• Viscosity: A measure of a fluid’s resistance to flow, indicating how “thick” or “thin” it is. Higher viscosity means more resistance. The SI unit of viscosity is Poiseuille (PI)
  • Velocity: The variation of flow velocity across a cross-section of the flow path. Laminar flows have a parabolic profile, while turbulent flows have a more uniform profile. The SI unit of velocity is m/s
  • Flow Rate: The volume of fluid passing through a cross-section of the flow path per unit time, commonly expressed in units such as litres per second or cubic meters per hour.
  • Reynolds Number (R): A dimensionless number that predicts flow patterns in different fluid flow situations. It is the ratio of inertial forces to viscous forces.
  • Pressure Drop: The reduction in pressure as the fluid flows through a system due to frictional losses, changes in elevation, or changes in flow path.
  • Boundary Layer: A thin layer of fluid near a solid boundary where the flow velocity changes from zero (at the surface) to the free stream velocity.
  • Streamline: A line that represents the path of a fluid particle in a steady flow. Streamlines never intersect and are used to visualize flow patterns.
  • Flow Regime: The classification of fluid flow into distinct patterns, such as laminar, transitional, or turbulent.
  • Shear Stress: The stress component that acts parallel to the surface, influencing fluid flow, especially in viscous flows.
  • Friction Factor: A dimensionless quantity used to quantify the resistance to flow in a pipe or duct due to frictional forces.
  • Flow Separation: A condition where the fluid flow detaches from the surface, usually due to an adverse pressure gradient, leading to turbulence and eddies.
  • Drag: The resistance force caused by the interaction between the fluid and the surface over which it flows.
  • Specific Gravity: The ratio of the density of a fluid to the density of a reference substance (usually water for liquids and air for gases), affecting buoyancy and flow characteristics.
  • Specific Volume: The volume occupied by a unit mass of fluid, the inverse of density.