Contents - Index


Brines

 

Brines are also called secondary refrigerants.  These fluids are mixtures of water and another substance that results in a reduction of the freezing point of the fluid.  The property functions applicable to brines and the units of the value that the function returns are:

 

Cp [kJ/kg-K] or [Btu/lbm-R]

Conductivity [W/m-K] or [Btu/hr-ft-R]

Density [kg/m^3] or [lbm/ft^3]

Enthalpy  [kJ/kg] or [Btu/lbm]

FreezingPt [C], [K], [F], or [R]

IntEnergy [kJ/kg] or [Btu/lbm]

MolarMass_soln [kg/kmol or Btu/lbmol]

Prandtl [-]

SpecHeat [kJ/kg-K] or [Btu/lbm-R]   (same as Cp}

Viscosity [Pa-s] or [lbm/ft-hr]

Volume [m^3/kg] or [ft^3/lbm]

 

The first parameter for all of these property functions must be the name of the mixture provided as a string constant or string variable.  (Quotes around the string constant are not required.)  The fluid mixture names for which data are provided are:

 

Name Complete Name

CACL2 Calcium Chloride-Water

EA Ethyl Alcohol-Water

EG Ethylene Glycol-Water

GLYC Glycerol-Water

K2CO3 Potassium Carbonate-Water

KAC Potassium Acetate-Water

KFO Potassium Formate-Water

LICL Lithium Chloride-Water

MA Methyl Alcohol-Water

MGCL2 Magnesium Chloride-Water

NACL Sodium Chloride-Water

NH3W Ammonia-water

PG Propylene Glycol-Water

 

The next one, two or three parameters are the temperature,  mass concentration, expressed as a percentage, and the pressure.  Concentration (in % on a mass basis) is required for all of the property functions.  The FreezingPt and MolarMass_soln functions require no other parameters.   The temperature must be supplied for all functions other than FreezingPt and MolarMass_Soln in the units specified in the Unit System dialogThe pressure is required only for the Enthalpy function.  It is ignored with a warning message if it is provided for any of the other property functions.  These parameters can be provided in any order. 

 

If EES is configured in molar units, then the specific properties of a brine solution will be returned on a molar basis.  However, the concentration must always be supplied in % on a mass basis. 

 

Example:

$UnitSystem SI C kPa kJ

rho=density(EG,T=25 [C],C=20 [%])

{Solution: rho=1022 [kg/m^3]}

 

Note that the FreezingPt function requires only one parameter in addition to the fluid name, e.g.,

$UnitSystem SI C kPa kJ

FP=freezingPt(EG,C=20 [%])

{Solution:  FP=-7.949 [C]}

 

However, the FreezingPt function will accept T as an input and ignore the value.

 

Note that the Enthalpy function requires inputs of temperature, composition and pressure.

$UnitSystem SI C kPa kJ

h=enthalpy(EG,T=25 [C], C=20[%], P=200 [kPa])

{Solution: h=73.56 [kJ/kg]}

 

 

Most of he correlations used in EES for brine properties were obtained from Properties of Secondary Working Fluids for Indirect Systems, IIF/IIR, Melinder, 2010, http://www.iifiir.org/en/details.php?id=1177

 

The enthalpy change of mixing for calcium chloride solutions is from M. Conde Engeering, 2009, "Aqueous Solutins fo Lithium and Calcium Chlorides: Property Formulations for use in Air Conditioning Equipment Design", http://www.mrc-eng.com/Downloads/Aqueous%20LiCl&CaCl2%20Solution%20Props.pdf

 

Specific internal energy and specific enthalpy are available for some brines for which enthalpy of mixing information data were available.  In this case, the specific internal energy is referenced to 0 for pure water at 0C.  The specific internal energy at a specified temperature and concentration is found by adding the enthalpy of mixing at 0C (and low pressure) at the specified concentration to the integral of the specific heat capacity with temperature.  Specific enthalpy is determined as the sum of the specific internal energy and the product of pressure and specific volume, in consistent units.

 

Note:  Brine properties in older versions of EES were provided with the BrineProp2 external procedure.  The brine property data in EES is based on newer correlations than used in BrineProp2.  However, BrineProp2 is provided with EES for backward compatibility.