Thermal Conductivity Of Thermal Interface Materials Research Articles

Experimental study of the influences of surface roughness and thermal interface material on the performance of a thermoelectric generator

Reducing surface roughness and using thermal interface materials (TIMs) at the interfaces between a thermoelectric generator (TEG), heat source, and heat sink are effective strategies for decreasing the thermal contact resistance (TCR) and enhancing the TEG performance. To evaluate the influences of parameters such as the surface roughness, the thermal conductivity of TIM and loading pressure, we conducted experiments to measure the open-circuit voltage and output power of the TEG under various installation conditions. We also analysed the changes in TCR and temperature difference across the TEG module. The experimental findings were validated with numerical simulations using COMSOL Multiphysics under specific conditions. Our results revealed that reducing surface roughness and using TIM could substantially reduce the TCR, increase the temperature difference across the TEG, and increase the output power from the TEG. In our experiments, we used a temperature controller, cartridge heaters and thermocouples to regulate and record the temperatures of the heat source and heat sink. When maintaining a temperature difference of 53 K between the heat source and heat sink, and loading pressure set at 0.2 MPa, without using TIM, as the surface roughness decreased from 2.2 μm to 0.37 μm and to 0.03 μm, leading to a reduction in the TCR from 0.22 K W−1 to 0.17 K W−1 and to 0.13 K/W. Simultaneously, the open-circuit voltage increased from 1.32 V to 1.65 V and to 1.86 V, and the maximum output power increased from 0.26 W to 0.44 W and to 0.58 W. Additionally, when the surface roughness was 0.37 μm, after using TIM with thermal conductivity of 1 W/m-K, 2 W m−1-K−1, and 5 W m−1-K−1, the open-circuit voltage reached 1.44 V, 1.74 V and 1.94 V, respectively, and the maximum power reached 0.31 W, 0.51 W and 0.65 W, respectively.

In-situ shear exfoliation and thermal conductivity of SBS/Graphite nanoplatelet nanocomposites

Rapid developments of miniaturization and integration of modern electronic devices have been accompanied by increasing power density, which bring about urgent demands for polymer-based thermal interface materials (TIMs) with efficient thermal conductive properties. However, poor dispersibility of thermal conductive nano-fillers severely limits further improvement in the thermal conductivity of TIMs. Herein, poly(styrene-b-butadiene-b-styrene) (SBS)/graphite nanoplatelet (GNP) nanocomposites with well-dispersed GNPs were fabricated by in-situ shear exfoliation of graphite in SBS solution, followed by a co-precipitation process. The SBS macro-molecules were immobilized on the surfaces of exfoliated GNPs through π-π interaction, which not only prevented the exfoliated GNPs from restacking in the suspension, but also improved their dispersibility in SBS matrix. Thus, GNPs were uniformly dispersed in SBS/GNP nanocomposites and possessed strong interfacial adhesion with SBS, which formed efficient thermal conductive filler networks with reduced interfacial thermal resistance. Hence, at 14.7 vol% filler, SBS/GNP nanocomposites displayed an excellent thermal conductivity of 1.55 W m−1 K−1, which is 204% higher than SBS/commercial GNP (c-GNP) composites (0.51 W m−1 K−1) prepared by simply adding c-GNPs in SBS matrix. Moreover, SBS/GNP nanocomposites displayed enhanced tensile moduli and higher glass transition temperatures. Therefore, this work has provided a facile and promising route to manufacture high-performance TIMs in large scale.

Theoretical and experimental evaluation of thermal interface materials and other influencing parameters for thermoelectric generator system

Thermal interface resistance of Thermoelectric Generator (TEG) plays a vital role in power production. Improving surface finish of contact surfaces, applying pressure between the contact surfaces and use of Thermal Interface Material (TIM) are few methods of reducing thermal resistance and thereby improving the efficiency of TEG. There is a need to evaluate the influence of these methods and use them optimally for TEG system. Experiments were carried out to study the influence of parameters such as thermal conductivity of TIM, contact pressure, surface roughness and heat source temperature on the voltage and power outputs from TEG. Experimental results are validated with simulations using mathematical heat transfer model and COMSOLTM Multiphysics numerical model. Appreciable agreement is seen between the experimental observations and model outputs. Experimental and model results indicate 0.6 W/mK as optimum thermal conductivity for TIM material. Hence, use of costly TIMs like MWCNT (Multi Wall Carbon Nano Tube) and copper nanoparticles may not be required for the selected application. The contact pressure and surface roughness have appreciable influence when air is used as TIM. These factors have insignificant influence for TIMs with higher thermal conductivity. Increase in heat source temperature increases voltage and power output of TEG.

Ball-milled dispersed network of graphene platelets as thermal interface materials for high-efficiency heat dissipation of electronic devices

Thermal interface material (TIM) is a key component to dissipate the accumulated heat in the majority of power electronic systems. In this work, a facile and solid-state ball-milling method is adopted for the solvent-free reduction of exfoliated graphite nanoplatelets (EGNs) into high-quality ball-milled exfoliated graphite nanoplatelet (BMEGN) fillers. In addition, BMEGN fillers are embedded and uniformly dispersed with polydimethylsiloxane (PDMS) matrix to make a highly stretchable BMEGN-embedded PDMS-TIMs (BMEGN/PDMS) with strongly enhanced thermal conductivity. Furthermore, material characterizations were thoroughly investigated using scanning electron microscopy, transmission electron microscope, Raman spectroscopy, thermogravimetric analysis, and x-ray diffraction. Improvements in the thermal conductivity of TIMs by adding BMEGN were compared, the thermal conductivity was observed for BMEGN fillers with 0- to 48-h ball-milling time, and an enhanced in-plane thermal conductivity of 15.04 to 16.91 W/mK and through-plane thermal conductivity of 1.03 to 1.19 W/mK can be experimentally measured. A strong anisotropy was observed in the range of 14.60 (BMEGN12h/PDMS) to 14.21 (BMEGN48h/PDMS). The results reveal that the ball-milled graphene filler network with branched morphology can effectively provide the synergetic effect of a thermally conductive pathway via diffusion of phonon vibration in flexible composites. The combination of thermal conductivity and thermal stability may facilitate the applications in thermal management.