flow terms Flashcards
Flow Rate
The quantity of fluid passing a point at a particular moment
Total Flow
Is the quantity of fluid that passes a point during a specific time period
Density
Fluids mass per unit volume
Relative Density
The ratio of fluid density to the density of a reference fluid
Absolute Viscosity
The resistance to the flow of fluid and has the units of centipoise(cP) (in the SI system Pa .s or kg/(s.m)
Kinematic Viscosity
The ratio of absolute viscosity to fluid density and has the units of centistokes(cS) (in the SI system m2/s)
Reynolds Number
The ratio between the inertial forces moving a fluid and viscous forces resisting that fluid.
Laminar Flow
Smooth fluid flow that has a flow profile that is parabolic in shape with no mixing between the streamlines.
Turbulent Flow
Fluid flow in which the flow profile is flattened parabola, the streamlines are not present and the fluid is freely intermixing
Incompressible Fluid
Is a fluid where there is little change in volume when subjected to a change in pressure
Compressible Fluid
Is a fluid where the volume and density change when subjected to a change in pressure
Standard Condition
Is an accepted set of temperature and pressure conditions used for measurement
Flowing Condition
Is the temperature and pressure of the gas or vapour at the point of measurement
Boyle’s Law
A law that states that the absolute pressure of a given quantity of gas varies inversely with its volume provided temperature remains constant
Charles Law
A law that states that the volume of a given quantity of gas varies directly with its absolute temperature provided the pressure remains constant
Gay-Lussac’s Law
Gas law that states that the absolute pressure of a given quantity of a gas varies directly with its absolute temperature provided the volume remains constant
Ideal Gas Law
The ideal gas law is the equation of state of a hypothetical ideal gas, often written in the form of PV= nRT
Primary Flow Element
A Pipeline restriction that causes a pressure drop used to measure flow.
Secondary Flow Element
A device that senses the differential pressure created by a primary flow element, usually a DP transmitter
Continuity Equation
States that, in any steady state process, the rate at which mass enters a system is equal to the rate at which mass leaves the system.
Bernoulli Equation
The sum of the pressure heads of an enclosed flowing fluid is the same at any two locations.
Differential Pressure Flowmeters
Flow meters that use the DP pressure across a restriction in a pipe to infer the flow rate through the pipe
Orifice Plate
A Primary flow element consisting of a thin circular metal plate with a sharp-edged round hole in it
Flow Nozzle
A Primary flow element consisting of a restriction shaped like a curved funnel that allows a little more flow than an orifice plate and reduces the straight run pipe requirements.
Venturi Tube
A Primary flow element Consisting of a fabricated pipe section with a converging inlet section, a straight throat, and a diverging outlet section.
Pitot Tube
A flow element consisting of small bent tube with a nozzle opening facing into the flow.
Averaging Pitot Tube
Is a tube consisting of several impact openings inserted through the wall of a pipe or duct and extending across the entire flow profile
Annubar Flowmeter
Is an Emerson Process Management registered trademark name for its averaging Pitot tube design
Target Flowmeter
Where a physical target is located directly in the fluid flow, the deflection of the target and the force bar is measured by the instrument
V-Cone Flowmeter
Is a flow meter with a centrally-located cone inside the flow tube which created a differential pressure proportional to the flow rate
Corner Tap
Orifice pressure taps or sensors located immediately upstream and downstream of the orifice plate
Impulse Lines
The tubing or piping connection that connects the flowmeter taps to any of the differential pressure instruments.
Beta Ratio
The Ratio between the diameter of the orifice plate (d) and the internal diameter of the pipe (D)
Coefficient of Discharge
is the ratio of the true flow to the theoretical flow and is applied to the theoretical flow equation to obtain the actual (true) flow
Velocity of Approach
Change in velocity between the upstream meter tube and the velocity in the orifice bore
Throat
May be considered the bore or diameter of the orifice opening in the orifice plate
Upstream
The region before the orifice pate with respect to direction of fluid flow
Downstream
The region after the orifice pate with respect to direction of fluid flow
Residual (permanent) Pressure Loss
The pressure loss due to a restriction in a pipe that is used to cause a pressure differential for flow measurement
Turndown Ratio
The Ratio of the maximum flow to the minimum measurable flow at the desired measurement accuracy.
Meter Run
Consists of an orifice fitting, upstream section of pipe and downstream section of pipe (& conditioner if required)

Flange Tap
taps placed 25.4mm (1 inch) upstream and downstream of the orifice plate, normally within specialized pipe flanges
Pipe Tap
Taps for connection to the secondary device on a orifice tube where the upstream tap is 2.5 pipe diameters and the downstream tap is located 8 pipe diameters from the orifice plate
