall ◽  
Normal Subjects ◽  
Cross Sectional Area ◽  
7 Tesla ◽  
Sectional Area ◽  
Cross Sectional ◽  
Rib Cage ◽  
Orientation Effects

A new device that utilizes the voltages induced in separate coils encircling the rib cage and abdomen by a magnetic field is described for measurement of cross-sectional areas of the human chest wall (rib cage and abdomen) and their variation during breathing. A uniform magnetic field (1.4 X 10(-7) Tesla at 100 kHz) is produced by generating an alternating current at 100 kHz in two square coils, 1.98 m on each side, parallel to the planes of the areas to be measured and placed symmetrically cephalad and caudad to these planes at a mean distance of 0.53 m. We demonstrated that the accuracy of the device on well-defined surfaces (squares, circles, rectangles, ellipses) was within 1% in all cases. Observed errors are due primarily to small inhomogeneities of the magnetic field and variation of the orientation of the coil relative to the field. Using a second magnetic field (80 kHz) perpendicular to the first, we measured the errors due to nonparallel orientation during quiet breathing and inspiratory capacity maneuvers. In 10 normal subjects, orientation effects were less than 2% for the rib cage and less than 0.7% for the abdomen. In five of these subjects, orientation effects at functional residual capacity in lateral and seated postures were generally less than or equal to 5%, but estimated tidal volume during spontaneous breathing was comparable to measurements in the supine posture. In five curarized patients, we assessed the linearity of volume-motion relationships of the rib cage and abdomen, comparing cross-sectional area and circumference measurements. Departures from linearity using cross-sectional areas were only one-third of those using circumferences. In seven normal subjects we compared cross-sectional area measurements with respiratory inductive plethysmography (RIP) and found comparable estimates of lung volume change over a wide range of relative rib cage contributions to tidal volume (-5 to 105%), with slightly higher standard deviations for the RIP (SD = 10% for RIP; SD = 4% for cross-sectional area).

Numerical investigation of the effect of bump and indent inside a vertical tube on the subcooled flow boiling and critical heat flux

2020 ◽  
Vol 14 (2) ◽  
pp. 6690-6708
Author(s):  
Kianoush DolatiAsl ◽  
Ehsan Abedini ◽  
Younes Bakhshan
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Vapour Phase ◽  
Vertical Tube ◽  
Ansys Fluent ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Euler Model

One of the essential industry problems is the critical heat flux (CHF) phenomenon in the flow boiling regime which leads to the temperature jumping and damaging to the systems. Increasing the vapour volume fraction decreases the heat transfer coefficient, and finally, temperature jump will occur. Also, the existence of the bumps and indent in the flow domain changes the flow pattern. In this study, by considering bumps and indent in the tube, the boiling of fluid flow in the vertical tube is discussed. For modelling and simulating the problems, the Euler-Euler model for studying the interaction of the liquid-vapour phases was used. Some models and material specifications are declared using the user-defined function (UDF) codes to the ANSYS Fluent program. The results show that the existence of bumps and indent inside the tube causes the flow of liquid phase to be less redirected in comparison to vapour phase flow due to having more momentum; therefore, at the end of the bumps in the tube, the amount of vapour volume fraction near the wall rises sharply. By increasing the flow mass flux, the vapour volume fraction at the end of bumps increases which lead to decreasing CHF value. It has also observed that if there are bumps and indents inside the tube, there will be no significant change in the liquid flow and vapour volume fraction in the other parts of the tube, as compared to the regular tube.    

Enhanced Flow Boiling Heat Transfer Using Radial Microchannels

2016 ◽  
Author(s):  
Alyssa Recinella ◽  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Cross Sectional Area ◽  
Working Fluid ◽  
Transfer Performance ◽  
Sectional Area ◽  
Cross Sectional ◽  
Flow Rates ◽  
Flow Cross

Flow boiling has the ability to remove high heat fluxes while maintaining a low wall superheat. Various researchers have developed enhanced microchannel geometries to improve the heat transfer performance of the system. Recently, a number of new studies have used the increasing flow cross-sectional area concept to overcome flow instabilities and record high CHF. In this work, a new geometry is experimentally investigated utilizing a radial cross-section, which provides the increasing fluid flow cross-sectional area in the flow direction. The flow boiling performance is studied using radial microchannels and water as the working fluid. Four different flow rates ranging from 120–400 mL/min are studied for this new geometry. Heat transfer performance (boiling curve and heat transfer coefficient) and pressure drop characteristics are discussed for all flow rates. Furthermore, the work is supported by high speed visualization of the bubble dynamics. The boiling performance obtained is compared to the existing data in the literature.

Experimental investigation and comparison of subcooled flow boiling of TiO2 nanofluid in a vertical and horizontal tube

2012 ◽  
Vol 227 (8) ◽  
pp. 1742-1753 ◽  
Author(s):  
E Abedini ◽  
A Behzadmehr ◽  
H Rajabnia ◽  
SMH Sarvari ◽  
SH Mansouri
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbulent Flows ◽  
Base Fluid ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Horizontal Tube ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

In this study, variations of local heat transfer coefficient are obtained in subcooled flow boiling conditions for water/TiO2 nanofluid in a vertical and horizontal tube. The results for the base fluid are compared with the predictions of the well known Shah correlation and Gnielinski formula for laminar and turbulent flows for single-phase forced convection and also with Chen correlation for subcooled flow boiling. A good agreement between the results is realized. At the subcooled regime, heat transfer coefficient of nanofluid is less than that of the base fluid and it decreases by increasing nanoparticle concentration for both of the channels; however, addition of the nanopraticles into the fluid causes that the vapor volume fraction increases.

Kinematic description of fluids in motion and approximations

2018 ◽  
Author(s):  
Marcel Escudier
Keyword(s):  
Fluid Velocity ◽  
Slip Boundary Condition ◽  
Cross Sectional Area ◽  
Constant Density ◽  
Sectional Area ◽  
Cross Sectional ◽  
Slip Boundary ◽  
Flow Problems ◽  
Mass Flowrate ◽  
Flow Through

In this chapter some of the terminology and simplifications which enable us to begin to describe and analyse practical fluid-flow problems are introduced. The terms ‘fluid particle’ and ‘streamline’ are defined. The principle of conservation of mass applied to steady one-dimensional flow through a streamtube of varying cross-sectional area resulted in the continuity equation. This important equation relates mass flowrate ṁ, volumetric flowrate Q̇, average fluid velocity V̄, fluid density ρ‎, and cross-sectional area A: m = ρ‎ Q̇ = ρ‎AV̅ = constant. For a constant-density fluid this result shows that fluid velocity increases if the cross-sectional area decreases, and vice versa. The no-slip boundary condition, a consequence of which is the boundary layer, is introduced.

scholarly journals CFD Analysis of Subcooled Flow Boiling in 4 × 4 Rod Bundle

2020 ◽  
Vol 10 (13) ◽  
pp. 4559
Author(s):  
Ye-Bon Seo ◽  
SalaiSargunan S Paramanantham ◽  
Jin-Yeong Bak ◽  
Byongjo Yun ◽  
Warn-Gyu Park
Keyword(s):  
Power Plants ◽  
Volume Fraction ◽  
Initial Conditions ◽  
Flow Boiling ◽  
Rapid Development ◽  
Model Verification ◽  
Constant Density ◽  
Subcooled Flow Boiling ◽  
Rod Bundle ◽  
Subcooled Flow

Rod bundle flow is an important research field related to reactor cooling in nuclear power plants. Owing to the rapid development of computerized performance assessments, interest in coolant flow analysis using computational fluid dynamics has garnered research interest. Rod bundle flow research data compared with experimental results under various conditions are thus needed. To address this, a boiling model verification study was conducted with reference to experiments. This study adopts the Reynolds-averaged Navier–Stokes equation, a practical analysis method compared to direct numerical simulation and large eddy simulation, including turbulence modeling, to predict the flow of coolant inside a rod bundle. This study also investigates void behavior in low-pressure subcooled flow boiling using a Eulerian approach (two-fluid model). The rod bundle has a length of 0.59 m and a hydraulic diameter of approximately 14.01 mm. At the cross-section at a height of 0.58 m, near the exit, numerical results were compared with the experimental values of the volume fraction of vapor and interfacial area concentration. The simulation results showed good agreement with the experimental data for six different initial conditions with constant density.

Experimental study of the subcooled flow boiling heat transfer of magnetic nanofluid in a vertical tube under magnetic field

2019 ◽  
Vol 140 (6) ◽  
pp. 2805-2816 ◽  
Author(s):  
Sajjad Ahangar Zonouzi ◽  
Rahmatollah Khodabandeh ◽  
Habibollah Safarzadeh ◽  
Habib Aminfar ◽  
Mousa Mohammadpourfard ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Experimental Study ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Subcooled Flow Boiling ◽  
Magnetic Nanofluid ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

Experimental investigations of aeration efficiency in high-head gated circular conduits

2014 ◽  
Vol 69 (6) ◽  
pp. 1275-1281 ◽  
Author(s):  
M. Cihat Tuna ◽  
Fahri Ozkan ◽  
Ahmet Baylar
Keyword(s):  
Froude Number ◽  
Cross Sectional Area ◽  
Experimental Investigations ◽  
Sectional Area ◽  
Flow Area ◽  
Cross Sectional ◽  
Air Bubble ◽  
Aeration Efficiency ◽  
High Head ◽  
Closed Conduit

The primary purpose of water aeration is to increase the oxygen saturation of the water. This can be achieved by using hydraulic structures because of substantial air bubble entrainment at these structures. Closed conduit aeration is a particular instance of this. While there has been a great deal of research on air-demand ratio within closed conduit, very little research has specifically addressed aeration efficiency of closed conduit. In the present work an experimental study was conducted to investigate the aeration efficiency of high-head gated circular conduits. Results showed that high-head gated circular conduits were effective for oxygen transfer. The effects of Froude number and ratio of the water cross-sectional flow area to the conduit cross-sectional area on aeration efficiency were particularly significant, whereas the effect of conduit length was only moderate. Further, a design formula for the aeration efficiency was presented relating the aeration efficiency to ratio of water cross-sectional flow area to conduit cross-sectional area and Froude number. The obtained results will be useful in future modeling processes and aid the practicing engineer in predicting aeration efficiency for design purposes.

scholarly journals Interface Tracking Simulation for Subcooled Flow Boiling Using VOSET Method

2021 ◽  
Vol 8 ◽  
Author(s):  
Kong Ling ◽  
Shuai Zhang ◽  
Wenxing Liu ◽  
Xiaowei Sui ◽  
Wenquan Tao
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Interface Tracking ◽  
Time Averaging ◽  
Subcooled Flow Boiling ◽  
Moving Interface ◽  
Subcooled Flow ◽  
Boiling Flow

This article presents a numerical simulation on subcooled flow boiling at a high-pressure condition. An interface tracking method, VOSET, was used to handle the moving interface, and conjugate heat transfer between the wall and the fluid was included in the numerical model. In order to consider the evaporation on the microlayer below a growing bubble, a depletable micorlayer model was employed. Our simulation illustrated typical processes of subcooled boiling flow including bubble sliding, coalescence, detachment and annihilation, and revealed many mechanisms in increasing the heat transfer coefficient. A transition in flow regime from isolated bubbly flow to elongated bubbly flow was reproduced by our simulations. The void fraction obtained by time-averaging the volume fraction of the vapor phase under various flow conditions was analyzed.

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