When talking about high accuracy mass flow meter , we often refer to Coriolis mass flow meter and Thermal mass flowmeter.
One of the basic physical sizes and characteristics of a body is mass. It cannot be created or destroyed. The amount of mass remains constant regardless of boundaries. But, if there is a mass flow beyond the boundaries, the sum of the mass entering and the mass exiting must be zero. The law of mass maintenance states that the mass entering the system must be equal to the mass leaving the system at the same time interval.
When measuring flow, two-phase mixtures should be avoided — gas/liquid, gas / solid, or liquid / solid flowing in the same pipe, because they can travel at different speeds and even in different directions, so it should be ensured that flow as homogeneous as possible (by sizing the pipe or positioning the meter).
There is a direct mass flow measurement in
which the measured parameter is directly related to the mass flow and an
indirect mass flow measurement, where the volume flow and the density of the
liquid are measured, so they are further combined into the mass flow.
A thermal mass flow meter dedicated to a
single gas component or fixed part of mixed gas measurement is widely used in
the oil and chemical industries, medical instrumentation, bioengineering,
combustion control, gas distribution, environmental monitoring, precision
instruments, scientific research, metallurgy, aviation, and other fields.
Gas flow measurement - depends on their temperature and pressure. Therefore, the gas flow is expressed concerning the normal state of the gas, which is defined by pressure and temperature at relative humidity.
A thermal dispersion mass flowmeter is designed on the principle of thermal diffusion. The heat dissipation of a heated object is proportional to the fluid flow rate when the fluid passes through the heating object. The sensor has two standard levels RTDs, one is used to create a heat source, and to measure the temperature of a liquid, when the liquid is flowing, the temperature difference between them is linearly related to the size Flow, and then through a microelectronic control technology, the ratio is converted into the linear output of the measurement signal.
Coriolis mass flow meters, based on their principle of measurement, can measure the flow of almost any medium. These devices are characterized by high measurement accuracy (± 0.1...0.5% of the measured value when measuring mass flow) and high costs. Thus, Coriolis flowmeters are recommended for use in commercial metering stations, dosing/filling processes or responsible technological processes where it is necessary to measure the mass flow of media or control several parameters at once (mass flow, density, and temperature).
They are named after Gaspard G. Coriolis (1792–1843), a French civil engineer and physicist. Coriolis flowmeters measure mass flow, unlike those that measure speed or volume. Coriolis meters are unaffected by fluid pressure, temperature, viscosity, and density. Because of this feature, these meters are used without recalibration and compensation for parameters specific to specific fluid types. They were used only for liquids, but more recently they have been adapted for gases.
This meter usually consists of one or two
inlet and outlet vibration tubes, which are generally made of stainless steel.
This is very important for the accuracy of the meter, to prevent any mechanical
or chemical attack of the flowing fluid on the pipes or linings. They are
mostly made in U-shape. Thinner tubes are used for gases, while thicker tubes
are more suitable for liquids.
The fluid enters the gauge in the inlet, the mass flow rate is determined by the action of the fluid in the vibration tubes. As the fluid moves from the inlet to the outlet, it develops different forces depending on the acceleration resulting from the vibration of the tube.
As a result of these forces, the tube moves by twisting as it passes through a vibrating cycle. The amount of bends is directly proportional to the flow of mass passing through the tube.
In a flow-free state, the tube vibrates identically at the inlet and outlet where there is a sine wave with zero phase shift between them. During flow, the tube is rotated and the sides vibrate differently with a phase shift between them.
As a rule, stainless steel and Hastelloy alloys are used as pipe metering materials in mass flow meters, and therefore these devices are not suitable for measuring the flow of highly corrosive media. Also, the accuracy of flow measurement using a mass flow meter is influenced by the presence of undissolved gas in the measured environment.
The main disadvantage of Coriolis flow meter is the relatively high initial cost. However, the versatility of Coriolis sensors in handling different fluids makes them very useful in production plants where multiple types of different fluids need to be measured.
Coriolis flow meter is a very reliable device that allows you to measure mass and volume flow, density, concentration and temperature with a single measuring device. There are frequent applications to measure the concentration and flow rate of sugar, alcohol and milk density in the food industry. Other typical applications are the dosing of expensive biocides and the high precision fuel supply of burners in power plants where efficiency is increased significantly by directly measuring the mass of the fuel.
Coriolis flow meter is ideal for dosing various types of viscous fluids, oils, solvents, and chemicals. Coriolis measures on-line mass and volume flow, density, concentration, and temperature. It is perfect for measuring various types of hydrocarbons and expensive chemicals.