Mass Flow Rate Calculator
Calculate the mass flow rate of water based on volumetric flow and density.
m³/s
m³/h
Liters/min
Gallons/min (US)
Mass Flow Rate (kg/s)
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Mass Flow Rate (kg/h)
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Mass Flow Rate (lb/s)
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Mass Flow Rate (lb/min)
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What is Mass Flow Rate?
Mass flow rate is a fundamental concept in fluid mechanics and thermodynamics representing the mass of a substance (in this case, water) which passes through a given surface per unit of time. Unlike volumetric flow rate, which measures the volume of space the fluid occupies over time, mass flow rate measures the actual amount of matter moving.
The standard symbol for mass flow rate is ṁ (pronounced "m-dot") and the SI unit is kilograms per second (kg/s).
The Formula
The calculation relies on the relationship between mass, volume, and density. The primary formula used by this calculator is:
ṁ = ρ × Q
Where:
- ṁ = Mass Flow Rate (kg/s)
- ρ (rho) = Density of the fluid (kg/m³)
- Q = Volumetric Flow Rate (m³/s)
Understanding Water Density
The density of water changes slightly with temperature. While 1000 kg/m³ is the standard approximation used for simple calculations, precision engineering requires adjusting for temperature:
| Temperature (°C) | Density (kg/m³) |
|---|---|
| 4°C | 1000.0 |
| 20°C | 998.2 |
| 40°C | 992.2 |
| 100°C | 958.4 |
Example Calculation
Suppose you have a pipe delivering water at a volumetric flow rate of 50 Liters per minute at room temperature (approx 20°C, density ~998 kg/m³).
- Convert Volume to SI Units: 50 L/min = 50 / 60,000 m³/s ≈ 0.000833 m³/s.
- Apply Formula: ṁ = 998 kg/m³ × 0.000833 m³/s.
- Result: ṁ ≈ 0.831 kg/s.
Why Calculate Mass Flow?
Calculating the mass flow rate is critical for:
- Energy Balance: Determining the energy required to heat or cool water in boilers and chillers.
- Pump Sizing: Ensuring pumps can move the specific mass of water required against gravity or friction.
- Chemical Dosing: Accurately mixing chemicals into water streams based on the mass of water present.