Температурный режим и механические напряжения в корпусированных фотоэлектрических преобразователях концентрированного солнечного излучения

In photovoltaic converters of concentrated sunlight, the thermal flow is directed from the photoactive region (p-n junction) to a heat-spreading basement through the substrate. The heat sink transfers the excess thermal to the environment by convection or cooled by a liquid carrier. Reducing the thickness of the substrate makes it possible to reduce the thermal resistance of the crystal and lower the operating temperature of the photoactive region. However, in this case, the mechanical stresses in it increase. This work discusses the balance between the mechanical strength of the sample and the decrease in its operating temperature.

Impacts of increasing the airflow rate on load-haul-dump heat spread at an underground mine

In the mining process, mining companies use various mining equipment to extract valuable materials. One of them is a load-haul-dump (LHD) machine. Although this equipment is very helpful in the production process, it also has drawbacks. This equipment emits heat that can affect air temperature in the mine tunnel and cause a decrease in the comfort of mineworkers, which then impacts the mine productivity. One of the methods that can be carried out to overcome this problem is to increase the amount of airflow by changing the ventilation network. Therefore, this study aims to determine the impacts of increasing airflow on the heat spread of the operated LHD machines. The results of this study are to provide a method for reduced temperature visually and can be used as a recommendation for temperature reduction in the future. To examine the heat spreading, the researchers applied a tunnel model made using CFD software that is ANSYS Fluent and use VentSim software to simulate the network changes. The results indicated that the increase of the airflow rate could reduce the temperature on the work front when the LHD machines are operating and can affect the heat spread.

Lightweight, Cost-Effective Power Modules Using Polymer Baseplates With Integrated Microconvective Cooling

The advent of wide bandgap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), has enabled power electronics with increasing current densities and switching frequencies. A byproduct of these improved electrical characteristics is an increase in thermal power density. Indeed, the full capability of WBG semiconductors may be underutilized if the thermal management solution cannot keep pace with the device heat generation density. Further, as many power electronics devices are integrated into a power module form factor containing a metal baseplate to allow heat spreading from high heat fluxes generated at semiconductor dies, system integrators are often sensitive to cost and weight considerations in building up systems with traditional power module designs. In this paper, a polymer baseplate with integrated microconvective cooling (PBIMC) is designed and built as a low-weight, cost-effective alternative for metal baseplates on power module devices. Microconvective cooling, featuring optimized single-phase impingement cooling and effluent fluid flow control, provides high power density heat removal from localized heat flux areas in power module packages to obviate the need for a metal heat spreader. Thermal performance of the PBIMC is tested on a thermal test vehicle representative of an IGBT power module to power densities up to 200W/cm2 and compared to an off the shelf minichannel cold plate. The PBIMC achieved equivalent per IGBT case-to-fluid areal thermal resistances of 0.15 K-cm2/W, a 69% decrease compared to the baseline cold plate. Additionally, thermal crosstalk was shown to be reduced by up to 89% when moving from the cold plate to the PBIMC, demonstrating potential advantages in utilizing thermal management techniques that do not feature heat spreading. The prototype-level polymer baseplates showed a > 80% decrease in weight compared to a traditional power module metal baseplate. The study concludes that the PBIMC shows promise as a solution for high current density power electronics in weight sensitive applications, while providing opportunities for cost savings.

Observation of giant and tunable thermal diffusivity of a Dirac fluid at room temperature

Conducting materials typically exhibit either diffusive or ballistic charge transport. When electron–electron interactions dominate, a hydrodynamic regime with viscous charge flow emerges1–13. More stringent conditions eventually yield a quantum-critical Dirac-fluid regime, where electronic heat can flow more efficiently than charge14–22. However, observing and controlling the flow of electronic heat in the hydrodynamic regime at room temperature has so far remained elusive. Here we observe heat transport in graphene in the diffusive and hydrodynamic regimes, and report a controllable transition to the Dirac-fluid regime at room temperature, using carrier temperature and carrier density as control knobs. We introduce the technique of spatiotemporal thermoelectric microscopy with femtosecond temporal and nanometre spatial resolution, which allows for tracking electronic heat spreading. In the diffusive regime, we find a thermal diffusivity of roughly 2,000 cm2 s−1, consistent with charge transport. Moreover, within the hydrodynamic time window before momentum relaxation, we observe heat spreading corresponding to a giant diffusivity up to 70,000 cm2 s−1, indicative of a Dirac fluid. Our results offer the possibility of further exploration of these interesting physical phenomena and their potential applications in nanoscale thermal management.

Liquid-Cooled Heat Sink Optimization for Thermal Imbalance Mitigation in Wide-Bandgap Power Modules

Power semiconductor die placement on substrates used in high-power modules is generally optimized to minimize electrical parasitic (e.g., stray inductance, common-mode capacitance), taking into account the minimum spacing between semiconductor dies for thermal decoupling. The layout assumes sufficient heat spreading and transfer from dies to the cooling structure. Insulated metal substrate-based power module designs may lead to asymmetrical thermal resistance across the dies, which may cause significant temperature differences among the devices. Such unintentional thermal asymmetries can lead to over sizing the cooling system design or under-using the semiconductor power processing capability. This article proposes a thermal imbalance mitigation method that uses evolutionary optimized liquid-cooled heat sinks to improve the thermal loading among devices.

Experimental Investigation of the Effect of Heat Spreading on Boiling of a Dielectric Liquid for Immersion Cooling of Electronics

This paper investigated the effect of heat spreading on the boiling of the Novec 649TM for two-phase immersion cooling of electronics. Reference pool boiling tests were performed by attaching a 25.4 by 25.4 mm square plate square copper plate to a same-sized heater, thus minimizing lateral heat spreading. Experimental measurements showed that the critical heat flux (CHF) happened at a heat flux of 17.4 ±0.8 W/cm2. Then, lateral heat spreading through the heat spreader was studied by attaching larger (47 mm by 47mm) spreaders with four different thicknesses to the copper plate. With an increase in the integrated heat spreader (IHS) thickness from 1 mm to 6 mm, the CHF increased by more than 60% at the saturation condition. One plate was a 1 mm-thick IHS removed from a commercial microprocessor. In this case, the CHF happens at 8.6 W/cm2 (50% lower compared to the reference case) in the saturation condition. At CHF, the boiling can be observed on the whole surface, with columns and slugs regime at the center and the fully developed nucleate boiling regime at the edges. This non-uniform boiling was more pronounced in sub-cooled conditions, in which the CHF occurred at the center while there were regions at the edges that had no boiling. Finally, the performance of a micro porous-coated IHS (with 3.15 mm thickness) was compared to the 6mm thick IHS. The thermal resistance was almost equal for powers above 200 W. This indicates that lateral heat spreading is a critical parameter for the thermal design of immersion cooling along with micro-porous coating.