Raman spectra method for measuring viscosity of supercritical fluids

Viscosity measurement of supercritical fluids is very important for industry applications. We developed a non-contact optical method for determining supercritical fluids' viscosity based on the pressure dependence of fluids' Raman spectra and Poiseuille flow principles. Firstly, we investigated the pressure dependence of Raman spectra for methane mixtures and carbon dioxide mixtures. We can use Raman spectra to accurately obtain the total pressure of methane mixtures, but the Raman spectra method for determining the total pressure of carbon dioxide mixtures needs further investigation. Further, we theoretically designed the measurement system and analyzed the sensitivity of the method. The measurement system consists of gas tanks, a pressure-controlling high pressure syringe pump, a temperature controlling plate, a capillary tube array plate and a Raman spectrometer. The pressures vary significantly between the inlet and outlet of the capillary tube array and this method is very sensitive for measuring viscosity of methane mixtures.