Role of Diluent Gases in Oxygen Sensing by Magnetic-Field Induced Viscosity Changes

Abstract

The viscosity of oxygen is reduced in the presence of a magnetic field. This is generally assumed to be due to a change in the collision probability of the paramagnetic oxygen molecules. With the aid of formulas derived by Chapman and Enskog, the viscosity change in a mixture of gases is calculated and compared with the change for 100% oxygen. The calculations predict that the magnitude of the change is not necessarily proportional to the mole fraction of oxygen. For a mixture of 50% oxygen and 50% helium the relative viscosity change is not 50% of the change obtained with 100% oxygen but larger, namely 71.5%. Conversely, when diluted with the heavier gas, carbon dioxide, it is smaller, namely 42.5%. An instrument using the viscosity change to measure the amount of oxygen in space vehicles is described. Measurements of different gas mixtures are made with this instrument. Contrary to earlier measurements by Senftleben of the change of heat conductivity of gas mixtures in a magnetic field, the measurements of a viscosity change reported herein agree satisfactorily with theory.