Screenshot instructions:
Windows
Mac
Red Hat Linux
Ubuntu
Click URL instructions:
Rightclick on ad, choose "Copy Link", then paste here →
(This may not be possible with some types of ads)
From: jmb <jmb365@gm...>  20120422 22:01:03

I have installed CompPad 0.3.04_a (w/ OpenOffice, LibreOffice) on two Ubuntu PCs and they work after some glitches that could be overcome from reading the FAQ on the CompPad SourceForge website. How ever I am running into a problem (bug?) with its unit awareness as follows: %% / %% To calculate condensation heat transfer coefficient of water vapor:/ unitSystem:="US" D_o:= {1.0 ft} g:={1.0 ft/hr2} %lambda:={1.0 BTU/lb} %rho_f:={1.0 lb/ft3} k_f:={1.0 BTU/{hr ft °F}} %DELTA_t:={1.0 °F} %mu_f :={1.0 lb/{ft hr}} h:= 0.725 left[ {{k_f}3 %rho_f2 %lambda g} over {%mu_f D_o %DELTA_t} right]^{1/4} h= %% This is from an old classical text book "Process Heat Transfer D.Q. Kern" Eqn: 12.34 pg 263 and the resultant units are h in [BTU/(hr ft2 F)]. However CompPad bungles it badly if I use units. The calculated value and the units are bizarre. I used 1.0 for all the variables just to check verify CompPad's accuracy. It should come back with h = 0.725 [BTU/(hr ft2 F)] CompPad comes up with 5.042 [lb/(s3 R)]! Earlier I tried the same with all SI units as well and got nothing close to what it should be in equivalent SI units either. If I remove all units then I get 0.7250 which is the correct value. If anybody could you try this out and possibly explain why I am not getting correct results, I would be grateful. Thanks! Regards, JMB 
From: Bernhard Schweighofer <schweigi@gm...>  20120424 05:26:34
Attachments:
comppad_unit_problem.zip

Am Sonntag, den 22.04.2012, 18:00 0400 schrieb jmb: > ... How ever I am running into a problem (bug?) with its unit > awareness as follows... I've tried to imitate the behaviour to see what's wrong, so I reentered your code. I think, the result you get is right! Just force comppad to use your desired unit. I've also attached the ".odt" file, so you can see what I mean... kind regards Bernhard 
From: jmb <jmb365@gm...>  20120425 01:01:21

Hello Bernhard Schweighofer, Thank you for your reply and details about forcing CompPad's output. But I am still perplexed by CompPad's logic. For example if I try: Q := {1 BTU over {ft^2}} = which defines Q as a heat flux, and I press the green calculate button I get: {{"2.504×10⁴"`{lb}over{s^2}`}} as the result. How and why is CompPad coming up with [lb/s^2] as the units? However Q := {1 BTU } = is evaluated as 1.000 BTU, just as I expect. Maybe I am missing something that is obvious to you, but not to me... Would you kindly explain? Regards, JMB Bernhard Schweighofer wrote: > Am Sonntag, den 22.04.2012, 18:00 0400 schrieb jmb: > >> ... How ever I am running into a problem (bug?) with its unit >> awareness as follows... >> > > I've tried to imitate the behaviour to see what's wrong, so I reentered > your code. I think, the result you get is right! Just force comppad to > use your desired unit. I've also attached the ".odt" file, so you can > see what I mean... > > kind regards > Bernhard > > 
From: Bernhard Schweighofer <schweigi@gm...>  20120425 05:33:56

Am Dienstag, den 24.04.2012, 21:01 0400 schrieb jmb: > ... For example if I try: > > Q := {1 BTU over {ft^2}} = > > which defines Q as a heat flux, and I press the green calculate button I > get: {{"2.504×10⁴"`{lb}over{s^2}`}} as the result. I guess it's because comppad tries to "simplify" the unit of the end result. During calculation the units will be broken down to their base units. For the further explanation I have to switch to SI units (I'm not used to calculate with BTU...), so the example would look: Q := 1 J over m^2 = 1 kg over s^2 What's the "base" unit of J? > we have to break down to kg, m, s. How to get there? e.g. energy = force * distance = mass * acceleration * distance = [kg * m/s^2 * m] = [kg * m^2 / s^2]. So "J over m^2" becomes "kg * m^2 / s^2 over m^2" > "kg / s^2" > But from here, comppad cannot guess back, that it "should be" "J / m^2"... BTW at least for me, I got easily used to put the "desired" unit at the end of a calculation. E.g. for energy I often use "Wh" and "kWh", instead of a simple "J", so I have to put it there anyway... bernhard 
Sign up for the SourceForge newsletter:
No, thanks