Area calculations

Similar discrepancies were found for other vapours by Harris and Emmett, who quoted their results as the ratio fi of the BET area calculated from the isotherm of the particular adsorbate to the BET nitrogen area (Table 2.7). The value of fi varied, again sometimes widely, for any one gas on different adsorbents, so that the divergences could not be removed by use of a single revised value of a for a given vapour. 

Molecular area, a ,(Ar), of argon at 77 K on nonporous oxides (Argon BET plots constructed withp (liquid) BET surface areas calculated from nitrogen isotherms, with a (Na) = 16-2 A )... 

The molecular area, calculated from the density of the supercooled liquid at 77 K is a ,(Kr) = 15-2 A, but Beebe found it necessary to adopt the higher value 19-5 A to bring the krypton-based area into line with the area of Harkins reference sample of anatase. ... 

Striking confirmation of the conclusion that the BET area derived from a Type IV isotherm is indeed equal to the specific surface is afforded by a recent study of a mesoporous silica, Gasil I, undertaken by Havard and Wilson. This material, having been extensively characterized, had already been adopted as a standard adsorbent for surface area determination (cf. Section 2.12). The nitrogen isotherm was of Type IV with a well defined hysteresis loop, which closed at a point below saturation (cf. F, in Fig. 3.1). The BET area calculated from it was 290 5 0 9 m g , in excellent agreement with the value 291 m g obtained from the slope of the initial region of the plot (based on silica TK800 as reference cf. p. 93). 

Wynne-Jones and Marshfound somewhat similar results with a number of carbons made by pyrolysis of eight organic polymers at a series of temperatures. The isotherms of Nj at 77 K and of COj at 195 K were measured, and the apparent surface area calculated by the usual BET procedure. (Owing to the microporous nature of the solids, these figures for area will be roughly proportional to the uptake at saturation and therefore... 

Scale-up Factors Factors used in thickening will vary, but, typically, a 1.2 to 1.3 multiplier applied to the unit area calculated from laboratory data is sufficient if proper testing procedures have been followed and the samples are representative. 

TABLE 26-18 Vent Areas Calculated for Propane May Be Used for the Following Quiescent Gases... 

All specimens should be measured carefully to permit accurate calculation of the exposed areas. An area calculation accurate to plus or minus I percent is usually adequate. 

If the downcomer area calculated above is less than 11% of the active area, use the smaller of... 

Add the areas calculated for the vapor and liquid components to obtain the total orifice area required. This may be somewhat conservative, since flashing does not take place instantaneously across the PR valve orifice. 

F2 = 0.691 interpolated from Figure 7-29 Area calculated substituting in above relation ... 

Vent or Relief Area Calculation [27] for Venting of Deflagrations in Low-Strength Enclosures... 

The effective tube length, L, of the bundle for surface area calculations is the mean of the tube lengths between the outside tubes and the inside tubes. See Figure 10-27A. 

Area Calculated as Cooler-Condenser (Inlet Mixture at Dew Point)... 

If the calculations were started by assuming a pipe size and length, determine the number of lengths from the total area calculation and surface area per length of pipe selected. 

There are various methods for the determination of the surface area of solids based on the adsorption of a mono-, or polymolecular layer on the surface of the solid. These methods do not measure the particle diameter or projected area as such, but measure the available surface per gram or milliliter of powder. The surface measured is usually greater than that determined by permeability methods as the latter are effectively concerned with the fluid taking the path of least resistance thru the bed, whereas the adsorbate will penetrate thru the whole of the bed as well as pores in the powder particles. These methods appear to be more accurate than surface areas calculated from weight averages or number averages of particle size because cracks, pores, and capillaries of the particles are included and are independent of particle shape and size... 

Sca = Surface area calculated from microscopic data... 

Theoretical Pt surface area calculated from Pt particle sizes. 

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