Monday, May 18, 2009

Molecular Spring and Chip Scale Dominoes

Think of the various energy storage media. There are countless types. Some involving mechanics, some chemicals, and some far more exotic, yet they all share one thing in common... the ability to hold energy and release it as needed. However, not all methods are equal. A typical method signifying the efficacy of the great spectrum of methods is the energy capacity per kilogram of mass.

Since ancient times, springs were the method of choice for compact portable devices requiring some source of power. Once wound up and let loose, a spring will attempt to revert to it's unwound state, which is the spring's lowest energy level. As this process occurs, the energy which was stored in the metal windings produces a force capable of performing work such as driving a pendulum clock, launching a catapult, cranking an electric turbine, etc.

But just how efficient are springs? Well, assuming a primarily steel construction, a spring can, at best, only contain about 300 joules of energy per kilogram. This could power a 60 watt light bulb for 5 seconds, but due to the limitations of efficient mechanical work to electricity converters, even 5 seconds would be pushing the limits. If one needs more energy, one would be forced to use more steel. If one kilogram seems small and you're thinking that 300 joules / kg is pretty impressive, consider the fact that a one kilogram lithium ion battery can easily hold 500,000 joules, enough to power that same light bulb for over 2 hours.

Looking back at the spring now, the cause for it's extremely poor energy density has it's roots in the fact that there is significant friction between each molecule of the steel. While a spring may possess the mass of one kilogram, the majority of the atoms it contains are not contributing to the overall capacity. It's simply not built to. If the atoms could be assembled one by one into long polymer chains, there would be virtually no friction at all. Think of a molecule of water. If you could some how pull on one of it's hydrogen atoms and slightly displace it further away from the oxygen atom, and then let go, what would happen? As it turns out, this is an example of a molecular spring. The energy potential is created due to an atom being in an energized state and naturally desiring to return to it's ground level. Friction is primarily a macroscopic epiphenomenon, and when dealing with the torsion of atoms in a molecule, there are no frictions to interfere. Constructing a one kilogram spring one atom at a time would be a monumental feat, however would it be worth it? Possibly. Such a spring would be able to put the lithium ion battery to shame, easily outperforming it by a factor of 20. A 1 kilogram molecular spring could power a laptop computer for weeks, rather than hours and could be recharged nearly infinitely, having very little internal degradation, very much unlike the usual chemical cell batteries.

Impressive as it sounds...of course, nothing can compare to the impossibly perfect energy storage capacity of pure matter / antimatter reactors. Apparently the power source of choice for the USS Enterprise in the world of Star Trek. One kilogram of such material could harness the required energy to effortlessly propel an automobile down the highway at 65 miles per hour, fuel gauge worry free, for over 8,000 years. The only precaution: Avoid crashing. The reactor would likely be compromised and part of the planet would vaporize.

2 comments:

littlelostgeek said...

Well worded and thoughtful articles. Looking forward to more out of you in the future.

Found this place via Entrecard and you are now in my blogroll.

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