# Thermodynamic Breakdown of a Fan

Discussion in 'General Science & Technology' started by Layman, Jun 10, 2014.

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1. ### exchemistValued Senior Member

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I myself took Layman at face value, for quite a while, and tried to help - until it became bloody obvious he was just fooling around and wasn't listening. If you bother to read the thread, you will see that.

Your example is useless. First, his point was to do with a ceiling fan circulating air in a closed room. Your example, obviously, is of a fan blowing cooler air from outside through a machine and back out again - a totally different situation. Secondly, as usual you made no effort to explain the point you were trying to get across with this example. The reader was left to guess at what the hell your contribution is designed to achieve.

I have yet to see a single contribution from you with enough explanation or commentary to make clear in what way it is relevant to the subject at issue. You may be brilliant for all I know, but your ability to communicate seems to be hopelessly inadequate. You appear to be either lazy or else not really at all interested in the science.

That is why I have no time for your contributions. I wish it were otherwise, as I am delighted to talk science with anybody.

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5. ### Aqueous Idflat Earth skepticValued Senior Member

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The question of closed systems escapes people who never took thermo. Your comment is certainly on point.

7. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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And if he was serious, and gave me some respect, he could've asked for clarification and I would have given it.

8. ### Aqueous Idflat Earth skepticValued Senior Member

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exchem is an excellent poster with a strong background in science and music. So don't let me get in the middle of that. Actually I think you're both great posters. I tend to read between the lines with your posts since they seem to be the subtle remarks of a person who knows a lot more than is directly evident. I assumed by your mention of closed systems that you were anticipating the remark (often posted by the member here known as wellwisher) that evolution and the Big Bang can't be true, since, by ignoring system boundaries, they claim it violates the laws of thermo. Maybe not, but I at least wanted to point this out.

9. ### exchemistValued Senior Member

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Respect has to be earned. As far as I am concerned you have yet to do this.

I do however respect the judgement of Aq Id and if he thinks you are not a lazy fool that gives me pause for thought. But I remain to see the value of what you post. Maybe if you cared to post a paragraph instead of a couple of lines it would be more apparent, I don't know.

10. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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If you don't respect me, that's fine.

I just don't want to be shown disrespect.

11. ### Aqueous Idflat Earth skepticValued Senior Member

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When I first noticed Beer, I thought this was a poster with a PhD trying to play things down. There was a lot of insight, I thought, in Beer's posts here.

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13. ### exchemistValued Senior Member

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What are you studying?

14. ### exchemistValued Senior Member

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OK, I will undertake to try harder to understand what Beer w Straw is getting at with her Delphic utterances.

15. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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Housekeeping.

16. ### LaymanTotally Internally ReflectedValued Senior Member

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Then I apologize for having enough common sense to know that portable AC units that fit in the window are often referred to as swamp coolers. I would be trolling if I actually cared rather or not the people in this forum also grasped that tid-bit of information along with me, but I am not trolling because I do not really care if they do or not.

17. ### Russ_WattersNot a Trump supporter...Valued Senior Member

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OK, that would explain it partly. But it isn't a common sense issue, it's just that you use some slang that happens to say something wrong. You should have recognized it though since you apparently have both the term and wrong definition: since I said it is an AC unit and you supposedly knew it was an AC unit, you shouldn't have said it wasn't.

18. ### LaymanTotally Internally ReflectedValued Senior Member

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Well, I am definitely not Arabian, because no matter how hard I try, I can never make a stubborn mule come to drink water.

19. ### LaymanTotally Internally ReflectedValued Senior Member

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Fine, believe that they are not swamp coolers all you want. I don't care. It really doesn't even matter. This thread wasn't intended to be about swamp coolers anyways. You can go on believing that the other 99% of the population is just wrong when someone would point at one and say "swamp cooler".

The point of the thread was that fans can cool a room, and that doesn't agree with the laws of thermodynamics.

I was told the explanations:

1. it lowers the humidity

2. it just feels cooler from sweat

I then replied with circumstances:

1. It was not humid.

2. I was not sweating.

As you can see explanation 1 and 2 would not be sufficient to explain circumstances 1 and 2. From my experience it is hard to cool a room with a fan that is already hot or well above 70 degrees Fahrenheit. What I was looking for was a breakdown of why a room would get cooler when it is already below 70 degrees Fahrenheit according to the laws of thermodynamics.

I will give an example. Johnny shuts his door and turns his ceiling fan on high before he goes to bed. He wakes up freezing the next morning and becomes sick. Calculate how hot his room should have been if the fan turned at 500 rpm and had two foot rotary blades after 8 hours starting at 70 degrees.

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That's just plain stupid!!! I've been around 71 years and seen TONS of window units. And not ONCE have I heard anyone call them "swamp coolers!"

21. ### LaymanTotally Internally ReflectedValued Senior Member

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Are you trolling me? I already said I don't care about what you call swamp coolers. Trolling on these forums seem to have gone to an all new level. You keep bringing up something I don't even care about that has nothing to do with the question. Then I get in trouble for responding to it. Just drop it already.

Isn't that what trolling even is? To keep bringing up the same nonsense over and over again to just irritate other people? It really looks like that is what you guys are doing. This is just, "gang up on the guy that questions the validity of science". Nothing more, or less. Then you all try say that is the person who is trolling, when in actuality you are all just sitting there trolling that person. I bet you don't even get a notification for this post this is obviously offensive, since you just flat out called me stupid.

How old you are has nothing to do with the question. You should be ashamed of yourself for being that old and being so caught up on something so trivial. It looks like your starting to show the symptoms of Alzheimer's Disease.

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Nope, never called YOU stupid - I was calling your CLAIM stupid. And it still is!

Age has a LOT to do with it - that's exactly how one gains life experiences (like the one I just mentioned).

If there's anyone in this thread that's displaying symptoms of Alzheimer's or some other form of of dementia, it's YOU layman. in fact, I've wondered that very thing about you after reading MANY of your posts in several threads.

And as to bringing up things again, I shall continue to do so unless and until you show SOME sign of acknowledgement of having been wrong in your claims.

No, I received no notification for that post because none was warranted.

As to your rather silly question about the guy going to sleep with the fan running when it's 70 degrees F in the room and then waking up cold, it's actually quite simple: The heat from the fan isn't enough to overcome the heat loss during the night when the outside temp drops well below 70.

23. ### originTrump is the best argument against a democracy.Valued Senior Member

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A fan does not cool the room. The laws of thermodynamics say so and any experiment you care to run will prove that.

Does a fan cool a person? Yes it does in most cases.

Here are the facts.

1. A fan moves air. Moving air does not cool it. The temperature of the air is a measure of the translational kenetic energy of the molecules, which is vibrational kenetic energy. The fan puts in a bulk movement of the molecues which does not cool the molecules they just move around.

2. The fan has a motor which will not run at 100% efficiency so there will be loss in the form of heat from the motor. So the overall effect of the fan on temeperature will be to slightly increase the temperature of the air. Realistically the slight increase in temperature will in all likelyhood not keep up with the heat loss of the room to the outside.

3. Assuming that you are not sweating at all if the temperature of the air is lower than your body temperature the fan will cool you simply from the heat tranfer. The equation for heat transfer shows this.

$\dot{Q} = c_p \dot{m} (T_a - T_b)$

$\dot{Q} =$ Heat flow

$c_p =$ heat capacity

$\dot{m} =$ mass flow rate

$T_a =$ temperature of the air

$T_b =$ temperature of your body

So if the temperature of the air is lower than your skin temperature the heat flow will be negative which means heat will flow from your body. The higher the mass flowrate the higher the heat leaves your body. The cooler the air temperature the faster the heat flows from your body.

So if the air temperature is higher than your body tempertaure the heat flow will be positive which means heat will flow into your body and you will heat up so the fan will make you feel hotter. If the air flows faster you will heat up more and feel even hotter.

4. If you have any sweat or moisture at all on your skin then a fan will cool you much more effeciently than can be accomplished through simple heat transfer. Even an air temperature above your body temperature will cool you due to the latent heat of evaporation.