WaFFLe

Managing thermal imbalance in contemporary chip multi-processors (CMPs) is crucial in assuring functional correctness of modern mobile as well as server systems. Localized regions with high activity, e.g., register files, ALUs, FPUs, and so on, experience higher temperatures than the average across the chip and are commonly referred to as hotspots. Hotspots affect functional correctness of the underlying circuitry and a noticeable increase in leakage power, which in turn generates heat in a self-reinforced cycle. Techniques that reduce the severity of or completely eliminate hotspots can maintain functional correctness along with improving performance of CMPs. Conventional dynamic thermal management targets the cores to reduce hotspots but often ignores caches, which are known for their high leakage power consumption. This article presents WaFFLe , an approach that targets the leakage power of the last-level cache (LLC) and hotspots occurring at the cores. WaFFLe turns off LLC-ways to reduce leakage power and to generate on-chip thermal buffers. In addition, fine-grained DVFS is applied during long LLC miss induced stalls to reduce core temperature. Our results show that WaFFLe reduces peak and average temperature of a 16-core based homogeneous tiled CMP with up to 8.4 ֯ C and 6.2 ֯ C, respectively, with an average performance degradation of only 2.5 %. We also show that WaFFLe outperforms a state-of-the-art cache-based technique and a greedy DVFS policy.

Development of Ammonia Fueled Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can generate electricity through an electrochemical conversion of the chemical energy of fuels including hydrogen, hydrocarbons, and biogas because of high operation temperatures. Ammonia has recently been considered as a promising hydrogen carrier that is relatively convenient to store and transport and can be decomposed into hydrogen and nitrogen with no carbon emission via catalytic cracking. Thus, much effort has been made to utilize ammonia as a clean fuel to SOFCs for power generation at high efficiency. This review is aiming at delivering the current progress of developing high temperature ceramic fuel cells fed with ammonia, particularly more focused on the achievements of a direct ammonia fueled SOFC (DA-SOFC) to shed light on the challenges of degrading the performance and durability. The problems are primarily attributed to a lack of rational catalysts, thermal imbalance, and the evolution of nitrides on the components including the Ni based anode, Ni mesh as current collector, and stainless steels of metallic interconnect that are exposed to the ammonia fuel environment incurring microstructural deformations and electrical and electrochemical deteriorations. Lastly, strategic pathways to overcome the inadequate performance and the instability are suggested to accomplish a commercialization of DA-SOFCs.

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.

Characterization of the Effects of Borehole Layouts in Geo-exchange

In a ground-source heat pump (GSHP) system, when the heating and cooling loads are not balanced, the ground temperature may migrate up or down after a few years of operation. This change in ground temperature can lower system efficiency because of the ineffective heat transfer temperatures. The present work contributes to fundamental understanding of thermal imbalance in borehole design. Long term ground temperatures were simulated using finite element methods to imitate the performance of GSHP systems. Borehole field configurations are explored and different aspect ratios of borehole layouts were compared. In addition, an alternative borehole configuration was studied, which involves alternating the length of individual boreholes within a single system. The results of the studies expressed potential in alleviating the effects of thermal imbalance by changing borehole field layout and potential in reducing borehole separation distance by altering individual borehole lengths.