Microçubukların frekans tepkisi ölçümleri kullanılarak yoğunluk ve ağdalık değerlerinin belirlenmesi

In this study, we investigate the resonant frequency and Q-factor of ferromagnetic nickel microcantilever immersed in Ar, N2, CO2 and CO2-N2 binary mixtures at 308.15 K and pressures up to 24 MPa. Measurements were performed using an experimental setup that includes a temperature controlled high-pressure vessel which can operate within a temperature range of 273 – 423 K and a pressure range of 1 – 30 MPa. A microchip containing microcantilevers and an electromagnet for microcantilever actuation were placed inside the vessel. The procedure followed for the determination of microcantilever frequency response then involved driving of microcantilevers with AC magnetic field at varying frequencies and detecting of the corresponding laser deflections from the driven cantilevers with a quadrant photodiode (QPD). At a constant temperature, resonant frequency and Q factor of microcantilever oscillations were found to decrease with increasing pressure as a result of increasing density and viscosity of the fluid. Experimental data was analyzed using Sader's model which describes oscillatory motion of immersed cantilevers incorporating the effects of density- and viscosity-dependent hydrodynamic forces. A very good agreement between the experimentally obtained cantilever resonant frequencies and quality factors and the predictions of Sader's model was observed. The low difference in experimental and theoretical values illustrates that our experimental approach is suitable for the density and viscosity measurement of gas and supercritical fluids and fluid mixtures at a wide range of pressures. Based on these results, we carried out simultaneous measurement of density and viscosity of nitrogen from the measured frequency responses of an oscillated microcantilever immersed in N2. To this end, using argon as a reference fluid of known density and viscosity, cantilever calibration parameters were obtained from nonlinear regression of cantilever resonant frequencies and quality factors recorded in argon. Subsequently, these calibration parameters were used in the model equations to determine the density and viscosity of nitrogen at the given experimental pressure and temperature. In the studied pressure range, the root-mean-square deviations of the measured density and viscosity of nitrogen from the reference values obtained from NIST database were 2.5% and 5.2%, respectively. Finally, we studied thermophysical properties of more complex fluid systems represented by fluid mixtures. In order to investigate the density and viscosity of fluid mixtures, CO2-N2 binary mixture was chosen as a model fluid. The average relative deviation range for different compositions of CO2-N2 binary mixture was found to be 0.96 % -13.27 % for density and 2.42 %- 15 % for viscosity when N2 was used as reference fluid.