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In the present work, the potential of using foam structures impregnated with phase change materials (PCMs) as heat sinks for cooling of electronic devices has been numerically studied. Different design parameters have been investigated such as foam properties (porosity, pore size, and thermal conductivity), heat sink shape, orientation, and use of internal fins inside the foam-PCM composite. Due to huge difference in thermal properties between the PCM and the solid matrix, two energy equation model has been adopted to solve the energy conservation equations. This model can handle local thermal nonequilibrium condition between the PCM and the solid matrix. The numerical model is based on volume averaging technique, and the finite volume method is used to discretize the heat diffusion equation. The findings show that, for steady heat generation, the shape and orientation of the composite heat sink have significant impact on the system performance. Conversely, in the case of power spike input, use of a PCM with low melting point and high latent heat is more efficient. [DOI: 10.1115/1.2912185] Keywords: heat sinks, PCM, foams, electronic devices

Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior. By using higher porosity aluminum foam, the steady-state temperature was reached faster as compared to the foams with lower porosity. Similarly for the bigger pore size foams the steady state was attained faster as compared to the smaller pore size foams. This was due to the greater effect of convection in both the higher porosity and bigger pore size foams. However, for the lower porosity foams the heater temperature was comparatively lower than the higher porosity foams due to greater heat conduction through the foam material. Therefore, an optimal value should be selected for the foam porosity and pore size such that the effects of both conduction and convection heat transfers can be completely utilized to have a greater and improved thermal performance for the wax/aluminum foam composite. [ABSTRACT FROM AUTHOR]

A numerical investigation study was performed to study the phase change behavior of wax/foam composite encapsulated in an aluminum casing. Two types of foam materials, namely, aluminum and carbon, were infiltrated with paraffin wax. The progress of melt interface and temperature distribution within the encapsulated composite was analyzed using computational fluid dynamics software (CFD). A two-energy equation model was implemented in the CFD software through the use of user defined function (UDF). Interfacial effects influencing the heat transfer process at the casing-composite junction and between the wax-foam surfaces within the composite were addressed through the use of separate UDF. In addition, the effect of capillary pressure developed within the foam matrix was incorporated using an area ratio parameter. The contact resistance at the foam-casing interface and the capillary pressure had a major influence on the thermal behavior of the system. These two factors lowered down the heat transfer rate considerably and the melting area was reduced by more than 30%. The temperature profiles for the foam material showed a different pattern as compared to the temperature within the wax, which was due to the effect of thermal nonequilibrium. [ABSTRACT FROM AUTHOR]

The present work involves a study on the thermal conductivity of nanoparticle-oil suspensions for three types of nanoparticles, namely, carbon nanotubes (CNTs), exfoliated graphite (EXG), and heat treated nanofibers (HTT) with PAO oil as the base fluid. To accomplish the above task, an experimental analysis is performed using a modern light flash technique (LFA 447) for measuring the thermal conductivity of the three types of nanofluids, for different loading of nanoparticles. The experimental results show a similar trend as observed in literature for nanofluids with a maximum enhancement of approximately 161% obtained for the CNT-PAO oil suspension. The overall percent enhancements for different volume fractions of the nanoparticles are highest for the CNT-based nanofluid, followed by the EXG and the HTT. The findings from this study for the three different types of carbon nanoparticles can have great potential in the field of thermal management. [ABSTRACT FROM AUTHOR]

This study was focused on the effect of carbon nanotubes on the impact resistance and damage evolution in laminate carbon nanotubes/epoxy composites under an impact loading. The composite panels were made from carbon fibers and carbon nanotubes randomly distributed into epoxy resin. The amount of carbon nanotubes dispersion was varied up to 4% by weight. Taylor impact tests were carried out to obtain the impact response of specimens with dimensions of 70×70×4 mm3. A projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 3 m/s, 7 m/s and 12 m/s. For the experimental test, three velocity levels were used: 3 m/s for the elastic deformation, 7 m/s for the penetration of the impactor and 12 m/s for the perforation of panels. Deformation histories and damage modes in specimens were recorded during the impact test using a high-speed camera. Processing of carbon nanotubes dispersed in laminates, testing, damage, and key findings is reported. It is observed that the impact resistance of laminates reinforced with a random distribution of carbon nanotubes increases up to 15.6% at high-strain rate compared with that of 0% of carbon nanotubes. It is also observed that the resistance to damage initiation and evolution increases with the addition of carbon nanotubes concentration. [ABSTRACT FROM AUTHOR]