الفهرس 
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Abstract
Thermal energy storage using solid-liquid phase change materials (PCMs) has been adopted in many industrial applications. The use of PCMs for thermal energy storage in renewable energy systems is well known. In recent years, PCMs have been used for thermal management (TM) of modern high power electronic systems. Recently, problem of heat dissipation in contemporary electronics is intensified due to micro/nano scale developments and pulsed heat inputs. The objective of the present work is to develop, test and evaluate new advanced composite materials (PCMs) for effective thermal management of electronic components. Three types of materials; paraffin wax (PW), multi-walled carbon nanotubes (MWCNTs) and carbon foam (CF) composites are used in a novel design configuration to produce new proposed composite for thermal management. A detailed analysis is performed for selection of best configuration of PCM/CNTs composite for TM composite system. Behavior of PCM/CNTs composites as phase change materials for thermal energy storage purposes have been experimentally investigated. The composites are prepared by dispersion of small amounts of MWNCTs (up to 1 wt. %) in the paraffin melt. Infusion of pure PW or PW/CNTs composites in the prepared CF samples has been done using a specially designed infuser. The present study shows that classical models for predicting the effective thermal conductivity of CNTs-based composites fail to explain the experimental results, mainly because these models assume the CNTs are randomly oriented and distributed in the matrix. Striking results have been obtained in relationship with the phase change behavior of PCM/CNTs composites. Indeed, the latent heat of the composites increases significantly and linearly with the MWCNTs loading. The ability of CNTs to increase the latent heat of phase change materials might lead to breakthroughs in the field of thermal energy storage, where energy density (energy stored by unit mass) is recognized as a major parameter for cost efficient storage solutions and compactness. However, liquid-solid transitions induced by carbon-based nanostructures remain largely unexplored and need much more theoretical and experimental studies to reach better understanding.
II
A detailed experimental study of a hybrid thermal management composite system has been performed for thermal control and protection of electronics against steady and pulsed power loads. Experiments have been carried out using two types of carbon foam samples with different thermal conductivities. Namely, CF-20 and KL1-250 with low and high thermal conductivities respectively.
TM modules using CF core and aluminum container have been assembled. The TM composite modules are tested for three different cases: TM module with pure CF, TM module with CF+RT65, and TM module with CF+RT65/CNTs composite with 1% mass fraction of MWCNTs. For CF-20 foam type and for each case, three different boundary conditions have been applied; namely uniform heat load with three different power levels, three different varying heat loads in stand-alone mode which simulates an ON/OFF cycling and varying Pulsed heat loads with high power spikes generated in the heater source.
Another TM modules using KL1-250 carbon foam of relatively high thermal conductivities as a base structure have been prepared, tested and evaluated at different operating power conditions. Results indicates a good capability of KL1-250 to control high order uniform and pulsed power loads.
For all CF types, TM modules corresponding to CF+RT65 composite show a reasonable delay in reaching the heater steady state temperatures as compared to pure CF. On the other hand TM modules corresponding to CF+RT65/CNTs composite are more effective in the delay and reduction of heater temperatures as compared to pure CF and CF+RT65 composites. It has been found that heat transfer enhancement due to entrapped MWCNTs in the different CF types micro cells have a significant effect on the thermal response of the TM system at low and high power loadings especially for varying power modes.
A numerical technique has been implemented using CFD software to study phase change process within a pure CF and an encapsulated CF/PW composites. Mathematical model is based on single-domain energy equation and a control volume based numerical scheme. Numerical results have been compared with results of the present experimental work and a good agreement between results has been found. The model has shown a good capability for future parametric studies.