Fall 2012 ME 395 - GSI Josh Lacey

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 Efficiency and Reynolds number

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ethanhal



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Join date : 2012-10-01

PostSubject: Efficiency and Reynolds number   Tue Nov 20, 2012 1:23 am

I was just wondering what diameter we use when calculating the reynolds number. Is it the inlet diameter or the outlet diameter? Also in your office hours today, you said that an efficiency of 25% was probably going to be about what our maximum efficiency will be. I have done this calculation and double checked it and my highest efficiency is about 17%. Would this still be considered too low?
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GSI Overlord
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PostSubject: Re: Efficiency and Reynolds number   Tue Nov 20, 2012 1:47 am

You can approximate your characteristic diameter D as the inlet diameter. In reality, D is the impeller diameter but that would have been hard for you to measure in the lab and I don't think they gave you the impeller diameter on CTools.

17% efficiency isn't out of the realm of possibility...some of those compressors are likely worse than others. Yours appears to be quite crummy.
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ethanhal



Posts : 13
Join date : 2012-10-01

PostSubject: Re: Efficiency and Reynolds number   Wed Nov 21, 2012 10:00 pm

Alright so Im getting better efficiency values except now at 4 V Im getting a maximum efficiency of well over 50% which I know is way too high. Could this be due to the fact that the data for 4 V isn't good just like its not very good for 2 V or did I most likely do something wrong
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GSI Overlord
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PostSubject: Re: Efficiency and Reynolds number   Wed Nov 21, 2012 10:05 pm

Are the efficiency values at the blower setting of 4 all substantially higher than at the other speed settings? What you should hopefully see is that your efficiency curves when plotted against flow coefficient 'collapse' (with perhaps the exception of the lowest blower speed setting of 2). If that curve at that speed setting of 4 is way higher than the others there could be a problem with either the data or perhaps just the calculations on the spreadsheet.
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