High Vacuum Technology

Abstract

High vacuum is a term generally referred to pressures below 0.1 mm. of mercury. A criterion for determining whether high vacuum conditions exist is that the mean free path of gases in a system must be of the same order of magnitude as the dimensions of the system, or larger. The requirement for high vacuum often stems from the need for chemically inert surroundings necessary for handling reactive metals at high temperatures. The inert gas is usually introduced to the heat-treating equipment following the reduction of air pressure to the high vacuum range. High vacuum technology has already made the transition from research laboratories to properly engineered installations. The beneficial influences of high vacuum are entirely analogous to those obtained in the use of high pressure for certain processes. The influence of high vacuum on diffusional unit operations, such as distillation, drying, impregnation, evaporation and desorption, is to reduce the partial pressure of the inert component, usually air, and thereby increase the rate of mass transfer of the diffusing fluids. This chapter discusses relation between high vacuum technology and chemical engineering by focusing on miss balance, heat transfer, fluid flow, reaction equilibrium, and mass transfer. Theory and applications of vacuum pumps and gages are also illustrated.