Excercise: How to draw a control volume

Exercise 1:

In the system below water flows from the upper tank to the lower tank via gravity. The top of both tanks is at ambient pressure (14.7 psi). Draw the control volume around the system.

Hint: 1 and 2 are the designations of the control volume.

Solution

The key to drawing the control volume is to draw the boundary around known pressures. In this case the pressures at the top of both tanks are equal. Thus, the control volume boundary will be drawn around the the system and the top of the tanks.