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Monday, August 3, 2020 | History

1 edition of Effect of vapor velocity on film condensation found in the catalog.

Effect of vapor velocity on film condensation

by James Hamilton Webber

  • 213 Want to read
  • 19 Currently reading

Published by Massachusetts Institute of Technology .
Written in English

    Subjects:
  • Mechanical engineering

  • Edition Notes

    Thesis ( )--Massachusetts Institute of Technology, 1955.

    ID Numbers
    Open LibraryOL24995437M

    Dropwise condensation occurs when a vapor condenses on a surface not wetted by the condensate. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. For instance, the heat transfer coefficient for dropwise condensation of steam is around 10 times that for film. effect on the properties of the liquid film). The areas of the calculational cells, which were periodically repeated in the x-y directions parallel to the surface [with no periodicity applied along the film thickness direction (z)], were X lo3 A2 (i.e., a linear dimension of A). A reflect-.

    Water changes its state between a solid in the form of snow and ice, liquid water and a gas in water vapor in a continual cycle. Water vapor condenses when the gas particles cool to a temperature that allows liquid droplet to form. The process in which water vapor turns to liquid is condensation. Condensation is the change in phase of a gas upon the surface of a solid due to its loss of energy to that solid. Water droplets often form on the surface of cool substances because the water vapor in the air loses energy when it comes into contact with the cold substance and turns to a liquid.

    Effects of Various Physical Conditions on Heat Transfer of the Free Convection Film Condensation ; Complete Similarity Mathematical Models on Laminar Free Convection Film Condensation from Vapor-Gas Mixture ; Velocity, Temperature, and Concentration Fields on Laminar Free Convection Film Condensation of Vapor-Gas Mixture. Get this from a library! Theory of heat transfer with forced convection film flows. [Deyi Shang] -- Developing a new treatment of 'Free Convection Film Flows and Heat Transfer' began in Shang's first monograph and is continued in this monograph. The current book displays the recent developments of.


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Effect of vapor velocity on film condensation by James Hamilton Webber Download PDF EPUB FB2

Film condensation occurs when the temperature of a vertical, impermeable, and wettable wall next to a porous medium saturated with vapor falls below saturation temperature (Fig. ).In addition to gravity-driven downward liquid flow, the liquid also infiltrates the vapor region due to capillary force.

The latter will create a two-phase region between the liquid film and the vapor region. As stated in the previous section, the condensate film becomes turbulent at approximately Re δ = The heat transfer rate in this turbulent regime is much larger than in laminar and wavy flow.

The turbulent region in film condensation, as in any turbulent flow, is extremely difficult to model, and all accurate results come from empirical correlations or from detailed numerical modeling. The best performing tube was that with fin spacing, height, and thickness of, and mm ⁠, respectively, which had an enhancement ratio (compared to the plain tube at the same vapor-side temperature difference and vapor velocity) of at the lowest vapor velocity tested, increasing to at the highest.

For all but two of the Cited by: 8. Gas film thickness and gas-liquid film separations have certain effects on vapor-gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data.

Turbulent film condensation is much less well-understood than the laminar case, particularly in the presence of significant vapor shear stress. Transition from laminar to turbulent film condensation occurs at a film Reynolds number (4Γ/η) between 1 and 2.

This non-film condensation is called pseudo-dropwise or Marangoni condensation. This paper aims to study the main influencing factors on the Marangoni condensation of steam–ethanol factors include the ethanol concentration, vapor pressure, vapor velocity and vapor-to-surface temperature by: Engineering Data Book III Condensation Inside Tubes θstrat is the angle from the top of the tube to the stratified layer and is thus equal to π when there is no stratified layer present.

θstrat is expressed in radians. αf is the mean heat transfer coefficient for the film obtained by integration of [] from 0 to (π-θstrat)/ heat transfer coefficient for the stratified flow.

For free convection dominated film condensation, the vapor superheating effect, Sp = (superheat parameter) results in an increase of % for a cylinder and % for a sphere in the mean. The effect of condensate-film turbulence on the.

con- densate-film coefficient is observed by Kirkbride (16). Other factors such as vapor velocity and its effect on the tur- bulence of the condensate film and literature related to them are reviewed in reference The condensation of superheated vapors.

Heat transfer measurements are reported for condensation of refrigerant and ethanediol (ethylene glycol) on a single horizontal tube with vertical downflow.

For refrigerant, vapor velocities up to around 6 m/s were obtained, while for ethanediol, velocities in Cited by: References.- 6 Condensation of Binary Vapors.- Forced-Convection Condensation of Mixtures of Vapor and Noncondensable Gas.- Mixture of Air and Saturated Steam - Graphical Solution.- Necessary Condition for the Appearance of Mist and its Effect on Condensation Characteristics.- An Approximate Solution in the Case of Small.

Nusselt already extended the film condensation theory and took into consideration the fact that the vapor flowing along the condensate film influences the velocity Cited by: 2. Condensation is the change of the physical state of matter from the gas phase into the liquid phase, and is the reverse of word most often refers to the water cycle.

It can also be defined as the change in the state of water vapor to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. Abstract. Accurate, repeatable heat-transfer data have been obtained for condensation of steam and CFC on integral-fin tubes made of copper, brass and bronze, with rectangular-section fins having fin spacing of 1 mm, fin heights in the range mm to mm and fin thicknesses in the range mm to mm; all other geometric parameters were the same for all tubes.

Film condensation • The condensate wets the surface and forms a liquid film. • The surface is blanketed by a liquid film which serves as a resistance to heat transfer. Dropwise condensation • The condensed vapor forms droplets on the surface.

• The droplets slide down when they reach a certain Size: 2MB. THE EFFECT OF VAPOR SUBCOOLING ON FILM CONDENSATION OF METALS by Eugene D.

Fedorovich+ and Warren M. Rohsenow ABSTRACT This work presents an analysis of the interfacial "vapor-condensate" temperature distribution, which includes. The process of condensation refers to the conversion of atmospheric water vapor (gas) into water (liquid).

This process is directly the opposite of evaporation. This process leads to the formation of clouds in the atmosphere. For condensation to take place, the region must experience cooler temperatures. A numerical study is performed on the laminar film condensation of pure saturated vapor flowing in the direction of gravity on a single horizontal elliptic cylinder or a bank of elliptical tubes.

Temperature, velocity distribution, and heat transfer coefficient of the fully developed flow are carried out with a fully implicit finite difference.

Heat transfer characteristics in Marangoni dropwise condensation. In the condensation of a binary vapor mixture, such as water−ethanol vapor, the Marangoni force (indicated by the arrows in Fig. 1) pulls the condensate liquid from the periphery toward the peak along the surface of a condensate drop, whereby dropwise condensation occurs.

The Marangoni force here is the driving force for Author: Yoshio Utaka, Zhihao Chen. viii. Check for allowable vapor velocity (u v) ([3] page ): The maximum vapor velocity (m/s) at the liquid surface should be less than that given by the expression below to avoid too much entrainment.

1/2 lv v v u UU U § ¨¸ ©¹ () l where, U = liquid density and, = vapor density If this criterion is not satisfied, go to step File Size: KB. within the vapor film and radiation across the vapor film.

In the absence of an experiment, the various segments of the boiling curve can also be predicted by Newton’s law of cooling, q " h (T w T sat), with the heat transfer coefficient, h, given by the following.The Leidenfrost effect is a physical phenomenon in which a liquid, close to a surface that is significantly hotter than the liquid's boiling point, produces an insulating vapor layer that keeps the liquid from boiling rapidly.

Because of this 'repulsive force', a droplet hovers over the surface rather than making physical contact with the hot surface.condensation is taken into consideration this additional species accumulates and creates noncondensable layer near the surface on water vapour condenses.

Due to this effect heat and mass transfer rates from gas mixture decreases. Also volume condensation (if it occurs) is affected by the presence of inert gases.