The Science of a Cool Drink of Water

I am  already longing for a cold glass of water filled to the brim with ice cubes when I return home. I can see the condensation on the outside of the glass and the moisture that will drip in small rivulets down the outside of the glass.

The temperatures here in South Sudan have been over 100℉ for the past two weeks with no relief in sight. 

The low temperatures of the day are in the high 70's, which occurs about 7 a.m. As a result, we enjoy a pleasant walk to school in the morning. The daily high is reached by about 4 p.m., shortly before our walk home.

We have solar power that we use for lights and for charging cell phones and computers. We also have a fan to blow the hot air around, but no refrigeration. 

Thanks to our creator God, and with a little understanding of science, I can still enjoy a fairly cool glass of water. On special occasions I even celebrate with a cool Coke.

The Science

When a liquid evaporates, its molecules convert from the liquid phase to the vapor phase as they escape from the surface. Heat drives this process. In order for the molecules to leave the liquid surface and escape as a vapor, it must take heat energy with it. The heat that it takes with it comes from the surface from which it evaporated. Since the molecule is taking heat with it as it's leaving, this has a cooling effect on the surface left behind. This is "evaporative cooling."

So, when I fill my water bottle with water as I leave in the morning, I wrap the bottle with a wet sock. By the time the sock is dry, my water is cool and refreshing. (Don't get too excited. It is not "cold." Yet it is definitely cooler and refreshing.)

I repeat this process several times throughout the school day. It is very important to stay hydrated when it is so hot. Thankfully there is often a light breeze as well that helps to dry the sweat!

My water refrigeration system