Transient Exergy Analysis for Solar Desalination Processes

2013 ◽  
Author(s):  
Gregory J. Kowalski ◽  
Masoud Modaresifar ◽  
Mansour Zenouzi
Keyword(s):  
Entropy Production ◽  
Alternative Energy ◽  
Second Law ◽  
Entropy Production Rate ◽  
Production Rates ◽  
Renewable Energy Systems ◽  
Solar Desalination ◽  
Second Law Analysis ◽  
Storage Term ◽  
Variable Energy

An investigation of the transient entropy property term, entropy storage, for a desalination device was performed. It was illustrated that entropy production rates provide a means of comparing alternative energy solutions and a measure of their sustainability. To satisfy these objectives one needs accurate calculation of entropy production rates. It was confirmed that neglecting the exergy storage term is not a valid approximation for the hourly and daily averaged values of the second law analysis. For a solar desalination system neglecting the exergy storage terms introduced a maximum difference in the entropy production rate of 7.4% and a difference of 7.3% in the daily average. In the solar desalination process with heat recovery the second law performance is greater than that for the reverse osmosis process, the chief competitor, when the exergy storage terms are correctly included in the analysis. The results demonstrate that for variable energy sources such as renewable energy systems, the second law analysis provides a measure of the sustainability of competing system and that the exergy storage terms should be included in the analysis.

Significance of Transient Exergy Terms in a New Tray Design Solar Desalination Device

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Gregory J. Kowalski ◽  
Masoud Modaresifar ◽  
Mansour Zenouzi
Keyword(s):  
Energy Recovery ◽  
Alternative Energy ◽  
Energy Systems ◽  
Second Law ◽  
Exergy Destruction ◽  
Renewable Energy Systems ◽  
Solar Desalination ◽  
Second Law Analysis ◽  
Storage Term ◽  
Variable Energy

An investigation of the transient exergy property term, exergy storage, for a new desalination tray design was performed. It was illustrated that exergy destruction rates provide a means of comparing alternative energy solutions and a measure of their sustainability. To satisfy these objectives one needs accurate calculation of exergy destruction rates. It was confirmed that neglecting the exergy storage term is not a valid approximation for the hourly and daily averaged values of the second law analysis. For a solar desalination system neglecting the exergy storage terms introduced a maximum difference in the exergy destruction rate of 7.4% and a difference of 7.3% in the daily average. In the solar desalination process with energy recovery the second law performance is greater than that for the reverse osmosis (RO) process, the chief competitor, when the exergy storage terms are correctly included in the analysis. The results demonstrate that for variable energy sources such as renewable energy systems, the second law analysis provides a measure of the sustainability of competing system and that the exergy storage terms should be included in the analysis.

A Micro Combined Heat and Power Thermodynamic Analysis and Optimization

2010 ◽  
Author(s):  
Ali Gholizadeh ◽  
M. B. Shafii ◽  
M. H. Saidi
Keyword(s):  
Combustion Chamber ◽  
Entropy Production ◽  
Thermodynamic Analysis ◽  
Second Law Of Thermodynamics ◽  
Combined Heat And Power ◽  
Second Law ◽  
Entropy Production Rate ◽  
Prime Mover ◽  
Operation Condition ◽  
Laws Of Thermodynamics

In modeling and designing micro combined heat and power cycle most important point is recognition of how the cycle operates based on the first and second laws of thermodynamics simultaneously. Analyzing data obtained from thermodynamic analysis employed to optimize MCHP cycle. The data obtained from prime mover optimization has been used for basic stimulus cycle. Assumptions considered for prime mover optimization has been improved, for example in making optimum operation condition by using genetic algorithms constant pressure combustion chamber was considered. The exact value of downstream and upstream pressure changes in the combustion chamber reaction has been obtained. After extraction of the appropriate relationship for the primary stimulus cycle, data required for the overall cycle analysis identified, By using these data optimum total cycle efficiency and constructing the first and second laws of thermodynamics has been calculated for it. After reviewing Thermodynamic governing relations in each cycle and using the optimum values that the prime mover has been optimized with, other cycles have been optimized. In best performance condition of cycle, electrical efficiency was 41 percent and the overall efficiency of the cycle was 88 percent, respectively. After using the second law of thermodynamics mathematical model Second law of thermodynamics efficiency and entropy production rate was estimated. Second law of thermodynamics yield best performance against the 45.14 percent and the rate of entropy production in this case equal to 0.099 kW/K respectively.

Second Law Analysis of Condensing Steam Flows

2018 ◽  
Author(s):  
Marius Grübel ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Entropy Production ◽  
Turbulent Flows ◽  
Operating Conditions ◽  
Second Law ◽  
Test Case ◽  
Relaxation Processes ◽  
Minor Importance ◽  
Two Phase ◽  
Second Law Analysis ◽  
Aerodynamic Losses

A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian-Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes. With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer and shock losses. The application of the method is demonstrated by means of the flow through a well known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.

Second Law Analysis of Condensing Steam Flows

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Marius Grübel ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Entropy Production ◽  
Turbulent Flows ◽  
Operating Conditions ◽  
Second Law ◽  
Test Case ◽  
Relaxation Processes ◽  
Minor Importance ◽  
Two Phase ◽  
Second Law Analysis ◽  
Aerodynamic Losses

A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work, the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian–Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes. With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer, and shock losses. The application of the method is demonstrated by means of the flow through a well-known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.

scholarly journals Continuum mechanics beyond the second law of thermodynamics

2014 ◽  
Vol 470 (2171) ◽  
pp. 20140531 ◽  
Author(s):  
M. Ostoja-Starzewski ◽  
A. Malyarenko
Keyword(s):  
Entropy Production ◽  
Continuum Mechanics ◽  
Past History ◽  
Decomposition Theorem ◽  
Viscosity Coefficient ◽  
Material Point ◽  
Second Law ◽  
Entropy Production Rate ◽  
Hyperbolic Heat Conduction ◽  
Spatial And Temporal Scales

The results established in contemporary statistical physics indicating that, on very small space and time scales, the entropy production rate may be negative, motivate a generalization of continuum mechanics. On account of the fluctuation theorem, it is recognized that the evolution of entropy at a material point is stochastically (not deterministically) conditioned by the past history, with an increasing trend of average entropy production. Hence, the axiom of Clausius–Duhem inequality is replaced by a submartingale model, which, by the Doob decomposition theorem, allows classification of thermomechanical processes into four types depending on whether they are conservative or not and/or conventional continuum mechanical or not. Stochastic generalizations of thermomechanics are given in the vein of either thermodynamic orthogonality or primitive thermodynamics, with explicit models formulated for Newtonian fluids with, respectively, parabolic or hyperbolic heat conduction. Several random field models of the martingale component, possibly including spatial fractal and Hurst effects, are proposed. The violations of the second law are relevant in those situations in continuum mechanics where very small spatial and temporal scales are involved. As an example, we study an acceleration wavefront of nanoscale thickness which randomly encounters regions in the medium characterized by a negative viscosity coefficient.

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