Friction Coefficient Of Disk Research Articles

Reduction of Disk Friction Loss by Applying a Fin to the Back of a Centrifugal Impeller

Abstract It is well known that the ratio of disk friction loss of low specific speed pumps is large. When the specific speed is 100 min−1, m3/min, m or less, the disk friction loss increases remarkably. In this study, focusing on the clearance flow from the diffuser outlet to the impeller outlet (This is called the outward flow) behind the centrifugal pump, a fin was installed on outer diameter side of the rotating wall on the back side of a centrifugal pump as a countermeasure, and the influence of changes in velocity distribution near the wall on disk friction loss was investigated by torque measurements, velocity measurement, and computational fluid dynamics (CFD) analysis. As a result, it was clarified that disk friction loss is decreasing by installing the fin in both torque measurements and CFD results, because the clearance flow is separated by fin and circumferential velocity is increased in the wake region of the fin in both measurements and CFD. In addition, it was clarified that disk friction coefficient (normalized torque) can be expressed as a function of the inlet swirl ratio and Reynolds number. Also, prediction equation is derived for each shape (with and without fin). According to the equation, it was found that disk friction loss reduction effect by installing a fin becomes larger when Reynolds number and the inlet swirl ratio are small.

PEMANFAATAN SERAT PELEPAH KELAPA SAWIT SEBAGAI BAHAN PEMBUATAN KAMPAS REM SEPEDA MOTOR

Brake pads are generally made of asbestos, which is less environmentally friendly and widely available in nature, therefore motorcycle brake pads are made that utilize palm frond fibers filled with alumina powder and bonded to a polyurethane matrix. This research was conducted at the Laboratory of Material Testing of Industrial Chemical Technology Polytechnic (PTKI) Medan. Research was carried out from February-July 2020, using two test, namely the Rockwell Hardness level test and the Pin On Disk Friction Coefficient test. The result showed that oil palm frond fibers can be made into motorcycle brake pads with the addition of alumina powder according to the predetermined composition. After going through the test, the Rockwell hardness level was obtained in A2 treatment (6% Alumina) with the highest and best hardness level, namely 52.75 Kg. And after testing the friction coefficient of the Pin On Disk type, brake pads from palm frounds with the addition of alumina powder composition which have the lowest coefficient value of the best are obtained in treatment A2 (6% Alumina) with a value of 0.000765 N/mm2. Keywords : biocomposite, brake shoes, palm fround fibers, alumina powder

Influence of Nonflow Zone (Back Cavity) Geometry on the Performance of Pumps as Turbines

The larger objective of this research comes from the fact that optimization studies in “pumps operated as turbines” have concentrated only within flow zones without any physical perception regarding the influence of nonflow zones such as back-cavities in standard end-suction pumps. Four pumps of different designs are selected and their back cavities are reduced by inserting solid material, leaving a very small axial clearance. The effects are investigated on an experimental platform, which reveal unique phenomena taking place. The first is associated with the reduction of expected disk friction (hence improvement in shaft torque), while the second is more intricate considering the effect on fluid momentum through reorganization of tangential velocities, based on the mixing zone theory proposed in the paper. The net effect of reducing the volume of nonflow zones (i.e., filling of cavity) is the enhancement of efficiency in the range of 1.3% to 3.6% (±0.4%) in turbine mode. The experimental disk friction coefficient as a function of blade Reynolds number is corroborated with the established theory proposed by different researchers. A significant phenomenon observed was the elimination of vibration and noise at overload operating conditions with the minimal axial clearance.

Adaptive Engagement Control of a Self-Energizing Clutch Actuator System Based on Robust Position Tracking

This paper considers the problem of designing an engagement controller for a clutch actuator system having a self-energizing mechanism. Since such a system includes a torque amplification mechanism, parametric uncertainties in the model may lead to large erroneous results in the clutch torque controller. To compensate this undesirable effect, adaptive sliding-mode control is applied based on the actuator position tracking. Estimations of the disk friction coefficient and actuator motion parameters are employed to control the engagement torque properly. The disk friction coefficient adaptation provides online stiffness inference for the engagement force while in contact. Moreover, the unstructured disturbance is also compensated by a disturbance observer. Experimental verifications show the improved performance of the developed control method.

Vibrational density of states and boson peak in two-dimensional frictional granular assemblies

In this paper, the two-dimensional granular assemblies composed of 2048 mono-dispersed frictional disks are simulated by the discrete element method. A set of eigenvalues and corresponding eigenvectors is obtained by diagonalizing the Hessian matrix for each stable configuration. The effects of the friction coefficient of disk on mechanical and geometrical properties of these systems under isotropic confining are studied. Results show that at a fixed pressure, with increasing from 0.001 to 1.0, the crossover frequency *, which separates the Debye scale region from the platform of vibrational density of states, and the boson peak BP gradually shift towards lower frequency, and the intensity of the boson peak D(BP) / BP increases. These results are mainly attributed to the fact that the system becomes more and more disordered with the increase of (i.e., the decrease of the average coordination number), resulting in more excess modes at *. For a better understanding of the different vibration modes of the two-dimensional frictional granular systems, we plot the polarization vector diagrams for different frequencies ( 1 = 0.15, 2 = 1.5 and 3 = 6.0) for configurations with = 0.001 and = 1.0, respectively. Mode analysis results show that the mode at low ( 1.0) has a mixed translational-rotational but translational-dominated character; the mode at intermediate frequency (1.0 4.0) is localized and has a mixed translational-rotational but translational-dominated character; and the mode at high frequency ( 4.0) have a strongly rotational in character. It is worth noting that the low-frequency modes become more localized and the rotational participation fraction also increases as increases, implying that the rotational modes play more important role in the system with higher friction coefficient.

THE INFLUENCE OF BRAKING TIME ON HEAT FLOW THROUGH THE FRICTION SURFACES OF THE FRICTION ELEMENTS OF DISK BRAKES FOR RAILWAY VEHICLES / STABDYMO LAIKO ĮTAKA ŠILUMOS SRAUTUI, SKLINDANČIAM GELEŽINKELIO TRANSPORTO PRIEMONIŲ DISKINIŲ STABDŽIŲ ELEMENTŲ PAVIRŠIŲ TRINTIES METU / ВЛИЯНИЕ ВРЕМЕНИ ТОРМОЖЕНИЯ НА ТЕПЛОВОЙ ПОТОК, ОБРАЗУЮЩИЙСЯ ИЗ-ЗА ТРЕНИЯ ПОВЕРХНОСТЕЙ ЭЛЕМЕНТОВ ДИСКОВЫХ ТОРМОЗОВ ЖЕЛЕЗНОДОРОЖНЫХ ТРАНСПОРТНЫХ СРЕДСТВ

Disk brakes were first introduced on the suburban and urban coaches and high speed freight cars (V > 120 km/h) for the following reasons: shoe brakes reached their potential limits, especially at high speeds; the maintenance of disc brakes is cheaper; greater comfort; the friction coefficient of disk brake elements (friction pad and brake disc) presents lower variation in velocity and pressure; disk brakes present lower temperatures of friction surfaces. The determination of uniform heat flow through the friction elements of disk brakes is very important since the early designing stage. Such way one avoids overheating both disk brakes and friction pads that may result when the physical properties (chemical and mechanical) of materials are not correctly matched and have negative effects on braking efficiency (small coefficient of friction, large braking distance etc.) This work studies the influence of braking time (30 s, 40 s, 50 s, 60 s) on the uniform heat flow of the friction element surface. Note that in the same area of disk brake friction 0.4 m2, heat flow decreases with an increased duration of braking, leading to longer braking space. At the same time, if pressure on the pad of disk brake friction decreases, heat flow increases. Santrauka Pirmą kartą diskiniai stabdžiai buvo panaudoti sausumos transporto priemonėse (taip pat ir geležinkelio) dėl tokių priežasčių: būgninių stabdžių kaladėlės nusidėvi, ypač esant dideliems greičiams; diskinių stabdžių remonto darbams reikia skirti mažiau išlaidų; diskiniai stabdžiai patogesni; didelis diskinių stabdžių stabdymo efektyvumas; mažesnė diskinių stabdžių trinties paviršių temperatūra stabdant. Labai svarbu nustatyti šilumos srautą, sklindantį per diskinių stabdžių elementus trinties metu dar ankstyvuoju projektavimo etapu. Tai padeda išvengti diskinių stabdžių ir greta jų esančių elementų perkaitimo, kuris gali atsirasti, kai medžiagos parinktos neteisingai ir pasikeitusios jų fizinės, cheminės ar mechaninės savybės po perkaitinimo daro neigiamą poveikį stabdymo efektyvumui (mažas trinties koeficientas, ilgas stabdymo kelias ir t. t.). Šiame straipsnyje nagrinėjama, kokią įtaką stabdymo laikas (30 s, 40 s, 50 s, 60 s) daro šilumos srautui į besitrinančius elementų paviršius trin Transport, 2011, 26(1): I a–I d I c ties (stabdymo) metu. Pažymėtina, kad toje pačioje diskinių stabdžių trinties srityje (stabdymo plotas—0,4 m2) šilumos srautas mažėja didėjant stabdymo trukmei ir todėl didėja stabdymo kelias. Tuo pat metu, jeigu diskinių stabdžių trinties sritis (stabdymo plotas) mažėja, šilumos srautas didėja. Резюме Дисковые тормоза впервые были применены в наземных транспортных средствах (в том числе и железнодорожных) из-за следующих причин – колодки барабанных тормозов быстро изнашиваются при больших скоростях, работы по ремонту дисковых тормозов требуют меньше затрат времени и средств, они более удобны и характеризуются большей эффективностью торможения, при торможении меньше нагреваются трущиеся поверхности. Очень важно на ранней стадии проектирования дисковых тормозов определить тепловой поток, образующийся из-за трения поверхностей элементов тормозов. Данная информация поможет предотвратить перегрев элементов самих дисковых тормозов и элементов, находящихся рядом с ними. Перегрев тормозов возможен из-за неправильно подобранных материалов их элементов. После перегрева изменившиеся физико-механические и химические свойства элементов тормозов могут отрицательно влиять на эффективность торможения (малый коэффициент трения, длинный путь торможения и т. д.). Автор исследует влияние времени торможения (30, 40, 50, 60 с) на тепловой поток, образующийся из-за трения поверхностей элементов дисковых тормозов во время торможения. Необходимо отметить, что при той же области трения элементов (площадь трения – 0,4 м2) тепловой поток уменьшается при увеличении времени торможения, поэтому увеличивается путь торможения. В то же время при уменьшении области трения элементов (площади трения) дисковых тормозов тепловой поток увеличивается.

Analysis of Gas Turbine Rotating Cavities by a One-Dimensional Model: Definition of New Disk Friction Coefficient Correlations Set

Reliable design of a secondary air system is one of the main tasks for the safety and unfailing performance of gas turbine engines. To meet the increasing demands of gas turbine designs, improved tools in the prediction of secondary air system behavior over a wide range of operating conditions are needed. A real gas turbine secondary air system includes several components, therefore, its analysis is not carried out through a complete computational fluid dynamics (CFD) approach. Usually, those predictions are performed using codes based on simplified approach, which allows to evaluate the flow characteristics in each branch of the air system requiring very poor computational resources and few calculation time. Generally, the available simplified commercial packages allow to correctly solve only some of the components of a real air system, and often, the elements with a more complex flow structure cannot be studied; among such elements, the analysis of rotating cavities is very hard. This paper deals with a design tool developed at the University of Florence for the simulation of rotating cavities. This simplified in-house code solves the governing equations for steady one-dimensional axisymmetric flow using experimental correlations, both to incorporate the flow phenomena caused by multidimensional effects such as heat transfer and flow field losses, and to evaluate the circumferential component of velocity. Although this calculation approach does not enable a correct modeling of the turbulent flow within a wheel space cavity, the authors tried to create an accurate model, taking into account the effects of inner and outer flow extraction, rotor and stator drag, leakages, injection momentum, and finally, the shroud/rim seal effects on cavity ingestion. The simplified calculation tool was designed to simulate the flow in a rotating cavity with radial outflow, both with the Batchelor and/or Stewartson flow structures. A primary 1D-code testing campaign is available in the literature (2008, “Analysis of Gas Turbine Rotating Cavities by a One-Dimensional Model,” ISROMAC Paper No. 12-2008-20161). In the present paper, the authors developed, using CFD tools, reliable correlations for both stator and rotor friction coefficients and provided a full 1D-code validation, due to the lack of experimental data, comparing the in-house design-code predictions with those evaluated by CFD.

Investigations on fluid friction of rotational disks with and without modified outlet sections in real centrifugal pump casings

In order to examine the relation between the height of disk friction losses and the geometry of disks in real centrifugal pump housing disks without and with modified outlet sections with various numbers, angles and widths are investigated. Disks with modified outlet sections were examined to approach a real impeller in real centrifugal pump housing. The outlet channels of this impeller are formed out, the rest of channels is replaced by firm material. Experimental results of disks without modified outlet sections show that the disk friction coefficient decreases with the increase of the Reynolds number, but becomes smaller with small values of the disk width and high values of the gap. The inset of the volute has only small influence on disk friction coefficient. Experiments on disk friction conducted with and without the cover of the impeller shroud show that the cover has more influence for high values of the axial gap. Experimental results of disks with modified outlet sections show that the disk friction coefficient don’t changes with the Reynolds number, but generally the number and the angle of the outlet sections of disks have an important influence on the disk friction coefficient.

Modeling and simulation of hard-particle interaction in head/disk interfaces

A hard particle interacting with a slider and a disk in the head/disk interface of hard-disk drives can produce a scratch on the disk and result in data loss. Our work emphasizes modeling and simulation of slider, particle, and disk interactions, scratch generating mechanisms, and linking of scratch to interface design parameters. Two models are presented. The Monte Carlo method was used to calculate scratch probabilities and parametric studies were performed to determine the effect on scratch probability of various parameters, such as friction coefficients, particle mean size, slider wall angles, the ion-milling (IM) etch depth from the air-bearing surface (ABS) of the slider, and the efficacy of additional ABS structures acting as particle shields. Simulation results show that the friction coefficient is a dominant parameter. If the disk friction coefficient is smaller than the slider friction coefficient, scratches are not produced. Using shallow IM depths is an effective and practical way to reduce the scratch probability. Experimental results are very close to the simulation predictions.

Friction coefficient of a disk in a sheet of viscous fluid: Numerical calculation

The translational friction coefficient of a porous cylindrical disk moving in a sheet of fluid which is embedded on both sides in a fluid of different viscosity, is calculated numerically for a wide range of the relevant parameters. These results are used to evaluate the region of validity of certain asymptotic formulae which have been derived previously in the limit of small ratios of the viscosities.

Frictional and Thermal Behaviors of Sliding-Rolling Concentrated Contacts

Sliding-rolling disk scuffing tests were conducted over a wide range of sliding and sum velocities, using a straight mineral oil and three aviation gas turbine synthetic oils in combination with two carburized steels and a nitrided steel. Geometrically-similar disks of two different sizes were tested in two different disk testers of nearly similar designs. In addition to disk size and metallurgy, the surface treatment, surface texture, and surface roughness of the disks were also varied. The investigation further covered variations in the oil supply configuration and flow rate. It is shown that the disk friction coefficient is dependent not only on the oil-metal combination, but also on the disk surface treatment and topography as well as the operating conditions. The quasi-steady disk surface temperature and the mean conjunction-inlet oil temperature are shown to be strongly influenced by the frictional power loss at the contact, but not by the specific makeup of the frictional power loss. They are also influenced by the heat transfer from the disks, mainly by convection to the oil and conduction through the shafts, which are dependent on system design and oil flow rate.

Analytical determination of the disk friction coefficient in turbulent region, (in Russian) : N. N. Kupriashin. Energomashinostroenie, v. 4, no. 8, Aug. 1958, p. 17–19

Analytical determination of the disk friction coefficient in turbulent region, (in Russian) : N. N. Kupriashin. Energomashinostroenie, v. 4, no. 8, Aug. 1958, p. 17–19