Fundamentals of exergy analysis, entropy generation minimization, and the generation of flow architecture

2002 ◽  
Vol 26 (7) ◽  
pp. 0-43 ◽  
Author(s):  
Adrian Bejan
Keyword(s):  
Entropy Generation ◽  
Exergy Analysis ◽  
Entropy Generation Minimization

Exergy Analysis and Entropy Generation Minimization of Thermoelectric Waste Heat Recovery for Electronics

2011 ◽  
Author(s):  
Kazuaki Yazawa ◽  
Ali Shakouri
Keyword(s):  
Entropy Generation ◽  
Energy Recovery ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Exergy Analysis ◽  
Waste Heat ◽  
Electronic Systems ◽  
Maximum Output ◽  
Entropy Generation Minimization ◽  
Energy Payback

Energy recovery from waste heat is attracting more and more attention. All electronic systems consume electricity but only a fraction of it is used for information processing and for human interfaces, such as displays. Lots of energy is dissipated as heat. There are some discussions on waste heat recovery from the electronic systems such as laptop computers. However the efficiency of energy conversion for such utilization is not very attractive due to the maximum allowable temperature of the heat source devices. This leads to very low limits of Carnot efficiency. In contrast to thermodynamic heat engines, Brayton cycle, free piston Stirling engines, etc., authors previously reported that thermoelectric (TE) can be a cost-effective device if the TE and the heat sink are co-optimized, and if some parasitic effects could be reduced. Since the heat already exists and it is free, the additional cost and energy payback time are the key measures to evaluate the value of the energy recovery system. In this report, we will start with the optimum model of the TE power generation system. Then, theoretical maximum output, cost impact and energy payback are evaluated in the examples of electronics system. Entropy Generation Minimization (EGM) is a method already familiar in thermal management of electronics. The optimum thermoelectric waste heat recovery design is compared with the EGM approach. Exergy analysis evaluates the useful energy flow in the optimum TE system. This comprehensive analysis is used to predict the potential future impact of the TE material development, as the dimensionless figure-of-merit (ZT) is improved.

scholarly journals Exergy Analysis of a Domestic Refrigerator

2018 ◽  
Vol 24 (9) ◽  
pp. 1 ◽  
Author(s):  
Loauy Abd Al-Azez Mahdi ◽  
Wahid S. Mohammad ◽  
Samir Akram Mahmood
Keyword(s):  
Entropy Generation ◽  
Exergy Analysis ◽  
Thermal Conductance ◽  
Internal Surface ◽  
Exergy Efficiency ◽  
System Component ◽  
Minimum Entropy ◽  
Internal Surface Area ◽  
Domestic Refrigerator ◽  
Entropy Generation Minimization

An energy and exergy thermodynamic analysis using EES program was done for a domestic refrigerator working with R-134a using vapor compression refrigeration cycle. The analysis deals with the system component, i.e. compressor, condenser, evaporator and the expansion device. The analysis depends on the entropy generation minimization approach to improve the refrigerator performance by exploring the optimum design points. These design points were derived from three different theories governing the entropy generation minimization using exergy analyzing method. These theories were first applied to find the optimum balance between the hot inner condenser area and the cold inner evaporator area of the refrigerator and between its hot and cold thermal conductances. Nine types of condensers were used according to its internal surface area and thermal conductance, in order to reach the minimum entropy generation in the refrigerator. The results showed that the compressor has the lowest exergy efficiency of 25%. The expansion device was the second component after the compressor with exergy efficiency of 92%, followed by the condenser with an efficiency of 93%. The evaporator was found to have an exergy efficiency of 98 %. The experimental tests were repeated for the nine condensers sizes with three different ambient temperatures 25℃, 30℃ and 35℃.  The exergy analysis showed that the design of the refrigerator mainly depends on thermal conductance calculations rather than the surface inner area estimation.  

Entropy Generation Minimization in a Tubular Solid Oxide Fuel Cell

2010 ◽  
Vol 132 (1) ◽  
Author(s):  
Adriano Sciacovelli ◽  
Vittorio Verda
Keyword(s):  
Fuel Cell ◽  
Solid Oxide Fuel Cell ◽  
Entropy Generation ◽  
Energy Equation ◽  
Solid Oxide ◽  
Geometrical Parameters ◽  
Oxide Fuel ◽  
Cell Geometry ◽  
Cell Efficiency ◽  
Entropy Generation Minimization

The aim of the paper is to investigate possible design modifications in tubular solid oxide fuel cell geometry to increase its performance. The analysis of the cell performances is conducted on the basis of the entropy generation. The use of this technique makes it possible to identify the phenomena provoking the main irreversibilities, understand their causes and propose changes in the system design and operation. The different contributions to the entropy generation are analyzed in order to develop new geometries that increase the fuel cell efficiency. To achieve this purpose, a CFD model of the cell is used. The model includes energy equation, fluid dynamics in the channels and in porous media, current transfer, chemical reactions, and electrochemistry. The geometrical parameters of the fuel cell are modified to minimize the overall entropy generation.

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