# Can a hair dryer burn? Thermodynamic considerations...

#### Merlin05

Hi all,
I actually work in physics (quantum physics) but my thermodynamics knowledge is a bit lacking these days. The following problem has had me puzzled for quite a long time.

Basically, if I point the hot air coming out of a hairdryer at a target, will that target's temperature ever go higher than the temperature of the hot air? I recall reading somewhere that hairdryers product air at 60 degrees C, which is just below the threshold that can cause burning.

Thanks.

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#### BvU

Homework Helper
Burning of the skin, not bursting into flames, is what they probably mean.

#### Nidum

Gold Member
Free flowing air probably stays within temperature limits most of the time . Problem with all heat gun devices is that if exit duct is partially blocked then temperature can rise considerably . Modern equipment is usually fitted with an over temperature trip out device or full thermostatic control for safety .

#### Merlin05

Free flowing air probably stays within temperature limits most of the time . Problem with all heat gun devices is that if exit duct is partially blocked then temperature can rise considerably . Modern equipment is usually fitted with an over temperature trip out device or full thermostatic control for safety .
To be clear, I'm talking about the hairdryer burning the skin, not the dryer bursting into flames. In fact I just gave the hairdryer as an example, I'm really interested in understanding the physics here: i.e. if I blow air at 60 degrees C at a wall can that wall's temperature exceed 60 degrees?

#### nasu

If that were possible, why not just blow air at room temperature and expect things to warm up?

#### Merlin05

If that were possible, why not just blow air at room temperature and expect things to warm up?

#### Nidum

Gold Member
It is possible to build machines which use a large flow of cold air to produce a small flow of hot air .

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