Momentum and Mass Transfer in Coaxial Gas Jets

Abstract

Abstract The mixing at constant pressure of a circular jet with an annular coaxial stream has been studied for conditions of nearly common density and temperature, but differing initial velocities. By using 10 per cent by volume of helium as a tracer in the inner stream, the mixing region was mapped with respect to both material and momentum transfer. It is concluded that material diffuses more rapidly than momentum; that the principal independent variable determining the shape of the mixing region is the velocity ratio of the streams; and that the integral method of Squire and Trouncer, using experimentally determined constants, is adequate for predicting approximate values of concentration and velocity in the mixing region of a jet flowing into a moving medium of the same density. Data for widely different experiments of various investigators show that the turbulent Prandtl and the Schmidt numbers are both within ±10 per cent of 0.70, independent of the nature of the experiment and the magnitudes of the laminar Prandtl and Schmidt numbers.