Fluid Mechanics Glossary

A dimensionless quantity that predicts flow patterns. Defined as Re = ρVD/μ, it indicates whether flow is laminar (Re < 2300), transitional, or turbulent (Re > 4000).

A dimensionless number used in the Darcy-Weisbach equation to calculate pressure drop. Depends on Reynolds number and pipe relative roughness.

An empirical equation for calculating pressure loss in pipes: ΔP = f·(L/D)·(ρV²/2). It accounts for pipe length, diameter, fluid properties, and flow regime.

The inner diameter of a hydraulic cylinder barrel, which defines the piston area. The bore area determines the extend (push) force: F = P × A_bore. Larger bore diameters provide more force at the same pressure.

The effective piston area on the rod side of a hydraulic cylinder, calculated as A_annular = A_bore - A_rod. This area determines retract (pull) force and flow requirements for retraction.

The distance a hydraulic cylinder piston can travel from fully retracted to fully extended position. Stroke length determines the volume of fluid required for each cycle and affects rod buckling calculations.

The total equivalent height a pump must overcome, including static head (elevation), friction head (pipe losses), pressure head (tank pressure), and velocity head. Determines pump operating point.

A graph showing the relationship between head and flow rate for a piping system. The curve rises parabolically because friction losses increase with the square of flow rate: H = Hs + KQ².

The absolute pressure at the pump inlet above vapor pressure, expressed as head. NPSHa (available) must exceed NPSHr (required by pump) to prevent cavitation. NPSHa = Ha - Hvp - Hf - Hs.

The total volume a tank can hold when completely filled, typically measured in gallons, liters, or cubic feet. Capacity depends on tank geometry (cylindrical, rectangular, spherical) and internal dimensions.

The volume of liquid in a partially filled tank. For vertical tanks, partial fill is proportional to height. For horizontal cylinders and spheres, partial fill requires segment or cap formulas due to the curved geometry.

The end closure designs for cylindrical tanks. Common types include flat (flanged or welded), hemispherical (half-sphere), 2:1 elliptical (most common pressure vessel), torispherical (dished with knuckle radius), and conical (for drainage).