Flow Measurements

• Mass flow rate

  Volume flow rate x density
• Flow rate units


  m/s, ft/s, GPM, SCCM
• Density


  p (kg/m³)
• Positive displacement (Oval Gear)


  1. Two oval gears inside the meter

  2. Flow of fluid causes gear rotation

  3. Each revolution is a 'pocket'

  4. Counting pocket frequency measures volumetric flow rate

  5. Sensor detects gear rotation to determine volume flow rate
• Positive displacement (Oval Gear)

  • Suitable for higher-viscosity fluids
  • Suitable for different measuring media (acid, alkali, chemical, petroleum, oil, food industries)
  • Can be made of cast steel, stainless steel 316
  • Displays cumulative flow, instantaneous flow and zero return
• Mechanical (Turbine)

  1. Turbine rotor placed in flow path

  2. Rotational speed of rotor depends on flow velocity

  3. Rotor blades generate electrical pulses as they pass a pickup point
• Fluid velocity


  Measurement of distance a particle travels per unit time, typically in ft/s or m/s
• Volumetric flow rate


  Volume of fluid passing a point per unit time, e.g. GPM, m³/s, ft³/s
• Industries using turbine flow meters

  • Oil and gas including fracking
  • Water and wastewater
  • Chemical
  • Power
  • Food and beverage
  • Aerospace
  • Pharmaceutical
  • Pulp and paper
• Turbine flow meters


  • Accurate (0.5% can be improved to 0.2%)
  • Suitable for gases and liquids
  • Stainless steel body
• Turbine flow meter installation

  • Requires 10 pipe diameters upstream of straight pipe and 5 pipe diameters downstream
• Turbine flow meter disadvantages

  • Not suitable for high viscosity fluids
  • Require frequent calibration
  • Only suitable for clean liquids
  • Max temperature 120°C
• Vortex


  Sensor tab bends and flexes as vortices pass, producing output frequency proportional to volumetric flow
• Vortex flow meters


  • Suitable for low viscosity liquids and gases/steam
  • Low pressure loss
  • High accuracy and stability
  • Wide measurement range
  • Reliable and advanced
• Vortex flow meter disadvantages

  • Poor anti-vibration performance
  • Can't measure dirty media
• Vortex flow meter components

  • Sensor tab
  • Shedder bar
  • Body
  • Electronics
• Rotameter


  1. Fluid enters tube from bottom and escapes through top

  2. Float moves upwards as flow area increases

  3. Float position indicates flow rate on scale
• Rotameters


  • Measure very low to high flow rates
  • No external power required
  • Simple and low cost
  • Low pressure drop
  • Good repeatability
  • Optional flow switches and alarms
• Rotameter disadvantages


  • Must be mounted vertically
  • Less accurate at high flow rates
• Differential pressure flow measurement

  1. Differential pressure across flow element (orifice, venturi, pitot tube) is proportional to square of flow rate

  2. Requires square root extraction to linearize signal
• Differential pressure transmitter


  Also called a DP transmitter or Delta P transmitter
• Differential pressure (ΔP)


  Proportional to square of flow rate (Q²)
• Square root extraction


  1. Converts quadratic ΔP-Q relationship to linear Q output

  2. Can be done internally in transmitter or with external device
• Orifice plate


  Basic element of an orifice meter, used to measure liquid or gas flow using differential pressure
• Orifice meters


  • Robust and economical
  • Durable
• Square root extraction function

  Available inside the transmitter (software configuration)
• No external relay device is necessary to characterize the DP transmitter's signal into a flow rate signal
• Orifice Meter


  A type of flow meter used to measure the rate of flow of Liquid or Gas, especially Steam, using the Differential Pressure Measurement principle
• Orifice Meter


  • Robust applications, known for its durability, very economical
• Orifice Plate


  The basic element of the Orifice Meter, when placed in a line, a differential pressure is developed across it
• Types of Orifice Plates

  • Concentric
  • Eccentric
  • Segmental
  • Quadrant edge
• Concentric Orifice Plate


  Used with pure liquid like gases
• Eccentric Orifice Plate


  Used for viscous flow
• Segment Orifice Plate


  Used for viscous flow
• Quadrant Edge Orifice Plate

  Used for crude oil, high-viscosity syrups or slurries
• Advantages of Orifice Meters

  • Very cheap
  • Less space required to install
  • Operational response can be designed with perfection
  • Installation direction possibilities: Vertical/Horizontal/Inclined
• Disadvantages of Orifice Meters

  • At higher fluid velocity causes turbulences
  • Solids in fluids causes damages
  • Low lifetime
• Flow Nozzle


  A device used to measure flow rate, has a minimum area at its throat
• Operation of Flow Nozzle

  1. Fluid enters the nozzle smoothly

  2. Pressure keeps reducing until it reaches the minimum cross section area called throat

  3. Minimum pressure p2 at the throat is maintained for a small length after being discharged in the downstream

  4. Differential pressure sensor records the pressure difference (p1-p2) which becomes an indication of the flow rate
• Advantages of Flow Nozzle

  • Installation is easy and cheaper than venturi meter
  • It is very compact
  • Has high coefficient of discharge