Byungho Sung

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.

Experimental Investigation on Boiling Phenomena of Bi-Layer Composite Porous Wicks Textured With Nano-Porous Layer

Miniature loop heat pipes (mLHP) are envisioned as one of the next generation electronic cooling technologies. They are closed loop, phase-change devices where the working fluid evaporates during heat addition and its flow is maintained by capillary forces developed inside the porous wick lining the evaporator. While they have many advantages such as high heat flux rates and heat rejection far from the heat source, potential problems are often associated with bubble nucleation and boiling incipience in the porous wicks. Bi-layer composite porous wicks consisting of a nano-porous layer textured onto the traditional micro-porous material are thought to possess enhanced capillary wicking, which could benefit mLHP applications. In this context, it is important to also understand their boiling characteristics. Therefore, a boiling heat transfer testing apparatus was developed and used to characterize the boiling incipience of bi-layer porous wicks. These results may guide material selection in the design of mLHP evaporators employing bi-layer porous wicks.Copyright

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

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

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