Review of Sensors Measuring FlowCHE 341: Process Controls Spring 2018Nina MalapitDayana ReyesCarolina Rojas-ChaidezNgan TranIntroductionFlowrate is an important variable that must be measured and controlled across a wide range of applications such as the petrochemical, pharmaceutical, utility distribution, and other industries. The transportation of fluid to and from destinations throughout the plant requires the implementation of flow meters to prevent tanks from overflowing, ensure the correct quantity of a chemical is added, maintain process conditions, quantify production, etc. Flowrate can be measured as a volumetric or mass quantity per unit time. In order to select the correct flow meter for a desired application, a few things to consider include the following: fluid type (gas, liquid, slurry), operating temperature and pressure, viscosity, corrosiveness, conductivity, easy of installation, accuracy, maintenance, and cost. There are various designs of flow sensors based on several driving principles such as differential pressure, the coriolis effect, and electromagnetism to name a few. Despite the many ways to measure flow, all flow meters contain a sensor component and a transmitter component to relay information to the control loop. The sections that follow explain the major forms of flow meters used in industry, the working principle behind its operation, main physical components, advantages, disadvantages, and typical application. Differential Pressure Flow Sensors (Orifice, Venturi, Nozzle, Pitot)Differential pressure is one of the methods to measuring flow and the principle was discovered by Swiss mathematician, physician Daniel Bernoulli about 300 years agoyoutube. In general, differential pressure flowmeters include primarily element places inside the pipe to create differential pressure and connected with a secondary element to transmit the measurement value from primary element to control system youtube2. There are many types of differential pressure flowmeter such as Orifice, Nozzles, Venturi and pitot tube meter.Orifice meter measures volumetric flow rate. It has an orifice plate with a hole on each side of the plate, there are tubes connect holes with a differential pressure sensor. Following Bernoulli’s principle, as the flow through the orifice increase, the pressure decreases because of the restriction through cross-section youtube. And the square root of the differential pressure proportional to the flowrate. Orifice flow meter is common use industry because it is inexpensive and all fluid can measure even though at high pressure and temperature. However, orifice flow meter creates high-pressure loss which effects on operating cost 1Venturi meter was discovered by Italian scientist Giovanni B Venturi. A venturi tube has an hourglass shape, therefore the pressure fluid traveling through the small cross-section of the tube drop lead to increase the flow velocity 2 As the flow through a venturi increase, the pressure decrease by Bernoulli’s principle. Like Orifice meter, the differential pressure directly proportional to the flow rate, however the pressure loss in venturi meter lower than Orifice meter. Venturi flow meter has a low-pressure loss but it expensive to install and manufacturing 3.Nozzles meter has flow through a funnel shape, therefore it can reduce the turbulence flow, lead to less pressure drop youtube. Nozzle meter is often use for flow with high velocity. Moreover, it is less expensive than Venturi but more expensive than Orifice meter.Pitot meter was discovered by Henri Pitot. The pitot tube is the bent glass tube, which one side of the tube placed in the center of the pipe to measure the total pressure and the other side place on the edge of the pipe to measure the static pressure 4. Like Orifice, Venturi and Nozzle meter, the pitot meter has the differential pressure proportional to the flowrate. Pitot flow meter is the cheapest and easy to buy. In the industrial, pitot meter measure air flow but not turbulence flow because it doesn’t accurate. 4Coriolis Flow Sensors Coriolis flow meters measure mass flow rate based on the principle of the Coriolis effect. This effect is often demonstrated by the swinging of a water hose from side to side. As water passes through the swinging hose, it begins to oscillate or twist. The apparatus consists of a tube inside the housing that is pulsed at a constant rate by an electromagnetic exciter. The tube swings in a two dimensional path when there is no flow through it. Sensors are located upstream and downstream of the exciter to detect twists or oscillations once fluid flows through the tube. The twisting of the tubes are directly related to the mass flow rate via the phase shift between the upstream and downstream sensor. The faster the flow, the greater the deformation or extent of twisting. Density of the fluid can also be determined based on the deflection frequency the sensor registers. Denser fluids such as honey will produce lower oscillation frequencies than a less dense fluid such as water. Using a Coriolis flow sensor is advantageous when transporting corrosive fluids or fluids with unknown properties 5. These sensors are incredibly accurate with highly repeatable results. However, the readings become less accurate for low flows (such as for gases) and the initial cost of the sensor can be expensive 5.Vortex Flow SensorsVortex flow meter is used for measuring the flow velocity of gases and liquids in pipelines when flowing full which was a principle developed by the Karman vortex shedding street. Vortex flow meters are commonly used for steam measurements, flow of liquid suspensions and for general water applications. Although vortex flow meters can also be used for pharmaceuticals, there are some advantages and disadvantages in using the vortex flow meter. Some disadvantages are that it can’t be used from low to medium pressure drop due to the flow path and that it can’t be used for very low flow rates. Although these are some drawbacks vortex flow meters have more advantages like that it can be used for liquids, gases, and steam, its also cost less, it’s stable for long term accuracy and repeatability, can be used in a wide range of temperatures and pipe sizes and can measure temperature and density. 6Ultrasonic Flow SensorsUltrasonic flow meter is a type of flow meter that can either be a transit time ultrasonic flow meter that measures velocity of a fluid with ultrasound to calculate volume flow or a doppler ultrasonic flow meter. The transit time ultrasonic flow meter is done by measuring the average velocity along the path of an emitted beam of ultrasound and by measuring the frequency shift from the Doppler Effect. Ultrasonic flow meters are commonly used with water and oils. Like every flow meter there are some advantages and disadvantages. Some advantages to why this flow meter would be used is that it is unaffected by changes in temperature, density or viscosity, its bi-directional flow capability, corrosion resistant and consumes less power. Some disadvantage is that its highly dependent on the Reynolds number, it requires certain types of pipe material like cast iron or cement, must be recalibrated frequently and gases can’t be measured accurately. For the doppler ultrasonic flow meter it is commonly used in raw sewage. Which include some advantages like its not affected due to change in viscosity, used for measuring in large water pipes and that the cost is independent of line size. Even though those are some advantages, some disadvantages is that it can detect some sound energy that causes interference in readings, it depends on the particle size, concentration and velocity and needs recalibration frequently. 6Electromagnetic Flow Meters Electromagnetic flow meters use Faraday’s Law of Electromagnetic Induction to determine the flow of liquid in a pipe, this law states that the voltage induced across any conductor as it moves at right angles through a magnetic field which is proportional to the velocity of that conductor 6. Electromagnetic flow meters are commonly used in water/wastewater, chemical, food and beverage, pulp and paper, metals and mining, and pharmaceutical industries. Some of the advantages of using these flow meters are: they have no flow obstruction, they are available with DC or AC power, they can measure multiphase and they can be used with fluids with conductivity greater than 200 umhos/cm. However, there are some disadvantages in using electromagnetic flow meters which include: they are above average cost, their accuracy is affected by slurries containing magnetic solids and they are large size meters.Thermal Flow Meters Thermal flow meters operate by monitoring the cooling effect of a gas stream as it passes over a heated transducer, they are based on King’s Law that reveals how a heated wire immersed in a fluid flow measures the mass velocity at a point in the flow. It is based on the principle of conductive and convective heat transfer 6 . Gas flow applications is where thermal flow meters are used the most. One advantage of using thermal flow meters Is that they can measure the flow of some low-pressure gases that are not dense enough for Coriolis meters, however these flow meters only can be used for gas flows only and also they are subject to blockage by foreign particles.References5″Coriolis Mass Flowrate Technology.” Universal Flow Monitors. http://www.flowmeters.com/coriolis-mass-technology6 Marionilo Labares, Crocodile Wrangler at Quezon, Bukidnon Follow. “Flow Sensors.” LinkedIn SlideShare, 22 Nov. 2015, www.slideshare.net/MaRi0niLo/flow-sensors-55384766.