The viscosity of normal butane, isobutane and their mixtures

The paper reports measurements of the viscosity of normal butane and isobutane at atmospheric pressure in the temperature range 25-195°C. In addition, the viscosity of mixtures of the two gases has been determined in the more limited temperature range 25-100°C. The absolute accuracy of the viscosity data is estimated as ±0.2%, whereas the ratio of the viscosity of the two pure components is determined with an uncertainty of ±0.1%. The viscosity data allow the evaluation of the diffusion coefficients for the n-butane-i-butane system. The experimental data demonstrate that there are discernible differences between the intermolecular potentials for the pair-interactions n-C₆H₁₀-n-C₄H₁₀; and i-C₄H₁₀-i-C₄H₁₀. All of the experimental data can be correlated within their experimental uncertainty with the aid of the extended law of corresponding states developed by Kestin, Ro and Wakeham. The optimum values of the two scaling parameters, σ_ij and ε{lunate}_ij, for each interaction which secure this agreement are determined.