Effect of convection

In considering the effect of mass transfer on the boiling of a multicomponent mixture, both the boiling mechanism and the driving force for transport must be examined (17—20). Moreover, the process is strongly influenced by the effects of convective flow on the boundary layer. In Reference 20 both effects have been taken into consideration to obtain a general correlation based on mechanistic reasoning that fits all available data within 15%. 

EXP AC analyzes an interconnected network of building rooms and ventilation systems. A lumped-parameter formulation is used that includes the effects of inertial and choking flow in rapid gas transienl.s. The latest version is specifically suited to calculation of the detailed effects of explosions in the far field using a parametric representation of the explosive event. A material transport capability models the effects of convection, depletion, entrainment, and filtration of... 

S. Coriell, R. Sekerka. Effect of convective flow on morphological stability. Physico-Chem Hydrodyn 2 281, 1981. 

P. Lehmann, R. Moreau, D. Camel, R. Bolcato. A simple analysis of the effect of convection on the structure of the mushy zone in the case of horizontal Bridgman solidification. Comparison with experimental results. J Cryst Growth 183 690, 1998. 

The resistances of the Sheetrock, siding, and insulation may be viewed as conductive resistances, while the resistance at the two surfaces combine the effects of convection and radiation between the surface and its surroundings. Typical values for these resistances in units of (W/m — W/m"-°C)" ((Btu/h-ft -°F) ) are as follows ... 

Langmuir, I., The velocity of reactions in gases moving through heated vessels and the effect of convection and diffusion, J. Am. Chem. Soc., 30, 1742-1754 (1908). 

More than 20 years ago, Matsushita et al. observed macroscopic patterns of electrodeposit at a liquid/air interface [46,47]. Since the morphology of the deposit was quite similar to those generated by a computer model known as diffusion-limited aggregation (D LA) [48], this finding has attracted a lot of attention from the point of view of morphogenesis in Laplacian fields. Normally, thin cells with quasi 2D geometries are used in experiments, instead of the use of liquid/air or liquid/liquid interfaces, in order to reduce the effect of convection. 

In this contribution we present preliminary estimates of the effect of convection in 3D model stellar atmospheres of red giants on the formation of spectral lines and on the derivation of chemical abundances in stars. 

The positive effect of convection of the substrate solution on mass transfer can be observed even better with macromolecular substrates that undergo processes such as protein digestion. For example, Fig. 9 compares reversed-phase chromatograms of cytochrome c digests obtained by cleavage with trypsin immobilized in both packed and molded column reactors, and clearly demonstrates the much higher activity of the monolithic device under otherwise similar circumstances [90]. 

However, the two mechanisms interact and molecular diffusion can reduce the effects of convective dispersion. This can be explained by the fact that with streamline flow in a tube molecular diffusion will tend to smooth out the concentration profile arising from the velocity distribution over the cross-section. Similarly radial dispersion can give rise to lower values of longitudinal dispersion than predicted by equation 4.39. As a result the curves of Peclet versus Reynolds number tend to pass through a maximum as shown in Figure 4.6. 

Phelan and his colleagues described in detail the techniques of the experiment and the complete results [15]. They also developed a predictive mathematical model along with the experiments. The experiment vividly illustrated results that have been regularly observed in field trials and are reflected in the last quotation above. These results clearly show the major effect of convection in the transport process. 

G. Popped, R. Goldbrunner, F.J. Gildehaus, F.W. Kreth, P. Tanner, M. Holtmannspotter, J.C. Tonn, K. Tatsch, 0-(2-[ F]fluoroethyl)-L-tyrosine PET for monitoring the effects of convection-enhanced delivery of paclitaxel in patients with recurrent glioblastoma, Eur. J. Nucl. Med. Mol. Imaging 32(9) (2005) 1018-1025. 

Tertiary amine Alamine-336 -do- -do- ELM Shrinking core model Effect of convective transport and swelling accoimted for modeling and model verification [70]... 

Before leaving this discussion, it is important to note that other forms of Peclet numbers are also possible and may be more appropriate depending on the type of convective influence studied. For example, in the case of oscillatory flows (as in oscillatory viscometers), it is more useful to define the Peclet number as (Rfa/D), where co is the frequency of oscillation. Regardless of the particular definition, the general significance of the Peclet number remains the same, i.e., it compares the effect of convection relative to diffusion. 

Labuntsov (LI), 1956 Heat transfer to falling films (laminar flow) effects of convective heat transfer and inertia forces (neglected in Nusselt theory) considered experimentally and theoretically. 

The study of rotating disk electrode behavior provides a unique opportunity to develop a model that predicts the effect of diffusion and convection on the current. This is one of the few convective systems that have simple hydrodynamic equations that may be combined with the diffusion model developed herein to produce meaningful results. The effect of diffusion is modeled exactly as it has been done previously. The effect of convection is treated by integrating an approximate velocity equation to determine the extent of convective flow during a given At interval. Matter, then, is simply transferred from volume element to volume element in accord with this result to simulate convection. The whole process repeated results in a steady-state concentration profile and a steady-state representation of the current (the Levich equation). 

Srinivasan, V., and W.I. Higuchi. 1990. A model for iontophoresis incorporating the effect of convective solvent flow. Int J Pharm 60 133. 

At longer times the concentration profile broadens and becomes more intense. The two images at t - 2,000 s clearly show the much stronger effect close to the critical point, cf. Fig. 12d. Convection causes an asymmetry of the profile and a detailed analysis shows that the main effect of convection is the solutal rather than the thermal expansion of the mixture. Radiation pressure effects due to the laser entering from below are approximately one order of magnitude smaller and negligible. 

An ultracentrifuge is a high-speed centrifuge equipped with a suitable optical system (usually schlieren or interference optics, the latter being particularly useful when low concentrations are involved) for recording sedimentation behaviour and with facilities for eliminating the disturbing effects of convection currents and vibration. The sample is contained in a sector-shaped cell mounted in a rotor (usually c. 

In gas-solid flows well beyond the Stokes regime, the effect of convective acceleration of the gas surrounding the particle is important. To incorporate this effect into the preceding formulation, modifications of the expressions for the Stokes drag, carried mass, and Basset force in the BBO equation are necessary [Odar and Hamilton, 1964]. The modified BBO equation takes the form [Hansell et al., 1992]... 

Incorporating both the effect of convection in the Him and the temperature dependence of the viscosity into the model improves the agreement between predictions and experimental measurements. It should be noted, however, that experimental conditions were such that viscous dissipation was insignificant and the temperature drop across the film was relatively small. Consequently, non-Newtonian effects, and effects due to the temperature dependence of viscosity, were less significant than were convection effects. This may not be the case in many practical situations, in particular with polymers, whose viscosity is more temperature sensitive than that of HDPE. 

Fluidized-bed Coating of an Article A rectangular metal article with dimensions of 0.5 x 5.0 x 10.0 cm is to be coated with PVC powder to a uniform coat thickness of 0.01 cm, using the fluidized-bed coating process. The fluidized-bed temperature is 20°C and the initial metal temperature is 150°C. (a) Assuming no convective losses to the fluidized bed, what would the metal temperature decrease need to be to form the desired coat thickness (b) Estimate the effect of convective heat losses on the temperature decrease of the metal. 

In this equation, the effect of convection on the temperature distribution in the melt film was neglected. This effect, however, is hardly negligible, and since equations with convection terms are hard to solve, we wish to include an approximate accounting for the effect. 

Coke microstructure is determined by the conditions in the coalesced mesophase prior to solidification. It is determined by the combined effects of convection currents, bubble percolation, and imposed shear stresses, all of which tend to deform the mesophase. 

Vertical Propagation of Flame.4—In tins case the effect of convection currents becomes increasingly pronounced. The tube in which the flame travels becomes a chimney, and, with bottom ignition, the speed of the flame is enhanced by that of the draught. With top ignition the flame tends to bum at the mouth of the tube until all the combustible mixture has risen to the top. 

To express the overall effect of convection, we use Newton s law of cooling ... 

The movement of electrically charged protein molecules in an electrical field, termed electrophoresis, is an important means of separating different protein molecules. In electrophoresis, proteins are banded into narrow zones, providing that the effects of convection are minimized, for example, by the use of a stabilizing support such as paper or polyacrylamide gel. 

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