viscometer

A viscometer (also called a viscometer) is a laboratory equipment and instrument used to measure the viscosity of liquids. For liquids with a viscosity that varies with different flow conditions , an instrument called a pressure gauge is used . Thus, affinity meter can be considered as a special type of viscometer. Viscometers are only measured under one flow condition.In general, either the fluid remains stationary an

d an object moves through it, or the object is stationary and the fluid moves behind it. The drag caused by the relative motion of the fluid and the surface is a viscometer. Flow conditions must have a small enough value of the Reynolds number for there to be laminar flow .At 20 ° the C, and dynamic viscosity (kinetic viscosity × density) of water is 1.0038 MPa · s and has a viscosity motor ( the product of the flow of time × factor) is 1.0022 mm ² / s. These values are used to calibrate certain types of viscometers.

Standard Laboratory Viscometers for Liquids

Ostwald viscometers measure the viscosity of a fluid with a known density.

U-shaped viscometers

These devices are also known as glass capillary viscometers or Ostwald viscometers , named after Wilhelm Ostwald . Another version is the Ubbelohde viscometer , which consists of a U-shaped glass tube installed vertically in a temperature-controlled bath. In one of the arms of the U there is a vertical section of a narrow fine lumen (capillaries)

. Above is a bulb, with another bulb under the other arm. During use, the fluid is drawn into the upper bulb by suction, and then allowed to flow down through the capillaries to the lower bulb. Two marks (one above the top lamp and one below the top lamp) indicate a known volume. The time it takes for the fluid level to pass between these marks is proportional to the kinematic viscosity. Calibration can be done with a liquid of known properties. Most commercial units are provided with a conversion factor.

The time required for the test fluid to flow through a capillary tube of a known diameter for a given factor is measured between two specified points. By multiplying the time taken by the viscometer factor, the kinematic viscosity is obtained.

These viscometers can be classified as direct flow or reverse flow. Reverse flow viscometers have the tank above the marks, and direct flow ones have the tank below the marks. Such ratings exist so that the level can be determined even when measuring opaque or smeared liquids, otherwise the liquid will cover the marks and make it impossible to measure when the level exceeds the mark.

This also allows the viscometer to have more than one set of marks to allow immediate timing of the time it takes to reach the third mark ^{[ clarification ]} , thus yielding two timings and allowing subsequent computation of determination to ensure accurate results. Two timings in one viscometer can only be used in one cycle if the sample being measured has Newtonian properties. Otherwise a change in the driving head, which in turn changes the shear rate, will result in a different viscosity for the two lamps.

Falling field viscometers

Creeper flows through the ball

Stokes’ law is the basis of the incident field viscometer, in which a liquid is stationary in a vertical glass tube. A ball of known size and density is allowed to descend through the liquid. If chosen correctly, it reaches a terminal velocity , which can be measured by the time it takes to pass two marks on the tube.

Electronic sensing of opaque liquids can be used. Knowing the final velocity, ball size, density, and fluid density , Stokes’ law can be used to calculate the fluid’s viscosity . In the classical experiment, a series of steel ball bearings of different diameters is usually used to improve the accuracy of the calculation.

The school experiment uses glycerol as a liquid, and the technique is used industrially to check the viscosity of fluids used in operations. It contains many oils and polymeric fluidsdifferent types as solutions ^{[ disambiguation ]} .

In 1851, George Gabriel Stokes derived an expression for the frictional force (also called the drag force ) exerted on spherical bodies with very small Reynolds numbers (for example, very small particles) in a continuous viscous liquid by changing the small liquid’s mass limit from Navier’s equations Stokes is generally insoluble.

\ \ displaystyle F = 6 \ pi r \ eta v,

where

$F$ is the force of friction,

$r$ is the radius of a spherical body,

$\ eta$ is the viscosity of fluids,

$v$ is the velocity of the particle.

If the particles fall into the viscous fluid according to their weight, then the final velocity, also known as the settling velocity, is reached when this force of friction and the buoyant force are exactly balanced with the force of gravity. The resultant settling velocity (or final velocity) is given by

V_{\text{s}}={\frac {2}{9}}{\frac {r^{2}g(\rho _{p}-\rho _{f})}{\mu }},

where:

V s

is the particle leveling velocity (m/s), vertically downward if

ρ r > ρ f

, upward if

ρ r < ρ f

r

is the Stokes radius of the particle (m),

g

is the gravitational acceleration (m/s ² ),

Ρ P

isparticle (kg / m density³ ),

ρ f

is the density of the liquid (kg / m³ ),

μ

is the viscosity of the (dynamic) fluid (Pa s).

Note that Stokes flow is assumed, so the Reynolds number must be small.

The determining factor for the validity of this result is the roughness of the ball used.

The straight falling ball viscometer adjustment is a rolling ball viscometer, which sets the ball rolling down a slope while submerged in the test liquid. This can be further improved by using the patented V-plate, which increases the number of cycles for mileage, allowing for smaller, more portable devices. The controlled rolling motion of the ball avoids turbulence in the fluid, which would otherwise occur with a falling ball. ^[2] This type of device is also suitable for use on board ships. ^[ Why? ]

viscosity ball fall

In 1932, Fritz Höppler was granted a patent for the drop-ball viscometer, for which he was named – the world’s first viscometer for the determination of dynamic viscosity. More other world-first viscometers developed by Fritz Hubler in Meidingen (Germany) are the types of ball pressure consistency gauge and rheometer, see ^[ Where? ]Kugeldruckviskosimeter = spherical pressure viscometer.

Piston falling viscometer

It is also known as the Norcross viscometer after its inventor, Austin Norcross. The principle of viscosity measurement in this powerful and sensitive industrial device is based on the piston and cylinder assembly. The piston is raised periodically by the air-lifting mechanism, which causes the material to be measured downward through the gap (gap) between the piston and the cylinder wall into the space formed under the piston as it is lifted.

The collector is then normally suspended for a few seconds and then allowed to fall by gravity, which causes the sample to be expelled through the same path it entered, creating a shear effect on the measured liquid, making this viscometer particularly sensitive and good for measuring certain liquids thixotropic variable.

Fall time is a viscometer, with a gap between the piston and inside the cylinder that forms the measuring hole. The viscosity controller measures the fall time (the time from falling back the viscosity is being measured) and displays the resulting viscosity value.Industrial use is popular due to simplicity, redundancy, low maintenance, and longevity. This type of measurement is not affected by flow rate or external vibrations. The operating principle can be adapted to many different conditions, making it ideal for process control environments.

oscillating piston viscometer

Sometimes referred to as electromagnetic viscometer or EMV viscometer, it was invented at Cambridge Viscosity (formally Cambridge Applied Systems) in 1986. The sensor (see figure below) consists of a measuring chamber and a magnetically affected piston. Measurements are taken as the sample is first introduced into the thermostatically controlled measuring chamber where the

plunger is located. The electronics drive the piston into an oscillatory motion within the metering chamber with a controlled magnetic field.

Shear stress is imposed on the liquid (or gas) by the movement of the piston, and the viscosity is determined by measuring the piston travel time. The construction parameters of the toroidal spacing between the piston and the measuring chamber, the strength of the electromagnetic field, and the piston travel distance are used to calculate the viscosity according to Newton’s law of viscosity.

The piston oscillating viscometer technology has been adapted for small sample viscosity testing and fine sample viscosity testing in laboratory applications. It is also adapted to high pressure viscometers and high temperature viscosity measurements in both laboratory and process environments.

Viscometers are scaled for a wide range of industrial applications, such as small-scale viscometers for use in compressors and motors, flow-through viscometers for dip coatings, inline viscometers for use in refineries, and hundreds of other applications. Improvements in sensitivity from modern electronics are spurring a growth in the popularity of the oscillator viscometer with academic laboratories exploring gas viscosity.

vibratory viscometers

Vibrational viscometers date back to the 1950s Bendix instrument, a class that works by measuring the damping of an oscillating electromechanical resonator immersed in a fluid whose viscosity is determined. The resonator generally oscillates in torsion or transversely (as a cantilever beam or tuning fork). The higher the viscosity, the greater the damping imposed on the resonator. Resonant damping can be measured in one of several ways:

Measure the power input required to maintain the vibration of an oscillator at a constant amplitude. The higher the viscosity, the more energy is required to maintain the amplitude of oscillation.
Measure the oscillation decay time once the excitation is stopped. The higher the viscosity, the faster the signal wears out.
Measurement of resonant frequency as a function of the phase angle between excitation and response waveforms. The higher the viscosity, the greater the frequency change for a given phase change.

The vibrating instrument also suffers from a lack of a specific shear field, which makes it unsuitable for measuring the viscosity of a fluid whose flow behavior is not known in advance.

Vibrational viscometers are durable industrial systems used to measure process condition viscosities. The active part of the sensor is a vibrating rod. The amplitude of the vibration varies according to the viscosity of the fluid in which the rod is immersed.

These viscometers are suitable for measuring blockage of fluids and highly viscous fluids, including those containing fibers (up to 1000 Pa). Currently, many industries around the world consider these viscometers to be the most efficient system for measuring the viscosity of a wide range of liquids; In contrast, rotational viscometers require more maintenance, are unable to measure clogging fluid, and require frequent calibration after extensive use. Vibrational viscometers have no moving parts and no weak parts and the sensitive part is usually small

. Even very basic or acidic liquids can be measured by adding a protective layer, such as enamel, or by changing the sensor material to a material such as 316L stainless steel.

quartz viscometer

Quartz viscometer is a special type of vibratory viscometer. Here, an oscillating quartz crystal is immersed in a liquid and the specific effect on the viscous oscillation behavior determines. The principle of viscosity measurement in quartz is based on the idea of W.B. Mason.

The basic concept is the application of a piezoelectric crystal to determine its viscosity. The high-frequency electric field applied to the oscillator causes the sensor to move and causes the fluid to shear. The motion of the sensor is then affected by external forces (shear stress) of the fluid, which affects the electrical response of the sensor.

The calibration procedure as a prerequisite for determining viscosity by means of a quartz crystal is due to B. Bode, who facilitated detailed analysis of the electrical and mechanical transmission behavior of the oscillating system. On the basis of this calibration, a quartz viscometer has been developed that allows continuous viscosity determination in flowing and resting liquids.^]

The exact amount of quartz crystal

The quartz micro-crystal microbalance acts as a vibratory viscometer through the inherent piezoelectric properties of quartz to make measurements of the conduction spectra of liquids and thin films exposed to the surface of the crystal.

From these spectra, frequency shifts and broadening peaks for the resonant and predominant frequencies of the quartz crystal are tracked and used to determine changes in mass as well as viscosity, shear modulus, and other viscoelastic properties of the liquid or thin.

One benefit of using quartz microbalance for viscosity measurement is the small amount of sample required to obtain an accurate measurement. However, as the viscoelastic properties depend on the sample preparation techniques and the thickness of the film or bulk liquid, there can be errors of up to 10% in viscosity measurements between samples.

An interesting technique for measuring the viscosity of a liquid using a quartz crystal microbalance which improves the consistency of measurements using the drop method. ^[7]^[8] Instead of forming a thin film or immersing the quartz crystal in a liquid, one drop of the liquid in question is dropped onto the surface of the crystal. The viscosity is extracted from the shift in frequency data using the following equation.

{\ displaystyle \ Delta f = -f_ {0} ^ {3/2} {\ sqrt {\ frac {\ eta _ {l} \ rho _ {l}} {\ pi \ mu _ {Q} \ rho _ {Q}}}}}

where is the resonance frequency, is the density of the liquid, is the shear modulus of quartz, and is the density of quartz. ^{[8] An} extension of this technique corrects the shift in the resonant frequency with the size of the droplet deposited on the quartz crystal. ^[7]

f_{0}

\ rho _ {l}

\mu _{Q}

\rho _{Q}

rotational viscometers

Rotational viscometers use the idea that the torque required to turn an object into a fluid is a function of that fluid’s viscosity. They measure the torque required to rotate a disc or bob in a fluid at a known speed.”Cup and bob” viscometers work by determining the exact size of a sample to be cut inside a test cell; The torque required to achieve a given rotational speed is measured and plotted. There are two classic geometries in the “cup and bob” viscometers, known as the “Couette” or “Searle” systems, and are distinguished by whether the cup or bob is rotating. The rotary cup is preferred in some cases because it reduces the appearance of Taylor vortices at very high shear rates, but the rotary cup is more commonly used, as the tool design can be more flexible relative to other geometries as well.”Conical and plate viscometers” use a narrow-angle cone near the flat plate. With this system, the shear rate between geometries is constant at any given speed of rotation. Viscosity can easily be calculated from shear stress (from torque) and shear rate (from angular velocity).If a test is performed in any geometry with a table of several shear rates or stresses, the data can be used to plot a flow curve, which is a graph of viscosity versus shear rate.If the above test is performed slowly enough for the measured value (shear stress if rate is controlled, or vice versa) to reach a constant value at each step, the data is said to be in ‘equilibrium’, hence the graph is the equilibrium flow curve. This is preferred over unbalanced measurements, as the data can usually be repeated across multiple other instruments or using other geometries.

Calculation of shear rate and shear stress factors

Viscometers and torque gauges work with torque and angular velocity. Since viscosity is usually considered in terms of shear stresses and shear rates, a method is needed to convert from “hardware numbers” to “rheology numbers”. Each measurement system used in an instrument has its associated “form factors” to convert torque to shear stress and convert angular velocity to shear rate.

We will call the shear stress form factor $C 1$ and the shear rate factor $C 2$ .

Shear stress = torque ÷

C 1

Shear rate =

C 2

x angular velocity.

For some metering systems such as parallel panels, the user can adjust the gap between the metering systems. In this case the equation used is

Shear rate =

C 2

x angular velocity/gap.

Viscosity = shear stress / shear rate.

The following sections explain how to calculate the form factors for each measurement system.

Cone Wolf

{\begin{aligned}C_{1}&={\frac {3}{2}}r^{3},\\C_{2}&={\frac {1}{\theta }},\end{aligned}}

where

r

is the radius of the cone,

θ

is the angle of the cone in radians.

parallel panels

{\begin{aligned}C_{1}&={\frac {3}{2}}r^{3},\\C_{2}&={\frac {3}{4}}r,\end{aligned}}

where $r$ is the radius of the plate.

Note: The shear stress varies across the radius of the parallel plate. The above formula indicates the position of the radius 3/4 if the test sample is Newtonian.

Coaxial cylinders

{\begin{aligned}C_{1}&={\frac {1}{3}}r_{\text{a}}^{2}H,\\C_{2}&={\frac {2r_{\text{i}}^{2}r_{\text{o}}^{2}}{r_{\text{a}}^{2}\left(r_{\text{o}}^{2}-r_{\text{i}}^{2}\right)}},\end{aligned}}

where:

r a = (r i + r o) / 2

is the mean radius,

r i

is the inner radius,

y x

is the outer radius,

H

is the height of the cylinder.

Note: $C 1$ takes the shear stress as that which occurs at the mean radius $r a$ .

Electromagnetic electromagnetic viscometer (EMS viscometer)

Measurement of the principle of viscometer in the electromagnetic field

The EMS viscometer measures the viscosity of fluids by observing the rotation of a ball driven by electromagnetic interaction: two magnets attached to a rotor create a rotating magnetic field. The sample ③ to be measured is contained in a small test tube ②. Inside the tube is an aluminum ball. The tube is located in a temperature controlled chamber ① and is set so that the ball is at the center of the two magnets.

The rotating magnetic field induces eddy currents in the ball. The resulting Lorentz interaction between the magnetic field and these eddy currents results in a torque rotating the ball. The rotation speed of the ball depends on the speed of rotation of the magnetic field, the size of the magnetic field, and the viscosity of the sample around the ball.

The movement of the ball is monitored by a video camera located under the cell. They applied torque on a scale commensurate with the difference in the corner speed of the magnetic field $Ω B$ one of the area $Ω S$ . Thus, there is a linear relationship between $(Ω B - Ω S) / Ω S$ and the viscosity of the fluid.

This new measurement principle was developed by Sakai et al. at the University of Tokyo. The EMS viscometer distinguishes itself from other rotational viscometers with three main characteristics:

All parts of the viscometer that are in direct contact with the sample are disposable and inexpensive.
Measurements are made in a sealed sample container.
The EMS viscometer only requires very small samples (0.3 ml).

Stabinger viscometer

By modifying the classic Couette type rotational viscometer, it is possible to combine the accuracy of determining the kinematic viscosity with a wide measurement range.

The external cylinder of a Stabinger viscometer is a sample-filled tube rotating at a constant speed in a temperature-controlled copper sheath. The hollow inner cylinder – shaped like a conical rotor – is centered inside the sample by the effects of hydrodynamic lubrication and centrifugal forces.

In this way the friction of the bearings is completely avoided, which is an inevitable factor in most rotating devices. The shear forces of the fluid drive the rotor rotor, while the magnet inside the rotor forms a vortex current brake with the surrounding copper housing. The equilibrium rotational speed is created between the driving and damping forces, which is an unambiguous measure of dynamic viscosity.

The speed and torque measurement is performed without direct contact by a Hall-effect sensor counting the frequency of the rotating magnetic field. This allows for a high torque accuracy of 50 pN m and a wide measurement range from 0.2 to 30,000 MPa with a single measurement system. Built-in density measurement based on the oscillating U tube principle allows determination of the kinematic viscosity from the measured dynamic viscosity using the relationship

{\ displaystyle \ nu = {\ frac {\ eta} {\ rho}},}

where:

ν

is the kinetic viscosity (mm ² / s),

η

is the dynamic viscosity (mPa s),

ρ

is the density (g / cm ³ ).

bubble viscometer

Bubble viscometers are used to quickly determine the kinematic viscosities of known liquids such as resins and varnishes. The time required for an air bubble to rise is directly proportional to the viscosity of the liquid, so the faster the bubble increases, the lower the viscosity.

The alphabetical comparison method uses 4 sets of lettered reference tubes, from A5 to Z10, of known viscosity to cover the viscosity range from 0.005 to 1000 Stokes. The direct time method uses a single 3-line times tube to define “bubble seconds”, which can then be converted to Stokes. ^[10]This method is fairly accurate, but measurements can vary due to differences in buoyancy due to the change in bubble shape in the tube. ^[10] However, this does not cause any kind of serious miscalculation.

Rectangular slit viscometer

The basic design of the rectangular slit viscometer/rheometer consists of a rectangular slit channel with a uniform cross-sectional area. The test fluid is pumped at a constant flow rate through this channel. Multiple pressure sensors installed at linear distances along the direction of the current to measure the pressure drop as shown in the figure:Measurement principle: The slit viscometer / regression meter is based on the basic principle that a viscous liquid resists flow, showing a decreasing pressure along the slit. Associated pressure drop or lower (

Δ p

) effort at the shear wall boundary. The apparent shear rate is directly related to the flow rate and the slit dimensions. The apparent shear rate, shear stress and apparent viscosity are calculated:

{\begin{aligned}{\dot {\gamma }}_{\text{a}}&={\frac {6Q}{wh^{2}}},\\\sigma &={\frac {wh}{2(w+h)}}{\frac {\Delta P}{l}},\\\eta _{\text{a}}&={\frac {\sigma }{{\dot {\gamma }}_{\text{a}}}},\end{aligned}}

where

{\dot {\gamma }}

is the apparent shear rate (s ⁻¹ ),

σ

is the shear stress (Pa),

η a

is the apparent viscosity (Pa s),

∆ P

is the pressure difference between the main pressure sensor and the last pressure sensor (Pa),

Q

is the flow rate (ml/s),

w

is the width of the flow channel (mm),

h

is the depth of the flow channel (mm),

l

is the distance between the main pressure sensor and the last pressure sensor (mm).

To determine the viscosity of a fluid, the fluid sample is pumped through the slit channel at a constant flow rate, and the pressure drop is measured. After these equations, the apparent viscosity of the apparent shear rate is calculated. For the Newtonian fluid, the apparent viscosity is the same as the true viscosity, and a single shear rate measurement is sufficient.

For non-Newtonian fluids, the apparent viscosity is not true viscosity. In order to obtain true viscosity, apparent viscosity is measured at multiple apparent shear rates. The true viscosity $η$ is then calculated at different shear rates using the Weissenberg- Rabinowitsch -Mooney correction factor:

{\frac {1}{\eta }}={\frac {1}{2\eta _{\text{a}}}}\left(2+{\frac {\mathrm {d} \ln {{\dot {\gamma }}_{\text{a}}}}{\mathrm {d} \ln {\sigma }}}\right).

The calculated real viscosity is the same as the cone and plate values for the same shear rate.

A modified version of the rectangular slit viscometer/rheometer can also be used to determine the apparent stretch viscosity.

Krebs Viscometer

The Krebs viscometer uses a digital graph and a small spindle of the side arms to measure the viscosity of a liquid. It is mostly used in the paint industry.

Various types of viscometers

Rotational ViscometersRotational viscometers are commonly used. They are simple to install and user-friendly, can measure a wide variety of materials, and can take highly accurate measurements. Viscosity is determined by measuring the torque (shear stress) used on a cylindrical rotor inserted into the sample and rotating at a constant speed.There are several types of rotors, including coaxial cylinder, single cylinder and conical plate rotors. In conical plate rotors, by varying the number of revolutions (the number of turns), the flow characteristics of non-Newtonian fluids can be obtained.

Capillary Viscometers

Kinematic viscosity is determined by passing the sample through a narrow tube and measuring how long it takes the sample to pass through. Viscosity can be calculated using the density of the sample (kinematic viscosity = viscosity ÷ density). Capillary tube viscometers can measure Newtonian fluids with a relatively high level of accuracy.

These viscometers are low cost and have been in use for a long time, but the narrow tube makes cleaning a complicated process, which inconveniences the user. 　►Uses: petroleum products and pharmaceutical industries.

Falling Ball Viscometers

Viscosity is determined by dropping a ball into the sample and measuring how long it takes for it to fall to the bottom. Since the ball is met by the fluid resistance of the sample, the velocity of the ball’s fall varies with the viscosity of the sample. These viscometers can accurately measure the viscosity of Newtonian fluids, from low viscosity fluids such as water to highly viscous fluids such as oil.

Vibrational Viscometers

Viscosity is determined by inserting a vibrating instrument into the sample and measuring the viscosity resistance when vibrating at a constant frequency. Vibrational viscometers have a fast response time and can perform sequential measurements. They are used as on-line process viscometers for their ability to measure liquid as it flows.

viscosity cup

Viscosity is determined by filling a metal cup with a sample, draining the sample through an opening (hole) in the base of the cup, and measuring how long it takes for the sample to flow out. The time it takes for a sample to flow out of the hole is generally measured using a stopwatch. 　►Uses: industrial coatings and oils (rarely used in the food industry).

Call Us Now

Kinematic viscometer

Kinematic viscometer

viscometer

Standard Laboratory Viscometers for Liquids

U-shaped viscometers

Falling field viscometers

viscosity ball fall

Piston falling viscometer

oscillating piston viscometer

vibratory viscometers

quartz viscometer

The exact amount of quartz crystal

rotational viscometers

Calculation of shear rate and shear stress factors

Cone Wolf

parallel panels

Coaxial cylinders

Electromagnetic electromagnetic viscometer (EMS viscometer)

Stabinger viscometer

bubble viscometer

Rectangular slit viscometer

Krebs Viscometer

Various types of viscometers

Capillary Viscometers

Falling Ball Viscometers

Vibrational Viscometers

viscosity cup

No Comments

Leave a Reply Cancel reply

About Us

Useful Links

About Us

Contact Us

Blog

Recent Posts

Contact Us

Call Us Now

Shopping Cart

Kinematic viscometer

Kinematic viscometer

viscometer

Standard Laboratory Viscometers for Liquids

U-shaped viscometers

Falling field viscometers

viscosity ball fall

Piston falling viscometer

oscillating piston viscometer

vibratory viscometers

quartz viscometer

The exact amount of quartz crystal

rotational viscometers

Calculation of shear rate and shear stress factors

Cone Wolf

parallel panels

Coaxial cylinders

Electromagnetic electromagnetic viscometer (EMS viscometer)

Stabinger viscometer

bubble viscometer

Rectangular slit viscometer

Krebs Viscometer

Various types of viscometers

Capillary Viscometers

Falling Ball Viscometers

Vibrational Viscometers

viscosity cup

Related Posts

FT-IR Spectrometer

What is gas chromatography?

microwave digester

No Comments

Leave a Reply Cancel reply

Recent Posts