Effect Of Centrifugal Acceleration Research Articles

An experimental study on evaporator heat transfer performance of radially rotating heat pipes with water as working fluid

The utilization of radially rotating heat pipes (RRHPs) provides a novel method for gas turbine cooling due to the high thermal conductance and simple structure. Centrifugal force is utilized to return the condensate from the condenser to the evaporator. In this paper, the evaporator heat transfer performance of a RRHP, including heat transfer regime and the effect of centrifugal acceleration on heat transfer, are investigated experimentally. The RRHP evaporator with 45 % filling ratio was heated by electric heating wire with heat input ranging 50 W to 200 W and the condenser was cooled by air. Centrifugal acceleration at the evaporator center ranged from 117 g to 1457 g. Temperature distribution along the RRHP was measured by thermocouples. Experimental results revealed that non-boiling regime and boiling regime could occur in the RRHP evaporator according to heat input while natural convection and nucleate boiling were the dominating heat transfer mechanisms respectively. Geyser boiling phenomenon at 117 g to 344 g and temperature overshoot at 682 g to 1457 g were first observed in RRHPs as the transition stage at which boiling started to occur and the heat transfer performance was enhanced by 23 % in average. The evaporator heat transfer coefficient ranged 5180 to 9866 W/(m2·K) in non-boiling regime and 10,621 to 15438 W/(m2·K) in boiling regime with a boundary around 10000 W/(m2·K). With increase of centrifugal acceleration, transition stage was delayed to higher evaporator temperature and heat input. Nucleate boiling was suppressed by 20.3 % while natural convection was enhanced by 14.9 % as accelerations increased from 117 g to 682g. Interestingly, it was first observed that boiling was not entirely suppressed at 1457 g and the RRHP evaporator showed high heat transfer coefficient of 13065 W/(m2·K) at 200 W under such a high acceleration.

Pulsating heat pipes filled with acetone and water under radial rotation conditions: Heat transfer performance and semi-empirical correlation

A significant amount of heat can be generated during the operation of rotary machinery, which degrades its working performance and lifetime. It has been proven that, under radial rotation conditions, pulsating heat pipes (PHPs) can operate with good thermal performance. PHPs have excellent potential for application in rotary machinery, owing to their enhanced heat transfer and material duration. Experimental studies on radially rotating PHPs remain scarce, and further in-depth physical understanding is required to achieve a better thermal design for practical configurations. In this study, the effects of centrifugal acceleration and heat flux on the heat transport in radially rotating PHPs were investigated in detail. The results demonstrate that centrifugal acceleration can promote the circular motion of chains of liquid plugs and vapor slugs with an improvement in thermal performance, particularly above a given heat flux threshold and a critical value of the rotation velocity. In addition, by considering the key influencing parameters, a semi-empirical correlation of dimensionless numbers was built to estimate the heat transport. Additionally, dimensionless numbers, i.e., Weber number, temperature number (ΔT/Tev), and a newly-defined number (Ψ1, represents the influence of heat flux, surface tension and centrifugal acceleration), significantly impact the thermal performance.

Centrifuge modeling of scale effect on hydraulic gradient of backward erosion piping in uniform aquifer under river levees

The hydraulic gradient that causes backward erosion piping under a river levee is influenced by the scale of the levee, which is a major concern in the physical modeling. In this study, the results of 1 g and centrifuge tests performed on backward erosion piping were analyzed to facilitate a better understanding of the scale effect mechanism. The three-dimensional profile of the pipe and the flow rate of water in the pipe were observed using a transparent model levee. Although the flow in the pipe was determined to be laminar in most tests, it was found to be transient and turbulent in the coarse sand model at high g levels. The hydraulic gradient in the pipe was significantly high in the turbulent flow. Additionally, the scale effect was investigated based on the hydraulic conditions that cause sand transportation in an ideal pipe. The critical Shields number (θc), estimated for the model pipes, was consistent with that observed in the Shields diagram. The effects of centrifugal acceleration on the hydraulic gradient of the extending pipes can be explained by the change in θc with the particle Reynolds number and the hydraulic gradient in the pipe.

Visualization study on pool boiling critical heat flux under rolling motion

Vapor behavior and critical heat flux (CHF) mechanism under rolling motion were experimentally analyzed in the present study using a rolling platform system. It was observed that the combination of centrifugal and tangential acceleration affected the vapor behavior and occurrence of CHF. When the platform rolled more quickly, CHF occurred earlier, while CHF occurred every time the platform rolled back after reaching its maximum rolling amplitude. Therefore, the observations of vapor behavior focused on the period during which the platform rolled to its maximum rolling amplitude and then rolled back down. When the platform rolled up to its maximum amplitude, the vapor drifted slowly due to the effect of tangential acceleration, which acted in the opposite direction to the platform. On the other hand, as the amount of vapor grew, it readily detached from the heated surface due to the lower centrifugal acceleration, significantly reducing the size and duration of dry patches on the heated surface. When the platform rolled back down, the tangential acceleration pulled the vapor bubbles down because it acted in the same direction as the platform. Consequently, the vapor bubbles pushed against the bubbles, causing them to coalesce and produce larger dry patches on the heated surface. At the same time, the effect of centrifugal acceleration became stronger, which pushed the vapor towards the heated surface, resulting in vapor could not detach easily from the heated surface. This process led to a further increase in the size and duration of dry patches on the surface. When the platform rolled down, more of the heated surface was covered with a vapor layer for a longer time, hindering the fluid from replenishing the surface and triggering CHF.

Implied physical phenomena of rotating closed-loop pulsating heat pipe from working fluid temperature

The effects of centrifugal acceleration and heat inputs on physical phenomena inside a rotating closed-loop pulsating heat pipe (RCLPHP) are considered by implying from the temperature variation of the working fluid, that are amplitude and frequency of temperature variations. The higher amplitude and frequency of the temperature imply to the longer vapor plugs and the higher flow velocity, respectively. From the experiments, when centrifugal acceleration increases, the temperature amplitude decreases. The flow pattern changes from the annular flow to the slug flow. The temperature frequency increases, the working fluid flows with a higher velocity. The flow direction changes from an oscillatory flow to a circulatory flow. Therefore, the thermal resistance decreases. Moreover, when the heat input increases, the temperature amplitude and frequency increase. The flow pattern changes from the slug flow to the annular flow with an intermittent liquid slug with higher flow velocity, thus, the thermal resistance decreases.

Numerical and experimental analysis of the sedimentation of spherical colloidal suspensions under centrifugal force

Understanding the sedimentation behaviour of colloidal suspensions is crucial in determining their stability. Since sedimentation rates are often very slow, centrifugation is used to expedite sedimentation experiments. The effect of centrifugal acceleration on sedimentation behaviour is not fully understood. Furthermore, in sedimentation models, interparticle interactions are usually omitted by using the hard-sphere assumption. This work proposes a one-dimensional model for sedimentation using an effective maximum volume fraction, with an extension for sedimentation under centrifugal force. A numerical implementation of the model using an adaptive finite difference solver is described. Experiments with silica suspensions are carried out using an analytical centrifuge. The model is shown to be a good fit with experimental data for 480 nm spherical silica, with the effects of centrifugation at 705 rpm studied. A conversion of data to Earth gravity conditions is proposed, which is shown to recover Earth gravity sedimentation rates well. This work suggests that the effective maximum volume fraction accurately captures interparticle interactions and provides insights into the effect of centrifugation on sedimentation.

歩行動作におけるモーションセンサを用いた膝関節角度の推定に関する研究（遠心加速度と接線加速度の影響に着目して）

歩行動作におけるモーションセンサを用いた膝関節角度の推定に関する研究（遠心加速度と接線加速度の影響に着目して）

Effect of Centrifugal Acceleration on Heat Transfer Characteristics of Rotating Closed-Loop Pulsating Heat Pipes

The objective of this paper is to qualitatively study the effect of centrifugal acceleration on heat transfer characteristic of a rotating closed-loop pulsating heat pipe (RCLPHP). RCLPHP can be applied to cool rotating devices, such as disc brake or steam turbine. It improves the lifetime and reduces the wear of the device. In recent studies, effects of several parameters on thermal performanceof CLPHP have been investigatede.g. inner diameter, length of evaporator section, meandering of turn and working fluid. Some researchersderivedthese parameters in dimensionless form, and then established correlation to predict thermal performance of CLPHP at specified inclination angles. Another parameter that affects rotating or moving heat pipe is centrifugal acceleration. The induced internal centrifugal acceleration of the RCLPHP affects the circulation of working fluid. When flow direction of condensate is in the same direction as the acceleration,the centrifugal acceleration is defined to be positive. In turn,thecondensate is in thecounter-flow direction to the acceleration, if centrifugal acceleration is negative. This acceleration affectsthe circulation of liquid phase. Because of heavier mass of the liquid, most of itaccumulatedat the end part of evaporator section. When the RCLPHPis heated, working fluid in this section changes from liquid to vapor phase. Then it circulates to condenser section, or another end, and condensed. When centrifugal acceleration is increased, thermal resistance decreases. The condensate can quickly circulate to evaporation sectionbecause working fluid velocityis higher than those at lower acceleration. In the future, researches to quantitatively study on the effects of centrifugal and parameters which related to the thermal performance of RCLPHP will be further conducted.

Centrifugal acceleration at high altitudes above the polar cap: A Monte Carlo simulation

AbstractA Monte Carlo simulation was used to study the outflow of O+ and H+ ions along three flight trajectories above the polar cap up to altitudes of about 15 RE. Barghouthi (2008) developed a model on the basis of altitude and velocity‐dependent wave‐particle interactions and a radial geomagnetic field which includes the effects of ambipolar electric field and gravitational and mirror forces. In the present work we improve this model to include the effect of the centrifugal force, with the use of relevant boundary conditions. In addition, the magnetic field and flight trajectories, namely, the central polar cap (CPC), nightside polar cap (NPC), and cusp, were calculated using the Tsyganenko T96 model. To simulate wave‐particle interactions, the perpendicular velocity diffusion coefficients for O+ ions in each region were determined such that the simulation results fit the observations. For H+ ions, a constant perpendicular velocity diffusion coefficient was assumed for all altitudes in all regions as recommended by Nilsson et al. (2013). The effect of centrifugal acceleration was simulated by considering three values for the ionospheric electric field: 0 (no centrifugal acceleration), 50, and 100 mV/m. It was found that the centrifugal acceleration increases the parallel bulk velocity and decreases the parallel and perpendicular temperatures of both ion species at altitudes above about 4 RE. Centrifugal acceleration also increases the temperature anisotropy at high altitudes. At a given altitude, centrifugal acceleration decreases the density of H+ ions while it increases the density of O+ ions. This implies that with higher centrifugal acceleration more O+ ions overcome the potential barrier. It was also found that aside from two exceptions centrifugal acceleration has the same effect on the velocities of both ions. This implies that the centrifugal acceleration is universal for all particles. The parallel bulk velocities at a given value of ionospheric electric field were highest in the cusp followed by the CPC followed by the NPC. In this study a region of no wave‐particle interaction was assumed in the CPC and NPC between 3.7 and 7.5 RE. In this region the perpendicular temperature was found to decrease with altitude due to perpendicular adiabatic cooling.

Macrokinetics and Practical Application of SHS Process under the Conditions of a Centrifugal Force

Extension of the possibilities of using SHS based on combustion with the aim to obtain impurity-free alloys, special ceramic materials with enhanced strength and thermal characteristics due to the effect of centrifugal acceleration is a practical task of this investigation. The use of a centripetal force in the method of SHS in layer oxide systems opens the prospect of using high temperature effects for creation of a wide spectrum of target products differing in composition and properties.

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

The fluidization behavior of the three kinds of nano-particles (TiO 2, SiO 2, Al 2O 3) was analyzed in a rotating fluidized bed (RFB). Bed pressure drop, minimum fluidization velocity, bed expansion, entrainment and particle mixing characteristics under various centrifugal accelerations were experimentally investigated. The effects of centrifugal acceleration on agglomerate size and density were analyzed based on a Richardson–Zaki approach coupled with a fractal model. The bed pressure drop behavior showed almost similar to that of A or B-particles of Geldart's classification. Dimensionless particle bed height became smaller when the centrifugal acceleration was larger. Size of agglomerate decreased and its density increased with an increase in centrifugal acceleration. The agglomerate size in the RFB showed smaller than that in other types of fluidized bed system such as vibration and magnetic field as well as in a conventional fluidized bed, and the agglomerate density became larger. Particle entrainment became smaller in the case of the higher centrifugal acceleration. These results confirmed that the RFB can reduce the size of a nano-particle agglomerate and fluidize nano-particles at high gas velocity without any significant entrainment. The RFB is thus expected as more effective gas–solid fluidization system for handling of a large amount of nano-particles than other types of fluidized bed.

Axisymmetric stability of the flow between two exactly counter-rotating disks with large aspect ratio

We study the first bifurcation in the axisymmetric flow between two exactly counter-rotating disks with very large aspect ratio is developed, in which curvature is neglected, but the centrifugal acceleration term is retained. The Navier–Stokes equations then reduce to leading order to those in a Cartesian frame, and the axisymmetric base flow to a parallel flow. This allows us locally to use a Fourier decomposition along the radial direction. In this framework, we explain the physical mechanism of the instability invoking the linear azimuthal velocity profile and the effect of centrifugal acceleration.

Effects of centrifugal acceleration on the flows and segregation in vertical Bridgman crystal growth with steady ampoule rotation

The effects of centrifugal acceleration on the flows and segregation in vertical Bridgman crystal growth with steady ampoule rotation are investigated through numerical simulation. The numerical model is based on the Boussinesq approximation in a rotating frame, and the fluid flow, heat and mass transfer, and the growth interface are solved simultaneously by a robust finite-volume/Newton method. The growth of gallium-doped germanium (GaGe) in the Grenoble furnace is adopted as an example. The calculated results at small Froude number (Fr<<1) are consistent with the previous prediction (Lan, J. Crystal growth 197 (1999) 983). However, at a high rotation speed or in reduced gravity, where the centrifugal acceleration becomes important (Fr∼1), the results are quite different due to the secondary flow induced. Since the direction of the induced flow is different from that of the buoyancy convection due to the concave interface, the flow damping is more effective than that due to the Coriolis force alone. More importantly, radial segregation can be reversed during the flow transition from one to the other.

Numerical Study of Mixed Heat and Fluid Flow in Annuli of Heated Rotating Cylinders

Convective flow in the annuli of rotating concentric cylinders were studied through a numerical model. The inner cylinder is heated and rotating in a range of Reynolds numbers where the effects of centrifugal acceleration and three dimensional Taylor vertices are considered negligible. The Prandtl number considered here varies from 0.01 to 1.0 and Rayleigh number varies from 103 to 105. Inner cylinder rotation in the Reynolds number range of 0 to 1120 was considered. Numerical experiments show that the mean Nusselt number increases generally with Rayleigh number. For Prandtl number of the order 0.01 to 0.1, the mean Nusselt number remains fairly constant when the inner cylinder is rotated. Above a critical Rayleigh number, for Prandtl number of order 1.0, when the inner cylinder is made to rotate, the mean Nusselt number decreases through out the flow. For both stationary and rotating cylinders, the flow patterns observed in the annular space are very different for the range of Prandtl number fluids considered here. Mono-thermal plume above the stationary inner was observed for higher Prandtl number fluids while bi-thermal plume above the stationary inner cylinder was observed for lower Prandtl number fluids. When the inner cylinder is made to rotate, the thermal plume for higher and lower Prandtl number fluids moved in different direction.

Effect of centrifugal acceleration on the polar wind

The ionospheric convection electric fields that occur at high latitudes cause plasma to drift across the cusp region and the polar cap. Since the magnetic field at high latitudes is close to vertical, pointing downward (upward) in the northern (southern) hemisphere, the convecting plasma experiences a centrifugal acceleration as it crosses the polar region because of the diverging magnetic field geometry. The centrifugal force is directly proportional to the mass of the plasma particles, and it is reasonable to ask whether this force has an effect on polar plasma outflow, particularly for the more massive ion O+. To date, a number of studies have addressed this question, but the theoretical models used in these studies were either overly simplified (i.e., neglected processes known to be important in the polar ionosphere) or else did not use appropriate boundary conditions or take account of the time variability of the problem. The results of these prior investigations were often contradictory. In order to overcome the limitations of these earlier studies, we have used a macroscopic particle‐in‐cell (PIC) code, which is sophisticated in the sense that a broad range of physical processes are incorporated in its description, in conjunction with time‐varying boundary conditions obtained from a time‐dependent, three‐dimensional, hydrodynamic model of the polar ionosphere. This enables us to properly account for the variation of boundary conditions along a flux tube trajectory. Initially, our macroscopic PIC model was solved for steady state conditions. This allowed us to compare results from our code with those of a prior study of centrifugal acceleration that uses a PIC formulation. Also, by obtaining steady state solutions for both low and high electron temperatures, we have been able to directly compare the effects of electron temperature and centrifugal force on the polar plasma outflow, a comparison that a time‐dependent simulation might obscure. Then time‐dependent PIC solutions were obtained for the plasma in a convecting flux tube, using solutions to a time‐dependent, three‐dimensional, hydrodynamic model to provide realistic boundary values for the electron and ion temperatures and the H+ and O+ densities and drift velocities along a flux tube trajectory. Both steady state and time‐dependent solutions indicate that centrifugal acceleration does not significantly contribute to the loss of plasma from the polar ionosphere.

Numerical studies of mixed recirculatory flow in annuli of stationary and rotating horizontal cylinders with different radius ratios

Mixed recirculatory flow in the annuli of stationary and rotating horizontal cylinders were studied numerically. A set of distorted ‘false transient’ parameters were introduced to speed up the steady state solution of the unsteady vorticity, energy and stream function—vorticity equations. The inner cylinder of the annuli is assumed heated and rotating at Reynolds numbers that exclude the effects of centrifugal acceleration and three‐dimensional Taylor vortices. The Prandtl number considered is in the range of 0.01 to 1.0 and Rayleigh number in the range of 102 to 106. Radius ratios of the cylinders considered are 1.25, 2.5 and 5.0. For a radius ratio of 2.5, inner cylinder rotation in the Reynolds number range of 0 to 1120 was considered. Vertical eccentricities in the range of ±2/3 were studied for cases of the rotating inner cylinder. Numerical experiments show that the mean Nusselt number increases with Rayleigh number for both cases of concentric and eccentric stationary inner cylinder. At a Prandtl number of order 1.0 with a fixed Rayleigh number, when the inner cylinder is made to rotate, the mean Nusselt number decreases throughout the flow. At lower Prandtl number of the order 0.1 to 0.01, the mean Nusselt number remained fairly constant with respect to the rotational Reynolds number.

Effect of centrifugal acceleration on heat transfer during cooling of metal-oxide ceramics with liquid nitrogen

This paper reports an experimental investigation of heat transfer to liquid nitrogen from samples of high temperature superconductor (HTSC) ceramics YBa 2Cu 3O x in the range of relative centrifugal accelerations from 1 to 1434. The effect of the porous, penetrable structure of the samples on thermal processes on their surface and inside them is shown. It has been established that in the porous samples an evaporation front arises, whose position depends on the centrifugal acceleration and on the heat flux density. For ceramics with lower porosity and higher thermal conductivity the heat transfer characteristics are similar to those for metallic samples.

The effect of centrifugal acceleration on the charging of a riming hailstone

A laboratory investigation of the charge acquired by a riming target, simulating a soft-hailstone, during collisions with ice crystals has shown that centrifugal acceleration of the target affects the magnitude and sign of the charge transferred when the acceleration exceeds a certain value. Above this critical value, which is dependent on the ambient temperature, the charging to the hailstone is positive under low liquid water content conditions whereas at lower rotational frequencies the charging is normally negative. During collisions with supercooled water droplets, no charging was observed at low rotational frequencies. However, at high frequencies, positive charging to the hailstone was detected at all temperatures. It is suggested that these spurious charging effects are due to the break-up of the rime ice on the target surface.

Kinetics of particle deposition from a stagnant suspension: Application to blood platelets

A theoretical model for the process of particle deposition from a stagnant suspension is presented. It is different from previous models in the treatment of the sedimentation of particles toward the deposition surface. The main feature is the consideration of concentration-dependent velocity of sedimentation. This refinement of the theory enables the simulation of experimental data, especially recent data on the effect of centrifugal acceleration on blood platelet deposition. The qualitative features of experimental deposition curves for platelets on various solid substrates are also discussed and explained.

The effect of centrifugal acceleration on axisymmetric convection in a shallow rotating cylinder or annulus

This paper considers the nature of stationary axisymmetric convection in a shallow rotating annulus or cylinder heated from below. The horizontal and vertical walls of the container are assumed to be perfect conductors and insulators respectively. The critical regime is considered in which the circulations due to the centrifugal force and the vertical gravitational instability are of equal significance. Among the effects of the centrifugal acceleration on the gravitational instability are a shift in the value of the Rayleigh number at which instability sets in, a modification in the distribution and amplitude of convection cells in the container and, most significantly, a smooth transition to finite amplitude convection as the Rayleigh number is increased.