scholarly journals Initiation of solid explosives by impact and friction: the influence of grit

1949 ◽  
Vol 198 (1054) ◽  
pp. 337-349 ◽  
Keyword(s):  
Melting Point ◽  
Hot Spots ◽  
Hot Spot ◽  
Threshold Value ◽  
Maximum Temperature ◽  
Melting Points ◽  
Solid Explosives ◽  
Lower Melting Point ◽  
Determining Factor ◽  
Spot Temperature

This paper describes an experimental study of the initiation of solid explosives, and in particular the effect of artificially introducing transient hot spots of known maximum temperature. This was done by adding small foreign particles (or grit) of known melting-point. The minimum transient hot-spot temperature for the initiation of a number of secondary and primary explosives has been determined in this way. It is shown that the melting-point of the grit is the determining factor , and all the grits which sensitize these explosives to initiation either by friction or impact have melting-points above a threshold value which lies between 400 and 550 ° C. Grit particles of lower melting-point do not sensitize the explosives. The same explosives initiated by the adiabatic compression of air required, for initiation, minimum transient temperatures of the same order as the threshold melting-point values. The results provide strong evidence that the initiation of solids as well as of liquids by friction and impact is thermal in origin and is due to the formation of localized hot spots. There is evidence that in the case of the majority of secondary explosives which melt at comparatively low temperatures, intergranular friction is not able to cause explosion and the hot spots must be formed in some other way. With the primary explosives which explode at temperatures below their melting-points, hot spots formed by intergranular friction can be important.

Predictions of Current Attachment at Thermionic Cathode for TIG Arcs

2008 ◽  
Vol 580-582 ◽  
pp. 319-322 ◽  
Author(s):  
Manabu Tanaka ◽  
Kentaro Yamamoto ◽  
Tashiro Shinichi ◽  
John J. Lowke
Keyword(s):  
Melting Point ◽  
Work Function ◽  
Atmospheric Pressure ◽  
The Other ◽  
Numerical Calculations ◽  
Maximum Temperature ◽  
Arc Plasma ◽  
Melting Points ◽  
Thermionic Cathode ◽  
Uniform Current

Study of current attachment at thermionic cathode for TIG arc at atmospheric pressure is attempted from numerical calculations of arc-electrodes unified model. The calculations show that the maximum temperature of arc plasma close to the cathode tip for W-2% ThO2 reaches 19,000 K and it is the highest value in comparison with the other temperatures for W-2% La2O3 and W-2% CeO2, because the current attachment at the cathode tip is constricted by a centralized limitation of liquid area of ThO2 due to its higher melting point. The calculations also show that, in cases of W- 2% La2O3 and W-2% CeO2, the liquid areas of La2O3 and Ce2O3 are widely expanded at the cathode tip due to their lower melting points and then produce uniform current attachments at the cathode. It is concluded that the current attachment at thermionic cathode is strongly dependent on work function, melting point and Richardson constant of emitter materials.

Silicon Hot Spot Remediation With a Germanium Self Cooling Layer

2011 ◽  
Author(s):  
Horacio Nochetto ◽  
Peng Wang ◽  
Avram Bar-Cohen
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Silicon Layer ◽  
Great Promise ◽  
Applied Current ◽  
Chip Cooling ◽  
Primary Driver ◽  
Germanium Layer ◽  
On Chip ◽  
Spot Temperature

Driven by shrinking feature sizes, microprocessor hot spots have emerged as the primary driver for on-chip cooling of today’s IC technologies. Current thermal management technologies offer few choices for such on-chip hot spot remediation. A solid state germanium self-cooling layer, fabricated on top of the silicon chip, is proposed and demonstrated to have great promise for reducing the severity of on-chip hot spots. 3D thermo-electrical coupled simulations are used to investigate the effectiveness of a bi-layer device containing a germanium self-cooling layer above an electrically insulated silicon layer. The parametric variables of applied current, cooler size, silicon percentage, and total die thickness are sequentially optimized for the lowest hot spot temperature compared to a non-self-cooled silicon chip. Results suggest that the localized self-cooling of the germanium layer coupled with the higher thermal conductivity of the silicon chip can significantly reduce the temperature rise resulting from a micro-scaled hot spot.

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.

scholarly journals Effect of Loads on Temperature Distribution Characteristics of Oil-Immersed Transformer Winding

2021 ◽  
Author(s):  
Zhengang Zhao ◽  
Zhangnan Jiang ◽  
Yang Li ◽  
Chuan Li ◽  
Dacheng Zhang
Keyword(s):  
Temperature Distribution ◽  
Hot Spots ◽  
Hot Spot ◽  
Transformer Oil ◽  
Distribution Characteristics ◽  
Thermal Circuit ◽  
Transformer Winding ◽  
Overload Capacity ◽  
The Impact ◽  
Spot Temperature

The temperature of the hot-spots on windings is a crucial factor that can limit the overload capacity of the transformer. Few studies consider the impact of the load on the hot-spot when studying the hot-spot temperature and its location. In this paper, a thermal circuit model based on the thermoelectric analogy method is built to simulate the transformer winding and transformer oil temperature distribution. The hot-spot temperature and its location under different loads are qualitatively analyzed, and the hot-spot location is analyzed and compared to the experimental results. The results show that the hot-spot position on the winding under the rated power appears at 85.88% of the winding height, and the hot-spot position of the winding moves down by 5% in turn at 1.3, 1.48, and 1.73 times the rated power respectively.

scholarly journals Eutectic Phenomenon of LiNH2-KH Composite in MH-NH3 Hydrogen Storage System

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1348 ◽  
Author(s):  
Kiyotaka Goshome ◽  
Ankur Jain ◽  
Hiroki Miyaoka ◽  
Hikaru Yamamoto ◽  
Yoshitsugu Kojima ◽  
...  
Keyword(s):  
Melting Point ◽  
Storage System ◽  
Atomic Mobility ◽  
Melting Points ◽  
Lithium Amide ◽  
Hydrogen Storage System ◽  
Lower Melting Point ◽  
Hydrogenation Temperature ◽  
The Individual ◽  
Potassium Hydride

Hydrogenation of a lithium-potassium (double-cation) amide (LiK(NH2)2), which is generated as a product by ammonolysis of litium hydride and potassium hydride (LiH-KH) composite, is investigated in details. As a result, lithium amide (LiNH2) and KH are generated after hydrogenation at 160 °C as an intermediate. It is noteworthy that the mixture of LiH and KNH2 has a much lower melting point than that of the individual melting points of LiNH2 and KH, which is recognized as a eutectic phenomenon. The hydrogenation temperature of LiNH2 in the mixture is found to be significantly lower than that of LiNH2 itself. This improvement of reactivity must be due to kinetic modification, induced by the enhanced atomic mobility due to the eutectic interaction.

Paper 12: Determination of the ‘Hot Spot’ Temperature Rise from P.V.C. Insulation Characteristics

1969 ◽  
Vol 184 (11) ◽  
pp. 117-130
Author(s):  
S. W. Twaites ◽  
R. F. Murray
Keyword(s):  
High Temperature ◽  
Temperature Rise ◽  
Hot Spot ◽  
Electrical Machines ◽  
Maximum Temperature ◽  
Spot Temperature ◽  
Operational Service

It is normal practice when designing electrical machines to design for operation within the maximum temperature limits of the insulation. If part of the winding is not effectively cooled under these conditions, the resulting temperature rise can damage the insulation and seriously reduce the length of operational service of the machine. This paper discusses a method of detecting high-temperature regions within a winding and of estimating the ‘hot spot’ temperature. The investigation has been concentrated on the design associated with a direct water-cooled winding, although the results could be applied generally on other electrical machines.

The surface temperature of sliding solids

1954 ◽  
Vol 223 (1152) ◽  
pp. 29-40 ◽  
Keyword(s):  
Melting Point ◽  
Surface Temperature ◽  
Hot Spots ◽  
Maximum Temperature ◽  
Physical Methods ◽  
Infra Red ◽  
Time Required ◽  
Very High ◽  
Red Radiation ◽  
Fluctuating Temperatures

The surface temperature developed at the points of rubbing contact between a metal and a transparent solid is determined by measuring the infra-red radiation transmitted through the solid. It is shown that high, fluctuating temperatures occur, and the results are in general agreement with those obtained by other physical methods. Some measurements are made of the time required for the formation and decay of the ‘hot spots’. In general, the maximum temperature rise is limited by the melting-point of the solid, but with readily oxidizable metals very high temperatures are occasionally observed because of the ‘burning’ of the metal.

Phase and Morphological Transformation of Preformed AZ91D Magnesium Alloys in Remelting

2005 ◽  
Vol 475-479 ◽  
pp. 473-476
Author(s):  
Ming-Xu Xia ◽  
Hong-xing Zheng ◽  
Sen Yuan ◽  
Jian Guo Li
Keyword(s):  
Melting Point ◽  
Magnesium Alloys ◽  
Semisolid State ◽  
Melting Points ◽  
Morphological Transformation ◽  
Lower Melting ◽  
Partial Remelting ◽  
Final Microstructure ◽  
Lower Melting Point ◽  
Two Stages

The phase and morphological transformation during the remelting process was investigated by isothermal soaking and rapidly quenching of preformed AZ91D magnesium alloys in semisolid state. It was revealed that the morphological transformation of preformed alloys is crucial to obtain homogenously fine spheroidal grains and affect the final forming ability. The transformation is divided into two stages, local remelting of the whole experiment and partial remelting of the respective grains, which behave as liquid bands and liquid cells structures, respectively. In the partial melting, the lower melting point phase, β-Mg17Al12, diffused to the grains boundary and center of the grains and separated to Al2Mg and Mg. The Al2Mg and Mg phases with lower melting points melt into cells structures. The final microstructure of the remelting experiments is composed of cells structures, spheroidal grains and liquid phase.

Local Hot Spots of Electric Water Pump Casing Over Various Pumping Loads

2020 ◽  
Author(s):  
Younghyeon Kim ◽  
Yoora Choi ◽  
Sangseok Yu
Keyword(s):  
Temperature Distribution ◽  
Joule Heating ◽  
Hot Spots ◽  
Cooling System ◽  
Hot Spot ◽  
Maximum Temperature ◽  
Water Pump ◽  
Ir Camera ◽  
Heat Rejection ◽  
Electric Water Pump

Abstract The cooling system of an electric vehicle adopts an electric water pump. Since the lifespan of the battery is very sensitive to a very narrow temperature band, the cooling system provides key solutions. The electric water pump is a core component of the cooling system which satisfies performance and durability criteria. Since, a local hot spot of motor casing results in the degradation of motor lifespan, it is necessary to design the motor casing for effective heat rejection. In this study, two different motor casing designs are applied to reject the joule heating of the motor efficiently. The temperature distribution of each casing is investigated with an IR camera. The IR camera was used to identify the local hot spot where the heat was most generated in the pump. Since the joule heating is proportional to pump power, it is necessary to understand the operating characteristics of the electric water pump. The experimental apparatus includes a water reservoir, a bypass valve, pressure and temperature sensors, DAQ, and IR camera. The operating temperature is ranged from atmospheric temperature to 50°C. When the pump is operated with 25°C coolant, each experiment takes 1 hour for the steady-state conditions and maximum temperature up to 55 °C. Three different pump performance are investigated with two different pump casing. The coolant temperature is also changed from 25 °C to 50 °C. As a result, the local hot spot is strongly dependent to pump load and it is mainly observed near the cable connector. Since temperature distribution on the casing surface is also affected by local hot spots, it is necessary to optimize heat rejection by extended surface.

Study of the Hot Spots in Integrated Circuits Cooled by Microfluidic Heatsinks

2007 ◽  
Author(s):  
Alireza Motieifar ◽  
Cyrus Shafai ◽  
Hassan M. Soliman
Keyword(s):  
Fluid Flow ◽  
Integrated Circuits ◽  
Heat Sink ◽  
Hot Spots ◽  
Hot Spot ◽  
Solid Material ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fem Method ◽  
Spot Temperature

The thermal input into high-power Integrated Circuits (IC) can have local peaks or hot spots with heat fluxes far exceeding 100 W/cm2. In this work, the temperature distribution on a microfluidic heatsink has been simulated using the FEM method. The effects of the fluid flow and thickness of the heatsink on the hot spot temperature have been studied. Simulations have been performed for a 1 cm × 1 cm heat sink loaded with 100 W/cm2 heating power, with a 1 mm hot spot of 1000 W/cm2 and a 3 mm hot spot of 500 W/cm2. Heat sinks fabricated from silicon, nickel, and copper are considered. These results show that the effect of increasing the thickness of the heatsink on the peak temperature of the hot spot depends on the solid material and the fluid flow. Simulations showed that the hot spot temperature rise can be about 40% higher if a nickel heat sink is used instead of a copper heat sink.

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