Basically title, you always hear “windchill only affects humans” but we use fans to cool things all the time?
In: Physics
Windchill also affects objects if they aren’t at that temperature.
A can of room temperature soda will cool down faster if it’s cold and windy outside rather than just cold.
Conversely, that’s how a convection oven or air fryer works – the “wind” generated inside the oven heats foods more quickly.
While wind chill will affect any object that’s warmer than the air, the numeric wind chill “apparent” or “feels like” temperatures reported by weather services are tuned to humans specifically.
It does affect some things. For example in cold weather we never had pipes in the walls at our 100+ yr old house freeze but at the same temp with negative wind chills we did get frozen pipes from the wind blowing through.
Windchill doesn’t affect objects that are already the same temperature as the air, it does affect objects that are the same temperature as a person.
Lets say the air is 20F, and the water of a pond is 35F. If there’s wind, the pond will freeze much faster.
So what’s happening is basically
If a human is 90 degrees and the air is 90 degrees. Moving air gives windchill
If an object is 90 degrees and the air is 90 degrees nothing happens
If an object is 90 degrees but the air is 50 degrees? Well the heat will radiate to the point where a pocket of 90 degree air will form around an object. Blow on it? It displaces that hot air with cool air
Energy is a zero sum game. If the air gets warmer the object gets cooler.
Who is saying objects don’t experience wind chill? Because anyone with a basic understanding of thermodynamics knows that’s incorrect.
Okay so technically it affects everything that’s warmer than the ambient temperature. Here’s how it works. If a random object (say a water tank) is in 10F weather, it will cool down to the ambient temperature and then stay that way, regardless of windchill. But humans generate heat and have to maintain a certain internal temp to survive. This is where windchill comes in. It doesn’t make it colder. But it makes warmer objects lose heat quicker. Basically heat is coming off the surface of your skin and if there’s wind, it wicks the heat off your skin faster. So in cold weather, your body is constantly trying to maintain temperature and the rate at which you lose temperature depends both on the ambient temp, and how fast wind is blowing heat of your skin, which is why the wind-chill makes it “feel like” a different temp. So for example, it’s 40F but feels like 20. That means the wind is such that you are losing heat at the same rate you would if it was 20 outside with no wind.
So back to our tank of water. If you put a warm tank of water outside, it would cool off faster with wind chill but it will eventually end up at the ambient temperature regardless of wind.
Two distinct parts to break apart here.
First is evaporative cooling. This makes sense. People are moist and evaporating water cools the object down more than just the air alone.
Second part is that air is insulative. By “blowing away” the small cold or hot air layer around us we become colder faster.
Now for fans and non human objects.
Fans speed up the air to move more hot or cold air faster to remove the hot or cold air surrounding the object faster. For instance cars have radiator fans to aid in air cooling in addition to air just moving through the radiator by driving.
Evaporative cooling also effects objects, however the effect is generally more noticable with people because we are so moist compared to everything around us.
Take a towel outside on a cold day and leave it out there for a couple hours. It will eventually become the same temperature as the environment. It will become the same temperature faster with wind, because the heat will transfer away faster.
Take a towel that is wet. It is actually possible for the wet towel to be colder(temporary) than the environment due to the additional heat lost due to evaporation. The towel will of course freeze or all the moisture will evaporated away and then the towel will become the same temperature as the environment.
Want to get a rough idea of wind chill? Moisten the tip of the thermometer. This helps simulate skin moisture and approximate temperature actually felt on the skin.
Wind chill is not unique to people, however is is a good approximation of actual temperature felt by the skin.
Big thing about the windchill is evaporation.
Your skin is always wet (even if you are not sweating profusely) and evaporation cools you down. In fact, it is the main contribution to cooling of living things.
When there is a wind it blows away wet air that was next to your skin and increases evaporation and, therefore, cooling.
For inanimate objects which are usually dry it does not work. Wind will cool them only if they are hotter then the air and only down to the air temperature.
However, if you get a wet towel on something, you’d get a wind chill all right and may get significantly below the ambient temperature.
It is a great way to cool drinks on a beach – take a towel, soak it and wrap around the bottle; put it where there is a wind (but in shadow). Usually it works better then putting them in the water (depending on water temperature and wind strength of course).
By definition: “Wind Chill is a term used to describe what the air temperature feels like to the human skin due to the combination of cold temperatures and winds blowing on exposed skin” https://www.weather.gov/ama/WindChill Namely it doesn’t refer to indoor thermal comfort. For inanimate objects, fans are used to drive [forced convection](https://en.wikipedia.org/wiki/Forced_convection) which does usually increase the heat flow.
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