Internal Irreversible Losses Research Articles

Performance evaluation and parametric optimum design of an updated thermionic-thermoelectric generator hybrid system

An updated model of the hybrid system consisting of a vacuum TIG (thermionic generator) and a multi-couple TEG (thermoelectric generator) is proposed, in which the main internal and external irreversible losses of the system are considered and the temperatures of the electrode plates of the TIG and the cold side of the TEG are determined by energy balance equations rather than some specified parameters. Analytical expressions for the power output and efficiency of the TIG, TEG, and hybrid system are derived. The effects of the voltage output and work functions of the TIG and the electric current of the TEG on the power output and efficiency are discussed. The maximum power output and efficiency of the hybrid system are numerically calculated. The optimally operating regions of main parameters are determined.

Parametric design criteria of an irreversible vacuum thermionic generator

A new model of the vacuum thermionic generator (TIG) including internal and external irreversible heat losses is proposed. The energy balance equations of the cathode and anode of the TIG are used to determine the operating temperatures of two electrode plates. Analytic expressions for the power output and efficiency of the system are derived. The power output and efficiency under different conditions are optimized. The effects of the work functions of electrode materials and the output voltage on the performance of the system are discussed. The optimal regions of several important parameters are determined. The optimum design criteria, which may provide some guidance for the choice of electrode materials and the operation of the TIG, are obtained.

Performance analysis of irreversible Atkinson cycle with considerations of stroke length and volumetric efficiency

This paper presents finite time thermodynamics analysis of an irreversible air standard Atkinson cycle. An irreversible Atkinson cycle model, which is closer to practice, is established. In this model, the effects of stroke length and volume efficiency by considering the non‐linear relation between the specific heats of working fluid and its temperature, the frictional loss, the internal irreversibility and heat transfer loss are analysed. The results show that if compression ratio is less than certain value, the power output increases with increasing stroke length, while if compression ratio exceeds certain value, the power output first increases and then starts to decrease with increasing stroke length. With further increasing compression ratio, the increase in stroke length results in a decrease in the power output. The results also show that, throughout the compression ratio range, the power output increases with increasing volumetric efficiency. The results obtained in the present study are of importance to provide good guidance for performance evaluation and improvement of practical internal combustion engines.