Does a Hairdryer blow harder with heat


by Jedi_Sawyer
Tags: blow, blowing, force, hairdryer, harder, heat, kinetic
256bits
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#55
Jan29-14, 12:06 AM
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[QUOTE=246ohms;4644734]It seems all agree that the heater increases the tempearature and hence its volume which directly means it needs to go faster to exit the dryer nozzle.
The pressure drop created by an increase in velocity will be both from friction losses and exit losses from the nozzle.
QUOTE]

And an increase in viscosity of the air with the higher temperature!
Less missing pieces of the puzzle.!
NascentOxygen
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#56
Jan29-14, 10:50 PM
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My present hairdrier has, in addition to the usual pair of multiposition slide switches, a press-and-hold button located at the trigger position. Depressing this cuts power to the heating element without any change in the set speed, and I observe no discernible change in the motor's tone or throughput.

However, watching in the mirror as I depressed the trigger, it was unequivocal that the hair was being significantly more strongly parted (i.e., pushed aside) when this trigger button was depressed, meaning when no heating was occurring.

This is a surprise finding.

The hairdrier is rated 1600W, and I never use it on its hottest setting. The emergent air bast at that setting is more suited to paint stripping.
sophiecentaur
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#57
Jan30-14, 05:03 AM
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Curiouser and curiouser. You'll all have to go to the boat chandler's and buy yourselves an explorer wind meter (only about 35). We are clearly dealing with several extra variables here and the air speed right across the output and input apertures must be relevant. Now where did I put my smoke machine?
Jedi_Sawyer
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#58
Jan30-14, 02:20 PM
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Involved in all of this is conservation of energy/momentum which is what I was originally experimenting for. I think I know what is going on in all of this, adding heat is expanding gas in all directions so its net effect is zero for adding momentum. I am in the process of building the next generation model and hopefully will have more to talk about in a week or two.

Nascent, I have a similar hair dryer and I do notice a change in pitch and a corresponding brightening of bath room lights when I push the button to turn heat off. Can not say that I noticed any change in hair blowing but with hair like mine I probably would not have noticed.

Go Seahawks, even though I wish Sherman was a Bronco, as he has tempted Karma, maybe other guys Karma will cancel that out, sort of like heat added to airflow.
246ohms
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#59
Jan30-14, 02:50 PM
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Quote Quote by 256bits View Post
And an increase in viscosity of the air with the higher temperature!
Less missing pieces of the puzzle.!
True, the density, viscosity and temperature will change so the Reynolds Number will follow and the friction factor will also change. Probably could be solved in a CFD program as they allow an input section to be assigned a mass flow then any section can be a fan followed by heating and a ambient far field exhaust. That would really give a nice set of results!
sophiecentaur
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#60
Jan30-14, 03:28 PM
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Quote Quote by Jedi_Sawyer View Post
Involved in all of this is conservation of energy/momentum which is what I was originally experimenting for. I think I know what is going on in all of this, adding heat is expanding gas in all directions so its net effect is zero for adding momentum. I am in the process of building the next generation model and hopefully will have more to talk about in a week or two.

Nascent, I have a similar hair dryer and I do notice a change in pitch and a corresponding brightening of bath room lights when I push the button to turn heat off. Can not say that I noticed any change in hair blowing but with hair like mine I probably would not have noticed.

Go Seahawks, even though I wish Sherman was a Bronco, as he has tempted Karma, maybe other guys Karma will cancel that out, sort of like heat added to airflow.
That is clearly wrong or a gun cartridge wouldn't work, would it? Momentum conservation doesn't rule out an imbalanced flow of air if the fan stops it flowing backwards. Conservation laws must be invoked carefully if you want to get a valid conclusion.

If you are doing experiments with a supply that actually changes volts with a tiny 1.5kW load then I suggest you need to move to somewhere with a better supply - like a good old UK ring main system. There are enough unknowns in this issue without introducing additional cable resistances.


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