High-temperature systems

The problems of a DTA apparatus for operation above 1200 C are quite different from those lhat operate below this lemperature. The electrical 

The furnace consisted of an alundum core, which was wound with platinum-20% rhodium resistance wire. A booster coil of Nichrome wire was also wound on the two ends of the core this was used only for the very high-temperature work. The differential temperatures were detected with platinum versus platinum-10% rhodium thermocouples, inserted in the indentations of the platinum sample and reference cups. To shield the thermocouple wires, platinum foil was wound around the ceramic insulating tubes used to bring them into the furnace hot zone. 

A commercially available temperature programmer, dc amplifier, and two-point recorder were employed. Furnace heating rates of from 0 to 30cC/min were possible. 

A high-temperature DTA furnace and sample holder which does not use thermocouples as temperature sensors has been described by Nedumov (80). A critical assessment of various instruments that do employ thermocouples found that they were unsatisfactory for quantitative DTA studies of metals and metallic alloys. Temperature detection in this apparatus is by use of tungsten resistance thermometers. The apparatus can be used to temperatures over 3000°C. 

Kocherzhinsky (137) described a DTA apparatus, using a special type of thermocouple, that is capable of operation in argon atmospheres to temperatures up to 2450°C. The thermocouples did not use ceramic insulation in the high-temperature furnace area. 

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Reforming is completed in a secondary reformer, where air is added both to elevate the temperature by partial combustion of the gas stream and to produce the 3 1 H2 N2 ratio downstream of the shift converter as is required for ammonia synthesis. The water gas shift converter then produces more H2 from carbon monoxide and water. A low temperature shift process using a zinc—chromium—copper oxide catalyst has replaced the earlier iron oxide-catalyzed high temperature system. The majority of the CO2 is then removed. 

For the high temperature systems, dicyandiamide and aromatic-amine hardeners are frequendy used. For room temperature systems, polyamide aminoamide, and aliphatic-amine hardeners are preferred. 

The values of s/k are less dran 600 K for most of the simple molecules which are found in high temperature systems, and hence the collision integral may be assumed to have a value of unity in tlrese systems. 

For a high-temperature system, a separate subheader may be run up to the point where the temperature drops down to the allowable limit of a less expensive material. It may then be connected to the main flare header (either low pressure or high pressure).To properly evaluate this a heat loss calculation is needed. As a rule of thumb a heat loss of 10 BTU/hr/ft may be assumed for a quick estimate for bare pipe. Consideration should also be given to the need for expansion joints. Main flare headers may be as large as 36 to 42 inches in diameter for a large-capacity plant. Expansion joints of such magnitudes may be so expensive as to call for a separate small header for the hot flare system. 

Fried, J. R, Heat-Transfer Agents for High-Temperature Systems, Chem. Eng, May 28 (1973) p. 89. 

A large variety of oils is available, and recommendations for any set of conditions, compressor type and refrigerant can be obtained from the refiners. They are naphthene or paraffin-based oils. Synthetic lubricants have been developed for ultra-low-and high-temperature systems, especially for process heat pumps. 

Besides the two battery systems, a third high temperature system has been under development for a long time lithium aluminum iron sulfide (LiAl/FeS2) [1], This... 

A prerequisite of long-life sodium/sulfur batteries is that the cells contain suitable corrosion-resistant materials which withstand the aggressively corrosive environment of this high—temperature system. Stackpool and Maclachlan have reported on investigations in this field [17], The components in an Na/S cell are required to be corrosion-resistant towards sodium, sulfur and especially sodium polysulphides. Four cell components suffer particularly in the Na/S environment the glass seal, the anode seal, the cathode seal, and the current collector (in central sodium arrangements, the cell case). 

As a rule, because of the high temperatures, electrochemical reactions in melts are fast and involve little polarization. For such reactions the exchange current densities are as high as 10 to KFmA/cm. Therefore, reactivities in melts (and also in high-temperature systems with solid electrolytes) are usually determined not by kinetic but by thermodynamic features of the system. 

In electrocatalysis, the major subject are redox reactions occurring on inert, nonconsumable electrodes and involving substances dissolved in the electrolyte while there is no stoichiometric involvement of the electrode material. Electrocatalytic processes and phenomena are basically studied in aqueous solutions at temperatures not exceeding 120 to 150°C. Yet electrocatalytic problems sometimes emerge as well in high-temperature systems at interfaces with solid or molten electrolytes. 

Grayson and Stread (1963) extended the Chao-Seader equation for use with hydrogen rich mixtures, and for high pressure and high temperature systems. It can be used up to 200 bar and 4700 K. 

The various contributions to the energy of a molecule were specified in Eq. (47). However, the fact that the electronic partition function was assumed to be equal to one should not be overlooked. In effect, the electronic energy was assumed to be equal to zero, that is, that the molecule remains in its ground electronic state. In the application of statistical mechanics to high-temperature systems this approximation is not appropriate. In particular, in the analysis of plasmas the electronic contribution to the energy, and thus to the partition function, must be included. 

The dispersive tendency dominates in a high-temperature system containing only a few particles, while the order tendency is important in a system in which the particles are themselves ordered, as in a crystal or the DNA helix. The real states of systems of matter lie somewhere between these two extremes. 

Brinkley, S. R., Jr., 1960, Discussion of A brief survey of past and curent methods of solution for equilibrium composition by H. E. Brandmaier and J. J. Harnett. In G. S. Bahn and E. E. Zukoski (eds.), Kinetics, Equilibria and Performance of High Temperature Systems. Butterworths, Washington DC, p. 73. 

With the exception of these fractionation pathways, studies of igneous systems chiefly focus on the potential of Li isotopes as geochemical tracers fingerprinting the cycling of Li derived from specific (low-temperature) sources through the solid Earth. The sections below deal with observations of Li isotopes in high-temperature systems, and the mechanisms for low-temperature fractionation processes are discussed after, imder the heading, Planetary surface systems. ... 

In a 1994 U.S. Department of Energy (DOE) study on system benefits associated with high-temperature melters. Brown et al. reported that high-temperature systems allowed for higher mass loading, a more dense final waste form, and required a lower characterization frequency than lower temperature Joule melters. In an estimate based on the treatment of DOE mixed... 

The installation cost for a humid air injection system varies from about 15,000 for a 50-kW plastic pipe system to about 45,000 for a 200-kW high-temperature system. The operating costs would be about 3600 and 8000 per month, respectively. 

Editors, "Kinetics, Equilibria and Performance of High Temperature Systems , Proceedings of the 1st Conference, Western States Section, The Combustion Institute, Los Angeles, Calif, 2-5 Nov 1959, published by Butterworths, Washington, DC (I960). This includes papers by ... 

Currently interest has now been directed toward a similar high temperature system, the ZEBRA Battery, which also uses P-alumina as a Na ion conductor. The sulfur electrode is replaced by nickel chloride or by a mixture of ferrous and nickel chlorides. Contact between the NiCl2 electrode and the solid electrolyte is poor as they are both solids, and current flow is improved by adding a second liquid electrolyte (molten NaAlCb) between this electrode and the P-alumina. The overall cell reaction is now ... 

R. L. Bond In studying high temperature systems the problems associated with minerals in coal should also be investigated, and 1 would make a plea that as much work should be done on the minerals at high temperatures as on the carbon/hydrogen-containing particles. 

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