Direction Of Centrifugal Force Research Articles

Wear of Al/Al 3Zr functionally graded materials fabricated by centrifugal solid-particle method

In this study, Al–5mass%Zr functionally graded materials (FGMs) were fabricated by the centrifugal solid-particle method (CSPM) under applied centrifugal force of 30, 60 and 120 G (units of gravity). Microstructural observation along the centrifugal force direction showed that Al 3Zr platelet particles are almost oriented normal to the applied centrifugal force direction. Volume fraction of Al 3Zr particles increases close to the ring surface. Moreover, this distribution range of Al 3Zr particles becomes broader with decreasing the applied centrifugal force. The wear anisotropy of the fabricated Al/Al 3Zr FGMs was strongly influenced by the platelet particles orientation at the test position. Investigating both of the worn surface morphology and the sub-worn surface layer showed that plastic deformation induced wear is the dominant mechanism during the wear process of Al/Al 3Zr FGMs samples. Therefore, some of the tested samples were severely deformed and an Al 3Zr particles-free layer containing Al–Zr supersaturated solid solution was observed very near to the worn surface during the wear test.

Numerical modeling and experimental validation of uniform microchamber filling in centrifugal microfluidics

In this paper, a comprehensive approach to numerical and experimental analysis of microchamber filling in centrifugal microfluidics is presented. In the development of micro total analysis systems, it is often necessary to achieve complete, uniform filling of relatively large microchambers, such as those needed for nucleic acid amplification or detection. With centrifugal devices, these large microchambers must often be orientated perpendicularly to the direction of centrifugal force and are usually bounded by materials with varying surface properties. The resulting fluidic flow in such systems can be complex and is not well characterized. To gain further insight into complex fluidic behavior on centrifugal microfluidic platforms, numerical modeling using the Volume of Fluids method is performed to simulate microchamber filling in a centrifugal microfluidic device with integrated sample preparation, amplification, and detection capabilities. Parametric analyses are performed using numerical models to predict microchamber filling behavior for a range of pressure conditions. High-speed flow visualization techniques are used to track the liquid meniscus during filling of the microchambers, and comparison to the numerical predictions for experimental validation is achieved by analyzing the liquid volume fraction as a function of the non-dimensional temporal profile during filling. When channel filling profiles are compared, the numerical model predictions utilizing static conditions are in strong agreement with the experimental data. When dynamic modeling conditions are used, the numerical predictions are extremely accurate as compared to the experimental data.

Investigation of the Mechanical Properties in Al/Al<sub>3</sub>Zr FGMs Fabricated by Centrifugal Casting Method

Al-5mass%Zr FGMs fabricated by centrifugal casting method (CCM) have a very interesting microstructure. Since the intermetallics compounds of Al3Zr are plate in shape, Al3Zr platelet particles are almost oriented normal to the applied centrifugal-force direction. Considering this microstructure, the mechanical properties of Al/Al3Zr FGMs would vary for the same sample depending on the particles orientation and their volume fraction in the tested position. In this study, some mechanical properties of Al/Al3Zr FGMs were investigated. Al/Al3Zr FGMs rings were produced by CCM, under applied centrifugal force of 30, 60 and 120G (units of gravity). Microstructural observation along the centrifugal force direction was carried out. The platelet Al3Zr particles were almost oriented normal to the applied centrifugal force direction. The volume-fraction of Al3Zr particles increases close to the ring surface. Moreover, this distribution range of Al3Zr particles becomes broader with decreasing the applied centrifugal force. The same distribution trends were also observed for the hardness values. The Compression tests were also performed for further investigation of the mechanical properties. Samples under G=30 showed the lowest the 0.2%proof stress while those cast under G=120 had the highest 0.2% proof stress.

Development, Dielectric, and Thermal Studies on HAF Carbon-filled Polyester Gradient Composites

In this study, high abrasion furnace carbon having particle size 28—36 nm has been incorporated in unsaturated polyester resin to develop gradient composites. Dielectric measurements have been conducted on the graded composites by using a LCR meter. Effect of temperature and frequency variation on dielectric constant (ε′), dielectric dissipation factor (tan δ) and on a. c. conductivity (σa.c.) of the samples have been determined. Dielectric measurements have been performed in the temperature range from 30°C to 150°C and in the frequency range 1—10 kHz. Dielectric constant increases gradually with the increase of filler content in the direction of centrifugal force, which shows the existence of gradient structure in the composite. This is confirmed based on the microstructures observed at different positions in the graded composites. On increase of frequency, reduction in dielectric constant in carbon-filled polyester composites has been formed. Dielectric constant and a.c. conductivity increased with increase in temperature. ε′ variation with temperature shows a plateau which shifts from 145°C to 125°C on increase of carbon content. Linear dependence of ln σ0 on Ea follows the compensation law for HAF carbon-filled polyester gradient composite, which is similar to semi conducting composite behavior. Tg obtained by DSC plots for samples 1—4 are higher as compared to polyester resin.

Isotope Fractionation due to Sedimentation of Atoms in Centrifuged Indium-Lead Alloy

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 x 106 g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). 206Pb/208Pb and 207Pb/208Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy 208Pb isotope abundance increased and the light 206Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of 206Pb/208Pb versus 207Pb/208Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.

Effect of Wind Pressure on Horizontal Alignment of Highways

The geometric design of highway alignment consists mainly of the design of horizontal alignment and Vertical alignment. The more important step in horizontal alignment design is the curve radius determination. The equation used for horizontal curve radius determination is developed with assumption that when vehicle run on curved section, there are an acting force on it. This force include the centrifugal force that try to push vehicle out off its path , on the other hand there are resisting forces try to keep the vehicle on its path. Those include the friction between road surface and tires and forces resulting from sloping the highway cross section. When a vehicle on rural highway with high embankment the wind Pressure will play an important role in force system acting on vehicle because of increasing in wind pressure intensity at these conditions (rural highway, i.e open areas, high embankment). The purpose of this paper is to present a new equation for horizontal curve radius determination taking in to account the wind force effect in addition to other forces acting on vehicle The resulting equation relates vehicle length, height and weight and the wind pressure as well as the other factors in traditional equation. Effect of each parameter on design radius was investigated for the case where the wind direction is acted with the same centrifugal force direction. It has been found that the required minimum radius increase with the decreasing of vehicle weight or in the other words the vehicle permitted speed decrease with the decreasing of vehicle weight. On the other hand, the required curve radius increases with vehicle height increasing. Consequently, permitted height of bags loaded on a truck is related to the type of loads. Derived equation can also be used for estimation of the permitted truck speed on existing roads especially in case of bad weathers The comparison between the traditional and suggested equation showed that maximum difference is about 160 % which results at high wind pressure while the difference is up to 20 % for low wind pressure

Isotope Fluctuation in Indium-Lead Alloy Induced by Solid Centrifugation

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge experiment under conditions that a gravitational field of 0.81 × 106G for 100 hours at 150°C (solid state) in our previous study. The isotope fluctuation on this sample was measured using secondary ion mass spectrometer (SIMS). The 115In/113In isotope ratio changed with positive gradient in the direction of centrifugal force approximately 1.2%. The isotope ratio fluctuation of centrifuged sample was 4 times larger than that of starting sample (<0.3%). This showed that the isotope fractionation effect was induced by solid centrifugation in this alloy, although achieved concentration gradients were small.

Investigations on d.c. conductivity behaviour of milled carbon fibre reinforced epoxy graded composites

This paper reports the d.c. conductivity behaviour of milled carbon fibre reinforced polysulphide modified epoxy gradient composites. Milled carbon fibre reinforced composites having 3 vol. % of milled carbon fibre and poly sulphide modified epoxy resin have been developed. D.C. conductivity measurements are conducted on the graded composites by using an Electrometer in the temperature range from 26°C to 150°C. D.C. conductivity increases with the increase of distance in the direction of centrifugal force, which shows the formation of graded structure with the composites. D.C. conductivity increases on increase of milled carbon fibre content from 0·45 to 1·66 vol.%. At 50°C, d.c. conductivity values were 1·85 × 10−11, 1·08 × 10−11 and 2·16 × 10−12 for samples 1, 2 and 3, respectively. The activation energy values for different composite samples 1, 2 and 3 are 0·489, 0·565 and 0·654 eV, respectively which shows decrease in activation energy with increase of fibre content.

Development and high stress abrasive wear behavior of milled carbon fiber‐reinforced epoxy gradient composites

AbstractMilled carbon fiber‐reinforced polysulfide‐modified epoxy gradient composites have been developed. Density and hardness increases with the increase of carbon fiber content in the direction of centrifugal force, which shows the formation of gradient structure in the composite. High stress abrasive wear test was conducted on the gradient composites by using a Suga Abrasion Wear Tester. Abrasive wear rate reduced on increase of milled carbon fiber content from 0.15 to 1.66 vol%. Reduction in abrasive wear rate in milled carbon fiber‐reinforced epoxy gradient composites has been attributed to the increase of hardness, presence of random milled fibers, and debris of composite materials, which gave resistance and reduced wear rate. There is a small decrease in specific wear rate on adding 0.15 vol% milled carbon fibers. Further decrease of specific wear rate is observed on adding 0.45 vol% milled carbon fibers. After 3 N load, there is a decrease in specific wear rate behavior on adding 0.45 vol% carbon fibers, which further decreases on adding 0.60 vol% of carbon fibers. There is a remarkable decrease in specific wear rate up to 5 N load for 1.66 vol% milled carbon fiber‐reinforced composite. Reduction in specific wear rate on adding milled carbon fibers is based on the formation of debris, which remained intact in their respective positions due to the interfacial adhesion between milled carbon fibers and epoxy resin. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Numerical study of turbulent forced convection in coiled flow inverter

A numerical study is done to investigate turbulent forced convection in a new device of coiled flow inverter. The proposed device works on the technique based on flow inversion by changing the direction of centrifugal force in helically coiled tubes thus enabling rotation of the plane of vortex. The objective of the present study is to characterize the flow development and temperature fields in coiled flow inverter (CFI) under turbulent flow for the range of 10,000 < N Re < 30,000. The flow pattern obtained for the curved tubes are in agreement to those observed by the previous investigators [1,2]. However, a slight rotation of contours was observed in case of helical coil with finite pitch. Similar rotation of contours was found even with fluids of different Prandtl number (0.7 ≤ N Pr ≤ 150) in helical coil with constant pitch. The study was also carried out for different fluids (air, water, kerosene and ethylene glycol). The coiled flow inverter shows 4–13% enhancement in the heat transfer as compared to the straight helical coil while relative pressure drop is 2–9%. The gain in heat transfer in coiled flow inverter for turbulent flow condition as compared to the straight tube for same flow rate and boundary conditions is 35–45% while the increase in pressure drop is 29–30%.

Estimation of Concentration of Particles in Polymerizing Fluid during Centrifugal Casting of Functionally Graded Polymer Composites

The concentration of uniformly distributed particles in a fluid changes with time in the direction of gravitational or centrifugal force to form a concentration gradient. The change in the concentration is an outcome of velocity variation of particles in a fluid. A modified equation for terminal velocity, vm of particles in polymerizing-fluid under centrifugal force is proposed to estimate the changes in the volume fraction of particles in the graded composites. The proposed equation introduces the effect of cure kinetics of polymer and its effect on particle movement in the model that was based on the modified Stoke’s law, considering the parameters related to particle hindrance, centrifugal force, particle dimensions, viscosity variation etc. The model predictions of concentration changes at the different locations of samples were compared with calcium carbonate filled polysulphide-modified-epoxy graded composites prepared by centrifugal casting.. The effect of particle size, delayed curing rate of matrix were explored. The simulated results are in good agreement with those of experiments.

Numerical simulation of steady flow fields in coiled flow inverter

Flatter velocity profiles and more uniform thermal environments are extremely desirous factors for improved performance in flow reactors and heat exchangers. One means of achieving it in laminar flow systems is to use mixers and flow inverters. In the present study a new device is introduced based on the flow inversion by changing the direction of centrifugal force in helically coiled tubes. The objective of the present study is to characterize flow development and temperature fields in the proposed device made up from the configurations of bent coils. The main mechanism generating the flow is the production of spatially chaotic path by changing the direction of flow using a 90° bend in helical coils (alternating Dean flow). If the direction of centrifugal force is rotated by any angle, the plane of vortex formation also rotates with the same angle. Thus in helical flow a 90° shift in the direction of centrifugal force cause a complete flow inversion. Complete flow fields and thermal fields in helical coil and bent coil configuration were studied using computational fluid dynamics software (FLUENT 6.0). The three-dimensional governing equations for momentum and energy under the laminar flow conditions were solved with a control-volume finite difference method (CVFDM) with second-order accuracy. The flow pattern obtained for the helical coil was in good agreement to those observed by the previous investigators [S.W. Jones, O.M. Thomas, H. Aref, Chaotic advection by laminar flow in twisted pipe. J. Fluid Mech. 209 (1989) 335–357; Ch. Duchene, H. Peerhossaini, P.J. Michard, On the velocity field and tracer patterns in a twisted duct flow. Phys. Fluids 7 (1995) 1307–1317]. The comparison of the flow fields and temperature fields in the helical tube and bent coil configuration are discussed. The bent coil configuration shows a 20–30% enhancement in the heat transfer due to chaotic mixing while relative pressure drop is 5–6%. The results of the present study can be used to model transport processes for developing flows in curved tubes such as chromatographic columns (less axial dispersion [A.K. Saxena, K.D.P. Nigam, Coiled configuration for flow inversion and its effect on residence time distribution. AIChE J. 30 (1984) 363–368]), Chemical reactors (narrower RTD), heat transfer devices, and some biomedical devices.

Particle Distribution and Orientation in Al-Al&lt;sub&gt;3&lt;/sub&gt;Zr and Al-Al&lt;sub&gt;3&lt;/sub&gt;Ti FGMs Produced by the Centrifugal Method

Al-Al3Zr and Al-Al3Ti functionally graded materials (FGMs) were produced by a centrifugal method from Al-5wt% Zr and Al-5wt% Ti alloys, respectively. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Microstructural characterization was performed to evaluate the intermetallic particles’ distribution and orientation. Knoop hardness tests were carried out, with the indenter’s long diameter normal to the centrifugal force direction. Both the Al3Zr and the Al3Ti intermetallic particles are platelet in morphology. These platelets tend to be oriented normal to the centrifugal force direction. Higher applied centrifugal force increases both the intermetallic platelet volume fraction as well as their orientation in the outer regions of the fabricated FGM rings. Also higher orientation and volume fraction distribution are observed in the Al- Al3Ti FGMs. Knoop hardness measurements in general follow the same trend as the intermetallic particle volume fraction for each sample.

Aluminum Matrix Texture and Particle Characterization in Al-Al&lt;sub&gt;3&lt;/sub&gt;Ti FGMs Produced by a Centrifugal Solid-Particle Method

The centrifugal solid-particle method has proved to be effective in producing functionally graded materials (FGMs). In this study, Al-Al3Ti FGMs, were produced by this centrifugal method, from an Al-5 wt % Ti master alloy. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Samples from the outer surface of each specimen were cut and aluminum matrix texture analyzed by Schulz reflection method. Analysis of the resulting pole figures indicates a preferred orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the applied centrifugal force enhances the orientation effect. Al3Ti platelet orientation and area fraction at the samples’ outer surface along three observation planes were also measured. The Al3Ti platelets in the outer region are orientated perpendicular to the centrifugal force direction along two of the observed planes, also an increase in centrifugal force leads to an increase in orientation in those two planes. The intermetallic particle volume fraction also increases with higher applied centrifugal force, although not significantly. A correlation appears to exist between particle orientation and the preferred orientation of the matrix.

Functionally Graded Material Fabricated by a Centrifugal Method from ZK60A Magnesium Alloy

Magnesium based functionally graded material (FGM) was fabricated by a centrifugal method from ZK60A (Mg–5.5 mass%Zn– 0.6 mass%Zr) alloy. The applied G numbers are 40, 80 and 120, where the G number is the centrifugal force in unit of gravity. The specimen shape was cylindrical with 18 mm in length. Microstructures of the fabricated FGM specimens were observed using SEM. Energy dispersive Xray analysis was performed to study the chemical compositional gradients within the fabricated FGM specimens. It was found that concentration of Zr in the specimens increases toward the centrifugal force direction, while no or quite small chemical compositional gradient of MgZn2 appears. A hardness change along the centrifugal force direction was also found. The graded structures are caused by the difference in the formation mechanisms of compositional gradient during the centrifugal method between Zr and Zn.

Centrifugal effects on combustion synthesis of (Ti–B–C) compound system

A centrifugal force plays an important role on the control of combustion synthesis. In the present work, the data of reaction propagation rates obtained by changing the direction of reaction propagation and centrifugal force are evaluated in order to make clear the effect of centrifugal force on reaction propagations and product formation. As a result, the reaction propagation rate in the case of the direction of centrifugal force inverse to reaction propagation is larger than that in the case of the same direction, and product grains become smaller in size. It is confirmed that the centrifugal effect is much larger for the present combustion synthesis process in the case that the reaction propagates inversely to the direction of centrifugal force. Since molten titanium near combustion front tends to coalesce into larger drops in that case, reactants of boron and carbon would diffuse more sufficiently into titanium.

Parametric acceleration - the effect of inward pull of the golf club at impact stage

The inward pull motion at the impact stage of the golf swing commonly observed with expert players was investigated in this paper. First, a model of nonconcentrated rotation was studied. It was found that, for a mass rotating around a pivot, if the pivot is moved in the direction opposite to the direction of centrifugal force of the mass, the kinetic energy of the mass could be increased. The increase is a result of the mutual action of the two governing factors of the system, which are the centripetal force and the pull velocity. A special type of equation of motion governs this phenomenon  ha _ n sin ha 0, and the parameter in the second term of the left-hand side of the equation _ n characterizes its behaviour. The phenomenon is called the parametric acceleration, following the parametric excitation of vibration problems also governed by a similar equation. Second, the golf swing was investigated using the above finding. In the golf swing, the club is accelerated by the hands in a tangential direction. Theoretically, the additional acceleration of the clubhead could be achieved by pulling the club in the radial direction at impact stage, assuming that the centrifugal force of the clubhead is fully developed. To test this idea, an emulation using a modified double-link model was carried out. It was shown that the clubhead velocity could be increased substantially by the inward pull motion of the club at the impact stage, at which point no other means of acceleration is available. Discussions include the actual movement of the body for the inward pull, the efficiency of the pull motion and application to other sports.

Evaluation of three-dimensional orientation of Al 3Ti platelet in Al-based functionally graded materials fabricated by a centrifugal casting technique

Al-Al 3Ti functionally graded materials (FGMs) are fabricated by a centrifugal casting technique. The Al 3Ti particle morphology is observed along three orthogonal planes, i.e. perpendicular to the rotation axis (OP1), perpendicular to the rotation direction (OP2), and perpendicular to the radial direction (the centrifugal force direction) (OP3). The Al 3Ti particles are platelet in morphology and their planes are oriented nearly perpendicular to the radial direction. It is found that the orientation of Al 3Ti platelets was distributed in the Al-Al 3Ti FGMs in a gradually graded manner as well as the volume fraction of Al 3Ti platelets. Namely, a larger volume fraction of Al 3Ti platelets and a greater orientation of them are observed in the outer region of the ring. Moreover, there is a three-dimensional correlation in the orientation of Al 3Ti platelets. Based on geometrical considerations, the orientation of the platelets on one observation plane of the orthogonal planes can be estimated from measurements on a plane perpendicular to the radial direction. The estimated orientation distribution closely agrees with that experimentally observed. Since each Al 3Ti platelet-particle has almost the same orientation angle on two different planes, the orientation profiles observed on OP1 are very similar to those along OP2.

Assessment of the otolith-autonomic response using spectral analysis of the R-R interval and blood pressure

The effects of otolith stimulation on systolic blood pressure (SBP) and R-R interval fluctuations were investigated in 12 healthy subjects and 5 patients with loss of labyrinthine function. The vestibular otolith organs were stimulated by centrifugal forces, the constant rotation of a chair fixed outside of the rotation axis on the horizontal plane. The chair was fixed along the direction of centrifugal force (eccentric rotation [ECR]) or along the tangent line (eccentric lateral rotation [ECLR]). The ECR stimulates both the utricular and saccular maculae, whereas the ECLR stimulates only the utricular maculae. Spectral analysis showed that in the healthy subjects, low-frequency SBP increased significantly during ECR but not during ECLR. There was no significant increase in low-frequency SBP in patients with labyrinthine loss. In the R-R interval analysis, however, the low- and high-frequency components did not change significantly in the healthy subjects during ECR. Our findings indicate that stimulation of the otolith maculae, especially the saccular organs, predominantly produces augmentation of the α-sympathetic activities rather than cardiac sympathovagal outflow to the heart. (Otolaryngol Head Neck Surg 2000;123:582-6.)

Three Dimensional Observation of Al&lt;sub&gt;3&lt;/sub&gt;Ti Platelets in Al-Al&lt;sub&gt;3&lt;/sub&gt;Ti FGMs Fabricated by Centrifugal Method

The Al-Al 3 Ti FGMs were fabricated by the centrifugal method the same way as in the previous work. The alloy was heated to a temperature where Al 3 Ti platelets remain solid in liquid Al matrix. Centrifugal force was then applied during solidification. The Al 3 Ti particle morphology was observed along three orthogonal planes, i.e, perpendicular to the rotating axis, perpendicular to the rotational direction, and perpendicular to the centrifugal force direction. The three-dimensional particle shape and distribution were discussed as a function of positions along the centrifugal force direction.