scholarly journals Considerations on the Primary Crystallisation Features of Various Cast Irons by means of the Apparent Viscosity Measurement in the Early Stages of Solidification

1979 ◽  
Vol 43 (2) ◽  
pp. 140-145
Author(s):  
Shoji Kiguchi ◽  
Nobutaro Kayama
Keyword(s):  
Apparent Viscosity ◽  
Viscosity Measurement ◽  
Cast Irons ◽  
Early Stages ◽  
Primary Crystallisation

scholarly journals Numerical Simulation of the Influence of Taylor Vortex on the Apparent Viscosity Measurement of Semi-Solid Metallic Based On ANSYS Fluent

2022 ◽  
Vol 2152 (1) ◽  
pp. 012061
Author(s):  
Enjie Dong ◽  
Gan Li ◽  
Xiaogang Hu ◽  
Zhong Li ◽  
Juan Chen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Apparent Viscosity ◽  
Viscosity Measurement ◽  
Taylor Vortex ◽  
Flow State ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Concentric Cylinder ◽  
Ansys Fluent ◽  
Semi Solid

Abstract The apparent viscosity of semi-solid metallic slurry with a low solid fraction, which is one of the most essential parameters for representing the rheological behavior, is mainly measured by the concentric cylinder rotational approach. The principle of this method is based on the assumptions that the fluid is in an ideal laminar flow state and obey the Newton’s internal friction law. However, as the angular velocity ω increases, the fluid undergoes a transition from a stable laminar flow state to a Taylor vortex and turbulent flow state. These unstable flow conditions such as Taylor vortex and turbulence have a severe impact on the accuracy of apparent viscosity measurement. However, these unstable flow conditions are difficult to monitored and analyzed in real time through experimental methods. Computer numerical simulation technology provides the possibility and convenience for the visualization of the flow state of the semi-solid metallic slurry in the measurement system. In this work, ANSYS Fluent was used to simulate the apparent viscosity measurement process of semi-solid slurry, and the flow state transition process of the semi-solid slurry in the measurement system was successfully visualized and analyzed. In order to avoid the influence of Taylor vortex, combined with the measurement principle of the concentric cylinder rotational rheometer and Taylor’s study on flow stability, the empirical equation of limiting speed to avoid Taylor vortex in the process of Searle rheometer viscosity measurement is given.

Viscosity (Part 1)

1981 ◽  
Vol 14 (3) ◽  
pp. 73-78 ◽  
Author(s):  
D. C-H. Cheng
Keyword(s):  
Apparent Viscosity ◽  
Absolute Measurement ◽  
Viscosity Measurement ◽  
Newtonian Fluids ◽  
Current Work ◽  
Practical Implementation ◽  
Newtonian Viscosity ◽  
Know How ◽  
The Subject ◽  
Newtonian Liquids

This article reviews the standard specifications related to viscosity measurement, issued by ASTM, BSI, IP and other standard bodies, and their applications. The know-how embodied in these specifications is discussed in relation to knowledge recorded in the literature and some aspects of practical implementation and use are considered. It is shown that standards and calibration are well established for Newtonian liquids and viscosity measurement can be accurate and precise. But, for non-Newtonian fluids, the specifications give apparent viscosity, not absolute values; and even then the results, although they can be precise, are of uncertain accuracy. It is pointed out that information exists in the literature on the subject of absolute measurement of non-Newtonian viscosity but that it needs to be simplified and codified before it can be incorporated into standard specifications. Current work towards this end is referred to.

Non-Newtonian numerical modelling of solder paste viscosity measurement

2019 ◽  
Vol 31 (3) ◽  
pp. 176-180 ◽  
Author(s):  
Tareq I. Al-Ma’aiteh ◽  
Oliver Krammer
Keyword(s):  
Apparent Viscosity ◽  
Material Model ◽  
Viscosity Measurement ◽  
Solder Paste ◽  
Material Models ◽  
Stencil Printing ◽  
Content Type ◽  
Shear Rates ◽  
Paste Viscosity ◽  
Measured Viscosity

PurposeThe purpose of this paper is to present the establishment of a computational fluid dynamics model for investigating different non-Newtonian rheological models of solder pastes by simulating solder paste viscosity measurement. A combined material model was established which can follow the measured, apparent viscosity values with lower error.Design/methodology/approachThe model included a parallel plate arrangement of rheometers. The diameter of the plate was 50 mm, whereas the gap between the plates was 0.5 mm. Only one quarter of the plate was modelled to enable using fine enough mesh, while keeping the calculation time low. Non-Newtonian properties were set using user defined function in Ansys, based on the Cross and Carreau–Yasuda material models. The viscosity values predicted by the mathematical models were compared to measured viscosity values of different types of solder pastes.FindingsIt was found that the Cross model predicts the apparent viscosity with a relatively high error (even approximately 50 per cent) at lower shear rates, whereas the Carerau–Yasuda model has higher errors at higher shear rates. The application of the proposed, combined model can result in a much lower error in the apparent viscosity between the calculated and measured viscosity values.Originality/valueThe error of Cross and Carreau–Yasuda material models has not been investigated yet in details. The proposed, combined material model can be applied for subsequent simulations via the described UDF, e.g. in the numerical modelling of the stencil printing. This can result in a more accurate modelling of the stencil printing process, which is inevitable considering the printing of solder paste for today fine-pitch, small size components.

scholarly journals Rheology of the gel formed in the California Mastitis Test

2008 ◽  
Vol 75 (4) ◽  
pp. 385-391 ◽  
Author(s):  
C Johan R Verbeek ◽  
Stephen S Xia ◽  
David Whyte
Keyword(s):  
Somatic Cell ◽  
Apparent Viscosity ◽  
Cell Concentration ◽  
Strong Dependence ◽  
Relative Viscosity ◽  
Viscosity Measurement ◽  
California Mastitis Test ◽  
Rotational Viscometry ◽  
Test Conditions ◽  
Viscosity Increase

The California Mastitis Test has previously been adapted for use in an inline, cow-side sensor and relies on the fact that the viscosity of the gel formed during the test is proportional to the somatic cell concentration. In this paper, the use of capillary and rotational viscometry was compared in light of the expected rheology of the gel formed during the test. It was found that the gel is non-Newtonian, but the initial phase of viscosity increase was not due to shear dependence, but rather due to the gelation reaction. The maximum apparent viscosity of the gel was shear dependent while the time it took to reach the maximum was not truly shear dependent, but was rather dependent on the degree of mixing during gelation. This was confirmed by introducing a delay time prior to viscosity measurement, in both capillary and rotational viscometry. It was found that by mixing the reagent and infected milk, then delaying viscosity measurement for 30 s, shortened the time it took to reach maximum viscosity by more than 60 s. The maximum apparent viscosity, however, was unaffected. It was found that capillary viscometry worked well to correlate relative viscosity with somatic cell count, but that it was sensitive to the reagent concentration. It can therefore be deduced that the rheology of the gel is complicated not only by it being non-Newtonian, but also by the strong dependence on test conditions. These make designing a successful sensor much more challenging.

Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

1983 ◽  
Vol 41 ◽  
pp. 518-519
Author(s):  
George G. Cocks ◽  
Louis Leibovitz ◽  
DoSuk D. Lee
Keyword(s):  
Crystal Structure ◽  
Crassostrea Virginica ◽  
Crystal Orientation ◽  
Developmental Changes ◽  
Gastrula Stage ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Stages Of Growth ◽  
Early Stages ◽  
Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

Formation of Dislocation Channels in Neutron Irradiated Molybdenum

1972 ◽  
Vol 30 ◽  
pp. 672-673
Author(s):  
S. Mahajan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ambient Temperature ◽  
Room Temperature ◽  
Channel Formation ◽  
Early Stages ◽  
Transmission Electron ◽  
Three Stages ◽  
Two Stages ◽  
Polycrystalline Molybdenum

The evolution of dislocation channels in irradiated metals during deformation can be envisaged to occur in three stages: (i) formation of embryonic cluster free regions, (ii) growth of these regions into microscopically observable channels and (iii) termination of their growth due to the accumulation of dislocation damage. The first two stages are particularly intriguing, and we have attempted to follow the early stages of channel formation in polycrystalline molybdenum, irradiated to 5×1019 n. cm−2 (E > 1 Mev) at the reactor ambient temperature (∼ 60°C), using transmission electron microscopy. The irradiated samples were strained, at room temperature, up to the macroscopic yield point.Figure 1 illustrates the early stages of channel formation. The observations suggest that the cluster free regions, such as A, B and C, form in isolated packets, which could subsequently link-up to evolve a channel.

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