A fan or, better yet, a fan saved our lives. Many students move out of their land and live in warmer places, as they are students and cannot afford air conditioning. Passing the unbearable heat is part of the northern ritual of studying the race below Burgos. However, while air conditioners and their portable versions can leave tight budgets tight, there’s always an alternative to help you sleep at night: fans. Its mechanism is simple. Its blades push air forward as it rotates like a mechanical fan. And yet, even though the air it blows is hot, it feels a little cool on your skin, or at least a little comforting. How is that possible?
The same reason why air cools down is the same reason we blow soup, and oddly enough, even though it’s almost 273 degrees below zero in space, we don’t freeze in seconds. But to understand it better and to understand the physical principles behind this technology, it is necessary to start with it principleAnd that principle is heat itself. What exactly?
Actually, there is no cold, it is no heat and you may have heard that when you open the windows in winter, no cold comes in, only heat comes out. There are ontological questions we could discuss about this statement, but instead we will focus on the mechanistic explanation of the process. What is heat?? We know that ordinary matter is made up of atoms of different elements, some grouped into molecules. We know that water molecules move more and more freely as we go from solid to liquid, and even more as we go from liquid to gas. Well, here goes the answer. Heat can be understood as the movement of molecules of a substance. When we provide heat, what we are doing is manipulating the energy in some way, which makes the molecules of matter vibrate more and therefore heats it up.
We can imagine it as quivering balls, though the atoms are not tiny spheres far from it. Therefore, we can provide heat in different ways: conduction, convection and radiation. Conduction involves putting two objects in contact, heating, causing their atoms to vibrate against each other, colliding, changing part of that motion and, therefore, heat. Conduction is an indirect process through a fluid. The two objects are not touching, but heat increases the temperature of a liquid that rises, as we explained earlier, exchanges its heat with another object, and when it cools, it descends again. Radiation, on the other hand, can occur in a vacuum. For example, heat from direct sunlight is radiation that travels through space in the form of photons, which are highly energetic particles that absorb our energy and increase their motion.
When the environment is below 36 degrees, we are one of the hottest things in the room, and therefore, we heat the air around us even more. In cold enough air we lose the motion of our molecules, but with very little temperature difference, the process becomes so slow that we begin to heat ourselves. The trick is to constantly change the air around us. If we have heated the air around us from 30 to 34 degrees, it is very difficult to raise it to 2 degrees, and therefore, we will lose that heat ourselves. However, if we push that air away from our bodies and replace it with 30 degree air again, it’s easier to lose heat and experience a certain cooling. That’s why it’s cold on windy days, and that’s why we blow on soup. In fact, there are so few atoms in space that we can rarely lose heat by heating them, and even if we do, there is no air to replace the atoms around us.
Now, the fan is not satisfied with this. When we are hot we sweat, and when this sweat evaporates, we lose some temperature with it, like walking in a pitcher. However, when we sweat a lot, the environment becomes so loaded with moisture that it doesn’t allow our new sweat to combine and we stop losing temperature. That’s why being hot in a humid environment is so oppressive. A fan pushes moisture-laden air away from our bodies and brings in fresh air that still admits sweat. So, anyway, we do the same thing with a fan, only in a less efficient way.
Don’t get it:
- Even if we can afford to buy an air conditioner, having a fan may be a wiser option. It all depends on the ecological conscience we have. On the one hand, air conditioners use a lot of energy. To put ourselves in context: a standing fan uses 90 kilowatt hours, a ceiling fan uses 60 hours, and an air conditioner, on the other hand, uses at least 1900. On the other hand, air conditioners make the environment too dry, which helps us lose heat through sweat, but also affects our mucous membranes, such as the throat, eyes or inside the nose. However, fans are not all advantages. It is clear that they do not cool us like an air conditioner, in fact, they are not recommended to face heat above 30 degrees, because it is already very close to our body temperature. At these times, the air the blades have to push per unit time, their noise is deafening.
Notes (MLA):
- Moran, Michael J., Howard N. Shapiro, Daisy D. Bodner and Margaret B. Bailey. Fundamentals of Engineering Thermodynamics. 8ª ed., Wiley, 2014.
