• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1997년도 제26회 추계학술대회
• /
• pp.211-216
• /
• 1997

The tungsten disulfide (WS$_2$) solid lubricant was synthesized by two different reaction processes, and the chemical and physical characteristics of synthesized WS$_2$ powder were analyzed in terms of the average particle size, morphology, crystalline phase. The solid WO$_3$ powder with the average size of 0.2 $\mu$m was reacted with CS$_2$ gas flowed with N$_2$ or 96% N$_2$ + 4% H$_2$ forming gas for 36 h and 24 h at 900$\circ$C respectively. In the case of vapour phase transport method, the 3.5 wt% iodine was added as a vapour transport reagent into the composition of tungsten and sulfur powders maintaining a constant molar ratio of W : S = 1 : 2.2. The mixture was then heat treated at 850$\circ$C for 2 weeks in vacuum The reaction product obtained showed the average size of 12 $\mu$m and the hexagonal plate shape of typical solid lubricant with 2H-WS$_2$ crystalline phase.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1800-1805
• /
• 2008

A "finite volume method" is proposed to predict heat transport in a spherical enclosure at micro/nanoscale with the Boltzmann transport equation (BTE). The gray version of the BTE with the relaxation time approximation has been applied. Pointing out similarity between radiative transfer equation (RTE) and BTE, the mapping process in RTE is adopted to treat the angular derivative term and linear algebraic discretization equation is derived by using the established method which is used in 2-D BTE in cartesian coordinates. The simulation results are compared to exact solution to RTE for various acoustic thicknesses and ratio of radii. The comparison shows that this method is logical and accurate, and it is possible to easily adopt various models in spherical BTE.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2008년도 정기 학술대회
• /
• pp.166-171
• /
• 2008

LNG carrier is a special-purpose vessel to transport natural gas (NG) from the place of origin to each consuming country. To increase the capacity of canying LNG carrier, the natural gas is conveyed as a state of liquid called LNG (Liquefied Natural Gas) during a voyage because the total volume of NG is surprisingly reduced when it is cooled down to $-162^{\circ}C$. That is why the design of insulation of the carriers is important to protect LNG from the external heat invasion, and it has been a great challenging subject for several decades in the shipbuilding industry. For this ultimate goal, the boil-off rate (BOR) needs to be accurately estimated during a voyage. Therefore, the goal of this study is to propose a numerical method for estimating the BOR of LNG for given insulation containment subject to external temperature conditions during voyage.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집E
• /
• pp.119-124
• /
• 2001

This experimental study was conducted to figure out the characteristics of convective heat transfer non boiling vertical downward flow with polymer additives. This experiment was studied in diameter, 800mm heating length and $1{\times}10^5 W/m^2$ heat flux. The polymer concentration ranged 0ppm to 500ppm with corresponding from superficial liquid velocity 1.25m/s to 2.5m/s in non bo vertical up and downward flow. Experimental results show that the characteristics of convective transfer was a strong function of polymer concentration and it has decreased with increasing polymer concentration in non boiling up and vertical downward flow.

• Journal of Mechanical Science and Technology
• /
• 제15권5호
• /
• pp.639-645
• /
• 2001

Experimental investigations were conducted to study forced convection of fully developed turbulent flows in horizontal equilateral triangular ducts with different surface roughness pitch ratios (P/e) of 4, 8, and 16 on one side. The ducts bottom wall was heated uniformly and the other surfaces were thermally insulated. To understand heat transfer enhancement mechanism, heat transfer rates were measured. Smooth triangular ducts were also tested for benchmark purposes. The results were compared with previous results for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1992년도 하계학술대회 논문집 B
• /
• pp.653-655
• /
• 1992

Longitudinal and transverse normal zone propagation in the superconducting coil are analyzed and propagation velocity is derived from the heat balance equations in the propagating boundary region. Transverse velocity is nearly $10^{-2}$ order of longitudinal velocity. Propagation velocity ie linearly proportional to the transport current. Increasing lamp current speeds up longitudinal velocity by 0.279 m/s under the applied field of 2T. Transient heat transfer has a significant effect on normal zone propagation velocity and it decreases longitudinal velocity by 4.2 m/s under the applied field of 2T as being compared to steady-state heat transfer.

• 대한기계학회논문집
• /
• 제18권5호
• /
• pp.1288-1300
• /
• 1994

Mathematical modeling and numerical calculation on the flow and thermal characteristics induced by fire in a partial enclosure are performed. The solution procedures include the Shvab-Zeldovich approximation for the physical transport equations, low Reynolds number k-.epsilon. model for the turbulent fluid flow and Discrete Ordinate method(DOM) to calculate the radiative heat transfer. PMMA(Polymethylmethacrylate) is adopted as a solid fuel. Two different cases are considered : combustions with and without gas radiation occuring in a open cavity for variable pyrolyzing location of PMMA. When the fire source is located at the left-wall, the flow region of flame gas is limited at the left-wall and ceiling and recirculation region of inlet gas is formulated at neat the floor. In case of neglecting the radiative heat transfer, more large flame size and higher temperature is predicted. It is essential to consider the radiative heat transfer for analysis of fire phenomenon.

• 한국유체기계학회 논문집
• /
• 제10권3호
• /
• pp.39-46
• /
• 2007

This study presents a numerical procedure to optimize the shape of staggered dimple surface to enhance turbulent heat transfer in a rectangular channel. The RBNN method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to-dimple print diameter (d/D), channel height-to-dimple print diameter ratio (H/D), and dimple print diameter-to-pitch ratio (D/S) are chosen as design variables. The objective function is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Latin Hypercube Sampling (LHS) is used to determine the training points as a mean of the design of experiment. The optimum shape shows remarkable performance in comparison with a reference shape.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 학술대회
• /
• pp.229-232
• /
• 2008

This study presents a numerical procedure to optimize the shape of stepped circular pin-fins to enhance turbulent heat transfer. The KRG method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The objective function is defined as a linear combination of heat transfer and friction loss related terms with a weighting factor. Ten training points are obtained by Latin Hypercube Sampling for two design variables. Optimum shape has been successfully obtained with the increased objective function.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.285-290
• /
• 2000

The present study was conducted to determine flooding heat transfer limitation of a two-phase closed thermosyphon using PFC as working fluid. The variables such as pipe inner diameter, working fluid property, operating temperature were examined by way of analytic method. Comparison of experimental data on flooding heat transfer limitation shows a fairly good agreement with the analytic results. An expression fur flooding maximum heat transfer rate was formulated as a function of Bond number and saturation pressure and written as follows ; $Q_{max} =0.989{\cdot}P_s^{0.286}{\cdot}Bo^{1.74}$.