Effect of channel size

The volumetric mass transfer coefficients were calculated for different channel sizes and as it can be seen in Fig. 6.14, for a constant channel length of 10.5 cm an increase in the mixture velocity leads to an increase of the kLU in all channel sizes. As discussed above, an increase in mixture velocity intensifies the mixing within the plugs and increases the interfacial area available for mass transfer. In addition, the mass transfer coefficients reduce as they channel size increases. This is attributed to more intense mixing and an increase in interfacial area as the channel size decreases. For example, for Unux = 0-01 m the specific interfacial area decreases by about 66 % by increasing the channel size from 0.5 to 1 mm ID and 60 % by increasing from 1 to 2 mm ID. At the same conditions, as it can be seen from Fig. 6.14 the kLtt decreases by about 50 % from 0.5 to 1 mm ID, and about 33 % from 1 to 2 mm ID. 

However, when the mass transfer coefficients achieved at a constant residence time, different trends are observed for the different chaimel sizes as it can be seen in Fig. 6.15. With increasing mixture velocity in the 0.5 mm ID channel the kL increases, in the 1 mm ID channel it remains almost constant, while in the 2 mm ID channel it reduces. These differences are attributed to the different circulation 

14 Mass transfer coefficient as a function of the mixture velocity for the 3 different ehannels and ehannel length Lch = 10.5 cm. TBP/[C4mim][NTf2] (30 %, v/v) used for the extraetions 

The evolution of kLa along the channel at a constant mixture velocity (Umix = 0.03 m s ) also seems to depend on channel size (Fig. 6.16). For these measurements the results from the different length channels (10, 20 and 30 cm) were used. For the 0.5 mm ID channel the mass transfer coefficient increases along the length of the channel until it reaches a maximum value and then decreases. The mass transfer coefficient reaches a value of 0.24 s in the first 10 cm channel length, while it subsequently increases by 12.5 % to 0.27 s followed by a decrease of 8 % to 0.25 s , in the next 20 and 30 cm respectively. This indicates that most of the mass transfer is achieved between the mixing point of the two fluids and the first 10 cm of the separator. In contrast, in the 1 mm and the 2 mm ID channels the mass transfer coefficient decreases continuously along the separator after the first 10 cm. 

6 Liquid-liquid Mass Transfer Using Ionic Liquids 

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The quasi-one-dimensional model of laminar flow in a heated capillary is presented. In the frame of this model the effect of channel size, initial temperature of the working fluid, wall heat flux and gravity on two-phase capillary flow is studied. It is shown that hydrodynamical and thermal characteristics of laminar flow in a heated capillary are determined by the physical properties of the liquid and its vapor, as well as the heat flux on the wall. 

It should also be noted that in single-phase flow heat transfer, the effect of channel size is expressed by equivalent diameter. This concept, however, should be... 

Effects of Channel Size on the Mass Transfer Performance... 

The last stage of the experimental part of this research involved extractions of dioxouranium(VI) ions from nitric acid solutions into TBP/IL mixtures (30 %, v/v), relevant to spent nuclear fuel reprocessing. The effects of channel size, ionic liquid type, initial nitric acid concentration, mixture velocity, flow rate ratio, and residence time on the extraction performance of the contactor were studied. The extraction experiments were carried out in Teflon capillaries with internal diameter ranging from 0.5 to 2 mm. The results were also compared to those obtained from equilibrium experiments. 

TSAOULIDIS, D. ANGELI, P. 2015. Effect of channel size on mass transfer during liquid-liquid plug flow in small scale extractors. Chemical Engineering Journal, 262, 785-793. 

Tan, W. and T. A. Desai 2003. Microfluidic patterning of cells in extracellular matrix biopolymers Effects of channel size, cell type, and matrix composition on pattern integrity. Tissue Engineering9 2) 255-267. 

Calculate the boiling heat transfer coefficient of CO2 flow at Pgat = -16.2 C, mass velocity inside micro-/minichannels with heat flux q = 5 W/cm for hydraulic diameter Df = 0.5 mm, 1 mm, 2 mm and at quality jc = 0.1 and comment on the effect of channel size on the boiling heat transfer coefficient. 

The effect of crystal size of these zeolites on the resulted toluene conversion can be ruled out as the crystal sizes are rather comparable, which is particularly valid for ZSM-5 vs. SSZ-35 and Beta vs. SSZ-33. The concentrations of aluminum in the framework of ZSM-5 and SSZ-35 are comparable, Si/Al = 37.5 and 39, respectively. However, the differences in toluene conversion after 15 min of time-on-stream (T-O-S) are considerable being 25 and 48.5 %, respectively. On the other hand, SSZ-35 exhibits a substantially higher concentration of strong Lewis acid sites, which can promote a higher rate of the disproportionation reaction. Two mechanisms of xylene isomerization were proposed on the literature [8] and especially the bimolecular one involving the formation of biphenyl methane intermediate was considered to operate in ZSM-5 zeolites. Molecular modeling provided the evidence that the bimolecular transition state of toluene disproportionation reaction fits in the channel intersections of ZSM-5. With respect to that formation of this transition state should be severely limited in one-dimensional (1-D) channel system of medium pore zeolites. This is in contrast to the results obtained as SSZ-35 with 1-D channels system exhibits a substantially higher... 

The effect of crystallite size and shape of K-L zeolite on the dispersion of Pt was examined by a variety of techniques by Resasco and coworkers [143], They obtained multiple overlapping CO bands on these samples and were able to assign them to Pt clusters located inside the zeoHte pores (<2050cm ), near the pore mouth (2050-2075 cm" ) and outside the pores (>2075 cm" ). They were able to correlate high -octane aromatization activity with the K-L zeolite samples with short channels where most of the Pt is inside the pores. 

Slentz et al. [133] described the effects of geometry (size, shape, and dimensions) on the performance of COMOSS. Vreeland and Barron [134] described the design of functional materials for genomic and proteomic analyses in NCE. The authors discussed different polymer chemistries for micro-channel surface passivation and improved DNA separation. 

The vapor phase studies also showed that the size of the pores has an important effect on the regioselectivity of the reaction. Fig. 2 illustrates the effect of pore size on product selectivity. The highest selectivity for para-nitrotoluene was observed over H-ZSM5 followed by Mordenite, L, and MCM. The kinetic diameters of the o-, m-, and p- isomers are 6.7, 6.7, and 5.25 A respectively. Experimental results shown in Fig. 2 verify that catalysts with channel diameters of less than 7 A preferentially form the para isomer. Based on these geometric arguments alone, the small amount of ortho isomer observed with the H-ZSM5 catalyst could be generated on acid sites located on the outer surface (2). 

When a cake of porous particles is washed, solute in the pores must first diffuse to the surface of the particles. This is a slow process compared to displacement from the external channels in the cake. The curves of concentration vs. time are similar to the breakthrough curves for adsorption or other fixed-bed processes, and the equations in Chap. 25 can be applied to predict the effects of particle size, fluid velocity, and other variables. 

Figure 12.8 Effects of shape, size of molecule, and channel dimensionality molecular seiving (adapted from [22]).

Figure 3 - Effect of cell density and of channel size on heat transfer efficiency of a monolith with constant external wall temperature = 500 K. Case of ceramic monolith (Cordierite). Gas=air.

The vent opening will pass through a boss in the baffle to the back or outside of the mold. In machined molds, care must be taken so that vents miss the drilled cooling channels. When core vents cannot be used because the slots mark on the blown part will show, small drilled holes can be used. The effect of the size of hole on the surface of the part is shown in Figure 26. 

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