Mass flowmeters are the types of flowmeters which are mainly employed in mass-related processes such as chemical reactions, heat transfer, etc. In all these processes, accurate measurement of flow is the prerequisite. There are numerous types of mass flowmeters available in the industry. However, the most widely used type is the Coriolis meter. Another type available is thermal type mass flowmeters.
Open Channel Flowmeter
Any conduit or channel in which the fluid or liquid is flowing with a free surface open to the atmosphere is referred to as an “open channel”. For instance, tunnels, nonpressurized sewers, partially filled pipes, canals, streams, and rivers, all these are Open channels. There are various techniques which can be used to monitor an open-channel flow. However, depth-related techniques are the most widespread. These techniques are based on the conjecture that one can instantaneously determine the flow rate of liquid by measuring its depth (or head). Two most commonly used primary devices for measurement of open-channel flows are Weirs and Flumes.
An ultrasonic flowmeter is one of the types of velocity type flowmeters. It is also known as non-intrusive Doppler flow meter. It is a volumetric flow meter which needs particulates or bubbles in the flow. The working principle is based upon the Frequency shift or Doppler Effect of an ultrasonic signal when it is reflected by suspended particles or gas bubbles i.e. discontinuities in motion. The discontinuities reflect the ultrasonic wave with a somewhat different frequency which is directly proportional to the rate of flow of the fluid. At least 100 parts per million (PPM) of 100 micron or larger suspended particles or bubbles must be contained by the liquid as per current technology.
Variable Area Flowmeter
Variable area flowmeters are a type of differential pressure flowmeters. These are simple and versatile devices which are used to measure the flow of liquids, gases, and steam. They work at a fairly constant pressure drop. In these types of flowmeters, a direct visual indication of flow rate is given by the position of the float, piston or vane. The position of their float, piston or vane gets changed as the rising flow rate opens a larger flow area to pass the flowing fluid. When the flow decreases, either the force of gravity or a spring is employed to return the flow element to its quiescent position. Gravity-operated meters also Rotameters must be installed in a vertical position, whereas spring operated meters can be mounted in any position. Each and every variable area flowmeter is available with local indicators. Moreover, they can also be provided with position sensors and transmitters i.e. Pneumatic, electronic, digital, or Fiberoptic types for linking to remote displays or controls.
Velocity Type Flowmeter
Velocity type flowmeters generally tend to follow a linear relationship with respect to the volume flow rate. Unlike differential pressure type flowmeters, there is no square-root relationship in these instruments. Hence, their rangeability is much better as compared to other flowmeters. Furthermore, they prove to be less sensitive to changes in viscosity when used at Reynolds numbers(Re) more than 10,000. Nearly all velocity-type flowmeter housings are outfitted with flanges or fittings. This arrangement enables them to be joined directly into pipelines. Major types of Velocity flowmeters include turbine, vortex shedding, electromagnetic, and sonic designs.
Venturi Flow Tube
A venturi tube is considered to be the most accurate flow-sensing element only if it is accurately calibrated. This tube basically consists of a converging conical inlet a cylindrical throat, and a diverging recovery cone.
Orifice plate is one of the most popular differential pressure type liquid flowmeter generally employed for detection (or measurement) of flow. It is one of the simplest and most cost-effective ways to restrict flow. Orifices are simply a flat piece of metal with a particular size of hole drilled in it. These flat plates are usually installed between a couple of flanges and in a straight run of smooth pipe. This is done to keep flow patterns turbulences away from fittings and valves. Orifice acts as a primary device. By means of an orifice, the liquid flow is obstructed in order to create a differential pressure across the plate. The fluid flow detection is done via measuring the pressure difference from the upstream side to the downstream side of a partially obstructed pipe.
Pitot tubes are another type of differential pressure flowmeters. They are named after Henri Pitot who came with this invention in the year 1732. Pitot tubes are basically used to detect flow velocity of fluids. Pitot tubes have the potential to measure two pressures at the same time i.e. impact (dynamic) and static. In a Pitot-static tube, the kinetic energy of the flowing fluid is transformed into potential energy for measurement of fluid flow velocity.
Positive Displacement Meters
Positive displacement (PD) meters are the types of flowmeters which are suitable for measurement of viscous liquid flows. These are also considered ideal for applications which require use of a simple mechanical meter system. In general, a positive displacement flowmeter consists of a chamber or cavity which restricts the flow. A rotating or reciprocating mechanical device is located inside the chamber to generate fixed-volume discrete parcels from the flowing liquid. Via PD meter units, liquids get separated into exactly calculated increments which are then further counted by a connecting register. Since every measured increment represents a distinct volume, these types of meters are widely used for automatic batching and accounting purposes.
Reciprocating Piston Meters
These are also known as oscillating piston flowmeters. These are one of the oldest positive displacement type flowmeter designs. These types of meters are mainly of single or multiple-piston types. Other types available are double acting pistons and rotary pistons. Selection of a particular type of piston meter depends on the range of flow rates necessary for an application. Although piston meters are smaller in size and considered apt for handling only low flows of viscous liquids, yet they are proficient enough to deal with an extensive range of liquids. Major application areas of a reciprocating piston meter include viscous fluid services like oil metering on engine test stands, specifically where turndown ratio is not considered much crucial. Also these meters can be employed on residential water service where they tend to pass partial quantities of dirt and fine sand along with water.