**$ConvertEESREFPROPUnits**

**$ConvertEESREFPROPUnits /mass **

This directive is only used in conjunction with the EES_REFPROP interface.

The EES_REFPROP interface requires inputs and outputs to use the SI unit system with temperature in K, pressure in kPa and all composition parameters (if needed) expressed as mole fractions. All specific properties are expressed on a molar basis. Viscosity is returned in microPa-s units and thermal conductivity is returned in W/m-K.

Units can be set in EES with the $UnitSystem directive or using the Unit System command in the Options menu.

If a $ConvertEESREFPROPUnits directive is placed in the Equations window, EES will automatically convert all inputs to and outputs from the EES_REFPROP interface so that they correspond to the unit system set in EES. Specific properties on a molar basis are also converted to a mass basis if EES is set to return properties on a mass basis.

The /mass flag is optional. Normally, the composition of a mixture is specified in terms of mole fractions and quality is input on a molar basis in Modes TQ (17) and PQ (27). Also, the composition of liquid and/or vapor phases calculated by REFPROP are returned as mole fractions. However, if the /mass flag is provided, all composition indices will be understood to be mass fractions, rather than mole fractions. In addition (starting with EES version 11.348), quality input for Modes TQ (17) and PQ (27) is expected on a mass (rather than molar) basis. Note that this option is only useful when the mixture is specified by using the + symbol between the names of the pure components to specify the mixture.

To disable the automatic unit conversion, follow the directive with the Off keyword, i.e., $ConvertEESREFPROPUnits Off or delete the directive.

**Example:**

$UnitSystem SI C kPa kJ mass

$CONVERTEESREFPROPUnits /mass

TP=12 "mode for calculation at a given temperature and pressure"

T=25 [C] "temperature"

mf1=0.333333 "mass fraction of R32"

mf2=0.333333 "mass fraction of R134a"

** Call** EES_REFPROP('R32+R134a+R22', TP, T, 1200 [kPa], mf1,mf2 :T1,P,rho,v,h,s,Q,Cv,Cp,w,Qm,x_R32,x_R134a,x_R22,y_R32,y_R134a,y_R22)

{**Solution**

Cp=-1.000E+07 [kJ/kg-K] {not defined for two-phase condition}

Cv=-1.000E+07 [kJ/kg-K] {not defined for two-phase condition}

h=341.1 [kJ/kg]

mf1=0.3333

mf2=0.3333

P=1200 [kPa]

Q=0.4937 {quality on molar basis}

Qm=0.4741 {quality on mass basis}

rho=87.000 [kg/m^3]

s=1.594 [kJ/kg-K]

T1=25 [C]

v=0.01149 [m^3/kg]

w=-1.000E+07 [m/s] {not defined for two-phase condition}

x_R134a=0.3874 {mass fraction of R134a in liquid}

x_R22=0.3327 {mass fraction of R22 in liquid}

x_R32=0.2799 {mass fraction of R32 in liquid}

y_R134a=0.2733 {mass fraction of R134a in vapor}

y_R22=0.3341 {mass fraction of R22 in vapor}

y_R32=0.3926 {mass fraction of R32 in vapor}