Thermodynamic modeling of heat engines including heat transfer and compression-expansion irreversibilities

2021 ◽  
pp. 1-15
Author(s):  
Julian D. Osorio ◽  
Alejandro Rivera ◽  
Obie Abakporo ◽  
Juan C Ordonez ◽  
Rob Hovsapian
Keyword(s):  
Heat Transfer ◽  
Maximum Power ◽  
Thermodynamic Cycles ◽  
Heat Exchanger Design ◽  
Heat Engines ◽  
Proposed Model ◽  
Compression And Expansion ◽  
Effective Conductance ◽  
Conductance Ratio ◽  
Isentropic Efficiency

Abstract In this work, a thermodynamic model based on endoreversible engine approach is developed to analyze the performance of heat engines operating under different thermodynamic cycles. The model considers finite heat transfer rate, variable heat source and sink temperatures, and irreversibilities associated with the expansion and compression. Expressions for the maximum power and efficiency at maximum power output are obtained as a function of hot and cold reservoir temperatures, the equivalent isentropic efficiency of compression and expansion components, and the effective conductance ratio between heat exchangers. In all cases, the Curzon-Ahlborn efficiency is retrieved at constant reservoir temperatures and neglected compression-expansion irreversibilities. The proposed model allows assessing the effect of isentropic efficiencies and heat exchanger design and operation characteristics for different thermodynamic cycles.

The Regenerative Criteria of an Irreversible Brayton Heat Engine and its General Optimum Performance Characteristics

2005 ◽  
Vol 128 (3) ◽  
pp. 216-222 ◽  
Author(s):  
Yue Zhang ◽  
Congjie Ou ◽  
Bihong Lin ◽  
Jincan Chen
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Pressure Ratio ◽  
Heat Engine ◽  
Optimal Performance ◽  
Performance Characteristics ◽  
Heat Transfer Area ◽  
Total Heat Transfer ◽  
Heat Engines ◽  
Compression And Expansion

An irreversible cycle model of the Brayton heat engine is established, in which the irreversibilities resulting from the internal dissipation of the working substance in the adiabatic compression and expansion processes and the finite-rate heat transfer in the regenerative and constant-pressure processes are taken into account. The power output and efficiency of the cycle are expressed as functions of temperatures of the working substance and the heat sources, heat transfer coefficients, pressure ratio, regenerator effectiveness, and total heat transfer area including the heat transfer areas of the regenerator and other heat exchangers. The regenerative criteria are given. The power output is optimized for a given efficiency. The general optimal performance characteristics of the cycle are revealed. The optimal performance of the Brayton heat engines with and without regeneration is compared quantitatively. The advantages of using the regenerator are expounded. Some important parameters of an irreversible regenerative Brayton heat engine, such as the temperatures of the working substance at different states, pressure ratio, maximum value of the pressure ratio, regenerator effectiveness and ratios of the various heat transfer areas to the total heat transfer area of the cycle, are further optimized. The optimal relations between these parameters and the efficiency of the cycle are presented by a set of characteristic curves for some assumed compression and expansion efficiencies. The results obtained may be helpful to the comprehensive understanding of the optimal performance of the Brayton heat engines with and without regeneration and play a theoretical instructive role for the optimal design of a regenerative Brayton heat engine.

Finite-Time Thermodynamics and Endoreversible Heat Engines

1993 ◽  
Vol 21 (4) ◽  
pp. 337-346 ◽  
Author(s):  
C. Wu ◽  
R. L. Kiang ◽  
V. J. Lopardo ◽  
G. N. Karpouzian
Keyword(s):  
Heat Transfer ◽  
Finite Time ◽  
Heat Engine ◽  
Power Production ◽  
Maximum Power ◽  
The Other ◽  
Finite Time Thermodynamics ◽  
Equilibrium Time ◽  
Heat Engines ◽  
Maximum Value

An endoreversible heat engine is an internally reversible and externally irreversible cyclic device which exchanges heat and power with its surroundings. Classical engineering thermodynamics is based on the concept of equilibrium. Time is not considered in the energy interactions between the heat engine and its environment. On the other hand, although rate of energy transfer is taught in heat transfer, the course does not cover heat engines. The finite-time thermodynamics is a newly developing field to fill in the gap between thermodynamics and heat transfer. Two types of engines are modelled in this paper—a reciprocating and a steady flow—with results obtained for maximum power output and efficiency at maximum power. It is shown that the latter is the same for both types of engines but that the maximum value of power production is different.

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