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So I'm in a tiny dorm room and I normally point my fan blowing outside the window to cool my room off. I've been in some debates on blowing air out or in is more effective, so I'm hoping to get some empirical data to back up my claim. Things I have

  • A Heater with only low, medium, high settings.

  • The Fan.

  • I do not have a thermometer.

So the best I could think of was melting ice cubes. I don't care about the exact temperature, just which method is more effective.
I've outline the basis of my experiment:

Shut the windows and turn the heat on high, 15 minutes

Open the windows, turn off the heat, turn on the fan on high, 15 minutes

Leave $n$ ice cubes out and take the average of how long it takes them to melt.

All the ice cubes are from the same tray. Can anyone devise a better experiment with no tools...

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marked as duplicate by David Z Jul 20 '13 at 20:51

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1  
    
Is the freezer (from which I assume you get your ice cubes) available for participation in your experiment (that is: in your room)? –  Glen The Udderboat Feb 6 '13 at 9:17
    
Alternatively, do you perhaps share your room with (or can you borrow from a neighbour) a cockroach willing to assist you in your experiment? –  Glen The Udderboat Feb 6 '13 at 10:02
    
Or a bottle of olive oil? –  Glen The Udderboat Feb 6 '13 at 10:35
    
Yes to fridge and olive oil - No to cockroach. –  Matt Feb 6 '13 at 17:36

3 Answers 3

(The OP has commented that the room also contains a fridge and a bottle of olive oil, but no cockroach.)

The viscosity of olive oil changes with temperature. At higher temperatures it becomes more fluid. If you first make sure that the olive oil has the current room temperature (pour it into a pan and back), you can then measure how fluid it is by letting light marbles fall in, or holding it upside down, and time it. You can repeat this for extra accuracy.

Too bad about the cockroach. Apparently its maximum speed goes up with the temperature (in the appropriate range of course).

And with the fridge you might try this. 1) Open its door until the motor starts, then shut the door until the motor stops. Then open the door and start blowing air in and time until the motor starts again. Repeat from 1), but now with blowing air out. (This will save you at least an hour compared to the original and other set-ups.)

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I like the idea with the fridge door. I attempted to do something similar with my heater, as it claims it has an "automatic" setting. You think the setting would work with all the tuition money I'm paying, but alas, it does not. –  Matt Feb 7 '13 at 18:10
    
Ha! But just to be clear: I actually meant blowing air into or out of the fridge (not the room)! So that your fridge becomes a(n even tinier) model of your room (with the temperature difference reversed of course, which shouldn't matter). –  Glen The Udderboat Feb 7 '13 at 18:27

You have to be precise on your experimental conditions.

Using the average time of melting ice cubes will work as a heat loss measure, as long as they are the same size icecubes and have been in the freezer the same time, though I am not sure about the temperature error width.

When blowing in air you should have the fan well outside the window. Usual fans have their blades shaped so they push air infront of them but not draw it from behind, so you should be sure to be blowing cool air in and not recirculating what is coming up to the window by convection back in.

Reverse is true for blowing out, there should be space in front of the blades where room air is pushed out and not outside window air.

Here is an article on natural cooling including use of fans. There exist window fans for taking air out of the room, or blowing it in.

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  • Blowing the air on you will be more effective, as it increases the convective heat transfer from your body to the room and thereby increasing the room temperature (provided your room is a closed or isolated system).
  • The effect of blowing the air in or out of the room depends on the outside temperature. A fan is merely a device which increases mass transfer (and hence energy transfer too). Neglecting the waste heat generated by fan, there will be no appreciable change in the room temperature whether the fan blows air in or out.
  • But blowing air on you is a different case where the convective heat transfer from your body to the surroundings will get enhanced by the fan.
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protected by Qmechanic Jun 2 '13 at 11:22

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