• 대한기계학회논문집B
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• 제22권11호
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• Journal of Advanced Marine Engineering and Technology
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• 제34권1호
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• pp.84-91
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• 2010

The centrifugal oil purifier is used in ships for purifying the engine lubrication oil. The momentum needed for the rotation of the cylindrical chamber is obtained by jet injections. The dust particles in the oil are separated by the centrifugal forces moving to the inner wall of the rotating cylindrical chamber body. The dust particles are eliminated when the particles are adsorbed onto the surface of the inner wall of the chamber body. The flow characteristics and the physical behaviours of particles in this centrifugal oil purifier have been investigated numerically and the filtration efficiencies have been evaluated. For the calculations, a commercial code has been used and the SST k-${\omega}$ turbulence model has been adopted. The MRF (Multiple Reference Frame) method has been introduced to consider the rotating effect of the flows. Under various variables, such as particle size, particle density and rotating speed, the filtration efficiencies have been evaluated. It has been verified that the filtration efficiency is increased with the increments of the particle size, the particle density and the rotating speed of the cylindrical chamber.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.42-48
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• 1998

Numerical study is presented for the analysis of three-dimensional incompressible turbulent flows in multiblade centrifugal fan. Reynolds-averaged Navier-Stokes equations with standard k - $\epsilon$ turbulence model are transformed to non-orthogonal curvilinear coordinates, and are discretized with finite volume approximations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. The computational area is divided into three blocks; core, impeller and scroll, which are linked by multi-block method. The flow inside of the fan is regarded as steady flow, and mathematical formula established from the cascade theory and empirical coefficient are employed to simulate tile flow through the impeller. From comparisons between the computational results and the experimental data, the validity of the mathematical formula for the blade forces was examined and good results were obtained qualitatively. Hence, we can get the flow characteristics of multi-blade centrifugal fan and it will be a corner stone of the development of the multiblade centrifugal fan.

• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.147-153
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• 2014

The centrifugal oil purifier is used in an engine for lubrication and to remove impurities. The momentum needed for the rotation of the cylindrical chamber is obtained by jet injections. An impure particle in the oil is separated by the centrifugal forces moving to the inner wall of the rotating cylindrical chamber body. The dust particles are eliminated when the particles are absorbed onto the surface of the inner wall of the chamber body. The flow characteristics and the physical behaviors of particles in this centrifugal oil purifier were investigated numerically and the filtration efficiencies was evaluated. For calculations, a commercial code is used and the SST (Shear Stress Transport) turbulence model has been adopted. The MFR (Multi Frames of Reference) method is introduced to consider the rotating effect of the flows. Under various variables, such as particle size, particle density and rotating speed, the filtration efficiencies are evaluated. It has been verified that the filtration efficiency is increased with the increments in the particle size, the particle density and the rotating speed of the cylindrical chamber.

• 대한기계학회논문집B
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• 제26권6호
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• pp.850-858
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• 2002

The present study investigates in detail the combined effects of the Coriolis force and centrifugal force on the development of turbulent flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a curved region of U-bend, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal force due to the curvature of U-bend. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct. On the other hand, under negative rotation, where these two forces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces. Under the condition that the value of Rossby number and curvature ratio is large, the flow field in a rotating U-bend can be represented by two dimensionless parameters : $K_{TC}$ =Re $\sfrac{1}{4}$√λand a body force ratio F=λ/Ro. Here, $K_{TC}$ has the same dynamical meaning as $K_{TC}$ =Re√λ for laminar flow.

• Tribology and Lubricants
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• 제16권6호
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• pp.415-424
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• 2000

The use of magnetoresistive (MR) head requires much tighter control of particle contamination in a drive since loose particles on the disk surface will generate thermal asperities (TA). In this study, a spinoff test was performed to investigate the adhesion and removal capability of a particle to disk surface. Numerical simulation was also performed to investigate dominant factor of particle detachment and to support experimental results. It was shown that particles are detached from the disk surface by the moment derived from the centrifugal force and the drag force and that the centrifugal force and capillary force are the dominant force, which determines spin-off of a particle on the disk surface. Removal of particles smaller than several micrometers, which are the main source of TA generation, is extremely difficult since the adhesion forces exceed the centrifugal force. Lubricant types and manufacturing process also influence the particle removal. Lower bonding ratio and lower viscosity of the lubricant will help to increase the removal rate of the particles from the disk surface.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 Handout for 2000 Inter. Machine Tool Technical Seminar
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• pp.35-49
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• 2000

Over the past ten years we have wethnessed a revolution in metalcutting in the field of High Speed Machining. As machining speeds continue to increase, particularly spindle RPM, forces created by unbalance in the spindle, cutting tool, and toolholder require close attaention. It has been observed that these forces, if left uncompensated, can results in poor surface finish, loss of tool life, and spindle bearing failure. The sources of this unbalance needs to be identified and elimated in order to create a smooth, vibration free condition and allow the machine tool and its spindle to operate properly.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1247-1254
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• 1998

The vaneless diffusers are widely used in industrial centrifugal compressors which are required to operate within a wide flow range. When very high pressure gases are handled by centrifugal compressor. rotating stall is a serious problem because of the occurance of large aerodynamic exciting forces. Rotating stall mostly often occurs in the impellers but it can occur in vaneless diffusers as well. In this experimental study, the rotating stall in vaneless diffuser with radial type centrifugal impeller was measured by changing the flow rate with I-type, X-type hotwire. As the result, it was cleared which type of rotating stall of the impeller stall would occur and how many stall cells would appear relating with the flow rate. As the flow rate reduced, the propagation speed of rotating stall was reduced. But the stall cell number unchanged with respect to the flow rate.

• 한국자동차공학회논문집
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• 제10권3호
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• pp.44-50
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• 2002

The connecting rod big-end bearing is one of the most heavily loaded components of the lubrication system of high-speed combustion engines. The supply oil flow has to pass to the main bearing and the rotating crankshaft before entering the connecting rod bearing. It is common knowledge that the centrifugal forces due to the crankshaft rotation influence the oil flow to connecting rod bearing through the oil supply bore, especially, when the oil supply system to the connecting rod bearing has a 180$^{\circ}$circumferential groove via a single drilling in the crankshaft. In this case, it should be confirmed that the groove oil pressure in the main bearing is sufficient to overcome these centrifugal forces. For the purpose, the dynamic oil pressure before entering oil supply bore to the connecting rod bearing was measured instead of averaged oil pressure in main gallery. Experimental test results show that the dynamic oil pressure in the oil groove was more useful than that of main gallery. And it was also found that the oil pressure fluctuation in the groove was sensitively affected by the reduction of the main bearing clearance.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권2호
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• pp.201-211
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• 2018

This paper illustrates recent advancements relative to a non-conventional propulsion system for boats and is based on two previous papers of the author presented at a conference (see Muscia, 2015a,b). The system does not consider propellers and utilizes the vibration generated by two or more pairs of counter rotating masses. The resultant of the centrifugal forces applies an alternate thrust to the hull that oscillates forward and backward along the longitudinal axis of the boat. The different hydrodynamic drag forces that oppose to the oscillation produce a prevalently forward motion of the vessel. The vibration that causes the motion can be suitably defined to maximize the forward displacement and the efficiency propulsion of the system. This result is obtained by using elliptical gears to rotate the counter rotating masses. The computation of the propulsion efficiency is based on a suitable physical mathematical model. Correlations between numerical experiments on models and possible full scale application are discussed. Some remarks in relation to practical applications and critical issues of the propulsive solution are illustrated. The results have been obtained with reference to a CAD model of a real boat already manufactured whose length is approximately equal to 13 m.