David V. Boger

Bio: David V. Boger is an academic researcher from University of Melbourne. The author has contributed to research in topics: Rheology & Viscosity. The author has an hindex of 61, co-authored 189 publications receiving 12111 citations. Previous affiliations of David V. Boger include Industrial Research Institute & Cooperative Research Centre.

Yield Stress Measurement for Concentrated Suspensions

Abstract: The measurement and use of the flow properties of highly concentrated solid‐liquid suspensions is a topic of considerable practical interest in a broad spectrum of industries. The yield stress is a rheological property that all highly concentrated suspensions may have in common. In this work four established methods for determining the yield stress are compared with a fifth and new method based on a vane test developed in soil mechanics. It is clearly shown that a single‐point measurement with the vane device is sufficient to determine accurately the yield stress in a region of high concentration where the four conventional methods are extremely tedious or not applicable. Furthermore, the vane method does not rely on any previous shearing of a suspension and hence is applicable for study of the kinetics of thixotropic systems. The work has been motivated by the need to know the yield stress of highly concentrated bauxite residue suspensions in order to establish a waste disposal strategy for the residue which is a waste product in the production of alumina from bauxite.

Direct Yield Stress Measurement with the Vane Method

Abstract: In the vane method for measuring the yield stress, the conventional analysis assumes that the stress is uniformly distributed on a cylindrical sheared surface to calculate the yield stress from the maximum torque and vane dimensions. By using two simple procedures, the present work shows that this assumption is justified at the moment of yielding. The yield stress calculated using the proposed methods compares favorably with that obtained with the conventional procedure. A comparison with the yield stress independently determined by other methods again confirms the usefulness of the vane technique as a simple but accurate method for direct yield stress measurement.

Microfluidics: Fluid physics at the nanoliter scale

Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

Drop Impact Dynamics: Splashing, Spreading, Receding, Bouncing ...

Abstract: The review deals with drop impacts on thin liquid layers and dry surfaces. The impacts resulting in crown formation are referred to as splashing. Crowns and their propagation are discussed in detail, as well as some additional kindred, albeit nonsplashing, phenomena like drop spreading and deposition, receding (recoil), jetting, fingering, and rebound. The review begins with an explanation of various practical motivations feeding the interest in the fascinating phenomena of drop impact, and the above-mentioned topics are then considered in their experimental, theoretical, and computational aspects.

Physics of liquid jets

Abstract: Jets, ie collimated streams of matter, occur from the microscale up to the large-scale structure of the universe Our focus will be mostly on surface tension effects, which result from the cohesive properties of liquids Paradoxically, cohesive forces promote the breakup of jets, widely encountered in nature, technology and basic science, for example in nuclear fission, DNA sampling, medical diagnostics, sprays, agricultural irrigation and jet engine technology Liquid jets thus serve as a paradigm for free-surface motion, hydrodynamic instability and singularity formation leading to drop breakup In addition to their practical usefulness, jets are an ideal probe for liquid properties, such as surface tension, viscosity or non-Newtonian rheology They also arise from the last but one topology change of liquid masses bursting into sprays Jet dynamics are sensitive to the turbulent or thermal excitation of the fluid, as well as to the surrounding gas or fluid medium The aim of this review is to provide a unified description of the fundamental and the technological aspects of these subjects

Thixotropy—a review

Abstract: The ensuing mechanical response to stressing or straining a structured liquid results in various viscoelastic phenomena, either in the linear region where the microstructure responds linearly with respect to the stress and strain but does not itself change, or in the nonlinear region where the microstructure does change in response to the imposed stresses and strains, but does so reversibly. The complication of thixotropy arises because this reversible, microstructural change itself takes time to come about due to local spatial rearrangement of the components. This frequently found time-response of a microstructure that is itself changing with time makes thixotropic, viscoelastic behaviour one of the greatest challenges facing rheologists today, in terms of its accurate experimental characterisation and its adequate theoretical description. Here a history of thixotropy is given, together with a description of how it is understood today in various parts of the scientific community. Then a mechanistic description of thixotropy is presented, together with a series of applications where thixotropy is important. A list of different examples of thixotropic systems is then given. Finally the various kinds of theories that have been put forward to describe the phenomenon mathematically are listed.