Whitman-Motzfeld equation

These factors are summarized in the Whitman-Motzfeld equation [3233] ... 

Here Pe is the equilibrium pressure inside the Knudsen cell,pm is the measured vapor pressure, Wc is the Clausing factor for the orifice, C is the surface area of the orifice, D is the surface area of the bottom of the cell cavity, Ov is the vaporization coefficient, and Wd is the Clausing factor for the cell itself. A number of assumptions have been made in this derivation, most notably that the condensation coefficient equals the vaporization coefficient. However, the important points about the design of a Knudsen cell are captured in the basic Whitman-Motzfeld equation. Our cells have a cavity with a diameter of 10 mm and height of 7.6 mm, and a typical orifice has a diameter of 1.5 mm and a length of 4.0 mm. If tabulated Clausing factors [27] and a vaporization coefficient of 1 are assumed, the ratio Pe. Pm has a value of 1.005. 

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See also in sourсe #XX -- [ ]

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