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seventenths 29th June 2008 10:42 PM

What might this mean for heat-sinks?
 
http://www.sciencedaily.com/releases...0626150930.htm



7/10

Jonathan Bright 29th June 2008 11:16 PM

Is an order of magnitude correct? That does seem like a lot.

wakibaki 29th June 2008 11:58 PM

Hmm, yes.... boiling.

It's not clear from this article exactly what has been achieved.

They can't be talking about the energy required to bring the water to boiling point, that's an established quantity called specific heat.

Similarly the energy required to go from water to steam is called the latent heat of condensation and is about 540 kcals/litre. So they must be talking about the efficiency of transfer of heat from the metal to the water.

If you put an immersion heater into water, the only place for the heat to go is into the water. So I guess they must be talking about combustion fed boilers. In which case you've got 2 interfaces, flue gas to metal and metal to water. The quicker you get the energy into the water, the steeper the heat gradient and quicker you can suck in more from the hot gas.

30-fold is a big increase tho', I'm surprised that existing systems waste that much energy. There may be an element of journalistic hype.

w

Ron E 30th June 2008 11:15 AM

maybe they rediscovered cold fusion...

d to the g 30th June 2008 08:32 PM

Quote:

Originally posted by wakibaki


Similarly the energy required to go from water to steam is called the latent heat of condensation and is about 540 kcals/litre. So they must be talking about the efficiency of transfer of heat from the metal to the water.

Please note that this value is quoted at a specific pressure. (As is the temperature at which water boils). As this decreases the amount of water bonded to water, it decreases the enthalpy of vaporization. I'm not sure of the specifics, but that's at least how I read it.

Yes, it would also increase the amount of area available for heat conduction, providing that the water is more pure than any cooling water known to man. I'd give these nanowires about 3 hours before scaling made them inoperative.

wakibaki 30th June 2008 09:43 PM

Quote:

Originally posted by shallbehealed


Please note that this value is quoted at a specific pressure.

I feel really remiss now, not having pointed that out. Somebody could have taken my numbers and made a fatal miscalculation at high altitude...

w

d to the g 1st July 2008 02:29 AM

Quote:

Originally posted by wakibaki


I feel really remiss now, not having pointed that out. Somebody could have taken my numbers and made a fatal miscalculation at high altitude...

w

Or someone could use the information I proffered as a possible explanation of the phenomena in the current discussion.

Or, ya know, they could just continue being wise regardless of their understanding of elementary thermodynamics.

wakibaki 1st July 2008 11:53 AM

BS.

The pressure is irrelevant.

I'm not interested in 'how it works' until I know 'what it does', and what it certainly doesn't do is 'reduce the amount of energy required to boil water'. Since the amount of energy recovered on condensation is always the same, anything else would mean you could build a perpetual motion machine.

If you've got a point to make, make it on your own account instead of trying to ricochet off my contribution.

w

AndrewT 1st July 2008 12:04 PM

Hi,
the piffle was written by an eejit.

The energy required to boil water cannot be changed.
Similarly the energy required to raise the temperature of water cannot be changed.
The temperature of boiling can be changed with changes in atmospheric pressure and contaminants.

The heat transfer is maybe more efficient, but there are so many errors in the text and the science being reported that I for one would not bet my life on any part of these claims.

Let's see the original scientific text.

croat47 1st July 2008 12:50 PM

http://en.wikipedia.org/wiki/Thermal_conductivity

Thermal transfer is a function of the cross section the heat is moving through, yes? It seems all they have done is create more surface area on the bottom of a pan. Why so small? Who wants to clean a pot with a sponge-like structure on the bottom. It would be brutal on knuckles and not too sanitary.

Isn't the idea of fins on a heatsink to increase the surface area for more effecient transfer of heat from whatever you are cooling to whatever liquid/gas you want to dissipate the heat into? All they did was make a high SA heatsink on the bottom of a pan. No one changed the specific heat or any other law of thermodynamics.

Edited for grammar.


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