Heat and mass transfer during condensation of steam in the presence of air at pressures of up to 21 bar

Authors

  • Dr.-Ing. Reiner Numrich,

    1. Fachgruppe Verfahrenstechnik, Fachbereich Maschinentechnik, Universität-GH Paderborn, Warburger Str. 100, D-4790 Paderborn
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  • Prof. Dr.-Ing. Rolf Rennhack

    1. Fachgruppe Verfahrenstechnik, Fachbereich Maschinentechnik, Universität-GH Paderborn, Warburger Str. 100, D-4790 Paderborn
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Abstract

Film theory under consideration of one-sided diffusion is a satisfactory basis for the calculation of vapour condensation from a flowing turbulent mixture with non-condensable gases. At atmospheric pressure and low condensate flow rates, coefficient equations for smooth tubes are used as a rule. At higher pressures and thus, at higher temperatures and gas densities, there are additional parameters. For instance, non-ideal behaviour of the gas phase or the surface roughness affects the condensation process. These parameters were examined in a test plant under variation of pressure, steam concentration and temperature in a vapour/air mixture. At pressures of up to 21 bar, the Reynolds number of the gaseous phase reaches a maximum value of 128 000 and of 720 for the condensed phase. After description of the test facility, the experimental results are explained and discussed. It is shown that the experimental results are not in a good agreement with the common calculating methods. Taking into account the non-ideal behaviour of the steam/air mixture and the roughness of condensate surface by using a friction factor ξr, all the results could be calculated with an accuracy of ± 20%. This was achived with a modification of the coefficient equation of Gnielinski [1] and by using the equation of Andreussi [2] for the friction factor of a cocurrent annular flow. With respect to one-sided diffusion, the film theory is still applicable. The described method for the determination of local transfer coefficients includes the common calculating method. It represents an extension of the general validity of the film theory.

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