Mass Flow Rate Calculator
Convert between mass and volumetric flow rates. Calculate mass flow from volumetric flow and fluid density, or vice versa.
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Mass & volumetric flow resultsHow It Works
The Mass Flow Rate Calculator converts between mass flow rate and volumetric flow rate using fluid density. Mass flow rate measures the amount of mass passing a point per unit time, while volumetric flow rate measures the volume passing per unit time. The two are related through the fluid's density.
Mass Flow Rate Formula
To convert from volumetric flow to mass flow:
ṁ = ρ × Q
Where:
- • ṁ = Mass flow rate (kg/s)
- • ρ = Fluid density (kg/m³)
- • Q = Volumetric flow rate (m³/s)
To convert from mass flow to volumetric flow:
Q = ṁ / ρ
Common Fluid Densities
| Fluid | Density (kg/m³) | Density (lb/ft³) |
|---|---|---|
| Water (20°C) | 998 | 62.3 |
| Seawater | 1025 | 64.0 |
| Diesel Fuel | 850 | 53.1 |
| Gasoline | 750 | 46.8 |
| Crude Oil | 870 | 54.3 |
| Ethanol | 789 | 49.3 |
| Glycol 50% | 1070 | 66.8 |
| Air (STP) | 1.225 | 0.0765 |
| Natural Gas | 0.72 | 0.045 |
When to Use Mass vs Volumetric Flow
Use mass flow rate when dealing with chemical reactions, combustion processes, steam systems, or any application where the actual amount of substance matters. Mass flow is independent of temperature and pressure, making it ideal for custody transfer, boiler feed water, and gas metering.
Use volumetric flow rate when sizing pipes, pumps, and valves, or when the physical space occupied by the fluid is the primary concern. Volumetric flow is commonly used in HVAC systems, water distribution, and general plumbing applications.
FAQ
Here you will find the answers to the frequently asked questions about mass and volumetric flow rate.
Frequently Asked Questions
What is the difference between mass and volumetric flow rate?
Mass flow rate measures the amount of mass (e.g., kilograms) passing a point per unit time, while volumetric flow rate measures the volume (e.g., liters or cubic meters) passing per unit time. They are related by the fluid's density: mass flow equals density multiplied by volumetric flow. The key distinction is that volumetric flow changes with temperature and pressure (as density changes), while mass flow remains constant for the same physical quantity of fluid.
When should I use mass flow rate instead of volumetric?
Mass flow rate is preferred in applications where the actual quantity of substance matters, such as chemical dosing, combustion processes, boiler feed water, custody transfer of gases or petroleum products, and steam systems. Since mass flow is independent of temperature and pressure variations, it provides more accurate accounting of material quantities. Volumetric flow is preferred for pipe and pump sizing, HVAC ductwork, and general water distribution where fluid conditions are relatively stable.
How does temperature affect mass flow rate?
Temperature does not directly affect mass flow rate, but it does affect the density of the fluid. As temperature increases, most liquids expand and become less dense. This means the same volumetric flow rate at a higher temperature corresponds to a lower mass flow rate. For gases, the effect is even more significant. For accurate conversions, always use the fluid density at the actual operating temperature rather than the standard reference temperature.
What are common units for mass flow rate?
In the metric system, mass flow rate is commonly expressed in kilograms per second (kg/s), kilograms per minute (kg/min), kilograms per hour (kg/h), or tonnes per hour (t/h). In the imperial system, common units include pounds per second (lb/s), pounds per minute (lb/min), and pounds per hour (lb/h). The SI base unit is kg/s. In process industries, kg/h and lb/h are the most widely used units for specifying equipment capacity and process requirements.
How do I convert kg/s to GPM?
To convert kg/s to GPM (US gallons per minute), you need to know the fluid density. First, divide the mass flow rate by the density to get the volumetric flow in m³/s, then multiply by 15,850.3 to convert to GPM. For example, 1 kg/s of water (density 998 kg/m³) equals approximately 15.87 GPM. The formula is: GPM = (mass flow in kg/s ÷ density in kg/m³) × 15,850.3.
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