Browsing by Author "Zega, James Alexander"
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Item Spin lattice relaxation in pure and mixed alkanes and their correlation with thermodynamic and macroscopic transport properties(1988) Zega, James Alexander; Kobayashi, RikiSpin-lattice, T$\sb1$, and spin-spin, T$\sb2$, relaxation times of the alkanes from n-pentane to n-hexadecane were measured at 25$\sp\circ$C. The T$\sb1$ values agree well with those of previous investigators. The values of T$\sb1$ and T$\sb2$ were equal for each alkane studied. Empirical correlations were found between T$\sb1$ and two parameters: the acentric factor and the rotational coupling coefficient. The product $\eta$T$\sb1$ was constant for all the alkanes except n-pentane. The spin-lattice relaxation time was dedimensionalized and a three parameter corresponding states correlation was developed following the treatment of Tham and Gubbins (42) for transport coefficients. Excellent correspondence was found for the saturated alkanes over the temperature range 22 to 90$\sp\circ$C and for benzene from 12 to 63$\sp\circ$C. Spin-lattice relaxation times of mixtures of n-hexane and n-hexadecane were measured at 25$\sp\circ$C. The decay of magnetization could not be described by a single exponential curve. The results were analyzed using three methods. (Abstract shortened with permission of author.)Item Spin-lattice relaxation in normal alkanes at elevated pressures(1991) Zega, James Alexander; Kobayashi, RikiA high pressure, variable temperature NMR probe for low signal to noise relaxation time and self-diffusion coefficient measurements was constructed and tested. The probe has a high pressure limit of 10,000 psia and a current temperature range of 10 to 250 C. Since the magnetic field gradient coils are inside the pressure vessel, the diffusion measurements may be performed with either pulsed or constant gradients. Spin-lattice relaxation times of octane, decane, dodecane, and hexadecane were measured at temperatures between 10 and 85 C and pressures between atmospheric and 6000 psia. These data are the first for these fluids at elevated pressures and represent a significant expansion of the data base. The relaxation rate at constant temperature is proportional to the ratio of the viscosity divided by the temperature, thus being in qualitative agreement with the Bloembergen, Pound, and Purcell (1948) theory. The corresponding states treatment of spin relaxation has been extended to fluids at arbitrary temperature and pressure. Using decane as a reference fluid, the calculated relaxation times of octane, dodecane, and, hexadecane were in good agreement with the experimental values. The low signal to noise capability of the probe was tested by measuring T$\sb1$ of $\sp{13}$CO$\sb2$ at 504 psia and 25 C. Agreement with the literature value (Smith, 1986) was excellent. The gradient coils were calibrated using benzene. Measurements of benzene at various temperatures, and water at 25 C, gave reliable diffusion coefficients when either the pulsed gradient or the constant gradient method was used.