Space-time Calculation Problem

[nrgeng]

Different (by a factor of 2) results are obtained for space-time, τ, from a CSTR simulation. Hopefully you can point to the calculation error.

Method 1:
τ = V/ν0
From Simulation Stream Report:
τM1 = 0.1 m3 / 0.08 m3/h = 1.25 h

Method 2:
for a CSTR, τ/CA0 = XA/-rA , τ = CA0XA/-rA
From Simulation Unit Report:

• XA = 0.245
  -rA = 0.0226 mol/m3/s

From Simulation Stream Report:

• CA0 = xA * ρm = 0.667 * 1252 mol/m3 = 835.1 mol/m3

τM2 = CA0XA/-rA = 835.1 mol/m3 * 0.245 / 0.0226 mol/m3/s / 3600 s/h = 2.51 h

τM2 = 2 * τM1, Why?

Calculations with Symbols Intact

Space-time Calculation Problem.jpg (101.35 KiB) Viewed 14553 times

[jasper]

Can you attach the simulation?

Thanks.

[jasper]

If "A" is hydrogen, then your problem is the rate:

rA = stoichiometry * r

where stoichiometry = -3.

If "A" is CO2, your problem is your initial X (xH2 = 0.75 = 3 * 0.25 = 3 * xCO2)

I am not sure which is your A, so pick which of the two answers above is more appropriate.

I am also not sure how this relates to the factor 2 in your post, as I do not have a complete set of details for that.

On another note: to insert the greek letters in the text box, the easiest is to copy them from somewhere else, e.g. the character map. You can also just write the text somewhere else entirely and just paste the entire text. Note that there is a problem with rtf pasting in some versions though (fixed in the upcoming alpha).

[nrgeng]

Thanks for discovering my error with stoichiometry.
I sent a different simulation where coefficient "a" of a*A was 3 not 2.
My text application properly pastes text into my email client but not into COFE or alpha COFE. I have to paste to Word then to COFE. Too bad.

[jasper]

Text: check the next alpha, still working on it - I did fix it last week. If the problem persists, let me know.