Endoreversible Heat Engine Research Articles

Performance of a regenerative Brayton heat engine

The performance of an endoreversible regenerative Brayton heat engine has been studied. The analysis is focused on minimizing irreversibilities associated with the hot and cold heat exchangers and regenerator.

Analysis of waste-heat thermoelectric power generators

A real thermoelectric power generator utilizing waste heat is proposed. The generator is treated as an external and internal irreversible heat engine. The specific power output of the generator is analyzed and compared with that of the Carnot, endoreversible and external reversible thermoelectric heat engines.

96/00738 Stabilization of a propane-air flame in longitudinal and transverse electric fields

The thermoeconomics of endoreversible heat engines has been studied based on the linear phenomenological heat-transfer law [i.e., the heat flux Q ∝ Δ(1/T), where T is the absolute temperature]. Analytical formulae for profit, the maximum profit and the corresponding efficiency are derived.

The Efficiency at Maximum Power Output of Endoreversible Engines under Combined Heat Transfer Modes

A mathematical model for investigating the performance of endoreversible heat engines under combined conduction, convection, and radiation heat transfer modes is presented. The model is suitable to be introduced to engineering students attending a course in thermodynamics who may apply it to predicting the performance of real engines and a variety of energy conversion systems in a simplified manner. Results generated by the model show that the relative contribution of conduction/convection and radiation heat transfer modes deeply affect the efficiency at maximum power output. Moreover, a number of well-known formulae presented in several references are shown to represent special cases of the new formulation.

The equivalent cycle system of an endoreversible absorption refrigerator and its general performance characteristics

We show that an absorption-refrigeration system affected by the irreversibility of finite-rate heat transfer may be modelled as a combined cycle, which consists of an endoreversible heat engine and an endoreversible refrigerator. Finite-time thermodynamics of endoreversible heat engines and refrigerators is used to optimize the primary performance parameters such as the coefficient of performance, specific cooling load, heat-transfer areas of heat exchangers, temperatures of the working fluid in heat exchangers, and rate of entropy production.

Performance of solar-pond thermoelectric power generators

SYNOPSIS A real thermoelectric power generator utilizing heat from a solar pond is proposed. The generator is treated as an external and internal irreversible heat engine. The specific power output of the generator is analysed and compared with that of the Carnot, endoreversible, and external reversible thermoelectric heat engines.

On an irreversible air standard Otto-cycle model

We present a simplified model for an irreversible Otto cycle which accounts for the characteristic power-versus-efficiency curve of real heat engines. This model avoids the usual hypotheses of endoreversible heat engines and it considers an air Otto engine with internally dissipative friction and a pure sinusoidal law for the piston velocity on the adiabatic branches.

The maximum power output and maximum efficiency of an irreversible Carnot heat engine

The effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine is investigated using a new cyclic model. The power output and efficiency of the heat engine are adopted as objective functions for heat engine optimization. The optimal performance of the heat engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the heat engine at maximum power output and the power output of the heat engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the heat engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot heat engine. It is pointed out that all the conclusions concerning a reversible Carnot heat engine, an endoreversible Carnot heat engine only affected by thermal resistance and an irreversible Carnot heat engine with internal irreversibility and/or heat leakage can be deduced from the results in this paper.

Finite-Time Thermodynamics and Endoreversible Heat Engines

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.

Power optimization of an irreversible heat engine

We study the power and efficiency of an irreversible heat engine coupled to heating and cooling fluids with finite heat-capacity rates. We consider a specific model, for which the irreversibilities result from the finite rates of heat conductance and the internal irreversibility of the heat engine. The maximum power obtainable from such a system and the corresponding efficiency are derived analytically to provide more realistic limits on the performance of an irreversible heat engine than those obtained from a reversible heat engine. It is seen that two different optimal conditions must be determined. These are the optimal operating temperatures of the working fluids and the optimal allocation fraction of the heat conductance between the heating and cooling fluids. In the limit in which the heat-capacity rates approach infinity, the efficiency of an endoreversible heat engine at maximum power approaches the Curzon-Ahlborn efficiency. The calculated efficiency at maximum power is close to that actually observed in well-designed power plants.

Generalized power versus efficiency characteristics of heat engines: The thermoelectric generator as an instructive illustration

The performance of real heat engines can be characterized by their power versus efficiency curves. Real heat engines with sources of irreversibility that include friction and heat leaks exhibit fundamentally different power versus efficiency curves than those predicted by many previous studies in the finite-time thermodynamics of endoreversible heat engines, in which finite-rate heat transfer was the only irreversibility considered. It is shown that the thermoelectric generator provides an instructive illustration of a cyclic, irreversible heat engine with a power versus efficiency curve that qualitatively reproduces the key features of the corresponding curves for real heat engines. The generic sources of irreversibility are easily identifiable and analytically expressed so as to reveal more transparently the basis for the power versus efficiency characteristic.

Endoreversible thermodynamics and chemical reactions

Endoreversible processes were originally modeled as the following special class of irreversible processes: In endoreversible processes the irreversibilities are all located in the transport of heat from the heat sources to the heat engine and from the heat engine to the heat sinks. The present paper demonstrates that it is advantageous to generalize this definition as follows: In endoreversible processes all irreversibilities are located in the transport of heat and/or matter from the heat and/or matter sources to the engine and from the engine to the heat and/or matter sinks. We demonstrate how this generalization allows us to model a class of chemical reactors in the same way as endoreversible heat engines

Power optimization of an endoreversible Brayton gas heat engine

The power output of a simple endoreversible Brayton gas heat engine is analyzed and optimized. The endoreversible engine is defined as a power cycle in which the two processes of heat transfer from and to the surrounding heat reservoirs are the only irreversible processes in the Brayton cycle. A mathematical expression is derived for the power output of the irreversible heat engine. The power optimization provides the basis for designing a real gas heat engine and for a performance comparison with existing Brayton power plants.

Finite-time optimizations of a heat engine

We study the power and efficiency of a finite-time heat engine. We consider an endoreversible Carnot heat engine coupled to heating and cooling fluids and determine the maximum power output and efficiency to obtain a bound on the power-conversion systems. While the maximum power and the operating temperatures of the heat engine are functions of the heat-reservoir temperatures, heat-reservoir capacity rates and heat-transfer rates, the efficiency at maximum power depends primarily on the initial temperatures of the heating and cooling fluids. The efficiency at maximum power provides a measure of the power available in a practical heat engine.

Observations on efficiency of heat engines operating at maximum power

The behavior of the efficiency of a general class of cyclic endoreversible heat engines at maximum power point is considered. The functional temperature dependence of heat transfer is considered as a variable, and its physical significance is addressed. It is shown that a broader spectrum of solutions emerges for efficiency at maximum power, as a function of the relevant system parameters, than originally realized. Specifically, it is proved that efficiency at maximum power is in general not independent of the heat-transfer coefficients, and that a type of ‘‘symmetry’’ exists relative to the functional temperature dependence of Newtonian heat conduction. The ‘‘Curzon–Ahlborn efficiency’’ of finite-time thermodynamics is shown not to be a fundamental upper limit on the efficiency of an endoreversible engine at maximum power point. Rather, this upper limit depends both on the functional temperature dependence of the heat transfer and on the relative value of the hot- and cold-side heat-transfer coefficients.

Production function of a simple model internal combustion engine

The paper deals with an analysis in terms of production function of a simplified Beau de Rochas irreversible engine. The combustion reaction is the main source of irreversibility. The production function is concave. This property is an extension of similar behaviours for endoreversible heat engines. Copyright © 1989 John Wiley & Sons, Ltd.

Optimal staging of endoreversible heat engines

One way to classify performance indices of irreversible heat engines is according to how the indices change when one engine is replaced by two (or more) of the same kind in series. We investigate the performance of two endoreversible engines (i.e., heat engines with the only irreversibility being heat resistance to the surroundings) which are put in series to form a single engine, whose power output is maximized. In this unconstrained optimization the interface between the two stages, which for the present model is the intermediate temperature and the relative timing of the two engines, is arbitrary and can be used to satisfy other, nonthermodynamic constraints. Adding any constraint on the volume of the working gas does not lift this indeterminacy. The optimum composite system is equivalent to a single endoreversible engine, thus displaying a sequencing property similar to Carnot engines.