Hertz-Knudsen vaporization equation

A material vaporizes freely from a surface when the vaporized material leaves the surface with no collisions above the surface. The free surface vaporization rate is proportional to the vapor pressure and is given by the Hertz-Knudsen vaporization equation (Eq. 6.1) ... 

The assumptions inherent in the derivation of the Hertz-Knudsen equation are (1) the vapor phase does not have a net motion (2) the bulk liquid temperature and corresponding vapor pressure determine the absolute rate of vaporization (3) the bulk vapor phase temperature and pressure determine the absolute rate of condensation (4) the gas-liquid interface is stationary and (5) the vapor phase acts as an ideal gas. The first assumption is rigorously valid only at equilibrium. For nonequilibrium conditions there will be a net motion of the vapor phase due to mass transfer across the vapor-liquid interface. The derivation of the expression for the absolute rate of condensation has been modified by Schrage (S2) to account for net motion in the vapor phase. The modified expression is... 

The method of quantitative vaporization is based on the Hertz Knudsen equation [87]. The mass loss rate dm/dt of a substance A, vaporized at the temperature T in the Knudsen cell, is determined by weighing, in addition to the ion intensity measurement, k is obtained by the equatiop... 

The maximum theoretical rate of vaporization V (kgm s ) from the surface of a pure liquid or solid under its own vapour pressure is given by the Hertz-Knudsen equation, which can be derived from the kinetic theory of gases ... 

In the calculations of partial pressures (Hastie et al., 1968), ionization of dimeric molecules accompanied by loss of more than one atom (especially in reaction steps that can interfere with ionization of monomers) was assumed to be improbable. This assumption was experimentally confirmed in studies of the congruent evaporation of SmCl3 (Chervoimyi et al., 1974). Isothermal evaporation of a sample of known weight was carried out at several temperatures, and the saturated vapor pressure was determined by the Hertz-Knudsen equation. In each experiment, the state of an imsaturated vapor caused by the presence of an nonvolatile species ( 1.5% SmCl2) was determined in the end of... 

---