What is “wet bulb temperature” and why does it matter?


What is “wet bulb temperature” and why does it matter?

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Evaporation cools you down. So a wet thermometer bulb is colder then a dry thermometer bulb. How much of a difference this makes depend on how much evaporation there is which depend on the temperature and humidity.

The wet bulb temperature matters a lot because us humans are better approximated by a wet thermometer bulb then a dry one. When it is hot we sweat which makes us wet. The evaporation of our sweat cause us to cool down. So the wet bulb temperature is a better approximation of how hot it feels then the dry bulb temperature. It describes why Florida feels so much hotter then Arizona even when the dry bulb temperature is the same in both places.

You take a wet cloth and cover the end of the thermometer, then pass the air over it. The water will evaporate and cool the thermometer so the temp will drop. This is the wet bulb temp. Lick your finger and blow on it, you’ll feel the same effect.

It is important because people sweat and cool themselves as the sweat evaporates. If the humidity is too high, water won’t evaporate readily and you won’t be able to cool down. You’ll over heat and die. This is a bad thing.

What makes it important is that it marks a point where heat and humidity get high enough that humans can’t survive without a climate controlled indoor environment, because it’s too humid for our sweat to work and too hot to survive without it. This point is becoming more common in countries worldwide.

When you take the temperature of the air, you use a thermometer. Traditionally a bulb thermometer 🌡️. Wet bulb means you have wet the bulb. Typically this is done by wrapping it in a cloth and wetting the cloth.

Why is this done? Because water evaporates. And when it evaporates it pulls heat from its surroundings, the thermometer, to do so, thus cooling the thermometer down. This lets us measure how hot it feels a little better, but more importantly, it lets us estimate how dangerous it is.

Why would we do that? Humans have a body temperature we regulate through various means, and the biggest one by far for staying cool is sweating. Sweat works the same way as that wet bulb thermometer, water evaporates taking heat away from us cooling is down. So what happens when the sweat isn’t enough? That’s when you start hearing wet bulb danger and such. This is saying that the bulb we use to determine temperature is so hot even when wet that it’s dangerous. This means we as humans have to take shelter or else we will overheat and die. It’s actually that serious, death is the consequence.

It’s the limit temperature that evaporative cooling can go. Below that temperature, it’s just not possible to cool by evaporation. It matters because sweating is how we thermoregulate. If wet bulm temperature is too high, getting close to our normal body temperature, we simply start overheating and in time die.

You can’t stay in a sauna indefinitely to bring one example. And a pet or a child can easily die in a car left in the sun, adult too if they dont get out of the car in time. But such temperatures can also rarely occur outdoors, in which case, air conditioning becomes a matter of survival.