Effects of Irreversibility and Economics on the Performance of a Heat Engine

Previous investigators have shown that an internally reversible Carnot cycle, operating with heat transfer limitations between the heat source and heat sink at temperatures TH and TL, achieves maximum power at an efficiency equal to 1−TL/TH independent of the heat exchanger transfer coefficients. In this paper, optimization of the power output of an internally irreversible heat engine is considered for finite capacitance rates of the external fluid streams. The method of Lagrange multipliers is used to solve for working fluid temperatures which yield maximum power. Analytical expressions for the maximum power and the cycle efficiency at maximum power are obtained. The effects of irreversibility and economics on the performance of a heat engine are investigated. A relationship between the maximum power point and economically optimum design is identified. It is demonstrated that, with certain reasonable economic assumptions, the maximum power point of a heat engine corresponds to a point of minimum life-cycle costs.

Download Full-text

A Micro Heat Engine Executing an Internal Carnot Cycle

ASME 2008 2nd International Conference on Energy Sustainability, Volume 2 ◽

10.1115/es2008-54266 ◽

2008 ◽

Cited By ~ 1

Author(s):

Eli Lurie ◽

Abraham Kribus

Keyword(s):

Strong Dependence ◽

Heat Engine ◽

Thermodynamic Cycle ◽

Maximum Power ◽

Working Fluid ◽

Carnot Cycle ◽

Heating And Cooling ◽

Engine Design ◽

Power Point ◽

Micro Heat Engine

A micro heat engine, based on a cavity filled with a stationary working fluid under liquid-vapor saturation conditions and encapsulated by two membranes, is described and analyzed. This engine design is easy to produce using MEMS technologies and is operated with external heating and cooling. The motion of the membranes is controlled such that the internal pressure and temperature are constant during the heat addition and removal processes, and thus the fluid executes a true internal Carnot cycle. A model of this Saturation Phase-change Internal Carnot Engine (SPICE) was developed including thermodynamic, mechanical and heat transfer aspects. The efficiency and maximum power of the engine are derived. The maximum power point is fixed in a three-parameter space, and operation at this point leads to maximum power density that scales with the inverse square of the engine dimension. Inclusion of the finite heat capacity of the engine wall leads to a strong dependence of performance on engine frequency, and the existence of an optimal frequency. Effects of transient reverse heat flow, and ‘parasitic heat’ that does not participate in the thermodynamic cycle are observed.

Download Full-text

Analytical expressions for the determination of the maximum power point and the fill factor of a solar cell

Solar Cells ◽

10.1016/0379-6787(82)90008-4 ◽

1982 ◽

Vol 5 (4) ◽

pp. 377-386 ◽

Cited By ~ 48

Author(s):

G.L Araujo ◽

E Sánchez

Keyword(s):

Solar Cell ◽

Fill Factor ◽

Maximum Power ◽

Maximum Power Point ◽

Power Point ◽

Analytical Expressions

Download Full-text

On the Impact of the Dynamics of Heat Transfer of the Thermal Machine Working Fluid and Heat Sources on the Shape of the Boundary of the Set of Realizable Regimes

ChemEngineering ◽

10.3390/chemengineering3020036 ◽

2019 ◽

Vol 3 (2) ◽

pp. 36

Author(s):

Margarita Zaeva ◽

Anatoly Tsirlin ◽

Olga Didina

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Energy Conversion ◽

Conversion Efficiency ◽

Heat Engine ◽

Energy Conversion Efficiency ◽

Maximum Power ◽

Working Fluid ◽

Transfer Coefficients ◽

The Impact

From the point of view of finite time thermodynamics, the performance boundaries of thermal machines are considered, taking into account the irreversibility of the heat exchange processes of the working fluid with hot and cold sources. We show how the dynamics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, in particular, energy conversion efficiency in the maximum power mode. This energy conversion efficiency can depend only on the ratio of the heat transfer coefficients to the sources, or not depend on them at all. A class of dynamic functions corresponding to “natural” requirements is introduced and it is shown that, for any dynamics from this class, the optimal cycle consists of two isotherms and two adiabats, not only for the maximum power problem, but also for the problem of maximum energy conversion efficiency at a given power. Examples are given for calculating the parameters of the optimal cycle for the cases when the heat transfer coefficient to the cold source is arbitrarily large, and for dynamics in the form of a linear phenomenological (Fourier heat transfer) law.

Download Full-text

Analytical Modeling of the Maximum Power Point with Series Resistance

Applied Sciences ◽

10.3390/app112210952 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10952

Author(s):

Alfredo Sanchez Garcia ◽

Rune Strandberg

Keyword(s):

Solar Cell ◽

Analytical Modeling ◽

Series Resistance ◽

Maximum Power ◽

Maximum Power Point ◽

Solar Cell Efficiency ◽

Cell Parameters ◽

Cell Efficiency ◽

Power Point ◽

Analytical Expressions

This paper presents new analytical expressions for the maximum power point voltage, current, and power that have an explicit dependence on the series resistance. An explicit expression that relates the series resistance to well-known solar cell parameters was also derived. The range of the validity of the model, as well as the mathematical assumptions taken to derive it are explained and discussed. To test the accuracy of the derived model, a numerical single-diode model with solar cell parameters whose values can be found in the latest installment of the solar cell efficiency tables was used. The accuracy of the derived model was found to increase with increasing bandgap and to decrease with increasing series resistance. An experimental validation of the analytical model is provided and its practical limitations addressed. The new expressions predicted the maximum power obtainable by the studied cells with estimated errors below 0.1% compared to the numerical model, for typical values of the series resistance.

Download Full-text