• 대한기계학회논문집B
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• 제25권5호
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• pp.645-652
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• 2001

Heat transfer data are presented which describe characteristics of the transitional thermal boundary layers on the NACA0012 airfoil with upstream wakes. The wakes are generated periodically by circular cylindrical rods which rotate around the airfoil like a squirrel cage. The unsteady wakes simulate those produced by the upstream rotating blade rows in axial turbomachines. The pressure or suction side of the airfoil is also simulated according to the rotating direction of circular rods. As the Reynolds number and the number of rotating rods increase, the boundary layer transition occurs earlier and the Nusselt number increases. The difference of heat transfer coefficient is less on the pressure side than on the suction side. At a constant Reynolds number, the Nusselt number is larger and smaller, respectively, before and after transition as the Strouhal number increases.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.51-53
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• 2004

An analytical method is developed which focused on the end effects for determining the thermal stress distribution in an laminated beam bonded with adhesive layer. This method gives the stress distribution which satisfy the stress-free boundary condition at edge completely. Numerical example, in which an Al-Cu beam bonded with solder(Pb-Sn) is treated, shows that the shear and peeling stresses at the interfaces are significant near the edge and become negligible in the interior region.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1654-1659
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• 2017

The boundary layer of a two-dimensional forced convective flow along a persistent moving horizontal needle in an electrically conducting magnetohydrodynamic dissipative nanofluid was numerically investigated. The energy equation was constructed with Joule heating, viscous dissipation, uneven heat source/sink, and thermal radiation effects. We analyzed the boundary layer behavior of a continuously moving needle in Blasius (moving fluid) and Sakiadis (quiescent fluid) flows. We considered Cu nanoparticles embedded in methanol. The reduced system of governing Partial differential equations (PDEs) was solved by employing the Runge-Kutta-based shooting process. Computational outcomes of the rate of heat transfer and friction factors were tabulated and discussed. Velocity and temperature descriptions were examined with the assistance of graphical illustrations. Increasing the needle size did not have a significant influence on the Blasius flow. The heat transfer rate in the Sakiadis flow was high compared with that in the Blasius flow.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.34-37
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• 2001

In this study, the capacitance-voltage properties of (Sr$_{1-x}$ .Ca$_{x}$)TiO$_3$(0.05$\leq$x$\leq$0.20)-based grain boundary layer ceramics were investigated. The ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 1480~150$0^{\circ}C$ and 4 hours, respectively. The 2nd phase formed by the thermal diffusion of CuO from the surface leads to very excellent dielectric properties, that is, $\varepsilon$$_{r}$>50000, tan$\delta$<0.05, $\Delta$C<$\pm$10%. The capacitance is almost unchanged below about 20[V] but it decreases slowly about 20[V]. The results of the capacitance-voltage properties indicated that the grain boundary was composed of the continuous insulating layers.ulating layers.s.

• Smart Structures and Systems
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• 제28권6호
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• pp.791-798
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• 2021

Current investigation aims to analyze the characteristics of magnetohydrodynamic boundary layer flow of bioconvection Casson fluid in the presence of nano-size particles over a permeable and non-linear stretchable surface. Fluid passes through the Darcy-Forchheimer permeable medium. Effect of different parameter such as Darcy-Forchheimer, porosity parameter, magnetic parameter and Brownian factor are investigated. Increasing Brownian factor leads to the rapid random movement of nanosize particles in fluid flows which shows an expansion in thermal boundary layer and enhances the nanofluid temperature more rapidly. For large values of Darcy-Forchheimer, magnetic parameter and porosity factor the velocity profile decreases. Higher values of velocity slip parameter cause decreasing trend in momentum layer with velocity profile.

• Advances in nano research
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• 제14권6호
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• pp.575-590
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• 2023

Many of small-scale devices should be designed to tolerate high temperature changes. In the present study, the states of buckling and stability of nano-scale cylindrical shell structure integrated with piezoelectric layer under various thermal and electrical external loadings are scrutinized. In this regard, a multi-layer composite shell reinforced with graphene nano-platelets (GNP) having different patterns of layer configurations is modeled. An outer layer of piezoelectric material receiving external voltage is also attached to the cylindrical shell for the aim of observing the effects of voltage on the thermal buckling condition. The cylindrical shell is mathematically modeled with first-order shear deformation theory (FSDT). Linear elasticity relationship with constant thermal expansion coefficient is used to extract the relationship between stress and strain components. Moreover, minimum virtual work, including the work of the piezoelectric layer, is engaged to derive equations of motion. The derived equations are solved using numerical method to find out the effects of temperature and external voltage on the buckling stability of the shell structure. It is revealed that the boundary condition, external voltage and geometrical parameter of the shell structure have notable effects on the temperature rise required for initiating instability in the cylindrical shell structure.

• 한국환경과학회지
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• 제11권9호
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• pp.865-880
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• 2002

As prevailing synoptic scale westerly wind blowing over high steep Mt. Taegulyang in the west of Kangnung coastal city toward the Sea of Japan became downslope wind and easterly upslope wind combined with both valley wind and sea breeze(valley-sea breeze) also blew from the sea toward the top of the mountain, two different kinds of wind regimes confronted each other in the mid of eastern slope of the mountain and further downward motion of downlsope wind along the eastern slope of the mountain should be prohibited by the upslope wind. Then, the upslope wind away from the eastern slope of the mountain went up to 1700m height over the ground, becoming an easterly return flow in the upper level of the sea. Two kinds of circulations were detected with a small one in the coastal sea and a large one from the coast toward the open sea. Convective boundary layer was developed with a thickness of about 1km over the ground in the upwind side of the mountain in the west, while a thickness of thermal internal boundary layer(TIBL) form the coast along the eastern slope of the mountain was only confined to less than 200m. After sunset, under no prohibition of upslope wind, westerly downslope wind blew from the top of the mountain toward the coastal basin and the downslope wind should be intensified by both mountain wind and land breeze(mountain-land breeze) induced by nighttime radiative cooling of the ground surfaces, resulting in the formation of downslope wind storm. The wind storm caused the development of internal gravity waves with hydraulic jump motion bounding up toward the upper level of the sea in the coastal plain and relatively moderate wind on the sea.

• 한국추진공학회지
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• 제23권2호
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• pp.27-37
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• 2019

쉘-튜브 열교환기가 나로우주센터 추진기관종합시험장(PSTC)에 설치되었으며, 이 열교환기는 극저온의 헬륨을 고온의 열매유와 열교환하여 약 500 K 까지 가열시키는 역할을 한다. 열교환기에서 토출되는 헬륨의 온도가 설계보다 100 K 낮게 나옴에 따라, 성능저하의 원인으로 열매유의 격막효과가 지목되었다. CFD 해석을 통해 격막효과의 유무를 확인하였으며, 격막효과에 의한 열교환기 성능저하는 미미한 것으로 판단되었다. 추가적으로 열교환기의 성능을 증가시키기 위하여 열매유 교체에 따른 열교환기 성능 변화를 알아보았다. 열매유를 사용하는 열교환기의 성능향상을 위해서는 500 K 부근에서 점성이 낮아야 하고, 열전도도가 높아야 한다는 것을 확인할 수 있었다. 추진기관종합시험장에서 운용된 극저온 헬륨과 고온 열매유의 열교환 시스템의 시험 결과를 본 논문에서 확인할 수 있다.

• Journal of Mechanical Science and Technology
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• 제14권6호
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• pp.690-698
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• 2000

The laminar boundary layer flow and heat transfer of anisotropic fluids in the vicinity of a wedge have been examined with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the stream wise-dependence in the coupled nonlinear boundary layer equations. The numerical solutions are presented using the fourth-order Runge - Kutta method and the distribution of velocity, micro-rotation, shear and couple stresses and temperature across the boundary layer are plotted. These results are also compared with the corresponding flow problems for Newtonian fluid over wedges. It is found that for a constant wedge angle, the skin friction coefficient is lower for micropolar fluid, as compared to Newtonian fluid. For the case of the constant material parameter K, however, the magnitude of velocity for anisotropic fluid is greater than that of Newtonian fluid. The numerical results also show that for a constant wedge angle with a given Prandtl number, Pr = I, the effect of increasing values of K results in increasing thermal boundary layer thickness for anisotropic fluid, as compared with Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for anisotropic fluid is lower than that of Newtonian fluid.

• 한국전산유체공학회지
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• 제18권1호
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• pp.77-82
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• 2013

The error in measuring temperature profiles by thermocouple inside boundary layer mostly comes from the conduction heat transfer of the thermocouple. The error is not negligible when the conductivity of the thermocouple is very high. In this study, the effect of conduction heat transfer of the thermocouple on the temperature profile inside boundary layer was examined by considering both free-stream velocity and a thermocouple position. The conduction error of an E-type thermocouple was investigated by numerical analysis of three-dimensional conjugate heat transfer for various velocity profiles of boundary layer and thermocouple positions.