Analysis of refraction errors for interferometric measurements in multicomponent systems

Analytical expressions for the refraction errors associated with interferometric measurements in multicomponent systems are derived. Two numerical examples are presented where these errors are calculated for the Mach-Zehnder as well as for the differential-type interferometers. In the first example, these errors are evaluated in a gaseous system having air and carbon-disulfide as two disparate components. The second example cites the application of these instruments to heat and mass transfer measurements in an aqueous salt solution. The refraction errors are found to be a monotonically increasing function of test section width, temperature, as well as concentration gradients. The focal plane of the interferogram has a significant influence on the refraction errors and reaches a minimum value, if the interferogram is focused at one-third the distance away from the exit plane into the test section. The chromatic influence of the source wavelength on the errors is found to be negligible for gas studies. However, for liquids the errors can be reduced significantly by using a higher-wavelength light source.