Reynold's number importance?

Discussion in 'General Discussions' started by Eric Kurtz, Jan 5, 2019.

  1. Eric Kurtz

    Eric Kurtz Member

    How important is the Reynold's number? I'm running 7.5 gpm thru 4 ground loops of 3/4” HDPE (ethanol for anti freeze). Which means my Reynold's number is relatively low (I haven't done all the calcs). According to what I've read, normally would want more like 10-12 gpm for 4 loops to get to optimum number. However, I've got nearly 90 gal in my loop. That means HP will run on low stage for 12 minutes before heat transfer during flow is important. Now I would assume that under constant run times, it becomes more important to get that optimum turbulent flow. Currently my system is not running long enough to do a lot of testing to prove one way or another. My gut feeling is that the difference will be hard to quantify. Maybe someone has an idea on how I could test this?
     
  2. nc73

    nc73 Member Forum Leader

    Did you use the spreadsheet from climatemaster? Anything over 2500 is good. It is important. Mine is 5500. Download the spreadsheet!
     
  3. nc73

    nc73 Member Forum Leader

    Yours wouldn't be low at all. Should be over 2500.
     
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    25% Ethanol in 3/4" pipe at 1.9 gpm flow has a Reymolds of 1261......

    The Reynolds number has more limited importance if your entering water temp is high enough. I would not sweat to it too much, even at a lower Reynolds number, you still have mixing going on....
     
  5. Eric Kurtz

    Eric Kurtz Member

    That's sounds like what I had calculated during design. Am I right in thinking that colder temps with higher percentage of run time might benefit from more turbulence.
     
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Yes, in general. But....it does not mean that with 120 that you do not have mixing.....
    2500 was originally arbitrarily picked, but I could never find scientific evidence about a detrimental impact of 1000, 1500, or 2000.

    We often run loops with Reynolds numbers of less than 1500, I yet have to monitor a major impact. If anyone has different data or reference....I am the first to listen. Please post here.
     
  7. Eric Kurtz

    Eric Kurtz Member

    Makes sense. Thanks. When EWT is lower, more flow is better anyway. Turbulent flow is just a side benefit that does help, but hard to quantify.
     

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