A mass flow meter is a device used to measure the mass flow rate of a fluid, either liquid or gas, in a particular system. There are two types of mass flowmeters, thermal flow meters (TMF) which measures the mass flow of gases, and Coriolis mass flow which measures mainly liquids and sometimes pressurized gases. TMFs operate based on the principle of thermal dispersion, which involves measuring the heat transfer from a heated surface to the fluid as it flows past it. Coriolis flow meters work on the principal vibration effect of fluid mass on a curved pipe. For more information on TMF please see: and for Coriolis read here
The mass flow meter calculates the mass flow rate of the fluid by measuring the difference in temperature between the heated surface and a reference temperature sensor. Mass flow meters are commonly used in industries such as food and beverage, chemical, and pharmaceutical to monitor and control mass flow rates in various processes. They offer advantages over other types of flow meters, such as high accuracy, stability, and repeatability, even in the presence of variations in fluid density and viscosity.
The installation and usage of a mass flow meter may vary depending on the type and manufacturer, but generally, it involves connecting the meter to the fluid supply line and reading the data displayed on the device. Proper installation, calibration, and maintenance of the mass flow meter are essential to ensure accurate and reliable data. Overall, mass flow meters are critical devices in various industries that provide valuable data for process optimization and quality control.
How does a TMF work?
A thermal mass flow meter (TMF) works based on the principle of thermal dispersion. The meter measures the mass flow rate of only gases, by sensing the heat transfer from a heated surface to the fluid as it flows past it. TMFs cannot measure the mass flow of liquids because the cooling effect on sensors is too fast limiting its range (minimum flow to maximum flow rates). TMFs consist of two temperature sensors, one that is heated and one that is not. Both sensors are located in a flow channel, and their temperature is kept constant by a heating element. The other sensor, called the reference sensor, measures the fluid ambient temperature.
As the fluid flows past the heated sensor, it carries away some of the heat, causing the temperature of the heated sensor to drop. The rate at which the temperature drops is proportional to the mass flow rate of the fluid. The reference sensor measures the changing temperature of the fluid and provides a baseline for comparison. By comparing the temperature difference between the heated and reference sensors, the mass flow rate of the fluid can be calculated using a mathematical formula.
How Does the Coriolis flowmeter work?
Coriolis meters artificially introduce positive and negative Coriolis acceleration into the metering process. As illustrated in the diagram above, the fluid media is split and redirected through two curved tubes. An oscillating excitation force is applied to the tubes via miniature velocity transducers or electric coils, causing a vibration measured by magnetic sensors. Coriolis flow meters vibrate at a minimal amplitude, usually less than 0.1” (2.5 mm). This frequency is near the natural frequency of the device, which is usually roughly 80 Hz.
When no flow is present, the tubes vibrate and the sine wave outputs of each hall-effect transducer are in phase. When flow is initiated, the fluid flowing through the tubes induces a rotation or twist to the tube due to acceleration of the Coriolis Effect, which operates in opposite directions on either side of the applied force.
For example, when the flow meter tube is moving upward during the first half of a cycle, the fluid flowing into the meter resists being forced up and pushes down on the tube. Conversely, liquid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube. This action causes the flow meter tube to twist. When moving downward during the second half of the vibration cycle, the tube twists in the opposite direction. This twist results in a phase difference (time lag) between the inlet and outlet sides and this phase difference is directly affected by the mass passing through the
The mass flow meter can measure mass flow rates accurately and stably, even in the presence of variations in fluid density and viscosity. This is because the device measures the actual mass flow rate of the fluid, rather than relying on its velocity or volume, which can be affected by changes in fluid properties.
Mass flow meters are commonly used in various industries, such as food and beverage, chemical, and pharmaceutical, to monitor and control mass flow rates in various processes. They offer high accuracy, stability, and repeatability, making them critical devices for process optimization and quality control. Proper installation, calibration, and maintenance of the mass flow meter are essential to ensure accurate and reliable data.
