Selection of Themodynamic package

[arvind.prasad]

I wish to simulate a Ammonia Absorption Refrigeration cycle. I have done a lot of research but am confused on which thermodynamic property package to select for the simulation. Any suggestions?

[jasper]

If you want to just use thermodynamics, this requires a specialty thermodynamic package; TEA cannot provide this. The refrigeration qualities follow from chemical equilibrium; the heat of reaction (the heat of absorption of ammonia back in the water) is the main heat sink.

Even if you would split the reaction from the thermo and implement these separately, e.g. in a reaction, the dissociation reaction of ammonia in water cannot be handled by TEA, so TEA cannot make accurate predictions for this system.

If you have accurate data both on the chemistry (reaction equilibrium constants) and thermo (models for the liquid phase activity) it is probably best to write a dedicated thermo package for such an application. Or perhaps use a commercial thermo server that can deal with it.

[arvind.prasad]

I was surfing the web for dedicated packages for thermodynamic routines for refrigerants. Refprop is can be downloaded and is expensive. Coolprop is free. I do no know how can I include it in the property packs.

[jasper]

REFPROP is inexpensive, as thermodynamic servers go.

COOLPROP does not (yet) have a CAPE-OPEN interface, it is however on the plan - I believe.

Refrigerants themselves are well covered by both. The system of ammonia, hydrogen and water is not. Due to the reactions. So neither would help with this particular system.

[arvind.prasad]

I got interested in the problem and decided to verify the accuracy of Cape Open Simulation for aqua ammonia absorption. The boiling temperature were read from the simulator at various pressures and concentrations of ammonia. The values of boiling temperatures were compared with Enthalpy Concentration diagram published in Perry's Eight Editions pp 2-220, Figure 2-7. The root mean square percentage error in prediction of boiling temperature is 1.4. Flash calculations were performed. The heat load was calculated reading the enthalpy from the Perry's Eight Editions pp 2-220, Figure 2-7. This heat load was compared with that predicted by Cape Open Simulator. The error was not greater than +_ 5%. In my view one can use Cape Open Simulator for Aqua Ammonia Absorption System. The thermodynamics use was Peng Robinson. Attached file gives the calculations of my work. Request interested members to go through and give their suggestions.

[jasper]

I am surprised the deviation is so small. In this case it would be worth checking the deviation of higher order equations of state, such as offered for example by REFPROP, with proper interaction parameters. Also predictive SRK, as implemented by ChemSep thermo, might be worth a go.

[arvind.prasad]

I am surprised the deviation is so small. In this case it would be worth checking the deviation of higher order equations of state, such as offered for example by REFPROP, with proper interaction parameters. Also predictive SRK, as implemented by ChemSep thermo, might be worth a go.

Sure will check and get back to you.

[arvind.prasad]

If we use the Chemsep Predictive SRK, the percentage error in prediction of boiling temperatures is 1.86%. The is greater than 1.46% from the TEA peng robinson equation. I have not checked for enthalpy calculations, as I am sure that if the error in bound to be high.

[jasper]

Interesting findings - thank you for posting them.

[arvind.prasad]

The refrigeration cycle is an closed loop system. Will I be able to simulate a flowsheet that has no feed, and product streams? Any settings to solve such a problem?