Mass Flow Control Systems
Mass Flow Control Systems: Mass flow meters and controllers for air and oxygen are precision instruments used to measure and regulate gas flow rates in various industrial and scientific applications. These devices, including those manufactured by Kelly Pneumatics, utilize thermal mass flow or differential pressure principles to provide accurate flow measurements and control, often incorporating advanced features such as digital displays, data logging, and multi-gas compatibility.
Thermal Mass Flow Sensors:
Thermal mass flow sensors operate on the principle of heat transfer to measure gas flow rates directly in mass units. These sensors typically consist of two temperature-sensitive elements: a reference sensor and a heated flow sensor. As gas flows past the heated element, it causes heat transfer, which is proportional to the mass flow rate. The power required to maintain a constant temperature difference between the two sensors is measured and correlated to the mass flow rate. This method offers several advantages, including direct mass flow measurement without the need for pressure and temperature corrections, high sensitivity at low flow rates, and wide turndown ratio. Thermal mass flow sensors are particularly useful in applications involving natural gas, hydrogen, and other gases where precise flow control is critical.
Coriolis Flow Meters:
Coriolis flow meters are highly accurate instruments that directly measure mass flow rate by exploiting the Coriolis effect. The meter consists of vibrating tubes through which fluid flows, causing a measurable twisting force proportional to the mass flow rate. The fundamental principle is expressed as Mass Flow=𝐹𝑐/(2𝜔𝑥), where 𝐹𝑐 is the Coriolis force, 𝜔 is the angular velocity, and 𝑥 is the displacement. These meters offer superior accuracy independent of fluid properties, with typical accuracies of 0.2% for liquids and 0.5% for gases. Coriolis meters can measure various fluid parameters simultaneously, including density and viscosity, making them versatile for applications in industries such as oil and gas, chemical processing, and food and beverage.
Digital Flow Controllers:
Digital flow controllers represent advanced instrumentation for precise gas flow regulation in industrial and scientific applications. These devices, such as the Series DFC Digital Flow Controller by Dwyer Instruments, integrate straight tube sensors with electromagnetic valves to measure and control gas flow rates accurately. They offer significant advantages over traditional variable area flowmeters, including higher accuracy, wider rangeability (up to 1:100), and the ability to work with multiple gases without recalibration. Many digital flow controllers, like the MASS-VIEW® series, operate on the principle of direct thermal mass flow measurement, eliminating the need for temperature and pressure corrections. These controllers typically feature built-in gas properties databases for numerous gases and gas mixtures, obviating the use of potentially error-prone k-factors. Flow control is achieved by maintaining a constant pressure drop across the valve, ensuring nearly constant flow even with varying upstream pressure.
Thermal mass flow meters and controllers find extensive use across various industries due to their accuracy and versatility. In industrial processing plants, they are employed for monitoring compressed air, natural gas flow to boilers, and combustion air flow. The petrochemical industry utilizes these devices for flare stack gas monitoring and fuel gas measurement. In wastewater treatment, thermal mass flow meters are crucial for measuring aeration air flow and digester gas. The food and pharmaceutical sectors rely on these instruments for tablet coating processes, CO2 measurement in beer manufacturing, and nitrogen flow in mayonnaise production. Additionally, thermal mass flow meters play a vital role in HVAC systems for air balancing and energy conservation. Their ability to accurately measure low gas flow rates (under 25 ft. per minute) makes them indispensable in applications such as semiconductor process gas measurement and gas chromatography.
Microelectromechanical Systems (MEMS) Technology:
Microelectromechanical Systems (MEMS) technology integrates miniaturized mechanical and electrical components on a single chip, typically ranging from 20 micrometers to 1 millimeter in size. MEMS devices are fabricated using modified semiconductor manufacturing techniques, including photolithography, etching, and deposition processes. The core principle of MEMS lies in exploiting silicon’s mechanical properties alongside its electrical characteristics, enabling the creation of sensors and actuators that can detect and manipulate physical phenomena at the microscale. MEMS devices often incorporate structures such as cantilevers, membranes, and microchannels, which interact with their environment through various transduction mechanisms. The technology’s strength lies in its ability to batch-produce high-performance, low-cost devices that combine sensing, actuation, and signal processing capabilities. MEMS has revolutionized numerous fields, including automotive (airbag sensors), consumer electronics (accelerometers in smartphones), and biomedical applications (lab-on-chip devices).
Kelly Flow Solutions:
Kelly Pneumatics offers a range of high-precision Digital Mass Flow Meters designed for accurate measurement and control of air and oxygen flow rates. These advanced instruments feature a touch screen interface for easy customization, allowing users to select preferred units and adjust for gas mixtures. The meters utilize multiple sensors, including an anemometer for mass flow, a thermistor for gas temperature, and pressure transducers for atmospheric and gas pressure measurements. With the ability to automatically adjust for back pressures up to 100 psig and provide optional analog output, these meters are suitable for various scientific and engineering applications. For more information on advanced flow control solutions, you can learn about the principles of thermal mass flow measurement and Coriolis flow meters. To learn more about Kelly Pneumatics’ offerings, including their Proportional Valves and Mass Flow Controllers, visit their Custom Solutions page or contact their sales department for volume discounts and lead time.
