Orifice Flowmeter for Measuring Extensional Rheological Properties (original) (raw)
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Akhter Salma Development of a Novel Rheometric Device For the Determination of Pressure Dependent Viscosity of Non Newtonian Fluids Master of Engineering Thesis Dublin City University, 2000
Special thanks to Mr Liam Domican and Mr Michael Tyrell for their technical assistance at various stages of this work I would also like to thank all the technicians of the workshop of the School of Mechanical and Manufacturing Engineering for their help and cooperation dunng the manufacturing of the ng I would also like to thank Michelle Considme for her cooperation in relation
Measuring uniaxial extensional viscosity using a modified rotational rheometer
Journal of Non-Newtonian Fluid Mechanics, 1999
Knowledge of the extensional behaviour of polymer melts is extremely important due to the industrial relevance of extensional flows in common processing techniques and sequences such as blow moulding, film blowing, fibre spinning, melt flow through extrusion dies and injection mould filling. One of the main problems both researchers and industrialists come across is the fact that, unlike shear flows, steady-state extensional flows are not easy to generate and maintain experimentally. This fact limits the extent to which one can characterise the materials and, therefore, the degree of optimisation of the productive process. In this paper, a modification to a commercially available controlled rate rotational rheometer is proposed in order to produce a cheap, easy to set-up, flexible extensional rheometer. This is based on the well-known Meissner-type extensional rheometer and makes use of the accurate velocity control and torque measurement possibilities of the rotational apparatus. In this case, the adaptation was performed on a TA Instruments Weissenberg Rheogoniometer, but the idea is applicable to most other similar devices. The feasibility of the modification will be discussed and confirmed, results being presented for two materials at different temperatures. These include the calculation of transient uniaxial extensional viscosity and a study of rupture conditions.
A Viscosity Function for Viscoplastic Liquids
2004
A viscosity function for highly-shear-thinning or yield-stress liquids such as pastes and slurries is proposed. This function is continuous and presents a low shear-rate viscosity plateau, followed by a sharp viscosity drop at a threshold shear stress value (yield stress), and a subsequent power-law region. The equation was fitted to data for Carbopol aqueous solutions at two different concentrations, a drilling fluid, an water/oil emulsion, a commercial mayonnaise, and a paper coating formulation. The quality of the fittings was generally good.
Inertial Method of Viscosity Measurement of the Complex Rheology Medium
Procedia Engineering
Modern lubricants have a complex content and complex rheological properties: the viscosity of oils depends on the shear rate, pressure and temperature. Strange as it is, the complication of the rheological properties of the studied medium requires the simplification of thermomechanical testing conditions. It is due to the necessity of development of the homogeneous distribution of the thermomechanical values and the flow conditions with the known type of the stress-strain state. The authors offer a theoretical justification of a new method of the viscosity measurement of the complex rheology medium which combines the advantages of known rotational and capillary methods. The medium under study moves in the torus-shaped channel under the influence of the inertial forces, during this movement the friction torque is measured and the viscosity is calculated. The problem of a non-stationary and non-isothermal movement of the complex rheology medium in the torus-shaped channel has been studied. Based on the similarity theory and the analysis of the equability of the dimensions, the conditions were determined, under which the strain rate tensor has the simplest form, on the surface of the torus the distributions of the thermomechanical values are homogeneous, and pressure and temperature are homogeneous across the whole object. Based on the movement equation projected on one of the axis in the toroidal coordinates, the method of viscosity calculation was developed. Moreover, the prototype of the test rig and the data acquisition and measurement system were developed which allow to apply the automated experimental study on the subject.
Development of a scraper-rheometer for food applications: Rheological calibration
Journal of Food Engineering, 2008
ABSTRACT In order to follow the rheology of food products during heat processes in scraped surface heat exchangers, an original device was developed. It consists of a cylindrical viscometer equipped with scraper blades and called “scraper-rheometer”. An experimental rheological calibration of this system was performed by using several calibrated Newtonian fluids (silicon oils) and non-Newtonian shear thinning fluids (xanthan and CMC solutions) in laminar and isothermal conditions. The Couette analogy was used with calibrated Newtonian fluids in order to calculate an outer equivalent radius of the cup. It was then possible to determine the viscosity of a Newtonian sucrose solution and the apparent viscosity of shear thinning xanthan and CMC solutions in scraper-rheometer. Measured viscosities in this atypical geometry were in good agreement with reported literature values or with measurements performed with a classical geometry. These results indicate that the scraper-rheometer is a promising tool to follow rheology of most food products subjected to heat transfer and shear rates and showing Newtonian or shear thinning behavior such as ice cream, butter or chocolate.
A new on-line process rheometer for highly viscous food and animal feed materials
Journal of Food Engineering, 2007
Rheological characterization of food and animal feed materials during manufacture is necessary to optimize processes, also to achieve better quality of products. Existing laboratory instruments measure accurately rheological parameters, but the complex rheological behavior of food/feed materials depends upon time, shear, temperature, pressure and process history that restricts the validity of results when retrieving information to the process. A new rheometer is developed having a similar working principle to the ones used during manufacturing process. The system allows measurement of materials taken form the process in a continuous manner. The developed rheometer uses torque and rotational speed to predict viscosity by means of an average shear stress and a mean shear rate. From a first prototype, it was possible to predict viscosity with an accuracy of ±25 Pa s over a large range of viscosities (30-450 Pa s), using polybuthene-1 as the process fluid. More research and developments are needed to describe additional capabilities given by an exchangeable die that can extend the range of viscosity measurements.
Journal of Non-Newtonian Fluid Mechanics, 2003
A method for measuring the elongational viscosity of polymer melts and solutions has been generalized and evaluated by means of numerical simulations. The method involves passing a material through a cylindrical, converging die whose semihyperbolic shape mandates a shear-free, or nearly shear-free, flow within the die, assuming wall slip. From the analysis of the relevant flow equations in the die, an expression for elongational viscosity is derived under less restrictive conditions than in previous studies. This expression consists of two terms, one of which is a measurable effective elongational viscosity defined in terms of the change in pressure over the die, the volumetric flow rate and the Hencky strain determined by the geometry. To evaluate this method, finite element techniques are used to calculate the flow of a low-density polyethylene melt in two semihyperbolically converging dies. After confirming that purely elongational flow is produced within the die, assuming wall slip, the effective elongational viscosity is computed from the calculated flow field and these values are compared with the values of elongational viscosity found by integrating the constitutive equation for the material in elongational flow. Over the wide range of elongation rates considered, very good agreement is found between these two sets of values when the time associated with the effective viscosity is appropriately specified. Further, a similar analysis for a Newtonian fluid showed that the effective elongational viscosity satisfies the Trouton ratio over the range of elongation rates considered. These results indicate that the measured effective elongational viscosity is an excellent approximation to the material's true elongational viscosity. Consequently, semihyperbolically converging dies can be used effectively to obtain transient elongational viscosity measurements at constant strain or constant strain rate.
Squeezing Flow for Rheological Characterisation of Food Materials
The rheological behaviour of commercial mayonnaises is investigated by means of a squeeze flow rheometer. Theoretical study is based on plastic flow analysis. Data analysis of this test shows that the mayonnaises behaviour at low shear rate is mainly plastic. Result analysis allows differentiating the material rheological response and the material friction effect on the plates. Results highlight the influence of the boundary conditions and roughness conditions. The increasing of compression speed changes the value of apparent plastic yield value and the friction yield value. A tribological law links friction stress and sliding velocity. The interface effects are not the same for all the tested mayonnaises. A probable change of internal structure explains this phenomenon. Finally, the simple compression test proved suitable for food materials characterisation.