Which geometric factors influence whether a release is choked?

• A. Vessel shape only.
• B. Opening size only.
• C. Blockage factor only.
• D. Vessel shape, opening size, and blockage factor influence whether a release is choked.

Answer: (D)

When gas leaves a high‑pressure vessel into the surroundings, flow becomes choked when the fastest part of the stream reaches sonic speed at the narrowest cross‑section the gas must pass through. Whether that sonic condition is reached depends on the effective throat area and the pressure conditions set up by the geometry ahead of and at the exit.

Opening size directly sets the available cross‑section for the gas to pass. A smaller opening forces the flow to accelerate more to get the same mass flow rate, making it easier for the flow at the throat to reach Mach 1. A larger opening reduces that acceleration demand, making choking less likely unless the upstream pressure is extremely high.

Blockage factor represents obstructions within the opening that reduce the effective flow area. Even with a nominally large opening, a high blockage factor creates a narrow passage, increasing the likelihood that the flow becomes sonic at that restricted region.

Vessel shape influences how pressure and velocity evolve as the gas approaches the exit. The upstream geometry can shape the pressure gradient, the development of the boundary layer, and how smoothly the flow can be channeled toward the restriction. This shaping determines whether the throat actually behaves as the choking point and how readily sonic conditions develop there.

Taken together, these geometric factors determine the effective throat area and the boundary conditions that govern whether the release reaches sonic flow.