## Monday, October 25, 2010

### Are you an Excel Math fan?

In the English language a single word can have many different meanings. Today we look at the FAN - a powered device for moving air.

FANS and MATH go together, and that's not just a bunch of hot air!

These fans are sitting around inside the Excel Math company offices:

We have floor fans, heater fans, fans with sanitizers, rotating and oscillating fans, etc. Some have vertical shafts around which the blades are set (the ones on either side of the photo) or horizontal shafts (the 2nd and 4th heater-fans). The middle fan with the blue lights is intended to kill germs.

The three middle fans are axial - meaning the blades are attached to a rotating shaft and air flow is in line with the shaft. The tall ones are centrifugal fans. On a centrifugal fan the air does not go in the direction of the rotating shaft.  Their blades are arranged in one of these ways:

I found lots more fans outside the company offices, in our warehouse:

How do we use math to understand fans?

Special units have been created to describe the air moved by fans. Because air can vary in many ways (temperature, density, humidity, particulates, etc.), people in the fan business have defined a set of standard air characteristics:

Standard air is clean, dry air with a density of 0.075 pounds mass per cubic foot (1.2 kg/m³), at barometric pressure of 29.92 inches of mercury (101.325 kPa) at sea level, at 70°F (21°C).

Using standard air allows companies to develop fans that compete on equal terms to move the maximum amount of air with the minimum of noise and power. Sorry, you can't design a fan with only elementary math, you have to be able to understand formulas like Specific Fan Power (how many kilowatts of electricity it takes to move some air):

If you want to know how loud some moving air is, you should understand sones, which describe the noise of moving air. (See my blog on horns and whistles if you like noise!) Here's a sones formula:

Of course, people who don't know math can still move air, and they can do it without electricity ...

If you were thinking about a different kind of FAN - educators, parents and kids who like Excel Math, that's a great use of the word FAN too.

These FANs happily follow and promote the activities of another person, or team, or company. Luckily for us, many educators and kids are fans of Excel Math:
Excel Math fans like to share their thoughts about our curriculum. Go here to read what they say or go to our Facebook page.