Wednesday, December 30, 2015

Think You Know How a Swamp Cooler Works?--Think Again

The simple swamp cooler it is a lot more sophisticated than it gets credit for.

Swamp Coolers
The evaporative cooler or "swamp cooler" uses evaporation to cool air. Notably it only works when the air outside is somewhat dry. At high altitudes evaporative coolers work great. For a small cost in electricity and water you get cooling with much better efficiency than a refrigerated cooling (AC) system.

But there are limits. It doesn't work in humid air (such as swamps), and typically it can only cool air a few tens of degrees at the most. So 100 degrees outside means 80 degrees inside.

The swamp cooler has a wet pad (like a rigid sponge) and a fan that draws air from outside through the pad and into the house. Pretty simple.

There two principles at work. One is evaporative cooling (not why it works). The other is heat of entropy (how it actually works).

Evaporative cooling
Interesting fact: the water in a bath tub always becomes cooler than the room it is in. The reason is that there are warm molecules and cold molecules in the water. The hot molecules have enough energy to escape into the air, leaving the cold ones behind. It's like picking teams for basketball. The hot players get picked first, leaving a pool of cool players. The faster the evaporation, the cooler the tub will become. But notice that the air picked up all the warm molecules, so how would that make the air cooler? Well, it wouldn't if this were the only principle at work. The cooler would get cold but the air would stay warm. There must be something else going on.

Heat of Entropy
To understand how this swamp cooler really works, you have to know what temperature actually is.  In a gas temperature is related to the average amount of energy per molecule. When hot dry air passes through the evaporative pad, it saturates with moisture.  Conceptually, the air did work to evaporate the moisture. The mixing of the water molecules with the air means the gas now has more ways to divide up its energy. With more entropy, or ways to divide up the energy, there is less energy per molecule. (More mouths to feed means everybody gets less food.) Another way to think about it is the air picked up more heat capacity without getting any additional energy, so it has to have a lower temperature.

The air, as it becomes laden with moisture, has more chaos for the amount of energy in contains. The scientific definition of coldness is the change in the number of ways to arrange the energy per change in energy. To make something colder you can either take away energy (refrigeration) or add ways to arrange the energy (load the air with moisture).

So that's it, the so-called "evaporative cooler" doesn't work on the principle of evaporative cooling, like bath tubs do. It works on heat of entropy. I suppose they could always market these things as "entropic coolers"....

Monday, December 14, 2015

Science Explained--in 140 characters or less

This week I've been posting explanations of science concepts on Twitter @authordanallen on the hashtag #SciFact.
Solar Prominence. Credit: NASA picture of the day
Below are some of the highlights. My favorite was explaining all 4 of Maxwell's equations in one tweet. Some of these concepts are really deep, like the definition of temperature as the derivative of energy with respect to entropy--they don't teach that in high school! And even when they teach it in college, we sometimes struggle grasping even basics ideas like why it is thermodynamically favorable for hot objects transfer energy to cold ones.

Hopefully all the fun analogies help.

Dig in. Think deep, and don't be afraid to get on Wikipedia and find out more if any of the concepts excites your curiosity and imagination.

I am also taking #SciFact requests @authordanallen. ...and yes, I will attempt relativity!

: Big Bang=bright. Universe stretches & dims. Darkness. Matter cools into stars--> light! :8

near gravity>far so moon stretches, spinning moon = rolling squishy ball, stops quickly. Thus, spin stops.

Electrons trade photons. Brokers trade stocks. One sells & others can buy (absorption) or sell (stim. emission)

1 Population Inversion=overvalued stock 2 Stim Emission=1 broker sells 3 Feedback(mirrors)=media --> lasing/mass selloff

There are more ways for a room to be messy than clean. Moving things randomly makes disorder more likely.

1 E fields spray from charge 2 Mag fields do loops. 3&4 Changing elec field bends mag field & viceversa

Temperature: difficulty to add chaos w/energy. Library (cold) shout = big change. Rave (hot) shout=meh. Combine & rave hypes lib.