Local Hot Spots Research Articles

Exact solution for conjugate heat transfer within a solar receiver tube: A comprehensive analysis

This study presents exact solutions for the phenomenon of conjugate heat transfer occurring within a solar receiver tube. The investigation focuses on three distinct configurations: (a) tubes with negligible wall thickness, (b) thin-walled tubes, and (c) thick-walled tubes. The primary objective is to offer precise mathematical representations for the distribution of temperature, as well as numerical values of local and average Nusselt numbers. Furthermore, the study delves into the examination of limiting cases to enhance the understanding of the problem at hand and validating the outcomes. The derived solutions are also utilized to conduct a comprehensive analysis of the specific practical scenario involving the flow of molten salt in both Alloy 625 and stainless steel solar receiver tubes. Inspection of the configurations presented in this study demonstrates that the circumferential conduction heat transfer in the tube wall helps to distribute the heat more evenly along the circumference and mitigate the occurrence of localized hot spots.

Assessment of CFD Predictions Using Experiments from a Heated Gas-Cooled Pebble Bed Facility

This paper presents computational fluid dynamics (CFD) simulations of the coolant gas flow in a pebble bed reactor core to assess the suitability of CFD models to accurately predict the temperature distribution and possible occurrence of local hot spots that may affect pebble integrity. This study assessed CFD predictions against temperature distribution measurements from the SANA test facility at the Research Center Jülich in Germany. A realistic pebble bed structure of randomly packed 1584 pebbles was produced using the discrete element method to model the pebble packing in detail. A total of 96 experimental temperature pebble points were used for the assessments, covering a broad range of heating powers (10 kW ≤ Poperation ≤ 35 kW). A good agreement between the CFD predictions and the SANA measurements was obtained for two coolants, nitrogen and helium, along the height of the pebble bed. It is anticipated that a better understanding of the suitability of the existing CFD models gained through this study will aid in the identification of gaps and areas of improvement for CFD to support the design and safety evaluations for pebble bed small modular reactors.

On-grid optimal MPPT for fine-tuned inverter based PV system using golf optimizer considering partial shading effect

Improving photovoltaic systems to better withstand variations in temperature and irradiance, lessen steady-state ripples, maintain high efficiency, require less tracking time, and have minimal complexity is becoming increasingly important. The PV array's overall power output is negatively impacted by partial shading because the shaded cells produce less power and consume less power overall, which lowers efficiency and creates localized hotspots. Although bypass diodes may be used to counteract these impacts by rerouting current around cells that are shaded, they can result in several peaks, which complicates maximum power point tracking (MPPT). To manage several peaks and optimize power output, metaheuristic algorithms are compulsory. A recently developed game-based optimization methodology known as Golf Optimization Approach (GOA) is used in this study to find a way to MPPT in a grid-connected photovoltaic (PV) system under partial shading conditions (PSCs). Additionally, the same suggested approach is applied to get optimal parameters for the inverter with the goal of optimizing its voltage and current regulators. It aims to evaluate a plan to lower the output voltage and current's total harmonic distortion and DC voltage error. The proposed technique is contrasted to other tracking approaches such as the traditional Perturb & Observe (P&O), Gray Wolf Optimization (GWO), and Sea-gull Optimization Approach (SOA). Simulation is performed in MATLAB R2022b/SIMULINK environment. The obtained outcomes demonstrate the ability of the suggested technique to enhance the utility grid's power quality and improve the tracking system under various partial shading effects and temperature alterations. The proposed technique achieves a tracking efficiency of 99.8 %, surpassing the effectiveness of both of the previous methods which are at 97.2 % and 96.7 %.

Superior molten FLiBe salt barrier properties of a mesophase-pitch-based carbon/carbon composite prepared via hot isostatic pressing

Carbon/carbon (C/C) composites are promising structural materials for molten salt reactors (MSRs) because of their exceptional high-temperature performance, resistance to fluoride salt corrosion, and low-neutron-absorption cross-section. However, fluoride salts can infiltrate the pores of C/C composites, potentially causing local hotspots and accelerating material degradation. In this study, a novel C/C composite was fabricated from mesophase-pitch-based carbon fibers and a pitch-based carbon matrix via hot isostatic pressing (HIP). To evaluate its performance under MSR conditions, the composite was exposed to molten FLiBe salt at 700 °C and 2–9 atm for a duration of 20 h. Weight gain, morphological characteristics, and crystallinity were characterized after the salt infiltration test. Compared with C/C composites fabricated via conventional chemical vapor infiltration (CVI), the HIP-C/C composite exhibited much better molten salt barrier properties owing to its compact structure and small pore diameter. The weight gain of the HIP-C/C composite was only 0.17 wt.% under 5 atm, significantly lower than the critical index proposed for carbon materials used in MSR. Morphological characterization revealed that FLiBe salt particles were rarely trapped in the small pores of the HIP-C/C composite. While the crystallinity of the salt-impregnated CVI-C/C composite increased, the HIP-C/C composite exhibited a slightly decreased degree of graphitization after salt infiltration. These findings provide insights into the design of high-performance C/C composites for applications in MSR systems.

Numerical Calculation and Direct Measurement of Local Hot Spot Temperatures in Transformer Clamping Plates

A verified multiphysics model is developed to simulate local hot spot temperatures in clamping structures. Stray field losses in clamping plates are obtained with the use of nonlinear impedance boundary condition through finite element method (FEM) while hot spot temperatures are simulated with the use of computational fluid dynamics (CFD). This multiphysics coupling is validated through direct measurements of local hot spot temperatures that were carried out with fiber optic temperature probes in real transformer. The local hot spot temperatures obtained with the simulations were in good agreement with the measured values, thus verifying overall approach and indirectly the calculation of local stray field losses.

A Simple Thermal Model for Junction and Hot Spot Temperature Estimation of 650 V GaN HEMT during Short Circuit

Temperature is a critical parameter for the GaN HEMT as it sharply impacts the electrical characteristics of the device more than for SiC or Si MOSFETs. Either when designing a power converter or testing a device for reliability and robustness characterizations, it is essential to estimate the junction temperature of the device. For this aim, manufacturers provide compact models to simulate the device in SPICE-based simulators. These models provide the junction temperature, which is considered uniform along the channel. We demonstrate through two-dimensional numerical simulations that this approach is not suitable when the device undergoes high electrothermal stress, such as during short circuit (SC), when the temperature distribution along the channel is strongly not uniform. Based on numerical simulations and experimental measurements on a 650 V/4 A GaN HEMT, we derived a thermal network suitable for SPICE simulations to correctly compute the junction temperature and the SC current, even if not providing information about the possible failure of the device due to the formation of a local hot spot. For this reason, we used a second thermal network to estimate the maximum temperature reached inside the device, whose results are in good agreement with the experimental observed failures.

Impact-induced energy release characteristics of Ti-Zr-Hf-Ta high-entropy alloys by using a temperature-pressure synchronous measurement method

Energetic structural materials (ESMs) are a new type of materials with structural strength and reactivity, and their impact-induced energy release characteristics are greatly influenced by the fragmentation behavior. In this study, the dynamic fragmentation behavior and energy release characteristics of Ti-Zr-Hf-Ta high-entropy alloys (HEAs) with different precipitate content were investigated based on split Hopkinson pressure bars (SHPB) tests. To quantitatively evaluate the reactivity of ESMs, a temperature-pressure synchronous measurement method combined with a modified calculation model for quasi-sealed chamber was proposed. The results showed that the precipitates were distributed at the grain boundaries. As the precipitate content increased, the quasi-static yield strengths increased from 1004 to 1132 MPa, the dynamic yield strengths increased from 1672 to 1874 MPa, while the fracture strains decreased from 0.47 to 0.29, and correspondingly, the released energy increased from 14±2–511±154 J/g. The results demonstrated that the impact-induced energy release characteristics of the materials are closely related to the fracture strain. It can be confirmed that the alloys with lower plasticity are more likely to fracture under impact conditions, and the combustion reaction will be more violent, which is well consistent with the measurement of the energy-release amounts. High-speed infrared temperature measurement and microstructural photography also provided the underlying mechanism: the fragment size of low plasticity materials is smaller and the local hot spots are more dispersed, both of which are conducive to the combustion reaction. By using this method, the relationship among mechanical properties, fragmentation behavior, and energy release characteristics can be established, and the results will provide new insights into the development of ESMs with superior energy release under impact loading and applicable mechanical properties for potential applications.

Experimental and numerical analysis of a liquid-air hybrid system for advanced battery thermal management

This study introduces an innovative hybrid Battery Thermal Management System (BTMS) that combines air and liquid cooling mechanisms for optimal thermal control in small-scale EV applications. Recognizing the limitations of the existing single-method cooling systems, we developed a novel Hybrid Battery Thermal Management System that combines air and liquid cooling to provide superior temperature management. Additionally, we performed a detailed experimental evaluation to verify the accuracy of our heat generation model for lithium-ion batteries. This included the construction and testing of the proposed hybrid cooling system in a controlled environment using a climate chamber that simulated various ambient temperatures. We assessed the system performance under different operational stresses, specifically at 1C and 2C discharge rates. The tests encompassed a range of temperatures, starting at a standard room temperature (20 °C) and increasing through three levels of ambient temperature: 30, 35, and 40 °C. Initial tests under natural convection conditions showed a non-uniform temperature distribution and temperatures near the upper safety limits, with a maximum of 51 °C. While the addition of an air-cooling system provided some improvement, it still resulted in localized hotspots. However, the hybrid battery thermal management system effectively addressed these challenges, achieving marked improvements in cooling efficiency and temperature uniformity, yielding a 21.04 % improvement in cooling by reducing the maximum temperature at 2C from 51.2 °C (no cooling) to 40.9 °C while also improving the uniformity of the temperature distribution among the packs. Further tests at elevated ambient temperatures confirmed the robustness and adaptability of this system. These findings highlight the scalability of the system and suggest its potential applicability to larger battery systems, opening avenues for future research and practical implementation.

A systematic literature review investigating the association between biodiversity and beaver lodges

Abstract The positive relationship between biodiversity and beaver‐modified habitats such as ponds, dams, and canals has been demonstrated; however, the association between biodiversity and beaver lodges is rarely investigated. Due to increasing habitat fragmentation, there is a growing need to identify local biodiversity hotspots. This systematic review assessed current scientific knowledge concerning the association between beaver lodges and biodiversity. Specifically, the study aimed to 1) investigate the evidence for beaver lodges being local biodiversity hotspots; 2) identify areas of future research centred around the relationship between biodiversity and beaver lodges; and 3) provide recommendations on how to monitor the relationship between biodiversity and beaver lodges within the UK. Through a stepwise process of database searching and literature sorting, a final dataset of 35 articles emerged, with each article including at least one species, besides beavers, interacting with beaver lodges. Analysis of the final dataset of articles showed beaver lodges offer multiple uses and fitness benefits for several species in highly seasonal environments, with daily and seasonal visitor variation influenced by intraspecific and interspecific interactions. Beaver lodges were shown to have higher species richness and diversity compared to microhabitats in the surrounding areas, supporting the concept of beaver lodges being local biodiversity hotspots. We recommend that future studies use videographic methodology to monitor beaver lodges and other treatment groups in the surrounding area. Using the described methodology, beaver management plans should monitor beaver lodges across the northern hemisphere, helping to further understand these important local biodiversity hotspots.

A Preliminary Case Study on the Compounding Effects of Local Emissions and Upstream Wildfires on Urban Air Pollution

Interactions between urban and wildfire pollution emissions are active areas of research, with numerous aircraft field campaigns and satellite analyses of wildfire pollution being conducted in recent years. Several studies have found that elevated ozone and particulate pollution levels are both generally associated with wildfire smoke in urban areas. We measured pollutant concentrations at two Utah Division of Air Quality regulatory air quality observation sites and a local hot spot (a COVID-19 testing site) within a 48 h period of increasing wildfire smoke impacts that occurred in Salt Lake City, UT (USA) between 20 and 22 August 2020. The wildfire plume, which passed through the study area during an elevated ozone period during the summer, resulted in increased criteria pollutant and greenhouse gas concentrations. Methane (CH4) and fine particulate matter (PM2.5) increased at comparable rates, and increased NOx led to more ozone. The nitrogen oxide/ozone (NOx/O3) cycle was clearly demonstrated throughout the study period, with NOx titration reducing nighttime ozone. These findings help to illustrate how the compounding effects of urban emissions and exceptional pollution events, such as wildfires, may pose substantial health risks. This preliminary case study supports conducting an expanded, longer-term study on the interactions of variable intensity wildfire smoke plumes on urban air pollution exposure, in addition to the subsequent need to inform health and risk policy in these complex systems.

Low Bacterial Diversity and Nitrate Levels in Cores from Deep Boreholes in Pristine Karst.

This study investigates the nitrate gradients within the deep biosphere of karst carbonate rocks and their resident microbiota. Samples were taken from borehole cores at depths down to 350 m below the surface, collected during geological site investigations for proposed railway tunnels and analysed using 16S rRNA amplicon sequencing. 16S rRNA amplicon sequencing analysis revealed relatively low microbial diversity, which can serve as a reliable indicator of the pristine nature of deep karst. However, some local hotspots of diversity are independent of depth. Pseudomonadota dominated the samples, with Gammaproteobacteria dominating at the class level. The low nitrate content in deep karst, in contrast to higher values closer to the surface, serves as an additional marker of its undisturbed and unpolluted status. Based on the prediction of functional profiles from 16S rRNA sequencing data, nitrates remain low due to indigenous microbial denitrification and assimilatory nitrate reduction. Pathways related to nitrogen fixation, ammonia assimilation, and nitrification were not confirmed. When elevated nitrate levels are observed in karst, they are most probably related to anthropogenic activities. Environmental factors other than depth and nitrate content play an important role in shaping bacterial communities.

Thermoelectric active cooling for transient hot spots in microprocessors

Modern microprocessor performance is limited by local hot spots induced at high frequency by busy integrated circuit elements such as the clock generator. Locally embedded thermoelectric devices (TEDs) are proposed to perform active cooling whereby thermoelectric effects enhance passive cooling by the Fourier law in removing heat from the hot spot to colder regions. To mitigate transient heating events and improve temperature stability, we propose a novel analytical solution that describes the temperature response of a periodically heated hot spot that is actively cooled by a TED driven electrically at the same frequency. The analytical solution that we present is validated by experimental data from frequency domain thermal reflectance (FDTR) measurements made directly on an actively cooled Si thermoelectric device where the pump laser replicates the transient hot spot. We herein demonstrate a practical method to actively cancel the transient temperature variations on circuit elements with TEDs. This result opens a new path to optimize the design of cooling systems for transient localized hot spots in integrated circuits.

MR Safety of Inductively Coupled and Conventional Intraoral Coils.

Intraoral coils (IOCs) in magnetic resonance imaging (MRI) significantly improve the signal-to-noise ratio compared with conventional extraoral coils. To assess the safety of IOCs, we propose a 2-step procedure to evaluate radiofrequency-induced heating of IOCs and compare maximum temperature increases in 3 different types of IOCs. The 2-step safety assessment consists of electric field measurements and simulations to identify local hotspots followed by temperature measurements during MRI. With this method, 3 different coil types (inductively coupled IFC, transmit/receive tLoop, and receive-only tLoopRx) were tested at 1.5 T and 3 T for both tuned and detuned coil states. High SAR and regular MRI protocols were applied for 2 coil positions. The measured E field maps display distinct hotspots for all tuned IOCs, which were reduced by at least 40-fold when the IOCs were detuned. Maximum temperature rise was higher when the coils were positioned at the periphery of the phantom with the coil planes parallel to B0. When neither active nor passive detuning was applied, maximum temperature increase of ΔT = 1.3/0.5/1.8 K was found for IFC/tLoop/tLoopRx coils. Hotspots detected by E field measurements, and simulations were consistent. In the simulations, the results were different for homogeneous phantoms compared with full anatomical models. The 2-step test procedure is applicable to different coil types. The results indicate that a risk for radiofrequency-induced heating exists for tuned IOCs, so that adequate detuning circuits need to be integrated in the coils to ensure safe operation.

Fluorinated porous covalent polymer nanofilm assembled sandwich separator: Lithiophilic sites engender uniform Li+ flux towards lithium metal battery

Lithium metal is renowned for its high theoretical specific capacity and extremely low reduction potential. Nevertheless, the repeated breaking/forming of the solid electrolyte interface and uncontrolled growth of lithium dendrites in lithium metal batteries significantly impede their commercial application. In this study, we propose a novel sandwich separator (F-BtTp@PP) composed of fluorinated porous covalent polymer nanofilms (F-BtTp-Nfilm) assembled using roll-to-roll technology. The F-BtTp@PP improves the pore distribution of PP, enhances its resistance to dendrite penetration, and promotes a uniform distribution of lithium ions flux. Furthermore, Fourier-transform infrared spectroscopy and density functional theory calculations confirm the energy affinity. Abundant lithophilic sites and strong electronegative groups effectively control the deposition behavior of lithium ions, resulting in a transfer number of 0.87. This mitigates effectively the occurrence of significant concentration gradients and localized hot-spots during cycles with high current density. The symmetrical cells of F-BtTp@PP Li|Li can maintain a stable cycling voltage of 52.2 mV for 5600 h under a current density of 20 mA cm−2 and capacity density of 10 mAh cm−2. This result robustly demonstrates the exceptional efficiency of F-BtTp@PP, which can be readily scaled up for protecting lithium metal anodes and provides valuable guidance for the design and industrial development of lithium metal batteries with modified separators.

Using clustering to understand intra-city warming in heatwaves: insights into Paris, Montreal, and Zurich

We introduce a novel methodological advancement by clustering paired near-surface air temperature with the planetary boundary layer height to characterize intra-city clusters for analytics. To illustrate this approach, we analyze three heatwaves (HWs): the 2019 HW in Paris, the 2018 HW in Montreal, and the 2017 HW in Zurich. We assess cluster-based characteristics before, during, and after heatwave events. While the urban clusters identified by this clustering align well with built-up areas obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover data, additional local hot spots spanning several kilometers can also be recognized, extending outside the built-up areas. Using the objective hysteresis model, we further determine the overall strength coefficient of the hysteresis loop between ground storage flux and all-wave downward radiative flux, ranging from 0.414 to 0.457 for urban clusters and from 0.126 to 0.157 for rural clusters during the heatwave periods. Across all cities, we observe a consistent refueling-restoration mode in the cumulative ground heat flux as the heatwaves progress. Future developments of this proposed two-component clustering approach, with the integration of more influential physics and advances in spatial and temporal resolutions, will offer a more comprehensive characterization of cities for urban climate analytics.

Effects of cell parameters on accurate calculation of activation dose after DT explosion for local hot spots in laser-driven ICF facilities

Instruments placed in the target chamber will be highly activated after DT explosion in laser-driven ICF experiments, especially for the part near the chamber center. Operations near those local hot spots are the main concern for radiation protection due to its high contribution to the occupation exposure dose, therefore it becomes very important to calculate the dose during the operating process accurately. Cell-based rigorous two-step (R2S) method has been introduced to deal with the activated objects with highly heterogeneous distribution, and the effects of cell size, materials as well as radiation source have also been specified to improve the accuracy of simulations. Results for a typical model sample show that with a given distribution of radiation source, cell size in the simulations placed a significant influence on the accuracy of the radiation field. A cell size of 50 cm for a 100 cm cone-shaped sample will lead to the inaccuracy of the radiation field as large as an order in magnitude within the location 50 cm from the surface of the sample. While for the same sample model, cell size should be limited to smaller than 2 cm to ensure an accuracy lower than ±10 %. In addition, the effects of the material and source energy on the calculation accuracy for the radiation field could be neglected if the cell size is limited to smaller than 5 cm. Furthermore, the influence of cell size increased as the distance from the sample surface decreased, which indicates that appropriate cell size must be chosen to ensure the accuracy of dose estimation, especially for surface contact operations. Besides, a significant difference between the effective dose and skin-equivalent dose has been observed for the typical mode used in the calculations.

Surface urban heat island analysis based on local climate zones using ECOSTRESS and Landsat data: A case study of Valencia city (Spain)

Extreme heat events in cities are becoming more intense, frequent and prolonged. The spatiotemporal dynamics of surface temperature are closely related to land cover and atmospheric conditions, especially for urban areas with extensive surface heterogeneity. Two high spatial resolution satellites, ECOSTRESS and Landsat, provide land surface temperature (LST) for a typical Mediterranean climate city, Valencia, Spain. In total of 17 images throughout two heatwaves in the period of July and August from 2022 to 2023 were selected to monitor LST and surface urban heat island (SUHI). The Local Climate Zone (LCZ) scheme and hotspot analysis were applied to analyze the patterns of LST and SUHI during and after the heatwaves. Daytime images show LCZ 2/3/6/8 and LCZ C/E/F exhibit elevated SUHI intensity, meanwhile the LCZ 4, A/B and G have lower SUHI. The SUHI intensity of compact buildings (LCZ 1/2/3), LCZ 8/E/G are significantly higher at night, especially on heatwave days, the SUHI of all types increased by 0.1–0.9 °C. Furthermore, the meteorological parameters were introduced trying to explain the obvious diurnal difference of SUHI during heatwaves. This research serves as a proxy for understanding the spatiotemporal dynamics of SUHI during heatwave events, offering valuable insights for city planners and policymakers to enhance thermal comfortable level and effectively cope with extreme weather.

Percolating cosmic string loops from evaporating primordial black holes

The Pulsar timing data from NANOGrav Collaboration has regenerated interest in the possibility of observing stochastic gravitational wave background arising from cosmic strings. Standard theory of formation of cosmic strings is based on a spontaneous symmetry breaking (SSB) phase transition in the early universe, with a string network forming via the so called Kibble mechanism. This string network rapidly evolves and reaches a scaling solution with a given spectrum of string loops and long strings at any given time. This scenario necessarily requires that the entire observable Universe goes through the SSB phase transition. This would not be possible, e.g., in models of low energy inflation, where the reheat temperature is much lower than the energy scale of cosmic strings. We point out a very different possibility, where a network of even high energy scale cosmic strings can form when the temperature of the Universe is much lower. We consider local heating of plasma in the early universe by evaporating primordial black holes (PBHs). It is known that for suitable masses of PBHs, Hawking radiation of evaporating primordial black holes may re-heat the surrounding plasma to high temperatures, restoring certain symmetries locally which are broken at the ambient temperature of the Universe at that stage. Expansion of the hot plasma cools it so that the locally restored symmetry is spontaneously broken again. If this SSB supports formation of cosmic strings, then string loops will form in this region around the PBH. Further, resulting temperature gradients lead to large pressure gradients such that plasma will develop radial flow with the string loops getting stretched as they get dragged by the flow. For a finite density of PBHs of suitable masses, one will get local hot spots, each one contributing to expanding cosmic string loops. For suitable PBH density, the loops from different regions may intersect. If that happens, then intercommutation of strings can lead to percolation, leading to the possibility of formation of infinite string network, even when the entire universe never goes through the respective SSB phase transition.

Genotypic analysis of a localised hotspot of Pestivirus A (BVDV-1) infections in Northern Ireland.

Bovine viral diarrhoea (BVD) is caused by Pestivirus A and Pestivirus B. Northern Ireland (NI) embarkedon a compulsory BVD eradication scheme in 2016, which continues to this day, so an understanding of the composition of the pestivirus genotypes in the cattle population of NI is required. This molecular epidemiology study employed 5' untranslated region (5'UTR) genetic sequencing to examine the pestivirus genotypes circulating in samples taken from a hotspot of BVD outbreaks in the Enniskillen area in 2019. Bovine viral diarrhoea virus (BVDV)-1e (Pestivirus A) was detected for the first time in Northern Ireland, and at a highfrequency, in an infection hotspot in Enniskillen in 2019. There was no evidence of infection with BVDV-2 (Pestivirus B), Border disease virus (pestivirus D) or HoBi-like virus/BVDV-3 (pestivirus H). Only 5'UTR sequencing was used, so supplementary sequencing, along with phylogenetic trees that include all BVDV-1 genotype reference strains, would improve accuracy. Examination of farm locations and animal movement/trade is also required. Genotype BVDV-1e was found for the first time in Northern Ireland, indicating an increase in the genetic diversity of BVDV-1, which could have implications for vaccine design and highlights the need for continued pestivirus genotypic surveillance.

Radiatively cooled magnetic reconnection experiments driven by pulsed power

We present evidence for strong radiative cooling in a pulsed-power-driven magnetic reconnection experiment. Two aluminum exploding wire arrays, driven by a 20 MA peak current, 300 ns rise time pulse from the Z machine (Sandia National Laboratories), generate strongly driven plasma flows (MA≈7) with anti-parallel magnetic fields, which form a reconnection layer (SL≈120) at the mid-plane. The net cooling rate far exceeds the Alfvénic transit rate (τcool−1/τA−1≫1), leading to strong cooling of the reconnection layer. We determine the advected magnetic field and flow velocity using inductive probes positioned in the inflow to the layer, and inflow ion density and temperature from analysis of visible emission spectroscopy. A sharp decrease in x-ray emission from the reconnection layer, measured using filtered diodes and time-gated x-ray imaging, provides evidence for strong cooling of the reconnection layer after its initial formation. X-ray images also show localized hotspots, regions of strong x-ray emission, with velocities comparable to the expected outflow velocity from the reconnection layer. These hotspots are consistent with plasmoids observed in 3D radiative resistive magnetohydrodynamic simulations of the experiment. X-ray spectroscopy further indicates that the hotspots have a temperature (170 eV) much higher than the bulk layer (≤75 eV) and inflow temperatures (about 2 eV) and that these hotspots generate the majority of the high-energy (>1 keV) emission.