# Diffference between mass weighted average and Area

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 January 3, 2008, 05:00 Diffference between mass weighted average and Area #1 giogio Guest   Posts: n/a Hi, I don't understand the difference between Mass weighted average and area weighted average, when i must use one or the other. (results are very different). Thanks adnanghreeb likes this.

 January 8, 2008, 13:19 Re: Diffference between mass weighted average and #2 Glenn Guest   Posts: n/a Mass averaging is summation of (value * mass flow) / summation of mass flow over the surface of interest. Area averaging is summation of (value * area) / summation of area over the surface of interest. elham-u and adnanghreeb like this.

 September 24, 2012, 13:13 regarding mass weighted average velocity #3 New Member   abhi Join Date: Sep 2012 Posts: 11 Rep Power: 6 Hi, i just want to know that is average velocity( mass weighted ) dependent on grid number ? Actually i am simulating flow through pipe , and flow is laminar so friction factor theoretical is 64/ Re . And flow is fully developed(done using C coding) .for Re 500 f th is 0.128. and i am getting 0.145 and its not acceptable i guess. U max is 0.01817. So actual avg. velocity value should be 0.01284813 but fluent giving me d value 0.012135. Can anyone tell me whats going wrong or how to improve avg. velocity value (mass weighted ) Since flow is laminar we cant get actual pressure drop(static) and its coming out 0.2396 and fluent giving me 0.24 so its close only problem is with velocity plz. tell what is wrong

September 24, 2012, 16:42
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Ehsan Asgari
Join Date: Apr 2010
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Quote:
 Originally Posted by ashgun Hi, i just want to know that is average velocity( mass weighted ) dependent on grid number ? Actually i am simulating flow through pipe , and flow is laminar so friction factor theoretical is 64/ Re . And flow is fully developed(done using C coding) .for Re 500 f th is 0.128. and i am getting 0.145 and its not acceptable i guess. U max is 0.01817. So actual avg. velocity value should be 0.01284813 but fluent giving me d value 0.012135. Can anyone tell me whats going wrong or how to improve avg. velocity value (mass weighted ) Since flow is laminar we cant get actual pressure drop(static) and its coming out 0.2396 and fluent giving me 0.24 so its close only problem is with velocity plz. tell what is wrong
I guess nothing! Fluent solves the fluid flow numerically, so it's obvious that there would be difference in comparison with analytical solution.When dealing with computational methods, you have to consider range of acceptable numerical error, for instance 5%. Here you may try to adjust your mesh in order to get desired solution.

 September 25, 2012, 01:36 #5 New Member   abhi Join Date: Sep 2012 Posts: 11 Rep Power: 6 I tried with 0.1 million cell count and 0.6 million, only i could see decrease in pressure drop but average velocity remained same

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