Falling Needle Viscometer Research Articles

Measurement of human blood viscosity a using Falling Needle Rheometer and the correlation to the Modified Herschel-Bulkley model equation

We measured the blood viscosity of 25 male and 25 female healthy people (total 50) using a compact-sized falling needle viscometer (Falling Needle Rheometer) capable of highly accurate measurements. Based on the analysis of the flow characteristics, most of the blood specific non-Newtonian fluid (Casson fluid) behavior was confirmed. Additionally, the blood from males has a higher apparent viscosity and Casson yield value than that from women. Furthermore, a new Herschel-Bulkley type model equation representing the relationship between the shear rate and apparent viscosity of human blood was proposed based on the measured blood flow characteristics. The proposed model improved the exponential term on the shear rate and added the constant term on the yield stress so that the measured value can be correlated with a high accuracy. Using the proposed model equation, the correlation accuracy of all of the measured human blood viscosities was better than in the Herschel-Bulkley model equation and Casson model in a wide range of shear rate regions. By incorporating numerical flow analysis (computational fluid dynamics), this model equation may contribute to analyses considering the non-Newtonian fluidity of human blood.

The Food Colloid Principle in the Design of Elderly Food

AbstractIt is necessary to control the rheological properties of bolus to prevent aspiration. To know the risk of aspiration for each person with difficulty in mastication and swallowing, it will be effective to use a test fluid which enables doctors to judge the safe range of the viscosity based on videofluorography. Since the knowledge of dominant factors which govern rheology is required, effects of shear rate, cooling rate, concentration of polysaccharides, coexisting seasonings on viscosity and viscoelasticity are overviewed. Since chemical senses are also known to affect the swallowing behavior, the relation between texture and flavor release is described briefly. Mixture of polysaccharides, proteins and fluid gels are overviewed as texture modifiers. Acoustic analysis of swallowing, extrusion method, a falling needle viscometer, tribological study on frictional coefficient of bolus are also described as each method is expected to be a useful tool to understand the complicated aspect of the disorder in mastication and deglutition. Mastication and swallowing of minced foods and model food gels are also described. Finally, the importance of the communication and collaboration between different disciplines is emphasized.Practical ApplicationsPolysaccharides have been used to modify the texture of foods. It is necessary to know how these polysaccharides influence the swallowing behavior to design foods for elderly. Since the texture of foods is influenced by taste, aroma and conversely these are influenced by texture, the knowledge on the relation between texture and flavor release is crucial to manipulate the foods to reduce the risk of aspiration. Some examples which are expected to be helpful to design foods for elderly are shown.

Pressure viscosity coefficients and traction properties of synthetic lubricants for wind turbine gear systems

ABSTRACTSynthetic lubricants are increasingly used to provide equipment reliability for wind turbine gear boxes. The majority of synthetic lubricants used today are based on polyalphaolefins. In gear systems where contact pressures are high, the pressure viscosity coefficient and traction values of the lubricant are important fundamental properties. A comparison of these properties for a wind turbine lubricant based on a polyalphaolefin and two lubricants based on polyalkylene glycols has been undertaken. Pressure viscosity coefficients were calculated from viscosity measurements made using an ultra‐high pressure falling needle viscometer at pressures up to 50 000 psi. Significant differences in properties were observed with both polyalkylene glycol lubricants showing lower pressure viscosity coefficients and much lower traction values. A calculation of the film thickness values in the Hertzian contact zone suggests that polyalkylene glycol lubricants may provide elastohydrodynamic films that are approximately 25% thicker than polyalphaolefin lubricants. Copyright © 2012 John Wiley & Sons, Ltd.

Limitation on the use of slender-body theory in Stokes flow: Falling needle viscometer errata

An attempt to model the “brush” flow, studied experimentally by Tachie et al. [Phys. Fluids 16, 445 (2004)], by means of slender-body theory revealed that a successful truncation procedure requires that a few orthogonal functions be sufficient to describe the singularity distributions. In previous applications, this was easily achieved. However, when walls and/or other slender bodies are in close proximity, a large number of basis functions are likely to be needed and a loss of diagonal dominance, indeed the eventual appearance of negative diagonal coefficients, precludes a successful truncation of the infinite system of linear equations. It was also noticed, but after the proofs had been checked, that a sign error, eradicating the above difficulty, had been made in the falling needle viscometer presentation [A. M. J. Davis and H. Brenner, Phys. Fluids 13, 3086 (2001)]. Fortunately, in that flow the bounding cylinder wall is sufficiently distant from the thin needle for a convergent truncation to be quickly achieved, and the modified numerical results, listed below, exhibit fairly limited changes.

The improvement on the falling needle viscometer

To overcome the shortcomings of the conventional falling needle viscometer, many improvements have been made, e.g., adopting new design of needle structure, collector, and launcher. Furthermore, Hall magnetic sensors and single-board computer are used in the system, which makes the measurement automatic and intelligent. It is proved in the experiment that the instrument is accurate enough and has excellent performance. The technique can also be applied in falling ball viscometers.

Experimental study of the velocity field around a falling needle viscometer

Fully developed velocity profiles around the side of a needle falling at terminal velocity in a falling needle viscometer and the flow disturbance region near the ends of the needle were experimentally investigated. A flow visualization technique was used to obtain the main features of the flow field around the falling needle. Comparisons made between the experimental and predicted fully developed velocity profile showed good agreement. The regions where the flow field is disturbed by the needle ends were analyzed from photographs and found to be about 6% of the total needle length.

Fast determination of polymer melt viscosity by optical falling needle viscometer

AbstractAn optical falling needle rheometer was employed to measure the melt viscosity of high density polyethylene (HDPE) and low molecular weight poly (tetrafluoroethylene) (PTFE). The temperature dependence of the melt viscosity of these two polymers was obtained and described by an empirical Arrhenius relation. At the present time, this method has been confirmed to be a simple and fast (within several tens of seconds for each measurement) approach to determine polymer melt viscosities of up to at least 1×105 Pa s. The sample cell containing ∼ 2.5 cm3 materials can be vacuum sealed and disposed of without the need of subsequent cleaning each time, which could be a useful feature. In comparison with HDPE, the PTEF sample melt was found to show a much higher melt viscosity with about the same degree of polymerization. © 1993 John Wiley & Sons, Inc.

Bimodal terminal velocities using the falling needle viscometer

The falling needle viscometer is a particularly useful instrument for measuring the shear viscosity when small sample volumes are necessitated. Under some conditions this instrument can exhibit bimodal terminal velocity observations which precludes a straightforward analysis to obtain the viscosity. This phenomenon is explained via an analysis for the fluid mechanics and associated entropy production of a needle falling asymmetrically with respect to the centerline of the instrument. This analysis provides a rationale for using only the smaller terminal velocities, thereby permitting an unambiguous data analysis.

Steady shear viscosity measurements of viscoelastic fluids with the falling needle viscometer

Previous measurements by other investigators of the purely viscous properties of viscoelastic fluids using the falling ball viscometer have been shown to yield anomalous results. These occur because the ball falling through the viscoelastic fluid creates a stress field which requires up to one hour to relax to its stress free state before another ball can be dropped. This is experimentally inconvenient. To further investigate this effect for a variety of viscometers, time interval measurements were made on a viscoelastic fluid (AP-273 Separan) using falling ball, falling needle and rotating cylinder viscometers. Although the falling ball measurements showed considerable time interval effects, the falling needle and rotating cylinder measurements did not. Thus the falling needle and rotating cylinder viscometers can be used to conveniently measure the steady shear viscosity of viscoelastic fluids.

Measurements of rheological fluid properties with the falling needle viscometer

The use of data from the falling needle viscometer to determine the rheological properties of purely viscous non-Newtonian fluids is described. From the solution of the basic flow equation, which is given in tabular and graphical form, a method is presented to determine rheological flow curves for both power law and more generalized rheological fluids. The use of the instrument to determine the zero shear rate viscosity is also described and a method of fitting appropriate constitutive equations to the data is discussed and illustrated by examples. Finally, a technique for measuring fluid densities using the falling needle viscometer is presented that is applicable to both Newtonian and power law fluids.

Effect of pressure on viscosity of naphthalene, phenanthrene and impregnation pitches

Viscosities of Allied 15V coal tar pitch and Ashland A-240 petroleum pitch were determined at pressures up to 101 and 67 MPa, respectively, at temperatures up to 608 and 588 K, respectively, using a falling needle viscometer. Measurements were also made on naphthalene and phenanthrene up to 101 MPa. Activation energies required to initiate shear flow under pressure were calculated from the data using the Eyring model and found to increase with pressure and to be 50%–100% greater for A-240 than for 15V. The viscosity of A-240 decreases more rapidly with increasing temperature so that at about 625 K, the effect of increasing pressure on viscosity is minimal. Activation energies for naphthalene and phenanthrene decrease with increasing pressure, suggesting increased alignment of these planar molecules and reduced resistance to initiation of flow.

The falling needle viscometer a new technique for viscosity measurements

A new type of viscometer, the “Falling Needle Viscometer” (FNV) has been developed. It has several advantages over the better known “Falling Ball Viscometer” (FBV) including better control over the trajectory and terminal velocity and a “wall correction” which is an integral part of the analytical solution. A Stokes' type solution for the FNV is presented which is compared with experimental measurements made on Glycerol. Experiments were also conducted with a Falling Ball Viscometer and Weissenberg Rheogoniometer using the same fluid and a comparison made among the three systems. Glycerol viscosities measured with the FNV agreed with those measured by the FBV and Weissenberg Rheogoniometer within approximately one percent. It is concluded that the Falling Needle Viscometer is a useful device that in some situations is superior to the Falling Ball Viscometer.