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 P2. So P2 = ?
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. P2 = P1 x T2 / T1 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
T1 = 20 ºC = 293 K
T2 = 50 ºC = 323 K
The Pressure Law gives us
P2 = P1 x T2 / T1
P2 = 7.5 x 323 / 293
P2 = 8.27 bar
6. 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.
