Showing papers by "Bao Yang published in 2007"

Application of hybrid sphere/carbon nanotube particles in nanofluids

Abstract: Previous studies on nanofluids have focused on spherical or long-fibre particles. In this work, a new type of complex nanoparticle—a hybrid sphere/carbon nanotube(CNT) particle, consisting of numerous CNTs attached to an alumina/iron oxide sphere—is proposed for applications in nanofluids. In such hybrid nanoparticles, heat is expected to transport rapidly from one CNT to another through the centre sphere and thus leading to less thermal contact resistance between CNTs when compared to simple CNTs dispersed in fluids. CNTs have an extremely high thermal conductivity, but thermal resistance between the CNTs and the fluid has limited their performance in nanofluids. The proposed hybrid sphere/CNT particles are synthesized by spray pyrolysis followed by catalytic growth of CNTs. The spheres are about 70 nm in diameter on average, and the attached CNTs have a length up to 2 µm. These hybrid nanoparticles are dispersed to poly-alpha-olefin with sonication and a small amount of surfactants to form stable nanofluids. The thermal conductivity of the fluids has been measured by a 3ω-wire method over a temperature range 10–90 °C. The results indicate that the effective thermal conductivity of the fluids is increased by about 21% at room temperature for particle volume fractions of 0.2%.

Mini-Contact Enhanced Thermoelectric Cooling of Hot Spots in High Power Devices

Abstract: Cooling hot-spots with high heat flux (e.g., >1000 W/cm2) is becoming one of the most important technical challenge in today's integrated circuit industry. More aggressive thermal solutions, than would be required for uniform heating, are highly desired. Recently, solid state thermoelectric coolers (TECs) have received more attention for hot-spot thermal management. However, present day TECs typically have cooling flux much lower than heat flux in the hot-spots. In this work, we reported an innovative technique-TE Mini-contact-to significantly increase cooling flux of TECs for the application in hot-spot cooling. A chip package featuring a TE Mini-contact cooler integrated with conventional integrated heat spreader and heat sink is designed. The cooling performance of such chip package has been investigated by using a 3-D numeric model. It is found that the cooling in the hot-spot (1250 W/cm2, 400 mum by 400 mum) can be about 19 degC better in the proposed package than that achieved in the conventional chip package without TEC. The effects of trench, die thickness, and TEC misalignment on the cooling of the hot-spot are also discussed.

Enhanced Thermoelectric Cooler for On-Chip Hot Spot Cooling

Abstract: Due to shrinking feature size and increasing transistor density, combined with the performance demanded from next-generation microprocessors, on-chip hot spots, with their associated high heat fluxes and sharp temperature gradients, have emerged as the primary driver for thermal management of today’s IC technology. This paper describes the novel use of thermoelectric coolers for on-chip hot spot cooling through the use of a copper mini-contact pad, which connects the thermoelectric cooler and the silicon chip thus concentrating the thermoelectric cooling power. A package-level numerical simulation is developed to predict the local on-chip hot spot cooling performance which can be achieved with such mini-contacts. Attention is focused on the hot spot temperature reduction associated with variations in mini-contact size and the thermoelectric element thickness, as well as the parasitic effect of the thermal contact resistance introduced by the mini-contact enhanced TEC. This numerical model and simulation results are validated by comparison to spot cooling experiments with a uniformly heated chip serving as the test vehicle. The experimental results demonstrate that a copper mini-contact pad can improve spot cooling performance by 80 ∼ 115% on a 500μm thick silicon chip under optimum operating conditions and that larger power dissipation on the chip leads to better spot cooling performance.Copyright © 2007 by ASME

Development of a polarized electron source for the MIT-Bates Linear Accelerator Center

Abstract: The polarized electron source at MIT-Bates has been developed to provide beams for nuclear physics experiments with a very diverse set of requirements. The source has combined operation at high peak and average current with high polarization. Developments have included the pioneering of several techniques used in parity violating experiments to remove helicity correlations from beam properties. This paper describes the design of the source and its performance during beam operations.

Nanofluids Containing Hybrid Sphere/Carbon Nanotube Particles

Abstract: Previous studies on nanofluids have focused on spherical or long-fiber particles. In this work, a new type of complex nanoparticles—hybrid sphere/carbon nanotube (CNT) particle, consisting of numerous CNTs attached to an alumina/iron oxide sphere—is proposed for applications in nanofluids. In such hybrid nanoparticles, heat is expected to transport rapidly from one CNT to another through the center sphere and thus leading to less thermal-contact-resistance between CNTs when compared to simple CNTs dispersed in fluids. CNTs have an extremely high thermal conductivity, but thermal resistance between the CNTs and the fluid has limited their performance in the nanofluids. The proposed hybrid sphere/CNT particles are synthesized by a spray pyrolysis followed by catalytic growth of CNTs. The spheres are about 70 nm in diameter in average, and the attached CNTs have a length up to 2μm. These hybrid nanoparticles are dispersed to poly-alpha-olefin with sonication and a small amount of surfactants to form stable nanofluids. The thermal conductivity of the fluids has been measured by a 3ω-wire method over a temperature range 10–90°C. The results indicate that the effective thermal conductivity of the fluids is increased by about 21% at room temperature for particle volume fractions of 0.2%.Copyright © 2007 by ASME