Friction and heat transfer coefficients were obtained in turbulentflow of dilute asbestos fiber suspensions through a smooth and arough tube. The 3/8 inch nickel tubes were heated electrically. Suspensionsof 50,300 and 600 ppm asbestos fibers were used at Prandtlnumbers of approximately 2, 6 and 11. These were obtained by varyingthe bulk temperature of the suspension. The surface of the rough tubeconsisted of a close-packed, granular type of roughness with a height-to-diameter ratio of 0.488. The Reynolds number range studies variedfrom 10,000 (Pr = 11) to 500,000 (Pr = 2).
Maximum friction reductions of 76% in the smooth tube and 87%in the rough tube were observed, along with even greater reductions inheat transfer rates, namely 86% in the smooth tube and 95% in the roughtube. (Heat transfer coefficients with asbestos fibers can be lower in arough tube than in a smooth tube.) In the present series of experimentsthe mechanism by which the fibers interfere with the flow lost its effectivenessat high Reynolds numbers.
The data was analyzed in light of analyses developed previouslyfor Newtonian fluids and extended to dilute fiber suspensions. The resultsindicate that the turbulent diffusivities are reduced in the wall regionand bring about a thicker viscous layer.
The most plausible mechanism which may explain the action ofthe fibers envisions interference of the fibers with the so-called "bursts"which are known to originate in the viscous layer.
