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Suppose I wanted to pump water at a rate of 5m3/s to a height of 5m. How much energy would that require in kW? If I doubled the height to 10m, would it require double or quadruple the energy? Mjroots (talk) 07:56, 24 November 2022 (UTC)[reply]
From my very rusty physics:
5m3 weighs 5,000 kg, so exerts a force downwards of 5,000g N. To lift this water 5m would therefore take 25,000g J. To do it in one second (ie 5m3/s to a height of 5m) requires 25,000g W, that is 25g kW or roughly 250 kW. All assuming no losses anywhere in the system. To lift to twice the height would indeed require twice the input. Martin of Sheffield (talk) 08:44, 24 November 2022 (UTC)[reply]
You will have to ensure that your pumps can deliver the higher pressure, 10m of water is near enough 1 bar. As the pressure increases the efficiency of the pump (particularly for non-displacement types) will reduce. With any luck a hydraulic engineer will happen along soon. Martin of Sheffield (talk) 14:15, 24 November 2022 (UTC)[reply]
5 m3/s is quite a lot of water, so this is not a small pump. In the image I put on the right (just uploaded from my collection) you can see two pumps that can handle 4 m3/s over 5 m each, powered by 450 kW electric motors, so that's the size of pump you're talking about. PiusImpavidus (talk) 10:10, 25 November 2022 (UTC)[reply]
An amusing thought, but our Dutch neighbors are fairly competent at water handling. It's probably just intended to deal with the small amounts of water arising from normal operations, some of it perhaps condensation, or when the janitor mops the floor. Any substantial volumes would probably flow to larger drains elsewhere out of the picture. {The poster formerly known as 87.81.230.195} 90.217.47.60 (talk) 16:18, 25 November 2022 (UTC)[reply]
When there's a leak, best to shut down the pump quickly. It's above polder water level, so no more water will come through. It may be below river level, but there's a check valve on the outside. This pumping station, in operation since 1933, drains about 160 km2, about half of it in Germany (hence the name), so a single pump can handle a precipitation rate of around 15 mm/week. There are 4 pumps, giving some redundancy. PiusImpavidus (talk) 18:41, 25 November 2022 (UTC)[reply]
Is this true considering the Pump Lawshead is proportional to the square of shaft speed and power is proportional to the cube of shaft speed for centrifugal pumps? If looking at the power applied to the pump shaft, wouldn't doubling the head require 23/2 or ~2.83 times the power? fiveby(zero) 17:23, 25 November 2022 (UTC)[reply]
Not in practice. I would guess that gases get into the mirror from the side and tarnish the silver. If you do an internet search on tarnished mirror you will see plenty of examples. I took a photo of one of our mirrors with tarnish. See the thumbnail image. --Phil Holmes (talk) 12:08, 25 November 2022 (UTC)[reply]
Basically, yes. The glass is a transparent support and seal, the actual mirror is the bright untarnished metal that reflects the light. Just putting the bulk metal behind glass though will not produce a good mirror, there may be surface imperfections and without an adequate seal air will get in and tarnish the reflective surface. Fifty years ago it used to be (maybe still is) a standard school chemistry experiment to make up silvering solution and apply it to a microscope slide. You ended up with a fragile mirror. Industrially the backing is then built up to protect the microscopically thin metal layer from scratches and wear. Martin of Sheffield (talk) 13:56, 25 November 2022 (UTC)[reply]
No. The sandwich consists of glass, foil and something to keep the foil pressed against the glass, such as another sheet of glass, MDF or anything reasonably flat. There is no glue. Read the articles quoted and when you've understood them, then come back here. Martin of Sheffield (talk) 15:14, 25 November 2022 (UTC)[reply]
No, there is no spoon glue. Unless you lay the whole thing flat, you need something to clamp the layers together though, which could be just your hands. The only thing that is important is to keep the aluminium smooth, without wrinkles. For most metals, any object of the material with a smooth polished surface works as a mirror; no glass is needed. --Lambiam19:24, 25 November 2022 (UTC)[reply]
Note, OP, that you have introduced an artificial situation. Actual mirrors are created by the methods described in the two articles linked by Martin of Sheffield above, where the deposited reflective material bonds to the glass at an atomic level (creating a very even and reflective surface). It was you who introduced the ad hoc comparison of placing a piece of pre-existent aluminium behind a sheet of glass: while this corresponds to the broad set-up, it is not how useful mirrors are actually made.
If you actually want to make a mirror at home, use chemicals as described: the process is not difficult – amateur astronomers have been silvering their own telescope mirrors for centuries. In that instance the silver is deposited on the front surface of the glass, not the rear, so it tarnishes quite quickly and has to be regularly re-done. Nowadays, however, most amateurs send their mirrors to professional companies who use vacuum deposition of Aluminium, which tarnishes much more slowly – this is likely beyond the capabilities of home hobbyists. {The poster formerly known as 87.81.230.195} 176.249.29.80 (talk) 08:31, 28 November 2022 (UTC)[reply]
