Meter Type
Parameters
Pipe diameter D₁100 mm
Diameter ratio β = D₂/D₁0.50
ISO 5167: 0.2 ≤ β ≤ 0.75
Differential pressure ΔP50.0 kPa
Fluid density ρ998 kg/m³
Discharge coefficient Cd0.610
Orifice: ~0.61 / Venturi: ~0.95–0.99
Kinematic viscosity ν1.0 cSt
— m³/h
Flow rate Q
— m/s
Pipe velocity v₁
—
Throat Re
—
Cd used
— %
Permanent loss %
—
Rangeability
± —%
Uncertainty (95%)
— mm
Throat dia. D₂
Meter Cross-Section Diagram
Q–ΔP Characteristic Curve
Permanent Pressure Loss Comparison by Meter Type
Theory Notes (ISO 5167)
Differential Pressure Flow Equation:
$$Q = C_d \cdot \frac{\pi}{4} D_2^2 \cdot \frac{\sqrt{2\Delta P/\rho}}{\sqrt{1-\beta^4}}$$
GUM Combined Uncertainty:
$$\frac{u_Q}{Q} = \sqrt{\left(\frac{u_{C_d}}{C_d}\right)^2 + \frac{1}{4}\left(\frac{u_{\Delta P}}{\Delta P}\right)^2 + \frac{1}{4}\left(\frac{u_\rho}{\rho}\right)^2}$$
Vena Contracta / β ratio: $\beta = D_2/D_1$, typical design range 0.3–0.65
Design note: Orifice permanent pressure loss ≈ ΔP × (1-β²)²/(1+β²)².
Venturi meters recover most of the differential pressure, making them energy-efficient for large-flow, continuous-duty systems.
Flow rangeability is limited by Q ∝ √ΔP — a 100:1 DP range gives only 10:1 flow range.