Fans Don’t Always Cool Things Down

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WHAT DO YOU do when you get hot? You could turn on a fan. Fans cool you off, right? Well, yes — but they don’t cool everything. In fact, fans make some things hotter.

What happens to a fan in a box?

Let’s put a fan in a box. This is a mostly normal fan in a foam cooler (for insulation). Along with the fan, I have two temperature sensors — one inside and one outside the box. The fan is also plugged into a power meter, just for fun.

If I put the fan on “high” setting, I get the following temperature data.

High Power Cmbl

Clearly the temperature inside the box is increasing while the outside temperature remains constant. If you were to look at the plot of power vs. time, you would see the fan using 40 Watts (fairly constant). It’s interesting that the inside temperature increases at a fairly constant 0.011 °C per second. I could put the fan on medium or the low setting, but it still increases in temperature inside the box — just not as fast.

Why does the closed box increase in temperature? It’s mainly because the fan is an electrical device. The fan has coil of wire with electric current running through it. The more current, the hotter the wire gets. It’s just a fact of life that electric currents make things hot. So, with a fan in a box and an electric current the box will warm up.

Read more at WIRED