Thickness normalized flow

In addition to the permeability coefficient, other parameters are also used to express the barrier characteristics of plastic materials. These include permeance (R), gas transmission rate (GTR), water vapor transmission rate (WVTR), and thickness normalized flow. The relationship between these parameters is shown in Fig. 14.3. 

You have the following permeation information about a flexible plastic structure WVTR (obtained at 100°F, 95% RH) =1.2 g/day, area = 100 in, thickness = 3 mil. Calculate, in SI units WVTR, permeance R, thickness-normalized flow N, and permeability coefficient P. Use SI units kg, sec. Pa, m. 

Terms other than permeability (Equation 12.6), such as permeant transmission rate, permeance, and thickness normalized flow, can be used to describe the steady-state permeation of molecules through the polymer films [2]. Permeant transmission rate is the amount of permeant passing through a plane of unit area normal to the direction of the flow during unit time (Equation 12.8). The term permeance is used when differences in partial pressure between both sides of the material are also taken into account (Equation 12.9), whereas thickness normalized flow considers material thickness but not difference in partial pressure (Equation 12.10). 

Viscosity is normally measured at two different temperatures typically 100°F (38°C) and 210°F (99°C). For many FCC feeds, the sample is too thick to flow at 100°F and the sample is heated to about 130°F. The viscosity data at two temperatures are plotted on a viscosity-temperature chart (see Appendix 1), which shows viscosity over a wide temperature range [4]. Viscosity is not a linear function of temperature and the scales on these charts are adjusted to make the relationship linear. 

The membrane performance for separations is characterized by the flux of a feed component across the membrane. This flux can be expressed as a quantity called the permeability (P), which is a pressure- and thickness-normalized flux of a given component. The separation of a feed mixture is achieved by a membrane material that permits a faster permeation rate for one component (i.e., higher permeability) over that of another component. The efficiency of the membrane in enriching a component over another component in the permeate stream can be expressed as a quantity called selectivity or separation factor. Selectivity (0 can be defined as the ratio of the permeabilities of the feed components across the membrane (i.e., a/b = Ta/Tb, where A and B are the two components). The permeability and selectivity of a membrane are material properties of the membrane material itself, and thus these properties are ideally constant with feed pressure, flow rate and other process conditions. However, permeability and selectivity are both temperature-dependent... 

For samples with a broad size distribution in the micron range, it is important to avoid the transition region between the normal and the steric mode during the measurement. This can be achieved by proper adjustment of the channel thickness, channel flow and the strength of the applied field [69]. The transition region in Fig. 6 can be experimentally determined by plotting the retention ratio vs. the particle size, as illustrated in Fig. 7 for the example of flow-FFF. 

When the filter cake has built up to a thickness whereby resistance over the filter has reached its desired maximum value. The fitter is cleaned by stopping circulation and transmitting a short pressure pulse, with duration of only a few milliseconds, into the filter element in the reverse direction to normal flow. The pressure wave fluidizes the sand and the sand moves slightly horizontally between the louvers. As a result, some of the sand together with the filter cake falls from the filter element, thereby cleaning the filter surface. The mixture of dust and sand is precipitated into a hopper for dust separation and sand recirculation. 

Fig. 18 End-view diagram of the triple-layer structure model for the injection-molded NCH bar 3 mm thick. The flow direction caused by injection-molding is normal to the paper plane. Curved arrows with one head mean random orientation round the axis normal to the plane containing the curve. Arrows with two heads indicate fluctuation...

At a wall thickness of 1mm (0.039in) a normal flow grade ranges from 250 to 280 1, and an easy flow grade fi-om 320 to 340 1. 

Figure 5.25. Field flow fractionation flactogiams of an iron oxide pigment, a) Fractionation using normal flow conditions in the chamber. (Conditions in a 210 pm thick channel channel flow 5.5 ml/min cross-flow 0.8 ml/min ) b) Fractionation usii Stearic flow conditions on the chamber [60]. (Conditions in a 100 pm thick channel channel flow 7.4 ml/min cross-flow 1.7 ml/min)...

FIGURE 11.24 (a) Effect of electrolyte thickness on the voltages and power densities of the cells. The cell operated at temperature of 600°C using hydrogen flow rate of 15 cm min" (20°C, 1 atm) and air flow rate of 40 cm min" (20°C, 1 atm) (b) the electrolyte thickness-normalized maximum power density of the cells as a function of electrolyte thickness. (Data from M.H.D. Othman et al.. Journal of Membrane Science, 365, 382-388, 2010.)... 

Let H and L be two characteristic lengths associated with the channel height and the lateral dimensions of the flow domain, respectively. To obtain a uniformly valid approximation for the flow equations, in the limit of small channel thickness, the ratio of characteristic height to lateral dimensions is defined as e = (H/L) 0. Coordinate scale factors h, as well as dynamic variables are represented by a power series in e. It is expected that the scale factor h-, in the direction normal to the layer, is 0(e) while hi and /12, are 0(L). It is also anticipated that the leading terms in the expansion of h, are independent of the coordinate x. Similai ly, the physical velocity components, vi and V2, ai e 0(11), whei e U is a characteristic layer wise velocity, while V3, the component perpendicular to the layer, is 0(eU). Therefore we have... 

Materials suitable as filter aids include diatomaceous earth, expanded perilitic rock, asbestos, ceUulose, nonactivated carbon, ashes, ground chalk, or mixtures of those materials. The amount of body feed is subject to optimisa tion, and the criterion for the optimisa tion depends on the purpose of the filtration. Maximum yield of filtrate per unit mass of filter aid is probably most common but longest cycle, fastest flow, or maximum utilisation of cake space are other criteria that requite a different rate of body feed addition. The tests to be carried out for such optimisation normally use laboratory or pilot-scale filters, and must include variation of the filtration parameters such as pressure or cake thickness in the optimisation. 

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