Abstract
A simplified mechanism of turbulent heat transfer, based on a modification of Prandtl's mixing-length hypothesis, has been proposed. It is assumed that there is a continuous change of momentum and energy during the flight of the eddy. Two expressions giving the ratio of eddy diffusivities for heat and momentum were obtained for fully developed pipe flow. One is for fluids of Prandtl number ranging from 0·6 to 15 and the other for liquid metals. Both correctly predict the influence of Reynolds number, Prandtl number and radial location across the pipe on the diffusivity ratio when compared to trends revealed by limited published data. Computation of Nusselt number and temperature profile in liquid metals were carried out under conditions of constant wall flux using the deduced expression for diffusivity ratio. They agree well with experimental results. For practical calculation of film coefficient of heat transfer, the following interpolation formula may be used: N Nu = 7 + 0·05 N Pr 0.25 N Pe 0.77 which fits the calculated data with a maximum deviation of less than 12 per cent for N Pr < 0·1 and N Pe < 15,000. Limiting values of Nusselt number as N Pr → 0 and N Re → ∞ were discussed.
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