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Old 08-31-13, 12:37 AM   #1541
AC_Hacker
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Quote:
Originally Posted by mejunkhound View Post
graphic COP vs. vent air temp and outside air temp (or ground temp minu 5-10F)
Which, if I'm not mistaken, is another way of expressing the Carnot Efficiency Theorem, and as the difference between the source air temperature and the environmental air temperature becomes greater (the temperature lift becomes greater) the efficiency, COP in your case, gets smaller.

Good chart, thanks.

-AC

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Old 09-01-13, 06:55 AM   #1542
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Quote:
Originally Posted by AC_Hacker View Post

The turbulent zone of fluid flow is really interesting. Fluid in a laminar flow mode doesn't exchange heat as readily as turbulent flow. And it takes more energy to drive fluid into the turbulent flow mode. In a conversation I had with a fluid engineer, he told me that the fluid friction losses from turbulent flow were lower than for laminar flow. Hard for me to believe. I also came across some fluid flow formulas that encapsulated the idea that the power required to pump fluid through pipe varies proportionally with the square of velocity.

Curious stuff, fluid dynamics...

-AC

Curious stuff indeed as turbulence is said to be one of the most profound complexities yet to be understood by classical physics.

Laminar flow shows a far less robust heat exchange compared with turbulent flow. But the energy required for turbulent flow is FAR higher. One of the most obvious hints to this is that turbulent flow causes micro eddies with the result being sound and frictional heat.

Bottom line; sizing a pump for high flow turbulent flow requires a larger size (power) compared to an identical flow situation under laminar flow conditions.

This has direct implications for sizing a pump where turbulence is intentionally created to maximize heat flow transfer.

Steve
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Old 09-01-13, 05:25 PM   #1543
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This is a case of cowboy engineering, but it seems to me turbulence would be a natural outcome of the "slinky" arrangement of source tubing as opposed to straight tubes.
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Old 09-01-13, 05:48 PM   #1544
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Quote:
Originally Posted by michael View Post
This is a case of cowboy engineering, but it seems to me turbulence would be a natural outcome of the "slinky" arrangement of source tubing as opposed to straight tubes.
Not so! Slinky ground loops normally have a D to d ratio (slinky D to tube ID) of about 50 to 1. Bend radius caused turbulence occours at ratios <2/1.
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Old 09-02-13, 02:10 PM   #1545
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Come on Guys

Install a little more tube in the ground than your local contractor would and size your pump as the status quo. I don't believe trying to induce turbulence will get you anymore heat then a standard installation would. Or in other words money in your pocket.

Although these techniques are interesting to discuss. I think its fly crap in pepper.

Would a pilot not eat lunch and ensure his bowel is empty before he jumps in his airplane knowing weight is a factor???

Randen

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Old 09-02-13, 02:14 PM   #1546
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Don't try to hit the turbulent sweet spot. None of us are that accurate and the conditions will change over time so as Randon says.....add the pipe. The biggest issue is surface area.
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Old 09-02-13, 02:14 PM   #1547
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Default Regarding Turbulent Flow...

The topic of turbulent flow is too important to be left to incomplete or incorrect advice...

Turbulent flow in heat carrying fluids is almost always desirable.

In the manuals I have read on GSHP design, careful attention is given to the many aspects that contribute to successfully achieving turbulent flow.

I strongly recommend anyone who is seriously contemplating doing a GSHP ground loop, to obtain a copy of a GSHP design manual. They are for sale HERE and also can be found through your local library, as hikerjohnson has happily discovered. I have also seen them pop up on Amazon.

I personally own the original manual, which has been added to and included in the updated manual.

Even if you are considering hiring out the construction of a GSHP system, I'd strongly advise getting and reading the manual first.

Knowledge is power.

-AC
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Old 09-02-13, 04:11 PM   #1548
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AC is correct, but sadly much of the flow in vertical and horizontal ground loops is laminar and not turbulent. Straight pipes have the highest laminar flow conditions, curled slinky just a bit below that.

But imagine if the ground loops could be induced to have a large amount of turbulent flow. It would cut off almost 50% or more of the necessary pipe length.

I have been working with the OSU team on injecting air bubbles into the loop so that the water going down the loop is maintained as a waterfall (clearly turbulent). The return has a vent on top that has a vent to remove the air.

Then we are also using a proprietary fluid additive that makes the fluid far more slippery and less viscous than water. This also promotes turbulence.

We are also working with a company to put spirals on the inside of the HDPE pipe to spin the water (think rifling in a gun barrel) and also spot divots inside the ground loops thereby minimizing laminar flow conditions and also creating turbulence around the many divots.

The extrusion process with inside spirals and divots is tough, but it has HUGE rewards.

We have also found that 1 inch tubing is far better than 3/4 inch HDPE if you can minimize laminar flow. The cost of pumping is higher with turbulent flow, but that is small stuff.

The goal is to reduce the length of the ground loop by 50% or more with minimal cost. A classical engineering problem . . . .

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Old 09-02-13, 04:40 PM   #1549
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Apparently you ignore the happenings on the other side of your heat exchange barrier, the pipe wall, in your desire to reduce the buried pipe length by 50%! The outside of the pipe is exposed to zero flow velocity, if a heat conducting fluid is even present, in moist or dry rock and soil.
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Old 09-02-13, 05:29 PM   #1550
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So, for those readers who may not be completely following this ramble, regarding turbulent flow, here is a chart that illustrates the idea:


As you can see, once the level of turbulent flow is reached, there is a noticeable jump in heat transfer.

So steve, who is funding this research and why is the flow enhansing fluid proprietary? Do you have any diagrams or photos of the 'improved' tube?

And what role are you playing in this study?

Lastly, what have you learned form this experience that will enable DIY folks to improve their efforts?

-AC

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