Considering that they had to bunker large amounts of water, limiting their range between refills and also increasing the weight, why did steam locomotives not feed the spent, cooled steam back into the boiler/water reservoir after expansion in the cylinders in a closed loop, instead of venting it out the chimney?
If it works in e.g. nuclear power plants with a closed loop, why not in a locomotive?
In: Engineering
Water simply wasn’t that hard to come by. So why bother with a closed loop system if you dont have to? Its more costly to build and maintain.
But arid locations and some other circumstances like underground trains did use them:
https://en.m.wikipedia.org/wiki/Condensing_steam_locomotive
Mainly, because in most cases it wasn’t worth it. Water is cheap, and mostly everywhere. And they got some benefit from the waste steam – the used steam was blown up the chimney in a jet, which drew air along with it, pulling the fire through the boiler and more air into the fire – which meant that the fire would burn more fuel and the boiler produce more steam the harder the engine ran.
But in places where water was scarce, [condensing steam locomotives](https://en.wikipedia.org/wiki/Condensing_steam_locomotive) were used.
You can’t get the used steam back into the boiler while it’s still steam: that would take huge amounts of pumping work. You have to *actively cool* it first, until it condenses back into liquid; then you can pump it in with a small amount of work because its volume is small.
In a train, the only coolant medium you have is outside air, and that would take a gigantic heat exchanger; it’s more practical to just build water tanks and make frequent stops.
Ocean-going steamships have the advantage of an endless supply of cool seawater, so they cool their used steam by running it through pipes immersed in the seawater. And they *have* to do that, because there’s no way to erect water tanks at sea, and seawater won’t work in a boiler.
Power plants have access to large bodies of water or enormous cooling towers. Otherwise you cannot condense all that steam.
You’re forgetting that power plants are strategically located next to MASSIVE bodies of water in order to cool the steam enough.
This simply isn’t portable or practical if water is readily available.
A very few locomotives did recycle the water. They are called condensing steam locomotives. Not a very practical design in most cases
The steam does not go out the top chimney. The steam exits the driving pistons, and there is very little steam. The smoke from the fire, exits the chimney.
As well as what everyone else has said.
Most steam trains didn’t actually need to stop to resupply water either. The flying scotsman and mallard for example was fitted with a water scoop and at certain points along the east coast mainline there would be water troughs. First class where kindly informed to close the windows before they got soaked.
Source. A plaque I read in front of mallard at the national railway museum york
If the diesel electrics had not been invented, and we had developed steam technology these last 70 years, what advances might we have seen and what sort of increased efficiency would have been possible?
Wouldn’t you also need a pretty intense heat sink for that to work??
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