The only economic way of producing sufficiently high flame temperature for m.h.d. power generation using fossil fuels is to burn them with air preheated to at least 1200° C. The factors affecting the design of suitable air heaters for the high temperature stage of this process will be discussed and the features of three general types will be described. One of these is a completely novel concept in which a circulating stream of molten material is used to transfer heat between hot combustion products and air. Experiments which are being carried out to provide design data for these three types will be described and cover the pumping and atomization of high temperature fluids; the testing of suitable refractory materials; aerodynamic model studies; the development of refractory seals. Seeding chemicals introduced to enhance gas conductivity pose special problems of corrosion and deposition in the air heaters and investigations into the interdependent processes of heat and mass transfer will be described. Since the seed cannot be allowed to escape from the system, studies of recovery processes will be referred to in the paper.
After some brief definitions, the paper deals with the influence of a regenerative air preheater on the performance of a simple open-cycle gas turbine, and formulas are given to show this influence, as well as the connection between the regenerator dimensions and the condition of minimum fuel consumption.
This paper deals with recuperative plate-type heat-exchanger elements for a composite air preheater for automotive gas turbines. The general requirements and optimization of the essential dimensions of such an element are discussed.
Such optimization leads to the smallest possible weight for a given temperature and pressure efficiency. As these two efficiencies affect the specific fuel consumption of the gas turbine, two further optimizations lead to: (a) The best pressure ratio of the turbomachines for given initial temperatures; and (b) the best temperature and pressure efficiency of the air preheater. The weight of this heat exchanger affects the performance of the vehicle propelled by the gas-turbine unit in different ways. Further optimization therefore leads to the best weight of the air preheater at a given average speed.
Cost considerations which affect the design of the element are influenced by the method of manufacture and the choice of materials as well as the method of maintaining clean channels in the heat-exchanger elements.
Possible configurations for an automotive gas-turbine unit are considered. Comparisons are made of designs taking the drive from the high-pressure and low-pressure portions of a split turbine, as well as the advantages to be gained with a divided-compressor and differential-gear arrangement.
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