Tuesday, March 27, 2018

Understanding Flow Sensing Technologies

When selecting a flow sensor, flow meter, or flow switch, one of the first considerations is always the process media: air, gas, steam or liquid. Some flow sensing technologies measure gas, some are better at liquids, some are best for a single media, such as steam, and others are good in multiple media. The industry’s major flow sensing technologies now available include:
Thermal
Thermal flow meters.
Depending on the process media and your application’s requirements, all of these technologies have their advantages/ disadvantages. By considering the process media to be measured, as well as your plant’s equipment and layout, environmental conditions, maintenance schedules, energy cost and ROI, you will be able to narrow the field to one or two best choices.

Coriolis
Coriolis
Coriolis (Mass): Coriolis flowmeters use the oscillating movement of two symmetric metal tubes that are made to vibrate from an internal driver coil.  When liquids or gases flow through the tubes, a phase shift occurs (like you see in the hose) and pickups measure the “twist” and then relate that value to the actual flow. In other words, the amount of twist is proportional to the mass flow rate of fluid passing through the tubes. The greater the twist, the larger the distance between, and the greater the flow.

Differential Pressure: The differential flow meter is the most common device for measuring fluid flow through pipes. Flow rates and pressure differential of fluids, such as gases vapors and liquids. The differential flow meter, whether Venturi tube, flow nozzle, or orifice plate style, is an in line instrument that is installed between two pipe flanges and measures the pressure drop across the flow restrictor and equates it to flow.

Magnetic
Magnetic
Electromagnetic: Magnetic flow meters, also called electromagnetic flow meters or "magmeters",operate on a very simple principal. An electrically conductive liquid moving through a magnetic field will generate a voltage that is related to the velocity of the liquid.

Positive Displacement: Provides a direct indication of actual volumetric flow rate. The fluid motion drives the mechanical assembly. As the fluid motion drives the positive displacement flowmeter assembly, its rotational, oscillating, or other regular movement is counted, often by electronic means using magnetic pickups on moving assembly. There are a number of different positive displacement flowmeter designs including oscillating piston, gear, nutating disk, rotary vane, and diaphragm.
Thermal
Thermal

Thermal (Mass): Measure flow by delivering heat into the flowing media and measuring the loss of heat between temperature measurement points. They are popular because they provide unrestricted flow, contain no moving parts, work well on large or small diameter pipes, provide accuracies over a wide range of flow rates, do not require temp/press compensation, and provide mass flow instead of volume.

Turbine
Turbine
Turbine: These types of flowmeters operate under the simple principle that the rotation of the turbine will be constant as the turbine is acted upon by a fluid passing through the flowmeter. The rotational velocity of the turbine is then interpreted as output, allowing for the operator to consistently monitor the flow rate of the process fluid. They are easy to maintain and reliable.
Ultrasonic
Ultrasonic

Ultrasonic: Measure, via sound waves, the velocity of liquid flowing through a pipe.  Doppler shift technology reflects ultrasonic beams off sonically reflective materials. The transit time method exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium. The use of ultrasonic flow technology is most used in the oil, nuclear, wastewater, pharmaceutical, food and beverage industries.
Variable Area
Variable Area

Variable Area: Measures flow rate by allowing the cross-sectional area the fluid travels through to vary, causing a measurable effect. Flow measurement is performed according to the float principle. Used to measure many different types of liquids and gases passing through closed piping.

Vortex Shedding
Vortex
Vortex Shedding: Refers to the phenomenon wherein flowing gas or liquid forms vortices around a solid obstruction placed in the flow path, which can be measured to calculate volumetric or mass flow. Measure the volumetric flow rate of steam, gas, and low viscosity liquids.

Contact Flow-Tech for any industrial or commercial flow application by calling 410-666-3200 in Maryland, or 804-752-3450 in Virginia. Visit https://flowtechonline.com.