Hasbi Yavuz

Efficiency of a Joule-Brayton engine at maximum power density

A new kind of power analysis is conducted on a reversible Joule-Brayton cycle. Although many performance analyses have been carried out resulting in famous efficiencies (Carnot, Curzon-Ahlborn), most do not consider the sizes of the engines. In the studies of Curzon and Ahlborn and others, researchers utilized the thermal efficiency at maximum power as an efficiency standard for practical heat engines. In this paper, instead of just maximizing power for certain cycle parameters, the power density defined as the ratio of power to the maximum specific volume in the cycle, is maximised. Therefore the effects of the engine sizes were included in the analysis. The result showed a new type of efficiency at the maximum power density which is always greater than that at the maximum power (Curzon-Ahlborn efficiency). Evaluations show that design parameters at the maximum power density lead to smaller and more efficient Joule-Brayton engines.

Maximum power density analysis of an irreversible Joule - Brayton engine

A performance analysis based on a power density criterion has been carried out for an irreversible Joule - Brayton (JB) heat engine. The results obtained were compared with those of a power performance criterion. It is shown that design parameters at maximum power density lead to smaller and more efficient JB engines than an engine working at maximum power output conditions. Due to irreversibilities in the heat engine, the power and thermal efficiency will reduce by a certain amount, however the maximum power density conditions still give a better performance than at the maximum power output conditions. The analysis demonstrated in this paper may provide a basis for the determination of optimal operating conditions and the design parameters for real JB heat engines.

Thermal efficiency of a regenerative Brayton cycle with isothermal heat addition

The effect of two heat additions, rather than one, in a gas turbine engine is analysed using a regenerative Brayton cycle model, where all fluid friction losses in the compressor and turbine are quantified by an isentropic efficiency term and all global irreversibilities in the regenerator are taken into account by means of an effective efficiency. It has been established that the application of an isothermal heat addition process in regenerative gas turbine engines may result in significant efficiency improvements of over 10% compared with conventional engines. Moreover, substantial reductions of pollutant emissions are expected.

Optimal design of the regenerative gas turbine engine with isothermal heat addition

A regenerative gas turbine engine, with isothermal heat addition, working under the frame of a Brayton cycle has been analyzed. With the purpose of having a more efficient small-sized gas turbine engine, the optimization has been carried out numerically using the maximum power (MP) and maximum power density (MPD) method. The effects of internal irreversibilities have been considered in terms of the isentropic efficiencies of the turbine and compressor and of the regenerator efficiency. The results summarized by figures show that the regenerative gas turbine engine, with isothermal heat addition, designed according to the maximum power density condition gives the best performance and exhibits highest cycle efficiencies.

Analysis of the stirling heat engine at maximum power conditions

The Stirling heat engine operating in a closed regenerative thermodynamic cycle is analyzed. Polytropic processes are used for the power and displacement pistons. Following regeneration, the maximum power density and efficiency are found and the compression ratio at maximum power density is determined.

Exergy analysis of a pressurized-water reactor nuclear-power plant

An exergy analysis based on the second law of thermodynamics is performed to evaluate the plant and subsystem irreversibility of a nuclear power plant (NPP) with a pressurized-water reactor (PWR). The construction of such a system having a maximum reactor core thermal power of 4250 MW is proposed in Turkey and China. This study concentrates on the questions of where and how much of the available work is lost in such a plant. The evaluated exergy destruction of this plant indicates that the reactor pressure vessel including PWR is the most inefficient equipment in the whole NPP, while the turbines take the second place.

The maximum cooling density of a realistic Stirling refrigerator

The maximum cooling density of a Stirling refrigerator operating in a closed regenerative thermodynamic cycle is presented in this paper. The cooling density is the cooling load per unit volume of the refrigerator. Since the size of the refrigerator is involved in the cooling density, the maximization of the cooling density has given a critical compression ratio. The maximum cooling density serves as a better comparison criterion for thermoeconomic considerations.

An analysis of an endoreversible heat engine with combined heat transfer

The power optimization of an endoreversible heat engine has been performed, and design characteristics have been described at maximum-power conditions. A technologically important example defined as heat exchange by combined radiation and convection has been considered. The analysis shows that the maximum power output of the heat engine is sensitive to the temperature, small values of the ratio of convective heat transfer coefficients of hot to cold ends and small values of the emittance ratio of heat source to heat sink. By considering the output power, and must be held around 0.2, 0.01 and 0.0125 for optimum design considerations, respectively.

Analysis of an irreversible Ericsson engine with a realistic regenerator

An internally irreversible Ericsson engine, with a realistic regenerator, has been analyzed. The study considers internal irreversibilities with the introduction of turbine and compressor thermal-efficiencies and pressure-drops present in realistic regenerators. The effects of internal irreversibilities on the power output and thermal efficiency of the cycle have been determined using the finite-time thermodynamics. Maximum power-density, rather than maximum power, was used as the criterion for optimization, with the objective of having a more efficient small-sized engine.

The optimum performance of an irreversible solar-driven Carnot refrigerator and combined heat engine

By employing the energetic optimization technique, the optimal performance of a focusing collector-driven, irreversible Carnot refrigerator with three heat sources and a combined heat engine is investigated. A minimum operating parameter and a relation between the maximum overall efficiencies are obtained for the systems under consideration. A minimum value for the total solar insolation needed to overcome internal irreversibilities for start-up of the systems is defined and the effect of the collector design parameters on this value is investigated.