In situ measurement of circulation composition of refrigerant mixture in heat pump system with NIR absorption spectroscopy

Abstract

Near-infrared absorption spectra of difluoromethane (R32) and 2,3,3,3-tetrafluoropropene (R1234yf) were experimentally measured for superheated gas and subcooled liquid under different temperature and pressure conditions. Molar attenuation coefficients at wavelengths of 1.59, 1.64, 1.70 and 1.78 μm were obtained using 1.5 μm wavelength data as a reference spectrum. Attenuation coefficient of the gas phase R32 refrigerant showed significant variation depending on the operating conditions, where liquid phase showed relatively constant absorption characteristics at different pressures and temperatures. Furthermore, the attenuation coefficients were distinctive between R32 and R1234yf and absorption peaks and intensities were identical. The estimation model of absorption characteristic for refrigerant mixture was then constructed using the liquid phase spectra of the pure refrigerants at each wavelength with validation using the experiment data of upward flow with circulation compositions of R32 : R1234yf = 30 : 70, 50 : 50 and 70 : 30 mass%. The estimated data qualitatively showed good agreement with the measured spectra in point of dependency on composition ratio. However, up to 15% deviation was found in the 1.59 μm spectra where R1234yf has relatively strong absorption. Further investigation, spectra dependency of refrigerant mixture on molecular interactions and of pure refrigerant on broader range of conditions, including pressure near critical point, are considered to be necessary to improve the estimation model.