Bahri Sahin

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.

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.

Finite time thermoeconomic optimization for endoreversible refrigerators and heat pumps

This paper reports a new kind of finite time thermoeconomic optimization for an endoreversible refrigerator and a heat pump. The cooling load for the refrigerator and the heating load for the heat pump per unit total cost are proposed as objective functions for the optimization. The optimum performance parameters which maximize the objective functions are investigated. Since the optimization technique consists of both investment and energy consumption costs, the obtained results are more general and realistic.

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.

Performance analysis of an endoreversible heat engine based on a new thermoeconomic optimization criterion

A new kind of finite time thermoeconomic optimization analysis for an endoreversible heat engine has been performed. The objective function has been taken as the power output per unit total cost. The optimum performance parameters that maximize the objective function are investigated. In this perspective, some analytical equations for the optimum working fluid temperatures, optimum thermal efficiency, optimal distributions of heat exchanger areas and optimum specific power output were found in terms of economical and technical parameters. The effects of the design parameters on the optimal conditions have been discussed.

A comparative performance analysis of irreversible regenerative reheating Joule-Brayton engines under maximum power density and maximum power conditions

A performance analysis based on the maximum power density criterion has been carried out for an irreversible regenerative reheating Joule-Brayton engine. The obtained results were compared with those obtained using the maximum power performance criterion. The design parameters under the optimal conditions have been derived analytically and their effects on the engines performance have been discussed. The overall effects of reheating, regeneration and internal irreversibilities are investigated. The obtained results may provide a general theoretical tool for the optimal design and operation of real non-regenerative and regenerative reheating gas turbines.

Performance and exhaust emission characteristics of a lower compression ratio LHR Diesel engine

Abstract In this study, the effects of reducing the compression ratio on the performance and exhaust emissions in a low heat rejection (LHR) indirect injection Diesel engine have been experimentally compared to those obtained from a standard Diesel engine (SDE) with fixed compression ratio. Reducing the compression ratio in a SDE without making any modification in the combustion chamber geometry and improvements in fuel properties cause the ignition delay time to be unduly long, and consequently, an unacceptable pressure rise is experienced. By means of high temperature increases in the combustion chamber of the LHR Diesel engine, the compression ratio was lowered from 18.20 to 16.10 in 0.7 intervals. Satisfactory performance was obtained at compression ratios of 17.50 and 16.80 in the LHR engine. In comparison to the SDE, at these compression ratios, the specific fuel consumption and NO x emissions are, respectively, decreased about 2.9% and 15%.

An approach for analysing transportation costs and a case study

One of the important parameters in the determination of optimal transportation system is economy. Therefore, a realistic method based on the technical, economical and operational parameters of various transportation modes, namely, road, railway, and sea routes is required in the analysis of costs. This method will take into consideration the probable price escalations during the lifetime of a certain transportation system. The cost of a unit of cargo or passenger per route length should be considered since it is an indicator of economics. In this paper, an approach for transportation cost analysis based on the economic analysis of the alternative modes of cargo or passenger transportation, is presented.

The effects of intercooling and regeneration on the thermo-ecological performance analysis of an irreversible-closed Brayton heat engine with variable-temperature thermal reservoirs

A thermo-ecological performance analysis of an irreversible intercooled and regenerated closed Brayton heat engine exchanging heat with variable-temperature thermal reservoirs is presented. The effects of intercooling and regeneration are given special emphasis and investigated in detail. A comparative performance analysis considering the objective functions of an ecological coefficient of performance, an ecological function proposed by Angulo-Brown and power output is also carried out. The results indicate that the optimal total isentropic temperature ratio and intercooling isentropic temperature ratio at the maximum ecological coefficient of performance conditions (ECOPmax) are always less than those of at the maximum ecological function ( ) and the maximum power output conditions ( ) leading to a design that requires less investment cost. It is also concluded that a design at ECOPmax conditions has the advantage of higher thermal efficiency and a lesser entropy generation rate, but at the cost of a slight power loss.