June 26, 2008
Nanomaterials Reduce Energy Needed To Boil Water
It is happening down at the nanoscale.
Troy, N.Y. — Whoever penned the old adage “a watched pot never boils” surely never tried to heat up water in a pot lined with copper nanorods.
A new study from researchers at Rensselaer Polytechnic Institute shows that by adding an invisible layer of the nanomaterials to the bottom of a metal vessel, an order of magnitude less energy is required to bring water to boil. This increase in efficiency could have a big impact on cooling computer chips, improving heat transfer systems, and reducing costs for industrial boiling applications.
This would be useful for camping equipment where cooking fuel can be in short supply.
The researchers weren't trying for this valuable result. So much for central planning.
“Like so many other nanotechnology and nanomaterials breakthroughs, our discovery was completely unexpected,” said Nikhil A. Koratkar, associate professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer, who led the project. “The increased boiling efficiency seems to be the result of an interesting interplay between the nanoscale and microscale surfaces of the treated metal. The potential applications for this discovery are vast and exciting, and we’re eager to continue our investigations into this phenomenon.”
30 times more bubble action. Sounds like an advertisement for a bathroom cleaner.
Koratkar and his team found that by depositing a layer of copper nanorods on the surface of a copper vessel, the nanoscale pockets of air trapped within the forest of nanorods “feed” nanobubbles into the microscale cavities of the vessel surface and help to prevent them from getting flooded with water. This synergistic coupling effect promotes robust boiling and stable bubble nucleation, with large numbers of tiny, frequently occurring bubbles.
“By themselves, the nanoscale and microscale textures are not able to facilitate good boiling, as the nanoscale pockets are simply too small and the microscale cavities are quickly flooded by water and therefore single-use,” Koratkar said. “But working together, the multiscale effect allows for significantly improved boiling. We observed a 30-fold increase in active bubble nucleation site density — a fancy term for the number of bubbles created — on the surface treated with copper nanotubes, over the nontreated surface.”
Does this bubbling cause a pot to absorb external heat more rapidly? Would it reduce heat loss from convection of air? I would expect the bubbles would carry away heat more rapidly so that more heat would get captured from a cooking flame.
Wouldn't the killer app here be toward improving efficiency (and thus viability) of desalination processes?
I think you may have missed something - it's not heating the water faster, it's just making it easier for the water to turn to steam. So it wouldn't help cooking, per se (you'd just *know* the water was hot sooner - it wouldn't actually *be* hot sooner). The real benefit would be in steam turbines, distillation, etc.
By the way - go RPI!
(That's Randall missing something - not Carter. Desalination would be another potential use)
This press release seems highly misleading. The energy required for the phase change wouldn't be reduced, just the speed and efficiency of heat transfer. As long as a boiler is well insulated, I can't see how this would reduce waste heat much - it might speed things up some.
Yeah. I can't see how the energy for the phase transfer can be reduced unless the usual process is very inefficient (that is needing much more energy in practice than needed in theory). I can't see how it can reduce the theoretical minimum energy needed to cause a phase transfer.
Water is terribly efficient about moving heat around, so you sort of have to boil the whole pot at once - not just the parts touching the pot. Maybe this changes that dynamic so that the water at the edge reaches boiling immediately without as much heat transfer? I really don't see how the amount of energy could be any less, but I could see how you could start producing bubbles much faster this way.
Yes, you are right. Faster boiling does not help heat the water. Dummy me.
Though maybe the boiling will increase the water circulation and therefore bring cooler water down where it can get heated more quickly? But still, then one is still losing a lot of heat in the steam.
This PR is completely misleading and surely must have gotten it completely wrong with "an order of magnitude less energy is required"
This would intrinsically change how we measure energy as I got taught - and I'm sure this hasn't changed:
"One kilojoule (kJ) equals 1000 J and is the amount of heat required to raise the temperature of 239 g of water by 1°C;"
An order of magnitute more bubbles doesn't translate into an order less energy!
One of the researchers has also been quoted to say "“If you can boil water using 30 times less energy, that’s 30 times less energy you have to pay for,” he said."
OK, so HOW did they define the kilojoule initially. How DID they raise the temperature (copper rod, flame under pot, pot with water in vacuum?) for the classic definition and maybe this needs to be revisted ??
It doesn't reduce the amount of energy needed to boil away a given amount of water. It reduces the *rate* of energy transfer needed to achieve a "rolling boil", by enhancing bubble nucleation. Normally, if you've got too low of energy input into a pot of water at the boiling point, circulation carries the heat away from the bottom too fast to cause "boiling", you just get a lot of evaporation off the top of the pot.
If the surface is reasonably durable, this would be of great use in the kitchen, since rolling boils are important for stirring the food you're cooking.
This would be interesting if it can enhance the rate of heat transfer across the surface/water boundary, since this would reduce the size, and hence cost, of a number of important industrial devices (possibly including boiling water nuclear reactors).
A few years ago, researchers found that adding nanoparticles to a liquid increases the rate of heat transfer into the liquid. I wonder if this effect could be due to particles depositing on surfaces.
This is falling into a the new category of nano materials that are making our tradition energy generating processes orders of magnitude more efficient. When I read this is makes me more of a believer in the MEA (Japanese Water Car from Genepax). If materials can affect at a molecular level, the way bonds are held together...than why not?! If true, this means an order of magnitude less fuel for electricity generation from standard turbines powered by nuclear, natural gas, coal...
The only plausible reason this could be useful in cooking mentioned in these comments is that it would reduce the rate of boiling needed to get the stirring effect of boiling. I'm not clear as to whether that's true, but even if it is true, wouldn't a mechanical stirrer truly be orders of magnitude more efficient as a way of stirring things?
Another point I did not see mentioned is that the surface area of the inside of the pot is increased significantly with a layer of coated nanorods compared to a conventional pot. Therefore given a constant energy output from a burner more energy should be transfered to water instead of the surroundings. If boiling a large pot of water this could decrease energy use considerably since the heat up time of pot would be reduced.