S-ST-1-3 Non-Isothermal Pressure Drop in Laminar and Transitional Flow of Liquids Inside of Tubes
For heating or cooling, the isothermal velocity profile is distorted on account of two phenomena: a) the viscosity gradient which develops between the wall and the liquid bulk, and, b) the natural convection currents which result from a corresponding density gradient.
For our investigation 450 data points from 3 different sources were used. Most of the data were proprietary to HTRI and covered a considerably wider range of parameters than was available to past researchers.
Three presently existing methods were evaluated: a) the film temperature method of McAdams, b) the viscosity gradient method of Sieder-Tate, and c) the semi-theoretical method of Yamagata. As a general rule, all the methods predicted within ± 30% a majority of the data on which they were based originally, but failed more or less badly when tested against our large data set of extreme parameters.
A new method of correcting for the non-isothermal effects is proposed. It is based on the viscosity ratio principle, and includes a correction factor for the natural convection effects.