Flow Measurement Flashcards
What is dimensional analysis
When dealing with experimental data, analytical solutions are rare due to the complex nature of fluid behaviour, including turbulence, viscosity and compressibility. Engineers and researchers rely on experimental data to understand and predict fluid flow behaviour.
Dimensional analysis: design experiments by identifying relevant variables and their relationships. (Which factors influence the system’s behaviour).
Concept of similitude
Creating a relationship between a small model and s full scale prototype.
What is Re- Reynolds number
Helps predict flow patterns in different fluid flow situations. Determines whether a flow is laminar/ turbulent, nature of fluid motion in various applications (pipe flow, open channel, flow over surfaces).
Laminar: Re< 2000, fluid particles move in smooth parallel layers.
Turbulent: Re> 4000, chaotic flow, inertial forces dominate over viscous forces.
Very small Re- viscous (internal forces that arise due to fluids viscosity) forces dominate.
For large Re- viscous effects are small.
Viscous effects
The result of a fluid’s viscosity, measure of how thick or sticky a fluid is.
What is a moody diagram, how does it work
3 axes, Reynolds number, friction factor, and relative roughness (ε/D. )
Calculates head loss/ pressure drop due to friction in a pipeline.
What is a moody diagram, how does it work
3 axes, Reynolds number, friction factor, and relative roughness (ε/D. )
Calculates head loss/ pressure drop due to friction in a pipeline.
Venturi meter
Measures the flow rate of a fluid in a pipe. Works based on the principles of Bernoulli’s equation, and continuity equation. (Both state that the total mechanical energy of the fluid remains constant along the streamline).
Discharge coefficient, Cd.
Account for the difference between theoretical and actual flow rate in flow measurement devices. (Venturi meters, orifice plates, nozzles). Compensates for energy=loses due to friction, turbulence and other factors that prevent ideal flow.
Cd= Qactual/ Qtheoretical.
Typically 0.95 to 0.99
Orifice plate
Thin, flat plate with a precisely machines hole, placed in a pipeline to measure fluid low rates. It restricts the fluid flow, causing a pressure drop across it, which can be used to calculate flow rate using Bernoullis equation and continuity.
For this plate, Cd values of 0.63, are typical due to pressure losses.
Positive displacement (PD) meter
Flow meter that measures fluid flow by mechanically displacing components within the meter. Consists of chambers that temporarily obstruct fluid flow, allowing fixed volumes to pass with each rotation or reciprocation of internal mechanisms. Device calculated total volume. With adjustments for pressure, temperature, PD meters can accurately measure mass flow rate as well.
Coriolanus meters
Measure fluid mass flow. Coriolanus effects causes moving objects to deflect when observed in rotating reference frame. FLUID flows through vibrating tubes. When mass flow is present, fluids momentum causes tubes to twist slightly due to the force. Amount of twist correlates with the mass flow rate, allowing direct measurement of mass flow through the meter.
Ultrasonic flow meters
Measure fluids velocity using ultrasound. Emitting ultrasound pulses with, against the direction of flow, the meter calculates the velocity based on the difference in transit times of these pulses. Affected by temperature, density and viscosity.
Rotameters
Measure fluid flow by allowing the cross sectional area within the meter to adjust in response to the flow rate. As fluid flows, it lifts a float within a tapered tube expanding the area until equilibrium is reached between fluid force and weight. Floats position indicates the flow rate.
Electromagnetic flow meters
Apply magnetic field across a metering tube. Generates voltage proportional to the fluids flow velocity (fluid is conductive). Magnetic field is reversed to cancel out unwanted static voltage shifts from electrochemical effects, prevents the use of permanent magnets. They are accurate and reliable, third most common type after differential pressure and positive displacement meters.
