Russell's Blog

Like coal and gas power stations, nuclear power plants are heat engines. They produce power by exploiting the difference in temperature between two heat reservoirs. When most people think of a nuclear power plant (or any heat engine, really) the component that naturally dominates one's attention is the hot reservoir -- the reactor. The reactor contains most of the clever science and engineering, so it commands attention. But it takes two reservoirs of comparable heat capacity to make a heat engine.

Surprisingly, though, the electricity production of a given power plant is usually not limited by the reactor. We know how to build staggeringly enormous reactors, and even small reactors can be designed to run extremely hot. Rather, the generating capacity is limited by the heat capacity of the cold reservoir, which is a function of the natural environment in which the power station is situated. Nuclear reactors are cooled by water, so the generating capacity of a nuclear power plant is directly proportional to the quantity and temperature of water available from the environment.

So, what happens when there is a drought? Or a heat wave? Or both? The heat capacity of the cold reservoir shrinks, and the generating capacity of the power plant shrinks with it. It doesn't matter how big and fancy the reactor is if there isn't enough cooling water.

The water in the Tennessee River has gotten so hot this summer -- more than 90 degrees Fahrenheit averaged over a day -- that the TVA was forced to shut down one of the reactors at Browns Ferry. The heat capacity of their cold reservoir has shrunk so much that they can only operate two of their three reactors. The TVA is already suffering from reduced production at their hydroelectric stations due to drought conditions.

The lesson here is that nuclear power isn't simply a solution to global warming. It a technology that is threatened by global warming.

As we all know, dust kills computers. It clogs up the fans and mucks up their bearings. Eventually they begin to emit an annoying grinding or mooing noise. Even if the racket is tolerated, eventually the computer will stop working.

But even a relatively clean computer suffers from dust. You don't need giant dust bunnies clogging your CPU fan to see a significant impact on its cooling effectiveness. The thin, translucent coating of dust that settles onto anything after a few weeks is actually a pretty good insulator. It's like wrapping your heat sync in thermal underwear.

Here is what happens when you clean off that thin little layer of dust:

I have the polling rate for the temperature set at 1/20 Hz, so this is actually a significant length of time. I mention this to demonstrate that the temperature drop wasn't caused by the compressed air.

It's also worth noting that the hotter a semiconductor (or, in most cases, an ordinary conductor) gets, the higher its resistance. The increased overall resistance will cause larger voltage drops within the gate logic. Semiconductors require a minimum voltage to work reliably. So, you have two options; raise the supply voltage, thus dissipating more power, or run the risk of the voltage dropping too low somewhere in the gate logic, thus causing a logic fault. Either way, it's bad.

If the machine adjusts the supply voltage to avoid a logic fault, the part will get hotter, causing its resistance to go up even more, which requires another increase in supply voltage. One hopes that the cycle damps out before it runs away and the part explodes. So, even a relatively small improvement in heat dissipation can lower the temperature significantly due to this compounding effect.

So, boys and girls, remember to keep your computer clean. It will run cooler, last longer, and use less electricity.