Friday, May 31, 2019

Rotameters a.k.a Variable Area Flow Meters

Rotameter
Rotameter
(Yokogawa)
Rotameters have diverse industrial processing applications that range from simple to sophisticated. The devices are easy to install, require no electrical connection, and provide direct flow rate reading. They provide fail-safe flow rate in different situations. 

The post will highlight the workings of rotameters, also known as a variable area flow meter.

Rotameters: An Overview 

Invented by German inventor Karl Kueppers in 1908, rotameters measure the volumetric flow rate of liquids and gases. The device was so named because it functions by rotating in a tube. 

Important elements of a rotameter include the tube and the float. 

The tube is fixed vertically and liquid is fed from the bottom. The fluid is fed from the bottom that travels upward and exits from the top. The float remains at the bottom when no liquid is present and rises upward when fluid enters the tube. 

The float inside the tube moves in proportion to the rate of fluid flow and the area between the tube wall and the float. When the float moves upward, the area increases while the differential pressure decreases. A stable position is reached when the upward force exerted by the fluid is equal to the weight of the float. A scale mounted on the tube records the flow rate of the liquid. 

Every float position shows a specific flow rate for the viscosity and density of a liquid. The device helps in determining the flow rate by matching the position of the float to a scale on the rotameter. The flow can be adjusted manually using a built-in valve. 

Types of Rotameters 

Rotameters can be categorized by the type of tube. A sharp metering edge is located on the float from where the reading is observed by a scale on the tube. The connections and end fittings of the various types of rotameters are different. 

Glass Rotameter
Rotameter
Glass rotameters
(Yokogawa)

The basic glass rotameters consist of borosilicate glass tube while the float is made of either glass, plastic, or stainless steel. The most common combination is a glass tube and metal float. This is suitable for a measure the flow rate of liquid of low to medium temperature and pressure. 

Flow rate is determined by the spring and piston combination of the rotameter. The materials and fittings should be chosen as per the temperature and pressure of the liquid. 

Metal Rotameter

Metal tube rotameters are another type that is suitable for temperatures and pressures beyond the glass tubes. They are generally manufactured of stainless steel, aluminum, and brass. The piston position is determined by the mechanical and magnetic followers that can be read from the outside of
the tube. 

Rotameter
Metal rotameter
(Yokogawa)
The meters are generally used for steam applications where glass tube rotameters are not suitable. They are also suitable in situations where other forces would damage the glass metering tubes. 

Industrial Applications of Rotameters

The use of rotameter extends across different industries. The device is extensively used in industries since its an economical way to measure a range of flow rates in almost any conditions. 

Sample Process Analysis 

Rotameters are widely used in sample process analysis. A device with 4 to 20 mA output is used to measure the flow of a sample system. Monitoring the flow rate ensures that the system does not become plugged that could result in big problems. The device can indicate when the flow starts to drop so that the maintenance crew can address the problem before it results in major damage. 

Transport of Liquid Natural Gas 

LNG must be re-gasified during transport to prevent system overpressure that could cause major damage to the storage system. Rotameter can measure the flow rate of vented vapor even at very low temperature. They are ideal for determining the LNG flow rate during transport due to being low cost and providing an accurate reading. 

Rotating Equipment 

Rotameters are also used in measuring the flow of liquid in large rotating equipment. They are used to measure the flow rate of dry gas, coolants, lubricant fluids to ensure safe operations. The device helps in monitoring of coolant flows a lube oil. The flow can be measured continuously due to the use of 4— 20 mA transmitting rotameters.  

Benefits of Rotameters

Rotameters, or variable area flow meters are cost-effective for use in different industrial applications. The price and low maintenance of the device contribute to significant savings for industrial concerns. 

Another advantage of rotameters is that no external power is required. They are mechanical device and no external power source is required to measure the flow rate. This makes it possible for the device to be used in remote and hazardous areas where installing an external power supply can be costly. 

The design of the rotameter allows not the only the measurement of fluid flow but also determine the quality of the liquid. The crew members can see whether the fluid is dirty thereby requiring a change of filter. They can also know whether bubbles are present in the liquid and also whether the liquid is of the correct color. 

Rotameters can be installed along with other flow measuring devices to ensure accurate readings. The device can continuously determine an accurate flow rate. They are simple to install and easy to maintain. Just connect the process line to rotameter’s inlet and outlet pipe. That’s why they are commonly used in many industries where it’s critical to accurately measure the flow rate of the liquid. 

Contact Power Specialties, Inc. with any questions regarding the use of rotameters. Call them them at (816) 353-6550 or visit https://powerspecialties.com.

Friday, May 24, 2019

Understanding the Operation of Coriolis Flow Meters

Coriolis Flow Meter
Coriolis flow meter (Yokogawa ROTAMASS)
The Coriolis patents for industrial application were filed back in the 1950s, and the first Coriolis flow meter was introduced in the 1970s. The device can accurately measure the density, mass flow, volumetric flow, and temperature of almost all types of fluids.

Coriolis flow meters are used in a variety of industries ranging from oil and gas, petrochemicals, and food to chemical, life sciences, and — particularly — in transfer applications.


How Does a Coriolis Flow Meter Work?

Coriolis flow meters work on the principle of Coriolis Force that was first explained by a French engineer and mathematician Gaspard-Gustave de Coriolis in the 19th century.  The Coriolis force represents an inertial force that acts on bodies in a rotating frame of reference.

Also known as inertial mass flow meters, Coriolis flow meters measure fluid flow through inertia. The device has one or more measuring tubes that vibrate due to the force produced by an actuator. The twisting force inside the measuring tube is directly proportional to the mass flow of the liquid.

Measurement Principle of the Coriolis Flow Meter (1)
(courtesy of Yokogawa)
Coriolis meters have sensors inside the measuring flow tube made of magnet and coil assemblies. The sensors are located both at the inlet and outlet of the tube. A voltage in the form a sine wave is created as the coils move through the magnetic field.

The sine waves are in phase with each other when there is no liquid flow. Once the liquid flows through the tube, the measuring tubes twist depending on the mass flow. The sensors detect the extent of the twist by assessing the phase shift in the sine waves. The difference in phase shift helps in determining the mass flow rate.

Volumetric flow is determined by dividing the mass flow rate by the density of the liquid.

Density change is determined by assessing the change in oscillation frequency in response to the excitation inside the tube. The higher the mass flow rate, the lower will be the frequency change and density of the liquid flow.
Measurement Principle of the Coriolis Flow Meter (2)
(courtesy of Yokogawa)

Lastly, Coriolis flow meters can also be used to measure the temperature inside the tube. The device has sensors inside the tube that can detect temperatures of up to 752 F or 400 C.

The Pros and Cons of Coriolis Flow Meters  

Coriolis flow meters can assess liquid flow in both forward and reverse directions. Advanced Coriolis meters have dual curved tubes that can measure with more accuracy. Moreover, the device with curved tubes is characterized by lower pressure drop, making them ideal in specific situations such as wastewater handling, chemical processing, pulp and paper processing, and oil and gas industries.

Another application of Coriolis flow meters is in the pharmaceuticals and food and beverage industries. They can be used with a straight tube design so they are easy to clean. The flow meters are also used in scientific studies for measuring corrosion and assessing liquids and gases. In addition, the flow meters are used in mining operations to monitor liquid flow rate.

While Coriolis meters allow accurate assessment of fluid flow, they are not free from errors. The device can show inaccurate reading when air bubbles are present. The bubbles create splashing that results in generate inaccurate readings. They change the energy required for tube oscillation, resulting in a false assessment of fluid flow.

A lot of energy is spent in the vibration of the tube, especially in case of large spaces. This can also result in failure of accurate assessment of liquid flow inside the tube.

Installation and Calibration of Coriolis Flow Meter

Coriolis flow meter must be installed with full liquid so that no air gets trapped inside the tube. The meter should also be drained completely before use. The ideal location for the flow meter is a vertical pipe mount with an upward flow of fluid.

The Reynolds number is not a limitation with the Coriolis meter. In addition, there is no need for accounting for swirl and velocity profile distortion. As a result, the device can be used without adjusting for straight runs of relaxation piping to condition the liquid flow.

An air release upstream of the meter should be installed if there is a likelihood of air bubbles. In addition, filters, strainers, or air/vapor eliminators can help prevent air bubbles inside the tube. Control valves can also be installed to increase the back-pressure and reduce the likelihood of flashing.

For more information on Coriolis flow meters contact Power Specialties by calling (816) 353-6550 or by visiting https://powerspecialties.com.