Are you a hydro-electric engineer?
October 14, 2011 7:29 PM Subscribe
Can anyone explain how the 'intake towers' at the Hoover dam work?
A set of photos depicting stages of construction of the Hoover Dam has been linked here and there on the net this week. (They are unfortunately not in chronological order, but are nonetheless very interesting.) Some of the views show the dam before the water in Lake Mead rose high enough to cover the structure, and my question relates to the way that the water intake system works.
Photo #26 [direct link to image] shows the intake towers during construction. Their bases will be deep in the lake water, with their tops poking out above the surface.
Photo #40 [direct link to image], shows the completed project.
But how does the intake water get from those towers into the generating system? For efficient use of water for power generation, the intake must be as far above the turbines as possible (a high 'head'). But the water cannot be flowing through those channels that we see connecting the tops of the intake towers to the dam (it can't flow uphill into those channels). The only other way through must be in hidden channels extending from the bases of the intake towers, but those bases are down near the bottom of the dam, as we saw in Photo 26.
Where does the 'head' come from?
A set of photos depicting stages of construction of the Hoover Dam has been linked here and there on the net this week. (They are unfortunately not in chronological order, but are nonetheless very interesting.) Some of the views show the dam before the water in Lake Mead rose high enough to cover the structure, and my question relates to the way that the water intake system works.
Photo #26 [direct link to image] shows the intake towers during construction. Their bases will be deep in the lake water, with their tops poking out above the surface.
Photo #40 [direct link to image], shows the completed project.
But how does the intake water get from those towers into the generating system? For efficient use of water for power generation, the intake must be as far above the turbines as possible (a high 'head'). But the water cannot be flowing through those channels that we see connecting the tops of the intake towers to the dam (it can't flow uphill into those channels). The only other way through must be in hidden channels extending from the bases of the intake towers, but those bases are down near the bottom of the dam, as we saw in Photo 26.
Where does the 'head' come from?
The generators are way below the water level, on the other side of the dam. The generators are about even with the base of the intake towers - the water level is pretty high up the intake tower.
Water enters the intake tower from highest point, the water level of lake. They can open and close valves in the intake tube, to allow water in at different heights of lake level. When the dam is full, the intake towers are taking in water many feet above the generators, creating downward water pressure.
Maybe this diagram of the water flow will help you.
posted by Flood at 7:40 PM on October 14, 2011
Water enters the intake tower from highest point, the water level of lake. They can open and close valves in the intake tube, to allow water in at different heights of lake level. When the dam is full, the intake towers are taking in water many feet above the generators, creating downward water pressure.
Maybe this diagram of the water flow will help you.
posted by Flood at 7:40 PM on October 14, 2011
It doesn't make any difference which holes in those towers are used. The water pressure at the generator isn't determined by that.
posted by Chocolate Pickle at 7:42 PM on October 14, 2011
posted by Chocolate Pickle at 7:42 PM on October 14, 2011
Yeah, head is pretty much just the vertical distance between the turbine itself and the surface of the reservoir, the route it takes to get there doesn't effect the "head" much.
posted by Stonestock Relentless at 7:42 PM on October 14, 2011
posted by Stonestock Relentless at 7:42 PM on October 14, 2011
Response by poster: OK, I found an image that shows the internal construction, and the path of water flow is clear. Where I was confused is that I was thinking that the water had to fall (directly) from a high place to hit and spin the turbines, and I wasn't seeing how that could be happening. But water under pressure can obviously do the job just as well as water 'falling'. Thanks ...
(But in that diagram linked by flood (heh!) above, the level of water in the outlet river is shown as being higher than the turbines, which I think wouldn't work, but I guess this is simply a question of 'image not to scale', etc. etc.
posted by woodblock100 at 7:54 PM on October 14, 2011
(But in that diagram linked by flood (heh!) above, the level of water in the outlet river is shown as being higher than the turbines, which I think wouldn't work, but I guess this is simply a question of 'image not to scale', etc. etc.
posted by woodblock100 at 7:54 PM on October 14, 2011
Actually it does still work. Not all of the energy in the water is consumed by the generators. It still has some kinetic energy (speed). When the water his the outlet water, it is brought back to zero speed, and that kinetic is converted back to potential energy by pushing the water that's already there out of the way.
posted by notsnot at 8:13 PM on October 14, 2011
posted by notsnot at 8:13 PM on October 14, 2011
If they didn't do that, the water would emerge at pretty high pressure, and cause erosion.
posted by Chocolate Pickle at 11:30 PM on October 14, 2011
posted by Chocolate Pickle at 11:30 PM on October 14, 2011
This thread is closed to new comments.
The towers don't even need to reach the surface, and in a lot of dams the intakes are deeply submerged.
posted by Chocolate Pickle at 7:33 PM on October 14, 2011