Naked Science Forum
Non Life Sciences => Technology => Topic started by: peppercorn on 01/03/2010 12:50:50
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I came across this info about spray cooling for electronics:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.embeddedtechmag.com%2Fimages%2Fstories%2Farticles%2F01_09feat3c.png&hash=5f95c7c30fbaa7a8385231ef60afc6eb)
As the latent heat allows higher heat removal than immersion - could the same idea be used to cool the outer walls of engine cylinders?
I know the quantity of heat needed removing is much higher than in electronics, but a high enough volume of liquid (not necessarily water) might have the capacity.
The other advantage could be far more fine-tuned, localised cooling with a infra-red cells monitoring for hot-spots and adjusting each spray nozzle dynamically to compensate.
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Is the plan to let the water evaporate to the outside air or somehow recycle it? If not recycled you would use a lot of water that you would have to continually replace. If you recycle it then you have to condense it a again via an air cooling system which leaves you back were you started. Perhaps I'm missing something.
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Might the thermal shock create some problems?
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Essentially an air cooled engine (like the original VW Beetle) that is running in the rain. The water jacket removes heat, but, more importantly, provides a lot of noise damping to the engine. Evaporative cooling can remove a lot of heat, and will work provided the desired temperature is above the vaporisation temperature of the fluid you use. In the typical ICE engine this would result in it running too hot, and would result in oil degradation and a larger amount of wear whilst heating up.
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Why not use a combination of aircooled and water cooled???? If your engine lost all its water then it would not seize up as the aircooling would suffice to prevent it from cooking itself. It would run hotter than normal but would still function acceptably to get you to the nearest point of repair. To add the air cooling to a motor simply requires a bit of extra material in the production phase when making the block...I think
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Is the plan to let the water evaporate to the outside air or somehow recycle it? If not recycled you would use a lot of water that you would have to continually replace. If you recycle it then you have to condense it a again via an air cooling system which leaves you back were you started. Perhaps I'm missing something.
The 'plan' would certainly be to use a condenser & recirculate the coolant. I don't think it leaves me back where I started as all engines are ultimately giving up excess heat to the air, but liquid coolants (& in some early cars - solely the lubricating oil) have a lower Q than vaporisation when used as the intermediate heat carrier.
Theoretically, vaporising a liquid as described in the original post should carry away 2-3 times the heat of an immersion system. So although the condenser will be somewhat larger than a standard car radiator, the coolant needed should be perhaps halved. If the condenser is made from lightweight materials the entire system might not be any heavier, plus the engine block would be smaller.
Another advantage in using an array of nozzles would be to allow peak head temperatures to be controlled whilst cylinder walls could be kept at optimum high temps.
Might the thermal shock create some problems?
Do you mean it could weaken the casting (like pouring boiling water into a cold glass)?
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You are trying to dissipate to the outside air the same amount of heat energy per second (power) however you do it. Conventionally, the pressurised water jacket controls block temperature to a safe tolerance. Some arrangement would be needed in this case too; a bit more complex, but possible. However, I still fail to see an advantage. It is between an air-cooled system and a water cooled system but with greater complexity. The hot water vapour needs to be cooled and recondensed which would mean forced air cooling. How is this condenser simpler/better than a radiator?
The technical gain that this system would give, as far as I can see, is in an ability to actively control engine temperature more quickly because you could reduce the engine's thermal mass and have a faster feedback system. But I was not aware that this is a problem. You could also run the engine at a much higher temperature if required but this could be more problematic in other ways and I'm not sure has any advantages.
The system may well be useful if there was some alternative form of engine that needed heat removing at a faster rate and also needed to run at some higher temperature, but I'm struggling to see an advantage with the good old internal combustion engine.
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I think there's some confusion here. I'm not trying to claim that this system is simpler that a water jacket, just that I would like to explore whether there *may* be some advantages to more precise and localised temperature control.
I will admit that I have only a rough picture of the stages of the condensing and cooling, but all vehicles today have some forced-air available if needed (ie. a cooling fan). Further, putting complexity & cost to one side for a moment could the system not generate a forced airflow by utilising a small steam turbine?
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The Crower six-stroke engine cools the cylinder walls from the inside, which additional to generating a further power stroke, allows the next combustion stroke to be more effective (η = 1-Tc/Th) - a major downside though is the water not only has to be re-condensed but becomes polluted.
BMW have experimented with bolt-on steam devices for their engines & exhaust systems, but the power recovered is poor.
In my vapour cooled system, if dwells could be formed in the head casting then pressurised nozzles would result in post-combustion cooling at the cylinder walls between firing (so, by the rule of Carnot engine η will increase).
Α small steam turbine could be a small, if relatively pricey addition, that could drive several types of energy recovering devices.
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I would have thought a well designed array of water jets could give a very even and very dynamic cooling effect. Further, water jacket systems aren't except from hot spots, both due to poor flow design & possible spots for furring up where poor quality coolant is used.
It just seems to me that, with two-thirds of an engine's fuel becoming unused heat even before the flywheel and the temps involved being easily high enough to boil water - a workable energy recovery process should exist. Αlthough, I have to admit that the lack of finding it in 100+ of the IC engine is not encouraging - still, just as well I'm arrogant [:D]
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BMW tried driving a steam engine from heat recovered from the exhaust. Not sure if they are selling it or not, but I seem to remember finding their patent.
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I love steam engines. Unfortunately, a certain French geezer called Carnot discovered that they tend to be be rather inefficient.
"the theoretical maximum efficiency of a heat engine equals the difference in temperature between the hot and cold reservoir divided by the absolute temperature of the hot reservoir."
From http://en.wikipedia.org/wiki/Carnot_cycle
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These points made about hp/lb and high 'hot reservoir' temperatures are the part of the reason we all ride around in metal boxes powered by internal combustion as opposed to the external varieties.
We know the old oil burners (or detonators) ain't going anywhere going anywhere soon. The key, to me, seems to be clever with what we've got...
Αs Dave says the 'cost' of all ICEs is the accelerated air throughput for the lively performance we have come to 'need'. The piston engine has the other limitation of not being suited to heat recuperation as the hot & cold reservoirs (from Carnot) are use the same physical space (as opposed to a GT). Of course Gas Turbines have their own problems (but the Capstone car (http://www.capstoneturbine.com/news/story.asp?id=536) is pretty promising).
Going back to the issue condensing, could something like methanol be used as an intermediate stage in condensing between steam and air? I guess you'd need loads of it (sprayed onto heat-exchanger) recirculated at very high rate, but -again- just putting it out there...
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Dave,
Sadly, turbochargers don't do much to improve thermal efficiency. What they do though is they allow an engine to produce more power for a given displacement, so that can reduce weight and result in reduced fuel consumption.
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The other advantage is that the turbochargers allow power on demand from a small engine that is capable of being very efficient. BMW and Mercedes have some rather good cars that get the tax advantage of good fuel consumption whilst allowing 0-60 on 7 to 8 seconds and top speed of 145mph.
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This type of condenser designed by Cyclone Inc. looks pretty neat:
http://www.globenewswire.com/newsroom/news.html?ref=nrdigest&vid=12370&topic=16&d=123874
Using their kind of design could cut the footprint of the heat recovery stage significantly...