Hi Jordan,

I am currently working on a model of a LiBr/water based absorption heat pump. For starters, I used CoolProp2Modelica (see http://www.thermocycle.net) which uses the external library CoolProp via a modified version of Modelica External Media.

However, I found that it runs rather slow since in Modelica Media you look up the aquaeous solution properties with Medium.*****_pTX()  allthough all LiBr/water properties are functions of T and X only.

Since I was "lucky" to find a great paper...

A computationally effective formulation of the thermodynamic properties of LiBr-H2O solutions from 273 to 500 K over full composition range (Pátek et al. 2006)

... describing the properties of LiBr/water with equations I decided to implement the equations in a Modelica package myself. When e.g. computing the (numerical) partial derivatives of density and enthalpy wrt. T and X it gave me a significan computation time reduction (10^3 for computing 500 data points!).

So unless I did something completely wrong when using the external medium library I would recommend that you implement the thermodynamic property functions directly in Modelica. Perhaps you should look into the two following papers:

Thermodynamic properties of the LiCl-H2O system at vapor-liquid equilibrium from 273 K to 400 K (Pátek et al. 2007)

Thermodynamic Properties of Aqueous Solutions of Lithium Chloride (Chaudhari et al. 2010)

Regards,
Rene Just Nielsen