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The cooling of the wall and bottom of a blast furnace hearth is a problem of great practical importance for the blast-furnace campaign. The aim of this paper is a review of the literature on the subject and the presentation of the results regarding the temperature distribution in the hearth refractories of a blast furnace obtained by numerical calculations and under suitable hypotheses.

Cogeneration, i.e. the combined production of electrical and thermal power at an energy conversion plant, has received significant attention particularly since the oil crises of the 70s. The idea of cogeneration is attractive due to the very low exergy efficiency of traditional separate heating plants, using every kind of fuel. The aim of this paper is to compare the usual energy analysis with a meaningful exergy analysis of a combined thermal and electrical power plant. The above exergy analysis is also the basis for a proper allotment of costs between electrical and thermal energy at various temperatures.

It is possible to obtain valuable energy recoveries by means of a combined plant for electrical energy production and liquid hydrogen vaporization and superheating with a closed cycle helium turbine with nuclear heating. Even if the properly defined exergy efficiency is not very high, it must be observed that the ratio of the exergy of the obtained electrical energy to the exergy of the thermal energy entering into the combined plant is higher than the one of the usual best combined plants. The energy and exergy analyses developed in this paper are aimed to evaluate pros and cons of the considered system.

The aim of this paper is to consider a combined system consisting of a gas turbine driving the compressor of a vapour compression refrigerating cycle with a non-azeotropic mixture to reduce irreversibilities in the evaporator and in the condenser; the exhaust gas energy is utilized in the generator of an absorption cycle with combination of H2O-LiBr; in addition, the energy released from the absorber and condenser of both cycles is recovered in the form of hot water to be used for different applications. From the point of view of thermodynamics the system considered in the paper has one exergy inlet and two useful exergy outlets, one at temperatures above that of the environment and the other under that of the environment. By the thermodynamic analysis of this paper, the entropy productions and exergy destructions of the several phases are put in evidence for a proper comparison.

Some authors assume that the second law efficiency of reversed cryogenic cycles is independent of the minimum temperature of the working fluid. On the contrary Bejan shows, by empirical and theoretical arguments, that exergy efficiency values decrease as the minimum temperature goes down. However, there is no guaranteeing that exergy efficiency vs. minimum temperature is continuous with its derivatives. The aim of this paper is to study the thermodynamic optimization by the variation of the heat transfer rate in a finite number of points through insulation for the general case of one-dimensional heat transfer (flat plate, hollow cylinder and hollow sphere) in systems, consisting of different materials in series, whose thermal conductivity is a function of temperature and of the coordinate in the heat flux direction. Besides, some parameters or their first derivative are assumed stepwise continuous.

The research to substitute chlorinated fluorocarbons (CFC) has brought to repropose fluids already used in the past and also totally new solutions. Among these, the utilization of air has been proposed since this fluid is devoid of any pollution effect; some authors have pointed out its advantages by means of rather sophisticated cycles. However, it is easy to demonstrate that air can not be a competitor as regards two-phase fluids when the cycle exergy efficiency is a fundamental element. Notwithstanding, there are cases in which other considerations are prevailing, as in the case of airplanes in which air is soundly used. An innovative concept of using aircycle technology for the development of a microclimate-cooling device for military and industrial applications has been recently proposed. For this last case, a thermodynamic analysis is here carried out to state pros and cons of such systems.