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bigben2k · 08-14-2002, 02:02 PM

No problem. It's only through discussion that we'll get to the bottom of this.

First off, the water heater tank: this is not a closed loop setup, because the water comes in from the city main, through the hot tank, then out to the faucet. The placement is important, because what goes out does not come back in. This is a big issue in skyscrapers, because the pressure at the bottom of a pipe (1st floor) would be tremendous (threatening the integrity of the pipe), just from the sheer weight of the water running all the way up to the top floor. That's why they use water tanks on multiple levels (that was a side note, and has nothing to do with anything!).

In this particular case, the water DOES return, as it does in a closed loop, so what goes up must come down. I will admit though that there may be a slight bit of flow induced because the hot water has a lesser density, and so the system would balance itself out by flowing in a (favorable) direction, until the density of the water on each side would be equal, but again, since the volume of water affected is so small, and the density change of that small volume may be in the order of 0.2%, this would be infinitesimal.

The other effect, where if you had a mass of hot water in the middle of a cold tank, would create a small flow where the hot water would rise to the top, but again, this is a density issue, as described above. That's convection.

As insignificant as this effect is, it does appear to work, at least sufficiently enough for the hot water to reach the rad, then be cooled.

To answer the water tower question: as I've described above, a city's waterworks is not a closed loop, where the water exiting one way is forced back in the system. The loop is broken by the drain (among other places): when you run the water, it is free to accumulate in a tub/sink, or flow right down the drain. The water that you are running will not be affected by the amount of water being drained. In a closed loop, that's not the case.

To answer the density issue: once the system is balanced, where the hottest of the water is cooled steadily by the rad, the volume of the water no longer increases: the system has reached a steady state. The amount of water being heated is the same as the amount of water being cooled, negating the volume change effect. The overall volume will change, but that'll only show up in the res as a level increase. Once the level has risen to where the system is in solid-state, there is no more expansion. That's why the volume change theory doesn't work.

Just to clarify, the water level in the res should be above the res intake: otherwise the system is not closed (which I'm assuming it is).

08-14-2002, 02:02 PM	#33
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	No problem. It's only through discussion that we'll get to the bottom of this. First off, the water heater tank: this is not a closed loop setup, because the water comes in from the city main, through the hot tank, then out to the faucet. The placement is important, because what goes out does not come back in. This is a big issue in skyscrapers, because the pressure at the bottom of a pipe (1st floor) would be tremendous (threatening the integrity of the pipe), just from the sheer weight of the water running all the way up to the top floor. That's why they use water tanks on multiple levels (that was a side note, and has nothing to do with anything!). In this particular case, the water DOES return, as it does in a closed loop, so what goes up must come down. I will admit though that there may be a slight bit of flow induced because the hot water has a lesser density, and so the system would balance itself out by flowing in a (favorable) direction, until the density of the water on each side would be equal, but again, since the volume of water affected is so small, and the density change of that small volume may be in the order of 0.2%, this would be infinitesimal. The other effect, where if you had a mass of hot water in the middle of a cold tank, would create a small flow where the hot water would rise to the top, but again, this is a density issue, as described above. That's convection. As insignificant as this effect is, it does appear to work, at least sufficiently enough for the hot water to reach the rad, then be cooled. To answer the water tower question: as I've described above, a city's waterworks is not a closed loop, where the water exiting one way is forced back in the system. The loop is broken by the drain (among other places): when you run the water, it is free to accumulate in a tub/sink, or flow right down the drain. The water that you are running will not be affected by the amount of water being drained. In a closed loop, that's not the case. To answer the density issue: once the system is balanced, where the hottest of the water is cooled steadily by the rad, the volume of the water no longer increases: the system has reached a steady state. The amount of water being heated is the same as the amount of water being cooled, negating the volume change effect. The overall volume will change, but that'll only show up in the res as a level increase. Once the level has risen to where the system is in solid-state, there is no more expansion. That's why the volume change theory doesn't work. Just to clarify, the water level in the res should be above the res intake: otherwise the system is not closed (which I'm assuming it is). __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101 Last edited by bigben2k; 08-14-2002 at 02:07 PM.