An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Thermal Aspects

1992 ◽  
Vol 114 (1) ◽  
pp. 169-178 ◽  
Author(s):  
R. Vijaykumar ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Vertical Wall ◽  
Leading Edge ◽  
Vertical Surface ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Film Boiling ◽  
Copper Block ◽  
Thermal Layer

Wall and liquid side heat fluxes near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The heat flux from the interface into the liquid and temperature profiles in the liquid thermal layer were measured using real time holographic interferometry. The wall heat flux was measured with thermocouples embedded in a copper block, one face of which served as the heated wall. The role of the leading edge vapor layer, ripples, and large bulges in modifying the liquid side heat transfer is quantified.

An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Hydrodynamic Aspects

1992 ◽  
Vol 114 (1) ◽  
pp. 161-168 ◽  
Author(s):  
R. Vijaykumar ◽  
V. K. Dhir
Keyword(s):  
Wave Amplitude ◽  
Vertical Wall ◽  
Interface Velocity ◽  
Leading Edge ◽  
Vertical Surface ◽  
Film Boiling ◽  
Smooth Interface ◽  
Wall Superheat ◽  
Highly Nonlinear ◽  
The Waves

Interface and liquid velocities near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The interface and liquid velocities in the boundary layer adjacent to the interface were measured using the hydrogen bubble flow visualization method. Photographs taken from the front and side showed the existence of a finite vapor layer at the leading edge and the existence of ripples and large-amplitude waves (bulges) on the interface. The bulges and ripples did not slide on the interface but moved in unison with the interface. The wave amplitude and wavelength were also measured. For a given subcooling and wall superheat, the amplitude, the interfacial velocity, and the wavelength were found to attain an equilibrium value several millimeters downstream of the leading edge. The waves were highly nonlinear and the interface velocities, which are found to be governed by the wave amplitude, were much larger than those predicted from the smooth interface, laminar flow theory. Streamlines in the liquid were found to expand into the wave valleys. At the wave peaks the streamlines appeared to be clustered together and the measured interface velocity gradients were high. The overall picture is one of expansion in the wave valleys and contraction (of flow) at the wave peaks. The flow field in turn is found to affect the liquid side heat transfer in subcooled film boiling significantly.

The Mechanism of and Stability Criterion for Nucleate Pool Boiling of Sodium

1969 ◽  
Vol 91 (3) ◽  
pp. 315-328 ◽  
Author(s):  
I. Shai ◽  
W. M. Rohsenow
Keyword(s):  
Heat Flux ◽  
Liquid Metals ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Thermal Layer ◽  
Minimum Heat ◽  
Bubble Growth And Departure ◽  
Recorded Temperature

Experimental data for sodium boiling on horizontal surfaces containing artificial cavities at heat fluxes of 20,000 to 300,000 Btu/ft2 hr and pressures between 40 to 106 mm Hg were obtained. Observations are made for stable boiling, unstable boiling and “bumping.” Some recorded temperature variations in the solid close to the nucleating cavity are presented. It is suggested that for liquid metals the time for bubble growth and departure is a very small fraction of the total bubble cycle, hence the delay time during which a thermal layer grows is the most significant part of the process. On this basis the transient conduction heat transfer is solved for a periodic process, and the period time is found to be a function of the degree of superheat, the heat flux and the liquid thermal properties. A simplified model for stability of nucleate pool boiling of liquid metals is postulated from which the minimum heat flux for stable boiling can be found as a function of liquid-solid properties, liquid pressure, the degree of superheat, and the cavity radius and depth. At relatively low heat fluxes, convection currents have significant effects on the period time of bubble formation. An empirical correlation is proposed, which takes into account the convection effects, to match the experimental results.

Pool Boiling Experiments on Multiwalled Carbon Nanotube (MWCNT) Forests

2006 ◽  
Vol 128 (12) ◽  
pp. 1335-1342 ◽  
Author(s):  
Hee Seok Ahn ◽  
Nipun Sinha ◽  
Mei Zhang ◽  
Debjyoti Banerjee ◽  
Shaoli Fang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Silicon Wafer ◽  
Pool Boiling ◽  
Chemical Vapor ◽  
Film Boiling ◽  
Copper Block ◽  
Multiwalled Carbon ◽  
Boiling Regime ◽  
Vertically Aligned ◽  
Working Liquid

In this study, two silicon wafer substrates were coated with vertically aligned multiwalled carbon nanotubes (MWCNT) “forests” and were used for pool boiling studies. The MWCNT forests (9 and 25μm in height) were synthesized on the silicon wafer substrates using chemical vapor deposition (CVD) process. The substrates were clamped on a cylindrical copper block with embedded cartridge heaters. The heat flux was measured using sheathed K-type thermocouples, which were placed inside the cylindrical copper block. Pool boiling experiments using refrigerant PF-5060 as the working liquid were conducted to obtain the pool “boiling curve.” The experiments were conducted in nucleate and film boiling regimes to investigate the effect of MWCNT height on pool boiling performance. Reference (control) experiments were also performed with an atomically smooth bare silicon wafer (without MWCNT coating). The results show that the MWCNT forests enhanced critical heat flux (CHF) by 25-28% compared to control experiments. For the film boiling regime, Type-B MWCNT (25μm in height) yields 57% higher heat flux at Leidenfrost point (film boiling regime) compared to control experiments. However, for the Type-A MWCNT (9μm in height) the film boiling heat flux values are nearly identical to the values obtained for the control experiments performed on bare silicon.

The Dominant Unstable Wavelength and Minimum Heat Flux During Film Boiling on a Horizontal Cylinder

1964 ◽  
Vol 86 (2) ◽  
pp. 220-225 ◽  
Author(s):  
J. H. Lienhard ◽  
P. T. Y. Wong
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Flat Plate ◽  
Transverse Direction ◽  
Horizontal Cylinder ◽  
Heat Fluxes ◽  
Taylor Instability ◽  
Film Boiling ◽  
Minimum Heat ◽  
Effect Of Surface

Predictions of the dominant unstable wavelength and the minimum heat flux during film boiling above a flat plate are found to be inapplicable in the case of boiling on small wires. New expressions are developed for the case of a horizontal cylinder, by accounting for the effect of surface tension in the transverse direction upon the Taylor instability of the interface. Original measurements of wavelengths and minimum heat fluxes on small wires are also provided. These data support the predictions.

Effect of Velocity on Heat Transfer to Boiling Freon-113

1980 ◽  
Vol 102 (1) ◽  
pp. 26-31 ◽  
Author(s):  
Salim Yilmaz ◽  
J. W. Westwater
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Film Boiling ◽  
Square Root ◽  
Peak Heat Flux

Measurements were made of the heat transfer to Freon-113 at near atmospheric pressure, boiling outside a 6.5 mm dia horizontal steam-heated copper tube. Tests included pool boiling and also forced flow vertically upward at uelocities of 2.4, 4.0 and 6.8 m/s. The metal-to-liquid ΔT ranged from 13 to 125° C, resulting in nucleate, transition, and film boiling. The boiling curves for different velocities did not intersect or overlap, contrary to some prior investigators. The peak heat flux was proportional to the square root of velocity, agreeing with the Vliet-Leppert correlation, but disagreeing with the Lienhard-Eichhorn prediction of an exponent of 0.33. The forced-flow nucleate boiling data were well correlated by Rohsenow’s equation, except at high heat fluxes. Heat fluxes in film boiling were proportional to velocity to the exponent 0.56, close to the 0.50 value given by Bromley, LeRoy, and Robbers. Transition boiling was very sensitive to velocity; at a ΔT of 55° C the heat flux was 900 percent higher for a velocity of 2.4 m/s than for zero velocity.

Heat transfer in film boiling at a vertical surface with a constant heat flux

1988 ◽  
Vol 65 (3) ◽  
pp. 718-722
Author(s):  
V. M. Budov ◽  
O. B. Samoilov ◽  
V. A. Sokolov ◽  
J. A. Shemagin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Vertical Surface ◽  
Constant Heat Flux ◽  
Film Boiling ◽  
Constant Heat

scholarly journals Characteristics of supercritical heat transfer during filmboiling of nanofluids on a vertical heated wall

2018 ◽  
pp. 29-35
Author(s):  
А. Avramenko ◽  
M. Kovetskaya ◽  
A. Tyrinov ◽  
Yu. Kovetska
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Heated Surface ◽  
Heated Wall ◽  
Film Boiling

Nanofluid using for intensification of heat transfer during boiling are analyzed. The using boiling nanofluids for cooling high-temperature surfaces allows significantly intensify heat transfer process by increasing the heat transfer coefficient of a nanofluid in comparison with a pure liquid. The properties of nanoparticles, their concentration in the liquid, the underheating of the liquid to the saturation temperature have significant effect on the rate of heat transfer during boiling of the nanofluid. Increasing critical heat flux during boiling of nanofluids is associated with the formation of deposition layer of nanoparticles on heated surface, which contributes changing in the microcharacteristics of heat exchange surface. An increase in the critical heat flux during boiling of nanofluids is associated with the formation of a layer of deposition of nanoparticles on the surface, which contributes to a change in the microcharacteristics of the heat transfer of the surface. Mathematical model and results of calculation of film boiling characteristics of nanofluid on vertical heated wall are presented. It is shown that the greatest influence on the processes of heat and mass transfer during film boiling of the nanofluid is exerted by wall overheating, the ratio of temperature and Brownian diffusion and the concentration of nanoparticles in the liquid. The mathematical model does not take into account the effect changing structure of the heated surface on heat transfer processes but it allows to evaluate the effect of various thermophysical parameters on intensity of deposition of nanoparticles on heated wall. The obtained results allow to evaluate the effect of nanofluid physical properties on heat and mass transfer at cooling of high-temperature surfaces. The using nanofluids as cooling liquids for heat transfer equipment in the regime of supercritical heat transfer promotes an increase in heat transfer and accelerates the cooling process of high-temperature surfaces. Because of low thermal conductivity of vapor in comparison with the thermal conductivity of the liquid, an increase in the concentration of nanoparticles in the vapor contributes to greater growth in heat transfer in the case of supercritical heat transfer.

scholarly journals HEAT TRANSFER FOR FILN BOILING OF A LIQUID ON A VERTICAL HEATED WALL IN A POROUS MEDIUM

2021 ◽  
Vol 43 (1) ◽  
pp. 20-29
Author(s):  
A.A. Avramenko ◽  
M.M. Kovetskaya ◽  
E.A. Kondratieva ◽  
T.V. Sorokina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Fluid Flow ◽  
Wall Temperature ◽  
Heated Wall ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients

The paper presents results of the modelling of heat transfer at film boiling of a liquid in a porous medium on a vertical heated wall. Such processes are observed at cooling of high-temperature surfaces of heat pipes, microstructural radiators etc. Heating conditions at the wall were the constant wall temperature or heat flux. An analytical solution was obtained for the problem of fluid flow and heat transfer using the porous medium model in the Darcy-Brinkman. It was shown that heat transfer at film boiling in a porous medium was less intensive than in the absence of a porous medium (free fluid flow) and further decreased with the decreasing permeability of the porous medium. A sharp decrease in heat transfer was observed for the Darcy numbers lower than five. The analytical predictions of heat transfer coefficients qualitatively agreed with the data [14] though demonstrated lower values of heat transfer coefficients for the conditions of the constant wall temperature and constant wall heat flux.

Computational fluid dynamics and experimental analysis of the heat transfer in a room with a roof solar chimney

2021 ◽  
pp. 1-26
Author(s):  
Adolfo Vazquez ◽  
Jose MA Navarro ◽  
Jesus Hinojosa ◽  
Dr. Jesús Xamán
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Experimental Analysis ◽  
Vertical Wall ◽  
Temperature Fields ◽  
Heated Wall ◽  
Transfer Coefficients ◽  
Solar Chimney

Abstract This study reports a numerical-experimental analysis of heat transfer and airflow in a scaled room with a heated wall coupled with a double-channel vertical roof solar chimney. For the experimental part, a parametric study was performed in the thermal system, considering different values of heat flux supplied to a vertical wall of the scaled room (75 and 150 W/m2) and the absorber surface of the solar chimney (151 and 667 W/m2). Experimental temperature profiles were obtained at six different depths and heights, and experimental heat transfer coefficients were computed for both heated surfaces. The renormalization group k-e turbulence model was evaluated against experimental data using computational fluid dynamics software. With the validated model, the effect of the heated wall and solar chimney on temperature fields, flow patterns, and heat transfer convective coefficients are presented and discussed. The cases with heat flux on the heated wall of the scaled room produce the biggest air changes per hour (ACH), being 30.1, 31.2, and 23.4 ACH for cases 1 to 3 respectively, while cases with no heated wall produce fewer ACH (11.72 and 12.28 for case 4 and 5). The comparison between cases with and without heat flux on one vertical wall but the same solar chimney heat flux shows that the ACH increases between 154 % and 156% respectively.

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