Reduction of eddy diffusion for momentum and heat in viscoelastic fluid flow in a circular tube

Abstract

The velocity profile, longitudinal turbulent intensity profile, and bursting period in drag reducing pipe flow were measured using a laser Doppler technique. The temperature distribution and heat transfer coefficient were measured with thermocouples in the same system. The results of the decrease in eddy diffusivities of momentum and heat near the wall, the gross flow measurements, and the velocity distribution were shown to be in a good agreement with the predictions of the eddy diffusivity model for viscoelastic fluids previously proposed. A simple method based on the eddy diffusivity model to calculate the rate of heat transfer in the fully developed pipe flow of viscoelastic fluids is proposed, and is ascertained to be effective by the previous experiments.

Turbulent heat transfer in circular tube flows of viscoelastic fluids

“…This is consistent with the earlier observations that the heat transfer reduction, as compared to the Newtonian values at the same Reynolds and Prandtl numbers, is more drastic than the friction factor reduction in these viscoelastic fluids [8,10,[12][13][14][15].…”

“…Several investigators reported such a minimum heat transfer asymptote on the basis of their own experimental results [4][5][6][7][8][9][10]. However, these reported heat transfer results varied widely since most of the experiments were in the thermal entrance region.…”

“…These recent findings indicate that the wide variations in the turbulent heat transfer results for viscoelastic fluids reported in the literature [4][5][6][7][8][9][10] are due to one or more of the following causes: (1) the test section was too short to provide established thermal conditions, (2) the extent of polymer degradation varied from experiment to experiment, (3) the chemistry of the solvent (generally, local tap water) was different from experiment to experiment.…”

Heterogene Widerstandsverminderung bei turbulenten Rohrstr�mungen

“…Turbulenzintensitgtsmessungen in Rohren mit quadratischem Querschnitt [14][15][16] zeigen im Vergleich zu solchen am reinen L6sungsmittel ein Anwachsen der mit der Schubspannungsgeschwindigkeit u~= ~ normierten Turbulenzintensit,it in StrSmungsrichtung in der N~ihe der Wand. Dies wird bei Kreisrohren indessen nicht gefunden [17][18][19] [23,24]. Dabei zeigte sich, dab eine Widerstandsverminderung erst dann erhalten wird, wenn die Polymere bis in die N~ihe der Wand diffundiert sind.…”

“…Der Verlauf der im Wandbereich gediimpften axialen Turbulenzintensit~it stimmt mit den Messungen von Mizushina [18] iiberein, der das Maximum ebenfalls an der Stelle y/R = 0,18 fand. Die deutliche Abnahme der radialen Schwankungsintensitiit wurde auch von Schiimmer [19] beobachtet.…”