Please ensure all values are positive and Throat Diameter is smaller than Inlet Diameter.
Volumetric Flow Rate (m³/s):0
Volumetric Flow Rate (m³/h):0
Volumetric Flow Rate (L/min):0
Velocity at Throat (m/s):0
function calculateVenturiFlow() {
var d1_mm = parseFloat(document.getElementById('v_inlet_d').value);
var d2_mm = parseFloat(document.getElementById('v_throat_d').value);
var dp = parseFloat(document.getElementById('v_pressure').value);
var rho = parseFloat(document.getElementById('v_density').value);
var c = parseFloat(document.getElementById('v_coeff').value);
var errorDiv = document.getElementById('v_error');
var resultDiv = document.getElementById('venturi-results');
if (isNaN(d1_mm) || isNaN(d2_mm) || isNaN(dp) || isNaN(rho) || isNaN(c) || d1_mm <= d2_mm || d2_mm <= 0 || dp <= 0 || rho <= 0) {
errorDiv.style.display = 'block';
resultDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// Convert mm to meters
var d1 = d1_mm / 1000;
var d2 = d2_mm / 1000;
// Calculate Areas
var a1 = Math.PI * Math.pow((d1 / 2), 2);
var a2 = Math.PI * Math.pow((d2 / 2), 2);
// Venturi Formula: Q = C * A1 * sqrt( (2 * dP) / (rho * ((A1/A2)^2 – 1)) )
var areaRatioSq = Math.pow((a1 / a2), 2);
var flowRateM3s = c * a1 * Math.sqrt((2 * dp) / (rho * (areaRatioSq – 1)));
// Conversions
var flowRateM3h = flowRateM3s * 3600;
var flowRateLmin = flowRateM3s * 60000;
var velocityThroat = flowRateM3s / a2;
// Display Results
document.getElementById('res_m3s').innerText = flowRateM3s.toFixed(6);
document.getElementById('res_m3h').innerText = flowRateM3h.toFixed(3);
document.getElementById('res_lmin').innerText = flowRateLmin.toFixed(2);
document.getElementById('res_velocity').innerText = velocityThroat.toFixed(2);
resultDiv.style.display = 'block';
}
How to Calculate Venturi Flow Rate: A Comprehensive Guide
A Venturi meter is a classic fluid dynamics instrument used to measure the flow rate of a fluid within a pipe. It operates based on Bernoulli's Principle, which states that as the velocity of a fluid increases, its static pressure decreases.
The Venturi Flow Rate Formula
The standard formula for calculating the volumetric flow rate (Q) through a Venturi meter is:
Q = C * A₁ * √[ (2 * ΔP) / (ρ * ((A₁/A₂)² – 1)) ]
Where:
Q: Volumetric flow rate (m³/s)
C: Discharge coefficient (typically between 0.95 and 0.99)
A₁: Cross-sectional area of the inlet pipe (m²)
A₂: Cross-sectional area of the throat (m²)
ΔP: Pressure difference between the inlet and the throat (Pa)
ρ (rho): Density of the fluid (kg/m³)
Step-by-Step Calculation Example
Let's calculate the flow rate for a water system with the following specifications:
Inlet Diameter (D1): 100 mm (0.1 m)
Throat Diameter (D2): 50 mm (0.05 m)
Pressure Drop (ΔP): 5,000 Pascals
Fluid Density (ρ): 1,000 kg/m³ (Water)
Discharge Coefficient (C): 0.98
Step 1: Calculate Areas
A₁ = π * (0.1 / 2)² = 0.007854 m²
A₂ = π * (0.05 / 2)² = 0.001963 m²
Step 2: Calculate the Area Ratio
(A₁ / A₂)² = (0.007854 / 0.001963)² = (4)² = 16
When calculating flow rates using a Venturi meter, several factors can influence the precision of your results:
Discharge Coefficient (C): This accounts for energy losses due to friction and viscosity. For a well-machined Venturi meter, this value is high, usually around 0.98.
Fluid Viscosity: Very viscous fluids may require a lower discharge coefficient or a Reynolds number correction.
Installation: For accurate readings, there should be a straight run of pipe before and after the Venturi meter to ensure laminar flow.
Cavitation: If the pressure at the throat drops below the vapor pressure of the liquid, bubbles can form, leading to inaccurate readings and potential equipment damage.
Applications of Venturi Meters
Venturi meters are widely used in various industries because they offer a low pressure loss compared to orifice plates. Common applications include:
Water treatment plants and distribution systems.
Chemical processing plants for measuring corrosive or slurry fluids.
Automotive carburetors (using the vacuum created at the throat to draw in fuel).