Condensation of steam

Steam is frequently used as a heating medium. The film coefficient for condensing steam can be calculated using the methods given in the previous sections but, as the coefficient will be high and will rarely be the limiting coefficient, it is customary to assume a typical, conservative, value for design purposes. For air-free steam a coefficient of 8000 W/m °C (1500 Btu/h ft °F) can be used. 

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The material to be steam-distilled (mixed with some water if a solid compound, but not otherwise) is placed in C, and a vigorous current of steam blown in from D. The mixture in C is thus rapidly heated, and the vapour of the organic compound mixed with steam passes over and is condensed in E. For distillations on a small scale it is not necessary to heat C if, however, the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner, otherwise the steady condensation of steam in C will produce too great a volume of liquid. 

Film-type condensation is more common and more dependable. Dropwise condensation normally needs to be promoted by introducing an impurity into the vapor stream. Substantially higher (6 to 18 times) coefficients are obtained for dropwise condensation of steam, but design methods are not available. Therefore, the development of equations for condensation will be for the film type only. 

General In comparison with design information on blowdown drums and cyclone separators, there is very httle information in the open technical hterature on the design of quench tanks in the Chernies industry. What is available deSs with the design of quench tanks (Sso called suppression pools) for condensation of steam or steam-water mixtures from nuclear reactor safety vSves. Information and criteria from quench tanks in the nuclear industry can be used for the design of quench tanks in the chemicS industry. There have been sev-... 

FIG. 26-47 Collapse of vessel jacket due to condensation of steam. (Vl- T. Allen, Michigan Engineering, The Dow Chemical Company, Midland, Mich., personal communication. May Z.9SS.)... 

Loss of heat input to waste heat boilers with resulting condensation of steam. 

Most steam turbines operate in the condensing (of steam on exhaust from turbine) mode or noncondensing or backpressure mode. (Steam is exhausted or extracted from the turbine at preselected exhaust pressure for other uses.) See Figures 14-17A-C, 14-18A, 14-18B, 14-19A, 14-19B, 14-20A, and 14-20B. 

Figure 26.7 Temperature profile during condensation of steam...

NOTE It is important to distinguish between water in steam resulting from partial condensation of steam and that resulting from carryover of entrained BW. Even where steam does not contain measurable carryover from mechanical action, it may still contain volatile amines, ammonia, carbon dioxide, oxygen, sulfur gases, and silica. 

Boyko, L. D. and Kruzhilin, G. N. (1967) Ini. J. Heat Mass Transfer 10, 361. Heat transfer and hydraulic resistance during condensation of steam in a horizontal tube and in a bundle of tubes. 

Case (iii). The lower left quadrant, where AH < 0, A5 < 0, is favorable only when the temperature is low enough, so that T < AH/AS. Examples are condensation of steam into water, freezing of water into ice, monomers polymerizing into polymers, CO2 absorbs into CaO. 

Drains and pots drains and pots are typically located at low points on the steam gathering system. Through valves on their lower side, any water that forms in the steam pipes by condensation of steam can be removed. 

U = he at-transfer coefficient—a constant, describing the rate of condensation of steam, on those tubes exposed to the condensing steam, (Btu/[(h)/(ft2)(°F)]... 

The total condensation of a vapor to a liquid is best illustrated by the condensation of steam to water. Figure 13.1 is a rather accurate reproduction of the radiator that heated my apartment in Brooklyn. Steam flowed from the boiler in the basement. The steam condensed inside the radiator, and flowed back into the boiler, through the condensate drain line. This is a form of thermosyphon circulation. The driving force for the circulation is the differential density between the water in the condensate drain line and the steam supply line to the radiator (see Chap. 5, discussion of thermosyphon reboilers). 

Effect of subcooling. When steam condenses at atmospheric pressure, it gives off 1000 Btu per pound of condensing steam. This is called the latent heat of condensation of steam. 

It takes less of the radiator s surface area to condense one pound of steam at 220°F than to cool off one pound of water from 220 to 120°F. And this is true, even though the condensation of steam generates 10 times as much heat as the cooling of hot water. 

The 5-1. flask is either heated with an electric mantle or placed on a steam bath to prevent condensation of steam and increase in volume of the suspension. The steam distillation must be continued beyond the point at which the distillate becomes clear. 

So, the condensation of steam releases 0.113 kj or 113 J. By the time the steam condenses and cools, it delivers 113 J + 13 J = 126 J of energy. This is nearly 10 times the amount of energy the hot water released. So, steam has the capacity to cause much more devastating burns than hot water. 

FIGURE 113 Heat transfer rates with film and dropwise condensation of steam on a vertical surface. 

In the situation being considered it will be seen that the vapor density is very small compared to the liquid density so pdpt pv) - PC is a good approximation This is usually true for the condensation of steam. 

The Jakob number is basically a measure of the importance of subcooling expressing, as it does, the change in the sensible heat per unit mass of condensed liquid in the film relative to the enthalpy associated with the phase change. The Jakob number is small for many problems, i.e the sensible heat change across the liquid film is small compared to the latent heat release. For example, for cases involving the condensation of steam, Ja, is typically of the order of 0.01. 

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