In a sealed room, a fan does not actually lower the air's temperature; instead, it creates the sensation of coolness through the movement of air. This phenomenon is known as "wind chill."
When the fan is turned on, it circulates the air in the room, which helps in two ways:
Increased evaporation: As the moving air passes over your skin, it increases the rate of evaporation of moisture (sweat) from your skin's surface. Evaporation is an endothermic process, meaning it absorbs heat from its surroundings to transform liquid water into water vapor. This process takes some of the heat away from your body, making you feel cooler.
Disruption of heat boundary layer: The fan helps break the heat boundary layer that typically surrounds your body. This layer consists of warm, stagnant air that reduces the rate of heat transfer from your body to the environment. When the fan blows this warm air away and replaces it with cooler room air, it allows your body to dissipate heat more effectively, contributing to the perception of coolness.
The actual temperature of the air in the room remains the same, but the moving air provided by the fan enhances your body's cooling mechanisms, resulting in the sensation of coolness. It's important to note that fans are effective in providing a cooling effect only when the air temperature is lower than your body temperature. In extremely hot environments, fans may not be sufficient to keep you cool, and additional measures like air conditioning or other cooling methods may be necessary.