Coupled heat and mass transfer

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)... 

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. 

The contents of the present contribution may be outlined as follows. Section 6.2.2 introduces the basic principles of coupled heat and mass transfer and chemical reaction. Section 6.2.3 covers the classical mathematical treatment of the problem by example of simple reactions and some of the analytical solutions which can be derived for different experimental situations. Section 6.2.4 is devoted to the point that heat and mass transfer may alter the characteristic dependence of the overall reaction rate on the operating conditions. Section 6.2.S contains a collection of useful diagnostic criteria available to estimate the influence of transport effects on the apparent kinetics of single reactions. Section 6.2.6 deals with the effects of heat and mass transfer on the selectivity of basic types of multiple reactions. Finally, Section 6.2.7 focuses on a practical example, namely the control of selectivity by utilizing mass transfer effects in zeolite catalyzed reactions. 

Various formulations and methodologies have been suggested for describing combined heat and mass transfer problems, such as the integral transform technique, in the development of general solutions. In this chapter, cross phenomena or coupled heat and mass transfer are discussed using the linear nonequilibrium thermodynamics theory. 

Equations (9.69) and (9.70) represent the modeling of reaction-diffusion systems with the thermodynamically coupled heat and mass flows excluding the coupling effects due to reaction. After combining Eqs. (9.64), (9.69), and (9.70) steady-state balance equations with the coupled heat and mass transfer become... 

For a typical chemical engineering problem, the dimensions considered are generally M, L, T and 0. The dimensions F, L, T, 9 can also be used but, in this case, especially for heat transfer problems and for coupled heat and mass transfer processes, complicated dimensional formulae are derived. To establish a dimensional formula for a variable, it is necessary to have a relationship containing this variable. This relationship can be independent of the process to which the dimensional analysis is applied. The use of tables containing dimensional formulae for physical variables can also be effective. 

Killion, J. D., and Garimella, S. (2001) A Critical Review of Models of Coupled Heat and Mass Transfer in Falling-Pilm Absorption, International Journal of Refrigeration, Vol. 24(8), pp. 755-797. 

Drying Process Coupled Heat and Mass Transfer... 

Figure 1 The principle of coupled heat and mass transfer, where the energy supplied, Qm,from the shelf balances the energy required to sublime water, Qout, given mass transfer rate dmjdt. is the latent heat of sublimation at the product temperature Tp...

Successful freeze-drying, on a commercial scale, of essentially labile materials depends on a detailed understanding of the complex interplay between several disciplines ice physics, chemistry of supersaturated solutions, pharmacology, materials science of water sensitive materials, engineering of coupled heat and mass transfer, production economics and IP law. The case histories discussed in this chapter originate mainly from projects undertaken by the author and his colleagues at Pafra Biopreservation during the period 1985-1999 and from various consultancy projects undertaken by the author since that time. ... 

COUPLED HEAT AND MASS TRANSFER IN NONISOTHERMAL LIQUID-PHASE TUBULAR REACTORS WITH STRONGLY EXOTHERMIC CHEMICAL REACTIONS... 

Multiple steady-state behavior is a classic chemical engineering phenomenon in the analysis of nonisothermal continuous-stirred tank reactors. Inlet temperatures and flow rates of the reactive and cooling fluids represent key design parameters that determine the number of operating points allowed when coupled heat and mass transfer are addressed, and the chemical reaction is exothermic. One steady-state operating point is most common in CSTRs, and two steady states occur most infrequently. Three stationary states are also possible, and their analysis is most interesting because two of them are stable whereas the other operating point is unstable. 

COUPLED HEAT AND MASS TRANSFER WITH CHEMICAL REACTION IN BATCH REACTORS... 

If a batch reactor is completely insulated from the surroundings and there is only one chemical reaction, then the mass and thermal energy balances can be combined analytically to yield the maximum temperature rise for exothermic reactions. The same procedure provides an estimate of the maximum temperature drop if the reaction is endothermic. If pressure effects are negligible, in accord with the previous analyses, coupled heat and mass transfer yield (see equation 6-15) ... 

Coupled heat and mass transfer yield the following ODE for the time dependence of reactor temperature after substitution for dNi/dt ... 

THERMAL ENERGY BALANCE IN MULTICOMPONENT MIXTURES AND NONISOTHERMAL EFFECTIVENESS FACTORS VIA COUPLED HEAT AND MASS TRANSFER IN POROUS CATALYSTS... 

Steady-state analysis of coupled heat and mass transfer within the pores of catalytic pellets is based on simultaneous solution of the mass transfer equation ... 

TABLE 27-3 Numerical Results for Coupled Heat and Mass Transfer with First-Order Irreversible Exothermic Chemical Reaction in Porous Catalysts with Rectangular Symmetry"... 

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