Questions

1. Why are the cans immersed for 3 minutes and not, say, just a few seconds?

2. Rearrange the equation above to make an expression for P

_{2}. So P

_{2}= ?

3. What is 0 ºC in Kelvin?

4. What is 50 ºC in Kelvin ?

5. If the initial pressure of a full bag on valve can with nitrogen propellant is 7.5 bar at 20 ºC, what will be the pressure if the can reaches 50 ºC in a water bath?

6. After manufacture, where would the danger of a leaking aerosol propellants such as propane be greatest?

7. Fill in the gaps in this table.

Answers

1. The can and the contents (propellant and product) have a heat capacity. It takes at least three minutes to raise the temperature of the contents to 50 ºC.

2. P

_{2 }= P

_{1 }x T

_{2 }/ T

_{1 }The pressure increase by the ration of temperatures, but ONLY if the temperatures are in Kelvin ( ºC + 273)

3. 273 K

4. 50 + 273 = 323 K

5. The first step is to convert ºC to K

T

_{1}= 20 ºC = 293 K_{ }

T

_{2 }= 50 ºC = 323 KThe Pressure Law gives us

P

P

P

_{2 }= P_{1 }x_{ }T_{2 }/ T_{1 }P

_{2 }= 7.5_{ }x_{ }323 / 293P

_{2 }= 8.27 bar6. The danger is greatest where the cans are concentrated in one place. This will be on a truck or in a warehouse, which is why special precautions are taken during handling.

7.