scholarly journals High-Speed Study of Drop-Weight Impact Ignition of PBX 9501 Using Infrared Thermography

2011 ◽  
Vol 2011 ◽  
pp. 1-4 ◽  
Author(s):  
Emily M. Hunt ◽  
Steve Malcolm ◽  
Matt Jackson
Keyword(s):  
Hot Spots ◽  
High Speed ◽  
Reaction Rate ◽  
Hot Spot ◽  
Exothermic Reaction ◽  
Strong Temperature Dependence ◽  
Explosive Materials ◽  
Weight Impact ◽  
Transfer Mechanisms ◽  
Ignition Site

Reaction in explosive materials does not occur as a result of homogenous heating of the sample, but rather from a localized region of high temperature called a hot spot. Observation of hot spot development is critical in understanding the heat transfer mechanisms occurring during reaction. Due to the strong temperature dependence of explosives, the overall reaction rate is dominated physically by these hot spots. Once formed, these hot spots either fail to react chemically due to thermal diffusion or react exothermically thus creating an ignition site in the solid explosive. The slightest difference of physical properties can change the positioning of hot spot development, creating an argument that the differences in material properties influence the formation of hot spots, which produce an exothermic reaction.

Hot-spot reaction under transient pressure conditions

1987 ◽  
Vol 413 (1845) ◽  
pp. 329-350 ◽  
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Thermodynamic Description ◽  
Exothermic Reaction ◽  
Pressure Change ◽  
Variable Pressure ◽  
Transient Pressure ◽  
Physical Mechanisms ◽  
Solid Explosives ◽  
Condensed Phase Explosives

The initiation of condensed-phase explosives is often caused by hot spots; that is, localized regions of high temperature created by a variety of physical mechanisms, particularly in solid explosives. Once the hot spots are created, further temperature change is governed by (i) self-heating due to chemical reaction, (ii) heat loss by conduction and radiation, and (iii) adiabatic effects due to pressure and specific volume variation. The last effect includes both self-induced pressure change due to thermal expansion against the surroundings, and externally generated pressure change when initiation is attempted by mechanical impact. This paper presents a thermodynamic description of exothermic reaction under conditions of variable pressure and volume. The reaction rate is assumed to be a function of temperature only. The effect of variable pressure enters through its influence on temperature. It is demonstrated that the effects of self-induced pressure change are small. In the case of externally generated pressure change, explosion times can be affected drastically. These results are discussed in terms of initiation by shock waves of finite duration.

Analysis of Hot Spots Evolution on Brake Disc Using High-Speed Infrared Camera

2009 ◽  
Vol 417-418 ◽  
pp. 317-320 ◽  
Author(s):  
Jeong Guk Kim ◽  
Sung Tae Kwon ◽  
Sung Cheol Yoon
Keyword(s):  
Hot Spots ◽  
High Speed ◽  
Hot Spot ◽  
Degradation Mechanism ◽  
Low Frequency ◽  
Infrared Camera ◽  
Material Design ◽  
Brake Disc ◽  
Ir Camera ◽  
Thermal Phenomenon

The hot spot generation has been considered as the main degradation mechanism in railway brake disc. Therefore, the understanding of hot spots, also called hot judder, which is undesirable low frequency vibrations developed by non-uniform contact area between brake pad material and brake disc, is important for a better understanding of material design as well as enhancement of materials properties in railway brake disc. Also, infrared (IR) thermography is a powerful NDE technique for the characterization of thermal phenomenon in engineering components and/or systems including engineering materials. The high-speed IR camera provides the measurement of temperature change during brake operation as well as the images of temperature contour on the brake disc surface. In this investigation, damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method. Moreover, based on obtained thermographic images of hot spots, the hot spots and thermal damage of railway brake disc during braking operation were qualitatively analyzed.

FLAME FRONT DYNAMIC STUDIES BEFORE THE ONSET OF DETONATION IN DILUTED STOICHIOMETRIC ACETYLENE-OXYGEN MIXTURES

2020 ◽  
Author(s):  
Ya. A. Baranyshyn ◽  
◽  
P. N. Krivosheyev ◽  
O. G. Penyazkov ◽  
K. L. Sevrouk ◽  
...  
Keyword(s):  
Shock Wave ◽  
Flame Front ◽  
Hot Spots ◽  
High Speed ◽  
Spatial Configuration ◽  
Hot Spot ◽  
Video Recording ◽  
Pressure Sensors ◽  
Front Propagation ◽  
Transition To Detonation

The results of experimental research of deflagration-to-detonation transition (DDT) in stoichiometric mixtures of acetylene-oxygen diluted by 70% argon or 60% nitrogen in round smooth tube with diameter of 0.04 m in the mode of low-energy initiation of combustion by a spark discharge (0.8 mJ) are presented. Simultaneous registration of shock wave propagation by high-frequency pressure sensors and the reaction front propagation by ionization sensors allowed us to obtain the quantitative data on the dynamics of the formed shock wave, local velocity of the flame front, and its spatial configuration (relative to the walls of the tube) and to determine the length of the flame and the distance between the shock wave and the flame front in the process of its acceleration. Two typical stages of flame acceleration were observed in experiments. At flame velocities less than the sound velocity of the products, the spatial configuration of the flame front was very unstable and its strong transverse oscillations were recorded. With further increase in the speed, the spatial configuration of the flame front was stabilized before transition to detonation. The high-speed video recording of the glow at the DDT made it possible to register the appearance of hot spots and to determine their position relative to the tube walls and the front flame front. It is established that after the flame front attains a speed of an order of sound speed in the products, near a tube wall between a shock wave and a flame front, there is a hot spot from which the detonation wave develops. In the mixture diluted with argon, several hot spots were often observed simultaneously. In the mixture diluted with nitrogen, weak initiation modes were observed, in which the emergence of the hot spot did not lead to the development of detonation over long distances (more than a meter). In a mixture diluted with argon, the occurrence of a hot spot always led to detonation.

Infrared Thermographic Analysis of Railway Brake Disc during Braking

2011 ◽  
Vol 488-489 ◽  
pp. 597-600 ◽  
Author(s):  
Jeong Guk Kim ◽  
Sung Tae Kwon ◽  
Sung Cheol Yoon ◽  
Byeong Choon Goo
Keyword(s):  
Hot Spots ◽  
High Speed ◽  
Hot Spot ◽  
Degradation Mechanism ◽  
Infrared Camera ◽  
Brake Disc ◽  
Ir Camera ◽  
Train Speed ◽  
Thermographic Analysis ◽  
Temperature Contour

The temperature monitoring on the surface of the railway brake disc was performed using high-speed infrared (IR) camera. The railway brake disc was developed for disc braking of maximum train speed of 180 km/h. The braking tests were conducted with a full scale dynamometer, and a high-speed infrared camera was employed to monitor temperature evolution on the brake disc during braking operation. The high-speed IR camera provides the measurement of temperature change during braking as well as the images of temperature contour on the brake disc surface. In general, the hot spot generation has been considered the main degradation mechanism in railway brake disc. In this investigation, damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method.

Thermographic Investigation of Hot Spots in Railway Brake Discs

2008 ◽  
Vol 385-387 ◽  
pp. 669-672 ◽  
Author(s):  
Jeong Guk Kim ◽  
Byeong Choon Goo ◽  
Sung Cheol Yoon ◽  
Sung Tae Kwon
Keyword(s):  
Hot Spots ◽  
High Speed ◽  
Hot Spot ◽  
Infrared Camera ◽  
In Situ Monitoring ◽  
Brake Disc ◽  
Brake Discs ◽  
Thermographic Investigation ◽  
Experimental And Theoretical Studies

Damage evolution due to generation of hot spots on railway brake disc was investigated using the infrared thermography method. A brake disc with gray cast iron, which is currently used in Korea, was employed for this investigation. A high-speed infrared camera was used to measure the surface temperature of brake disc as well as for in-situ monitoring of hot spot evolution. From the thermographic images, the observed hot spots and thermal damage of railway brake disc during braking operation were qualitatively analyzed. Moreover, in this investigation, the previous experimental and theoretical studies on hot spots phenomenon were reviewed, and the current experimental results were introduced and compared with theoretical prediction.

Spatial Hotspot Analysis of Bucharest’s Urban Heat Island (UHI) Using Modis Data

2018 ◽  
Vol 18 (1) ◽  
pp. 14-22 ◽  
Author(s):  
Georgiana Grigoraș ◽  
Bogdan Urițescu
Keyword(s):  
Surface Temperature ◽  
Air Temperature ◽  
Land Surface Temperature ◽  
Hot Spots ◽  
Land Surface ◽  
Hot Spot ◽  
Monitoring Network ◽  
Residential Areas ◽  
Hotspot Analysis ◽  
The City

Abstract The aim of the study is to find the relationship between the land surface temperature and air temperature and to determine the hot spots in the urban area of Bucharest, the capital of Romania. The analysis was based on images from both moderate-resolution imaging spectroradiometer (MODIS), located on both Terra and Aqua platforms, as well as on data recorded by the four automatic weather stations existing in the endowment of The National Air Quality Monitoring Network, from the summer of 2017. Correlation coefficients between land surface temperature and air temperature were higher at night (0.8-0.87) and slightly lower during the day (0.71-0.77). After the validation of satellite data with in-situ temperature measurements, the hot spots in the metropolitan area of Bucharest were identified using Getis-Ord spatial statistics analysis. It has been achieved that the “very hot” areas are grouped in the center of the city and along the main traffic streets and dense residential areas. During the day the "very hot spots” represent 33.2% of the city's surface, and during the night 31.6%. The area where the mentioned spots persist, falls into the "very hot spot" category both day and night, it represents 27.1% of the city’s surface and it is mainly represented by the city center.

The family Orthotrichaceae (Bryophyta) in flora of Russia: results of revision and biogeographical review

2018 ◽  
Vol 52 (2) ◽  
pp. 519-534 ◽  
Author(s):  
V. E. Fedosov
Keyword(s):  
Hot Spots ◽  
Latitudinal Gradient ◽  
Hot Spot ◽  
Spatial Differentiation ◽  
Taxonomic Composition ◽  
Undescribed Species ◽  
Longitudinal Gradient ◽  
Biogeographic Pattern ◽  
The Family ◽  
North Pacific Region

Recent studies on Orthotrichoid mosses in Russia are summarized genus by genus. Orthotrichum furcatum Otnyukova is synonymized with Nyholmiella obtusifolia. Orthotrichum vittii is excluded from the Russian moss flora. Description of O. dagestanicum is amended. Fifty four currently recognized species from 9 genera of the Orthotrichaceae are presently known to occur in Russia; list of species with common synonyms and brief review of distribution in Russia is presented. Numerous problematic specimens with unresolved taxonomy were omitted for future. Revealed taxonomical inconsistencies in the genera Zygodon, Ulota, Lewinskya, Nyholmiella, Orthotrichum are briefly discussed. Main regularities of spatial differentiation of the family Orthotrichaceae in Russia are considered. Recently presented novelties contribute to the certain biogeographic pattern, indicating three different centers of diversity of the family, changing along longitudinal gradient. Unlike European one, continental Asian diversity of Orthotrichaceae is still poorly known, the Siberian specimens which were previously referred to European species in most cases were found to represent other, poorly known or undescribed species. North Pacific Region houses peculiar and poorly understood hot spot of diversity of Orthotrichoid mosses. Thus, these hot spots are obligatory to be sampled in course of revisions of particular groups, since they likely comprise under-recorded cryptic- or semi-cryptic species. Latitudinal gradient also contributes to the spatial differentiation of the revealed taxonomic composition of Orthotrichaceae.

scholarly journals Family Practices and Temporality at Breakfast: Hot Spots, Convenience and Care

Sociology ◽  
2021 ◽  
pp. 003803852110155
Author(s):  
Daniela Pirani ◽  
Vicki Harman ◽  
Benedetta Cappellini
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Family Meals ◽  
Personal Integrity ◽  
Structured Interviews ◽  
Time Saving ◽  
Family Time ◽  
Dominant Feature ◽  
Family Practices ◽  
Cold Spots

Drawing on 34 semi-structured interviews, this study investigates the temporality of family practices taking place in the hot spot. It does so by looking at how breakfast is inserted in the economy of family time in Italy. Our data show that breakfast, contrary to other meals, allows the adoption of more individualised and asynchronous practices, hinged on the consumption of convenience products. These time-saving strategies are normalised as part of doing family. Although the existing literature suggests that convenience and care are in opposition, and consumers of convenience products can experience anxiety and a lack of personal integrity, such features were not a dominant feature of our participants’ accounts. These findings suggest that the dichotomies of hot/cold spots and care/convenience are not always experienced in opposition when embedded within family practices. Hence, this study furthers understandings of family meals, temporality and the distinction between hot and cold spots.

Investigation of On-Chip Hot Spot Cooling Using Microchannel Heat Sink

2013 ◽  
Vol 455 ◽  
pp. 466-469
Author(s):  
Yun Chuan Wu ◽  
Shang Long Xu ◽  
Chao Wang
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Hot Spots ◽  
Hot Spot ◽  
High Heat ◽  
High Heat Flux ◽  
Microchannel Heat Sink ◽  
Three Dimensional Model ◽  
Spot Cooling ◽  
On Chip

With the increase of performance demands, the nonuniformity of on-chip power dissipation becomes greater, causing localized high heat flux hot spots that can degrade the processor performance and reliability. In this paper, a three-dimensional model of the copper microchannel heat sink, with hot spot heating and background heating on the back, was developed and used for numerical simulation to predict the hot spot cooling performance. The hot spot is cooled by localized cross channels. The pressure drop, thermal resistance and effects of hot spot heat flux and fluid flow velocity on the cooling of on-chip hot spots, are investigated in detail.

scholarly journals Energetic-Materials-Driven Synthesis of Graphene-Encapsulated Tin Oxide Nanoparticles for Sodium-Ion Batteries

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2550
Author(s):  
Yingchun Wang ◽  
Jinxu Liu ◽  
Min Yang ◽  
Lijuan Hou ◽  
Tingting Xu ◽  
...  
Keyword(s):  
Tin Oxide ◽  
Energetic Materials ◽  
High Speed ◽  
Coulombic Efficiency ◽  
Sno2 Nanoparticles ◽  
Direct Synthesis ◽  
Exothermic Reaction ◽  
Rate Capability ◽  
Rapid Expansion ◽  
Core Shell

By evenly mixing polytetrafluoroethylene-silicon energetic materials (PTFE-Si EMs) with tin oxide (SnO2) particles, we demonstrate a direct synthesis of graphene-encapsulated SnO2 (Gr-SnO2) nanoparticles through the self-propagated exothermic reaction of the EMs. The highly exothermic reaction of the PTFE-Si EMs released a huge amount of heat that induced an instantaneous temperature rise at the reaction zone, and the rapid expansion of the gaseous SiF4 product provided a high-speed gas flow for dispersing the molten particles into finer nanoscale particles. Furthermore, the reaction of the PTFE-NPs with Si resulted in a simultaneous synthesis of graphene that encapsulated the SnO2 nanoparticles in order to form the core-shell nanostructure. As sodium storage material, the graphene-encapsulated SnO2 nanoparticles exhibit a good cycling performance, superior rate capability, and a high initial Coulombic efficiency of 85.3%. This proves the effectiveness of our approach for the scalable synthesis of core-shell-structured graphene-encapsulated nanomaterials.

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