Thermal Conductivity Determination of Ga-In Alloys for Thermal Interface Materials Design

Thermal interface material (TIM) that exists in a liquid state at the service temperature enables efficient heat transfer across two adjacent surfaces in electronic applications. In this work, the thermal conductivities of different phase regions in the Ga-In system at various compositions and temperatures are measured for the first time. A modified comparative cut bar technique is used for the measurement of the thermal conductivities of GaxIn1−x (x = 0, 0.1, 0.214, 0.3, and 0.9) alloys at 40, 60, 80, and 100 °C, the temperatures commonly encountered in consumer electronics. The thermal conductivity of liquid and semi-liquid (liquid + β) Ga-In alloys are higher than most of the TIM’s currently used in consumer electronics. These measured quantities, along with the available experimental data from literature, served as input for the thermal conductivity parameter optimization using the CALPHAD (calculation of phase diagrams) method for pure elements, solution phase, and two-phase region. A set of self-consistent parameters for the description of the thermal conductivity of the Ga-In system is obtained. There is good agreement between the measured and calculated thermal conductivities for all of the phases. Due to their ease of manufacturing and high thermal conductivity, liquid/semi-liquid Ga-In alloys have significant potential for TIM in consumer electronics.

Thermal conduction characteristics of silicone composites including ultrasonic-treated graphite

The microstructural change of graphite was studied after ultrasonic treatment of the graphite. When the graphite solution was treated with varying ultrasonic power and time, the microstructure changed gradually, and accordingly, the thermal conductivity characteristics of the composite containing the as-treated graphite was also different with each other. Thermal conductivity showed the best result in the silicone composite containing graphite prepared under the optimum condition of ultrasonic treatment, and the thermal conductivity of the composite improved proportionally along with the particle size of graphite. When the silicone composite was prepared by using a mixture of inorganic oxides and graphite rather than graphite alone, the thermal conductivity of the silicone composite was further increased. A silicone composite containing graphite was used for LED (light emitting diode) lighting system as a thermal interface material (TIM), and the temperature elevation due to heat generated, while the lighting was actually operated, was analyzed.

Development of polyvinyl alcohol-based carbon nano fiber sheet for thermal interface material

Polyvinyl alcohol (PVA)-based carbon nanofiber (CNF) sheets are fabricated as an innovative thermal interface material (TIM), which is a potential substitute for traditional TIMs. Five types of PVA-based CNF sheets were fabricated at different mass ratios of PVA:vapor-grown carbon fiber (VGCF) (1:0.100, 1:0.070, 1:0.050, 1:0.030, 1:0.025). The thickness of the PVA-based CNF sheets was 30–50 µm, which was controlled by the amount of VGCF. The microstructure of the CNF sheets indicated that VGCFs were arranged in random directions inside the sheet, and PVA was formed as a membrane between two VGCFs. However, many pores were found to exist between the VGCFs. The porosity of the PVA-based CNF sheets decreased from 25 to 13% upon decreasing the mass ratio of VGCF from 43.38 to 16.13%. The density and Shore hardness of all CNF sheets were 1.03–1.15 × 106 g m−3 and 82.4–85.0 HS, respectively. The highest thermal conductivity, measured as the mass ratio of PVA:VGCF, was achieved at 1:0.05, with the in-plane thermal conductivity of the fabricated sheet being 14.3 W m−1 k−1.

System-Level Modeling and Thermal Simulations of Large Battery Packs for Electric Trucks

Electromobility has gained significance over recent years and the requirements on the performance and efficiency of electric vehicles are growing. Lithium-ion batteries are the primary source of energy in electric vehicles and their performance is highly dependent on the operating temperature. There is a compelling need to create a robust modeling framework to drive the design of vehicle batteries in the ever-competitive market. This paper presents a system-level modeling methodology for thermal simulations of large battery packs for electric trucks under real-world operating conditions. The battery pack was developed in GT-SUITE, where module-to-module discretization was performed to study the thermal behavior and temperature distribution within the pack. The heat generated from each module was estimated using Bernardi’s expression and the pack model was calibrated for thermal interface material properties under a heat-up test. The model evaluation was performed for four charging/discharging and cooling scenarios typical for truck operations. The results show that the model accurately predicts the average pack temperature, the outlet coolant temperature and the state of charge of the battery pack. The methodology developed can be integrated with the powertrain and passenger cabin cooling systems to study complete vehicle thermal management and/or analyze different battery design choices.

Effect of Thermal Interface Materials on Heat Dissipation of Light-Emitting Diode Headlamps with Thermally-Conductive Plastics

We study the effect of thermal interface material such as thermal-conductive plastic on the dissipation of generated heat from the light-emitting diodes (LEDs) based headlamp for the application of environment-friendly green energy in vehicles. The thermal distribution and the performances of thermal-conductive plastic with heatsink are consistently investigated by using experimental and numerical results. Various thicknesses of thermal-conductive plastics from 0.3 mm to 1.0 mm used in this research work. Basically the thermal-conductive plastic reduces the thermal interface resistance between the contact of two solid surfaces. As a result, High electrical power of about 15 W (1 A and 15 V) can be possible for applying to the high-power LED package without any damage. The soldering temperature of LED package without thermal-conductive plastic shows approximately 138.7 °C which is higher compared to the LED package with thermal-conductive plastic (124.3 °C). On the other hand, the soldering temperature increases from 124.3 to 127.6 °C with increasing the thicknesses of thermal-conductive plastic. In addition, the soldering temperature decreases from 138.7 to 124.3 °C with increasing the thermal conductivities of thermal-conductive plastic. Finally, a highly thermal conductive property of thermal-conductive plastic will propose for optimum dissipation of generated heat from the LEDs-based headlamp. We also successfully estimate the junction temperature of packaged LEDs by using soldering temperature.

Noncured Graphene Thermal Interface Materials for High-Power Electronics: Minimizing the Thermal Contact Resistance

We report on experimental investigation of thermal contact resistance, RC, of the noncuring graphene thermal interface materials with the surfaces characterized by different degree of roughness, Sq. It is found that the thermal contact resistance depends on the graphene loading, ξ, non-monotonically, achieving its minimum at the loading fraction of ξ ~15 wt %. Decreasing the surface roughness by Sq~1 μm results in approximately the factor of ×2 decrease in the thermal contact resistance for this graphene loading. The obtained dependences of the thermal conductivity, KTIM, thermal contact resistance, RC, and the total thermal resistance of the thermal interface material layer on ξ and Sq can be utilized for optimization of the loading fraction of graphene for specific materials and roughness of the connecting surfaces. Our results are important for the thermal management of high-power-density electronics implemented with diamond and other wide-band-gap semiconductors.

A Comparative Study of 1-D and 3-D Simulation Methodologies To Predict the Thermal Performance of a Power Electronics Hardware

Extruded radial fin heat sinks are typically used in power electronics for temperature management. The goal of this study is to compare the temperature predictions of LPTN (Lumped Parameter Thermal Network), Finite element based thermal analysis (using ANSYS Mechanical) and Finite volume based CFD (Computational Fluid Dynamics) & thermal analysis in power electronics hardware. The power electronics hardware under study is used for control of compressors / heaters used in a medical thermal management device. The hardware consists of 2 SCRs (Silicon Controlled Rectifiers) and 2 TRIACs (TRIodes for Alternating Current) arranged in straight in-line configuration with the TRIACs having a higher internal heat generation (1.643E7 W/m3) than the SCRs (4.53E6 W/m3). Each of these four devices is bolted to a separate anodized aluminum heat sink using a TIM (Thermal Interface Material). It was found that CFD based Conjugate Heat Transfer (CHT) analysis with S2S (Surface to Surface) Radiation transfer gave the most accurate thermal predictions (within 6°C). These were comparable to the predictions from 3-D Solid energy equation with uniform convection and S2S radiation. Depending on the availability of computational time and resources, either full CHT study or 3-D Solid energy equation based thermal analysis with uniform convection and S2S radiation is recommended for initial design study.