THE VENTURI EFFECT WHEN USING A PUMP

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PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
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As a pump repair and replacement company, we are constantly being asked

about our business and our training, so over the years we have decided to add to our website the training that we have received and how pumps and plumbing works, hoping that you the homeowner will understand the training that is involved in pump repairs, pump replacement and how plumbing works.  Here is a great example:

The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after Giovanni Battista Venturi (1746–1822), an Italian physicist.

Contents

  • 1 Background
    • 1.1 Choked flow
  • 2 Experimental apparatus
    • 2.1 Venturi tubes
    • 2.2 Orifice plate
  • 3 Instrumentation and measurement
    • 3.1 Flow rate
    • 3.2 Differential pressure
  • 4 Examples
  • 5 See also
  • 6 References
  • 7 External links

Background

In fluid dynamics, a fluid’s velocity must increase as it passes through a constriction in accord with the principle of mass continuity, while its static pressure must decrease in accord with the principle of conservation of mechanical energy. Thus any gain in kinetic energy a fluid may accrue due to its increased velocity through a constriction is balanced by a drop in pressure.

By measuring the change in pressure, the flow rate can be determined, as in various flow measurement devices such as venturi meters, venturi nozzles and orifice plates.

Referring to the diagram to the right, using Bernoulli’s equation in the special case of incompressible flows (such as the flow of water or other liquid, or low speed flow of gas), the theoretical pressure drop at the constriction is given by: p 1 − p 2 = ρ 2 ( v 2 2 − v 1 2 ) {\displaystyle p_{1}-p_{2}={\frac {\rho }{2}}\left(v_{2}^{2}-v_{1}^{2}\right)} p_{1}-p_{2}={\frac {\rho }{2}}\left(v_{2}^{2}-v_{1}^{2}\right)

where ρ {\displaystyle \scriptstyle \rho \,} \scriptstyle \rho \, is the density of the fluid, v 1 {\displaystyle \scriptstyle v_{1}} \scriptstyle v_{1} is the (slower) fluid velocity where the pipe is wider, v 2 {\displaystyle \scriptstyle v_{2}} \scriptstyle v_{2} is the (faster) fluid velocity where the pipe is narrower (as seen in the figure).

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Call one of our offices listed below

PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
St Augustine, Florida      St Johns County             904-824-7144
Orange Park, Florida       Clay County                   904-264-6444
Jacksonville Beaches, Florida    Duval County      904-246-3969
Fernandina, Florida         Nassau County               904-277-3040
Macclenny, Florida          Baker County                 904-259-5091
Palm Coast, Florida         Flagler County                386-439-5290
Daytona, Florida             Volusia County               386-253-4911

Jacksonville,  Florida     Duval County                 904-346-1266

Gainesville, Florida          Alachua County              352-335-8555

Choked flow

The limiting case of the Venturi effect is when a fluid reaches the state of choked flow, where the fluid velocity approaches the local speed of sound. In choked flow the mass flow rate will not increase with a further decrease in the downstream pressure environment. However, mass flow rate for a compressible fluid can increase with increased upstream pressure, which will increase the density of the fluid through the constriction (though the velocity will remain constant). This is the principle of operation of a de Laval nozzle. Increasing source temperature will also increase the local sonic velocity, thus allowing for increased mass flow rate but only if the nozzle area is also increased to compensate for the resulting decrease in density.

Experimental apparatus

  Venturi tube demonstration apparatus built out of PVC pipe and operated with a vacuum pump

A pair of venturi tubes on a light aircraft, used to provide airflow for air-driven gyroscopic instruments

Venturi tubes

The simplest apparatus, as shown in the photograph and diagram, is a tubular setup known as a Venturi tube or simply a venturi. Fluid flows through a length of pipe of varying diameter. To avoid undue aerodynamic drag, a Venturi tube typically has an entry cone of 30 degrees and an exit cone of 5 degrees.

Venturi tubes are used in processes where permanent pressure loss is not tolerable and where maximum accuracy is needed in case of highly viscous liquids.

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Call one of our offices listed below

PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
St Augustine, Florida      St Johns County             904-824-7144
Orange Park, Florida       Clay County                   904-264-6444
Jacksonville Beaches, Florida    Duval County      904-246-3969
Fernandina, Florida         Nassau County               904-277-3040
Macclenny, Florida          Baker County                 904-259-5091
Palm Coast, Florida         Flagler County                386-439-5290
Daytona, Florida             Volusia County               386-253-4911

Jacksonville,  Florida     Duval County                 904-346-1266

Gainesville, Florida          Alachua County              352-335-8555

Orifice plate

Venturi tubes are more expensive to construct than a simple orifice plate which uses the same principle as a tubular scheme, but the orifice plate causes significantly more permanent energy loss.

Instrumentation and measurement

Venturis are used in industrial applications and in scientific laboratories for measuring the flow rate of liquids.

FREE ESTIMATES

Call one of our offices listed below

PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
St Augustine, Florida      St Johns County             904-824-7144
Orange Park, Florida       Clay County                   904-264-6444
Jacksonville Beaches, Florida    Duval County      904-246-3969
Fernandina, Florida         Nassau County               904-277-3040
Macclenny, Florida          Baker County                 904-259-5091
Palm Coast, Florida         Flagler County                386-439-5290
Daytona, Florida             Volusia County               386-253-4911

Jacksonville,  Florida     Duval County                 904-346-1266

Gainesville, Florida          Alachua County              352-335-8555

Flow rate

A venturi can be used to measure the volumetric flow rate, Q {\displaystyle \scriptstyle Q} \scriptstyle Q.

Since Q = v 1 A 1 = v 2 A 2 p 1 − p 2 = ρ 2 ( v 2 2 − v 1 2 ) {\displaystyle {\begin{aligned}Q&=v_{1}A_{1}=v_{2}A_{2}\\p_{1}-p_{2}&={\frac {\rho }{2}}(v_{2}^{2}-v_{1}^{2})\end{aligned}}} {\begin{aligned}Q&=v_{1}A_{1}=v_{2}A_{2}\\p_{1}-p_{2}&={\frac {\rho }{2}}(v_{2}^{2}-v_{1}^{2})\end{aligned}}

then Q = A 1 2 ρ ⋅ ( p 1 − p 2 ) ( A 1 A 2 ) 2 − 1 = A 2 2 ρ ⋅ ( p 1 − p 2 ) 1 − ( A 2 A 1 ) 2 {\displaystyle Q=A_{1}{\sqrt {{\frac {2}{\rho }}\cdot {\frac {\left(p_{1}-p_{2}\right)}{\left({\frac {A_{1}}{A_{2}}}\right)^{2}-1}}}}=A_{2}{\sqrt {{\frac {2}{\rho }}\cdot {\frac {\left(p_{1}-p_{2}\right)}{1-\left({\frac {A_{2}}{A_{1}}}\right)^{2}}}}}} Q=A_{1}{\sqrt {{\frac {2}{\rho }}\cdot {\frac {\left(p_{1}-p_{2}\right)}{\left({\frac {A_{1}}{A_{2}}}\right)^{2}-1}}}}=A_{2}{\sqrt {{\frac {2}{\rho }}\cdot {\frac {\left(p_{1}-p_{2}\right)}{1-\left({\frac {A_{2}}{A_{1}}}\right)^{2}}}}}

A venturi can also be used to mix a liquid with a gas. If a pump forces the liquid through a tube connected to a system consisting of a venturi to increase the liquid speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), the gas will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of liquid and gas will appear. See aspirator and pressure head for discussion of this type of siphon.

Differential pressure

Main article: Pressure head

As fluid flows through a venturi, the expansion and compression of the fluids cause the pressure inside the venturi to change. This principle can be used in metrology for gauges calibrated for differential pressures. This type of pressure measurement may be more convenient, for example, to measure fuel or combustion pressures in jet or rocket engines.

FREE ESTIMATES

Call one of our offices listed below

PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
St Augustine, Florida      St Johns County             904-824-7144
Orange Park, Florida       Clay County                   904-264-6444
Jacksonville Beaches, Florida    Duval County      904-246-3969
Fernandina, Florida         Nassau County               904-277-3040
Macclenny, Florida          Baker County                 904-259-5091
Palm Coast, Florida         Flagler County                386-439-5290
Daytona, Florida             Volusia County               386-253-4911

Jacksonville,  Florida     Duval County                 904-346-1266

Gainesville, Florida          Alachua County              352-335-8555

Examples

The Venturi effect may be observed or used in the following:

  • Cargo eductors on oil product and chemical ship tankers
  • Inspirators that mix air and flammable gas in grills, gas stoves, Bunsen burners and airbrushes
  • Water aspirators that produce a partial vacuum using the kinetic energy from the faucet water pressure
  • Steam siphons using the kinetic energy from the steam pressure to create a partial vacuum
  • Atomizers that disperse perfume or spray paint (i.e. from a spray gun).
  • Carburetors that use the effect to suck gasoline into an engine’s intake air stream
  • Wine aerators, used to infuse air into wine as it is poured into a glass
  • The capillaries of the human circulatory system, where it indicates aortic regurgitation
  • Aortic insufficiency is a chronic heart condition that occurs when the aortic valve’s initial large stroke volume is released and the Venturi effect draws the walls together, which obstructs blood flow, which leads to a Pulsus Bisferiens.
  • Protein skimmers (filtration devices for saltwater aquaria)
  • In automated pool cleaners that use pressure-side water flow to collect sediment and debris
  • The barrel of the modern-day clarinet, which uses a reverse taper to speed the air down the tube, enabling better tone, response and intonation
  • Compressed air operated industrial vacuum cleaners
  • Venturi scrubbers used to clean flue gas emissions
  • Injectors (also called ejectors) used to add chlorine gas to water treatment chlorination systems
  • Steam injectors use the Venturi effect and the latent heat of evaporation to deliver feed water to a steam locomotive boiler.
  • Sand blasters used to draw fine sand in and mix it with air
  • Emptying bilge water from a moving boat through a small waste gate in the hull—the air pressure inside the moving boat is greater than the water sliding by beneath
  • A scuba diving regulator to assist the flow of air once it starts flowing
  • In recoilless rifles to decrease the recoil of firing
  • Ventilators
  • The diffuser on an automobile
  • Large cities where wind is forced between buildings – the gap between the Twin Towers of the original World Trade Center was an extreme example of the pheonomenon, which made the ground level plaza notoriously windswept. In fact, some gusts were so high that pedestrian travel had to be aided by ropes.
  • In windy mountain passes, resulting in erroneous pressure altimeter readings
  • The leadpipe of a trombone, affecting the timbre
  • Foam proportioners used to induct fire fighting foam concentrate into fire protection systems
  • Trompe air compressors to entrain air into a falling column of water

The Bernoulli Principle and its corollary, the Venturi effect, are essential to aerodynamic as well as hydrodynamic design concepts. Airfoil and hydrofoil designs to lift and steer air and water vessels (airplanes, ships and submarines) are derived from applications of the Bernouoli Principle and the Venturi effect, as are the instruments that measure rate of movement through the air or water (velocity indicators). Stability indication and control mechanisms such as gyroscopic altitude indicators and fuel metering devices, such as carburetors, function as a result of gas or fluid pressure differentials that create suction as demonstrated and measurable by gas/fluid pressure and velocity equations derived from the Bernoulli Principle and the Venturi Effect.

A simple way to demonstrate the Venturi effect is to squeeze and release a flexible hose in which fluid is flowing: the partial vacuum produced in the constriction is sufficient to keep the hose collapsed.

Venturi tubes are also used to measure the speed of a fluid, by measuring pressure changes at different segments of the device. Placing a liquid in a U-shaped tube and connecting the ends of the tubes to both ends of a Venturi is all that is needed. When the fluid flows though the Venturi the pressure in the two ends of the tube will differ, forcing the liquid to the “low pressure” side. The amount of that move can be calibrated to the speed of the fluid flow.

See also

  • Venturi flume
  • Bernoulli’s principle
  • De Laval nozzle
  • Bunsen burner
  • Choked flow
  • Orifice plate

FREE ESTIMATES

Call one of our offices listed below

PALATKA    AND PUTNAM COUNTY    FLORIDA   OFFICE      1-386-328-7255
St Augustine, Florida      St Johns County             904-824-7144
Orange Park, Florida       Clay County                   904-264-6444
Jacksonville Beaches, Florida    Duval County      904-246-3969
Fernandina, Florida         Nassau County               904-277-3040
Macclenny, Florida          Baker County                 904-259-5091
Palm Coast, Florida         Flagler County                386-439-5290
Daytona, Florida             Volusia County               386-253-4911

Jacksonville,  Florida     Duval County                 904-346-1266

Gainesville, Florida          Alachua County              352-335-8555