In the dairy industry in particular, there are cream and cultured milk products whose characteristics can be partially or completely spoiled if their flow behaviour is not understood. What follows here is a brief guide to the flow behaviour of some typical dairy industry products. Rheology is defined as the science of deformation and flow of matter. The term itself originates from Greek rheos meaning 'to flow'. Rheology is applicable to all types of materials, from gases to solids.
A main issue is also the measurement, adaptation and application of viscosity data, which concerns the design calculations of processing equipment.
BUILDING BLOCKS OF DAIRY PROCESSING
The science of rheology is young, but its history is very old. Reiner, this expression means everything flows if you just wait long enough , a statement that is certainly applicable to rheology. Professor Reiner, together with Professor E. Bingham, was the founder of the science of rheology in the mids. Rheology is used in food science to define the consistency of different products.
Rheologically, the consistency is described by two components, the viscosity thickness, lack of slipperiness and the elasticity 'stickiness', structure. In practice, therefore, rheology stands for viscosity measurements, characterisation of flow behaviour and determination of material structure.
Basic knowledge of these subjects is essential in process design and product quality evaluation. One of the main issues of rheology is the definition and classification of materials. Normal glass, for instance, is usually defined as a solid material, but if the thickness of an old church window is measured from top to bottom, a difference will be noted.
Glass does, in fact, flow like a liquid, albeit very slowly. One way of characterizing a material is by its relaxation time, i.
- Non-Newtonian fluid - Wikipedia.
- THE MASTER, THE MUSE & THE POET: An Autobiography in Poetry.
- First Families.
- Course - Rheology and Non-Newtonian Fluids - KT - NTNU.
- Lethal Ladies Quizbook;
Typical magnitudes of relaxation times for materials are:. Another way of defining materials rheologically is by the terms viscous, elastic or viscoelastic. Gases and liquids are normally described as viscous fluids. By definition an ideal viscous fluid is unable to store any deformation energy. Hence, it is irreversibly deformed when subjected to stress; it flows and the deformation energy is dissipated as heat, resulting in a rise of temperature. Solids, on the other hand, are normally described as elastic materials. An ideal elastic material stores all imposed deformation energy and will consequently recover totally upon release of stress.
A viscous fluid can therefore be described as a fluid which resists the act of deformation rather than the state of deformation , while an elastic material resists the act as well as the state of deformation.
A number of materials show viscous as well as elastic properties, i. In rheology, shearing of a substance is the key to knowledge of flow behaviour and structure. A sheared flow is achieved through flow between parallel planes, rotational flow between coaxial cylinders where one cylinder is stationary and the other one is rotating, telescopic flow through capillaries and pipes, and torsional flow between parallel plates.
To enable study of the viscosity of a material, the shearing must induce stationary flow of the material. The flow occurs through rearrangement and deformation of particles and through breaking of bonds in the structure of the material.
Branding/Logomark
Shearing between parallel planes is normally used for the basic definition of shear stress and shear rate , corresponding to how much deformation is applied to the material and how fast. Newtonian fluids are those having a constant viscosity dependent on temperature but independent of the applied shear rate.
One can also say that Newtonian fluids have direct proportionality between shear stress and shear rate in laminar flow. The proportionality constant is thus equal to the viscosity of the material. A Newtonian fluid can therefore be defined by a single viscosity value at a specified temperature. Water, mineral and vegetable oils and pure sucrose solutions are examples of Newtonian fluids. Low-concentration liquids in general, such as whole milk and skim milk, may for practical purposes be characterized as Newtonian fluids.
Materials which cannot be defined by a single viscosity value at a specified temperature are called non-Newtonian. The viscosity of these materials must always be stated together with a corresponding temperature and shear rate. If the shear rate is changed, the viscosity will also change. Generally speaking, high concentration and low temperature induce or increase non-Newtonian behaviour.
Apart from being shear-rate dependent, the viscosity of non-Newtonian fluids may also be time-dependent , in which case the viscosity is a function not only of the magnitude of the shear rate but also of the duration and, in most cases, of the frequency of successive applications of shear. Non-Newtonian materials that are time independent are defined as shear-thinning, shear-thickening or plastic. Non-Newtonian materials that are time-dependent are defined as thixotropic, rheopectic or anti-thixotropic.
There was a problem providing the content you requested
The viscosity of a shear-thinning fluid also known as pseudoplastic fluid decreases with increasing shear rate. Most liquid food systems belong to this category of fluids. The shear rate dependency of the viscosity can differ substantially between different products, and also for a given liquid, depending on temperature and concentration. Typical examples of shear-thinning fluids are yoghurt, cream, juice concentrates, and salad dressings. Other Papers By First Author. Rheology of synthetic latices: Influence of shear rate and temperature journal of colloid and interface science [IF: Rheology of viscoelastic fluids: Kinetic interpretation of non-newtonian flow journal of colloid and interface science [IF: An introduction to rheology Howard A.
Krieger , Thomas J. Are you looking for Proceedings of an International Conference Submersible Technology: Proceedings of an international conference Subsea Controls and Data Acquisition ' Rheological Measurements of Non-Newtonian Fluids. Abstract The design and performance of many operations common to the petroleum industry depend upon the unique properties of a class of materials known as non-Newtonian fluids. Introduction Non-Newtonian fluids are not new in the petroleum industry. About us Contact us Help Terms of use. Publishers Content Coverage Privacy. Sheriff's Encyclopedic Dictionary of Applied Geophysics, fourth edition.