The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
S J Uitterdijk - One of the best experts on this subject based on the ideXlab platform.
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method for reducing surface tension effects in relative viscosity measurements with ostwald type Viscometers
Metrologia, 1997Co-Authors: S J UitterdijkAbstract:The reference for (relative) measurements of the viscosity of liquids is the viscosity of bi-distilled water at 20 °C. Applying the so-called step-up method to calibrate a series of capillary Viscometers can result in deviations of roughly 0,2 % in the first liquid, normally an oil, that is used after the distilled water. This error is mainly caused by the difference in surface tension between water and oil. This report shows that with a special Ostwald-type Viscometer, this deviation can be reduced significantly.
Fulong Liao - One of the best experts on this subject based on the ideXlab platform.
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the criteria for evaluating shear stress measuring range and the lowest measurable shear stress of rotational Viscometer
Clinical Hemorheology and Microcirculation, 2009Co-Authors: Qixue Qi, Yufen Li, Fulong LiaoAbstract:In the Guidelines for measurement of blood viscosity and erythrocyte deformability by ICSH in 1986, it points out that the Viscometer for hemorheology should ideally be able to operate over a wide range of shear conditions, and for a constant shear-rate Viscometer a high-shear measurement at 200/second and a low-shear measurement at 1/second (or shear-rates approximating to these values if they are not attainable in the instrument used) should be made [1]. It also states that a high degree of instrument sensitivity is required for measuring viscosity at low shear. A suitable shear stress measuring range and a high degree sensitivity at low shear-rate are required for measuring blood viscosity. Unfortunately, many of the industrial Viscometers do not meet the requirements [2]. In fact, the lowest measurable shear-stress is a critical parameter for a rotational blood Viscometer. However, the criteria for evaluating shear measuring range and the lowest measurable shear-stress are not clearly described in the guidelines. We proposed double 5% criteria for the evaluation, i.e. less than 5% error in viscometry and less than 5% in coefficient of variation as “measurable” criteria. Recently, we experienced the criteria with a domestic rotational Viscometer (anonym for avoiding possible conflicts in commercial interests). The Viscometer is a shear-rate controlled rotational Viscometer with double gap cylinder sensor designed for measuring blood and plasma viscosities. A suspending torsion strip is employed as the shearstress sensing element. The Viscometer works in the shear-rate range of 1–220/second and shear-stress range of 10–2000 mPa according to the specifications described in the user’s manual. The sensor temperature is controlled at fixed 37 ± 0.5◦C. The required sample volume is 1.2 ml. We selected a number of standard oils (provided by the Chinese Academy of Metrology), including GBW(E)130251, GBW(E)130253, GBW(E)130254 and GBW(E)130255, for evaluation of the viscome-
Qixue Qi - One of the best experts on this subject based on the ideXlab platform.
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the criteria for evaluating shear stress measuring range and the lowest measurable shear stress of rotational Viscometer
Clinical Hemorheology and Microcirculation, 2009Co-Authors: Qixue Qi, Yufen Li, Fulong LiaoAbstract:In the Guidelines for measurement of blood viscosity and erythrocyte deformability by ICSH in 1986, it points out that the Viscometer for hemorheology should ideally be able to operate over a wide range of shear conditions, and for a constant shear-rate Viscometer a high-shear measurement at 200/second and a low-shear measurement at 1/second (or shear-rates approximating to these values if they are not attainable in the instrument used) should be made [1]. It also states that a high degree of instrument sensitivity is required for measuring viscosity at low shear. A suitable shear stress measuring range and a high degree sensitivity at low shear-rate are required for measuring blood viscosity. Unfortunately, many of the industrial Viscometers do not meet the requirements [2]. In fact, the lowest measurable shear-stress is a critical parameter for a rotational blood Viscometer. However, the criteria for evaluating shear measuring range and the lowest measurable shear-stress are not clearly described in the guidelines. We proposed double 5% criteria for the evaluation, i.e. less than 5% error in viscometry and less than 5% in coefficient of variation as “measurable” criteria. Recently, we experienced the criteria with a domestic rotational Viscometer (anonym for avoiding possible conflicts in commercial interests). The Viscometer is a shear-rate controlled rotational Viscometer with double gap cylinder sensor designed for measuring blood and plasma viscosities. A suspending torsion strip is employed as the shearstress sensing element. The Viscometer works in the shear-rate range of 1–220/second and shear-stress range of 10–2000 mPa according to the specifications described in the user’s manual. The sensor temperature is controlled at fixed 37 ± 0.5◦C. The required sample volume is 1.2 ml. We selected a number of standard oils (provided by the Chinese Academy of Metrology), including GBW(E)130251, GBW(E)130253, GBW(E)130254 and GBW(E)130255, for evaluation of the viscome-
Jürgen Einfeldt - One of the best experts on this subject based on the ideXlab platform.
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comments on high accuracy viscosity measurements using capillary Viscometers
Metrologia, 2001Co-Authors: Jürgen EinfeldtAbstract:The working equation of a capillary Viscometer, used generally in the form ? = k? ? B/? (where ? is kinematic viscosity; ? is outflow time; k and B are Viscometer constants), can be deduced directly from the Navier-Stokes equation. The surface tension only affects the k parameter. For a Ubbelohde-type Viscometer with suspended level, the curvature of the meniscus, which compensates the influence of the mean surface tension, has been calculated. The relation often used for the capillary pressure in tubes, p? = 2?/R, is only approximately valid for radii R < 0.3 mm. The Knibbs method, which uses external variable pressure, provides a means of calibrating Viscometers to high accuracy using only one reference liquid.
Norman M. Wereley - One of the best experts on this subject based on the ideXlab platform.
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constitutive models of electrorheological and magnetorheological fluids using Viscometers
Smart Materials and Structures, 2005Co-Authors: Young-tai Choi, Seungbok Choi, Norman M. WereleyAbstract:A key aspect of application of electrorheological (ER) and magnetorheological (MR) fluids is the characterization of rheological properties. In this study, two rotational Viscometers to measure the field-dependent flow behavior (shear stress versus shear rate) of ER/MR fluids are theoretically analyzed. One is a rotational coaxial cylinder Viscometer, and the other is a rotational parallel disk Viscometer. The equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the Bingham-plastic, biviscous, and Herschel–Bulkley constitutive models. The shear stress for the rotational coaxial cylinder Viscometer can be straightforwardly calculated from the measured torque. However, in order to determine the shear rate, three approximation methods are applied. Meanwhile, the shear stress and shear rate in the rotational parallel disk Viscometer can be obtained directly from the torque and angular velocity data. In order to comprehensively understand the flow behavior of ER/MR fluids with respect to the constitutive models, nondimensional analyses are undertaken in this study.
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constitutive models of electrorheological and magnetorheological fluids using Viscometers
Smart Structures and Materials 2003: Damping and Isolation, 2003Co-Authors: Young-tai Choi, Norman M. WereleyAbstract:A key aspect of application of electrorheological (ER) and magnetorheological (MR) fluids is the characterization of rheological properties. For this purpose, two rotational Viscometers are theoretically analyzed. One is a rotational coaxial cylinder Viscometer, and the second is a rotational parallel disk Viscometer. A key goal is to determine the shear stress and shear rate of ER/MR fluids for both Viscometers from the torque and angular velocity data. To do this, the equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the Bingham-plastic, biviscous, and Herschel-Bulkley constitutive models. For simplicity in mathematical form, the Bingham-plastic model is used to describe the flow behavior of ER/MR fluids. The biviscous model characterized by static and dynamic yield stresses is used to capture the preyield behavior. The preyield region where the local shear stress is smaller than the static yield stress has much larger viscosity than the postyield region. In order to account for the shear thinning or thickening in postyield region, the Herschel-Bulkley constitutive model is used in this study. The shear stress for a rotational coaxial cylinder Viscometer can be calculated directly from measured torque. However, three approximation methods are applied to determine the shear rate. For rotational parallel disk Viscometers, the shear rate and shear stress can be obtained directly from the torque and angular velocity data. In order to comprehensively understand the flow behavior of ER/MR fluids with respect to the constitutive models, the nondimensional analyses are undertaken in this study.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Comparative analysis of Bingham characteristics of ER/MR fluids with different Viscometers
Smart Structures and Materials 2002: Damping and Isolation, 2002Co-Authors: Young-tai Choi, Norman M. WereleyAbstract:This paper theoretically presents Bingham characteristics of ER (electrorheological)/MR (magnetorheological) fluids with respect to different rotational Viscometers through comparative analysis. For doing so, two different types of rotational Viscometers are introduced and configured for ER/MR fluids; one is a rotational coaxial cylinder Viscometer and the other is a rotational parallel disk Viscometer. In order to determine the shear stress and shear rate of fluids tested in both Viscometers, the fundamental equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the biviscous constitutive model. The biviscous model is characterized by a yield stress: when the shear stress is less than this yield stress, the preyield viscosity is relatively large compared to the postyield viscosity when shear stress is greater than the yield stress. For rotational coaxial cylinder Viscometers, the shear stress can be calculated directly from the measured torque. However, for the determination of the shear rate, some strategies are required. In this study, different methods of determining the shear rate are developed and their accuracy is assessed. In the case of rotational parallel disk Viscometers, the calculation of the shear rate is straightforward from angular velocity measurements, but the shear stress requires a relatively complicated calculation. In this study, for simplicity, the shear stress is approximated and the error of this approximation is evaluated with respect to important rotational parallel disk Viscometer geometry. Finally, the Bingham characteristics of ER/MR fluids at two different rotational Viscometers are theoretically presented and compared in the shear stress vs. shear rate response.
