## Italian Masters: Venturi and the Venturi Effect

Figure 1: Giovanni Battista Venturi

[i]

Glew’s News is doing a short series highlighting the lives and accomplishments of the Italian Masters of science, engineering, and mathematics.  In the last blog, I wrote about Evangelista Torricelli, a mathematician and physicist from the 17th century.  In this blog, I’m focusing on Giovanni Venturi (Figure 1), an accomplished physicist, hydrodynamicist and engineer.

# Giovanni Battista Venturi (1746-1822)

Giovanni Venturi was born to a wealthy family in Reggio, Italy in 1746.  A talented young student, by the age of 23 the local seminary had already ordained him as a priest and professor.  His talents in mathematics didn’t long escape notice at the nearby University of Modena, which appointed him as a professor of geometry and philosophy a short five years later in 1774.  As respect for his scientific and engineering spread, the University promoted him to the Professor of Experimental Physics in 1786.  During his tenure, he also served the Duke of Modena as the State engineer and auditor, as well as the ducal mathematician.  He later served in many diplomatic appointments in France and Switzerland, his time in these countries well-spent studying and meeting with fellow scientists.  Venturi retired from this work in 1813, but continued to publish his own works and compile works of other famous scientists until his death in 1822.

# The Venturi Effect

Figure 2: Venturi effect in a pipe
Blinder, “The Venturi Effect” from the Wolfram Demonstrations Project
http://demonstrations.wolfram.com/TheVenturiEffect/

Venturi’s primary expertise was fluid dynamics and hydraulic engineering.  In his studies of fluid flow (in scientific terms, a “fluid” is any substance that flows, such as water or gases), expanding the work performed by Daniel Bernoulli and Leonhard Euler, he discovered and explained a certain very useful behavior of fluid flowing in pipes of different diameters.  Venturi found that when fluid flowing through a pipe enters a constricted section, two of its properties change:

• The fluid’s velocity increases. This is due to the conservation of mass; the mass flow rate must remain the same through the pipe (otherwise mass would be appearing or disappearing), so when the cross-section decreases then the speed must increase.  This keeps the same amount of mass flowing through the pipe.
• The fluid’s static pressure decreases. This is due to the conservation of energy; with the increased fluid velocity, the fluid’s kinetic energy will increase as well, and some other energy needs to decrease to compensate.  In this case, the fluid pressure in the constricted section decreases to balance the system’s energy.

This effect is shown in action in Figure 2, generated in Wolfram Mathematica, and is described by the equations below, with the terms defined as follows:

 (Eqn 1) (Eqn 2)
• p = pressure
• ρ = density
• v = velocity
• A = cross-sectional
• Q = volumetric flow rate.
• Subscript 1 indicates the initial conditions of the flow.
• Subscript 2 indicates the flow conditions in the nozzle.

Equations 1 and 2 describe two different aspects of the physical behavior of the fluid flow.  Equation 1 describes the conservation of mass.  It shows that fluid velocity and cross-sectional area are inversely proportional.  For examble, if A2 is smaller than A1, then for the equation to be equivalent v2 must be proportionally larger than v1.  Equation 2 describes the conservation of energy.  It shows a similar inverse relationship between pressure and velocity, albeit in a more complicated form.

Figure 3: Drawings made by Giovanni Venturi [i]

With provided with a fluid at a high pressure, a Venturi nozzle can generate a high velocity and a pressure low enough to draw a vacuum.  These two effects have countless uses, in practically any application that involves moving liquids or gases.  You can see some of Venturi’s many explorations of the phenomenon in Figure 3.  We recently used the Venturi and Bernoulli equations to analyze the effectiveness of different types of roof vents designed to secure the waterproof membranes used on large flat roofs.  Some of these vents took advantage of the Venturi effect through different-shaped configurations, and kept the membrane on the roof by lowering the pressure in the space beneath it, compared to atmospheric pressure.  Countless other devices have taken advantage of the Venturi effect, including:

• Flood control pumps
• Musical instruments like the clarinet and trombone
• Carburetors
• Recoilless rifles
• Pool cleaners
• Scuba diving regulators

# Engineering Application and History

Venturi’s expertise with hydraulics, fluid dynamics, mathematics and physics also led him into the engineering profession.  As an engineer “he was engaged on many works, such as the building of bridges; rectification of water courses; draining of marsh land; and the establishment of State regulations for the construction of river dams.”[i]  His engineering expertise was lauded by many of his colleagues, to the point that he caught Napoleon Bonaparte’s eye.  The Emperor would look out for Venturi in his later life, giving Venturi the appointment at the University of Pavia and in various diplomatic corps, and finally granting him the maximum allowable pension upon retirement.

Venturi also spent his time as a historian of science and engineering, as fascinated by the history of science as he was by its application.  He was one of the first to call attention to Leonardo da Vinci’s work as a scientist and engineer, where he had perviously been recognized for his art.  Venturi also compiled and published works by Galileo Galilei and Hero of Alexandria, scientific figureheads of the near and distant past.  His interest in writing and history extended beyond science as well, inspiring him to compose the memoirs for his longtime residence of Modena.

# Lasting Impact

As one biographer wrote, “In reflecting on the widely varied character of the many offices and functions Venturi was called upon to fill and perform, one cannot fail to be impressed by the great gifts and versatility of the man.” [i]  Apart from the inspiring breadth of his engineering and scientific work, Venturi’s name will not be forgotten for many years considering the widespread utilization of his eponymous Venturi effect.  His method for easily generating low pressures and high gas or liquid velocities is used in countless industries, including construction, hydraulics, laboratory equipment, medical devices, and Glew Engineering’s own mechanical engineering consulting services.

# References

2017-05-03T14:48:59-07:00

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