This article will examine the use of fluids in the sugar industry and cogeneration plants. First, we will discuss the various fluids present, including cane juice, imbibition water, syrup, massecuite, molasses, return condensate, boiler feedwater, main steam, and exhaust steam.
The selection of the proper flow meter is an essential part of the process industry. With various fluids available, choosing a suitable flow meter for the application is vital. This article will help professionals identify the best flow meter for their needs.
How Are Flow Meters Classified?
- Mechanical types: orifice plates, mass flow meters and flow nozzles.
- Electrical type: Electromagnetic flow meter.
- Inferential type: Rotameter
How Are Flow Meters Selected?
- For lower viscosity and conductivity
- Orifice meter
- Mass flow meter
- For higher viscosity and conductivity
- Magnetic flow meter
The table below shows the selection of flow meters according to the type of fluid.
The Principle of the Orifice Meter states that when an orifice plate is installed in a pipeline, it causes a decrease in the flow velocity and an accompanying reduction in pressure. This decrease in pressure creates a maximum velocity and minimum pressure drop at the vena contract – effectively reducing the fluid flow through the orifice. Professional engineers rely on this principle to accurately measure and control the flow of fluids in pipelines.
The orifice works on two principles:
- Continuity equation: According to this equation, the flow is inversely proportional to the fluid velocity.
Q=A1*V1=A2*V2 = Constant
- Bernoulli’s equation: This equation provides a basis for correlating the increase in velocity head with the decrease in pressure head.
- P1 & P2 are pressures at sections 1 & 2
- V1 and V2 are the speeds of the 1st and 2nd segments
- Z1 & Z2 are raising at sections 1 & 2
The velocity V2 increases in section 2 and therefore the kinetic energy in section 2 is higher
Any change in the flow velocity through the restrictor can therefore be measured by the differential pressure across it.
Working of Orifice Meter
The orifice plate is a device used to measure a fluid’s flow rate in line with a pair of flanges. It obstructs the form of an orifice, with its cross-sectional area of “A” being more significant than that of “B.”
As the fluid approaches the orifice, the flow lines run parallel and widely spaced. Near the orifice, the fluid flow slowly converged at the upstream side and diverged at the downstream side, creating the minimum flow area.
At the upstream side of the orifice, the static pressure is more significant than at the vena contracta, which is the downstream point of the orifice where the fluid flow rate is determined. This is because the position of the vena contracta varies according to the fluid flow rate.
Vena contracta: It is the region in the fluid flow near the orifice where the diameter of the stream is less, and the velocity of fluid flow is maximum.
The beta ratio is the ratio of the orifice bore to the internal pipe diameters.
The beta ratio is given by β = d/D
D = diameter of the restriction
D = diameter of the pipe
It consists of an orifice plate as a primary element and a liquid column manometer or flow transmitter as a secondary element to measure the flow rate of the fluid.
What are the different types of Orifice Plates?
- Concentric: This orifice plate is specially designed to precisely measure water, steam, and gas. Its unique Beta Ratio ensures that regardless of the fluid in question, it provides accurate readings every time. With its professional construction and reliable results, this is the perfect tool for any measurement task.
For liquid, the beta ratio falls between 0.15 to 0.75.
For best results, the beta ratio must lie between 0.4 and 0.6.
- Eccentric: This orifice plate is a specialized device for measuring fluid containing solid particles, oil with water, and wet steam. It features an eccentric hole that is offset from the center, thus reducing the problems associated with services of fluids containing solid materials. The flange tap in the eccentric-type orifice plates must be positioned either at 90º or 180º to the opening, using either vena contracta or flange taps. This ensures accurate and reliable measurements for a variety of services. With its superior design and reliable measurements, the Eccentric Orifice Plate is ideal for professionals needing a reliable and accurate measuring device.
- This orifice plate is essential for accurately measuring slurry and colloidal fluids. Its unique design enables a hole in the form segment of a circle, and for maximum accuracy, the tap location should be 180º from the center of tangency. With its professional design and accuracy, this orifice plate is a must-have for any task involving slurry and colloidal fluids.
- Simple construction and inexpensive.
- Easily fitted between flanges.
- They have no moving parts.
- Large range of sizes.
- Suitable for all types of fluids.
- Can be installed at any angle.
- Low discharge coefficient.
- The density, pressure & viscosity fluctuations affect the accuracy by 1%.
The operating principle of a magnetic flow meter is based on Faraday’s law of magnetic induction. This law states that when a conductor moves at right angles through a magnetic field, it produces a voltage across the conductor that is directly proportional to the voltage of the conductor.
In a magnetic flow meter, the conductive fluid works as a conductor in a magnetic field. According to Faraday’s law, when this conductive fluid flows through the magnetic field, it generates a voltage. This voltage is directly proportional to the fluid flow rate; the greater the flow rate, the greater the voltage (EMF) generated.
This reliable and efficient method of measuring fluid flow allows professionals to accurately measure flow rate, providing fast and accurate readings in various applications.
The volume flow rate is given by:
Q = V* (π*D2/4)
- B — Magnetic flux density
- L — The length of the conductor
- V — The velocity of conductive fluid
- D — Pipe diameter
- Q — Volume flow rate
Working of Magnetic Flow Meter
- A magnetic flow meter is an effective tool for measuring fluid volume in a pipeline. This meter is installed between a pair of flanges and is designed to measure electrically conductive fluids. 2
- When the fluid passes through the flow meter, it can be visualized as a continuous movement, as it contains both positive and negatively charged particles evenly distributed.
- This continuous flow of charged particles produces an electromotive force applied to an electromagnetic coil. This coil generates a constant magnetic field across the cross-sectional area of the flow tube.
- The magnetic field then applies a force to the charged particles, causing them to separate and collect on the opposite side of the flow tube.
- With this setup, the electromagnetic flow meter can accurately measure the fluid volume in the pipeline.
- Now, electrical voltage is generated when a magnetic field is applied to the flow meter; this electrical voltage is picked up by the electrodes and sent to a transmitter either mounted on the flow meter or connected remotely. 3
- The induced voltage is directly proportional to the velocity of the fluid in the pipe, allowing us to quickly calculate the flow volume by knowing the fluid velocity and the cross-section area of the pipe.
- Minimal pressure drop.
- Measure slurries and greasy materials.
- Handle small as well as large flow rates.
- The parameters like viscosity, density, and temperature don’t affect the flow measurement.
- High response.
- Low maintenance.
- No moving parts.
- Small-length meters are cumbersome and expensive.
- The fluid flow pipe must run full, so there is a need for regulating valves at the upstream side of the meter.
- These meters may be used best for fluids that have affordable electric conduct.
The Mass Flow Meter utilizes the Coriolis Effect to measure the flow rate of a liquid or gas. This effect is introduced by vibrating the liquid or gas tube passing through with an undersized actuator. The resulting twisting force creates a phase shift that can be measured, allowing for accurate flow measurement. By using this principle, professionals can accurately measure the flow rate of liquids and gases.
Working of Mass Flow Meter
- A highly sophisticated flow meter uses a tube inside its body to measure the direct flow of fluids. If there is no flow in the tube, an exciter is used to create a constant and uniform oscillation.
- When fluid starts to flow through the tube, the liquid inertia causes an additional twisting of the oscillation, known as the Coriolis Effect. This, in turn, causes the upstream and downstream sections of the tube to oscillate in different directions simultaneously. The sensors pick up this change in oscillation, referred to as the phase shift, and use it to measure the fluid’s direct flow through the line.
- With its sophisticated technology, the flow meter is a reliable and professional tool for measuring the direct flow of fluids.
- The fluid velocity is proportional to the more significant deflection of the oscillating tube.
- To measure the velocity of a fluid, we need to use a Coriolis mass flow meter. This device can determine the flowing fluid’s density and how often it moves back and forth in one second.
- The tube oscillation relies upon the viscosity of the flowing fluid. Putting a tube filled with a lower viscosity fluid like water or cane juice into motion will oscillate more frequently than a higher viscosity fluid like honey or syrup.
- The oscillating frequencies are direct measures of fluid density and flow and are determined simultaneously during tube oscillations. Using this device, you can simultaneously measure mass flow rate, volumetric flow volume density, and temperature.
- Capable of measuring complex handling fluids.
- Independent of density changes.
- No routine maintenance is required.
- High accuracy.
- Not to be had for massive pipes (as much as one hundred fifty mm only)
- Expensive in comparison to different flow meters.
- Difficulty in measuring low-strain gasses.
VARIABLE AREA FLOW METER (ROTAMETER)
The rotameter works at the precept of up-thrust pressure exerted with the aid of using fluid and pressure with the aid of using gravity. The stress distinction throughout an annular orifice is immediately proportional to the rectangular of the go with the drift rate.
The rotameter consists of a vertical column filled with a liquid having a given density and viscosity. A nozzle is placed in line with the orifice, which passes through the liquid column. When a fluid flows through this nozzle, it exerts pressure on the bottom of the column equal to its weight multiplied by its velocity squared. This pressure difference causes fluid to flow up through the orifice at a rate proportional to this pressure difference. The importance of fluid flowing up through the orifice is thus also proportional to its flow rate (which can be measured with an accuracy of 0.03%).
This principle has been used for measuring gas flow in pipelines for decades; it has also been applied to liquids such as water, oil, and alcohol in industrial applications where accurate measurements are needed to determine production rates or quality control levels.
Working of Rotameter
- The rotameter measures the velocity of a fluid flow. The meter consists of a hollow vertical tube with an oversized top and bottom end that is open to the atmosphere. The meter is placed vertically so that the more prominent upper end faces upward.
- The glass tube is made of borosilicate glass, which has high resistance to chemical and thermal shocks. It is also resistant to corrosion from metals such as steel or lead.
- The meter is mounted vertically, and fluid flows upward through it. The float comprises steel or lead, which weighs more than the fluid. The density of the float must be greater than that of the fluid flow rate measured.
- The float sits inside the rotameter and has a specific position relative to its surroundings at any given time. When this position changes, it impacts how much fluid flows through the tube; this creates an interference pattern between kinetic energy (motion) and potential energy (pressure).
- Low-pressure drop
- Handle any corrosive fluid
- High accuracy at lower flow rates.
- Provides linear scale.
- It ought to be hooked up in a vertical function only.
- Expensive for high temperatures and pressure.
- It can’t be used for liquid having a significant percentage of solid.
- Uncertainty of measurement.