Friction and Heat Transfer Characteristics in Turbulent Swirl Flow Subjected to Large Transverse Temperature Gradients

Abstract

Friction and heat transfer characteristics of turbulent air flowing through tubes with twisted strip swirl promoters were studied experimentally and analytically. Data were obtained for pitch-to-diameter ratios as low as 3.15 and for Reynolds numbers up to 100,000. Both heating and cooling tests were run for tube wall to fluid bulk temperature ratios from 0.6 to 1.9 (degR/degR) to evaluate compressibility and buoyancy effects. Both temperature-varying properties and the centrifugal force field imposed on the compressible fluid by the twisted strips cause considerable deviations from the incompressible heat transfer predictions. Experimental results are presented as deviations to the incompressible predictions and can be correlated by f=fo(Tˆw/Tˆb)−0.1(HeatingandCooling)Nu=Nuo(Tˆw/Tˆb)−0.32(1+0.25Gr/Re)(Heating)Nu=1.07Nuo(Tˆw/Tˆb)−0.1(1−0.25Gr/Re)(Cooling) where the subscript “o” refers to the incompressible analytical solution. The analysis presented is more direct and complete than the previous development by Smithberg and Landis [3]2 by also accounting for curvature effects and the significant tape distortions encountered with tightly twisted strips.