Due to El Nino and its global effects on the weather I am being toasted by a regular daily temperature of 30 to 34.( Sorry to all you shivering in England) This means that the fans are working almost 24/7 and it led me to wonder how the fan works in providing cooler air to a room.
The room is closed and all the air therein is of the same temperature but a fan sucks in that warm air and apparently blows out cooler air.
Possible reasons.
The air is cooled by the fan?? No way!!
Air in motion is cooler than still air?? How does that work if it is true??
I know that air in horizontal motion creates less downward pressure but does it decrease its temperature also. I cant see it somehow.
I am of the opinion that the decrease in temperature is apparent rather than real.The decrease in pressure I have mentioned will encourage evaporation of sweat and this would give the impression that the air is cooler where in fact the body of the person feeling the lower temperature is himself cooler not the air.
I would welcome the input of the scientific elements of this forum.
Meanwhile I sweat and enjoy the caress of a nearby fan, watch the geckos wander the walls and my partner outside cleaning her motorbike using her ever attendant rock to support it in an upright position.

No way is the air any cooler because you have fans. The temperature is just the same. The fan just causes a downdraught and keeps the air in motion. This maybe helps perspiration evaporate more easily , so causing you to feel a cooling effect.

Years at KBGS e.g. 1958-1964 (optional) 58-64

Current location (optional) Wirral

When I was a child my mother used to be delighted if she'd managed to get the washing done on "a good drying day" i.e. when it was windy.
Water evaporates when in contact with air - "in contact with" being of particular relevance. A given volume of air has a maximum capacity for supporting evaporation. If air is not in motion the air close to the water will rapidly exhaust its' capacity to support evaporation. Moving the air around enables less moist air to come into contact with the water and thus facilitate more evaporation to take place ... or so I've been told.

Years at KBGS e.g. 1958-1964 (optional) 58-65

Current location (optional) leeds

I think the more rapidly circulating air helps to "distribute" heat away from your body, a bit like fans in computers. Your body is obviously much warmer than the air temperature. So, I would say the fan lowers the temperature in your immediate vicinity (when compared to still air).

This is in addition to the perspiration effect.

I sit writing this in humid and hot Singapore, with a fan pointing nicely at me.

Thanks everyone. So it seems much as I figured.
I wonder if this is the same phenomena as the Wind Chill factor although I always thought this only kicked in below certain lower temperatures.
By the way given a closed room where the heat is well distributed and not in layers the use of a fan by its use of energy, and generating some heat as a by product and its movement of heat from my body should in fact raise the temperature in the room . Have I got that bit right, too??

Yes, for both questions.
"Wind Chill" when the weather is cold, "cooling breeze" when it's hot - the same phenomenon - both transport heat away from your skin.

Years at KBGS e.g. 1958-1964 (optional) 58-65

Current location (optional) leeds

On the topic of fans, I have often wondered what would happen if you had a boat with a battery powered fan behind the sail. Anybody know?

Current location (optional) melbourne

The battery would run out at the most inconvenient time.

Years at KBGS e.g. 1958-1964 (optional) 58-65

Current location (optional) leeds

IW. Let us waterproof the fan, uprate the power unit invert the fan and attach it to the rear of the boat.You now have what is essentially an outboard motor and Newtons third does not stop this working , why then should it cause no movement when it is a fan and used in the manner described by Paul?? I am prepared to go with it making movement of the boat. Of course the fan wouold need to be huge and solar powered, the boat feather light and the sail of gossamer wrought!!

I'm not a physicist, but wouldn't the action of the fan "drawing the air" through the blades to popwer the sail cause an opposite action in that it would be pulling the boat against the wind direction? I must admit that I have also thought about this in the past along with thinking, if a car battery is charged via the alternator whilst driving, wouldn't it be possible to have enough battery power to drive an electric car and at the same time harvest the energy from the turning wheels to turn an alternator and recharge the batteries? As I said, I'm not a physicist, but I did enjoy sitting in front of the fan when the temperature hit the 40s recently

Years at KBGS e.g. 1958-1964 (optional) 1958-61

Current location (optional) Blue Mountains, Australia via Haworth

Hi John. To revert to the fan/outboard analogy. The water is just a medium being used to travel through that medium. The same is true of the aircraft propellor. The air/water is pulled upon. Going back then to the fan on the boat the air is pulled from behind it and propelled with force in front of it.Having stood behind a Lancaster while some maniac ran the wonderful and beautiful Merlin engine at full revs I will need very powerful persuading to believe that it will not move the boat. It removed my beret and contributed in no small part to my eventual baldness.
By the way having now referred to my RAF days I am reminded about the motor used in an electric fan. It was called a squirrel cage motor because of the manner of its wiring. We were told it could only be used with very low loads eg a fan blade. It was also reputed to run away with its speed if run without a load and would eventually throw itself to pieces. We decided to test the theory! We removed the fan blades ie the very low load, and started the motor. It gained speed and we hid in various corners of the hanger as it began to scream. The intervention of an angry and brave sergeant ruined our experiment, refusing to accept our explanation that it was all in the name of science.

Years at KBGS e.g. 1958-1964 (optional) 1944-49

Current location (optional) Philippines

The fan as propeller "throws" water away from the boat and so there is a movement of the boat in reaction to this.

The fan as wind "throws" air and so there is initially a movement of the boat in reaction to this. However, the air immediately hits the sail, and so there is an opposite reaction cancelling any movement.

This would be true if the sail was a sqaure rig or (possibly)a spinnaker, but if it was a fore and aft lateen type, what then? There are so many unknowns in the question it is impossible to answer simply. An answer including all the possibles would run to a thesis!

Years at KBGS e.g. 1958-1964 (optional) 55-60;

Current location (optional) Harrogate

Chris,
On the question of the cooling effect, your assertion (that the body is obviously much warmer than the surrounding air) surely applies only up to a point. Contributors claim to enjoy the fan's cooling effect at temperatures higher than that normal inside the human body ie. in the 40s (I wouldn't know from direct experience!). I go generally with the perspiration effect, akin to "windchill" or sticking a sucked finger in the air to test wind direction.

I'm with you 100% on your fan and sail analysis though. "3rd Law" pairs of forces need to be considered between every pair of interacting bodies in order to establish whether or not there is any net overall thrust on the vessel. Any force blowing the air forward is paired with an equal backwards force on the fan (plus whatever it is attached to - in this case the boat). As the air is brought to rest by a force on it from the sail, the boat experiences a corresponding forwards force. Fan, air and sail form a "closed system" with no external forces and therefore no change of motion.

Years at KBGS e.g. 1958-1964 (optional) 1958-65

Current location (optional) Dudley, West Midlands

Yes the effect may break down at very high room temperatures, although I suspect the hotter air rises enough to leave a cooling temperature gradient at sitting height.

The perspiration effect may be a small contributor. A fan can be effective even when one is fully clothed.

Any heating engineers from KBGS?

It might be that I have little to pass my time with here on the Islands. It might be the constant company of a fan. It is most likely the combination of both that makes me wonder at the mechanics of the fan on the ship question posed earlier.
I have accepted the proscriptions of Newton’s Third law but it led me to think of ways around this.
How if the fan were mounted on a second vessel, independently powered, and directed at our vessel surely then there would be motion for us.
But what if the second vessel’s independent power was a third vessel in the same way as the second moves us. And how if the third were moved by a fourth and so on in a great circle of vessels closing in front of us as our fan moves the last vessel in the chain.
We must accept appropriately powered fans, calm water and no breeze for our mind experiment.
If then this actually worked what if the vessels were then linked by towing ropes would the ring of vessels be brought to a halt by Newton‘s Third??.
Is this experiment worth proposing for the next Isle of Wight Regatta and while I am on the subject can anyone explain how tacking against the wind works??