fluid presentation fluid mechanics .pptx

Fluid mechanics

1. FLOW REGIMES AND NPSH

2. Flow regimes In fluid dynamics, flow regimes refers to different patterns or behaviours of fluid motion that occur under certain conditions. These regimes characterised by specific physical properties such as velocity profiles, pressure gradients and dominant forces governing the flow.

3. Examples of flow regimes Lamina flow Turbulent flow Transitional flow Steady flow Unsteady flow

4. Laminar flow 1. In laminar flow, the fluid moves smoothly in layers or streamlines, with minimal mixing between adjacent layers. The velocity profile is typically well-defined, and the flow is relatively stable. The dominant force is viscous drag, and the Reynolds number (a dimensionless parameter) is typically low.

5. Turbulent flow 2. Turbulent flow is characterized by irregular fluctuations and mixing of the fluid. The flow velocities vary in magnitude and direction, resulting in a chaotic motion. Turbulence occurs when the flow velocity exceeds a critical value, leading to the development of eddies and vortices. The dominant forces in turbulent flow are inertial forces, and the Reynolds number is high.

6. Transitional flow 3. Transitional flow is an intermediate regime between laminar and turbulent flow. It exhibits characteristics of both laminar and turbulent flow, with intermittent fluctuations and less organized motion. Transitional flow is often sensitive to disturbances and can transition to either laminar or turbulent flow depending on conditions.

7. Steady flow 4. In steady flow, the fluid properties and velocity at any given point remain constant over time. The flow rate is consistent, and the velocity profile does not change with time. Steady flow can occur in both laminar and turbulent regimes.

8. Unsteady flow 5. Unsteady flow refers to fluid motion where the properties and velocity change with time. The flow rate may vary, and the velocity profile can undergo temporal changes. Unsteady flow can occur in both laminar and turbulent regimes and is commonly observed during transient events or when there are time-varying external influences.

9. Npsh available NPSH stands for "Net Positive Suction Head." It is a parameter used in fluid mechanics to assess the potential for cavitation to occur in a pumping system. Cavitation is the formation and subsequent collapse of vapor bubbles within a liquid due to low pressure, leading to damage to pumps and reduced performance. NPSH is a measure of the pressure head available at the suction side of a pump relative to the vapor pressure of the pumped fluid. It determines the margin between the absolute pressure at the pump inlet and the vapor pressure of the fluid. The NPSH is typically expressed in units of length, such as meters or feet.

10. Example one