The correct answer is: B. unsteady.
Steady flow is a type of fluid flow in which the fluid properties (velocity, pressure, density, etc.) at a given point in space do not change with time. Unsteady flow is a type of fluid flow in which the fluid properties at a given point in space do change with time.
When a valve is being opened, the flow of fluid through the pipeline is unsteady because the velocity of the fluid changes with time. The velocity of the fluid is initially zero when the valve is closed. As the valve is opened, the velocity of the fluid increases. When the valve is fully open, the velocity of the fluid reaches a maximum value.
The other options are incorrect because they do not describe the flow of fluid through a pipeline when a valve is being opened.
- Option A: Steady flow is a type of fluid flow in which the fluid properties (velocity, pressure, density, etc.) at a given point in space do not change with time. This is not the case when a valve is being opened, because the velocity of the fluid changes with time.
- Option C: Laminar flow is a type of fluid flow in which the fluid particles move in smooth, parallel layers. This is not the case when a valve is being opened, because the fluid particles move in a turbulent manner.
- Option D: Vortex flow is a type of fluid flow in which the fluid particles move in a circular motion. This is not the case when a valve is being opened, because the fluid particles move in a straight line.