Heat transfer turbulent mixing

In turbulent flow, part of this extra energy buys something. It increases turbulence and improves heat transfer and mixing. 

Figure (10) neatly shows up the importance of the solid for providing a direct pathway for radial heat transfer. Radial mixing experiments in beds of uniform spheres would indicate a turbulent conduction limit to e of MO. Yet, measured Peclet numbers are consistently lower than this, and clearly depend upon the thermal conductivity of the packing. However, the effect of pellet conductivity appears to be logarithmic, rather than linear. 

Flow in tubular reactors can be laminar, as with viscous fluids in small-diameter tubes, and greatly deviate from ideal plug-flow behavior, or turbulent, as with gases, and consequently closer to the ideal (Fig. 2). Turbulent flow generally is preferred to laminar flow, because mixing and heat transfer... 

Neglecting flow nonuniformities, the contributions of molecular diffusion and turbulent mixing arising from stream sphtting and recombination around the sorbent particles can be considered additive [Langer et al., Int. ]. Heat and Mass Transfer, 21, 751 (1978)] thus, the axial dispersion coefficient is given by ... 

Landi,s E, and A. H. Shapiro. 1951. The Turbulent Mixing of Coaxial Gas Jets. Heat Transfer and Fluid Mechanics Institute, Preprints and Papers. Stanford University Press, California. 

Similarity for scale up, 312, 313 Dynamic, 313 Geometric, 312, 313 Kinematic, 313 Turbulence, 323 Mixing heat transfer... 

Cavitations generate several effects. On one hand, both stable and transient cavitations generate turbulence and liquid circulation - acoustic streaming - in the proximity of the microbubble. This phenomenon enhances mass and heat transfer and improves (micro)mixing as well. In membrane systems, increase of fiux through the membrane and reduction of fouling has been observed [56]. 

Rodgers, J. T., and R. G. Rosehart, 1972, Mixing by Turbulent Interchange Bundles, Correlation and Inference, Paper 72-HT-53, ASME-AIChE Natl. Heat Transfer Conf , ASME, New York. (App.)... 

Now let us consider the mixing time, t. This will be estimated by an order of magnitude estimate for diffusion to occur across the boundary layer thickness, <5Bl- If we have turbulent natural conditions, it is common to represent the heat transfer in terms of the Nusselt number for a vertical plate of height, , as... 

Fluidized-bed combustion (FBC) is a different technology from conventional pulverized-coal-fired boilers. A mixture of powdered rather than pulverized coal and a sorbent (usually limestone) are injected directly into the furnace and burned while suspended on a bed of high-velocity air. The turbulent mixing of coal and sorbent causes the solids to behave as a pseudo-fluid, enhancing heat generation and transfer at much lower temperatures (800-900 °C) compared to conventional pulverized-coal-fired furnaces (1500 °C) (US Department of Energy 1992). 

In what follows, the preceding evaluation procedure is employed in a somewhat different mode, the main objective now being to obtain expressions for the heat or mass transfer coefficient in complex situations on the basis of information available for some simpler asymptotic cases. The order-of-magnitude procedure replaces the convective diffusion equation by an algebraic equation whose coefficients are determined from exact solutions available in simpler limiting cases [13,14]. Various cases involving free convection, forced convection, mixed convection, diffusion with reaction, convective diffusion with reaction, turbulent mass transfer with chemical reaction, and unsteady heat transfer are examined to demonstrate the usefulness of this simple approach. There are, of course, cases, such as the one treated earlier, in which the constants cannot be obtained because exact solutions are not available even for simpler limiting cases. In such cases, the procedure is still useful to correlate experimental data if the constants are determined on the basis of those data. 

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