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

2010 ◽  
pp. 33-33
Author(s):  
Chen Lingen ◽  
Li Jun ◽  
Sun Fengrui
Keyword(s):  
Complex System ◽  
Heat Transfer ◽  
Power Output ◽  
Maximum Power ◽  
Maximum Power Output

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.

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.

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.

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

1996 ◽  
Vol 24 (1) ◽  
pp. 25-36 ◽  
Author(s):  
F. Moukalled
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Engineering Students ◽  
Radiation Heat Transfer ◽  
Maximum Power ◽  
Radiation Heat ◽  
Maximum Power Output ◽  
Relative Contribution ◽  
Special Cases ◽  
New Formulation

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.

scholarly journals Local Stability of Curzon-Ahlborn Cycle with Non-Linear Heat Transfer for Maximum Power Output Regime

2013 ◽  
Vol 04 (07) ◽  
pp. 22-27 ◽  
Author(s):  
Delfino Ladino-Luna ◽  
Pedro Portillo-Díaz ◽  
Ricardo T. Páez-Hernández
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Local Stability ◽  
Maximum Power ◽  
Maximum Power Output ◽  
Linear Heat ◽  
Non Linear
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