Laser heterodyne spectrometer with a microcomputer for measuring the thermophysical properties of fluids

This paper considers a heterodyne spectrometer used to measure the surface tension of fluids in the range from ultralow values 0.001 mN/m to 100 mN/m and the shear viscosity. Results of an investigation of the spectrometer parameters are represented. Underlying the measurement method is the spectrum analysis of light scattered by capillary waves at the interphasal surface. The spectrometer uses the He-Ne beam of an LG-38 laser; the beam optics are given. Dependences of surface tension coefficients on the interphasal liquid-liquid boundary and shear viscosity of the lower and upper phases on reduced temperature are given in a double logarithmic scale for a mixture of acetic anhydride and heptane. Errors in measuring the surface tension and shear viscosity coefficients as a function of the proximity to the stratification temperature are, respectively, 1-3 and 3-8%.