• Title/Summary/Keyword: Friction Coefficients

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Rotordynamic Analysis for Stepped-Labyrinth Gas Seals Using Moodys Friction-Factor Model

  • Ha, Tae-Woong
    • Journal of Mechanical Science and Technology
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    • v.15 no.9
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    • pp.1217-1225
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    • 2001
  • The governing equations are derived for the analysis of a stepped labyrinth gas seal generally used in high performance compressors, gas turbines, and steam turbines. The bulk-flow is assumed for a single cavity control volume set up in a stepped labyrinth cavity and the flow is assumed to be completely turbulent in the circumferential direction. The Moodys wall-friction-factor model is used for the calculation of wall shear stresses in the single cavity control volume. For the reaction force developed by the stepped labyrinth gas seal, linearized zeroth-order and first-order perturbation equations are developed for small motion about a centered position. Integration of the resultant first-order pressure distribution along and around the seal defines the rotordynamic coefficients of the stepped labyrinth gas seal. The resulting leakage and rotordynamic characteristics of the stepped labyrinth gas seal are presented and compared with Scharrers theoretical analysis using Blasius wall-friction-factor model. The present analysis shows a good qualitative agreement of leakage characteristics with Scharrers analysis, but underpredicts by about 20%. For the rotordynamic coefficients, the present analysis generally yields smaller predictied values compared with Scharrers analysis.

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A Study on the Transitional Flows in a Concentric Annulus with Rotating Inner Cylinder (안쪽 축이 회전하는 환형관내 천이유동에 관한 연구)

  • 김영주;황영규;우남섭
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.10
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    • pp.833-843
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    • 2002
  • The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin- friction coefficients have been measured for the fully developed flow of water and glycerine-water solution (44%) with the inner cylinder rotating at speed of 0∼600 nm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime.

A Study on Transport and Heat Utilization of Ice Slurries (아이스 슬러리의 수송 및 냉열이용에 관한 연구)

  • 길복임;이윤표;정동주;조봉현;최은수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.11
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    • pp.1065-1071
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    • 2001
  • To investigate hydraulic and thermal characteristics of ice slurries in a circular tube, ice slurries were tested in a flow loop with a constant heat flux test section, for ranges of flow velocity, ice fraction and heat flux. Heat transfer coefficients and friction factors of ice slurries were calculated by measuring the outer wall temperatures of the test section and the pressure drops over the test section. Heat transfer coefficients of ice slurries were 9% higher than the heat transfer coefficients expected by Petukhov. Friction factors were about 4% lower than the friction factors expected by Petukhov. The effective thermal capacity of ice slurry with 12.8% ice fraction, was found to be about 3 times higher than the thermal capacity of water.

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A Study on the Friction and Wear Characteristics of Carbon Fiber Reinforced Plastics by Surface Modification (표면개질에 따른 탄소섬유복합재의 마찰마모 특성에 관한 연구)

  • O, Seong-Mo;Lee, Bong-Gu
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.8
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    • pp.122-128
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    • 2001
  • The objective of the present study was to investigate the characteristics of the friction and wear according to the amount of ion-irradiation for the carbon fiber reinforced plastic(CFRP). Unidirectional carbon fiber reinforced composites were fabricated with epoxy resin as a matrix and carbon fiber as a reinforcement, and its surface was modified by the ion-assisted reaction. When the amount of ion-irradiation was $1{\times}10^{16}$ ions/$cm^2$, the friction coefficients of composites were about 0.1 and the wear mode was stable, whereas, the friction coefficient of non-treatment composites were about 0.16 and the wear mode was very unstable. But if the amount of ion-irradiation was $5{\times}10^{16}$ ions/$cm^2$, the friction coefficients were higher rather than that of $1{\times}10^{16}$ ions/$cm^2$. Consequently, the amount of ion-irradiation was not in proportion to the friction coefficients, and it was conformed that the optimal conditions would exist between broth of them.

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Wet Surface Performance Test of PF Heat Exchanger (PF열교환기의 습표면 성능시험)

  • Cho, J.P.;Kim, N.H.;Choi, K.K.
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.314-320
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    • 2000
  • In this study, the wet surface heat transfer coefficients and friction factors of PF heat exchangers are presented. Two sample with different fin pitch(1.25mm, 1.5mm) were tested. Tests were conducted in a open loop wind tunnel. The wet surface heat transfer coefficient was reduced following the procedure given in ARI 410-81. Results showed that the heat transfer coefficients of the heat exchanger with 1.5mm fin pitch were approximately the same as those with 1.25mm fin pitch, except at low reynolds number(Re<100), where the heat transfer coefficients of 1.5mm fin pitch were slighly higher than those with 1.25mm fin pitch. The friction factors of the 1.25mm fin pitch, however was 120 % to 160 % higher than those of the 1.5mm fin pitch. The wet surface heat transfer coefficients were lower than those of the dry surface. The wet surface friction factors, however, were higher than those of the dry surface.

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An Experimental Study on Tube-Side Heat Transfer Coefficients and Friction Factors of the Enhanced Tubes Used in Regenerators of Absorption Chillers (흡수식 냉동기의 재생기에 사용되는 전열촉진관의 관 내측 열전달계수 및 마찰계수에 대한 실험적 연구)

  • Kim, Nea-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.3
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    • pp.716-723
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    • 2016
  • Enhanced tubes are used widely in the heat exchangers of absorption chillers. In regenerators, corrugated, ribbed or floral tubes are commonly used. In this study, the tube-side heat transfer coefficients and friction factors of enhanced tubes were obtained experimentally using the Wilson Plot method. The results showed that the heat transfer coefficients and the friction factors were the largest for the corrugated tube, followed by the ribbed tube. The heat transfer coefficients and friction factors of the floral tube matched those of the smooth tube within 4%, which suggests that the heat transfer and friction characteristics of the floral tube may be accounted for properly by the hydraulic diameter. The B(e+) and g(e+) were obtained from the experimental data of the corrugated and ribbed tube. The B(e+) and g(e+) of the corrugated tube matched those of the existing correlation within 20%. The present results may be used for an assessment of the heat transfer and friction characteristics of the enhanced tubes for regenerators.

Analysis on the Friction Losses of a Bent-Axis Type Hydraulic Piston Pump

  • Hong, Yeh-Sun;Doh, Yoon-Ho
    • Journal of Mechanical Science and Technology
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    • v.18 no.9
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    • pp.1668-1679
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    • 2004
  • The design of an axial piston pump for electro-hydrostatic transmission systems requires accurate information where and how much the internal friction and flow losses are produced. This study is particularly focused on the friction losses of a bent-axis type hydraulic piston pump, aiming at finding out which design factors influence its torque efficiency most significantly. To this end, the friction coefficients of the pump parts such as piston heads, spherical joints, shaft bearings, and valve plate were experimentally identified by a specially constructed tribometer. Applying the experimental data to the equations of motion for pistons as well as to the theoretical friction models for the pump parts, the friction torques produced by them were computed. The accuracy of the computed results was confirmed by the comparison with the practical input torque of the pump. In this paper, it is shown that the viscous friction forces on the valve plate and input shaft bearing are the primary source of the friction losses of the bent-axis type pump, while the friction forces and moments on the piston are of little significance.

Study on the strain state during cladding of SUS/AL/SUS sheets (SUS/AL/SUS 판재의 cladding시 변형상태 고찰)

  • 김종국;지광구;허무영
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.136-138
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    • 2003
  • Strain states of clad sheets consisted of AL3003 and SUS430 were studied by FEM simulation. Main simulation parameters include roll size, reduction, material properties, material temperature, and friction between roll and material (or friction between materials). To investigate the effect of friction on the evolution of strain states, the friction coefficient between roll and material (or fraction coefficients between materials) was varied. Components of strain rate, strain were compared according to the variation of friction coefficients. And strain states during cladding were compared with those induced by simple rolling process.

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A new proposed Friction Multi-layered Elastomeric Seismic Isolator (FMESI)

  • Mirali-Katouli, Gholamali;Abdollahzadeh, Gholamreza
    • Structural Engineering and Mechanics
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    • v.77 no.3
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    • pp.407-416
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    • 2021
  • Seismic isolation is one of the best-advanced methods for controlling seismic vibrations in buildings, bridges and nuclear facilities. A new Friction Multi-Layer Elastomeric Seismic Isolator (FMESI) has been modeled, analyzed and investigated by ABAQUS finite element analysis software and then, compared to real models. A number of friction cores have been used instead of the lead core therefore, some of the previous isolator problems have been almost resolved. Moreover, Studies show that the proposed isolator provides suitable initial stiffness and acceptable hysteresis behavior under different vertical and horizontal loading conditions and also internal stresses in different layers are acceptable. Also, as a result, the initial stiffness and overall area of the curves increase, as friction coefficients of the cores increase, although the frictional coefficients must be within a certain range.

An Experimental Study on The Friction Coefficient of Rubbers for Clutch Master Cylinder Cup-Seals (클러치 마스터실린더 컵-시일 고무의 마찰계수 실험 연구)

  • 이재천;임문혁;이병수;장지현;정용승;허만대;최병기
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.5
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    • pp.112-118
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    • 2003
  • The friction coefficients of the rubber for clutch master cylinder were experimentally measured in this study. The cylindrical rubber samples for primary cup-seal and secondary cup-seal were tested against the aluminum or the steel plates of master cylinder housing under the various conditions of brake oil temperatures and normal loads. Dry sliding friction coefficients were also measured under various load conditions. The test revealed following results. First, the friction coefficient under fluid lubrication condition in general decreases, as the oil temperature or normal load increases. Second, the steel plate of low surface roughness yielded comparatively low friction coefficient on the range of 0.30∼0.67. On the other hand, the aluminum plate of high surface roughness yielded high friction coefficient on the range of 0.31∼1.15. Third, the friction coefficient of dry surface contact decreases as the normal load increases. This is contrary to the general principle of friction coefficient between metal plates.