Viscosity Correlation for Isobutane over Wide Ranges of the Fluid Region1

A new representation of the viscosity of isobutane has been developed. The representative equations include zero-density and initial-density dependence correlations. The higher density contributions to the residual viscosity are formed by a combination of double polynomials in density and reciprocal tem- perature and of a free-volume term with a temperature-dependent close-packed density. The new full surface correlation is based on primary experimental data sets selected as a result of a critical assessment of the available information. The validity of the representation extends from the triple point to 600 K and 35 MPa in accordance with the modified Benedict Webb Rubin equation of state by Younglove and Ely (1987). The uncertainty of the representation varies from \0.40 in the dilute gas phase between room temperature and 600 K to \30 in the thermodynamic ranges in which the equation of state is valid as well as where primary experimental data are available.