Horizontal Slinky vs. Straight Pipe

Discussion in 'Geothermal Loops' started by bengee, Nov 12, 2010.

  1. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm not sure I agree with "poor conductivity"

    Here's my offer: I'll prepare a pan of 110-115*F water. You agree to dip your hand into it very very slowly so that there is no mixing or turbulence.

    I solemnly swear not to stir, move or otherwise disturb the pan or the water while your hand is in it, thereby preventing turbulent flow.

    I bet that in a few seconds you'll be able to tell me if any heat transfer is occurring...

    Along the same vein I find that a glass of beer left unattended (a rare error on my part, but not unheard of, sad to say) does warm up undesirably fast.
     
  2. Looby

    Looby Member Forum Leader

    Bogus experiment, temperature != heat. The equally poor thermal conductivity of
    your (non-turbulent) precious bodily fluids allows your hand's surface temperature
    to rapidly match that of the water, with minimal heat transfer. In fact, at the very
    surface of the skin, the temperature change is literally instantaneous -- because
    the temperatures on both sides of any point-of-contact must be equal. (In physics,
    that's one technically excellent definition of "in contact.")

    Please put a thermometer under your tongue and repeat the experiment.

    Bubble-convection? No way to eliminate the dT/dt, but it's easy to minimize the
    undesirable effects: switch to (Lucas-tolerant) bottom-fermented barley soups...

    ...save the ales!

    Looby
     
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I've seen videos of blood cells bouncing around in capillaries - they look pretty turbulent to me!

    My point in all this is that there is still useful heat transfer to be had in laminar flow, just not as much in turbulent.

    IPA, all they way!
     
  4. TNsteve

    TNsteve New Member

    We are in the later stages of putting in a Water Furnace 7 series system with a horizontal loop. In a moment of weakness (or cheapness), I said I would dig the trench. Two 300’ trenches, 24” wide, 6’ deep - no problem right? Well, we are in a hollow in middle Tn with a stream running through. 6’ deep puts the bottom of the trench below stream level. Soil consists of 2’ of sticky clay that adheres to my backhoe bucket, followed by a water saturated sand / gravel mixture. In trying to dig below 4’, the gravel erodes into the trench, leading to the sidewalls collapsing. I have probably dug the damn trench 4 times now, only to have it cave in, then bale it out - it’s 8’ wide in places.
    In the midst of this, the fellow we had been working with at the dealer retired and we have a new guy. The first guy was talking a slinky loop, the new guy is talking straight pipe. I believe a slinky is the best design, given the irregular trench width, and being 6’ down is not necessary when the pipe is in water saturated soil. Any thoughts there?
     

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