Questions
1. Why are the storage tanks painted white?
2. Why is propane added to the blend of propellants?
3. From the graph what is the vapour pressure of pure butane at 0ºC
4. Which of these statements is true about the graph?
a. The graph shows a linear relationship between temperature and pressure.
b. The graph is non-linear. The rate of pressure increase rises with temperature.
5. Compare the pressure increase for 100% propane (the top line) from 10 to 20 ºC and from 30 to 40 ºC.
6. For a 50/50 mix (the green line,) what would you recommend to can designers as the maximum safe working pressure for the can at 50 ºC
Answers
1. White paint reflects sunlight to prevent overheating.
2. Propane has a high vapour pressure. Butane has a low vapour pressure. By mixing the two the ideal pressure can be set.
3. At 0 ºC butane exerts almost no vapour pressure.
4. b is true. The gradient of the lines increases with temperature. This shows that as the gas gets hotter the pressure increase for each degree rise is higher.
5. From 10 to 20 ºC the rise is about 2 bar and from 30 to 40 ºC the rise is about 3 bar.
6. You need to extrapolate the line to estimate the pressure at 50 ºC. My estimate is just over 10 bar. To design in a safety margin I would recommend 15 bar.
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