Convective enhancement factor

Regimes 2 and 3 - moderate reactions in the bulk (2) or in thefdm (3) and fast reactions in the bulk (3) For higher reaction rates and/or lower mass transfer rates, the ozone concentration decreases considerably inside the film. Both chemical kinetics and mass transfer are rate controlling. The reaction takes place inside and outside the film at a comparatively low rate. The ozone consumption rate within the film is lower than the ozone transfer rate due to convection and diffusion, resulting in the presence of dissolved ozone in the bulk liquid. The enhancement factor E is approximately one. This situation is so intermediate that it may occur in almost any application, except those where the concentration of M is in the micropollutant range. No methods exist to determine kLa or kD in this regime. 

Thus far, we are merely confirming what we did before, but when we come to the equation for the flux of solute from the surface, we have probably wrapped too much up in the dimensionless time. The empirical factor 1 + 0.672 Re1/2Sc1/3 in kc accounts for the convective enhancement of the mass transfer and the time the sphere takes to be dissolved in a stagnant fluid is the time for x to decrease from 1 to 0, which is... 

Here p, is the pressure scaled by a critical pressure, and the wall roughness Rp was 5 pm. The forced convection heat transfer enhancement factor and boiling suppression factor were used as in [27] ... 

If we want to assess the importance of convection we need to define the enhancement factor for poisoned catalysts,... 

Deactivation of large-pore slab catalysts where intraparticle convection, diffusion and first order reaction are competing mechanisms was analyzed by uniform and shelLprogressive models. For each situation, analytical solutions for concentration profiles, effectiveness factor and enhancement factor due to convection were developed thus providing a sound basis for steady-state reactor design. 

Fig. IL Enhancement factor E as a function of a and in the presence of convection (X 10). Shell-progressive model.

The convective part a c of the heat transfer coefficient includes a contribution for the heat transfer to the single-phase liquid. The rapidly flowing vapour and the vapour bubbles that are still present mean that the heat transfer coefficient ac of the single-phase forced liquid flow will be greater and has to be improved by an enhancement factor F > 1 ... 

Model equivalence (Fig. 3.4-5) leads to Eq. 4 where the enhancement factor for pore diffusivity due to convection is 1//(A) shown in Fig. 3.4-6, with... 

In contrast to rigid particles, there exists an internal circulation in drops that enhances mass transfer rates. This internal convection is accounted for by an enhancement factor E which is combined with the diffusion coefficient... 

Hamilton, J.F. et al.. Heparin coinfusion during convection-enhanced dehvery (CED) increases the distribution of the ghal-derived neurotrophic factor (GDNF) Ugand family in rat striatum and enhances the pharmacological activity of neurturin, Exp. Neurol., 168,155,2001. 

Abstract The mass transferred from one phase to the adjacent phase must diffuse through the interface and subsequently may produce interfacial effect. In this chapter, two kinds of important interfacial effects are discussed Marangoni effect and Rayleigh effect. The theoretical background and method of computation are described including origin of interfacial convection, mathematical expression, observation, theoretical analysis (interface instability, on-set condition), experimental and theoretical study on enhancement factor of mass transfer. The details of interfacial effects are simulated by using CMT differential equations. 

As stated in previous section, the mass transfer process can be enhanced by the presence of Marangoni convection. Xiao analyzed the mass transfer condition under Ma > Ma r to find the enhancement factor as follows [12]. 

Under the condition of existing Marangoni convection, the enhancement factor F can be expressed as follows ... 

The renewal of interfacial cells demonstrates the effect of Rayleigh convection in enhancing the mass transfer and promoting the mixing of the interfacial fluid with the bulk liquid. Obviously, the enhancement factor F of mass transfer is increased with increasing Rayleigh convection or Ra number. 

In the actual mass transfer process, the liquid mass transfer coefficient is enhanced by the interfacial convection, usually represented by the enhancement factor F as described in Sect. 8.8.2. The F factor calculated by Chen [32] for acetone desorption at different Ra and Rcq as given in Fig. 8.44. As shown in figure, the F factor increases with increasing Ra and Rea. The corresponding critical Ra Ra at F = 1) is seen around 10 at Reo = 13.78. 

Figure 8.44 displays the relationship between enhancement factor F and Ra at different Rcq- It is shown that F increased firstly with Ra and Rbq and became flat when F was up to about 4. This result indicates that the Rayleigh convection can promote the liquid surface renewal and intensify the mass transfer significantly only to a certain limit, which is in consistent with the experimental measurement in Sect. 8.5.2. 

Yang, W., Barth, R. R, Adams, D. M., Ciesielski, M. J., Fenstermaker, R. A., Shukla, S., Tjarks, W., and Caligiuri, M. A. 2002. Convection-enhanced delivery of boronated epidermal growth factor for molecular targeting of EGF receptor-positive gliomas. Cancer Res 62(22), 6552-6558. 

Modeling studies by Muller and Brasseur (1999) and Prather and Jacob (1997) found high contributions to P(HO , ), of up to 60% at 10-14 km, from peroxides and aldehydes during convective events over the tropics. Peroxides were the main contributor over the oceans and aldehydes over land. Jaegle et al. found large enhancements (factors of 2-5) of HO , concentrations during convective outflows in STRAT and SUCCESS, with the additional sources exceeding the contributions of 0( D) + H2O and acetone by factors of 2-10. 

Some researchers have noted that this approach tends to underestimate the lean phase convection since solid particles dispersed in the up-flowing gas would cause enhancement of the lean phase convective heat transfer coefficient. Lints (1992) suggest that this enhancement can be partially taken into account by increasing the gas thermal conductivity by a factor of 1.1. It should also be noted that in accordance with Eq. (3), the lean phase heat transfer coefficient (h,) should only be applied to that fraction of the wall surface, or fraction of time at a given spot on the wall, which is not submerged in the dense/particle phase. This approach, therefore, requires an additional determination of the parameter fh to be discussed below. 

For G/S particle systems, enhancement in convective heat transfer is achieved at the expense of increased pressure drop in moving the gas at higher velocities. A measure of the relative benefit of enhanced heat transfer to added expenditure for fluid movement can be approximated by an effectiveness factor, E, defined as the ratio of the heat transfer coefficient to some kind of a pressure drop factor. For G/S systems in which particles are buoyed by the flowing gas stream, this pressure drop factor is expressed by the Archimedes number Ar, and E can be written... 

The development of the first transdermal patches in the 1980s generated considerable interest in this route of drug administration. Soon afterwards, iontophoresis was rediscovered and its potential to contribute to the new field of transdermal drug delivery was examined. This work provided the basic principles for modern iontophoretic devices [13,18-21]. Furthermore, and importantly, they demonstrated the existence of a (primarily) electroosmotic, convective solvent flux during transdermal iontophoresis [10,11,22-24], and it was shown that the permselective properties of the skin (a) could be exploited to enhance the transport of neutral, polar species and (b) have a clear impact on ionic transport. Subsequent research has better characterized skin permselectivity and the factors which determine the magnitude of electroosmosis [25-27],... 

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