Data are reported for the evaporation of spheres of naphthalene into air, helium, carbon gators have reported values of increasing dioxide, and Freon-12, and of liquid diethyl adipate into air at pressures from 0.1 to 3,OOOfi in successive tests as continuing efforts Hg and at Reynolds numbers from 0 to 1.37. By use of suitable values of the surface-were made to remove minute traces of evaporation coe5cient and the assumption of additivity of surface evaporation and d8u-impurities, and Hickman (24) postulates sional resistances, the data are well correlated. The results lend semiquantitative support that a should be unity for pure liquids to the theory of sublimation of crystals developed by Stranski.
with absolutelv clean surfaces. in sunnort Mass transfer between a solid or liquid and a gas a t low pressure is a subject of wide scientific and technological interest. Vacuum sublimation of ice ("freezedrying") has been developed in recent years as a useful process for drying antibiotics, sera, blood plasma, and other heat-sensitive materials (52, 22, 16, 17, 18). Metals and inorganic salts are evaporated at low pressures t o coat plastics; lenses, and other parts. Objects moving a t high velocities in the upper atmosphere attain high temperatures and tend to sublime; for scientific purposes it is desirable to estimate the rate of sublimation of meteors and satellites.
The subject is also one of considerable interest in conjunction with various mass transfer operations in chemical engineering, as knowledge of evaporation at low pressures throws considerable light on the interfacial, or surface, resistance to mass transfer, about which relatively little is known.
THEORETICAL BACKGROUND
It is well known that solids and liquids evaporate at a finite rate in the absence of any gas-phase diffusional resistance. This rate is given by 1.0 0.8 3 0.6 ?j B 2 2 0.4 0.2 0 0 0.1 0 . 2 0.1