The watched pot: How scientists are making a better boil


    Virus nano-coating is leading to a more efficient heat transfer. 

    Making water boil is not the most scientifically rigorous experiment. Fill a pot, apply heat, presto! Spaghetti is on the way. On an industrial scale, however, like in a power plant, more efficient boiling has the potential to save a huge amount of resources.

    At Drexel University, engineering professor Matthew McCarthy is researching how a strain of the tobacco mosaic virus, a former nuisance to farmers, could help form a coating that improves the boiling process.

    We need to take this one step-by-step.

    Throw ’em in the blender 

    Let’s start with the young tobacco plants huddled in a corner of McCarthy’s laboratory. The green shoots are healthy now, but will soon be infected with a modified strain of the virus.

    “It kills tobacco primarily, and when the tobacco gets sick, it develops this splotchy pattern that looks like a mosaic. So, they call it the tobacco mosaic virus,” he explains.

    Once the plants start showing the tell-tale signs of illness, “throw ’em in a blender. And then what you have in the blender is a big soup full of all sorts of plant material.”

    Since the plant material is much larger than the virus, McCarthy is able to isolate it using centrifuges and other chemical separation techniques.

    Once he has a sample containing just the rod-shaped virus particles, they get spread around on a surface. Picture swishing them inside a sauce pan, so that they coat the bottom.

    Next step, he pours into the ‘sauce pan’ a liquid solution containing bits of nickel. Again, swish it around so the metal mixes, coats, and ultimately hardens around each individual virus rod. At this point, the virus is simply scaffolding for the metal to bind onto, an interaction that takes place on a nano-scale.

    “They are about a micron tall, and a micron is a million times smaller than a meter, so these things are…incredibly, ridiculously tiny. And it just looks like grass. A surface with a million little blades of grass standing up that are metals.”

    There’s a number of different ways to manufacture a surface like this, but McCarthy says the tobacco virus base is attractive because it’s cheap, quick to produce, and doesn’t require a clean room.

    Release the bubbles 

    Now that the metallic ‘grass’ is in place at the bottom of the pan, McCarthy is ready to boil water. Once bubbles start to form, the coating acts to nudge them loose from the bottom of the pan by sucking water down in between the tiny blades.

    “They are constantly drawing liquid in like a wick, like a sponge, that wants to constantly keep the surface wet,” he says.

    To boil more efficiently, you need a wet surface. You need those bubbles gone from the bottom as fast as possible, so that more of the heat can transfer into more of the liquid. If a situation arises where the heat isn’t transferring because the bubbles are getting in the way, something called critical heat flux can occur.

    “What happens is, the surface temperature will increase dramatically. Very, very, fast, very, very abruptly, because your surface is no longer wet, basically, and that’s what happens in a nuclear meltdown.

    “The nuclear reactor gets too hot, and the coolant that is running through it to keep it cold undergoes critical heat flux, and it can’t do its job anymore.”

    In theory, the grass-like surface could prevent this by ensuring more heat transfers into the fluid. And because less heat is lost in the process, it’s also more efficient, requiring less energy to produce the same amount of steam, which can power a turbine.

    McCarthy cautions, though, his stuff isn’t ready for prime time.

    “That’s far away. The manufacturing process, the reliability of these surfaces long term, if you put on a power plant today would they still be doing their job a year from now? It is highly still in question.”

    With backing from the National Science Foundation, he’s going to keep looking for answers.

    Beyond power plants, there could be applications for large scale heating and cooling systems, and in electronics, where computer chips can overheat.

    A faster tea kettle, however, is not on the horizon.

    “Tea kettle, no? No, the issue with the tea kettle is when you boil water in your tea kettle, as soon as it boils, you are done. All you are trying to do is get the water hot.”

    So while this technology may not end up in our kitchens, if we can increase efficiency in power plants by even a fraction, it could have large implications for a more sustainable future. 

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