Axial dispersion for turbulent flow with a large radial heat flux

Abstract

In 1954, G. I. Taylor derived an expression for an apparent axial dispersion coefficient for mass transfer in turbulent flow under the assumption of no mass transport between the tube wall and the fluid inside the tube. Taylor's expression has been verified in a number of experimental efforts for both mass and heat transfer. This work extends the results of Taylor to the case where there is a significant transport of heat from the tube wall to the fluid in the tube, such as in a double‐pipe heat exchanger. Using an analysis similar to Taylor's, it is shown that the apparent axial dispersion coefficient is about one order of magnitude larger when a large radial gradient is present. Experimental data on a double‐pipe heat exchanger show significantly improved correspondence with a dispersion‐based model of the system when the larger dispersion coefficients are used.

Hydrothermal processing of Hanford tank wastes: Process modeling and control

“…For example, Taylor derived an expression for the axial dispersion for mass in turbulent flow.15 When his analysis is applied to the analogous problem of axial dispersion of heat, there is both experimental data and analysis indicating that, in the presence of large radial heat fluxes, values of the turbulent heat dispersion coefficient predicted by Taylor's analysis are an order of magnitude too 1ow. 16 Several other factors may cause significant deviations from plug flow in the hydrothermal reactors. These are denoted pictorially in Figure 11.…”

Hyperbolic axial dispersion model for heat exchangers

“…A significant breakthrough in this direction has been achieved using the concept of apparent axial dispersion phenomenon in mass transfer by Taylor [1,2] and Danckwerts [3]. From heat and mass transfer analogy it is established [4,5] that the same concept can be used for heat transfer as well. The main attraction of axial dispersion model is its power to effectively amend the prediction of plug flow model while still retaining the latter's simplicity of unidirectional characteristics.…”