How does geometry of equipment influence the source term?

• A. Vessel shape has no impact; only opening size matters.
• B. Opening size only determines the release duration.
• C. Blockage factor only affects whether the release is choked.
• D. Vessel shape, opening size, and blockage factor affect mass flow rate, duration, and whether the release is choked.

Answer: (D)

Geometry shapes how a release behaves by controlling three connected aspects of the source term: how much mass can flow out (mass flow rate), how long the release lasts (duration), and whether the flow becomes choked (velocity limited by the speed of sound at the throat).

The opening size sets the flow area. A larger opening generally allows more mass to leave per unit time, raising the flow rate, while a smaller opening reduces it. But the time the vessel can supply that mass—the duration—depends on how quickly the material is being expelled, so you can’t determine duration from opening size alone.

The vessel shape affects pressure distribution and how the material accelerates as it moves toward the outlet. This influences how readily the flow can reach or maintain a choked condition and how the pressure inside the vessel changes during release. In short, shape can modify both the instantaneous rate and the likelihood of choking.

The blockage factor changes the effective flow area inside the opening path. More blockage lowers the actual area available for flow, reducing mass flow rate, extending duration, and potentially altering whether the flow is choked depending on the resulting pressure ratios and throat size.

Because mass flow rate, duration, and choking behavior all depend on geometry in concert, incorporating vessel shape, opening size, and blockage factor gives the complete picture of the source term. The other ideas are incomplete: opening size alone misses how shape and blockage shift flow dynamics; focusing only on opening size misses duration; and focusing only on blockage misses how area and shape influence rate and choking.