Hotspot Mitigation Research Articles

Output-Power Enhancement for Hot Spotted Polycrystalline Photovoltaic Solar Cells

Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades PV panel output-power performance. High PV cell temperature due to hot spotting can damage the cell encapsulate and lead to second breakdown, where both cause permanent damage to the PV panel. Therefore, the development of two hot-spot mitigation techniques is proposed using a simple and reliable method. PV hot spots in the examined PV system were inspected using the FLIR i5 thermal imaging camera. Multiple experiments have been tested during various environmental conditions, where the PV module $I - V$ curve was evaluated in each observed test to analyze the output-power performance before and after the activation of the proposed hot-spot mitigation techniques. One PV module affected by the hot spot was tested. The output power during high irradiance levels is increased to approximately 1.26 W after the activation of the first hot-spot mitigation technique. However, the second mitigation technique guarantees an increase in the power up to 3.97 W. An additional test has been examined during the partial shading condition. Both proposed techniques ensure a decrease in the shaded PV cell temperature; thus, there is an increase in PV output power.

Novel hot spot mitigation technique to enhance photovoltaic solar panels output power performance

Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades PV panel output power performance. High PV cell temperature due to hot spotting can damage the cell encapsulate and lead to second breakdown, where both cause permanent damage to the PV panel. Therefore, the design and development of a hot spot mitigation technique is proposed using a simple, low-cost and reliable hot spot activation technique. The hot spots in the examined PV system is detected using FLIR i5 thermal imaging camera.Several experiments have been studied during various environmental conditions, where the PV module P-V curve was evaluated in each observed test to analyze the output power performance before and after the activation of the proposed hot spot mitigation technique. One PV module affected by hot spot was tested. The output power increased by approximate to 3.6 W after the activation of the hot spot mitigation technique. Additional test has been carried out while connecting the hot spot PV module in series with two other PV panels. The results indicate that there is an increase of 3.57 W in the output power after activating the hot spot mitigation technique.

PV output power enhancement using two mitigation techniques for hot spots and partially shaded solar cells

Hot spotting is a reliability problem in photovoltaic (PV) panels where a mismatched cell heats up significantly and degrades PV panel output power performance. High PV cell temperature due to hot spotting can damage the cell encapsulate and lead to second breakdown, where both cause permanent damage to the PV panel. Therefore, the design and development of two hot spot mitigation techniques are proposed using a simple, costless and reliable method. The hot spots in the examined PV system was carried out using FLIER i5 thermal imaging camera.Several experiments have been examined during various environmental conditions, where the PV module I–V curve was evaluated in each observed test to analyze the output power performance before and after the activation of the proposed hot spot mitigation techniques. One PV module affected by hot spot was tested. The output power during high irradiance levels is increased by approximate to 1.25W after the activation of the first hot spot mitigation technique. However, the second mitigation technique guarantee an increase of the power equals to 3.96W. Additional test has been examined during partial shading condition. Both proposed techniques ensure a decrease in the shaded PV cell temperature, thus an increase in the output measured power.

Shielding measures of power transformer to mitigate stray loss and hot spot through coupled 3D FEA

Leakage flux generated in the power transformers cause stray losses in metallic parts of the transformer. Stray losses largely affect the transformer hot spot which leads to thermal failure. It is necessary to mitigate the impact of leakage flux on metallic parts by employing magnetic shunts and eddy current shields. Preeminently clamping structures like flitch plate and end frames experience substantial losses, hence combinations of shielding can be used for better loss reduction. In this study, a case study is performed on a 315 MVA, 420/27 kV single-phase generator power transformer. This work is based on coupled three-dimensional (3D) finite-element analysis (FEA) of the transformer model. A new type of magnetic shunt is explored; also different design combinations of shielding are specified in this work for efficient mitigation of hot spots as well as tank walls.

Selecting Optimal Parallel Microchannel Configuration(s) for Active Hot Spot Mitigation of Multicore Microprocessors in Real Time

Design of effective microcooling systems to address the challenges of ever increasing heat flux from microdevices requires deep examination of real-time problems and has been tackled in depth. The most common (and apparently misleading) assumption while designing microcooling systems is that the heat flux generated by the device is uniform, but the reality is far from this. Detailed simulations have been performed by considering nonuniform heat load employing the configurations U, I, and Z for parallel microchannel systems with water and nanofluids as the coolants. An Intel® Core™ i7-4770 3.40 GHz quad core processor has been mimicked using heat load data retrieved from a real microprocessor with nonuniform core activity. This study clearly demonstrates that there is a nonuniform thermal load induced temperature maldistribution along with the already existent flow maldistribution induced temperature maldistribution. The suitable configuration(s) for maximum possible overall heat removal for a hot zone while maximizing the uniformity of cooling have been tabulated. An Eulerian–Lagrangian model of the nanofluids shows that such “smart” coolants not only reduce the hot spot core temperature but also the hot spot core region and thermal slip mechanisms of Brownian diffusion and thermophoresis are at the crux of this. The present work conclusively shows that high flow maldistribution leads to high thermal maldistribution, as the common prevalent notion is no longer valid and existing maldistribution can be effectively utilized to tackle specific hot spot location, making the present study important to the field.

Control of Nanoplane Orientation in voBN for High Thermal Anisotropy in a Dielectric Thin Film: A New Solution for Thermal Hotspot Mitigation in Electronics.

High anisotropic thermal materials, which allow heat to dissipate in a preferential direction, are of interest as a prospective material for electronics as an effective thermal management solution for hot spots. However, due to their preferential heat propagation in the in-plane direction, the heat spreads laterally instead of vertically. This limitation makes these materials ineffective as the density of hot spots increases. Here, we produce a new dielectric thin film material at room temperature, named vertically ordered nanocrystalline h-BN (voBN). It is produced such that its preferential thermally conductive direction is aligned in the vertical axis, which facilitates direct thermal extraction, thereby addressing the increasing challenge of thermal crosstalk. The uniqueness of voBN comes from its h-BN nanocrystals where all their basal planes are aligned in the direction normal to the substrate plane. Using the 3ω method, we show that voBN exhibits high anisotropic thermal conductivity (TC) with a 16-fold difference between through-film TC and in-plane TC (respectively 4.26 and 0.26 W·m-1·K-1). Molecular dynamics simulations also concurred with the experimental data, showing that the origin of this anisotropic behavior is due to the nature of voBN's plane ordering. While the consistent vertical ordering provides an uninterrupted and preferred propagation path for phonons in the through-film direction, discontinuity in the lateral direction leads to a reduced in-plane TC. In addition, we also use COMSOL to simulate how the dielectric and thermal properties of voBN enable an increase in hot spot density up to 295% compared with SiO2, without any temperature increase.

Thermal Management of Densely-packed EV Battery with Forced Air Cooling Strategies

The modern development of electric vehicle requires higher power density to be packed into a battery pack. It is always expected that the battery can be arranged as much as possible, however, which leads to the serious thermal management issue due to the heat generation inside the battery packs. As extreme temperature affects performance, reliability, safety and lifespan of batteries, thermal management of battery system is critical to the success of all electric vehicles. The objective of this study is to explore the air cooling capability on the temperature uniformity and hotspots mitigation of a compact battery pack subject to various air flow paths, airflow rates. The numerical results show that the improvement of effective heat transfer areas between air-coolant and battery surfaces is able to obviously lower the maximum temperature and improve the maximum temperature difference in the densely-packed battery box.

IPM Use With the Deployment of a Non-High Dose Bt Pyramid and Mitigation of Resistance for Western Corn Rootworm (Diabrotica virgifera virgifera).

Recent detection of western corn rootworm resistance to Bt (Bacillus thuringiensis) corn prompted recommendations for the use of integrated pest management (IPM) with planting refuges to prolong the durability of Bt technologies. We conducted a simulation experiment exploring the effectiveness of various IPM tools at extending durability of pyramided Bt traits. Results indicate that some IPM practices have greater merits than others. Crop rotation was the most effective strategy, followed by increasing the non-Bt refuge size from 5 to 20%. Soil-applied insecticide use for Bt corn did not increase the durability compared with planting Bt with refuges alone, and both projected lower durabilities. When IPM participation with randomly selected management tools was increased at the time of Bt commercialization, durability of pyramided traits increased as well. When non-corn rootworm expressing corn was incorporated as an IPM option, the durability further increased. For corn rootworm, a local resistance phenomenon appeared immediately surrounding the resistant field (hotspot) and spread throughout the local neighborhood in six generations in absence of mitigation. Hotspot mitigation with random selection of strategies was ineffective at slowing resistance, unless crop rotation occurred immediately; regional mitigation was superior to random mitigation in the hotspot and reduced observed resistance allele frequencies in the neighborhood. As resistance alleles of mobile pests can escape hotspots, the scope of mitigation should extend beyond resistant sites. In the case of widespread resistance, regional mitigation was less effective at prolonging the life of the pyramid than IPM with Bt deployment at the time of commercialization.

Use of proactive and reactive hotspot detection technique to reduce the number of virtual machine migration and energy consumption in cloud data center

The increasing demand of cloud computing motivates the researchers to make cloud environment more efficient for its users and more profitable for the providers. Though virtualization technology helps to increase the resource utilization, still the operational cost of cloud gradually increases mainly due to the consumption of large amount of electrical energy. So to reduce the energy consumption virtual machines (VM) are dynamically consolidated to lesser number of physical machines (PMs) by live VM migration technique. But this may cause SLA violation and the provider is penalized. So to maintain an energy-performance trade-off, the number of VM migration should be minimized. VM migration primarily takes place in two cases: for hotspot mitigation and to switch off the underutilized nodes by migrating all its VMs. If a host is found to be overloaded then instead of immediately migrating some of its VMs we can check whether the migration is really required or not. For this we have proposed a load prediction algorithm to decide whether the migration will be performed or not. After the decision has been taken the algorithm finds a suitable destination host where the VM will be shifted. For this we have proposed a novel approach to decide whether a particular host is suitable as destination depending on its probable future load. We have simulated our algorithms in CloudSim using real world workload traces and compared them with the existing benchmark algorithms. Results show that the proposed methods significantly reduce the number of VM migration and subsequent energy consumption while maintaining the SLA.

Citizen science and smartphones take roadkill monitoring to the next level

Road networks, even in industrialized countries, become denser year after year and traffic volumes continue to increase at a steady pace. It is imperative that we monitor the impact of this trend on wildlife, but monitoring roads for flattened fauna is a time consuming effort and roadkill monitoring projects conducted up till now have been relatively small scale both in terms of time and space. This hampers the progress of road ecology analyses at the population level and at larger landscape extents. We demonstrate that citizen science projects in combination with smartphones and other new technologies allow analysis at this level and extent, and simultaneously offer more complete data for safer transportation and mitigation of roadkill hotspots. Monitoring roadkill with citizen scientists poses certain challenges regarding data quality and people management, but we show that these challenges can be addressed, which allows researchers to benefit from the many other advantages and possible applications of monitoring roadkill with citizen scientists, including raising public awareness on the matter.

Virtual Machine Migration Triggering using Application Workload Prediction

Dynamic provisioning of physical resources to Virtual Machines (VMs) in virtualized environments can be achieved by (i) vertical scaling-adding/removing attached resources from existing virtual machine and (ii) horizontal scaling-adding a new virtual machine with additional resources. The live migration of virtual machines across different Physical Machines (PMs) is a vertical scaling technique which facilitates resource hot-spot mitigation, server consolidation, load balancing and system level maintenance. It takes significant amount of resources to iteratively copy memory pages. Hence during the migration there may be too much overload which can affect the performance of applications running on the VMs on the physical server. It is better to predict the future workload of applications running on physical server for early detection of overloads and trigger the migration at an appropriate point where sufficient number of resources are available for all the applications so that there will not be performance degradation. This paper presents an intelligent decision maker to trigger the migration by predicting the future workload and combining it with predicted performance parameters of migration process. Experimental results shows that migration is triggered at an appropriate point such that there are sufficient amount of resources available (15–20% more resources than high valued threshold method) and no application performance degradation exists as compared to properly chosen threshold method for triggering the migration. Prediction with support vector regression has got decent accuracy with MSE of 0.026. Also this system helps to improve resource utilization as compared to safer threshold value for triggering migration by removing unnecessary migrations.

Control Principles and On-Chip Circuits for Active Cooling Using Integrated Superlattice-Based Thin-Film Thermoelectric Devices

Superlattice thin-film thermoelectric coolers (TECs) are emerging as a promising technology for hot spot mitigation in microprocessors. This paper studies the prospect of on-demand cooling with advanced TECs integrated at the back of the heat spreader inside a package (integrated TEC). Using thermal compact models of the chip and package with integrated TECs, the control principles for TEC-assisted transient cooling are presented. The control principles are implemented in a 130-nm CMOS process and cosimulated with the thermal system to show their feasibility and energy overheads. The simulation results show potential for extending the time for which a chip and package can sustain a high power load.

Characterizing Moose–Vehicle Collision Hotspots in Northern British Columbia

AbstractTo have a better understanding of the ecological factors that may contribute to moose Alces alces and vehicle collisions in northern British Columbia, we analyzed Wildlife Accident Reporting System data that were collected between 2000 and 2005 by highway maintenance contractors. We delineated 29 moose-vehicle collision hotspots and 15 control sites at which we assessed environmental and road infrastructure attributes through field surveys and remotely sensed data. A logistic regression model including both coarse- and fine-scale environmental factors suggested that hotspots were more likely to be characterized by the number of roadside mineral licks and bisection of the highway corridor through black spruce forest–sphagnum bog habitat and swamps. The absence of rivers within 1 km and less lake area within 500 m of the highway also better characterized hotspots than controls. At the fine scale, deciduous forest cover along the highway edge and the proportion of browse to nonbrowse vegetation between the road shoulder and forest edge were also related to collision sites. Based on these data, the mitigation of collision hotspots should include decommissioning roadside mineral licks where they occur and cutting roadside brush to improve driver visibility and reduce browse resprouting and attractiveness. Where new road construction or road realignments are being contemplated, we recommend considering routes with more lake area, more rivers, fewer swamps, and fewer black spruce forest–sphagnum bog habitats to help reduce collisions. We discuss the utility of installing novel warning signage in areas where collisions are recurrent.

Mortar

Data center servers are typically overprovisioned, leaving spare memory and CPU capacity idle to handle unpredictable workload bursts by the virtual machines running on them. While this allows for fast hotspot mitigation, it is also wasteful. Unfortunately, making use of spare capacity without impacting active applications is particularly difficult for memory since it typically must be allocated in coarse chunks over long timescales. In this work we propose re- purposing the poorly utilized memory in a data center to store a volatile data store that is managed by the hypervisor. We present two uses for our Mortar framework: as a cache for prefetching disk blocks, and as an application-level distributed cache that follows the memcached protocol. Both prototypes use the framework to ask the hypervisor to store useful, but recoverable data within its free memory pool. This allows the hypervisor to control eviction policies and prioritize access to the cache. We demonstrate the benefits of our prototypes using realistic web applications and disk benchmarks, as well as memory traces gathered from live servers in our university's IT department. By expanding and contracting the data store size based on the free memory available, Mortar improves average response time of a web application by up to 35% compared to a fixed size memcached deployment, and improves overall video streaming performance by 45% through prefetching.

Hot-spot mitigation in PV arrays with distributed MPPT (DMPPT)

A lack of maintenance in PV systems can cause hot-spots due to localized or irregular dirt, causing permanent losses and reducing the reliability of the system. By-pass diodes were introduced to lessen this problem although they do not eliminate it completely, as recent literature has shown. This paper analyzes the use of distributed MPPT (DMPPT) in relation to mitigation of hot-spot problems. A full analysis is performed, including simulations of I–V curves under different shading situations and an in-field analysis. The results show that DMPPT is less prone to hot-spots than central MPPT in a different range of shadows depending on the module type.

Hotspot Mitigating With Obliquely Finned Microchannel Heat Sink—An Experimental Study

Sectional oblique fins are employed, in contrast to continuous fins, in order to modulate the flow in a microchannel heat sink. The breakage of continuous fin into oblique sections leads to reinitialization of boundary layers and generation of secondary flows that significantly enhance the cooling performance of the heat sink. In addition, an oblique finned microchannel heat sink has the flexibility to tailor local heat transfer performance by varying its oblique fin pitch. Clusters of oblique fins at higher density can be created in order to promote a greater degree of boundary layer redevelopment and secondary flow generation to provide more effective cooling at the high heat-flux region. Thus, the variation of oblique fin pitch can be exploited for hotspot mitigation. Experimental studies of a silicon chip with two hotspot scenarios show that the temperature hike and the temperature difference for the enhanced microchannel heat sink with variable pitch are reduced by as much as 17.1 °C and 15.4 °C, respectively. As a result, temperature distribution across the silicon chip is more uniform. In addition, the associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective hotspot mitigating strategy for the single-phase microchannel heat sink.

A comparative study of flow boiling heat transfer and pressure drop characteristics in microgap and microchannel heat sink and an evaluation of microgap heat sink for hotspot mitigation

Two phase microgap heat sink has a large potential to minimize the drawbacks associated with two phase microchannel heat sink, especially flow instabilities, flow reversal and lateral variation of flow and wall temperature between channels. This new concept of the two-phase microgap heat sink is very promising due to its high heat transfer rate and ease of fabrication. However, comparison of the performance of microgap heat sink (heat transfer, pressure drop and instability characteristics) with some conventional heat sink has not been investigated extensively. In this study, experiments have been conducted to investigate the heat transfer and pressure drop characteristics of deionized water (DI) in microgap heat sink and compare these experimental results with similar data obtained for microchannel heat sink. These studies are carried out with the inlet DI water temperatures 86°C at different mass fluxes ranging from 400 to 1000kg/m2s, for effective heat flux 0–85W/cm2. High speed flow visualizations are conducted simultaneously along with experiments to illustrate the bubble characteristics in the microchannel and microgap heat sink. Experimental result shows that microgap heat sink performs better at high heat flux and low mass flux due to confined slug and annular boiling dominance and consequent delay of dryout phase. So, this microgap technology is promising and an effective method to dissipate very high heat fluxes in compact space with a smaller rate of coolant flow. Moreover, pressure drop is higher in microchannel than microgap heat sink at all the heat fluxes. In addition, encouraging results have been obtained using microgap as it can potentially mitigate local hotspot, reduce flow instabilities, flow reversal and maintain uniform wall temperatures over the heated surface.

Characterizing Vulnerability of Network Interfaces in Embedded Chip Multiprocessors

In Networks-on-Chip (NoC), with ever-increasing design complexity and technology scaling, soft errors have become a key design challenge. In this work, we extend the concept of architectural vulnerability factor (AVF) from the microprocessor domain and propose a network vulnerability factor (NVF) to characterize the susceptibility of Network Interfaces (NIs) to soft errors. For the first time, a detailed characterization of vulnerability is performed on a state-of-the-art AXI-based NI architecture using full system simulation. Our studies reveal that different NI buffers behave quite differently in the presence of transient faults and each buffer can have different inherent tolerance to faults. Our analysis also considers the impact of thermal hotspot mitigation techniques on the NVF estimation.

Centrality-based power control for hot-spot mitigation in multi-hop wireless networks

When shortest path routing is employed in large scale multi-hop wireless networks such as sensor networks, nodes located near the center of the network have to perform disproportionate amount of relaying for others. Nodes in such traffic hot-spots deplete their batteries faster than others due to their high relay load. These traffic hot-spots also adversely affect the network capacity due to increased congestion in the regions. To solve the problem, various divergent routing schemes are used which route the data on center-avoiding divergent routing paths. Though they achieve better load balancing, overall relaying is increased significantly due to their longer routing paths. In this paper, we propose power control as a way for balancing relay load and mitigating hot-spots in wireless sensor networks. Using a heuristic based on the concept of centrality, we show that if we increase the power levels of only the nodes which are expected to relay more packets, significant relay load balancing can be achieved even with shortest path routing. Different from divergent routing schemes, such load balancing strategy is applicable to any arbitrary topology and traffic pattern. With extensive simulations, we show that centrality based power control can drastically increase the network lifetime of sensor networks. We compare its performance with other divergent routing schemes and multiple battery level assignment strategy. Also, it is shown that centrality based power control results into better throughput capacity in many different topologies.

Fighting fire with fire

Local thermal hot-spots in microprocessors lead to worst-case provisioning of global cooling resources, especially in large-scale systems where cooling power can be 50~100% of IT power. Further, the efficiency of cooling solutions degrade non-linearly with supply temperature. Recent advances in active cooling techniques have shown on-chip thermoelectric coolers (TECs) to be very efficient at selectively eliminating small hot-spots. Applying current to a superlattice TEC-film that is deposited between silicon and the heat spreader results in a Peltier effect, which spreads the heat and lowers the temperature of the hot-spot significantly and improves chip reliability . In this paper, we propose that hot-spot mitigation using thermoelectric coolers can be used as a power management mechanism to allow global coolers to be provisioned for a better worst case temperature leading to substantial savings in cooling power. In order to quantify the potential power savings from using TECs in data center servers, we present a detailed power model that integrates on-chip dynamic and leakage power sour-ces, heat diffusion through the entire chip, TEC and global cooler efficiencies, and all their mutual interactions. Our multi-scale analysis shows that, for a typical data center, TECs allow global coolers to operate at higher temperatures without degrading chip lifetime, and thus save ~27% cooling power on average while providing the same processor reliability as a data center running at 288K.