A survey of experimental work on mass, momentum, and energy transport at the axis of pipes relates the ratio of turbulent diffusivity to kinematic viscosity, ε/ν, to the flow Reynolds number. A single relationship is applicable for all three transport processes. Measurements of turbulent parameters also are surveyed and related to the flow Reynolds number. From a combination of the two sets of results a correlation is obtained between ε/ν and the turbulent Reynolds number, Rl, which is possibly of general validity for isotropic turbulence. The results are based upon transport transverse to the flow (“y” direction) and yield εy/ν = 11 Rly0.65 for Rly > 100.

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