Mass-transferrate

At a particular location in a distillation column, where the temperature is 350 K and the pressure 500 m Hg, the tnol fraction of the more volatile component in the vapour is 0.7 at the interface with the liquid and 0.5 in the bulk of the vapour. The molar latent heat of the more volatile component is 1.5 times that of the less volatile. Calculate the mass transferrates (kmol m s-11 of the two components. The resistance to mass transfer in the vapour may be considered to lie in a stagnant film of thickness 0.5 mm at the interface. The diffusivity in the vapour mixture is 2 x )() ° mV. ... 

Constant Pattern Behavior In a real system the finite resistance to mass transfer and axial mixing in the column lead to departures from the idealized response predicted by equilibrium theory. In the case of a favorable isotherm the shock wave solution is replaced by a constant pattern solution. The concentration profile spreads in the initial region until a stable situation is reached in which the mass transferrate is the same at all points along the wave front and exactly matches the shock velocity. In this situation the fluid-phase and adsorbed-phase profiles become coincident. This represents a stable situation and the profile propagates without further change in shape—hence the term constant pattern. 

The limit Sc - oo implies that the normal velocity V(x,0) is asymptotically small regardless of the size of B. Thus the change in V(x, 0) is too small to affect the leading-order boundary-layer velocity distributions. Nevertheless, we shall see that the mass transferrate is still changed. The other two limits B -> oo or B - -1 both correspond to V(x, 0) —> oo, which means that the velocity profiles will change and there is an intimate coupling between the momentum and mass transfer equations. 

Because the catalysts employed in fluidized bed reactors for gas feedstocks have characteristic dimensions in the range 10 to 300 pm, the external surface area per unit weight of catalyst is significantly greater than that characteristic of fixed-bed reactors. This fact ensures that even in relatively low density fluidized beds, overall mass transferrates... 

The traditional study of suspension crystallization has been carried out using the MSMPR crystallization model. It has been found that uniform mixing in a commercial-size crystallizer, as required by the MSMPR model, is impossible to achieve. Therefore, the understanding of industrial crystallization is hampered by the use of the MSMPR model. Also, it is difficult to experimentally study the effects of mixing on crystallization, as described earlier in Section 64.2.5. Therefore, the CFD presents the means for local simulation in the tank. Furthermore, CFD simulation enables the tank to be designed so that the shape and the positioning of the impellers and the liquid velocity create the optimal level of supersaturation and mass transferrate in all locations. This is likely to result in a narrowing of the particle size distribution. 

Sward, B.K. and LeVan, M.D., Frequency response methodfor measuring mass transferrates in adsorbents via pressure perturbation. Adsorption, 9, 37-54, 2003. 

C Consider a condenser in which steam at a specified temperature is condensed by rejecting heat to the cooling water. If the beat transferrate in the condenser and the temperature rise of the cooling water is known, explain how the rale of condensation of Ihe steam and the mass flow rate of Ihe cooling water can be determined. Also, explain how the total thermal resistance R of this condenser can be evaluated in this case. 

The individual component balances are conceptually identical to component balances written for a homogeneous system. Equation 1.6, but there is now a source term due to mass transfer across the interface. There are two equations (ODEs) and two primary unknowns, ag and a/. The concentrations at the interface, af and a, are also unknown but can be found using the equilibrium relationship. Equation 11.1, and the equality of transferrates. Equations 11.5 and 11.6. For membrane reactors. Equation 11.9 supplements Equation 11.1. Solution is possible whether or not Kh is constant, but... 

The overall driving force for mass transfer is AP, = Pgo — P/Oj where (Poj) is the concentration of oxygen in the liquid phase expressed as an equivalent partial pressure. For the experimental conditions, (Pqj)/ 0 due to the fast liquid phase reaction. The oxygen pressure on the gas side varies due to the liquid head. Assume that the pressure at the top of the tank was 1 atm. Then Po2)g = 0.975 atm since the vapor pressure of water at 20°C should be subtracted. At the bottom of the tank, (Pojlj = 1 0635 atm. The logarithmic mean is appropriate AP, = 1.018 atm. Thus the transferrate was... 

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