scholarly journals Incipience of the intensive heat transfer regime at cooling high-temperature bodies in subcooled liquid

2021 ◽  
Vol 2057 (1) ◽  
pp. 012049
Author(s):  
P K Kanin ◽  
V V Yagov ◽  
A R Zabirov ◽  
M A Lexin
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Solid Wall ◽  
Longitudinal Velocity ◽  
Vertical Plane ◽  
Film Boiling ◽  
Vapor Film ◽  
Subcooled Liquid ◽  
Wall Superheat ◽  
Good Agreement

Abstract Cooling in film boiling is usually an unwanted process in many technologies due to low intensity of heat transfer. Thus, predicting the solid wall superheat at vapor film destabilization is useful to avoid this phenomenon. In the present paper, two new semi-empirical models for evaluation of the wall superheat at destabilization of vapor film around the metallic body cooled in saturated or in subcooled liquid are proposed. Both models with fitted empirical multipliers are in good agreement with an experimental dataset. To evaluate the contribution of the natural convection in the model for temperature head at cooling in subcooled liquid, a problem about the natural convection near the vapor film, occurring during film boiling along the vertical plane, is numerically solved by means of ANES20XE CFD-code. The computational results of longitudinal velocity are in good agreement with the theoretical velocity of natural convection used in the model.

Subcooled Pool Film Boiling Heat Transfer From Spheres With Superhydrophobic Surfaces: An Experimental Study

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Li-Wu Fan ◽  
Jia-Qi Li ◽  
You-You Su ◽  
Huan-Li Wang ◽  
Ting Ji ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Atmospheric Pressure ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Superhydrophobic Surfaces ◽  
Film Boiling ◽  
Vapor Film ◽  
Wall Superheat ◽  
Static Contact

Pool film boiling was studied by visualized quenching experiments on stainless steel spheres in water at the atmospheric pressure. The surfaces of the spheres were coated to be superhydrophobic (SHB), having a static contact angle greater than 160 deg. Subcooled conditions were concerned parametrically with the subcooling degree being varied from 0 °C (saturated) to 70 °C. It was shown that film boiling is the overwhelming mode of heat transfer during the entire course of quenching as a result of the retention of stable vapor film surrounding the SHB spheres, even at very low wall superheat that normally corresponds to nucleate boiling. Pool boiling heat transfer is enhanced with increasing the subcooling degree, in agreement with the thinning trend of the vapor film thickness. The heat flux enhancement was found to be up to fivefold for the subcooling degree of 70 °C in comparison to the saturated case, at the wall superheat of 200 °C. A modified correlation in the ratio form was proposed to predict pool film boiling heat transfer from spheres as a function of the subcooling degree.

Film Boiling Incipience at the Departure From Natural Convection on Flat, Smooth Surfaces

1998 ◽  
Vol 120 (2) ◽  
pp. 402-409 ◽  
Author(s):  
J. Y. Chang ◽  
S. M. You ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Smooth Surface ◽  
Boiling Curve ◽  
Film Boiling ◽  
Smooth Surfaces ◽  
Wall Superheat ◽  
Boiling Incipience ◽  
Minimum Heat

The present research is an experimental study of pool boiling nucleation behavior using flat, smooth surfaces immersed in saturated highly wetting liquids, FC-72 and FC-87. A flush-mounted, copper surface of 10 mm × 10 mm is used as a heat transfer surface, simulating a microelectronic chip surface. At the nucleation incipient points of higher wall superheats with steady increase of heat flux, vapor film blankets the smooth surface and remains on the surface. To predict this film boiling incipience phenomenon from the smooth surface, an incipience map is developed over the boiling curve. When the incipient heat flux is higher than the minimum heat flux (MHF) and the incipient wall superheat value is higher than the transition boiling curve value at the incipient heat flux, the transition from single-phase natural convection to film boiling is observed at the incipient point. To prevent film boiling incipience, a microporous coating is applied over the smooth surface, which decreases incipient wall superheat and increases minimum heat flux. The film boiling incipience should be avoided to take advantage of highly efficient nucleate boiling heat transfer for the cooling of high-heat-flux applications.

scholarly journals CuO–Water Nanofluid Magnetohydrodynamic Natural Convection inside a Sinusoidal Annulus in Presence of Melting Heat Transfer

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
M. Sheikholeslami ◽  
R. Ellahi ◽  
C. Fetecau
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Melting Heat ◽  
Melting Heat Transfer ◽  
Limiting Case ◽  
Good Agreement ◽  
Melting Parameter

Impact of nanofluid natural convection due to magnetic field in existence of melting heat transfer is simulated using CVFEM in this research. KKL model is taken into account to obtain properties of CuO–H2O nanofluid. Roles of melting parameter (δ), CuO–H2O volume fraction (ϕ), Hartmann number (Ha), and Rayleigh (Ra) number are depicted in outputs. Results depict that temperature gradient improves with rise of Rayleigh number and melting parameter. Nusselt number detracts with rise of Ha. At the end, a comparison as a limiting case of the considered problem with the existing studies is made and found in good agreement.

THE COEFFICIENT OF HEAT TRANSFER FOR VERTICAL SURFACES IN STILL AIR

1937 ◽  
Vol 15a (7) ◽  
pp. 109-117
Author(s):  
R. Ruedy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Loss ◽  
Temperature Difference ◽  
Plane Surface ◽  
Vertical Plane ◽  
Black Body ◽  
Average Temperature ◽  
Fourth Root

For a vertical plane surface in still air the coefficient of heat transfer, valid within the range of temperatures occurring in buildings, depends on the temperature and the height of the surface. If black body conditions are assumed for the heat lost by radiation, the coefficient is equal to 1.39, 1.50, 1.62, and 1.73 B.t.u. per sq. ft. per ° F. at 32°, 50°, 68°, and 86° F. respectively, the height of the heated surfaces being 100 cm. Convection is responsible for about one-third, and radiation, mainly in the region of 10 microns, for about two-thirds of the heat loss. Convection currents depend on the temperature difference, while radiation depends on the average temperature. When attempts are made to stop convection currents by placing obstacles across the surface, the loss of heat due to natural convection varies inversely as the fourth root of the height, providing that the nature of the flow of air remains unchanged.

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