On the Development of Correlations for Bubble Liftoff Parameters During Subcooled Nucleate Flow Boiling Using Nonintrusive Dynamic Measurements

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Gulshan Kumar Sinha ◽  
Atul Srivastava
Keyword(s):  
Reynolds Number ◽  
Flow Boiling ◽  
Strong Dependence ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Maximum Deviation ◽  
Experimental Measurements ◽  
Dynamic Parameters ◽  
Bubble Dynamic ◽  
Wide Range

Abstract Accurate prediction of bubble dynamic parameters is essential to improve boiling heat transfer models. Considering the complexities and challenges associated with performing a large number of boiling experiments, researchers have realized the importance of experimental correlations for predicting bubble dynamic parameters. In this direction, we report an experimental work concerned with the development of correlations for various bubble liftoff parameters during nucleate flow boiling regime. As a definite advancement, the experimental measurements have been performed in a purely nonintrusive manner, thereby minimizing the errors arising due to the interaction of any external probe with the process under study. The measurement approach makes use of a gradient-based imaging technique to simultaneously map the bubbling features and thermal field around a single vapor bubble generated under subcooled flow boiling conditions. Experiments have been performed in a rectangular channel for a wide range of heat fluxes (q" = 20–50 kW/m2), subcooling level (ΔTsub = 2–9 K), and Reynolds numbers (Re = 600–6000) with water as the working fluid. Results show a strong dependence of bubble liftoff parameters on Reynolds number, subcooling level, and applied heat flux. Based on the experimental measurements, empirical correlations have been developed for various bubble liftoff parameters as a function of Jacob number and Reynolds number. Predictions made through the developed correlations are found to be in good agreement with the measured values as well as with the values reported in the available literature. Of all the bubble parameters, maximum deviation between the predicted and measured values (≈23%) was found to be in bubble release frequency.

Analyses of Convection Heat Transfer From Discrete Heat Sources in a Vertical Rectangular Channel

2004 ◽  
Vol 127 (3) ◽  
pp. 215-222 ◽  
Author(s):  
H. Bhowmik ◽  
C. P. Tso ◽  
K. W. Tou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Convection Heat Transfer ◽  
Working Fluid ◽  
Convection Heat ◽  
Empirical Correlations ◽  
Flux Flow ◽  
Wide Range

Steady-state experiments are performed to study the convection heat transfer from four in-line simulated chips in a vertical rectangular channel using water as the working fluid. The experimental data cover a wide range for laminar flow under natural, mixed, and forced convection conditions with the Reynolds number based on the channel hydraulic diameter ranging from 40 to 2220 and on the heat source length ranging from 50 to 2775. The heat flux ranges from 0.1W∕cm2to0.6W∕cm2. The effects of heat flux, flow rates, and chip number are investigated and results indicate that the Nusselt number is strongly affected by the Reynolds number. To develop empirical correlations, the appropriate value of the exponent n of ReD is determined to collapse all the lines into a single line to show the independence of heat flux. Based on experimental results, the empirical correlations are developed for relations using Nuℓ, ReD, and GrD. The results are compared to predictions from a three-dimensional numerical simulation, and a numerical correlation is also developed.

Computer Simulation of Mixed Convection of Alumina-Deionized Water Nanofluid Over Four In-Line Electronic Chips Embedded in One Wall of a Vertical Rectangular Channel

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Nalla Ramu ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Al2o3 Nanoparticles ◽  
Enhancement Factors

Abstract This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.

scholarly journals CFD for Subcooled Flow Boiling: Parametric Variations

2013 ◽  
Vol 2013 ◽  
pp. 1-22 ◽  
Author(s):  
Roland Rzehak ◽  
Eckhard Krepper
Keyword(s):  
Heat Flux ◽  
Power Systems ◽  
Nuclear Power ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Working Fluid ◽  
Model Parameters ◽  
Two Phase ◽  
Radial Profiles ◽  
Wide Range

We investigate the present capabilities of CFD for wall boiling. The computational model used combines the Euler/Euler two-phase flow description with heat flux partitioning. Very similar modeling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant nondimensional numbers have been realized in the DEBORA tests using dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature, and bubble size. Robust predictive capabilities of the modeling require that it is validated for a wide range of parameters. It is known that a careful calibration of correlations used in the wall boiling model is necessary to obtain agreement with the measured data. We here consider tests under a variety of conditions concerning liquid subcooling, flow rate, and heat flux. It is investigated to which extent a set of calibrated model parameters suffices to cover at least a certain parameter range.

An Experimental Study of Transient Heat Transfer From Discrete Heat Sources in Water Cooled Vertical Rectangular Channel

2004 ◽  
Vol 127 (3) ◽  
pp. 193-199 ◽  
Author(s):  
H. Bhowmik ◽  
K. W. Tou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Source ◽  
Rectangular Channel ◽  
Convection Heat Transfer ◽  
Uniform Heat Flux ◽  
Heat Sources ◽  
Discrete Heat Sources ◽  
Wide Range ◽  
Transfer Behavior

Experiments are performed to study the single-phase transient forced convection heat transfer on an array of 4×1 flush-mounted discrete heat sources in a vertical rectangular channel during the pump-on transient operation. Water is the coolant media and the flow covers the wide range of laminar flow regime with Reynolds number, based on heat source length, from 800 to 2625. The applied uniform heat flux ranges from 1 to 7W∕cm2. For flush-mounted heaters the heat transfer characteristics are studied and correlations are presented for four chips as well as for overall data in the transient regime. The experimental results indicate that the heat transfer coefficient is affected strongly by the number of chips and the Reynolds number. Finally the general impacts of heat source protrusions (B=1, 2 mm) on heat transfer behavior of four chips are investigated by comparing the results obtained from flush-mounted (B=0) heaters.

Heat Transfer in Rotating Rectangular Cooling Channels AR=4 With Angled Ribs

2002 ◽  
Vol 124 (4) ◽  
pp. 617-625 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Strong Dependence ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Rib Turbulators

An investigation into determining the effect of rotation on heat transfer in a rib-roughened rectangular channel with aspect ratio of 4:1 is detailed in this paper. A broad range of flow parameters have been selected including Reynolds number (Re=5000–40000), rotation number (Ro=0.04–0.3) and coolant to wall density ratio at the inlet Δρ/ρi=0.122. The rib turbulators, attached to the leading and trailing surface, are oriented at an angle α=45deg to the direction of flow. The effect of channel orientations of β=90 deg and 135 deg with respect to the plane of rotation is also investigated. Results show that the narrow rectangular passage exhibits a much higher heat transfer enhancement for the ribbed surface than the square and 2:1 duct previously investigated. Also, duct orientation significantly affects the leading and side surfaces, yet does not have much affect on the trailing surfaces for both smooth and ribbed surfaces. Furthermore, spanwise heat transfer distributions exist across the leading and trailing surfaces and are accentuated by the use of angled ribs. The smooth and ribbed case trailing surfaces and smooth case side surfaces exhibited a strong dependence on rotation number.

The Discharge Coefficient of a Planar Submerged Slit-Jet

2003 ◽  
Vol 125 (4) ◽  
pp. 613-619 ◽  
Author(s):  
S. K. Ali ◽  
J. F. Foss
Keyword(s):  
Reynolds Number ◽  
Velocity Distribution ◽  
Excellent Agreement ◽  
Potential Flow ◽  
Discharge Coefficient ◽  
Strong Dependence ◽  
Streamwise Velocity ◽  
Exit Plane ◽  
Nozzle Design ◽  
Wide Range

The discharge coefficient, CD, of a planar, submerged slit-jet has been determined experimentally over a relatively wide range of Reynolds number values: Re=100-6500, where the slit width (w) and the average streamwise velocity (〈U〉) at the exit plane are used to define the Reynolds number. The CD values exhibit a strong dependence on Re for Re<800. For Re>3000,CD achieves an apparent asymptotic value of 0.687 for the present nozzle design. This value is about 12% higher than the potential flow value. In contrast, the velocity distribution along the centerline was in excellent agreement with that of the potential flow solution. The experimental techniques that were used to evaluate the CDRe values, their numerical values, the corresponding uncertainties, and the possible influence of the geometrical design of the nozzle on the results are presented.

scholarly journals Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021 ◽  
Vol 931 ◽  
Author(s):  
Gulshan Kumar Sinha ◽  
Surya Narayan ◽  
Atul Srivastava
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Growth Process ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Vapour Bubble ◽  
Subcooled Flow Boiling ◽  
High Speed Cinematography ◽  
Fringe Patterns

The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

scholarly journals Numerical Scrutiny on Friction Factor Characteristics for Protruded Channel under Turbulent Cross-Flow Condition

2019 ◽  
Vol 8 (6S4) ◽  
pp. 146-150
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Working Fluid ◽  
Nozzle Flow ◽  
Duct Flow ◽  
Enhancement Of Heat Transfer ◽  
Energy Equations ◽  
Volume Method

In the present study, the effect of protrusion pitch, protrusion height, and duct Reynolds number on friction factor characteristics of small rectangular channel with protrusions in cross-flow scheme is analyzed to obtain a suitable configuration of protrusion pattern. Cross-flow is obtained by combining main duct flow (along the direction of length of duct) and nozzle flow which ejects air normal to the protruded bottom wall for the enhancement of heat transfer rate. Finite volume method is used to solve conservation of mass, momentum, and energy equations along with k-ω turbulence model for the analysis of hydraulic performance of protruded channel. Reynolds number from 8360 to 33950 for duct flow and 5120 for nozzle flow are considered with air as working fluid. It is predicted that the friction factor is increased with the increase in protrusion pitch.

Subcooled Flow Boiling in a Rectangular Channel With Added Turbulence and Longitudinal Vortices

2012 ◽  
Author(s):  
Gregor Bloch ◽  
Christina Jochum ◽  
Tobias Schechtl ◽  
Thomas Sattelmayer
Keyword(s):  
Isotropic Turbulence ◽  
Flow Boiling ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Vertical Channel ◽  
Nucleate Boiling ◽  
Secondary Flows ◽  
Heated Wall ◽  
Working Fluid ◽  
Flow Velocities

Experiments are conducted to analyze the influence of turbulence and secondary flows on heat transfer and CHF in sub-cooled flow boiling. Inserts creating turbulence and stationary vortices are placed below a vertical channel with a heated wall and upward flow direction with flow velocities up to 1.2 m/s. The boiling chamber is of square shape with inner dimensions of 40 × 40 mm2. Boiling regimes range from onset of nucleate boiling up to fully developed film boiling. Influence of the inserts is measured for varying flow velocities and subcooling from 4 K to 27 K. Flow parameters are measured with Particle Image Velocimetry (PIV). A decay of nearly isotropic turbulence within only few diameters is observed, while stationary swirls exhibit longer penetration depths. Boiling experiments are conducted with unsteady heating with a low boiling hydrocarbon (dodekafluoromethylpentanone) as working fluid. Results from boiling experiments show a positive influence of the inserts on the boiling process, increasing with higher subcooling and flow velocities.

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