> [Fans] can only provide cooling at air temperatures below the mean skin temperature, which is about 35°C (95°F). Fans cannot cool people above that treshold, because moving air cannot reduce the skin temperature below the ambient temperature – no matter how high the air speed.
The statement applies to passive heat sinks. If a device's heat sink has a surface temperature of 35°C, then blowing 40°C air across it faster will not only help, but it will be counterproductive: the warmer air heats the heat-sink, and moving air does it faster.
In 40°C relatively dry air, your skin is 35°C only because of active heat removal: evaporation. This changes the picture. Moving air can speed this up even though it is warmer. If the air doesn't move, then evaporation wraps you in a blanket of humid air. Ventilation displaces the humid air, replacing it with dry air that can take up moisture.
The statement applies to passive heat sinks. If a device's heat sink has a surface temperature of 35°C, then blowing 40°C air across it faster will not only help, but it will be counterproductive: the warmer air heats the heat-sink, and moving air does it faster.
In 40°C relatively dry air, your skin is 35°C only because of active heat removal: evaporation. This changes the picture. Moving air can speed this up even though it is warmer. If the air doesn't move, then evaporation wraps you in a blanket of humid air. Ventilation displaces the humid air, replacing it with dry air that can take up moisture.