Physics Help Forum loss coefficient

 Feb 3rd 2016, 05:04 AM #1 Senior Member   Join Date: Jun 2014 Posts: 306 loss coefficient in the notes , why the author said when the inlet diameter equals to the outlet diameter , the loss coefficient can be determined? if the inlet diameter not equal to the outlet diameter , the loss coefficient can't be determined? Attached Thumbnails
 Feb 3rd 2016, 01:15 PM #2 Senior Member     Join Date: Apr 2008 Location: Bedford, England Posts: 668 The loss coefficient is determined from the difference in entry velocity to exit velocity. If the entry diameter is different to the exit diameter, then this would have a larger influence on the velocity difference than the loss coefficient. The effect of the difference in diameter on the difference in velocity could be factored into the calculations, but would substantially complicate the calculations. I am guessing that the author is avoiding this complication by just saying "don't do it". __________________ You have GOT to Laugh !
Feb 3rd 2016, 10:06 PM   #3
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Join Date: Jun 2014
Posts: 306
 Originally Posted by MBW The loss coefficient is determined from the difference in entry velocity to exit velocity. If the entry diameter is different to the exit diameter, then this would have a larger influence on the velocity difference than the loss coefficient. The effect of the difference in diameter on the difference in velocity could be factored into the calculations, but would substantially complicate the calculations. I am guessing that the author is avoiding this complication by just saying "don't do it".
do u mean if the diameter is constant for entering and exit entrance , the velocity will somehow change due to work against friction force?

 Feb 5th 2016, 01:27 PM #4 Senior Member     Join Date: Apr 2008 Location: Bedford, England Posts: 668 No, the velocity through the pipe for a given head will vary due to the friction. so if you force water through two pipes using the same pressure, it will travel faster through the smooth pipe than the rough one. so you can judge the relative roughness of pipes by how fast the water flows through through them using the same input pressure in each case __________________ You have GOT to Laugh !

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