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Friction factor characteristics for flow regime transition in concentric annuli Foster, Allan Wilson

Abstract

Friction factors have been determined experimentally for flow of water and various aqueous solutions of polyethylene glycol in four different concentric annuli. The annuli studied covered a diameter ratio range of 0.0406 to 0.6331. The annular entrance was sharp-edged and no spacers were used within the system. The Reynolds number range investigated was approximately 200 to 26,000, based on equivalent diameter equal to four times the hydraulic radius. The fully developed friction factors for all four diameter ratios were correlated by the Nikuradse equation for a smooth pipe when the Reynolds number exceeded 3500 and by the Knudsen and Kata theory for laminar flow when the Reynolds number was less than 2200. Deviations from the theory of Hanks for laminar - turbulent transition in the well-developed flow region of concentric annuli could be tentatively accounted for by the extra turbulence arising from the sharp-edged entrance in the present investigation. For well-developed flow the critical Reynolds numbers for the various diameter ratios ranged between 2650 and 3700, and the mode of transition was sharp. However, for low, intermediate and high values of entrance length, respectively, three different modes of transition were found to exist in the annuli studied. Local friction factors were based on pressure gradient, uncorrected for changes in kinetic energy due to the developing velocity profile.

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