Rheometer - Wikipedia, The Free Encyclopedia

7/29/2019 Rheometer - Wikipedia, The Free Encyclopedia

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Rheometerm Wikipedia, the free encyclopedia

rheometer is a laboratory device used to measure the way in which a liquid, suspension or slurry flows in response to

plied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more

ameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.

ere are two distinctively different types ofrheometers. Rheometers that control the applied shear stress or shear strain

called rotational or shear rheometers, whereas rheometers that apply extensional stress or extensional strain are

ensional rheometers. Rotational or shear type rheometers are usually designed as either a native strain-controlled

trument (control and apply a user-defined shear strain which can then measure the resulting shear stress) or a native

ss-controlled instrument (control and apply a user-defined shear stress and measure the resulting shear strain).

Contents

1 Meanings and origin

2 Types of shear rheometer

2.1 Pipe or Capillary

2.2 Rotational cylinder

2.3 Cone and plate

2.4 Linear Shear

3 Types of extensional rheometer

3.1 Commercially available extensional rheometers

3.1.1 Rheotens

3.1.2 CaBER

3.1.3 FiSER

3.1.4 Sentmanat3.2 Other Types of Extensional Rheometers

3.2.1 Acoustic rheometer

3.2.2 Falling Plate

3.2.3 Capillary/Contraction Flow

4 See also

5 References

6 External links

Meanings and origin

e word rheometer comes from the Greek, and means a device for measuring flow. In the 19th century it was commonly

d for devices to measure electric current, until the word was supplanted by galvanometer and ammeter. It was also used

the measurement of flow of liquids, in medical practice (flow of blood) and in civil engineering (flow of water). This latter

persisted to the second half of the 20th century in some areas. Following the coining of the term rheology the word

me to be applied to instruments for measuring the character rather than quantity of flow, and the other meanings are

olete. (Principal Source: Oxford English Dictionary) The principle and working of rheometers is described in several

ellent texts.[1][2]

ypes of shear rheometer

pe or Capillary
http://en.wikipedia.org/wiki/Oxford_English_Dictionaryhttp://en.wikipedia.org/wiki/Galvanometerhttp://en.wikipedia.org/wiki/Ammeterhttp://en.wikipedia.org/wiki/Oxford_English_Dictionaryhttp://en.wikipedia.org/wiki/Rheologyhttp://en.wikipedia.org/wiki/Ammeterhttp://en.wikipedia.org/wiki/Galvanometerhttp://en.wikipedia.org/wiki/Stress_(mechanics)http://en.wikipedia.org/wiki/Extensional_stresshttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Rheologyhttp://en.wikipedia.org/wiki/Viscometerhttp://en.wikipedia.org/wiki/Viscosity


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Rheometer with cylinder measuring

system (left) and cone/plate

measuring system (right)

uid is forced through a tube of constant cross-section and precisely known dimensions under conditions of laminar flow.

her the flow-rate or the pressure drop are fixed and the other measured. Knowing the dimensions, the flow-rate can be

nverted into a value for the shear rate and the pressure drop into a value for the shear stress. Varying the pressure or flow

ws a flow curve to be determined. When a relatively small amount of fluid is available for rheometric characterization, a

crofluidic rheometer with embedded pressure sensors can be used to measure pressure drop for a controlled flow

e.[3][4]

Newtonian fluids, the pressure drop increases linearly with flow rate and the measured viscosity does not depend upon

plied deformation rate or stress. On the other hand, since non-Newtonian fluids or complex fluids can display shear

nning or shear thickening, the pressure drop versus flow rate data must be analyzed using Weissenberg-Rabinowitch-oney equation.

otational cylinder

e liquid is placed within the annulus of one cylinder inside another. One of the

inders is rotated at a set speed. This determines the shear rate inside the

nulus. The liquid tends to drag the other cylinder round, and the force it exerts

that cylinder (torque) is measured, which can be converted to a shear stress.

e version of this is the Fann V-G Viscometer, which runs at two speeds, (300

d 600 rpm) and therefore only gives two points on the flow curve. This isficient to define a Bingham plastic model which used to be widely used in the

industry for determining the flow character of drilling fluids. In recent years

ometers that spin at 600, 300, 200, 100, 6 & 3 RPM have been used. This

ws for more complex fluids models such as Herschel-Bulkley to be used.

me models allow the speed to be continuously increased and decreased in a

grammed fashion, which allows the measurement of time-dependent

perties.

one and plate

e liquid is placed on horizontal plate and a shallow cone placed into it. The angle between the surface of the cone and the

te is of the order of 1 degreei.e. it is a very shallow cone. Typically the plate is rotated and the force on the cone

asured. A well-known version of this instrument is the Weissenberg Rheogoniometer, in which the movement of the cone

esisted by a thin piece of metal which twistsknown as a torsion bar. The known response of the torsion bar and the

gree of twist give the shear stress, while the rotational speed and cone dimensions give the shear rate. In principle the

issenberg Rheogoniometer is an absolute method of measurement providing it is accurately set up. Other instruments

erating on this principle may be easier to use but require calibration with a known fluid. Cone and plate rheometers can

o be operated in an oscillating mode to measure elastic properties, or in combined rotational and oscillating modes.

near Shear

e example of a linear shear rheometer is the Goodyer Linear Skin Rheometer, which is used to test cosmetic cream

mulations, and for medical research purposes to quantify the elastic properties of tissue. The device works by attaching a

ear probe to the surface of the tissue under test, a controlled cyclical force is applied, and the resultant shear force

asured using a load cell. Displacement is measured using an LVDT. Thus the basic stress/strain parameters are captured

d analysed to derive the Dynamic Spring Rate of the tissue under test.

ypes of extensional rheometere development of extensional rheometers has proceeded more slowly than shear rheometers, due to the challenges

ociated with generating a homogeneous extensional flow. Firstly, interactions of the test fluid or melt with solid interfaces

l result in a component of shear flow, which will compromise the results. Secondly, the strain history of all the material
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ments must be controlled and known. Thirdly, the strain rates and strain levels must be high enough to stretch the

ymeric chains beyond their normal radius of gyration, requiring instrumentation with a large range of deformation rates

d a large travel distance.

mmercially available extensional rheometers have been segregated according to their applicability to viscosity ranges.

terials with a viscosity range from approximately 0.01 to 1 Pa.s. (most polymer solutions)are best characterized with

illary breakup rheometers, opposed jet devices, or contraction flow systems. Materials with a viscosity range from

proximately 1 to 1000 Pa.s. are used in filament stretching rheometers. Materials with a high viscosity >1000 Pa.s., such

polymer melts, are best characterized by constant-length devices.[5]

ensional rheometry is commonly performed on materials that are subjected to a tensile deformation. This type of

ormation can occur during processing, such as injection molding, fiber spinning, extrusion, blow-molding, and coating

ws. It can also occur during use, such as decohesion of adhesives, pumping of hand soaps, and handling of liquid food

ducts.

ist of currently and previously marketed commercially available extensional rheometers is shown in the table below.

ommercially available extensional rheometers

Instrument Name Viscosity Range[Pa.s]

Flow Type Manufacturer

urrently

arketed

Rheotens >100 Fiber spinning Gottfert

CaBER 0.01-10Capillary

breakupThermoFisher

Sentmanat extensional

rheometer>10000 Constant length Xpansion Instruments

FiSER 1-1000

Filament

stretching

Cambridge Polymer

Group

eviously

arketed

RFX 0.01-1 Opposed Jet Rheometric Scientific

RME >10000 Constant length Rheometric Scientific

MXR2 >10000 Constant length Magna Projects

eotens

e Rheotens is a fiber spinning rheometer, suitable for polymeric melts. The material is pumped from an upstream tube,

d a set of wheels elongates the strand. A force transducer mounted on one of the wheels measures the resultantensional force. Because of the pre-shear induced as the fluid is transported through the upstream tube, a true extensional

cosity is difficult to obtain. However, the Rheotens is useful to compare the extensional flow properties of a homologous

of materials.

BER

e CaBER is a capillary breakup rheometer. A small quantity of material is placed between plates, which are rapidly

tched to a fixed level of strain. The midpoint diameter is monitored as a function of time as the fluid filament necks and

aks up under the combined forces of surface tension, gravity, and viscoelasticity. The extensional viscosity can beracted from the data as a function of strain and strain rate. This system is useful for low viscosity fluids, inks, paints,

hesives, and biological fluids.

ER


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FiSER filament stretching

extensional rheometer

e FiSER is based on the works by Sridhar et al. and Anna et al.[6] In this instrument,

et of linear motors drive a fluid filament apart at an exponentially increasing velocity

ile measuring force and diameter as a function of time and position. By deforming at

exponentially increasing rate, a constant strain rate can be achieved in the samples

rring endplate flow limitations). This system can monitor the strain-dependent

ensional viscosity, as well as stress decay following flow cessation. A detailed

sentation on the various uses of filament stretching rheometry can be found on the

T web site.[7]

ntmanat

e Sentmanat extensional rheometer (SER) is actually a fixture that can be field

alled on shear rheometers. A film of polymer is wound on two rotating drums, which

ly constant or variable strain rate extensional deformation on the polymer film. The

ss is determined from the torque exerted by the drums.

her Types of Extensional Rheometers

oustic rheometer

oustic rheometers employ a piezo-electric crystal that can easily launch a successive wave of extensions and contractions

o the fluid. This non-contact method applies an oscillating extensional stress. Acoustic rheometers measure the sound

ed and attenuation of ultrasound for a set of frequencies in the megahertz range. Sound speed is a measure of system

sticity. It can be converted into fluid compressibility. Attenuation is a measure of viscous properties. It can be converted

o viscous longitudinal modulus. In the case of a Newtonian liquid, attenuation yields information on the volume viscosity.

s type of rheometer works at much higher frequencies than others. It is suitable for studying effects with much shorter

axation times than any other rheometer.

ling Plate

impler version of the filament stretching rheometer, the falling plate rheometer sandwiches liquid between two solid

faces. The top plate is fixed, and bottom plate falls under the influence of gravity, drawing out a string of the liquid.

pillary/Contraction Flow

her systems involve liquid going through an orifice, expanding from a capillary, or sucked up from a surface into column

a vacuum.

ee also

Food rheology

Piezometer

Rheometry

Acoustic_rheometer

eferences

1. ^ Macosko, Christopher W. (1994). Rheology: Principles, Measurements, and Applications. Wiley-VCH. ISBN 0-471-

18575-2.

2. ^ Ferry, JD (1980). Viscoelastic Properties of Polymers. Wiley. ISBN 0-471-04894-1.

3. ^ Pipe, CJ; Majmudar, TS, McKinley, GH (2008). "High Shear-Rate Viscometry". Rheologica Acta47 (5-6): 621642.

doi:10.1007/s00397-008-0268-1 (http://dx.doi.org/10.1007%2Fs00397-008-0268-1).
http://dx.doi.org/10.1007%2Fs00397-008-0268-1http://en.wikipedia.org/wiki/Digital_object_identifierhttp://en.wikipedia.org/wiki/Special:BookSources/0-471-04894-1http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0-471-18575-2http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Acoustic_rheometerhttp://en.wikipedia.org/wiki/Rheometryhttp://en.wikipedia.org/wiki/Piezometerhttp://en.wikipedia.org/wiki/Food_rheologyhttp://en.wikipedia.org/wiki/Acoustic_rheometerhttp://en.wikipedia.org/wiki/File:Fiser.jpg


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4. ^ Chevalier, J; Ayela, F. (2008). "Microfluidic on chip viscometers". Rev. Sci. Instrum.79: 076102.

Bibcode:2008RScI...79g6102C (http://adsabs.harvard.edu/abs/2008RScI...79g6102C). doi:10.1063/1.2940219

(http://dx.doi.org/10.1063%2F1.2940219).

5. ^ Springer Handbook of Experimental Fluid Mechanics, Tropea, Foss, Yarin (eds), Chapter 9.1(2007)

6. ^ Sridhar, J. Non-Newtonian Fluid Mech., vol 40, 271-280 (1991); Anna, J. Non-Newtonian Fluid Mech., vol 87, 307-335

(1999)

7. ^ G. McKinley (http://web.mit.edu/nnf/presentation/sld001.htm) A decade of filament stretching rheometry

K. Walters (1975)Rheometry (Chapman & Hall) ISBN 0-412-12090-9

A.S.Dukhin and P.J.Goetz "Ultrasound for characterizing colloids", Elsevier, (2002)

xternal links

[1] (http://www.atsrheosystems.com) - Research Rheometers, Capillary Rheometers, Viscometers, Rheology

Consulting and Testing by ATS RheoSystems

[2] (http://www.malvern.com/rheology) - Rotational and Capillary Rheometers from Malvern Instruments

[3] (http://www.anton-paar.com/001/en/60/47) - Physica Rheometer from Anton Paar

[4] (http://www.brookfield.eu/products/rheometers/laboratory-rs-cone-plate.asp) - Brookfield Rheometer

[5] (http://www.thermo.com/mc) - Thermo Fisher Scientific

[6] (http://www.rheosys.com) - Rheosys Merlin VR Rotational Rheometer

[7] (http://www.rubber-testing.com) - MonTech Rubber Testing Instruments, Germany

[8] (http://www.rheotec.de/en/?doc=products-index) - Rheometer/Viscometer from RheoTec Messtechnik GmbH

[9] (http://www.tainstruments.com) - A R Series Rheometer from T A instruments Inc

[10] (http://www.acoem-group.fr/solution-materiaux.php) - Metravib DMA+ series from ACOEM

[11] (http://www.thermo.com/com/cda/product/detail/1,,17848,00.html) - CaBER extensional rheometer

[12] (http://www.testsysteme.cz/_data_app_catalogue/attachements/103_rheotens_e.pdf?PHPSESSID=10) -

Rheotens rheometer

[13] (http://www.xinst.com/results_rheology.htm) - Sentmanat Rheometer

[14] (http://www.campoly.com/fiser.html) - FiSER Extensional Rheometers[15] (http://www.zyworld.com/egoodyer/index.htm) - Goodyer Linear Skin Rhometer

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tegories: Fluid dynamics Measuring instruments

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