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Hotness powered ship

Grind fissile materials and pour water over them.
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I am thinking of a steam powered ship. Not this James Watt boiler rotary motion stuff. Though the dudes with handlebar moustaches and derbies could stay. This ship would have behind and under it some very hot stuff that does not cool down easily. Probably nuclear type stuff. An inlet pipe brings water into contact with this hot stuff and it turns to steam. The steam then blasts out of a tube in the back, pushing the boat along.

I suppose a jet is sort of this principle except one makes hot stuff via combustion of fuel, and that combustion also contributes additional hot gas. This scheme uses only the working fluid around the ship. I think that working fluids with lower specific heats might work better than water - this idea was prompted by scheming about how a boat floating in liquid nitrogen might propel itself.

Could this work with air? Could one have a plane with no moving parts (ok ailerons allowed, to steer) that propels itself by virtue of an electrically heated coil in the inlet pipe?

bungston, Mar 26 2014

Cold cold coldness The_20coldest_20place
Inspiration! [bungston, Mar 26 2014]

(?) Meredith Effect en.wikipedia.org/wiki/Meredith_effect
Used on Spitfires for a little extra thrust [TomP, Mar 26 2014]

Meredith Effect http://en.wikipedia...iki/Meredith_effect
for some reason TomP's link isn't pointing to the right place. [Loris, Mar 26 2014]

[link]






       I thought "Hotness powered ship" was a clever reference to Helen of Troy.
hippo, Mar 26 2014
  

       This makes me think of two things. Firstly, in principle it's a bit like an unpulsed version of a putt-putt (or pop-pop boat), only using a nuclear source rather than a candle and putting the heat in through a heat exchanger.   

       Secondly, radiators of Spitfires famously had a negative drag coefficient for this reason. The expansion of the air passing through the radiator provided a forward thrust greater than aerodynamic drag on it : [link]. They also turned the exhaust nacelles rearwards after they worked out they could squeeze some extra thrust out of those: 70lbs I've just read.
TomP, Mar 26 2014
  

       Thanks for those comments TomP. I saw one of those poppop candle powered boats for the first time in the movie Ponyo. They scaled it up and rode it around.   

       The no moving parts piece is attractive to me. No propellor or fan blade to foul or chop on some manatee. Low draft.   

       Maybe a powered blimp would be easier to mockup than a boat. I think just heating the water behind the boat will not propel much as the water will not change volume. I think the poppop boats make steam which would be harder to do down in the water. A coil of wire in the back of a blimp with a Vshaped baffle next to it could move the blimp forward with expanding air - air caught beneath the blimp and the baffle and so leaving by the back door.
bungston, Mar 26 2014
  

       /Could this work with air?/   

       Yes. This is essentially a ramjet with an external heat source. It will work but only once you're already moving. Practically speaking, ramjets are only any good above Mach 0.6 or so, when the inlet dynamic head is sufficient to counter the various losses in the system. They're also inefficient at subsonic Mach Numbers because the pre-compression is so small. What you need is a turbine-driven compressor upstream of the heater. Oh wait, now it's a turbojet.
EnochLives, Mar 26 2014
  

       The pop-pop boat pulses so as to have a seperate intake and exhaust cycle, perhaps a little like a pulse jet. How do you stop your continuous-flow design from squirting steam forwards as well as backwards? In other words, how does it suck?
pocmloc, Mar 26 2014
  

       // some very hot stuff that does not cool down easily. Probably nuclear type stuff. An inlet pipe brings water into contact with this hot stuff and it turns to steam. The steam then blasts out of a tube in the back, pushing the boat along. //   

       The exhaust thus created would have a 250,000 year half- life.
Alterother, Mar 26 2014
  

       //The exhaust this created would have a 250,000 year half- life.//   

       Not necessarily. The water needn't (and shouldn't) directly flow over the nuclear material. As long as it's not picking up radioisotopes, then the exhaust should be quite benign.   

       On the other hand, this is a nuclear ramjet, and we all remember Project PLUTO...
Hive_Mind, Mar 26 2014
  

       // The water needn't (and shouldn't) directly flow over the nuclear material //   

       I completely agree, which is why I pointed out the obvious flaw as described here:   

              // An inlet pipe brings water into contact with this hot stuff //      

       I criticize to encourage innovation.   

       And for fun.
Alterother, Mar 26 2014
  

       //Project PLUTO   

       Ditto other nuclear powered planes of cold war paranoia days.
not_morrison_rm, Mar 27 2014
  

       Richard Feynman had the patent on submarines powered this way. Somebody beat him to the ship and the airplane.   

       That was all based on him telling some government man that all these were obviously possible, it was implementation that was the trick. The gov guy went and patented the sub idea for Feynman, and said somebody already had the others.
baconbrain, Mar 28 2014
  

       // unpulsed version of a putt-putt boat //   

       Cannot work. That's a pulsejet, specifically a valveless one. If you somehow stop the pulsation, you stop the propulsion.   

       The Meredith effect is interesting, though. I never would have guessed that some historical airplanes used the heat from their piston engines to power a supplementary thermal ramjet.
notexactly, Jan 14 2016
  
      
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