After some trouble reading NH3-H2O equilibrium diagram, I decided to implement a code to run an algorithm to give me the values without having to search in the fuss of lines of the graphical diagram (see image below). The plataform I used was the HP50g calculator.
NH3-H2O equilibrium diagram
source: ASHRAE
One good thing in doing that is the elimination of the gross errors while reading the diagram.
The functions used to code is referenced in:
PÁTEK. J.; KLOMFAR, J. Simple
functions for fast calculations of selected thermodynamics properties of the
ammonia-water system. International
Journal of Refrigeration, 18(4), pp. 228-234, 1995.
T=temperature;
P=pressure; x=molar fraction of ammonia (NH3) for the mixture in the liquid phase ; y=molar fraction of ammonia (NH3) for the mixture in vapour phase
Equation for temperature in function of pressure and molar fraction of ammonia (NH3) for the mixture in the liquid phase
Equation for specific entalphy in function of pressure and molar fraction of ammonia (NH3) for the mixture in the liquid phase
Equation for temperature in function of pressure and molar fraction of ammonia (NH3) for the mixture in the vapour phase
Equation for specific entalphy in function of pressure and molar fraction of ammonia (NH3) for the mixture in the vapour phase
Altough the equations are fully empirical, they have shown excellent results for pressures up to 30 bar.
Setting the equations in the calculator is undertaking, but for HP50g users I will provide a link with the files.
The files can be found here.
How to use?
Very simple, First you download the files and move them to the calculator. There are two ways to do that, one is via the connectivity kit, or easier yet, using a SD card.
In the calculator you call the numeric solver function (press orange button then 7), browse to the files and you're in the business.
Thanks for reading.
Eddie
