The volumetric flow measurement records the flow of a medium, be it a liquid or a gas, within a pipe or an open duct. The volume flow (Q) indicates the volume of the medium that flows through a certain cross-sectional area per unit of time. This measured variable is of crucial importance in numerous industrial areas in order to control processes, optimize efficiency and ensure safety. The basics, functions and areas of application of volume flow measurement are explained in more detail below.
Basics of volume flow measurement
The volume flow (Q) defines how much volume of a fluid (liquid or gas) flows through a certain cross-section per unit of time. The unit of volumetric flow is usually given in cubic meters per second (m³/s) or liters per minute (l/min). The volume flow is calculated using the formula Q = A ⋅ v, where A is the cross-sectional area of the pipe through which the flow passes and v is the average flow velocity of the medium.
It is important to know the difference to the mass flow (ṁ), which indicates the mass of the medium per unit of time (kg/s). The mass flow can be calculated from the volume flow and the density (ρ) of the medium: ṁ = Q ⋅ ρ.
How does the volume flow measurement work?
There are basically two main methods for measuring the volume flow:
- Direct measurement: With this method, the volume of the medium flowing through is counted directly by dividing it into discrete units. Examples of this are positive displacement meters such as oval gear meters or gear meters.
- Indirect measurement: This involves measuring a physical variable that correlates with the flow velocity. The volume flow is then calculated from this measured variable. Examples of this are the measurement of pressure differences, magnetic induction or the flow velocity itself.
Depending on the application and the medium to be measured, different measuring principles based on these direct or indirect methods are used.
How is the volume flow calculated mathematically?
The basic mathematical relationship for calculating the volume flow (Q) is, as already mentioned, Q = A ⋅ v. The individual variables represent the following:
- Q represents the volume flow itself, typically specified in cubic meters per second (m³/s) or liters per minute (l/min).
- A is the cross-sectional area of the pipe or duct through which the medium flows. The unit for this is usually square meters (m²).
- v stands for the average flow velocity of the medium within the cross-sectional area, measured in meters per second (m/s).
This simple formula makes it clear that the volume flow depends directly on the size of the flow area and the velocity of the flowing medium. In practical applications, the determination of the cross-sectional area (for known pipe dimensions) and the measurement of the mean flow velocity can be carried out using various sensors and measurement methods, as already indicated in the previous sections. It is important to note that this basic calculation is directly applicable for incompressible media such as liquids. For compressible media such as gases, additional factors such as pressure and temperature may need to be considered as these can affect the density and therefore the volume.mperatur berücksichtigt werden müssen, da diese die Dichte und somit das Volumen beeinflussen können.
Methods and technologies of volume flow measurement in industry
In industrial practice, there are various methods and technologies for precisely measuring the volume flow. The selection of the appropriate method depends on a variety of factors, including the type of medium (liquid or gaseous), viscosity, conductivity, temperature, pressure and the desired measuring accuracy. Costs, maintenance requirements and the specific requirements of the application also play an important role.
DDM Sensors offers a wide range of flow meters that are based on different measuring principles and are therefore suitable for a variety of industrial applications. Common methods and technologies for volume flow measurement include:
Mechanical flow meters
This category includes devices such as impeller meters and oval gear meters. Impeller meters use a rotating wheel whose speed is proportional to the flow velocity and are well suited for water, oils and fuels. Oval wheel meters, on the other hand, use two rotating oval wheels that encapsulate defined volume units and are particularly suitable for highly viscous media such as oils, paints and foodstuffs.
Ultrasonic flow meter
This technology uses ultrasonic signals to measure the volume flow. In transit time difference measurement, ultrasonic signals are sent and received in and against the direction of flow. The time difference makes it possible to calculate the velocity and thus the volume flow. This method is suitable for ultrapure water, chemicals and large pipes. Doppler ultrasound uses the Doppler effect to measure the velocity of particles in the medium and is used in dirty water and suspensions.
Magnetic-inductive flow meters (MID)
These measuring devices use the principle of electromagnetic induction. A magnetic field is generated and the flowing conductive medium induces a voltage that is proportional to the flow velocity. EMFs are particularly suitable for conductive liquids such as water, conductive chemicals and waste water.
Thermal flow meters
With this method, a heated sensor is cooled by the medium flowing past it. The cooling is proportional to the mass flow and is particularly suitable for gases and air volume measurements.
Differential pressure measurement
With this method, the pressure drop is measured via a constriction in the piping system, such as an orifice plate, a Venturi tube or a Pitot tube. The volume flow can be derived from this pressure drop. These methods are used in steam, gas and water pipes.
Coriolis flow meter
These measuring devices use the Coriolis effect, which causes a twist in vibrating measuring tubes due to the mass flow. The mass flow rate can be precisely determined from this twisting, and the volume flow rate can be derived if the density is known. Coriolis flow meters are used for high-precision measurements in the chemical, pharmaceutical and food industries.
The products from DDM Sensors cover some of these technologies and thus offer solutions for various requirements in industrial volume flow measurement.
Application of volume flow measurement in industry
Volume flow measurement plays a crucial role in numerous industrial sectors. The precise measurement of liquid and gas flows is essential for controlling and optimizing production processes, monitoring consumption, quality assurance and ensuring safety. The areas of application are diverse and range from the automotive and chemical industries to mechanical engineering and the food and pharmaceutical sectors. Different media are measured in different industries and the choice of the appropriate measuring method depends heavily on the specific requirements of the application in question. The following section takes a closer look at some specific application examples in various industries.
Volume flow measurement in the chemical industry
An important area of application for volumetric flow measurement in the chemical industry is the monitoring of solvent flows in distillation plants. Here, solvents are evaporated in many chemical processes and then condensed again. Volumetric flow measurement is crucial for monitoring the coolant supply, which is necessary for the condensation process, as well as for monitoring the solvent return flow to optimize the entire process. Typical sensors used in this area are ultrasonic flow meters for non-contact monitoring.
Volume flow measurement in mechanical engineering
In the mechanical engineering industry, lubricant supply in machine tools is another important field of application for volume flow measurement. CNC milling machines, lathes and other machine tools require a precise supply of lubricants to prevent overheating and dry running of the machine components and to extend the service life of the tools through optimum lubrication. Depending on the application and viscosity of the lubricant, various sensors are used here, such as impeller flow meters for cost-effective applications with low-viscosity coolants or oval gear meters for high-pressure lubrication systems.
Volume flow measurement in the automotive industry
Another application example for volume flow measurement in the automotive industry is the measurement of fuel consumption during real road tests. Here, the exact fuel consumption is recorded in order to analyze and optimize vehicle efficiency under real conditions. Different flow meters can be used depending on the accuracy requirements and test environment. The data obtained is important for the development of fuel-efficient vehicles and compliance with emission standards.
Sources of error in volume flow measurement
Various factors can lead to inaccuracies and errors when measuring volume flow. The way in which the volume flow is measured and the specific conditions of the application play a decisive role. It is important to be aware of these potential sources of error in order to obtain reliable measurement results and to be able to take countermeasures if necessary. The sources of error can be roughly divided into measurement principle-dependent and application-related sources of error. In addition, maintenance and calibration can also have an influence on the accuracy of the measurement.