Limits of Performance for Alternate Fuel Energy to Mechanical Work Conversion Systems

2005 ◽  
Vol 128 (3) ◽  
pp. 229-235 ◽  
Author(s):  
George A. Adebiyi
Keyword(s):  
Heat Exchangers ◽  
Direct Conversion ◽  
Mechanical Work ◽  
Second Law ◽  
Alternate Fuel ◽  
Cell Conversion ◽  
Second Law Analysis ◽  
Exergy Consumption ◽  
Combustion Systems

The major alternatives for producing work from fuel energy include combustion systems and fuel cells. Combustion systems are subject to several performance-limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility of practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work. The significant exergy input required must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a simplified first- and second-law analysis for the limits of efficiency of these alternate systems for the conversion of fuel exergy to mechanical work, thus providing a more realistic comparison of the potential of both systems.

Limits of Performance for Alternate Fuel Energy to Mechanical Work Conversion Systems

2003 ◽  
Author(s):  
George A. Adebiyi
Keyword(s):  
Direct Conversion ◽  
Mechanical Work ◽  
Chemical Energy ◽  
Second Law ◽  
Alternate Fuel ◽  
Cell Conversion ◽  
Second Law Analysis ◽  
Exergy Consumption ◽  
Combustion Systems

The major alternatives for producing work from the chemical energy of fuels include combustion systems and fuel cells. Combustion systems are subject to several performance limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility or exergy consumption in practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work; such processes require significant exergy input that must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a first- and second-law analysis of the alternate systems for conversion of fuel exergy to mechanical work thus providing a more realistic comparison of the potential of both systems.

scholarly journals Evaluación de irreversibilidades en un sistema de refrigeración por absorción amoniaco-agua empleando tres modelos matemáticos diferentes para calcular las propiedades termodinámicas

2018 ◽  
Vol 27 (47) ◽  
Author(s):  
Iván Vera-Romero ◽  
Christopher Lionel Heard-Wade
Keyword(s):  
Individual Component ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Second Law ◽  
Base Case ◽  
Water Mixture ◽  
Absorption Refrigeration ◽  
Second Law Analysis ◽  
Exergy Analyses

Second Law or Exergy Analyses of Absorption Refrigeration Systems (ARS) are very important for optimisations based on available work; these analyses are derived from the operating conditions and property calculations. There are several methods available for calculating the thermodynamic properties used in modelling these systems. A thermodynamic study on an ARS with the ammonia-water mixture (base case) was carried out with the objective of analysing the sensitivity of the overall and individual component irreversibility to the thermodynamic property. To this end, three existing methods were used: (M1), a model proposed by Ibrahim and Klein (1993) and used in the Engineering Equation Solver (EES) commercial software; (M2), a model proposed by Tillner-Roth and Friend (1998) and embodied in REFPROP v.8.0 developed by the National Institute of Standards and Technology (NIST); and (M3), a method proposed by Xu and Goswami (1999) that was programmed for this analysis. The obtained differences in the properties and the first law performance of the ARS are insignificant in the determination of the coefficient of performance (COP) (base case: 0.595, M1: 0.596, M2: 0.594, M3: 0.599). For the second law analysis, the overall irreversibility was the same (123.339kW) despite the irreversibilities per component had important differences: the solution heat exchanger (M1: 5.783kW, M2: 6.122kW, M3: 8.701kW), the desorber (generator) (M1: 51.302kW, M2: 45.713kW, M3: 49.098kW) and the rectifier (M1: 0.766kW, M2: 3.565kW, M3: 0.427kW). The components that destroy exergy the most are the desorber, the absorber and the condenser.

scholarly journals Determination of the Real Loss of Power for a Condensing and a Backpressure Turbine by Means of Second Law Analysis

Entropy ◽  
2009 ◽  
Vol 11 (4) ◽  
pp. 702-712 ◽  
Author(s):  
Henrik Holmberg ◽  
Pekka Ruohonen ◽  
Pekka Ahtila
Keyword(s):  
Second Law ◽  
The Real ◽  
Second Law Analysis ◽  
Backpressure Turbine

Two Principles of Differential Second Law Heat Exchanger Design

1991 ◽  
Vol 113 (2) ◽  
pp. 329-336 ◽  
Author(s):  
R. B. Evans ◽  
M. R. von Spakovsky
Keyword(s):  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Second Law ◽  
First Principle ◽  
Heat Exchanger Design ◽  
Geometric Average ◽  
Mean Temperature ◽  
Second Law Analysis ◽  
Basic Treatment

In this paper, two fundamental principles of differential Second Law analysis are set forth for heat exchanger design. The first principle defines a Second Law temperature, while the second principle defines a Second Law temperature difference. The square of the ratio of the Second Law temperature difference to the Second Law temperature is shown always to be equal to the negative of the partial derivative of the rate of entropy generation (for heat transfer) with respect to the overall conductance of the heat exchanger. For the basic design of elementary heat exchangers, each of these two Second Law quantities is shown to take the form of a simple geometric average. Nonelementary considerations result in corrected geometric averages, which relate directly to the corrected log-mean temperature difference. Both the corrected log-mean temperature difference (nonelementary considerations) and the uncorrected or just log-mean temperature difference (elementary considerations) are widely used in heat exchanger analysis. The importance of these two principles in both exergy and essergy analysis is illustrated by a unified basic treatment of the optimum design of elementary heat exchangers. This results in a single optimization expression for all flow arrangements (i.e., counterflow, parallel flow, and certain crossflow cases).

scholarly journals Second-Law Analysis of a Double-Effect Evaporator with Thermal Vapor Compression

2021 ◽  
Vol 8 ◽  
pp. 50-61
Author(s):  
Ali Snoussi ◽  
Maha BenHamad
Keyword(s):  
Theoretical Work ◽  
Double Effect ◽  
Performance Criterion ◽  
Second Law ◽  
Vapor Compression ◽  
Future Design ◽  
Second Law Analysis ◽  
Work Input ◽  
Energy Balances

In this paper, we present a steady-state analysis of a double-effect evaporator with thermal vapor compression (MED-TVC) installed in the Tunisian Chemical Group (GCT) factory. A thermodynamic model including mass and energy balances of the system is developed and integrated in a Matlab program. The model resolution yields to the determination of the operating parameters of the plant and the Gain Output Rate (GOR) was found to be roughly equal to 5. In a second step, the simulation results served to conduct a second law analysis of the unit. The performance criterion used in this analysis is the second law efficiency, i.e., the ratio of the least theoretical work of separation to the actual work input to the plant. The second law efficiency was found to be 2.4%. The distribution of the irreversibility between the different components of the plant was, in addition, assessed. As a conclusion, it was established that the most irreversibility occurs in the thermo-compressor which contributes with more than 50% to the global imperfection and which presents an exergy efficiency of less than 77%. The remaining irreversibility comes from the three exchangers (the two evaporators and the condenser) with an average contribution of 16%. As it is very difficult to introduce modifications into an existing unit, we assume that the importance of the results is not limited to the studied unit. They serve, rather, as an aid to the future design of a MED-TVC plant.

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