Condensation vertical plate

Kinoshita, E, and Uehera, H., Turbulent Film Condensation of Binary Mixture on a Vertical Plate, ASME/JSME Thermal Engineering Conf., Vol. 2, pp367-373, 1995. 

Mori, Y, K. Hiyikata, and K Utsunomiya, The Effect of Noncondensable Gas on Film Condensation Along a Vertical Plate in an Enclosed Chamber, ASME Journal Heat Trans., V. 99, May (1977) p. 257. 

Surface tension measurements. Solutions of the betaines were prepared with quartz-condensed, distilled water, specific conductance, 1.1 X 10" mho cm" at 25°C. All surface tension measurements were made by Wilhelmy vertical plate technique. Solutions to be tested were immersed in a constant-temperature bath at the desired temperature 0.02°C and aged for at least 0.5 h before measurements were made. The pH of all solutions was > 5.0 (usually, in the range 5.5-5.9), where surface properties show no change with pH. 

The situation shown in Fig. 11.5 s considered here, i.e., consideration is given to film condensation on a cold isothermal vertical plate, held at temperature 7, which is exposed to a reservoir of saturated vapor at saturation temperature, Ts. 

The above analysis of condensation on a vertical plate can be easily extended to condensation on an inclined plate. Consider a plate inclined at an angle, 0, with respect to the gravity vector as shown in Fig. 11.10. 

The basic Nusselt analysis ignores inertial effects in the condensed film and subcooling effects. Approximate methods of accounting for subcooling were discussed above. A method of accounting for both effects is discussed in this section. To illustrate the method, condensation on an isothermal vertical plate is again considered [52] to [54]. Interfacial shear stress effects will be neglected. 

The rate of condensation on a vertical surface is controlled by the force of gravity acting on the condensed liquid film. A consideration of Eq. (11.20) shows for example that for a vertical plate the mean heat transfer rate from the plate with laminar flow in the film is proportional to gw. Attempts have therefore been made to increase condensation rates by using centrifugal forces instead of the gravitational force to drain the condensed liquid film from the cold surface [55], The simplest example of this would be condensation on the upper surface of a cooled circular plate rotating in a horizontal plane. This situation is shown in Fig. 11.23. A Nusselt-type analysis of this situation will be considered in the present section. 

Stagnant saturated steam at 100°C condenses onto a vertical plate with a surface temperature of 70°C. Approximately how far down the plate does the film become wavy ... 

An 8-m high by 1.5-m wide vertical plate is maintained at 5°C. Calculate the rate of condensation and the heat transfer rate, when the plate is exposed to stagnant saturated water vapor at 20°C. Include the effect of film subcooling. 

Stagnant saturated steam at 80°C condenses on a 0 -m high vertical plate with a surface temperature of 75°C. Calculate the heat transfer rate and condensation rate per meter u idth of the plate assuming that the flow in the liquid film is steads and laminar. Also find the maximum film thickness. 

Consider laminar film condensation on a vertical plate when the vapor is flow ing parallel to the surface in a downward direction at velocity, V. Assume that a turbulent boundary layer is formed in the vapor along the outer surface of the laminar liquid film. Determine a criterion that will indicate when the effect of the shear stress at the outer edge of the condensed liquid film on the heat transfer rate is less than 59c. Assume that pv [Pg.602]

Film condensation on a vertical plate may be analyzed in a manner first proposed by Nusselt [I], Consider the coordinate system shown in Fig. 9-2. The plate temperature is maintained at 7 ,. and the vapor temperature at the edge of the him is the saturation temperature TK. The him thickness is represented by <5, and we choose the coordinate system with the positive direction of. v measured downward, as shown. It is assumed that the viscous shear of the vapor on the him is negligible at y -- 8. It is further assumed that a linear temperature distribution exists between wall and vapor conditions. The weight of the fluid element of thickness dx between y and 8 is balanced by the viscous-shear force at y and the buoyancy force due to the displaced vapor. Thus... 

Show that the condensation Reynolds number for laminar condensation on a vertical plate may be expressed as... 

A 50 by 50 cm square vertical plate is maintained at 95 C and exposed to saturated steam at 1 atm pressure. Calculate the amount of steam condensed per hour. 

B Derive a relation for the heat transfer coefficient in laminar film condensation over a vertical plate,... 

We now consider film condensation on a vertical plate, as shown in Fig. 10 21. I he liquid film starts fornring at the top of the plate and flows downward under the influence of gravity, The thickness of the film S increases in the flow direction x because of continued condensation at the liquid-vapor interface. Heat in the amount hf (the latent heat of vaporization) is released during condensation and is transferred through the film to the plate surface at temperature 7j, Note that must be below tlie saturation temperature of the vapor for condensation to occur. 

Flow regime.s during film condensation on a vertical plate. 

Consider a vertical plate of height L and width b maintained at a constant temperature r, that is exposed to vapor at the saturation temperature The downward direction is taken as the positive x-direction with the origin placed at the lop of the plate whete condensation initiates, as shown in Fig. 10-24. The surface temperature is below the saluratioii temperature (7 j < r <) and thus the vapor condenses on the surface. The liquid film flows downward under the influence of gravity. The film thickness S and thus the mass flow rate of the Condensate increases with x as a result of continued condensation on the existing film. Then heal transfer from the vapor to the plate must occur through the film, which offers resistance to heat transfer. Obviously the thicker the film, ihe larger its thermal resistance and thus the lower the rate of heal transfer. 

The volume element of condensate on a vertical plate cotisidererl ill Nusselt s analysis. 

At a Reynolds number of about 1800, the condensate flow becomes turbulent.. Several empirical relations of varying degrees of complexity are proposed for the heat transfer coefficient for turbulent flow. Again assuming Pv < p, for simplicity, Labuntsov (1957) proposed the following relation for the turbulent flow of condensate on vertical plates ... 

Nondimensionalized heat transfer coefficients for the wave-free laminar, wavy laminar, and turbulent flow of condensate on vertical plates are plotted in Fig, 10-26. 

Equation l,p-22 was developed for vertical plates, but it can also be used for laminar fififi eondensation on the upper surfaces of plates that are inclined by an angle S.ifrom the vertical, by replacing g in that equation by g cos (Fig, 10-27). This approximatiot) gives satisfactory results especially for d 60 . Note that the condensation heat transfer coefficients on vertical and inclined plates are related to each other by... 

Equation 10 22 for vertical plates can also be used to calculate the average heat transfer coefficient for laminar film condensation on the outer surfaces of vertical lubes provided that the tube diameter is large relative to the thickness of the liquid film. 

SOLUTION Saturated steam at 1 atm condenses on a vertical plate. The rates of heat transfer and condensation are to be determined. 

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