regarding rate model

[ptc-5491269]

Hi all,

I am new to Mathcad and started working on the rate based model.

I am trying to solve this through the above assumptions.

I am Assuming Kgprime for MEA/CO2/H2) from an experimental study and calculating the ncO2, nH2O, h and q

Using the following relation.

Function calculating gas and liquid outlet molar flow rate and enthalpy for a given amount of mass transfer of CO2, H2O and heat transfer (MW) (fo)

and foa.

any help would be great thanks

Lisa

[AlanStevens]

Your file needs Mathcad file 97stm.mcd (contained on your M drive) in order to work. Since you haven't attached this, your file won't work for those of us who don't have access to your M drive. You could either upload 97stm.mcd, or extract the functions your program needs and include them explicitly in the worksheet. Then we will stand a better chance of helping.

Alan

[ptc-5491269]

the 97stm.mcd file attached thanks

[AlanStevens]

Ok. Your problems stem from the fact that M15 (and earlier) won't accept variables with different units in the same vector - see attached.

Alan

[ptc-5491269]

Alan,

Thanks i tried to make the changes accordingly but still i am experiencing problem with units.

Please see attached

Thanks in advance

Lisa

[AlanStevens]

li sa wrote:

Alan,

Thanks i tried to make the changes accordingly but still i am experiencing problem with units.

Please see attached

Thanks in advance

Lisa

Nothing attached!

Alan

[ptc-5491269]

sorry please find the attachement

[AlanStevens]

The attached shows where you have mixed up units.

Alan

[ptc-5491269]

Alan,

Thanks for the corrections. Is there anyway to get around this problem. Any suggestions.

Thanks in advance

Lisa

[AlanStevens]

li sa wrote:

Alan,

Thanks for the corrections. Is there anyway to get around this problem. Any suggestions.

Thanks in advance

Lisa

Yes, you have to separate out the various components. However, I think you should go through the worksheet checking the units of each item very carefully. You've been unneccesarily complicated in places (for example, dividing through by kJ/mol in the elements of hgas_datum, and then multiplying the overall vector by the same thing!) - this can easily lead to errors. I suggest you also put a few words of explanation against each statement. This makes it easier to understand what you are trying to do.

Alan

[ptc-5491269]

HI Alan,

Can you help me with it. I am still struggling to get around this problem. I didn't get on how to do this.

THanks

lisa

[AlanStevens]

li sa wrote:

HI Alan,

Can you help me with it. I am still struggling to get around this problem. I didn't get on how to do this.

THanks

lisa

I'll have a go. It might take a while!

Alan

[ptc-5491269]

Thanks. Would be happy to provide any information you may require. In the meantime i would also try.

Thanks in advance

Lisa

[AlanStevens]

See if the attached helps. Note, some of my modifications near the end of the worksheet are definitely wrong! They are there to give guidance on not mixing up terms with different units.

Alan

[ptc-5491269]

Hi Alan,

Thanks for taking time and valuable suggestions.

I am trying to calculate further a bit, but again when i try to introduce the enthalpies in function getting the errors.

Can you kindly check and let me know where i am going wrong.

Thanks in advance

lisa

[AlanStevens]

...

I am trying to calculate further a bit, but again when i try to introduce the enthalpies in function getting the errors.

Can you kindly check and let me know where i am going wrong.

Thanks in advance

lisa

G1 and L1 have units of mol/s. HG1 and HL1 have units of W. You cannot have mixed units in a vector in this version of Mathcad. You must calculate them separately. Use one function for G1 and L1 and a completely different function for HG1 and HL1.

Alan

[ptc-5491269]

Hi Alan,

Thanks once again. When i wanted to calculate Kg and kgprime values explicitly on function f3 and f5 i am not sure where my definition is wrong.

any suggestions.

thanks

[AlanStevens]

li sa wrote:

Hi Alan,

Thanks once again. When i wanted to calculate Kg and kgprime values explicitly on function f3 and f5 i am not sure where my definition is wrong.

any suggestions.

thanks

I see - further down the worksheet than I was looking!

You have several terms that have an exponential with a unitless number divided by a temperature in K. You need to make the ratio unitless by making the other numbers have units of K (or, equivalently, make the temperature unitless by dividing by K).

You define k.g but then try to use k.G in your definition of h. If you make this k.g you have another error, namely M.MEA doesn't exist; you probably want M[MEA (i.e. true subscript, not a cosmetic one). Correcting this, gives a further error, because it thinks T in the call to fCpgas is Teslas! Make h a function of T to avoid this.

Alan

[ptc-5491269]

Alan,

Thanks i made the changes according to the suggestions.

But still not sure if my approach for calculating the function f3 and also getting funny untis for my klprod.

Thanks

lisa

[AlanStevens]

li sa wrote:

Alan,

Thanks i made the changes according to the suggestions.

But still not sure if my approach for calculating the function f3 and also getting funny untis for my klprod.

Thanks

lisa

I'm of limited help here as I don't know what klprod is meant to be nor how it should be calculated (in fact I don't know anything about the physical nature of your problem); but, first: what is D and what units should it have? Second, you haven't given units to height, circumference or Area, and you've raised them to some strange powers! You need to be consistent in your use of units and you need to make sure you know what the units of all your terms are and that you are using the correct expressions for all the terms.

Alan