Turbine flow meter
Turbine flow meter
A turbine flow meter is used for volumetric total flow and/or flow rate measurement and has a relatively simple working principle. As fluid flows through the turbine meter, it impinges upon turbine blades that are free to rotate about an axis along the center line of the turbine housing.
Turbine flow meters use the mechanical energy of the liquid to rotate a rotor within the flow stream. The rotational speed is directly proportional to the velocity of the fluid traveling through the meter. These meters are used in multiple industries to reliably measure liquids, gases and vapors.
Introduction
Turbine flow meters are used to measure clean, dry gases and liquids such as hydrocarbons, chemicals, gases and vapors, fuels and other types of liquids with lower viscosity, and for applications requiring highly accurate and precise measurements.
These turbine flow meters are mostly used for military applications. They are also used in blending systems in the petroleum industry. They are effective in aerospace and airborne applications for energy fuel and cryogenic (liquid oxygen and nitrogen) flow measurements.
Typically, their applications are found across various industries such as petroleum, automotive, laboratory and water treatment. In some cases, applications are also found in the beverage and chemical industry as well.
A few examples
- Particle cleanliness testing,
- Water treatment,
- Monitoring input flow to an analyzer,
- Dispensing chemicals in a laboratory
Turbine Flow Meter Working Principle
A turbine flow meter unit is constructed of a multiple-bladed rotor installed with a pipe in a perpendicular direction to the fluid flow. As the liquid flows through the blades, the rotor rotates. The rotational speed of the rotor is correlated to the flow rate of the liquid. The speed of the rotor can be sensed by various mechanisms such as magnetic pick-up, photoelectric cell, or gears. A tachometer can also be attached to the turbine for measuring its rotational speed which in turn helps in determining the liquid flow rate. After proper installation, turbine meters offer good accuracy, mainly with low-viscosity liquids. Hence, turbine meters are widely employed in applications where accurate measurements are required. When a turbine flowmeter is calibrated and operated for a single fluid, constant conditions, its turndown ratio can go beyond 100:1. Moreover, accuracy of a turbine flowmeter can be as good as +/-0.1%. The major problem associated with the usage of turbine meters is bearing wear. To prevent this problem, a “bearingless” turbine meter design has been introduced recently. Various turbine flowmeter designs have been manufactured. However, they all operate on the same basic principle which says “If a fluid moves through a pipe and acts on the vanes of a turbine, the turbine will start to spin and rotate. The rate of spin is measured to calculate the flow”.
specifications
Services:-
- Relatively clean liquids, gases, and vapors (some units for gas service are also covered.
Sizes :-
- 3/16 to 24 in. (5 to 610 mm) in flow-through designs.
Outputs:-
- Generally, linear frequency outputs are provided, but 4- to 20-mA DC can also be obtained through conversion.
Operating Pressure :-
- 1500 PSIG (10.3 MPa) in standard and 5000 PSIG (34.5 MPa) in special designs.
Pressure Drops:-
- Usually, one velocity head or about 3 to 5 PSIG (20 to 35 kPa).
Operating Temperature :-
- − 58 to 300 ° F ( − 50 to 150 ° C) in standard and − 328 to 840 ° F ( − 200 to 450 ° C) inextended pickup designs.
Turbine flow meter Installation Procedure
Before installation, the flow meter should be checked for foreign material and to ensure that the rotor spins freely. All upstream fluid lines should also be cleared of any debris. Also, make sure that fluid flow has been shut off and all pressure in the lines has been released prior to installing the flow meter into an existing system.
The flow meter must be installed with the flow direction arrow pointing in the direction of fluid flow. The flow direction arrow can be found on the side of the flow meter. The flow meter is designed to work in any orientation, but the preferred orientation is to have the meter installed in horizontal piping. The fluid to be measured is recommended to be filtered. The best location for the filter/strainer would be upstream of the flow meter, after any other system components, while maintaining straight piping requirements. The preferred plumbing setup is one containing a bypass line.
This allows meter inspection and repair without interrupting flow, as well as the ability
to cycle the fluid through the system filter before diverting to the flow meter. If a bypass line is not used, it is important that all flow control valves be located downstream of the flow meter.
For optimum flow meter performance a minimum length of upstream and downstream piping is required. It is recommended that a minimum length equal to 10 pipe diameters of straight pipe be installed directly on the upstream side of the flow meter and 5 pipe diameters on the downstream side of the flow meter. This helps to eliminate turbulence in the fluid. Having shorter pipe lengths, other system components and elbows to close to the flow meter may adversely affect the accuracy and repeatability of the flow meter. Piping should be the same size as the meter bore or port size.
Do not locate the flow meter or the connection cable close to electric motors, transformers, sparking devices, high voltage lines or place connecting cable in a conduit with wire supplying power for such devices. These devices can induce false signals in the flow meter coil or cable, causing the meter to read inaccurately
What is Turbine Flow Meter ?
Turbine flow meter use a free-spinning turbine wheel to measure fluid velocity, much like a miniature windmill installed in the flow stream.
Turbine flow meters are used in many industrial applications to measure the flow of liquid and gas. It consists of a multi-blade rotor mounted with a pipe perpendicular to the fluid flow. When the liquid passes through the blades, the rotor will spin. The speed of the rotor is depended upon the flow rate, so it can be measured by using a photoelectric cell or gears. This flow meter would convert the mechanical action of the turbine as the fluid flow rate. This device would rotate according to the flow in which it is placed, the number of revolution is proportional to the flow.
Turbine Flow Meter
The fundamental design goal of a turbine flow meter is to make the turbine element as free-spinning as possible, so no torque will be required to sustain the turbine’s rotation.
If this goal is achieved, the turbine blades will achieve a rotating (tip) velocity directly proportional to the linear velocity of the fluid, whether that fluid is a gas or a liquid:
Turbine tip velocity is quite easy to sense using a magnetic sensor, generating a voltage pulse each time one of the ferromagnetic turbine blades passes by. Traditionally, this sensor is nothing more than a coil of wire in proximity to a stationary magnet, called a pickup coil or pick-off coil because it “picks” (senses) the passing of the turbine blades.
Magnetic flux through the coil’s center increases and decreases as the passing of the steel turbine blades presents a varying reluctance (“resistance” to magnetic flux), causing voltage pulses equal in frequency to the number of blades passing by each second. It is the frequency of this signal that represents fluid velocity, and therefore volumetric flow rate.
Turbine Measuring Principle
A turbine flow meter is constructed with rotor and blades that use the mechanical energy of the fluid to rotate the rotor in the flow stream. Blades on the rotor are angled to transform energy from the flow stream into rotational energy. The rotor shaft spins on bearings: when the fluid moves faster, the rotor spins proportionally faster. Shaft rotation can be sensed mechanically or by detecting the movement of the rotor blades.
Rotor movement is often detected magnetically, where movement of the rotor generates a pulse. When the fluid moves faster, more pulses are generated. Turbine flow meter sensors detecting the pulse are typically located external to the flowing stream to avoid material of construction constraints that would result if wetted sensors were used. The RPM of the turbine wheel is directly proportional to the mean flow velocity within the tube diameter and corresponds to the volume flow over a wide range.
A flow transmitter processes the pulse signal to determine the flow of the fluid. Flow transmitter and sensing systems are available to sense flow in both the forward and reverse flow directions. High accuracy turbine flowmeters are available for custody transfer of hydrocarbons and natural gas. This fuel flow meter often incorporates the functionality of a flow computer to correct for pressure, temperature, and fluid properties in order to achieve the desired accuracy for the custody transfer application.
Care should be taken when using a turbine flow meter on fluids that are non-lubricating because the flowmeter can become inaccurate and fail if its bearings prematurely wear. A turbine flow meter can be outfitted with grease fittings for applications with non-lubricating fluids. In addition, a turbine flow meter that is designed for a specific purpose, such as natural gas service, can often operate over a limited range of temperatures (such as up to 140oF or 60ºC) whereby operation at higher temperatures can damage the flowmeter.
A turbine flow meter is less accurate at low flow rates due to rotor/bearing drag that slows the rotor. Care should be taken when operating these flowmeters above approximately 5 percent of maximum flow. A turbine flow meter should not be operated at high velocity because premature bearing wear and/or damage can occur. When measuring fluids that are non-lubricating, bearing wear can cause the flowmeter to become inaccurate and fail. Bearing replacement may be needed in some applications to maintain good accuracy. Application in dirty fluids should generally be avoided so as to reduce the possibility of flowmeter wear and bearing damage.
Turbine flow meters have moving parts that are subject to degradation with time and use. Abrupt transitions from gas flowmeter applications to liquid flowmeter use should be avoided because they can mechanically stress the flowmeter, degrade accuracy, and/or damage the flow meter. These conditions generally occur when filling the pipe and under slug flow conditions. Using the turbine flow meter for two-phase flow conditions such as steam flow metering applications can also cause a turbine flow meter to measure inaccurately.
A turbine flow meter measures the velocity of liquids, gases and vapors in pipes, such as hydrocarbons in fuel flow measurement, chemical flow metering, water flow metering, cryogenic liquid flow metering, air or gas flow metering, and general industrial flow metering. High accuracy turbine flowmeters are available for custody transfer of hydrocarbons and natural gas. A mass flow computer is often used in custody-transfer applications to correct for pressure, temperature and fluid properties in order to achieve the desired accuracy. Other low viscosity applications are tap and demineralized water, fuel flow meter solvents, and pharmaceutical fluids.
How turbine flow meter is constructed ?
The major part of this device is a multi-blade rotor and this rotor is mounted at an angle that the fluid flow can rotate the rotor. A ball bearing supports the rotor on a shaft which is retained in the flow meter housing by shaft support section. A magnetic pick up is mounted to the turbine wheel, and the sensor would record the voltage pulse that is created. Then the voltage information is then translated into actual flow meter reading.
What is the principle of turbine flow meter and how does it work ?
The turbine is rotated by the flowing fluid, these rotating blades would create pulses that would be recorded and the flow rate is determined by this. The pulse rate is depended upon the flow rate. This device would convert the mechanical action of the rotating turbine in the liquid flow around an axis into a user-readable rate of flow. The blades on the rotor is placed in a way that, can transform the energy of the flow into rotational energy. The rotor shaft spins on the bearings when the fluid moves faster then the rotor would spin faster too. These flow meters are used to measure the velocity of fluids and gases in pipes. Shaft rotation is sensed mechanically or by the blade movements. The movement of the blade is also detected magnetically. More pulse would be generated when the fluid flows faster and this flow could be measured, the transmitter would process the pulse signal to determine the flow rate. These meters can be used when accuracy, compact size, and fast response is required.
Industrial used
Oil & Gas
- Water injection
- Test and production separators
- Disposal wells
- Hydraulic fracturing
- Chemical injection
- Natural gas pipelines
Aerospace/Defense
- Engine Testing
- Fuel flow measurement
- Shipboard reverse osmosis systems
- Monitor fuel supply to ship engines
Pharma-Bio Tech, Food & Beverage
- Sanitary measurement
- Pill coating
Power Generation
- Custody transfer
Industrial & Municipal
- Building automation
- HVAC
- Water metering
Cryogenics
- Liquids measurement for plant applications and truck deliveries
Turbine flow meter Advantage
- Wide flow rangeability including low flow rates
- Turndown ratio is up to 35:1
- Good level of accuracy at an economic price
- Simple, durable construction
- Easy to install and maintain
- Flexible connection to flow instruments for flow control
- Wide variety of process connections
- Turbine meters can operate over a wide range of temperatures and pressures
- Low pressure drop across the turbine
- Provides a convenient signal output
Disadvantage of turbine flow meter
- High cost
- Limited use for slurry applications
- Problems caused by non-lubricating fluids
- Less accurate at low flow rates
- It cannot be operated at high velocity
- Moving parts
- Sensitive to flow profile
- Interchangeability from unit to unit is very poor
- The bearing is depended on the cleanliness and lubricity of the process fluid
- Wear and tear could happen to the turbine blades and it needs to be calibrated frequently
- For certain liquid applications, there could be problems such as cavitation, specific gravity, and viscosity
Turbine flow Meter Limitations
- Requires constant backpressure to prevent cavitation
- Accuracy adversely affected by bubbles in liquids
- Turbine meters can be used with clean liquids and gases only (may need to install a strainer upstream to prevent damage from particulates)
- Not applicable for measuring corrosive fluids
- Requires a turbulent flow profile (consistent fluid velocity across the pipe diameter) for accuracy
- Sensitive to changes in fluid viscosity
- Require a straight run of pipe before and after the turbine meter to allow swirl patterns in the flow stream to dissipate
- May not function properly with high viscosity fluids where the flow profile is laminar
Turbine Flow Meter Application
- is used in the blending system of the petroleum industry
- Airborne applications for energy fuel and cryogenic flow measurement
- Chemical industries
- Food and beverage
- Oil and gas
- Refining
- Semiconductor
- Agricultural
- Pharmaceutical
- Photo development
- Process control
- Food beverage dispensing
- The turbine meters are widely used for military applications.
- They are particularly useful in blending systems for the petroleum industry.
- They are effective in aerospace and air borne applications for energy-fuel and cryogenic flow measurements.
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