FALLING FILM HEAT TRANSFER ON VERTICAL, DOUBLY FLUTED TUBES. (VOLUMES I AND II)

An investigation of falling film heat transfer on vertical, doubly fluted tubes was performed. An experimental system was designed and constructed to investigate the performance of a single, vertical, doubly fluted tube with stem condensing on the outer surface and a falling liquid film of distilled water evaporating on the inner surface. The temperature of the condensing steam was varied from approximately 135(DEGREES)F to 205(DEGREES)F. The temperature difference between the condensing steam and the evaporating water was varied from approximately 5(DEGREES)F to 40(DEGREES)F. The liquid feedrate to the inner falling film was varied from approximately 0.125 gpm to 5 gpm.;The original analytical model of Gregorig was modified to remove certain of its limiting assumptions and then applied to the experimental data in which heat and mass balances checked within 15%. The results of this analysis were combined with a finite element analysis procedure to map the temperature field across a flute. This approach illustrated the flow path of heat from the outer condensing steam to the inner evaporating film.;A predictive model for fluted tubes was developed, and computed results were compared to the experimental results. By introducing an apparent fouling resistance into the predictive model, the results compared quite well to the experimental results for the 22-flute tube. For the 22-flute tube, the apparent fouling resistance used was 0.00032 hr.-sq.ft.-(DEGREES)F/Btu for near-atmospheric condensing conditions and 0.00076 hr.-sq.ft.-(DEGREES)F/Btu for vacuum condensing conditions. For the 44-flute tube, the apparent fouling resistance used was 0.00032 hr.-sq.ft.-(DEGREES)F/Btu for both condensing conditions. Somewhat better agreement was obtained with the 22-flute tube than the 44-flute tube. The poorer agreement obtained with the 44-flute tube was believed to be due to the sharp corner on the outer surface flute profile. The results computed with the model also compared favorably to the experimental results of others.;Two different doubly fluted tubes were investigated. Both had nominal diameters of 2 inches, a fluted length of 9.5 feet, and were made of 90% copper and 10% nickel. One tube had 22 flutes around the perimeter, and the other had 44 flutes.