[Bolvan (OP)]

Hi!
We have syringe size 10 liters.
Plunger is located almost at the bottom, air volume in it is 1 liter, T = 20 deg C.
We pull plunger to the very top and hold it.
What will be temperature of air in syringe?

[alancalverd]

P₁V₁/T₁ = P₂V₂/T₂

[Bolvan (OP)]

Please, show how to use that formula.
Pressure in the room where experiment is conducted is normal atmospheric.

[Bored chemist]

It'#s not a simple problem.
You also need this
https://en.wikipedia.org/wiki/Adiabatic_process#Derivation_of_P.E2.80.93T_relation_for_adiabatic_heating_and_cooling

[chiralSPO]

same as room temp if you wait until tomorrow to measure it 

[Bolvan (OP)]

So, gas after forced expansion does not reduce temperature?

[evan_au]

Expansion reduces the temperature of a gas, and compression increases the temperature.

But if you wait for long enough, the temperature will equalize with the surrounding temperature.

[Bolvan (OP)]

We have syringe size 10 liters.
Plunger is located almost at the bottom, air volume in it is 1 liter, T = 20 deg C, normal atmospheric pressure.
We pull plunger to the very top and hold it, so now 1 liter of air is in 10 liter chamber.
What will be pressure and temperature of air in syringe?

[Bolvan (OP)]

And we have "perfectly" insulated syringe , so no thermal exchange taking place between syringe and surrounding environment.

[chiralSPO]

for a "perfectly insulated syringe, this would be an adiabatic process https://en.wikipedia.org/wiki/Adiabatic_process

Using this equation, which I got from the wiki article T₂ = T₁ *(P₂/P₁)^((γ-1)/γ)

and plugging in T₁ = 300 K, P₁ = 1.0 tam, P₂ = 0.1 atm, and γ = 7/5

I get T₂ = 300*(0.1/1)^(2/7) = 155 K

[Bolvan (OP)]

As we can see temperature drop is large. Heat transfer need repression measurement.
I'm trying to understand necessity of freons vs use of plain air or CO2?

[Bolvan (OP)]

Word " repression" is wrong . Precision was meant.

[chiralSPO]

As we can see temperature drop is large. Heat transfer need repression measurement.
I'm trying to understand necessity of freons vs use of plain air or CO2?

In this particular instance the temperature drop of the isolated gas is significant. However, the heat capacity of that gas is fairly very small, so 10 liters of low pressure gas at 150 K will not have a significant effect on the temperature of its surroundings. On the other hand, using freeon etc. takes advantage of a phase change, where the molar heat of vaporization is significantly greater than the molar heat capacity of the gas over the temperature range covered by adiabatic pressures. This makes for a much more effective heat transfer method.

[evan_au]

freons or CO₂

These were once used in fire extinguishing systems for computer rooms.

The cold gas is useful for cooling flammable materials below their ignition temperature, which prevents the fire from spreading.
But they also work because the relatively dense, non-flammable gas excludes oxygen from the flame, so the fire goes out.

Today, many uses of freons are frowned upon; if they escape into the atmosphere they can break down the protective ozone layer in Earth's upper atmosphere.

On one occasion I saw a tradesman welding in a computer room, which had set off the fire alarm. He was just seconds away from being blasted with CO₂ snow when I shut off the alarm.

[Bored chemist]

freons or CO₂

These were once used in fire extinguishing systems for computer rooms.

The cold gas is useful for cooling flammable materials below their ignition temperature, which prevents the fire from spreading.
But they also work because the relatively dense, non-flammable gas excludes oxygen from the flame, so the fire goes out.

Today, many uses of freons are frowned upon; if they escape into the atmosphere they can break down the protective ozone layer in Earth's upper atmosphere.

On one occasion I saw a tradesman welding in a computer room, which had set off the fire alarm. He was just seconds away from being blasted with CO₂ snow when I shut off the alarm.

The freons work as fire suppressants by a different mechanism- they are free radical scavengers.
(and they are also disproved of because they are potent greenhouse gases.

[Bolvan (OP)]

Interesting situation : I can not find pictures of Kelvins "heat multiplier" on english websites! Last year I could, now those sites are gone!
Besides conspiracy theory, any suggestions?
I have red many articles pointing out that CO2 ( R-744 ) outperforms any other "freons".
Very first "heat multiplier" of Kelvin worked just on air.
Why are we still using environmentally dangerous freons?

[Bolvan (OP)]

Snapshot is from here:
https://www.abok.ru/for_spec/articles.php?nid=5353 [nofollow]