Fluted tubes

Of these special surfaces, only the double-fluted tube has seen extended services. Most of the gain in heat-transfer coefficient is due to the condensing side the flutes tend to collect the condensate and leave the lauds bare [Caruavos, Proc. First Int. Symp. Water Desalination, 2, 205 (1965)]. The coudeusiug-film coefficient (based on the actual outside area, which is 28 percent greater than the nominal area) may be approximated from the equation... 

By oxidizing 3 X 10 3 to 1 X 10 5M hydroperoxide with a large excess of ceric ammonium nitrate in methanol. The ceric and hydroperoxide solutions were mixed in an efficient mixer and then flowed through a highly fluted tube of 0.5-cc. volume before entering the ESR cavity. 

Kang, Y. T., and Christensen, R. N. (1994) Development of a Counter-Current Model for a Vertical Fluted Tube GAX Absorber, Proceedings of the International Absorption Heat Pump Conference, Jan 19-21 1994, New Orleans, LA, USA, ASME, New York, NY, USA, pp. 7-16. 

Qi, Y. Kawaguchi, Y. Lin, Z. Ewing, M Christensen, R.N. Zakin, J.L. Enhanced heat transfer of drag reducing surfactant solutions with fluted tube-in-tube heat exchanger. Int. J. Heat Mass Trans. 2001, 44 (8), 1495-1505. 

The extension of these PECs to two-phase heat transfer is complicated by the dependence of the local heat transfer coefficient on the local temperature difference and/or quality. Heat transfer and pressure drop have been considered in the evaluation of internally finned tubes for refrigerant evaporators [14] and for internally finned tubes, helically ribbed tubes, and spirally fluted tubes for refrigerant condensers [15]. Pumping power has been incorporated into the evaluation of inserts used to elevate subcooled boiling critical heat flux (CHF) [16, 17]. A discussion of the application of enhancement to two-phase systems is given by Webb [373],... 

Cox et al. [101] used several kinds of enhanced tubes to improve the performance of horizontal-tube multiple-effect plants for saline water conversion. Overall heat transfer coefficients (forced convection condensation inside and spray-film evaporation outside) were reported for tubes internally enhanced with circumferential V grooves (35 percent maximum increase in U) and protuberances produced by spiral indenting from the outside (4 percent increase). No increases were obtained with a knurled surface. Prince [102] obtained a 200 percent increase in U with internal circumferential ribs however, the outside (spray-film evaporation) was also enhanced. Luu and Bergles [15] reported data for enhanced condensation of R-113 in tubes with helical repeated-rib internal roughness. Average coefficients were increased 80 percent above smooth-tube values. Coefficients with deep spirally fluted tubes (envelope diameter basis) were increased by 50 percent. 

Several studies considered commercial deep spirally fluted tubes for horizontal singletube and tube-bundle condensers [152-154]. Commercially available configurations bear some resemblance to the Gregorig profile shown in Fig. 11.21. The derived condensing coefficients (envelope basis) range from essentially no improvement to over 300 percent above the plain-tube values. 

Barnes and Rohsenow [161] present a simplified analytical procedure for determining the performance of vertical fluted-tube condensers. For a sine-shaped flute, the average condensing heat transfer coefficient depends on tube geometry approximately as follows ... 

An important large-scale test of a doubly fluted tube for OTEC condenser service was reported by Lewis and Sather [162]. The tube is the same one noted earlier under enhancement of falling-film evaporation [136]. The ammonia-side heat transfer coefficient was enhanced several times to a value of 3730 Btu/(h-ft2-°F), or 21,181 W/(m2-K). 

A major study of condensing on the outside of vertical enhanced tubes has been carried out at Oak Ridge National Laboratory in connection with geothermal Rankine cycle condensers. About 12 tubes were tested with ammonia, isobutane, and various fluorocarbons. The report by Domingo [163] on R-ll concluded that the best surface was the axially fluted tube, followed, in order, by the deep spirally fluted tube, spiral tubes, and roped tubes. The composite (vapor and tube wall) heat transfer coefficient was as much as 5.5 times the smooth-tube value. This high performance was further improved to a factor of 7.2 by using skirts to periodically drain off the condensate. 

J. J. Lorenz, D. T. Yung, D. L. Hillis, and N. F. Sather, OTEC Performance Tests of the Camegie-Mellon University Vertical Fluted-Tube Evaporator, ANL/OTEC-PS-5. Argonne National Laboratory, Argonne, IL, July 1979. 

C. G. Bames Jr. and W. M. Rohsenow, Vertical Fluted Tube Condenser Performance Prediction, Proc. 7th Int. Heat Trans. Conf, Hemisphere, Washington, DC, vol. 5, pp. 39-43,1982. 

S. M. MacBain and A. E. Bergles, Heat Transfer and Pressure Drop Characteristics of Forced Convection Evaporation in Deep Spirally Fluted Tubing, in Convective Flow Boiling, J. C. Chen ed., pp. 143-148, Taylor Francis, Washington, DC, 1996. 

The catalyst can also be cast into a monolith form and used for counter-current vapor-liquid contact, Lebens et al. [39] have developed a monolith construction consisting of fluted tubes, Fig. 7.15b. The monolith construction has good gas-liquid mass-transfer characteristics. 

Althoug)i only a portion of the tube surface is available for condensation, the mean heat-transfer coefficient over the total surface is 5 to 10 times that of a smooth tube of equivalent length. Heat transfer on a fluted tube approaches that of dropwlse condensation. The flute profile is determined by the properties of the condensate. Fluids with lower surface tensions require flutes with a more pronounced curvature. The trough geometry is also determined by the amount of fluid to be removed and the fluid properties. 

The Linde surface can be used in conjunction with fluted tubes or other enhanced surfaces to greatly increase heat transfer rates. 

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