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June 29, 2013, 05:29 
simple CEL expression debuging

#1 
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Meimei Wang
Join Date: Jul 2012
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Hi
I'd like to define a position dependent variable by: ' length = 0.0033 [m] heat transfer coefficient = 0.1x*(0.10.07)/length [m s^1] ' . But the error message is ' Units ([m s^1]) are associated with a term that is not dimensionless. ' It is quite strange because the unit of 'x' is [m], right? I'm really confused. Could anyone help?
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Best regards, Meimei 

June 29, 2013, 07:11 

#2 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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The error message is quite clear. You assigne dthe variable "length" units of [m], but then try to reassign it units [m s^1] in the next line. You need to fix this by putting the units against the constants in both equations, do not put units against variables.


June 29, 2013, 08:45 

#3  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
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Quote:
If it's written in this way: ' length = 0.0033 [m] ratio = x/length [] heat transfer coefficient = 0.1(0.10.07)/ratio [m s^1] ' , then the error message will be ' Error at position 10. Units ([]) are associated with a term that is not dimensionless. ' .
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Best regards, Meimei Last edited by Anna Tian; June 29, 2013 at 11:08. 

June 29, 2013, 08:54 

#4 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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You cannot just assign x/length (which is dimensionless) a dimension. Instead multiply it by 1[m/s] to convert it to a velocity. But then you will have to make the 0.1 a velocity as adding a dimensionless number with a velocity is not meaningful either. And finally you appear to be setting a variable which looks like a heat transfer coefficient with a velocity and that does not make sense either. It's late. I'm going to bed. 

June 29, 2013, 08:58 

#5  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
If it's written in this way: ' length = 0.0033 [m] ratio = x/length [] heat transfer coefficient = 0.1x*(0.10.07)/ratio [m s^1] ' , then the error message will be ' Error at position 10. Units ([]) are associated with a term that is not dimensionless. ' Btw, sorry that it does not mean heat transfer coefficient. It is wall function transfer coefficient. I just name it as 'heat transfer coefficient'. You can ignore the name 'heat transfer coefficient'.
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Best regards, Meimei 

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