Solid or liquid? Discover with our viscometer the differences between liquids

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The Ball Drop Viscometer is based on the Höppler measurement system and is designed to measure the viscosity of Newtonian liquids. To do this, it uses the different rate of fall that a solid sphere presents in the bosom of a liquid depending on the viscosity of it, which, in turn, will depend on its temperature, decreasing with this unlike what happens with the gases.

FL 14.1 – VISCOSITY AND RESISTANTE COEFFICIENT DETERMINATION

Viscometer
FL 14.1 – VISCOSITY AND RESISTANCE COEFFICIENT
DETERMINATION

Two types of fluids are mainly distinguished:

Newtonian fluid

“A typical fluid.” A fluid is said to be Newtonian if its viscosity — the measure of a fluid’s ability to resist flow — varies only in response to changes in temperature or pressure. Viscosity is the same for all shear rates applied to the fluid. Examples of these types of fluids are: water, sugar solutions, glycerin, silicone oils, light hydrocarbon oils, air and other gases.

FL 14.1 – VISCOSITY AND RESISTANTE COEFFICIENT DETERMINATION

Viscometer
FL 14.1 – VISCOSITY AND RESISTANCE COEFFICIENT
DETERMINATION

The non-Newtonian fluids

“It is not a typical fluid.” Unlike a Newtonian fluid, which behaves exclusively like a liquid, a non-Newtonian fluid has the properties of a liquid and a solid. Under certain conditions, a non-Newtonian fluid flows like a liquid and under other conditions, it exhibits properties of elasticity, plasticity, and strength similar to those of a solid. In addition, unlike Newtonian fluids, the viscosity of many non-Newtonian fluids varies with shear rate.

Non-Newtonian fluids are classified based on how their viscosity varies in response to the duration and magnitude of the applied shear rate.

They are non-Newtonian fluids:

• Thixotropic fluids, in which the viscosity decreases over time when a shear stress is applied. For example, honey in a solid state turns liquid after constant stirring.

• Rheopectic fluids, in which the viscosity increases with time when the shear stress is increased. For example, the cream thickens after constant stirring.

• Pseudoplastic fluids, the viscosity decreases with increasing deformation speed; These fluids exhibit shear-stress fluidization-type behavior. For example, ketchup flows out in a stream at high speed through the hole in the spout of a bottle, but remains stable when served as a portion on a plate.

• Expanding fluids, viscosity increases with increasing deformation speed; these fluids exhibit shear-thickening-type behavior. For example, the fluid made based on the mixture made with corn starch and water as you can see in the experiment in the following video.

https://www.youtube.com/watch?v=JJfppydyGHw

What do you know about cavitation and how it affects the operation of a water pump?

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The word cavitation comes from the Latin cavus, which means hollow space. At a technical level it is defined as the rapid formation and collapse of cavities in areas of very low pressure in a liquid flow.

The fundamental physical condition for the appearance of cavitation is that the pressure at the point of formation of these cavities decreases up to the vapour pressure of the fluid in question.

Cavitation is a common phenomenon in hydraulics, it affects the operation of centrifugal pumps, decreases the performance of the installation, it presents noise and vibrations that directly influence maintenance costs.

Venturi, Bernoulli and Cavitation effects.

Some of the actors involved in cavitation are related to

  • The fluid, such as: temperature, density, physical-mechanical properties, chemical composition.
  • The characteristics of the network: suction height, atmospheric pressure, suction losses
  • The pump: flow rate and rotation speed

To study this phenomenon, Dikoin proposes the following equipment to carry out very interesting laboratory practices due to their simplicity for teaching and researching the fundamental aspects of the phenomenon.

FL 06.3 Cavitation Study

It consists of a venturi tube in whose throat the phenomenon of cavitation occurs due to the depression created in it by the acceleration of the flow (Venturi effect). For a correct observation of the phenomenon, the methacrylate’s Venturi has been built The equipment also has two manovacuometers with which we can measure the overpressures and depressions produced. For the regulation of the flow, a regulation valve is used that allows a fine adjustment of it.

FL 06.1 Venturi, Bernoulli and Cavitation effects

Whose objectives that are intended to be achieved with the realization of the practices with this equipment, are both the study of the venturi effect from its initial theoretical conception, Bernoulli’s theorem, and the observation and use of some of its practical applications; applications that we can find in fields as diverse as industry, agriculture, leisure, etc. as well as the study and observation of cavitation, it is also possible to change the pressure conditions in the suction tank, with which we can study the phenomenon for different flows and pressures.

Venturi, Bernoulli and Cavitation effect

Título MH 05.1 Visualization NPSH

It has been designed to visualize the phenomenon of cavitation that occurs when the pressure of the liquid we are pumping decreases to its vapor pressure for the operating temperature. At that time, the liquid vaporizes, forming cavities or pockets of vapor that are drawn into areas with a higher pressure where they condense again, generating very high point overpressures.

Visualization NPSH

The most direct consequences of the phenomenon described above are strong vibrations in the machine, oxidation, detachment of the material and a decrease in both the manometric height and performance.

The stroboscope arranged, and adjusted in frequency to the speed of rotation of the pump, makes us see the impeller “stopped”, so that the visualization of the phenomenon is unbeatable.

Why do planes fly?

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Discover with the study of Bernoulli’s equation and its demonstration why planes fly.

Bernoulli’s equation describes the energy conservation law in a fluid. To do this we need the components of energy that can have a moving fluid. In a ideal situation, without friction or viscosity, the 3 components of energy would be:

  • Kinetic energy: Kinetic energy is due to the speed of fluid.
  • Potential energy: The potential energy is due to the height of the fluid.
  • Pressure energy: It is energy due to the pressure that a fluid has.

The 3 parts of the energy, in formula, would look like this:

  • Bernoulli’s equation

The first part corresponds to kinetic energy, the second to pressure energy and the third to potential due to the high jumps it may have.

The fact that the sum of the 3 energies stays constant means, if there’s a variation in one of them, there must be one variation in another to keep it constant.

For example, if you change the speed of a fluid without changing its height, the pressure must vary. If we increase the speed (e.g. making it go through a narrower section, the pressure exerted by the fluid will be lower. If we slow down, the pressure will be higher. This simple approach explained by Bernoulli’s principle, gives the reason for the lift that occurs on the wings of an aircraft.

Plane wing profile

The speed at the top of the wing increases by the law of mass continuity, where the flow at the inlet should be equal to the flow at the outlet. By increasing the speed above, the kinetic energy of the fluid increases and according to Bernoulli’s principle, so that the sum of energies remains constant, either its height or its pressure varies. The height does not vary, therefore, the pressure of the fluid is lower.

A lower pressure at the top of the wings and higher pressure down causes the wing to suffer a force due to the difference in pressures in its area.

To understand why aircraft fly and the equation in a practical and visual way, use our FL 06.1 EFFECT VENTURI, BERNOULLI and CAVITATION lab teaching equipment and get experimental learning that will help strengthen knowledge.

FL 06.1 Effect Venturi, Bernoulli and Cavitation