ARTICLE:

• WAVE CHARACTERISTICS OF LIQUID FILMS - CORRELATION OF HEAT TRANSFER DATA WITH VISUAL OBSERVATIONS  download article

C. Philipp
Institute of Thermal Engineering, Technische Universität Bergakademie Freiberg, Freiberg, Germany

A. Doeg
Institute of Thermal Engineering, Technische Universität Bergakademie Freiberg, Freiberg, Germany

S. Kufaas Tellefsen
Norwegian University of Science and Technology (NTNU), Trondheim, Norway

U. Gross
Institute of Thermal Engineering, Technische Universität Bergakademie Freiberg, Freiberg, Germany

ABSTRACT

Temporally averaged local condensation heat transfer coefficients previously measured by the present authors inside a vertical tube with countercurrent fully developed flow of vapour and liquid in wide ranges of Prandtl and Reynolds Numbers (Re = M /(πDμ)) have been evaluated for the limiting case of zero shear stress and referred to respective results from Nusselt's (1916) theory. The well known wave-induced enhancement of heat transfer is represented by wave factors (f_w = NU/NU_NU(1916) with NU/NU_NU(1916) = (3Re)^−1/3) which are plotted vs. Reynolds Numbers and faced with wave characteristics (shape, effective wave frequency, velocity, etc.) obtained from visual observations. It is pointed out that there is a relation between the discontinuities of heat transfer and changes of wave characteristics. For this, various video cameras have been used inside and outside vertical tubes for recording pictures of the film flow with water and isopropanol.

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