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Dr. Barber

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About Dr. Barber

  • Rank
    Project Manager

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  • Engineering Field
    Mechanical
  • License
    PE
  • Discipline
    Mechanical

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  1. You don’t need any of that. Haven’t you seen the official specs? https://ncees.org/wp-content/uploads/PE-Mech_Thermal-Apr-2017.pdf
  2. Are you referring to the CLTD one? thats super-duper obsolete. It’s scary that that is there...
  3. Some more clarification: https://www.eng-tips.com/viewthread.cfm?qid=89032
  4. Agreed. I haven’t said they’re wrong. I guess I was “thinking out loud” and figuring out when to use similarity and when to use affinity. Still not clear.
  5. Equations 18-45, and 18-47 of MERM13 are valid when you reduce the diameter by trimming the impeller. The relationships for changes within a family of geometrically similar pumps are different (I guess trimming the impeller makes the new pump not "geometrically similar" as the original) Consider Equation 18-52 and set n1=n2 (same speed for both pumps), the result is Q2 = Q1 (D2/D1)^3, which is NOT equation 18-45. Consider Equation 18-53 and set n1=n2 (same speed for both pumps), the result is P2 = P1 (D2/D1)^5, which is NOT equation 18-47. This is also done in Fluids textbooks. Here is a screenshot of the book by Munson, Young and Okiishi. I guess the take-away message is to be careful and make sure to know how is the impeller diameter changing: Is it being trimmed? or is it being replaced by a smaller one, but geometrically similar? The equations can be quite different.
  6. 1st day of week 5 spam
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