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This work reports on the significant enhancement of the thermal properties of the FR3 natural ester dielectric oil after the addition of pentyl-graphene nanosheets, as confirmed by thermal diffusivity and specific heat studies at different concentrations and temperatures (30 °C–90 °C). Experimental results of the dielectric constant demonstrated a constant value in the kHz region while increased in the low-frequency region, decreased with increased temperature, and saturated at 0.008% w/w concentration. In addition, light absorption is used for a better understanding of the properties variation upon changing graphene’s concentration as a method to estimate the agglomeration level. The optimum concentration for its best performance in terms of thermal and dielectric properties is 0.008% w/w, whereby the thermal diffusivity and the dielectric constant increased by 43.04% and 6.18%, respectively. [ABSTRACT FROM AUTHOR]

An accurate and efficient algorithm is presented, which allows deriving the structure function of a discretized 3-D heat conduction problem. In this approach, the partial thermal conductances and capacitances in the structure function are computed in terms of weighted spatial averages of thermal resistivity and volumetric heat capacity. As a result, the exact influence of all materials and geometric details on each part of the structure function is determined. The approach is validated on a state-of-the-art SiGe heterojunction bipolar transistor (HBT) for high-frequency applications. [ABSTRACT FROM AUTHOR]

Rare-earth barium copper oxide (REBCO) tape is used for resistive type superconducting fault current limiters (RSFCLs) owing to its quick response and simple structure. To shorten the recovery time, film boiling on the REBCO tape should be suppressed as it exhibits poor heat transfer performance. To address the aforementioned issue, this study utilized low thermal conductivity materials as the thermal/electrical interface material for porous-stabilized REBCO tape. The experimental results showed that the cooling and recovery performances were dramatically improved by utilizing an insulating epoxy, which has a thermal conductivity of 0.6 W/mK. Based on the visualization of the boiling behavior, the liquid-solid contact between liquid nitrogen and the REBCO tape was promoted by the insulating epoxy, in which the film boiling was easily broken. [ABSTRACT FROM AUTHOR]

The relevance of anisotropic heatsinks for heat-assisted magnetic recording (HAMR) is investigated. First, 3-D thermal modeling is used to demonstrate that the heatsink performance on a glass substrate is determined by the heatsink in-plane thermal conductivity. The out-of-plane thermal conductivity has almost no impact on the heatsink ability to carry heat away from the hot spot. As a result, an anisotropic heatsink can be a good alternative to some conventional isotropic heatsink materials when its in-plane thermal conductivity is larger than that of the isotropic material. Second, time-domain thermo-reflectance (TDTR) measurements are presented to extract both the in-plane and the out-of-plane thermal conductivities of a (Cu/Ta) multilayer heatsink. The sensitivity to in-plane thermal conductivity is achieved by using small laser beam sizes and by combining measurements at multiple modulation frequencies on both a low and a high thermally conductive substrate. The fitting of all TDTR spectra gives for the (Cu[5.1]/Ta[1.4]) multilayers an effective out-of-plane thermal conductivity of 11.5 W/mK and an in-plane thermal conductivity of 69 W/mK. These thermal properties make such multilayer material an interesting candidate as HAMR heatsink, equivalent to a 70 W/mK isotropic material. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are considered as a next-generation lighting due to their high luminous efficiency, low power consumption, and long lifetime. However, the low heat dissipation of LEDs is an inevitable roadblock. Here, a high heat-conducting Cu nanoparticle (NP) paste was prepared and demonstrated for high-power LEDs. The effects of sintering temperature on the electrical and thermal properties of the Cu NP paste were investigated. The junction temperature change and thermal resistance of LEDs were measured and compared with the traditional die-attach materials. Consequently, the Cu NP paste sintered at 250 °C possesses low electrical resistivity of $5.1~{ \mu \Omega \cdot }$ cm and high thermal conductivity of 142.37 W/(m.K). The packaged LEDs display the low thermal resistance of 6.58 K/W and the low junction temperature change of 3.22 °C, which are significantly lower than those of LEDs packaged by the traditional die-attach materials. These results demonstrate that the promising Cu NP paste provides a feasible and effective strategy for enhancing the heat dissipation of high-power LEDs. [ABSTRACT FROM AUTHOR]

The thermal response test (TRT) is the standard method for characterizing the thermal properties of the ground and those of a borehole heat exchanger (BHE). During the TRT, the inlet and outlet temperatures of the BHE are monitored. However, this test typically considers the ground as a homogeneous, isotropic, and infinite media, and therefore, it only determines the bulk and effective parameters, such as effective thermal conductivity and thermal borehole resistance. Hence, the enhanced TRT protocols are necessary where the depth-dependent temperatures are measured to estimate depth-specific thermal properties. Thus, a novel instrument with a data logger to automatically obtain the temperature measurements along the BHE is introduced. This device is based on a Zynq-7000 all programmable system on a chip. It has a dual-core central processing unit and a field-programmable gate array on one chip, thus providing a versatile architecture that reduces cost and improves efficiency in comparison with other systems of similar characteristics. This paper describes the implemented hardware and software developments that range from user interface application to a free-distribution operating system based on an embedded Linux. The proposed instrument can be easily incorporated throughout a TRT, and the nonspecialized staff can remotely manage or visualize the results through a menu-driven interface. The device is tested in a specific BHE installation and validated with standard Pt100-temperature-sensors. The results are comparable and, therefore, demonstrate the applicability of this novel instrument called Geowire. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs) play a major role in the performance of semiconductor devices by optimizing the thermal contact between device and heatsink. Their influence is further increasing with the usage of novel chip materials such as SiC and GaN. In this methodology study, we compared five of the most established evaluation methods for solid TIMs with each other: transient plane source, LaserFlash, DynTIM, TIMA, and an application-oriented $R_{\mathrm{ th}}$ measurement system. We investigated a wide range of typical TIMs in order to explore the limits of the different measurement systems. The results show that, despite existing norms, the used characterization method has a significant influence on the measured thermal conductivity. We also show that the temperature and pressure dependence has a significant influence on the thermal performance of TIMs and that these data need to be included in device specifications. Additionally, detailed error analysis and discussion about sample selection, error influence, and measurement effort for the presented methods are given. [ABSTRACT FROM AUTHOR]