Technical note: The yield stress—An engineering reality

Hartnett, J.P.; Hu, Robert

doi:10.1122/1.550006

Cited by 118 publications

(39 citation statements)

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“…', where he presents numerous viscosity versus shear stress curves with viscosity plateaus at low stresses (Barnes 1999). Following the initial publication by Barnes, a number of papers appeared that discuss the definition of yield stress fluids, whether such things existed or not, and how to demonstrate them either way (Hartnett & Hu 1989;Schurz 1990;Evans 1992;Spaans & Williams 1995;Barnes 1999Barnes , 2007. The outcome of this debate has been that the rheology community at present holds two coexisting and conflicting views: (i) the yield stress marks a transition between a liquid state and a solid state and (ii) the yield stress marks a transition between two fluid states that are not fundamentally different-but with very different viscosities.…”

Section: (B) Simple Yield Stress Fluidsmentioning

confidence: 99%

An attempt to categorize yield stress fluid behaviour

Møller

Fall

Chikkadi

et al. 2009

Phil. Trans. R. Soc. A.

240

208

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We propose a new view on yield stress materials. Dense suspensions and many other materials have a yield stress-they flow only if a large enough shear stress is exerted on them. There has been an ongoing debate in the literature on whether true yield stress fluids exist, and even whether the concept is useful. This is mainly due to the experimental difficulties in determining the yield stress. We show that most if not all of these difficulties disappear when a clear distinction is made between two types of yield stress fluids: thixotropic and simple ones. For the former, adequate experimental protocols need to be employed that take into account the time evolution of these materials: ageing and shear rejuvenation. This solves the problem of experimental determination of the yield stress. Also, we show that true yield stress materials indeed exist, and in addition, we account for shear banding that is generically observed in yield stress fluids.

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Section: (B) Simple Yield Stress Fluidsmentioning

confidence: 99%

An attempt to categorize yield stress fluid behaviour

Møller

Fall

Chikkadi

et al. 2009

Phil. Trans. R. Soc. A.

240

208

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show abstract

“…Following these publications, a series of papers appeared discussing the proper definition of yield stress fluids, whether they existed or not, and how to demonstrate either way, e.g. [4][5][6][7][8]. The outcome of this debate has been that the rheology and soft matter communities presently hold two coexisting yet conflicting views: 1) the yield stress marks a transition between a liquid state and a solid state, and 2) the yield stress marks a transition between two fluid states that are not fundamentally different -but with very different viscosities.…”

mentioning

confidence: 99%

Origin of apparent viscosity in yield stress fluids below yielding

Møller¹,

Fall²,

Bonn³

2009

Europhys. Lett.

165

132

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Origin of apparent viscosity in yield stress fluids below yieldingMøller, P.C.F.; Fall, A.; Bonn, D. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract -For more than 20 years it has been debated if yield stress fluids are solid below the yield stress or actually flow; whether true yield stress fluids exist or not. Advocates of the true yield stress picture have demonstrated that the effective viscosity increases very rapidly as the stress is decreased towards the yield stress. Opponents have shown that this viscosity increase levels off, and that the material behaves as a Newtonian fluid of very high viscosity below the yield stress.In this paper, we demonstrate experimentally (on four different materials, using three different rheometers, five different geometries, and two different measurement methods) that the low-stress Newtonian viscosity is an artifact that arises in non-steady-state experiments. For measurements as long as 10 4 seconds we find that the value of the "Newtonian viscosity" increases indefinitely. This proves that the yield stress exists and marks a sharp transition between flowing states and states where the steady-state viscosity is infinite -a solid!

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“…While the existence of yield stress has been challenged by arguing that all materials will flow when exposed to a shear stress given sufficient time from a practical standpoint there is little doubt that yield stress is an engineering reality [3,4].…”

Section: Rheology Backgroundmentioning

confidence: 99%

Plugging of Parallel-Tube Devices with Fluid Foods

Br¹,

C²,

L³

2016

J Food Process Technol

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Plugging often occurs when fluid foods are processed in parallel-tube devices (e.g., tubular heat exchangers and membrane filtration modules, especially when fluids are concentrated). Plugging reduces productivity by reducing performance and causing downtime to remove the plug. The cause of plugging is explained here for the first time and a means of avoiding it is described. Plugging rarely occurs during normal operation while fluid food is being pumped through the tubes, but rather when the tubes are flushed with water, e.g., prior to routine cleaning. The study identified two prerequisites for plugging to occur: tubes must have unequal resistances to flow and the fluid food must possess a yield stress that exceeds a value which depends on the device geometry.

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Technical note: The yield stress—An engineering reality

Cited by 118 publications

References 0 publications

An attempt to categorize yield stress fluid behaviour

An attempt to categorize yield stress fluid behaviour

Origin of apparent viscosity in yield stress fluids below yielding

Plugging of Parallel-Tube Devices with Fluid Foods

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