FLOW

“Flow” in the context of fluid dynamics generally refers to the motion and behavior of fluids, which can include liquids and gases. Fluid flow is a fundamental concept in physics and engineering, and it encompasses various characteristics and phenomena. Here are some key aspects of flow in the context of fluid dynamics:

1. 1. Types of Flow:

      • Steady Flow: The fluid properties at any given point do not change with time.
      • Unsteady Flow: The fluid properties at a point change with time.
      • Uniform Flow: The fluid velocity is constant at every point in space.
      • Non-Uniform Flow: The fluid velocity varies at different points.
   2. Flow Regimes:
      • Laminar Flow: Smooth and orderly flow characterized by well-defined layers.
      • Turbulent Flow: Chaotic and irregular flow with eddies and fluctuations.
      • Transitional Flow: An intermediate state between laminar and turbulent flow.
   3. Streamlines, Pathlines, and Streaklines:
      • Streamlines: Imaginary lines representing the instantaneous direction of the fluid velocity at every point.
      • Pathlines: Actual trajectories followed by fluid particles over time.
      • Streaklines: Lines formed by marking the fluid particles as they pass through a specific point in space.
   4. Flow Patterns:
      • Stagnation Point: A point in the flow where the velocity is zero.
      • Separation: Detachment of the fluid flow from a surface, often leading to the formation of vortices.
      • Reattachment: The point where the separated flow reattaches to the surface.
   5. Incompressible and Compressible Flow:
      • Incompressible Flow: The fluid density remains constant during the flow.
      • Compressible Flow: The fluid density changes significantly during the flow, requiring consideration of compressibility effects.
   6. Flow Velocity:
      • Average Velocity: The total volumetric flow rate divided by the cross-sectional area.
      • Local Velocity: The velocity of the fluid at a specific point in space.
   7. Mass Flow Rate:
      • The rate at which mass flows through a given cross-sectional area per unit time.
   8. Conservation of Mass:
      • In an incompressible flow, the mass flow rate remains constant along a streamline.
   9. Conservation of Energy (Bernoulli’s Equation):
      • Describes the relationship between pressure, velocity, and elevation in a steady, inviscid flow.
   10. Fluid Forces:
       • Drag Force: Resistance force experienced by a body moving through a fluid.
       • Lift Force: Upward force on a body due to pressure differences.
   11. No-Slip Condition:
       • The velocity of fluid particles at a solid boundary is zero, adhering to the boundary.
   12. Head Loss and Friction:
       • Loss of energy due to friction and other factors as fluid flows through pipes and channels.
   13. Flow Measurement:
       • Techniques such as flow meters and pitot tubes for measuring flow rates in practical applications.
   14. Critical Flow:
       • Flow conditions at which the flow velocity equals the speed of sound, often associated with choking in nozzles and diffusers.
   15. Mach Number:
       • A dimensionless parameter representing the ratio of flow velocity to the speed of sound.
   16. Cavitation:
       • Formation of vapor bubbles in a fluid due to low pressure regions, followed by their collapse, potentially causing damage to equipment.
   17. Shock Waves:
       • Compression waves associated with supersonic flow, leading to abrupt changes in pressure and temperature.
   18. Viscous Effects:
       • Effects of fluid viscosity on flow behavior, leading to boundary layers, shear stresses, and drag forces.

   Understanding and analyzing fluid flow is crucial in various engineering applications, including the design of aircraft, ships, pipelines, and many other systems involving the movement of liquids and gases.

   Flow Measurement

   Flow measurement is a critical aspect of various engineering and industrial processes where the precise quantification of fluid movement is essential. Accurate flow measurements are crucial for monitoring, controlling, and optimizing processes across a wide range of applications, from water distribution and wastewater treatment to oil and gas production. Several techniques and devices are employed for flow measurement, each suitable for specific scenarios. Here are some common methods of flow measurement:

   1. Orifice Plate:
      • An orifice plate is a thin, flat plate with a hole in the center, installed in a pipeline. The pressure drop across the orifice is used to calculate the flow rate.
   2. Venturi Meter:
      • Similar to an orifice plate, a venturi meter consists of a constricted throat in the pipeline. It measures the pressure difference between the throat and upstream to determine the flow rate.
   3. Flow Nozzles:
      • Flow nozzles are devices with a smooth, rounded inlet and a short cylindrical throat. They operate on the principle of creating a pressure drop to calculate flow rates.
   4. Magnetic Flow Meters:
      • These meters use Faraday’s law of electromagnetic induction. A magnetic field is applied to the fluid, and the voltage induced is proportional to the flow rate.
   5. Ultrasonic Flow Meters:
      • Ultrasonic flow meters use the transit time or Doppler shift of ultrasonic waves through a fluid to determine the flow rate.
   6. Coriolis Flow Meters:
      • Based on the Coriolis effect, these meters measure the deflection of a vibrating tube to calculate mass flow rate directly.
   7. Positive Displacement Meters:
      • These meters trap and measure fixed volumes of fluid as it moves through the meter. Examples include piston meters and rotary vane meters.
   8. Turbine Flow Meters:
      • Turbine meters have a rotor with blades placed in the fluid flow. The rotation speed of the rotor is proportional to the flow rate.
   9. Vortex Shedding Flow Meters:
      • These meters exploit the vortex shedding phenomenon created by an obstruction in the flow. The frequency of vortices is used to determine flow rates.
   10. Rotameters:
       • Rotameters consist of a tapered tube through which the fluid flows. The position of a float in the tube indicates the flow rate.
   11. Pitot Tubes:
       • Pitot tubes measure the dynamic pressure of a fluid. The velocity is determined using the difference between static and dynamic pressures.
   12. Mass Flow Controllers:
       • Commonly used in gas flow applications, these controllers measure and control the mass flow rate of a fluid.
   13. Weirs and Flumes:
       • Open channel flow measurement devices, such as weirs and flumes, use the geometry of flow over a structure to estimate the flow rate.
   14. Differential Pressure Flow Meters:
       • Devices like the flow nozzle, orifice plate, and venturi meter fall into this category, measuring flow based on the pressure difference across a constriction.
   15. Variable Area Flow Meters:
       • Also known as rotameters, these meters measure flow by the position of a float or piston in a tapered tube.

   Choosing the appropriate flow measurement method depends on factors such as the type of fluid, flow conditions, accuracy requirements, and the specific needs of the application. Each method has its advantages and limitations, and the selection is often based on the characteristics of the fluid being measured and the operational conditions of the system.

   • • Orifice Plate: Measures the pressure drop across a constriction in the flow path.
   • This type of flow sensor has a disc-type structure and it is installed in the straight run of the pipe. The orifice plate would be installed perpendicular to the fluid flow. This plate would have a hole in the center of it so when the fluid comes in contact with the plate then it would flow through the hole and the flow velocity would be increased and the pressure would be decreased. So when the fluid flows beyond the orifice plate the flow velocity and pressure would change. The relation between the pressure drop and the velocity can be observed to determine the flow rate.

     Advantages of the orifice plate

     • Economical
     • Maintenance is easy
     • Generates high differential pressure
     • It can be easily replaced
     • No moving parts
     • High accuracy

     Disadvantages of orifice plates

     • Permanent pressure loss is high
     • It can’t be used with dirty fluids
     • Frequent calibration is needed
     • Measurement is affected due to the variation in density, viscosity, etc.

     Applications of the orifice plate

     • Neutral gas transfer
     • Gas and fluid measurement
     • Refining
     • Oil and gas
   • Ventury Tube: Utilizes a converging-diverging nozzle to measure pressure drop.

   This type of sensor is a tube that has a cone structure. The operation of the Differential pressure flow meters is based on Bernoulli’s principle which states that if the fluid velocity increases then the pressure would decrease and vice versa.

   The tube structure is in a way that there is a convergent part and also a divergent part. So when the fluid flows through the converging part of the tube then it would be accelerated and during this process, the fluid pressure will be dropped. The end part of the tube section is expanded and in this part, the fluid flow would almost gain its actual pressure. So the velocity and pressure relation is checked and according to this, we could determine the flow rate.

   Advantages of venturi meter

   • Good accuracy
   • High velocity and pressure recovery
   • It can be used with fluids that have small solid particles
   • High repeatability
   • Less maintenance

   Disadvantages of venturi meter

   • Installation cost is high
   • Abrasive or sticky fluid would affect the measurement

   Applications of venturi meter

   • Measurement of compressible and non-compressible fluids
   • Gases and liquid flow measurement
   • Chemical industries
   • Oil and gas
   • Power industries

   • Velocity-Based Flow Sensors:
     • Turbine Flow Meter: Measures the rotational speed of a turbine rotor placed in the fluid stream.
     • In this type of flow measurement, a rotor will be placed in the pipe and this rotor is supported by two bearings. A magnetic pick-up would be placed at the top of the pipe’s section where the rotor is installed. When the fluid flows the rotor would rotate and this would create a frequency. The rotor pulse would be calculated to determine the flow rate.Advantages of the turbine flow sensor
       • Easy installation
       • It is not affected by the variation in the fluid density
       • Compact
       • Less head loss
       • Good temperature and pressure ratings
       • Good repeatability and range

       Disadvantages of the turbine flow sensor

       • It can’t be used with high viscous fluids
       • Due to the moving parts damages could happen if the speed increases

       Applications of the turbine flow sensor

       • Military applications
       • Petroleum industry
       • Energy fuel and cryogenic flow measurement
       • Vortex Shedding Flow Meter: Detects vortices created by an obstruction in the flow.
       • Swirl Flow Meter: Measures the rotational movement of fluid swirl.
   • Positive Displacement Flow Sensors:
     • Rotary Piston Flow Meter: Utilizes a rotating piston to displace fluid in discrete steps.
     • Oval Gear Flow Meter: Measures the volume of fluid displaced by rotating oval gears.
   • Ultrasonic Flow Sensors:
     • Doppler Flow Meter: Measures the frequency shift of ultrasonic waves scattered by particles in the fluid.
     • Transit Time Flow Meter: Measures the time difference between upstream and downstream ultrasonic pulses.Advantages of ultrasonic flow sensors
       • Non-intrusive
       • There is no pressure drop
       • Good accuracy
       • Good range
       • High reliability

       Disadvantages of the ultrasonic flow sensor

       • It can’t be used with dirty liquids
       • A straight pipeline would be required for the flow measurement
       • The transmission path will be affected by attenuation
   • Magnetic Flow Sensors:
     • Magnetic Inductive Flow Meter: Measures the induced voltage generated by a conductive fluid passing through a magnetic field.
   • In this type of flow sensor, a magnetic field would be applied to the pipe or conduit in which the flow is meant to be measured. This operating principle of this flow sensor is based on Faraday’s law, which states that when a conductive fluid passes through a magnetic flux an EMF will be created. So when the conductive fluid passes the magnetic field then a voltage will be induced. The voltage which is formed will be proportional to the flow velocity.

     Advantages of the magnetic flow sensor

     • It doesn’t have any moving parts and also there is no fluid obstruction
     • Very less pressure drop
     • Non-contact measurement
     • Good electrical insulation and corrosion resistant
     • It can be used with extremely low flow
     • It can be used for bidirectional flow measurement
     • Measurement won’t be affected by viscosity

     Disadvantages of the magnetic flow sensor

     • Only conductive fluid can be measured, we won’t be able to measure gases and hydrocarbons with this
     • Expensive

     Applications of the magnetic flow sensor

     • Measurement of slurries and dirty fluids can be done
     • It can be used with acid, base, water, and also for aqueous solution
   • Coriolis Flow Sensors:
     • Coriolis Mass Flow Meter: Measures the deflection of a vibrating tube caused by Coriolis forces.

   The working principle of this flow sensor is based on newton’s second law which states that force is equal to the value of the mass multiplied by the acceleration. In this meter, the flow will be divided into two parallel tubes and these tubes would be vibrated by the electromagnetic drive coil. So when the fluid flows through these tubes then there will be an upward and downward force and due to this there will be a tube deflection and this deflection is known as the Coriolis effect. The deflection of the tube corresponds to the mass flow in the tube.

   Advantages of Coriolis flow sensor

   • High accuracy
   • Very low-pressure drop
   • It can be used for liquid and gas flow

   Disadvantages of Coriolis flow sensor

   • Costly
   • Mounting is difficult

   Applications of Coriolis flow sensor

   • Metering of natural gas consumption
   • Custody transfer
   • Syrups and oil monitoring
   • Gas & liquid flow measurement
   • Solid content concentration can be determined
   • Thermal Flow Sensors:
     • Thermal Mass Flow Meter: Measures the heat transfer from a heated sensor to the fluid.
     • Hot-Wire Anemometer: Measures the cooling effect of fluid flow on a heated wire.
   • In this type of sensor, the flow measurement is done by utilizing the thermal properties of the fluid. In this sensor, a specified amount of heat will be provided to the heater which is situated inside the sensor. So when the fluid flows, a portion of the heat will be lost and if the flow is increased then the heat loss will be increased too. This loss of heat would be measured by the sensor’s temperature measuring instrument.Advantages of thermal mass flow meter
     • Measurement is not affected by variation in pressure
     • Pressure drop is really low
     • Less maintenance because there are no moving parts
     • Installation is really easy
     • Economical

     Disadvantages of thermal mass flow meter

     • Measurement would be affected by moistures
     • Sensitivity is less for high flow
     • If there is any variation in gas composition then it would require recalibration
     • Accuracy would be reduced due to the flow sensor build-up

     Applications of the thermal mass flow sensor

     • Measurement of gases like nitrogen, hydrogen, helium
     • Measurement of pure gases