Showing posts with label flowmeter. Show all posts
Showing posts with label flowmeter. Show all posts

Thursday, November 30, 2017

Differential Flowmeters: How They Work

Differential Flowmeters
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, are explored using the orifice plate flow meter in the video below.

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.

The orifice plate flow meter is comprised the circular metal disc with a specific hole diameter that reduces the fluid flow in the pipe. Pressure taps are added on each side at the orifice plate to measure the pressure differential.

According to the Laws of Conservation of Energy, the fluid entering the pipe must equal the mass leaving the pipe during the same period of time. The velocity of the fluid leaving the orifice is greater than the velocity of the fluid entering the orifice. Applying Bernoulli's Principle, the increased fluid velocity results in a decrease in pressure.

As the fluid flow rate increases through the pipe, back pressure on the incoming side increases due to the restriction of flow created by the orifice plate.

The pressure of the fluid at the downstream side at the orifice plate is less than the incoming side due to the accelerated flow.

With a known differential pressure and velocity of the fluid, the volume metric flow rate can be determined. The flow rate “Q”, of a fluid through an orifice plate increases in proportion to the square root the pressure difference on each side multiplied by the K factor. For example if the differential pressure increases by 14 PSI with the K factor of one, the flow rate is increased by 3.74.


Thursday, November 17, 2016

Applying Turbine Flow Meters For Clean Liquids and Gases

turbine flow meter flange connections Hoffer
Turbine Flow Meter
Courtesy Hoffer Flow Controls 
A turbine flow meter provides a volumetric measurement of liquid or gas flow through the use of a vaned rotor (turbine) inserted in the fluid flow path. Fluid movement causes the turbine to rotate at an angular velocity proportional to the flow rate. A pickup senses the passage of the rotor vanes, producing a sine wave electrical signal output which is detected by the unit electronics. The frequency of the signal relates directly to the flow rate.

Generally, a turbine flow meter is applied to measure unidirectional flow. Some turbine flow meters, through the use of two pickups, have the capability to measure flow in both directions.

There are a number of considerations when selecting a turbine flow meter:

  • Material of construction: Numerous material options are available for the housing and internal parts. Proper selection considers media characteristics and cost.
  • Bearing selection: The combination of bearing type and material will likely be selected by the device manufacturer, based upon a comprehensive application information set.
  • Pickup selection: Several pickup options may be available, with the manufacturer making a recommendation that best suits the application parameters.
turbine flow meter installation schematic
Typical Turbine Flow Meter Installation Schematic
Courtesy Hoffer Flow Controls
Here are a few other things to consider about applying turbine flow meters:
  • Turbine flow meters are precision instruments and will not tolerate debris well. An installation should include a strainer configured to trap debris that may damage the instrument of hinder its operation.
  • For longevity, it is advisable to size the flow meter to avoid extended operation near the upper end of its rotational range. Excessive rotational speeds can accelerate wear on bearings.
  • Lower rotor mass will provide more rapid response to changes in flow, allowing use of the device in applications with flow pulsations.
  • Maintain sufficient downstream pressure to prevent flashing or cavitation. This condition will cause the instrument to produce readings higher than the actual flow rate.
  • Sufficient straight pipe length should be installed at the inlet and outlet of the flow meter to provide flow conditioning necessary for accurate readings. In some cases, a flow staightener may be needed on the upstream side.
  • The output signal from the pickup may need amplification or other signal conditioning. Electrically noisy environments or long cable lengths may require special treatment.
Careful consideration of what is necessary for proper operation will pay off with reliable and accurate performance, low maintenance, and a long service life. Share your flow measurement challenges with product application experts, combining your process knowledge with their product application expertise to develop effective solutions.


Friday, July 22, 2016

The Transit-Time Difference Method to Measure Flow

Transit-time flowmeter
Transit-time flowmeter
(courtesy of FLEXIM)
The transit-time difference method for measuring flow exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium.

Similar to a swimmer swimming against the current, an ultrasonic signal moves slower against the flow direction of the medium than when in the flow direction.

For the measurement, two ultrasonic pulses are sent through the medium, on in the flow direction, and a second on against it. The transducers are alternatively working as an emitter and receiver.

The transit-time of the ultrasonic signal propagating in the flow direction is shorter than the transit-time of the signal propagating against the flow direction.

A transit-time difference, Δt, can thus be measured and allows the determination of the average flow velocity based on the propagation path of the ultrasonic signals.

An additional profile correction is performed by the proprietary FLEXIM algorithms, to obtain an exceptional accuracy on the average flow velocity on the cross-section of the pipe - which is proportional to the volume flow.

Since ultrasounds propagate in solids, the transducers can be mounted onto the pipe. The measurement is therefore non-intrusive, and thus no cutting or welding of pipes is required for the installation of the transducers.

Tuesday, May 31, 2016

The Coriolis Effect Simply Explained. And Then Not So Simply Explained.

This video very simply (and very elegantly) demonstrates the Coriolis Force through the use of a ordinary garden hose.




An Now the Not So Simple Explanation

This force occurs, when the medium being measured is flowing at velocity ν through a tube that is rotating around an axis perpendicular to the direction of flow at angular ϖ.
coriolis force

When the medium moves away from the axis of rotation it must be accelerated to an increasingly high peripheral velocity. The force required for this is called Coriolis force, after its discoverer. The Coriolis force reduces the rotation. The opposite effect occurs, when the medium flows towards the axis of rotation. Then the Coriolis force amplifies the rotation.

The formula for the Coriolis force is as follows:
coriolis force

The entire measurement tube is deformed slightly by the Coriolis forces, in the way shown. This deformation is registered by movement sensors at points S1 and S2 .

For practical exploitation of this physical principle, it is sufficient for the tube to perform sympathetic oscillations on a small section of a circular path. This is achieved by exciting the measurement tube at point E by means of an electromagnetic exciter.

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.


The general construction of a Coriolis mass flowmeter looks like the following:
Coriolis flowmeter
Coriolis flowmeter diagram (Yokogawa)

Monday, May 16, 2016

An Economical, No Maintenance Gas and Liquid Flow Measurement Solution for Tight Spots

Wafer-Cone
Wafer-Cone Internal View
Engineers with small line size processes rely on the versatile are challenged finding a flowmeter with accuracy and repeatability. Many times orifice plates are specified for the job. An excellent alternative to an orifice plate, and one that should be carefully considered, is the Wafer-Cone, manufactured by McCrometer.

Unlike an orifice plate, the Wafer-Cone has no sharp edges so extensive maintenance and inspection are not required. The flangeless Wafer-Cone® is a space-saving unit is that is easy to install and ideal for tight-space installations and retrofits.  The cone conditions the flow so the Wafer-Cone requires minimal upstream or downstream pipe runs and can be installed virtually anywhere in a piping system.

Ideal for small line sizes and with no moving parts, no replacement parts or scheduled maintenance,
Wafer-Cone
Components of Wafer-Cone
this meter offers a low cost of ownership and long life.

This device also offers interchangeable cones for flexibility in accommodating changing flow conditions without the need for recalibration. When flow conditions change over time, the cone can be removed and replaced with a cone at a different beta ratio eliminating the need to buy a new meter.

Finally, the Wafer-Cone is available with remote or direct mount configuration. The direct mount option minimizes installation labor while ensuring accuracy. Direct mounting the transmitter eliminates impulse lines, which not only lowers installation costs but also reduces potential leak points by more than 50 percent. Simple plug-and-play mounting ensures the meter is installed correctly the first time and eliminates a potential source of ow measurement errors.

Wafer-Cone with Transmitter
Wafer-Cone
with Transmitter
Common applications are:
  • Natural Gas Wellheads
  • Gas, Water, and CO Injection
  • Gas Lift
  • Compressor Anti-Surge
  • Fuel Gas
  • Separator Discharge
  • Biogas Reactors
  • Cooling Systems
  • Plant HVAC
  • Process Gas Lines
Advantages of the Wafer-Cone
  • No straight pipe runs
  • Maximum flexibility
  • Economical
  • Accuracy to +/- 1%
  • Repeatability to 0.1%
  • Machineable in any material
  • No moving parts, low maintenance

Wednesday, April 27, 2016

Eliminate Shutdown and Cost When Pulling Flow Meters for Calibration Verification

FCI's VeriCal
FCI's VeriCal System Diagram
FCI's VeriCalTM In-Situ calibration verification system provides you the ability to perform periodic field validation and verification of your FCI flow meter's measuring performance without extracting the meter from the pipe or process. Calibration is complete in minutes without removing the meter from the pipe or process. In the past, flow meters had to endure the cost and hassle of being pulled from the process, then returned to the manufacturer or a calibration lab for testing. and then shipped back for re-installation.

The FCI ST100 is quickly becoming the industry benchmark in process and plant air/gas flow measurement. Designed for rugged industrial processes and plants, ST100 Flow Meters include service up to 850oF (454oC) and are available with both integral and remote (up to 1000 feet [300 meters]) electronics versions. The ST100 is agency approved for hazardous environments, including the entire instrument, the transmitter and the rugged, NEMA 4X/IP67 rated enclosure. Instrument approvals in addition to SIL-1 include ATEX, IECEx, FM and FMc.

Now, with the VeriCalTM In-Situ Calibration Verification System with the ST100 Series Thermal Mass Flow Meter, routine flow meter calibration doesn’t require pulling the meter, installing a spare and paying a lab fee. 

The video below demonstration illustrates the VeriCalTM procedure and ease of sensor installation. Validate performance on-site in minutes and comply with ISO and local regulations for periodic calibration verification with FCI's In-Situ Flow Meter Calibration Solution.

Thursday, January 28, 2016

Advanced Differential Pressure Flowmeter Technology

McCrometer V-Cone
McCrometer V-Cone
The McCrometer V-Cone® flowmeter accurately measures flow over a wide range of Reynolds numbers, under all kinds of conditions and for a variety of fluids. It operates on the same physical principle as other differential pressure-type flowmeters, using the theorem of conservation of energy in fluid flow through a pipe.

The V-Cone’s remarkable performance characteristics, however, are the result of its unique design. It features a centrally-located cone inside the tube. The cone interacts with the fluid flow, reshaping the fluid’s velocity profile and creating a region of lower pressure immediately downstream of itself. The pressure difference, exhibited between the static line pressure and the low pressure created downstream of the cone, can be measured via two pressure sensing taps. One tap is placed slightly upstream of the cone, the other is located in the downstream face of the cone itself. The pressure difference can then be incorporated into a derivation of the Bernoulli equation to determine the fluid flow rate. The cone’s central position in the line optimizes the velocity profile of the  ow at the point of measurement, assuring highly accurate, reliable  ow measurement regardless of the condition of the  ow upstream of the meter.

The V-Cone is a differential pressure type flowmeter. Basic theories behind differential pressure type flowmeters have existed for over a century. The principal theory among these is Bernoulli’s theorem for the conservation of energy in a closed pipe. This states that for a constant  ow, the pressure in a pipe is inversely proportional to the square of the velocity in the pipe.

Simply, the pressure decreases as the velocity increases. For instance, as the fluid approaches the V-Cone meter, it will have a pressure of P1. As the fluid velocity increases at the constricted area of the V-Cone, the pressure drops to P2. Both P1 and P2 are measured at the V-Cone’s taps using a variety of differential pressure transducers. The Dp created by a V-Cone will increase and decrease exponentially with the flow velocity. As the constriction takes up more of the pipe cross-sectional area, more differential pressure will be created at the same flowrates.