Coupled heat/mass transfer

COUPLED HEAT/MASS TRANSFER IN NONISOTHERMAL REACTORS... 

Equation (230) reduces to the familiar equations for the simplified case of heat transfer (not coupled with mass transfer) if we let... 

Gas-liquid reactors present a number of interesting problems in reactor analysis and design which arise from the coupling of mass transfer and chemical reaction processes. Thus, the difficulty of resolving the relative contributions of filmwise and bulkwise reaction remains unsolved for all but the simplest kinetics. Such difficulties are compounded when thermal effects and significant heat release accompany the absorption and reaction. 

Figure 7.1. Change of the degree of coupling q with the alkane concentrations x, at 30°C and ambient pressure (a) and (c) straight chain alkanes, (—) /7-hexane, (—) n-heptane, (—) n-octane (b) and (d) branched-chain alkanes, (—) 3-methylpentane, (—) 2,2-dimethylpentane, (—) 2,2,4-trimethylpentane. Reprinted with the permission from Elsevier, Y. Demirel and S.l. Sandler, Int. J. Heat Mass Transfer, 43 (2002) 75.

Perrd, P. And Degiovanni A., Simulation par Volumes finis des Transferts Couple s en Milieux Poreux Anisotropes Sechage du Bois tl Basse et a haute Temperature , Int. J. Heat Mass Transfer, 33,2463,1990. 

Nordon P. and David H.G. (1967) Coupled diffusion of moisture and heat in hygroscopic textile materials, Int. J. Heat Mass Transfer, vol. 10, pp. 853-866. 

K. G. T. Hollands, G. D. Raithby, R. B. Russell, and R. G. Wilkinson, Coupled Radiative and Conductive Heat Transfer Across Honeycomb Panels and Through Single Cells, Int. J. Heat Mass Transfer (27/11) 2119-2131,1984. 

Perre, P. and Degiovanni, A., 1990. Simulations par volumes finis des transferts couples en milieu poreux anisotropes s chage du bois a basse et a haute temperature (Einite-volume simulation of the coupled transfer in anisotropic porous media Wood drying at low and high temperature), Int. J. Heat Mass Transfer, 33(11) 2463-2478. 

Heat and mass transfers in porous media are coupled in a complicated way. On the one hand, heat is transported by conduction, convection, and radiation. On the other hand, water moves under the action of gravity and pressure gradient whilst the vapor phase moves by diffusion caused by a gradient of vapor density. Thus, the heat transfer process can be coupled with mass transfer processes with phase changes such as moisture sorption/desorption and evaporation/condensation. 

Turner, J. S. 1%5. The Coupled Turbulent Transports of Salt and Heat Across a Sharp Density Interface, Int. J. Heat Mass Transfer 8, 759-767. 

L. Coupled Heat Transfer and Multicomponent Mass Transfer, with Residence-... 

The general case of coupled heat-transfer and multicomponent mass-transfer in swarms of bubbles with residence-time and size distributions is treated in Section IV, L. In previous sections simplified cases of uncoupled mass transfer are considered starting from the most simplified models available for gas-liquid dispersions. 

In this section, a general formulation will be given for the effect of bubble residence-time and bubble-size distributions on simultaneous and thermodynamically coupled heat- and mass-transfer in a multicomponent gas-liquid dispersion consisting of a large number of spherical bubbles. Here one can... 

The independent transport fluxes of simultaneous (coupled) heat- and mass-transfer in an n-component gas-liquid dispersion consisting of two phases (a = 1,2) can be written as (G3)... 

In most cases, however, heat transfer and mass transfer occur simultaneously, and the coupled equation (230) thus takes into account the most general case of the coupling effects between the various fluxes involved. To solve Eq (230) with the appropriate initial and boundary conditions one can decouple the equation by making the transformation (G3)... 

Curing of Polyimlde Resin. Thermoset processing involves a large number of simultaneous and interacting phenomena, notably transient and coupled heat and mass transfer. This makes an empirical approach to process optimization difficult. For instance, it is often difficult to ascertain the time at which pressure should be applied to consolidate the laminate. If the pressure is applied too early, the low resin viscosity will lead to excessive bleed and flash. But if the pressure is applied too late, the diluent vapor pressure will be too high or the resin molecular mobility too low to prevent void formation. This example will outline the utility of our finite element code in providing an analytical model for these cure processes. 

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