AN EXPERIMENTAL STUDY OF HEAT AND MOMENTUM TRANSFER IN PIPE FLOW OF VISCOELASTIC FLUIDS.

摘要

Heat transfer and pressure drop results are presented for pipe flow of aqueous solutions of polyacrylamide and polyethylene oxide in weight concentration of a few thousand parts per million. Experiments were conducted in two experimental set-ups.; The first set-up consisted of two different diameter tubes. The turbulent flow hydrodynamic entry length was found to be 110 pipe diameters. Laminar friction factor data were in good agreement with correlations for purely viscous non-Newtonian fluids. The turbulent friction factor data confirmed the existence of a maximum drag reduction asymptote. Virk's asymptote was found to be about 15% higher than the present data. It is hypothesized that some data included in Virk's correlation were taken in the entrance region and/or involved degraded solutions.; The thermal entry lengths for all flows exceeded the two test section lengths of 110 and 251 pipe diameters. Heat transfer data at X/D of 83 and 236 were analyzed. Laminar heat transfer results were in agreement with correlations for purely viscous non-Newtonian fluids. In the turbulent region, the Stanton number was found to have a Prandtl number power dependence of -2/3. Accordingly, the dimensionless heat transfer coefficients (StPr('2/3)) became a unique function of the Reynolds number at each X/D location.; The second set-up consisted of three different diameter tubes with heat transfer length-to-diameter ratio of 282, 489, and 648. The turbulent flow thermal entry length was found to be about 400 pipe diameters. The asymptotic dimensionless heat transfer coefficients were observed to be independent of pipe diameter, polymer molecular weight, and polymer concentration, suggesting the existence of a maximum heat transfer reduction asymptote. The reduction in heat transfer was found to be greater than the reduction in the friction factor when compared to the corresponding Newtonian values. All previously reported heat transfer correlations were found to predict substantially higher values than the present data. Based on the present data, heat transfer correlations in the thermal developing and fully developed regions were proposed. The phenomenological study suggests that the eddy diffusivity of heat is smaller than the eddy diffusivity of momentum in viscoelastic fluid flow.; Degradations tests were conducted by circlating polymer solution continuously in the flow loop. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI