The characteristic dimension in scraped surface heat transfer

Abstract

Previous published work on scraped surface falling film heat exchangers has used the tube diameter as the characteristic dimension. The present investigation confirms that in such equipment the liquid is carried as a fillet, roughly triangular in shape in front of the blades. Using an equivalent diameter based on flow area of the fillet and the length of the are in contact with the transfer surface, a correlation based on earlier results is developed which is independent of tube diameter, except in defining the rotary inertia forces. The refined correlation is:—

Flow in Agitated Thin Film Horizontal Evaporator

“…In Eq. (8), Vis the circumferential velocity of the wiping blade tip and v is the kinetic viscosity. By using the Boussinesq coefficient."…”

HEAT TRANSFER IN THIN‐FILM WIPED‐SURFACE EVAPORATION of MODEL LIQUID FOODS

“…Liquid film thickness varies in such units both axially and circumferentially . According to visual observations (Bott and Romero 1966;Kiss ef ul. 1977;Nakamura and Watanabe 1982), the rotating wiper pushes the liquid layer in front of it forming so called "bow wave" or "liquid fillet".…”

“…A number of researchers (Lustenader ef al. 1959;Bott and Romero 1966) main-tained that the evaporation process takes place only from the interface between the liquid f i l m and the vapors, and that the violent wiping action at the heat transfer surface surpresses nucleation. However, contrary opinion was presented by Ziolkowski and Skoczylas (1966).…”

HYDRODYNAMICS and HEAT TRANSFER IN THIN FILM SCRAPED SURFACE HEAT EXCHANGERS — A REVIEW

“…(27) the tube diameter has been used as the characteristic dimension. Bott and Romero (1966), and Bott (1966) pointed out at the time that this criterion may not be reliable when the tube diameter is substan-tialIy different from the one used in the experiments. It would be an improvement if the correlations were expressed in a form which would not change with variation in the diameter of the tube.…”