Advanced Energy Conversion最新文献

For the design of efficient joining methods and the evaluation of the long term stability of thermoelectric junctions, a basic knowledge of the appropriate phase equilibria is desirable. The chemical reaction behavior of lead- and tin-telluride with a number of metals was therefore surveyed.

Guertle's “Klar-Kreuz” method has been used to establish the direction of the reactions: $\text{x}\text{PbTe}\text{+ y}\text{M}\text{↔}\text{M}{}_{\mathrm{y}}\text{Te}{}_{\mathrm{x}}\text{+ x}\text{Pb}$ or the corresponding reactions with SnTe.

For the metals investigated with PbTe it was found, that in the case of Ti, V, Cr, Mn, Zn, Ga, Zr, Nb, Cd, In and Ta the reaction goes from left to right. For Fe and W it proceeds from right to left. In the cases of Ni, Cu, Ag and Mo the equilibria are more complex and cannot be described by the cited equation. Reactions of SnTe with metals were quite similar. Again, Mn, Zn, Cd and Ta were found to react from left to right, Fe and W from right to left. Here, too, Ni, Cu, Ag and Mo followed more complex equilibria.

The relations governing the conversion of chemical energy to mechanical or electrical energy are examined. It is shown that there is no fundamental disadvantage in having a heat engine as part of the conversion system. The free energy change of the chemical reaction limits the upper temperature at which heat can be supplied to a heat engine.

A study is presented for the optimization of the coefficient of performance of a thermoelectric heat pump through the use of cascaded stages. Throughout the investigation it is assumed that the electrical and thermal conductivities of the n- and p-type elements are the same and are constant. It is further assumed that there are no electrical or thermal contact resistances and that the element is completely insulated except at the hot and cold junctions. It is shown that small variations about the optimal interstage temperatures have a negligible effect on the C.O.P. of the cascade. In addition it is shown that in many cases only limited gains are made in the C.O.P. through cascaded thermoelectric heat pumps.

In the report a brief account is given of a large experimental complex MHD-power plant for open-cycle operation with combustion products of natural gas. The main distinguishing feature of such a plant in comparison with existing ones consists in the fact that with its help it is possible to investigate not only the MHD-generator itself but also other complicated components of MHD-power plants as well as to investigate the operation of major components of the MHD-power plant. Presumably the question as to the prospective application of open-cycle MHD-power plants for large-scale power generation can be answered only after the solution of complicated research and engineering problems associated with the development of a large-scale commercial pilot plant.

Another distinguishing feature of the described plant lies in the fact that it is intended for a long-period service.

The report gives main parameters of the plant, describes the technological scheme and its major components: the combustion chamber, the MHD-channel, the magnet system, facilities for injection and recovery of ionizing seeding, high-temperature air preheaters, end heat-exchanger systems, current inverting systems, etc.

Also the report gives a summary of the obtained experimental results. The MHD-generator output power amounted to 30 kW.

The comparison of the results on thermal and gasdynamic investigation carried out in the MHD-channel with theoretical calculations made on a refined one-dimensional flow model showed that they agree

After the investigations carried out on the described plant conditions were obtained not only for further wide-scale magnetohydrodynamic thermophysical and electrophysical investigations of MHD-power plants but also for the continuation of the work for investigating a simultaneous operation of the MHD-generator with other components of the plant as well as for developing more rational designs of the components and conditions for their operation.

The approach taken has been to utilize experimental heat loss data in a computer synthesization of operating boundaries. Further selective running was then undertaken to confirm the results obtained.

The purpose of this paper is to describe, and to indicate the possible operating range of, a new unit which employs unique multiply-overlapped electrodes operating on the re-entrant rail accelerator principle. It has been developed to simulate re-entry conditions and the inlet conditions of air-breathing propulsion devices.

This paper describes an experimental evaluation of cesiated tungsten and cesiated rhenium thermionic emitter surfaces prepared by different methods. Two sorts of evaluation are presented. In the first, the average emission characteristics of these surfaces are described by graphs of cesiated work function φ vs the ratio of surface temperature T to cesium reservoir temperature T_R. Details of the work function distribution for certain surfaces are also obtained and related to the average characteristics. In the second method, surfaces are evaluated in terms of the electrical output of thermionic converters utilizing these surfaces as emitters (cathodes). For certain materials curves of power density, and of current density, vs. output voltage are presented, where each curve has cesium reservoir temperature and interelectrode spacing optimized, and emitter temperature appears as a parameter. Other curves show output power density as a function of emitter temperature, at specified output voltage and spacing.

It is well known that sintered samples of Bi₂Te₃ and its alloys have an apparent electrical conductivity that is highest perpendicular to the direction of pressing. However, measurements of electrical resistance do not indicate whether this is due to preferred orientation of the grains or to the formation of aligned cracks. Studies of sintered material have, therefore, been made using an X-ray reflection technique and, also, measurements of the Seebeck coefficient in the region of mixed-conduction. Preferred orientation has been found throughout hot-pressed samples, but in cold-pressed material such orientation has either been absent or confined to the surface layers. It is concluded that hot-pressing is preferable to cold-pressing in the production of sintered thermoelements.

In preparing ingots of thermoelectric materials by pressing anisotropic powders partial alignment occurs. A theoretical model is proposed which enables the electrical and thermal conductivities of the ingot to be predicted. For the purpose of this prediction measurements of the conductivities in principal directions have been made on good single crystals of alloys in the range 0–20 mol.% Bi₂Se₃ in Bi₂Te₃. The theory is compared with pressed powdered materials from this system. It is concluded that some alignment occurs.

During recent months it has become possible to make thin film solar cells with conversion efficiencies greater than 5 per cent and areas as large as 50 cm². The state of the art in this field is reviewed with emphasis on papers presented at the past several photovoltaic Specialists Conferences. Solar cells using thin films of CdS, CdTe and GaAs are discussed in detail. The fabrication, structure and properties of these cells are described and related to their solar conversion efficiency, specific power to weight ratio and environmental stability. In addition, the characteristics of these thin film cells are discussed in terms of criteria for practical space application.