a pressurized can of sprayPaint

[vmars316]

Greetings,
I would like to know the physics of a 'pressurized can of sprayPaint', or insecticide, etc..
When the gas is released: some area heats up, and another area cools off.
Could someone explain this to me. Or aim me at an article, with diagrams, that
will explain why and which?
Thanks...vmars316

[LURCH]

The cooling off is because the density of the fluids inside the can is decreasing.

Try looking up "Boyle's law," it shoul dgive you Wiki articles and other links that will explain everything.

I've never noticed "certain parts" heating up; which parts? If it's near the nozzle, that may just be the friction of the ags and paint moving quickly through the nozzle.

[vmars316]

[ "certain parts" heating up; which parts? ]

Holding the can while spraying:
the can itself gets cooler.
Does it get hot elsewhere? Nozzle? etc..
Thanks...vmars316

[Kevin VdM]

A gas thad is expanding needs energy or otherwise heat to make thad expansion possible.
So when the gas leaves the can it needs energy to expand and so it cools down the can itself as well as the air around the can.

[yinx]

correct me if i am wrong, the gas that is release actually cools down (adiabatic expansion of gas) and the nozzle of the can (the hole which the gas escapes) heats up due to friction between the nozzle and gas molecules.

[Drakkith]

This effect actually happens in an Air Conditioner. The coolant is compressed and cooled, which causes it to liquify. Then it passes through an evaporator and a portion of the coolant changes to a gas once the pressure drops, causing the rest of the coolant to cool further and keeping it in a liquid state. Then this liquid/gas coolant reaches the coil and absorbs heat from the intake, cooling the air and causing the coolant to completely evaporate into a gas state. That gas gets compressed and cooled again and the cycle repeats.

I think that the spray can goes through the same effect.


correct me if i am wrong, the gas that is release actually cools down (adiabatic expansion of gas) and the nozzle of the can (the hole which the gas escapes) heats up due to friction between the nozzle and gas molecules.

The heating of the nozzle wouldn't be noticeable in everyday life, but I think it would happen.

[russ_watters]

The nozzle will dissipate some of the energy from the gas moving through it, but it will still cool down because the gas is cooler than the ambient temperature.

[vmars316]

* I found a pretty good answer here:
http://www.math.montana.edu/frankw/ccp/before-calculus/function/boyle/learn.htm

Boyle's Law involves a relationship between three properties of a gas in a container.
The volume of the container -- denoted V. Volume is measured in units of length^3 -- for example, cubic centimeters or cubic inches.
The pressure of the gas -- denoted P. Pressure is measured in units of force per area -- for example, pounds per square inch.
The temperature of the gas -- denoted T. Temperature is in many ways more complicated than pressure or volume.
It is usually measured using one of three units -- degrees Fahrenheit, degrees Celsius, or degrees Kelvin.

Boyle's Law states
PV = kT
where k is a constant, or
Pressure * Volume = Constant * Temperature
The value of the constant k depends on the units used for
the other quantities but once the units are fixed, k is also fixed.
When any one of the quantities V, P, or T is changed,
one or two of the others must change so that the equation above still holds.
Thanks...vmars