• Tribology and Lubricants
• /
• v.20 no.5
• /
• pp.225-230
• /
• 2004

Most studies of elsatohydrodynamic lubrication are oriented only to the measurement of film thickness itself with optical interferometer. In order to exactly investigate the tribological characteristics of a certain lubricant, it is also important to get the information of traction behaviors as well. In this work, we developed a device for measuring the friction force of ehl contact condition as well as the film thickness. To verify the validity of the measuring system, the friction forces and film thicknesses under ehl condition are simultaneously measured with the variations of additive ratios of viscosity index improvers which cause non-linear tendencies of film thickness to contact velocity.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.3
• /
• pp.298-304
• /
• 1986

The friction reduction by dilute polymer solutions was investigated experimentally in journal bearings. Flow pattern visualization and torque measurements were performed for a concentric case (.epsilon.=0). The effects of polymer concentration, bearing clearance, and polymer molecular weight on friction reduction were examined. The frictional torque and the intensity of vortices of the case of polymer solution were reduced compared with those of base oil only.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.14 no.4
• /
• pp.32-38
• /
• 2006

A clutch hydraulic system for automotive manual transmissions transfers hydraulic pressure generated by driver's pedal manipulation to the clutch mechanism. The foot effort when the clutch pedal is pushed is different than that when the clutch is returned. The effort or load difference, called hysteresis, is caused by the friction produced between rubber seal and inner wall inside the hydraulic cylinder. This clutch pedal travel foot effort hysteresis is essential for a clutch hydraulic system design and analysis. The dynamic model for a clutch hydraulic system is developed and a simulation analysis is performed to estimate the fiction coefficient as a function of the cylinder pressure. The simulation result is then compared to the measurements obtained from a clutch hydraulic system tester to ensure the reliability of the dynamic model and the coefficients estimated. Also the estimated friction coefficients at various pressure values are compared to those reported by an independent study.

• Tribology and Lubricants
• /
• v.26 no.4
• /
• pp.224-229
• /
• 2010

A new test rig is presented to measure friction losses at journal bearings in a reciprocating compressor. This rig consists of a test bearing, torque sensor, driving motor and loading parts especially for vertical shaft. Friction losses are obtained by measuring torque between motor and test bearing. The experiments are carried out at several rotational speeds and temperatures. The test results are presented and discussed.

• Smart Structures and Systems
• /
• v.4 no.3
• /
• pp.279-290
• /
• 2008

The modeling and parameter estimation of a damped one-degree-of-freedom mass-spring system is examined. This paper presents a method for estimating the system parameters (damping coefficients and natural frequency) from measured free-vibration motion of a system that is modeled to include both subcritical viscous damping and kinetic Coulomb friction. The method applies a commercially available least-squares curve-fitting software function to fit the known solution of the equations of motion to the measured response. The method was tested through numerical simulation, and it was applied to experimental data collected from a laboratory mass-spring apparatus. The mass of this apparatus translates on linear bearings, which are the primary source of light inherent damping. Results indicate that the curve-fitting method is effective and accurate for both perfect and noisy measurements from a lightly damped mass-spring system.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.241-247
• /
• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed at e/De=0.0476, P/e=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.5
• /
• pp.341-347
• /
• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to height ratio, and aspect ratio of channel width to height are fixed at $e$/De=0.0476, P/$e$=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2001.05a
• /
• pp.100-105
• /
• 2001

The present paper is to present the results of studied of pressure drop in annuli with corrugated and spirally fluted inner tubes for the turbulent flow regime. To understand the underlying physical phenomena responsible for heat transfer enhancement, flow mechanism documented elsewhere are combined with pressure drop measurements to confirm the friction factors obtained from the annuli with the grooved inner tubes for the Reynolds number of 1000 to 8000. Friction factors were found to be functions of trough depth, pitch and angle, and the annulus radius ratio. friction factor increases in the spirally fluted tubes were larger than those in the corrugated tubes.

• Journal of Power System Engineering
• /
• v.11 no.4
• /
• pp.44-49
• /
• 2007

Generally, the economic concept of optimized design and operating conditions in fluidized bed heat exchangers can hardly be realized. Because the lack of fundamental knowledge about the particle flows, the optimum design of the fluidized bed heat exchanger is rather limited. In the present work, measurements are made on pressure drops and friction factors in the horizontal circular tube with solid particles in the circulating water. Two different solid particles of diameters of 3mm and 4mm are covered. The Reynolds numbers are ranged from 10,000 to 45,000. It is concluded that the friction factors for the particles of 4mm diameter are much higher than those for the particles of 3mm diameter. And at the lower particle concentration, the friction factors are strongly influenced by the fluid velocity rather than the particle concentration; However, the effect of the particle concentration on friction factors is also significantly higher at a higher particle concentration operating condition.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.159-159
• /
• 2013

Atomically thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro and nano-mechanical devices. Here, we report that the tribological properties can be easily altered via simple chemical modifications of the graphene surface. Friction force microscopy measurements show that hydrogenated, fluorinated, and oxidized graphenes exhibit, 2-, 6-, and 7-fold enhanced nanoscale friction on their surfaces, respectively, compared to pristine graphene. The measured nanoscale friction should be associated with the adhesive and elastic properties of the chemically modified graphenes. Density functional theory calculations suggest that, while the adhesive properties of chemically modified graphenes are marginally reduced down to ~30%, the out-of-plane elastic properties are drastically increased up to 800%. Based on these findings, we propose that nanoscale friction on graphene surfaces is characteristically different from that on conventional solid surfaces; stiffer graphene exhibits higher friction, whereas a stiffer three-dimensional solid generally exhibits lower friction. The unusual friction mechanics of graphene is attributed to the intrinsic mechanical anisotropy of graphene, which is inherently stiff in plane, but remarkably flexible out of plane. The out-of-plane flexibility can be modulated up to an order of magnitude by chemical treatmentof the graphene surface. The correlation between the measured nanoscale friction and the calculated out-of-plane flexibility suggests that the frictional energy in graphene is mainly dissipated through the out-of-plane vibrations, or the flexural phonons of graphene.