Heat-generating Devices

Tungsten, barium chromate and potassium perchlorate Gasless 

Lead chromate, barium chromate and manganese Gasless 

The burning rate of delay compositions can be very fast (mm ms 1) or quite slow (mm s-1). Delay compositions which have a fast burn rate of greater than 1 mm ms-1 are used in projectiles and bombs that explode on impact. Delay compositions which have a slow burn rate between 1 and 6 mm s-1 are used in ground chemical munitions such as smoke pots, tear gas and smoke grenades. Delay compositions which have intermediate burn rates are used in effective blasting in quarries and salt mines. Here, the explosions in the boreholes are staggered to reduce vibration and improve fragmentation. 

Tetranitrocarbazole and potassium nitrate Boron, silicon and potassium dichromate Tungsten, barium chromate and potassium perchlorate Lead chromate, barium chromate and manganese Chromium, barium chromate and potassium perchlorate 

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Pyrotechnic compositions which are used in primers or first fires are very sensitive to initiation, whereas compositions which are used in heat-generating devices are less sensitive. The sensitivity of the compositions can be controlled by reducing the amount of oxidizer and choosing a less sensitive oxidizer. 

FIGURE 2.84 Temperature field in vulcanizate cross-section with the use of heating wire as heat-generating device. (Reprinted from Yu. Borisov, S. Matreninskiy, and R. Sapelkin, Process of Heat Transfer during Vulcanization of the Concrete Based on Liquid Polybutadine Binder, J. Scientific Israel Technological Advantages, 11, no. 1 (2009) 15-22. With permission.)... 

As a result of analysis of heat-generating devices, the infrared radiation generator was selected as a supplementary source of thermal energy (Figure 2.85). This device produces directional heating of the surface and has a high coefficient of efficiency of 65%. 

Figure 2.87 shows the temperature field distribution in the vulcanizate cross-section with heating wire as the heat-generating device, with supplementary infrared radiation on the outside surface. 

Heat sinks are used to increase the surface area exposed to the air or other cooling gas. They are the final interface between the heat generating devices and the outside world. The most common type is the finned heat sink, which consists of a flat plate and a number of fins extending from the surface. The fins are formed in a number of ways extrusion, casting, machining, molding, or by attachment with a thermally conductive material. In some applications, only a flat plate is used for the heat sink. 

To prevent blistering in the large areas of copper plafing, vent or relief holes in the copper metallization are required. These holes relieve stress during process temperature excursions. The manufacturer of substrates using this process recommends that the vent holes be used whenever a copper pad area exceeds 4 square inch. The holes should be 0.010 in. in diameter on a 0.050-in. pitch. Because vent holes in the metallization will introduce voids, they are not recommended on pads located directly under a high-heat-generating device. 

The removal of heat from laser diodes or other small localized heat generating devices. 

The heat loads rejected by active components such as the pumps, motors and other heat generating devices that are necessary for the operation of the auxiliary systems serving and dependent on the ultimate heat sink should be considered in selecting the ultimate heat sink for all operational states and design basis accident conditions. 

Reaction can be initiated by several means, aH of which depend on deHvery of heat at a relatively high temperature to a starting cone. Cartridge-actuated and electric match units are usuaHy used. The former is in the majority. A water-activated unit has been described (12). The heat generated by the starting device initiates reaction in a cone, which is a smaH amount of candle that is higher in fuel content, eg, 30 wt % iron. Compared to... 

The dust-ignition-proof protection concept excludes dust from entering the device enclosure and will not permit arcs, sparks, or heat generated by the device to cause ignition of external suspensions or accumulations of the dust. Enclosure requirements can be found in ANSI/UL 1203-1994, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous Locations. ... 

With normal interrupting devices the fault current would last for only a few cycles (maximum up to one or three seconds, depending upon the system design). This time is too short to allow heat dissipation from the conductor through radiation or convection. The total heat generated on a fault will thus be absorbed by the conductor itself. 

The physical structures of microchip assemblies usually contain a number of thin films in contact, each of which plays a separate role in the performance of the device. As an example, in one structure a silicon thin film would be contacted on one face by a copper rod which conducts away die heat generated during computer operations, and on the other face by an aluminium thin film which acts as a connector to other silicon films. This aluminium film is in turn in contact with a ceramic layer containing other thin film devices, and widr copper pins which plug into the circuit board. 

Any of a number of steel tubes used simultaneously as heat transfer devices for both steam generation and boiler furnace cooling. Boiler tubes may be straight or bent. 

The dielectric and the conductors are selected to maximize data transmission speed while miiumizing signal loss. In addition, dissipating heat generated by the microcircuits is rapidly becoming an important consideration. If too much heat builds up in the microelectronic device. 

To evaluate the heat exchange/productivity performances of the device and its environment, an acid-base neutralization involving sulfuric acid and soda has been performed. It is an instantaneous and exothermic reaction with AH = —92.4 kj moP (NaOH). Each experiment is characterized by the initial concentration of the reactants (from 10 to 30% in mass of soda and from 5 to 12% in mass of sulfuric acid). These concentrations are varied in order to evaluate the behavior of the reactor with respect to different amounts of heat generated (from 0.4 to 1.3 kW). Each run is performed with a variable utility flow rate (from 1 to 3 m h ). 

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