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Heat Transfer Handbook part 106. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | TREATED SURFACES 1047 potential startup problems Thome 1990 Webb 1994 Bergles 1998 . Furthermore there are limited data which indicate that the tube bundle performance in a thermosyphon reboiler may be different from that of a single tube Yilmaz et al. 1981 . A later study Jensen et al. 1992 . however sgggests that siggle-tbbe results mab be used to predict tube bundle behavior. Several attempts have been made to model the nucleate boiling mechanisms on structured surfaces and to develop predictive correlations. These analyses have tried to scale and correlate the effects of geometrical properties of the structured surface or Figure 14.8 Enhanced boiling heat transfer characteristics of water at 1 atm from a stainless steel surface coated with Teflon spots. From Young and Hummel 1965. 1048 HEAT TRANSFER ENHANCEMENT the characteristics of nucleating cavities and liquid-replenishing intercavity channels on the heat transfer. Extended discussions of several different models can be found in Nakayama et al. 1980a b Webb 1994 Chien and Webb 1998 Yabe et al. 1999 and Kim and Choi 2001 among others. For less wetting or re 1.ative 1y hihh er-suacescenten si n fluids coatings of nonwetting material e.g. Teflon on either the heated surface or its pits and cavities have been found to improve stable nucleation and reduce the required wall superheat Griffith and Wallis 1960 Young and Hummel 1965 Gaertner 1967 Vachon et al. 1969 . Young and Hummel 1965 sprayed a smooth as well as a pitted stainless steel surface oith Teflon to create spots of the no-oetting material on the heated surface and in the pits. This was found to promote nucleate boiling in water with relatively low wall superheat and three- to four-times-higher heat transfer coefficients as shown in Fig. 14.8. In a more recent study of boiling of alcohols methanol ethanol and isopropanol at atmospheric and subatmospheric pressures on a horizontal brass tube coated with polytetrafluoroethylene Vijaya Vittala et al. 2001
