Air Density

Most of us have heard stories about temperatures getting so high in the south that airplanes are not able to take off. Most of us have also seen pictures or videos of hot air balloon pilots operating a big burner below their hot air balloon as they work to leave the ground or to increase their altitude. And of course, we have all played with helium balloons tied to the end of a string at some point in our lives and admired how they floated through the air with ease.

Have you ever really stopped to wonder about these things though? Why does hot weather affect the performance of an airplane, how does the act of shooting flames into the opening at the bottom of a hot air balloon cause the balloon to rise from the earth, why does helium cause a balloon to float at the end of the string. Well, it all basically boils down to air density.

Remember our discussion on temperature in a previous blog discussion? We discussed the fact that temperature is a measure of the motion of molecules in a substance. As it turns out, in a gas like air, as the motion of molecules increases, the gas expands resulting in a decrease in the density of the air and the air becomes lighter.

Think of air just like water. When you throw something into a swimming pool that is less dense than the water in the pool (like a life jacket), it floats. The same thing happens in air. If something is less dense than the air around it, it floats. So, our helium balloon is kind of like a life jacket and the same holds true for the hot air balloon because the hot air inside the balloon is less dense than the air around it. In the case of the airplane, the low air density caused by the high temperatures reduces an airplane’s wings ability to create the lift needed to make the airplane fly.

Unfortunately, temperature is not the only thing that affects the density of air. The molecules that make up the air also affect air density. One example of a molecule that can affect the density of air is a water molecule and believe it or not, water molecules are lighter than the other main molecules that make up air. The more water molecules, the less dense the air is. To say it another way, the higher the humidity, the less dense the air is. So, hot humid air is less dense than cold dry air.

The last factor we will talk about in this discussion is pressure. Pressure also affects the density of air which is probably kind of intuitive when you think about it. When you squeeze something it gets more dense right? Kind of like when Superman squeezes coal into diamonds…

Now that we understand air density and some of the things that affect it, how do we relate our new found understanding to our drying processes? We will start to tie these things together into something more tangible in the next couple blog posts. If you can’t wait and would like to hear more about how EnviroStar can help you improve the yield, reduce energy consumption, and improve the quality of your drying equipment, give us a call at (320) 316-3170 or email us at, we’d love to talk to you about ways we can help.