**ISOBUTANE and R600a**

ISOBUTANE (also referred to as R600a) provides high accuracy thermodynamic and transport properties for isobutane (R600a, Molar mass =58.122 g/mol) using the Fundamental (or Helmholtz Free Energy) Equation of State formulated by:

Miyamoto, H., and Watanabe, K.,

"A thermodynamic property model for fluid-phase isobutane,"

Int. J. Thermophys., 23(2):477-499, 2002.

The equation of state is valid for temperatures between 113.56 K (the triple point temperature) and 573 K at pressures up to 35 MPa. ** ** The default reference state is the IIR standard for which: h=200.0 kJ/kg, s=1.0 kJ/kg-K. The reference state can be changed using the $Reference directive.

__Thermal conductivity data are provided by:__

R. Perkins,

"Measurement and correlation of the thermal conductivity of isobutane from 114 K to 600 K at pressures to 70 MPa,"

J. Chem. Eng. Data **47** (2002).

__Viscosity information is provided by:__

B.A. Younglove and J.F. Ely,* *

*"Thermophysical Properties of Fluids. II Methane, Ethane, Propane, Isobutane and Normal Butane"*,

J. Phys. Chem. Ref. Data Vol. 16, No. 4, 1987.

__Surface tension data are provided through a correlation developed by__:

G.R. Somayajulu

"A Generalized Equation for Surface Tension from the Triple Point to the Critical Point"

International Journal of Thermophysics, Vol. 9, No. 4, 1988

A computationally more efficient but potentially less accurate formulation for isobutane thermodynamic and transport properties may be available if file R600a.mhe is in the USERLIB\mhe Property Files folder. In this case, the fluid name should be set to R600a_MH.