Numerical Study of CNT Micro Fin Array for Cooling Application

Heat removing from a microelectronic chip packaging has grand effect on performance and durability of the chip. Today’s microchips with high power densities would require efficient methods of cooling. Recently, vertical alignment CNTs, due to their superior thermal, electrical and mechanical properties, was suggested as an effective micro cooler on the level of modern electronics demands. In this paper, the cooling performance of the CNT fin structures is studied numerically. Flow of air was considered as the working fluid flow. CFD simulations have been carried out for a series of CNT micro-fin cooling architectures based on one and two dimensional fin array models. The modeling results indicate that fluid speed is the key factor in heat transfer capacity of the device. Also, the results of 2D carbon nanotube fin array model show more precise and greater thermal performance than that of 1D model. Finally, the examination of pressure drop between inlet and outlet of the cooling device is presented as an important factor which could limit the fluid speed and fin height effect on heat sink performance also investigated

Effect of Source Solution Components on Quality of Electrospun PVDF Nanofibers for Nanogenerator Application

High surface area flexible thin films of Polyvinylidene Difluoride (PVDF) nanofibers are vastly used because of low cost, simple, safety and environmentally friendly production methods. PVDF nanofibers are inherently piezoelectric when produced by high voltage electrospinning method. In this paper, PVDF nanofibers are synthesis in a electrospinning apparatus, using a solution that contains PVDF dissolved in two solvents, THF (Tetrahydroforan) and DMF (N,N-Di-Methyl Formamid), which DMF has a higher boiling point than THF. The effects of THF to DMF ratio in the solution, and also, PVDF concentration on the morphology and diameter of the synthesised nanofibers are studied. Field emission scanning electron microscopy analysis of the nanofiber thin films indicates that by adding THF in the source suspension, smoother and more uniform nanofibers with lower diameter are resulted. However, by further increasing THF ratio, the cone-jet mode is formed on the tip of the needle, rapidly dried, before reaching the collector substrate. Results of the further experiments indicate that decreasing of PVDF concentration in the deposition source solves the latter problem. On the other hand, by decreasing the THF ratio to DMF, the solution cannot completely be dried, before collecting by the substrate. The best and uniform nanofibers with the diameter of 200 to 300 nm are obtained from a ratio of 3:1 For THF:DMF and 10 % PVDF concentration. Fabricated nanogenerator, based on the best mentioned sample, shows an output power of 0.56 W/m2 when actuated by a vibration mechanical force with the frequency of 8 Hz

ICHMT2014-XXXX Investigation of CNT Growth Regimes in a Tubular CVD Reactor Considering Growth Temperature

Abstract In Carbon nanotube (CNT) growth process via Chemical vapor deposition (CVD) method, there are two distinct regimes based on growth temperatures, so called mass transfer controlled and surface reaction controlled regimes, which represent different type of behaviour in growth. Operating in each regime has different characteristic that can influence on other operating condition effects on CNTs growth. Thus study of these regimes is important for better understanding of CNTs growth; also it helps to control of other operating conditions effect on growing CNTs. In this paper these two regimes is established and then relevant processes in reactor is studied in details. Results show that CNTs total production in mass transfer controlled regime has higher order and less sensitivity to the growth temperature compared to surface reaction controlled regime. Also produced CNTs in mass transfer controlled regime has less length uniformity compared to surface reaction controlled regime