• Journal of the Korea Institute of Military Science and Technology
• /
• v.5 no.1
• /
• pp.83-95
• /
• 2002

Thermal conductivity of ceramic fibrous insulator was analysed and predicted by using the modeling/simulation technique. Ceramic fibrous insulators are widely used as high temperature insulator on account of their lightweight mass and heat resisting properties. Especially it is suitable to protect the high speed aircraft and missiles from severe aero-thermodynamic heating. Thermal conductivity of ceramic fibrous insulator could be determined from the conductive heat transfer and the radiative heat transfer through the insulator. In order to estimate conductive thermal conductivity, homogenization technique was applied, while radiative thermal conductivity was computed by means of random number and radiation probability. Particularly radiation probability can make it possible to estimate the conductivity of fibrous insulator without any experimental constant. The calculated conductivity predicted in the present study have a reasonable accuracy with an average error of 7 percent to experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.11
• /
• pp.861-869
• /
• 2015

In this study, wall to bed heat transfer and hydrodynamic characteristics in a conical fluidized bed combustor was investigated using computational fluid dynamics method. A two-fluid Eulerian-Eulerian model was used with applying the kinetic theory for granular flow(KTGF). The effects of the two drag models, Gidaspow and the Syamlal-O'Brien model, different inlet velocities($1.4U_{mf}{\sim}4U_{mf}$) and different particle sizes on the hydrodynamics and heat transfer were studied. The results showed that the hydrodynamic characteristics such as bed expansion ratio and pressure drop were not affected significantly by the drag models. But the heat transfer coefficient was different for the two drag models, especially at lower gas inlet velocities and small particle sizes.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.1
• /
• pp.57-63
• /
• 2012

In this study, numerical analyses were performed on pressure drop and heat transfer characteristics in a rectangular horizontal channel with dimple and protrusion arrays of different height. The dimples/protrusions were installed at both top and bottom walls of the rectangular channel. The dimple and protrusion depths are 0.125, 0.2, 0.25, 0.3, and 0.375 times diameter. In case of the dimple, the highest Nusselt number occurred at the rear side of the dimple, and the average Nusselt number tended to decrease slightly with increase of depth. In case of protrusion, on the other hand, the highest Nusselt number occurred at the front side of the protrusion, and the average Nusselt number was increased with the increase of height. In both dimple and protrusion, the average Nusselt number and pressure drop were increased with the increase of velocity. Performance factor was decreased with the increase of velocity, and it was found that the best performance factor was obtained in the low velocity region.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.1
• /
• pp.591-596
• /
• 2016

Numerical analyses were performed on the heat flow characteristics of a heat transfer plate with six different shapes (basic, rectangle, triangle, wave type) to reduce the level of white smoke at a stack. In this study, to examine the heat transfer performance (heat transfer capacity, pressure drop, turbulence kinetic energy, heat transfer coefficient) on the heat transfer plates, simulations were conducted using the commercial computational fluid dynamics software, ANSYS CFX Ver.14 under uniform flow conditions. The thermal flow phenomenon in a channel with six heat transfer plates could be predicted adequately under uniform flow conditions. The heat transfer capacity, pressure drop, turbulence kinetic energy, and heat transfer coefficient were affected by the flow rate, aspect ratio and plate shape. These results provide guidelines to design an effective heat exchanger with the wave type to reduce white smoke.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.8
• /
• pp.725-732
• /
• 2013

This study examined the convective heat transfer characteristics of nanofluids flowing over a heated fine wire. Convective heat transfer coefficients were measured for four different nano-engine-oil samples under three different temperature boundary conditions, i.e., both or either variation of wire and fluid temperature and constant film temperature. Experimental investigations that the increase in the convective heat transfer coefficients of nanofluids in the internal pipe flow often exceeded the increase in thermal conductivity were recently published; however, the current study did not confirm these results. Analyzing the behavior of the convective heat transfer coefficient under various temperature conditions was a useful tool to explain the relation between the thermal conductivity and the boundary layer thickness of nanofluids.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.470.1-470.1
• /
• 2014

InAs는 high mobility를 갖는 III-V 화합물 반도체로 최근 InAs 나노선 기반 electronic transport에 대한 연구가 활발히 진행되고 있다. 또한, InAs는 n-type의 중온 영역대의 열전물질로서 나노선이나 나노박막과 같은 저 차원 구조의 열전 특성에 대한 보고가 이루어 지고 있다. 대부분의 InAs 나노선의 성장 방법은 화학기상증착법에 의한 것으로, 상온에서 $100{\mu}V/K$ 이하의 낮은 Seebeck 계수 값을 나타내고 있다. 본 연구는 무촉매 상태에서 MBE (Molecular beam epitaxy) 성장시킨 InAs 나노선의 열전 특성을 측정하였다. MTMP (Microfabricated Thermoelectric measurement platform)를 이용하여 50 K에서 300 K까지의 온도 영역에서 전기전도도, Seebeck 계수의 측정을 진행하였다. 그 결과 Seebeck 계수 값은 상온에서 대략 $200{\mu}V/K$로 높게 나타나고 있으며, 동일한 나노선의 상온 전기전도도는 대략 9800 S/m로 많은 보고들과 비슷한 수준의 수치가 나타나고 있다. Transconductance 측정을 통한 field-effect mobility와 carrier 농도를 평가한 결과가 Mott formula에서 계산된 carrier 농도와 유사한 결과를 나타내었다. 매우 큰 Seebeck 는 carrier 농도가 낮은 것에 기인한 것으로 판단된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.8
• /
• pp.84-91
• /
• 2005

An experimental investigation has been carried out to examine heat-transfer characteristics of an axisymmetric, under-expanded, sonic jet impinging on a flat plate and the local measurement of surface pressures and heat transfer coefficients on a plate have been achieved together with a visualization test of shock structure in a jet. Heat transfer coefficients on a plate have been found to be changed significantly depending on the under-expansion ratio as much as the nozzle-to-plate distance. These phenomena could be explained by the wall pressure measurement and the shock visualization.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.4
• /
• pp.315-321
• /
• 2012

In this study, a sequential multiscale homogenization method to characterize the effective thermal conductivity of nano particulate polymer nanocomposites is proposed through a molecular dynamics(MD) simulations and a finite element-based homogenization method. The thermal conductivity of the nanocomposites embedding different-sized nanoparticles at a fixed volume fraction of 5.8% are obtained from MD simulations. Due to the Kapitza thermal resistance, the thermal conductivity of the nanocomposites decreases as the size of the embedded nanoparticle decreases. In order to describe the nanoparticle size effect using the homogenization method with accuracy, the Kapitza interface in which the temperature discontinuity condition appears and the effective interphase zone formed by highly densified matrix polymer are modeled as independent phases that constitutes the nanocomposites microstructure, thus, the overall nanocomposites domain is modeled as a four-phase structure consists of the nanoparticle, Kapitza interface, effective interphase, and polymer matrix. The thermal conductivity of the effective interphase is inversely predicted from the thermal conductivity of the nanocomposites through the multiscale homogenization method, then, exponentially fitted to a function of the particle radius. Using the multiscale homogenization method, the thermal conductivities of the nanocomposites at various particle radii and volume fractions are obtained, and parametric studies are conducted to examine the effect of the effective interphase on the overall thermal conductivity of the nanocomposites.

• Journal of Energy Engineering
• /
• v.15 no.1 s.45
• /
• pp.60-66
• /
• 2006

An experimental investigation on the flow and convective heat transfer characteristics has been carried out far aluminum foam heat sink inserted into the annulus to examine the feasibility as a heat sink. Two aluminum foams or different permeability were selected to provide the friction factor and heat transfer correlations as function of Darcy, Reynolds and Prandtl number. Experimental results show that the friction factor is higher than clear annulus without aluminum foam, while $6\sim10$ times augmentation in Nusselt number is obtained. This technique can be used for the compactness of the heat exchanger.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.294-296
• /
• 2017

In this study heat transfer characteristics of kerosene at supercritical condition was predicted. And a sample heat transfer calculation was performed using this result. The prediction was done by assuming kerosene as a mixture of a number of pure substances, and combining the thermodynamic properties of them, using NIST SUPERTRAPP. A regeneratively cooled supersonic combustor will be desinged using the resultant thermophysical property data of supercritical kerosene. Comparing with the combustion test results of the regenerative cooling combustor, the predicted thermophysical property data will be verified.