Friction loss to vertical pipes in a closed system?

In summary, Chet found out that he's been doing something wrong all these years when it comes to his heating system design and he plans to change things up. He thinks that treating the vertical lengths of piping as if they were horizontal can cause a lot of unnecessary friction losses, so he's going to start taking elevation loss into account from now on. He's also going to size his pump correctly based on the elevation changes he knows will be present.
  • #1
TSN79
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So in designing closed systems, mostly heating systems, I realized today that I've probably been doing one thing wrong all these years. In such a system one doesn't take elevation loss due to gravity into account since you "get it back" on the way down. This I've always been aware of, but what I've still been doing is treating the vertical lengths of pipe as if they were horizontal, that is applying to them a friction loss per meter. Can someone just confirm that I can stop doing this? I'll just go back to my corner and be ashamed...
 
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  • #2
Have you estimated how much of a pressure difference is involved as a result of the elevation differences, as compared with the frictional losses?

Chet
 
  • #3
Chestermiller said:
Have you estimated how much of a pressure difference is involved as a result of the elevation differences, as compared with the frictional losses?

Pressure loss due to elevation would be much higher than the major head loss per meter. Elevation loss is just a result of gravity, 9,8 kPa/m in addition to the friction loss, compared to about 0,15 kPa/m in the horizontal piping. But I believe the elevation loss doesn't need to be considered at all in a closed circulating system.
 
  • #4
What about when you select the fan? Doesn't it need to have enough ooomph to get significant air flow to the upper floor(s)?

Chet
 
  • #5
Chestermiller said:
What about when you select the fan? Doesn't it need to have enough ooomph to get significant air flow to the upper floor(s)?

It's a central heating system, so there is a water circulation pump, not a fan.
 
  • #6
TSN79 said:
So in designing closed systems, mostly heating systems, I realized today that I've probably been doing one thing wrong all these years. In such a system one doesn't take elevation loss due to gravity into account since you "get it back" on the way down. This I've always been aware of, but what I've still been doing is treating the vertical lengths of pipe as if they were horizontal, that is applying to them a friction loss per meter. Can someone just confirm that I can stop doing this? I'll just go back to my corner and be ashamed...

Technically you should consider the elevation changes so you can size your pump correctly. I imagine that since it's a closed loop system that is being constantly recirculated that you'll end up with the same answer. Why not just run a couple of hand calcs and do one like you've been doing it and then one that includes the elevations and see what the results tell you?

CS
 
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1. What is friction loss in a closed system?

Friction loss in a closed system refers to the loss of energy due to the resistance of fluid flow against the internal surfaces of pipes, valves, and other fittings. It is caused by the friction between the fluid and the surface of the pipe, which results in a decrease in pressure and flow rate.

2. How does friction loss affect vertical pipes in a closed system?

Friction loss in vertical pipes is affected by the length and diameter of the pipe, as well as the viscosity and velocity of the fluid. The longer the pipe, the greater the friction loss, and the smaller the diameter, the larger the friction loss. Higher viscosity fluids also experience greater friction loss, as well as higher velocities.

3. What factors can increase friction loss in vertical pipes?

In addition to the length, diameter, viscosity, and velocity of the fluid, other factors that can increase friction loss in vertical pipes include roughness of the pipe surface, bends and elbows in the pipe, and obstructions such as valves and fittings. Changes in elevation, such as going from horizontal to vertical pipes, can also increase friction loss.

4. How is friction loss calculated in vertical pipes?

The most common method for calculating friction loss in vertical pipes is using the Darcy-Weisbach equation, which takes into account the length, diameter, roughness, and velocity of the fluid. Other methods, such as the Hazen-Williams and Manning equations, may also be used depending on the specific application and fluid properties.

5. How can friction loss in vertical pipes be minimized?

There are several ways to minimize friction loss in vertical pipes, including using larger pipe diameters, reducing the length of the pipe, and using smoother pipe surfaces. Minimizing obstructions such as valves and fittings, as well as keeping fluid velocities within a recommended range, can also help reduce friction loss. Proper maintenance and regular cleaning of pipes can also prevent build-up and decrease friction loss.

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