Mass Flow Rate and Volumetric Flow Rate: Key Differences and Conversion

Cryogenic mass flowmeter measures Mass Flow Rate of liquid nitrogen

When it comes to flow measurement, understanding the distinction between mass flow rate and volumetric flow rate is crucial. Both concepts are widely used in various industries, but they differ in several aspects. We’ll explore the key differences between mass flow rate and volumetric flow rate, examine the factors that affect flow rate conversions, and walk you through the conversion process step by step.

RFQ

Defining Mass Flow Rate and Volumetric Flow Rate

What is Mass Flow Rate?

Mass flow rate refers to the mass of a fluid (Gas-Liquid-Powder) passing through a specific cross-sectional area per unit time. It focuses on the weight, not the volume, of the flowing medium.

Common units:

The common symbol for mass flow rate is ṁ. The SI unit for mass flow rate is kg/s. Other commonly used units include:

Kilograms per second (kg/s): International standard
Tons per hour (t/h): Industrial production
lbs per hour (lb/h): US industry
Ggrams per minute (g/min): Mass flow control

From\To	kg/s	kg/h	t/h	lb/h
1 kg/s	1	3600	3.6	7936.6
1 t/h	0.278	1000	1	2204.6

Our Sino-Inst mass flow meters can directly display mass flow rates in units such as g/h, kg/h, t/h, g/m³, kg/m³, and t/m³.

The Importance of Mass Flow Rate

In many industries, mass flow rate is crucial for ensuring accurate measurement and control of processes.

Mass flow rate measurement eliminates inaccuracies caused by the physical properties of gases or fluids. Changes in temperature or pressure can affect volumetric flow rate.
Many processes in the chemical, pharmaceutical, and food industries are quality-dependent. Chemical reactions depend on the quality of reactants or ingredients and must be added at the correct mass ratio.
In trade transfer applications, the quality of exchange fluids determines their price, especially in the oil and gas industry.
Gas mass flow rate is just as important as liquid mass flow rate. Gas mass flow rate ensures a stable gas supply that meets process requirements during production. This is applicable to gas proportioning in semiconductor manufacturing, reaction condition control in chemical production, and sterile gas supply in the pharmaceutical industry.
Furthermore, mass flow rate monitoring of solid powders allows for tracking material consumption and output, enabling data statistics and production process control.

Featured Mass Flow Meters

**SI-3504 Coriolis Liquid Mass Flow Meter**

What is Volumetric Flow Rate?

Volumetric flow rate, on the other hand, measures the volume of fluid passing through a given cross-sectional area per unit time. It focuses on the volume of the medium flowing through, not its weight.

Common Units:

Common symbols for volume flow rate are Q and V. The SI unit for volume flow rate is m³/s.

Common Units for Volumetric Flow Rate:

Cubic meters per hour (m³/h): International standard, Chinese industrial standard
Cubic meters per second (m³/s): Hydraulic engineering
Liters per minute (L/min): Laboratory equipment
Gallons per minute (GPM): US and UK industrial system
Cubic feet per minute (CFM): US HVAC industry
Barrels per day (bbl/d): Petroleum industry

From\To	m³/h	L/min	GPM(USA)	CFM
1 m³/h	1	16.67	4.4	0.589
1 L/min	0.06	1	0.264	0.0353
1 GPM(USA)	0.227	3.785	1	0.134
1 CFM	1.699	28.32	7.48	1

The Importance of Volumetric Flow Rate

Volumetric flow rate is essential for sizing equipment, monitoring fluid flow, and assessing system performance.

First, volumetric flow rate measurement is less expensive than mass flow rate measurement. Therefore, volumetric flow rate has a wider range of applications.
Monitoring the volumetric flow rate of water in water treatment and municipal water pipelines can help conserve water and prevent leaks.
By monitoring the volumetric flow rate of diesel and gasoline consumption, cost calculations and trade transactions can be performed.
In chemical plants, monitoring the volumetric flow rate of chemical fluids, such as sulfuric acid and alcohol, allows for understanding the production process and optimizing efficiency.
Monitoring the volumetric flow rate of gases, such as nitrogen, helium, and oxygen, provides energy consumption data, thereby optimizing energy utilization and reducing production costs.

Featured Volumetric Flow Meters

**SI-3305 Intelligent Gas Precession Vortex Flowmeter**

**SI-3101 Electromagnetic Digital Water Flow meter**

Key Differences between Mass Flow Rate and Volumetric Flow Rate

1. Factors Influencing Measurements

One of the main differences between mass flow rate and volumetric flow rate lies in the factors that influence their measurements. Mass flow rate is affected by the fluid’s density, while volumetric flow rate is influenced by the fluid’s compressibility and changes in temperature and pressure.

2. Measurement Devices

Mass flow meters and volumetric flow meters are used to measure mass flow rate and volumetric flow rate, respectively. Some common mass flow meters include Coriolis flow meters, thermal mass flow meters, and differential pressure flow meters. Volumetric flow meters, on the other hand, may include turbine flow meters, positive displacement flow meters, and ultrasonic flow meters.

3. Applications

Mass flow rate measurements are critical in applications where the fluid’s mass is vital, such as chemical reactions, combustion processes, and mass balancing. Volumetric flow rate measurements are more commonly used in applications where the fluid volume is important, like water distribution systems and HVAC systems.

Mass Flow Rate and Volumetric Flow Rate: Key Differences and Conversion

Relationship between Volumetric Flow Rate and Mass Flow Rate

Theoretically, the mass flow rate and volumetric flow rate of a gas or liquid can be converted using the fluid’s density. This conversion assumes a constant fluid density. In reality, density is affected by temperature and pressure. For fluids or gases with varying temperature/pressure, you need to measure the density in real time. For gases, you may need to consider the ideal gas law or use a specific gas constant.

Mass flow rate can be directly measured using a mass flow meter, or it can be obtained by multiplying the volumetric flow rate by the accurate density.

Volume flow rate can be obtained by dividing the mass flow rate by the fluid density. Volumetric flow rate varies with temperature and pressure, while mass flow rate remains constant when temperature or pressure changes.

Converting Volumetric Flow Rate to Mass Flow Rate

1. The Conversion Formula

To convert volumetric flow rate to mass flow rate, you need to multiply the volumetric flow rate by the fluid’s density:

Mass Flow Rate = Volumetric Flow Rate × Density

2. Factors to Consider

When converting volumetric flow rate to mass flow rate, keep in mind that fluid density can change with temperature and pressure variations. Therefore, you should consider the fluid’s specific properties and conditions when performing the conversion.

3. Practical Example

Imagine you have a volumetric flow rate of 10 m³/s for water at 20°C (68°F). To convert this to mass flow rate, you need to know the density of water at 20°C, which is approximately 998 kg/m³. Using the conversion formula:

Mass Flow Rate = 10 m³/s × 998 kg/m³ = 9,980 kg/s

More about: Relationship Between Pressure And Flow Rate: Key Insights. And How To Calculate Pressure From Flow Rate And Vice Versa.

How to Measure and Control Mass Flow Rates and Volumetric Flow Rates?

For measuring mass flow rate, a mass flow meter can be selected. For gases, a thermal mass flow meter can be used; for liquids, a Coriolis mass flow meter can be used. There are also dedicated powder flow meters for solid powders. Alternatively, a volumetric flow meter can be selected, and flow rate can be converted from density.

For measuring volumetric flow rate, a volumetric flow meter can be directly selected. For liquids, electromagnetic flow meters, turbine flow meters, and oval gear flow meters can be used. For gases, vortex flow meters can be used.

For controlling mass flow rate and volumetric flow rate, a suitable flow controller can be selected. Alternatively, a flow meter can be configured with a flow controller system.

We offer a variety of mass flow rate and volumetric flow rate measuring instruments for measuring and controlling the flow rate of gases and liquids. We can also customize flow measurement and control solutions according to your requirements.

Choosing the Right Flow Measurement Method

Before deciding whether to measure mass flow rate or volumetric flow rate, we recommend considering the following factors:

Fluid: Do you need to measure a gas or a liquid? Gases are generally compressible and sensitive to temperature and pressure; is temperature and pressure compensation required?
Process Parameters: What are the temperature and pressure of the medium? High temperature and high pressure will affect the selection of the flow meter.
Pipe Diameter and Flow Range: Based on your pipe size, is the flow range that the flow meter can measure compatible with the flow range you actually need to measure? If not, can the pipe be changed?
Volumetric Flow Rate or Mass Flow Rate More Important? For your monitoring purposes, is volumetric flow rate more critical, or is mass flow rate more important? You need to know what data you must obtain.
Accuracy Requirements: Mass flow meters typically provide higher accuracy under dynamic conditions. Of course, other parameters should also be considered when selecting the most accurate flow meter.
Cost and Maintenance: While volumetric flow meters are generally more economical and easier to maintain, their accuracy may not meet your project requirements. Mass flow meters, while highly accurate, have a higher initial cost.

Frequently
Asked
Questions

Help Center

To convert volumetric flow to mass flow, multiply the volumetric flow rate by the fluid’s density. Make sure you account for any changes in temperature and pressure that may affect the fluid’s density.

To find mass flow rate from volumetric flow rate, multiply the volumetric flow rate by the fluid’s density. This will give you the mass flow rate in units such as kg/s or lb/min, depending on the units used for volumetric flow rate and density.

No, mass flow rate and volumetric flow rate are not the same. Mass flow rate refers to the mass of a fluid passing through a specific cross-sectional area per unit time, while volumetric flow rate measures the volume of fluid passing through a given cross-sectional area per unit time.

The main difference between mass flow and volumetric flow lies in the factors influencing their measurements and their applications. Mass flow rate depends on the fluid’s density and is crucial in processes where the fluid’s mass is important. Volumetric flow rate, on the other hand, is influenced by the fluid’s compressibility and changes in temperature and pressure, and is more commonly used in applications where the fluid volume is important.

Volume flow rate is affected by system design, fluid characteristics, and operating conditions (such as pressure and temperature).

Yes. By using valves, pumps, and flow controllers, volumetric flow rate can be controlled to meet specific operational requirements or to cope with changing conditions.

The selection of a volumetric flow rate meter needs to be based on actual parameters such as the medium, pipe diameter, pressure, and temperature. For example, for measuring wastewater, an electromagnetic flow meter is the best choice. For measuring the volumetric flow rate of diesel fuel, an oval gear flow meter is the best choice.

In industrial applications, electromagnetic flow meters, turbine flow meters, and elliptical tooth flow meters are generally considered top-rated volumetric flow rate sensors. For gaseous media, vortex flow meters are typically used.

When selecting a suitable volumetric flow meter for a chemical process, the compatibility of the flow meter material is a key consideration. Chemical processes often involve corrosive media, such as sulfuric acid, nitric acid, and sodium hydroxide solutions. If ordinary 304 stainless steel is insufficient, materials such as 316L and PTFE can be considered.

In industrial applications, the best mass flow rate sensor is the Coriolis mass flow meter. Currently, the Coriolis mass flow meter is the most accurate type of flow sensor, with an accuracy of up to 0.1%.

Commercial mass flow rate controllers add control systems, valves, etc., to the mass flow meter. They can not only monitor the mass flow rate in real time, but also control the flow rate according to the user’s flow settings. They can stabilize the pipeline flow rate within the set range, or control the pipeline to open or close when the accumulated flow rate reaches a certain level.

Mass Flow Rate and Volumetric Flow Rate: Key Differences and Conversion