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Enthalpy, Entropy Base Values And References In Prode

enthalpy entropy base reference values prode

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#1 twell

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Posted 17 February 2014 - 02:54 AM

In Prode Properties one can define a reference temperature and a initial value for enthalpy and entropy.  For example I can set as initial temperature 1 K in order to obtain only positive values for enthalpy and entropy; the same, if I set a high positive value as for example 50000 Kj/Kg.  This is useful since by changing initial temperature and base value I can match the results from other simulators and tables of values.

However Prode has another option which is the enthalpy (and entropy) of formation in database.  I do not know when to use this option and the manual gives little information about.  Can you explain ?

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#2 marchem

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Posted 17 February 2014 - 09:09 AM

Standard Enthalpy of Formation is the change in enthalpy that accompanies the formation of a defined amount of a compound from its elements at standard states.  For some additional information see

http://en.wikipedia....py_of_formation

You would need these values for solving chemical reactions, with Prode Properties you can solve directly or use
the reactor module (which does that).
 



#3 twell

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Posted 26 March 2014 - 05:58 AM

thanks,

so that option is for reactions, is that ?



#4 marchem

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Posted 27 March 2014 - 05:05 PM

Yes, enthalpy of formation is required with reactions.  Prode has specific methods for solving reactors etc.

However there are several ways to use these values.  For example, by setting the enthalpy reference as enthalpy of formation you can solve a reaction of combustion such as

1*CH4 + 2*O2 -> 1*CO2 + 2*H2O

directly as difference in enthalpy between the two streams with composition

1*CH4 , 2*O2

and

1*CO2 + 2*H2O

See the attached example in Excel.  Of course, much more complex examples are possible.

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#5 twell

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Posted 31 March 2014 - 09:25 AM

Thanks marchem,

Which are the differences of that method (enthalpy based) and the Excel macro

 

= StrHC()

 

which calculate and return the heat of combustion for a stream ?



#6 marchem

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Posted 01 April 2014 - 04:55 AM

The function

 

=StrHC(stream)

 

which is available as a macro in Microsoft Excel, returns the Net heat of combustion (gas phase) for a stream.  Calculated values are based on the Net heats of combustion stored in a database,  This is useful when you wish

to calculate the heat of combustion for gas mixtures.  But suppose you wish to solve

 

N2O5 + H2O ---> 2 HNO3

 

For that, you can utilize the method discussed in my previous post.  Set the enthalpy reference as enthalpy of formation

and then calculate the difference.



#7 twell

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Posted 14 April 2014 - 11:40 AM

in most cases I need the heat of combustion and for that there is macro =StrHC,

does Prode utilize enthalpy of formation when solving columns ?



#8 PaoloPemi

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Posted 15 April 2014 - 07:11 AM

You need the distillation column module which is available in the commercial version.  The module allows to include the contribution of chemical reactions in a way similar to other simulators.



#9 twell

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Posted 18 April 2014 - 10:25 AM

thanks,

I have the licence for base version which do not include VLL column (and, I presume, distillation with reactions as well)



#10 marchem

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Posted 28 April 2014 - 04:40 AM

yes,

you need the extended version for reactions and batch column.



#11 twell

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Posted 22 May 2014 - 10:40 AM

thanks marchem,

When working with enthalpy & entropy bases for temperatures, a reference is -200 F but others adopt different values.  This may generate some confusion when comparing results from simulations.  Is there a recognized standard to follow ?



#12 PaoloPemi

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Posted 23 May 2014 - 11:08 PM

I do not know of such standards for thermodynamic properties.  However, there are no problems with PRODE to start integrating enthalpies from different points.

 

As discussed in previous posts you can define temperature and base values for enthalpy and entropy and store these values in a project file (archive file) with units, stream's compositions, settings etc.



#13 frpe

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Posted 12 June 2014 - 09:21 AM

Do you know if PRODE methods

 

setHB()

setSB()

 

that allow you to define temperature and initial value for enthalpy and entropy in Excel, also work in Mathcad (15) ?

My Mathcad extension doesn't appear to recognize those names.



#14 marchem

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Posted 12 June 2014 - 10:31 AM

could it be that you have installed a old extension (for Mathcad) ?

Check this page for latest versions

 

http://www.harveyhen...properties.html



#15 frpe

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Posted 05 July 2014 - 09:50 AM

thanks marchem,

I'll verify that.






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