MIT Produces Electricity Using Thermopower Waves

MikeChino writes "MIT scientists have discovered a never-before-known phenomenon wherein carbon nanotubes can be used to harness energy from 'thermopower waves.' To do this they coated the nanotubes with a reactive fuel and then lit one end, causing a fast-moving thermal wave to speed down the length of the tube. The heat from the fuel rises to a temperature of 3,000 kelvins, and can speed along the tube 10,000 times faster than the normal spread of this chemical reaction. The heat also pushes electrons down the tube, which creates a substantial electrical current. The system can output energy (in proportion to its weight) about 100x greater than an equivalent weight lithium-ion battery, and according to MIT the discovery 'opens up a new area of energy research, which is rare.'"

Re:That's some hot stuff...

[jellomizer]

For some perspective that is about the heat that a filament in a lightbulb is at.

Re:That's some hot stuff...

[ircmaxell]

Well, on the scale of the tube, we're not talking about that much thermal energy. Sure, it's a high temperature, but something the size of a nanotube (around 1/50,000 the width of a human hair) won't have a significant amount of energy. It really depends on the density of these tubes that's needed to achieve a usable amount of energy. And don't forget, we're talking about localized heating here... It's not that the tubes and structure need to get to 3000*k, that's just the temperature of the flame front.. A good example of the difference is the internal combustion engine... The flame front can reach around 2300*K, but the parts its made of would begin to weaken long before that: Iron's melting point is 1800*K (the material commonly used as a cylinder lying), Aluminum's melting point is only 900*K (the material commonly used for the engine block). But engines rarely melt... Steel (commonly used for the valves in the combustion chamber) loses about 50% of its strength at only 800*K... Yet these parts --aside from mechanical failure-- survive...

Link to the Nature Materials article

[reverseengineer]

The orignal article may be found here [nature.com]- subscription to Nature Materials or payment required for full text. Abstract:

Theoretical calculations predict that by coupling an exothermic chemical reaction with a nanotube or nanowire possessing a high axial thermal conductivity, a self-propagating reactive wave can be driven along its length. Herein, such waves are realized using a 7-nm cyclotrimethylene trinitramine annular shell around a multiwalled carbon nanotube and are amplified by more than 104 times the bulk value, propagating faster than 2 m s-1, with an effective thermal conductivity of 1.28±0.2kWm-1K-1 at 2,860K. This wave produces a concomitant electrical pulse of disproportionately high specific power, as large as 7kW kg-1, which we identify as a thermopower wave. Thermally excited carriers flow in the direction of the propagating reaction with a specific power that scales inversely with system size. The reaction also evolves an anisotropic pressure wave of high total impulse per mass (300 N s kg-1). Such waves of high power density may find uses as unique energy sources.

The "fuel" used, cyclotrimethylene trinitramine, may be better known as the explosive RDX.

Re:Kelvins are degrees on an absolute scale...

[wizardforce]

3000-273=2727C They were rounding. Also thermodynamic efficiency is easier to calculate in kelvins and is standard practice in thermodynamics; see carnot cycle for details.

Re:Link to the Nature Materials article

[reverseengineer]

Despite my efforts to fix those exponents after pasting in the abstract, it looks like I missed one- it should read,"amplified by more than 10^4 times the bulk value," not "amplified by more than 104 times the bulk value." The above linked abstract uses superscripts, and (hopefully) contains the correct values for everything.