Chulju Kim

The effects of interfacial bonding on mechanical properties of single-walled carbon nanotube reinforced copper matrix nanocomposites

The effects of interfacial bonding on mechanical properties of single-walled carbon nanotube reinforced copper matrix nanocomposites were investigated. The nanocomposites were fabricated by means of a powder metallurgy process, which consists of mixing carbon nanotubes with matrix powder followed by hot-pressing. The mixing process was carried out by ultrasonicating the nanotubes and copper powder in ethanol. The interfacial strength between the nanotubes and the copper matrix was improved by coating the nanotubes with nickel. The displacement rate of the nanotube reinforced nanocomposites was found to increase at 200 °C, whereas that of the nickel-coated nanotube reinforced nanocomposites significantly decreased. The incorporation of carbon nanotubes and nickel-coated carbon nanotubes in the copper matrix composites improved tribological properties compared with those of pure copper specimens.

An Experimental Investigation of the Miniature Loop Heat Pipe Cooling Systems for High Power Density Computer Chips

The implementation of high power density, multi-core central and graphic processing units (CPUs and GPUs) coupled with higher clock rates of the high-end computing hardware requires enhanced cooling technologies able to attend high heat fluxes while meeting strict design constrains associated with system volume and weight. Miniature loop heat pipe (mLHP) systems emerge as one of the technologies best suited to meet all these demands. This paper investigates experimentally a mLHP system designed for workstation CPUs. The system incorporates a two-phase flow loop with capillary driving force. Since there is a strong demand for miniaturization in commercial applications, emphasize was also placed on physical size during the design stage of the new system. Hence system weight is reduced to around 450g, significantly smaller than that of commercial coolers consisting of copper heat sinks that weight around 782g. Experimental characterization shows that the system can reach a maximum heat transfer rate of 170W with an overall thermal resistance of 0.12 K/W. The heat flux is 18.9 W/cm2 , approximately 30% higher than that of larger size commercial systems. To further miniaturize the evaporator module while maintaining the same heat flux, a new structure for the porous evaporator is proposed, which consist of a porous bi-layer, with nanopores at the top surface. The role of the nanoporous layer is to provide a larger surface area for phase-change, enhancing the evaporation rate.Copyright

Numerical Analysis of Flow Distribution for Combined Weapon System in Environmental Tester

Thermal behaviors of combined weapon systems have been analyzed in this study by developed computational programs. Also, temperature distributions of the materials of the system have been measured for the experimental conditions. Field tests in the large environmental tester have been prepared by the calculated thermal flow characteristics and the measured temperature distributions of the materials for the weapon systems. The boundary conditions of the analysis are composed of inlet and outlet conditions of the environmental tester and the limit of low temperature of −32°C. The soaking time of the system including a fuel tank and a battery in the environmental tester has been obtained by developed programs in this study to carry out the experiment in the predicted conditions.Copyright

The Sintered Porous Metal Media Development and Measurement of LHP Systems for Electronic Cooling Device

Due to the continuous increase of power applied in electric device, the growing demand on cooling systems have led with using various cooling device to conduct the thermal management. As a new cooling device, a Loop Heat Pipe (LHP) system has been taken notice recently. The performance of the LHP systems depends mainly upon the operating performance of the wick structure should possess flow properties such as permeability, maximum capillary pressure and so on. However, expressions on packed metal spherical particles are not related with various particle shapes. In this work, therefore, an experimental apparatus was set up to measure the flow properties of sintered porous metal wicks manufactured with spherical, needled, and corn shape particles. The results of the such experiments gave very accurate and consistent.Copyright

Development of Cooling Design Technique for an Electronic Telecommunication System Using HPHE

The purpose of this study is to investigate the cooling performance of Heat Pipe Heat Exchanger(HPHE) for an electronic telecommunication system by adequate convection condition. Heat generation rates of electronic components, the temperature distributions of HPHE and surrounding air are analyzed experimentally and numerically. In order to perform the heat transfer analysis for the thermal design of telecommunication system, a program is developed. The program is useful to a user who is not familiar with an electronic telecommunication system. The simulation results showed that the HPHE were able to achieve a cooling capacity of up to 230W at the maximum temperature difference of . To verify the results from the numerical simulation, an experiment was conducted under the same condition as the numerical simulation, and their results were compared.

Characterization of Mechanical Properties of Carbon Nanotubes in Copper-Matrix Nanocomposites

Carbon nanotubes have received considerable attention because of their excellent mechanical properties. In this study, carbon nanotube - copper composites have been sintered by a mechanical mixing process. The interfacial bonding between nanotubes and the copper matrix was improved by coating nanotubes with nickel. Sintered pure copper samples were used as control materials. The displacement rate of nanotube-copper composites was found to increase at 200°C whereas that of nickel-coated nanotue-copper composites significantly decreased. The incorporation of carbon nanotubes and nickel-coated carbon nanotubes in the copper matrix decreased friction coefficients and increased the time up to the onset of scuffing compared with those of pure copper specimens.Copyright