Area and edge effects in radiometric forces

The radiometric force on several configurations of heated plates placed in a stagnant gas is examined experimentally, with a high-resolution thrust stand, and numerically using the direct simulation Monte Carlo method and a discrete ordinate solution of a model kinetic equation. A wide range of pressures from 0.006 to 6 Pa was examined, corresponding to Knudsen numbers from 20 to 0.02, in argon and helium test gases. The radiometric force, important in a number of emerging micro- and nanoscale applications, is shown to be mostly area dependent in the transitional regime where it reaches its maximum at Kn approximately 0.1.