Diffusion apparatus

We can imagine measuring experimental curves equivalent to those in Fig. 9.11 by, say, scanning the length of the diffusion apparatus by some optical method for analysis after a known diffusion time. Such results are then interpreted by rewriting Eq. (9.85) in the form of the normal distribution function, P(z) dz. This is accomplished by defining a parameter z such that... 

Wiley, R.C. et al.. Efficiency studies of a continuous diffusion apparatus for the recovery of betalaines from the red table beet, J. Food Sci., 44, 208, 1979. 

I Hidalgo, K Hillgreen, G Grass, R Borchardt. Characterization of the unstirred water layer in Caco-2 cell monolayers using a novel diffusion apparatus. Pharm Res 8 222, 1991. 

The permeation technique is another commonly employed method for determining the mutual diffusion coefficient of a polymer-penetrant system. This technique involves a diffusion apparatus with the polymer membrane placed between two chambers. At time zero, the reservoir chamber is filled with the penetrant at a constant activity while the receptor chamber is maintained at zero activity. Therefore, the upstream surface of the polymer membrane is maintained at a concentration of c f. It is noted that c f is the concentration within the polymer surface layer, and this concentration can be related to the bulk concentration or vapor pressure through a partition coefficient or solubility constant. The amount... 

The enzyme urease was discovered in soybeans by Takeuchi in 1909 it catalyzed the conversion of urea to ammonium carbonate. Jack beans were another excellent source of the enzyme. Jack bean powder could be stored for considerable periods and very active, soluble, urease extracted. After the action of urease, the ammonia could be estimated colorimetrically by Nesslerisation or titrimetrically. The Conway diffusion apparatus was specially developed for the estimation of urea titrimetrically and remained in use into the 1950s. 

The crystals of NCPs containing a-satellite DNA palindrome and chicken erythrocyte histones diffracted isotropically to 3.0 A using an in-house rotating anode X-ray source and to better than 2.5 A at a moderate intensity synchrotron beamline [30,31]. The crystals used for structure determination were grown in the microgravity environment using a counter-diffusion apparatus [32]. Ground-based... 

A set of three hairless mice about 6-8 weeks old were sacrificed for each experiment by snapping the spinal cord at the neck. The circular section of the abdominal portion of the skin was excised, sufficient to fit in the diffusion apparatus. The adhering fat and visceral debris were carefully removed from each sample of the skin and soaked in normal saline solution just prior to their use in the diffusion studies. 

The phenomenon of diffusion may be used to separate various materials, Benedict and Halle et al in Kirk Othmer (Refs 12 27) describe several devices for diffusion separations, such as mass diffusion, thermal diffusion gas diffusion apparatuses... 

Gas permeabilities were measured in a Skirrow-Barrer gas diffusion apparatus operating at a partial vacuum (7). The asymmetric membrane separated a large upstream gas chamber and a small downstream gas chamber. The gas pressure change in the downstream chamber was monitored with a differential pressure transducer (MKS Baratron 586/386). 

Loschmidt diffusion apparatus (a) curves showing schematically the quantity A7 = 75, - 7 (h) cell ... 

Oxygen transport measurements were conducted at 25°C, 0% and 50% relative humidity RH, 1 atm partial oxygen pressure difference using the commercially manufactured diffusion apparatus OX-TRAN 2/20 (Modem Control Inc.). This apparatus employs a continuous-flow method (ASTM-D 3985-81) to measure oxygen flux, J(t), through polymer films or thin sheets. In order to obtain the diffusion coefficient and to accurately determine the permeability coefficient, the data, flux, J(t), were fitted to the solution of Fick s second law ... 

The main advantages of reactors with composite membrane catalysts arc the higher hydrogen permeability and smaller amount of precious metals in comparison with those presented in Section II. All constructions of the reactors with plane membrane catalyst may be used for composites of thin palladium alloy film and porous metal sheet The design of reactors with composite membranes on polymeric support may be the same as for diffusion apparatus with polymeric membranes (see, for example. Ref. 138). A very promising support for the composite membrane catalysts is hollow carbon fiber [139], once properly thermostable adhesives are found. 

Figure 7.2. General uptake and transport configurations for cell culture models. Depending on the cell type, cell suspensions may be (1) seeded into and grown on plastic surfaces for uptake studies, (2) seeded and grown on permeable supports in Transwell -type systems, or (3) seeded and grown on permeable supports that can be placed in a side-by-side diffusion apparatus.

Hidalgo IJ, Hillgren KM, Grass GM, and Borchardt RT. Characterization of the Unstirred Water Layer in Caco-2 cell Monolayers Using a Novel Diffusion Apparatus. Pharm Res 1991 8 222-227. 

The Fick diffusion coefficients may be termed practical in the sense that the binary coefficient P and the corresponding multicomponent diffusion coefficients can be obtained from composition profiles measured in a diffusion apparatus. The measurement of binary and multicomponent diffusion coefficients, a subject with an extensive literature, is beyond the scope of this book. The interested reader is referred to Dunlop et al. (1972), Cussler (1976) and Tyrrell and Harris (1984) for descriptions of techniques and summaries of experimental results. Most experimental data are reported for [P ]. This matrix must be... 

An analysis of binary diffusion in the two bulb diffusion apparatus has been presented by Ney and Armistead (1947) (see, also, Geankoplis, 1972). Their development is extended below for multicomponent systems. 

Figure 5.3. Schematic diagram of two bulb diffusion apparatus.

Our task here is to derive an expression that describes how the composition of a multicomponent mixture changes with time in a Loschmidt diffusion apparatus of the kind described in Section 5.5. The composition profile for a binary system is given by Eqs. 5.5.5 and 5.5.6) the solution to the binarylike multicomponent problem is given by the same expressions on replacing the binary diffusivity in those equations by the effective diffusivity. The average composition in the bottom tube after time Z, for example, is given by... 

FIGURE 2.2 (b) A cartoon showing a typical hanging drop vapor diffusion apparatus. Crystals grow as the concentration of protein and precipitants increase in the drop. 

FIGURE 2.3-9 (a) Loschmidt diffusion apparatus, and (b) composition profiles... 

C at five different heating rates (0.5, 1, 5, 10, and 15°C/min). The thermal properties of the samples were then measured in x, y, and z directions with a Xenon flash diffusivity apparatus. The thermal conductivity of the samples was calculated from their thermal diffusivity. Table 2 lists the Z-direction thermal conductivity values for each graphitization heating rate and position within the furnace. From these data, it is clear that the thermal conductivity is directly related to the graphitization heating rate. A similar trend was observed in the crystal properties of the foams determined from X-ray diffraction (not shown here for brevity). However, it is not understood why there is a maximum at l°C/min. 

After being washed (for total process overview cf. Figure 9.3.5) the beets are sliced into strips (cossettes), which afterwards are fed into the so-called diffusers where about 98% of the sucrose is extracted. High temperatures (65-70 °C) in the diffusion apparatus denature the plant cells and open the cell membranes for improved sucrose transfer. The entire extraction of the sucrose is carried out via a counter current flow of the extraction medium, i.e. water and the denatured cossettes. 

The determination of / by gradient diffusion and sedimentation velocity is firmly established on the thermodynamics of irreversible processes. However, it needs time-consuming experiments, and has rapidly lost popularity in recent years. At present, few polymer laboratories in the world have the routine use of a gradient diffusion apparatus or an analytical ultracentrifuge. 

Another method that has been used to enrich uranium on the industrial scale is thermal diffusion (Vasaru 1975). Under the influence of a temperature gradient, the heavier molecular component of a mixture of two isotopes will tend to concentrate at the lower temperature. A thermal diffusion apparatus consists of two concentric, chemically resistant vertical tubes, where the inner tube carries high-temperature steam and the outer tube is jacketed and cooled by circulated water. The annular space between the two tubes is very narrow, less than 1 mm in thickness. UFg is introduced into the annulus between the two tubes at a pressure of... 

The thermal conductivity of samples with composition (Cai.x,Mgx)Zr4(P04)6 where x= 0.2 and 0.5 was investigated using a laser flash thermal diffusivity apparatus and a differential scanning calorimeter (DSC) at. ..e HTML facility, Oak Ridge National Laboratory, Thermal conductivity was determined by the product of the thermal diffusivity, specific heat, and bulk density of each sample. Samples were made by sol-gel Process 1. 

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