Tamer Yilmaz

Effects of internal irreversibility and heat leakage on the finite time thermoeconomic performance of refrigerators and heat pumps

By using finite time thermodynamic theory, a performance analysis based on the thermoeconomic criterion has been performed for an irreversible refrigerator and a heat pump. The thermoeconomic objective function is defined as the cooling load for the refrigerator and the heating load for the heat pump per unit total cost. The optimal performances and design parameters which maximize the objective functions are investigated. The design parameters under the optimal conditions have been derived analytically, and then, the effects of internal irreversibility, heat leakage and the economical parameter on the global and optimal performances have been discussed.

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.

Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps

A performance analysis using finite time thermodynamic based on a thermoeconomic objective function has been performed for absorption irreversible refrigerators and heat pumps. The optimal design parameters at the maxima of the thermoeconomic objective functions for an absorption refrigerator and heat pump have been derived analytically, and the effects of the internal irreversibility, the economical parameter and the external temperatures on the global and optimal performances have been discussed.

Exergy optimization for an endoreversible cogeneration cycle

Exergy optimization has been carried out for an endoreversible cogeneration cycle using finite-time thermodynamics. The optimum values of the design parameters of the cogeneration cycle at maximum exergy output were determined. Our model is more general than the endoreversible power cycle found in the literature. The effects of design parameters on exergetic performance are investigated and the results discussed.

Optimization of cogeneration systems under alternative performance criteria

In this study, a performance analysis based on alternative performance criteria has been performed for a reversible Carnot cycle, modified for cogeneration, with external irreversibilities. The optimum values of the design parameters of the cogeneration cycle were determined for different criteria. In this context, the effects of design parameters on the exergetic performance are investigated, and the results are discussed. The obtained results may guide towards a more realistic criterion for actual cogeneration plants.

Optimization of a regenerative gas-turbine cogeneration system based on a new exergetic performance criterion: Exergetic performance coefficient

Abstract A performance analysis and an optimization based on a new exergetic performance criterion named exergetic performance coefficient (EPC) have been carried out for an irreversible regenerative gas-turbine cogeneration system. The EPC objective function defined as the total exergy output per unit loss rate of availability is taken as the optimization criterion. The design parameters and performances under optimal conditions have been investigated and the results obtained are compared with those obtained using the alternative criteria given in the literature. It is shown that for the regenerative gas-turbine cogeneration system, a design based on the maximum EPC conditions is more advantageous from the viewpoint of entropy generation rate, exergy efficiency, and investment cost.

A new performance criterion for heat engines: efficient power

AbstractMany performance analyses have been carried out based on two comparative criteria namely maximum power (mp) and maximum power density (mpd). Researchers involved in power maximization studies have utilized the thermal efficiency at mp (Curzon–Ahlborn efficiency) as an efficiency standard for practical heat engines. On the other hand, maximum power density studies showed that the efficiency at mpd is always greater than that at the mp, while the power output from heat engines reduces. In this study, a new performance analysis is applied to a reversible Carnot cycle based on a new criterion which is proposed for all kind of heat engines. The proposed criterion, called efficient power, is defined as the multiplication of power by efficiency. This criterion considers not only the power output, but also the cycle efficiency. Maximizing the efficient power gives a compromise between power and efficiency. The results showed that the design parameters at maximum efficient power (mep) conditions lead to mo...

A comparative performance analysis of irreversible Carnot heat engines under maximum power density and maximum power conditions

This paper reports the finite time thermodynamic optimization based on the maximum power density criterion for an irreversible Carnot heat engine model which includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The obtained results are compared with those results obtained by using the maximum power criterion. The design parameters under the optimal conditions have been derived analytically and the effects of the irreversibilities on the general and optimal performances are investigated. The results showed that the design parameters at maximum power density lead to smaller and more efficient heat engines. It is also seen that the irreversibilities have a greater influence on the performances at maximum power density conditions with respect to the ones at maximum power conditions. Also in this study, the optimal conductance allocation parameter is investigated at both maximum power density and maximum power conditions by assuming a constrained total thermal conductance in the case when there is no heat leakage. The relation between the conductance allocation parameter and the thermal efficiencies at maximum power density and maximum power is also investigated. The obtained results generalize the result of previous studies on this subject and provide guidance to optimal design in terms of power, thermal efficiency and engine sizes for real heat engines.

Performance optimization of a gas turbine-based cogeneration system

In this paper an exergy optimization has been carried out for a cogeneration plant consisting of a gas turbine, which is operated in a Brayton cycle, and a heat recovery steam generator (HRSG). In the analysis, objective functions of the total produced exergy and exergy efficiency have been defined as functions of the design parameters of the gas turbine and the HRSG. An equivalent temperature is defined as a new approach to model the exergy rate of heat transfer from the HRSG. The optimum design parameters of the cogeneration cycle at maximum exergy are determined and the effects of these parameters on exergetic performance are investigated. Some practical mathematical relations are also derived to find the optimum values of the adiabatic temperature ratio for given extreme temperatures and consumer temperature.

Power and Efficiency Analysis of Brayton Cycles with Internal Irreversibility

Abstract In this article, power and efficiency analysis of irreversible Brayton cycle, which is one of the well-known heat engine cycles by the undergraduates, are carried out based on alternative criteria. Power, power density, and efficient power optimizations are also realized and the thermal efficiencies of the cycle are determined at maximum power and efficiency outputs. The efficient power is relatively new criterion and defined as the multiplication of power by efficiency. Therefore, this criterion considers not only the power output but also the cycle efficiency. Maximizing the efficient power function gives a compromise between power and efficiency. The effects of the external irreversibilities on the performances are investigated for various cycle parameters.