scholarly journals Optimal temperatures and maximum power output of a complex system with linear phenomenological heat transfer law

2009 ◽  
Vol 13 (4) ◽  
pp. 33-40 ◽  
Author(s):  
Lingen Chen ◽  
Jun Li ◽  
Fengrui Sun
Keyword(s):  
Complex System ◽  
Heat Transfer ◽  
Power Output ◽  
Finite Time ◽  
Heat Engine ◽  
Thermal Capacity ◽  
Maximum Power ◽  
Finite Time Thermodynamics ◽  
Maximum Power Output ◽  
Different Temperatures

A complex system including several heat reservoirs, finite thermal capacity subsystems with different temperatures and a transformer (heat engine or refrigerator) with linear phenomenological heat transfer law [q ? ?(T -1)] is studied by using finite time thermodynamics. The optimal temperatures of the subsystems and the transformer and the maximum power output (or the minimum power needed) of the system are obtained.

Finite Time Thermodynamics: Realizability Domain of Heat to Work Converters

2019 ◽  
Vol 44 (2) ◽  
pp. 181-191 ◽  
Author(s):  
M. A. Zaeva ◽  
A. M. Tsirlin ◽  
O. V. Didina
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Finite Time ◽  
Heat Engine ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Working Fluid ◽  
Finite Time Thermodynamics

Abstract 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. It is shown how the kinetics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, with a focus on the 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 kinetic functions corresponding to “natural” requirements is introduced and it is shown that for any kinetics 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 case when the heat transfer coefficient to the cold source is arbitrarily large and for kinetics in the form of a Fourier law.

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.

Maximum Power From Fluid Flow: Results From the First and Second Laws of Thermodynamics

2012 ◽  
Author(s):  
German Amador Diaz ◽  
John Turizo Santos ◽  
Elkin Hernandez ◽  
Ricardo Vasquez Padilla ◽  
Lesme Corredor
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Power Output ◽  
Power Plants ◽  
Cross Sectional Area ◽  
Maximum Power ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Power Output ◽  
Piston Cylinder

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is ηmax = 1/2(1 − P2/P1). This result is analog to the efficiency at maximum power for power plants, ηmax = 1 − (T2/T1)1/2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.

The Efficiency at Maximum Power Output of a Carnot Engine with Heat Leak

1995 ◽  
Vol 23 (2) ◽  
pp. 157-165 ◽  
Author(s):  
F. Moukalled ◽  
R. Y. Nuwayhid
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Maximum Power ◽  
Heat Leak ◽  
Suggested Model ◽  
Maximum Power Output ◽  
Transfer Processes ◽  
Newton’S Law ◽  
New Formulation ◽  
Special Case

Endoreversible thermodynamics are used for studying the performance of Carnot engines with heat leak. This is done by adding a heat leak term into a variation of the model suggested by DeVos [1]. Heat transfer across the engine is assumed to occur via a conduction/convection mechanism and Newton's law of cooling is employed to model the heat transfer processes. The efficiency at maximum power output is found to be deeply affected by the rate of heat leak. Moreover, the Curzon-Ahlborn relation [2] is shown to represent a special case of the new formulation. Since the suggested model allows more flexibility in predicting actual engines' performance, its use is recommended in thermodynamics courses.

Local-stability analysis of a low-dissipation heat engine working at maximum power output

2017 ◽  
Vol 96 (4) ◽  
Author(s):  
I. Reyes-Ramírez ◽  
J. Gonzalez-Ayala ◽  
A. Calvo Hernández ◽  
M. Santillán
Keyword(s):  
Stability Analysis ◽  
Power Output ◽  
Local Stability ◽  
Heat Engine ◽  
Maximum Power ◽  
Maximum Power Output ◽  
Local Stability Analysis ◽  
Low Dissipation

Enhancement and Optimization of Planar Impingement Heat Transfer for Thermoelectric Power Generation

2015 ◽  
Author(s):  
Kazuaki Yazawa ◽  
Stephen D. Heister ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Power Output ◽  
Heat Exchangers ◽  
Fluid Flows ◽  
Impinging Jet ◽  
Maximum Power ◽  
Counter Flow ◽  
Maximum Power Output ◽  
Impingement Heat Transfer

We present an analytic model and optimization of impingement heat transfer in fluid-to-fluid heat exchangers with integrating a thermoelectric (TE) generator between the hot and cold fluid flows. In power generation systems, designing for maximum power output generally involves balancing the external thermal resistances while the generator contacts the hot and cold temperature reservoirs. In fluid-to-fluid heat exchangers, fluid temperatures are not constant or uniform. They gradually change along the flow direction. In general, counter-flow heat exchangers outperform parallel flow configurations in maximizing TE power generation using internal fluid flows. We show here the performance of our impingement model compared with a counter-flow configuration as the base line. To obtain the maximum power output from practical thermoelectric materials (ZT values are 1.2–1.8), the enhancement of liquid-to-wall heat transfer is significant. An array of traditional impinging jet orifices provides a uniformly planar and focused heat transfer process that spatially targets the TE elements. This approach provides more uniform hot and cold side temperatures among the TE elements. We investigate the impact of introducing impingement orifices directly at the locations of the TE elements. The major focus of this work is the trade-off between the advantage of increasing power generation by impingement and the disadvantage of introducing additional pressure drop. Decreasing the external thermal resistances yields not only a larger maximum power output but also requires thinner TE elements. This enables lower cost per power generation capacity approaching the 0.2–0.3 $/W range as well as a more lightweight design. We report here the associated cost impacts for the impinging jet arrangement. Design optimization depends on the specific constraints and parameters, such as TE material and substrate thickness, flow design to avoid the stagnation, and required exit temperatures. In some cases, active pumping by an additional actuator can augment the enhancement, while a fraction of generated power is consumed for the actuation. In the paper, we show examples of gas and liquid flow cases.

Sign in / Sign up

Export Citation Format

Share Document