For the following scenarios identify the material of interes

For the following scenarios, identify the material of interest, and whether it would qualify as a control mass or a control volume. If a control volume, describe the process as either steady state or transient. A football is deflated (before use in a Patriots game). A garden hose has water flowing through it. A helium balloon warms up and expands. A can of spray paint is used.

Solution

Control volume process involves change in mass and energy of the system. A control mass process involves change in energy while keeping the mass constant. For cases of fixed boundries like cylinder containing gas, mass remains constant but there is a flow of energy into or outside the system. In case of balloons, both mass and energy of the system varies during expansion or contraction.

1. A football is deflated - Control volume transient process ( Since state variables vary with time)

2. A garden hose has water flowing through it - Control mass process

3. A helium balloon warms up and expands - Control volume steady state process ( since state variables do not change with time).

4. A can of spray paint is used - Control mass process.