Selahattin Göktun

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.

Design parameters of a radiative heat engine

By employing an endoreversible heat-engine model, the design parameters of a heat engine operating under radiative heat-transfer conditions were examined to find the maximum power output. It was found that the ratio of the cold to the hot reservoir temperature must be less than 0.2 for an optimal design. Increasing the heat-transfer area of the cold side rather than that of the hot side improves the thermal efficiency. When the temperature ratio is greater than 0.6, the efficiency of such a cycle approaches that of Curzon and Ahlborn.

Optimal performance of an irreversible refrigerator With three heat sources (IRWTHS)

An IRWTHS may be treated as a combined cycle of a finite-size irreversible Carnot heat engine driving an irreversible Carnot refrigerator. This system is analyzed using finite-time thermodynamics. The combined effects of finite-rate heat transfer and internal dissipation on optimal performance have been investigated.

Performance analysis of a heat engine driven combined vapor compression-absorption-ejector refrigerator

An endoreversible heat engine driven refrigeration cycle based on the combination of an absorption cycle with vapor and ejector compression cycles is described. This integration maximizes the performance of the conventional ejector and absorption cycles and provides high performance for refrigeration. The analysis shows that the combined cycle has a significant increase in system performance over the heat engine driven vapor compression refrigerators and heat engine driven combined vapor compression and absorption refrigerators.

Optimal performance of a combined absorption and ejector refrigerator

The performance of a combined absorption and ejector refrigerator for which the only irreversibility results from the finite rate of heat conduction is studied. A steady flow approach of finite time thermodynamics is applied to calculate the optimum coefficient of performance (COP). The combined cycle gives an increase of about 40% in the COP compared to that of an absorption cycle.

The optimum performance of a solar-assisted combined absorption–vapor compression system for air conditioning and space heating

The technique of energetic optimization is employed to investigate the optimal performance of an irreversible hybrid air-conditioning/heat pumping system consisting of a vapor compression refrigerator cascaded with a solar-driven absorption refrigerator. To get closer to a real system, the effect of internal irreversibilities on the performance of the hybrid system is considered. The optimal operating temperature of the solar collector and the maximum overall coefficient of performance (COP) of the cooling and heating modes of the system are derived. The results obtained here have more realistic meaning than those of reversible thermodynamics for the optimal design and operation of practical solar-driven hybrid systems.

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.

Solar powered cogeneration system for air conditioning and refrigeration

By employing the energetic optimization technique, the optimal performance of a focusing collector-driven, an irreversible Carnot cogeneration system for air conditioning and refrigeration is investigated. A minimum value for the total solar insolation needed to overcome internal irreversibilities for start-up of the system is defined and the effect of the collector design parameters on this value is investigated.

Optimization of irreversible solar assisted ejector-vapor compression cascaded systems

The technique of energetic optimization is employed to investigate the optimal performance of focusing collector driven, irreversible Carnot ejector-vapor compression cascaded cooling and heating systems. The optimal operating temperature of the solar collector and the maximum overall coefficient of performance of the cooling and heating modes of the combined system are derived. The results obtained here may serve as a good guide for the evaluation of existing real solar assisted hybrid systems.