The figure shows volume flow rates (in cm3/s) for all but one tube. What is the volume flow rate through the unmarked tube ? Is the flow direction in or out ?
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This problem applies the principle of conservation of mass (continuity) for incompressible fluid flow at a junction.
The sum of volume flow rates into the junction must equal the sum of volume flow rates out of the junction.
Let the unknown flow rate be Q. First, identify directions: flows into the junction are positive, flows out are negative.
Given flows: 5 cm3/s and 4 cm3/s are in. 3 cm3/s and 8 cm3/s are out.
Set up the equation: 5 + 4 – 3 – 8 + Q = 0.
Solving: Q = 2 cm3/s. The positive value means it is a flow into the junction.
Final answer: 2 cm3/s in