For example if you are sitting in a car with the windows down and the air outside is hot. Yet when you start moving the air feels much colder.
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The wind helps sweat evaporate from your skin faster. The sweat takes away some heat from your skin when it turns to vapor. Also, as the car sits in the sun, it’s going to warm up along with the air inside. The car roof and doors may be helping keep the hot air inside your car instead of it blowing away and mixing with cooler air.
When moisture evaporates it cools whatever is the source of the moisture. Your skin, especially if you sweat, cools through that evaporation process.
If the relative humidity is high, evaporation is less. So evaporative cooling is not effective in dry climates.
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Have you ever felt hot wind? Because I have
Vapor pressure https://en.wikipedia.org/wiki/Vapor_pressure
Evaporation of sweat (primarily water) cools your body because the molecules making the transition from liquid to gas remove heat. When the body of air reach the vapor pressure of the liquid being evaporated the net evaporation and thus the cooling stops because as much water gas is becoming liquid as liquid is becoming gas. When a breeze comes along that vapor pressure is never realized so the cooling continues as long as there is a breeze. If you have ever been to Arizona where the air is very dry you will notice that when you get out of a pool you will feel cold even on a warm day because the air around you will never reach the vapor pressure of water since it was so dry to begin with. Very different from a humid day in the midwest where the air might already be at the vapor pressure of water.
Your skin feels when it loses heat. When the air is cooler than your body temperature, your skin heats up the air around you a bit, and you feel slightly cooled. But now that air is warmer. If it moves on by you it gets replaced by air that hasn’t been skin-warmed, and now your skin warms up the new air, losing more heat.
Also, air doesn’t just absorb heat directly from your skin, it also dries your sweat. When it does that, it gains moisture that used to be on your skin, and that moisture also takes heat along with it. So even if the air isn’t cooler than your body temperature, it can still take heat away from your skin. Again the same concept applies: wind means new air is always coming in to take a new bit of heat from your skin.
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