First, a small amount of liquid water was poured into the barrel. This water was

Question

First, a small amount of liquid water was poured into the barrel. This water was then heated until it was boiling and steam started to escape from the barrel. The barrel was then sealed and a large quantity of ice was placed on top of the barrel. The ice cooled the contents of the barrel. A few minutes later the barrel collapsed spontaneously.

Assume that when the barrel was sealed, it contained pure saturated water vapour (no air) at 1 bar (100 kPa) pressure. The volume of the barrel is 0.21 m3 (55 US gallons).

When solving any thermodynamics problem, defining the system is a key step. This problem is easiest if you define the system to be the water (both liquid and vapour) that remains in the barrel when it is sealed. The attached thermodynamic tables give the values of different thermodynamic quantities for saturated water vapour (steam) and saturated liquid water.

Consider a similar barrel which contains just air and is unsealed and has a diameter of 1 metre.

Estimate the mass of the steam inside the barrel when it is sealed. What fraction of the water in the barrel is in the liquid phase? (Hint: How much water is in the barrel if it was entirely steam when the barrel was sealed?)

Explanation / Answer

mass of steam= 0.21/1.6941= 0.1239kg

fraction of liquid= 1.6941/(1.6941+0.001043)=0.99938

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