scholarly journals Exergy Analysis in Hydrogen-Air Detonation

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Abel Rouboa ◽  
Valter Silva ◽  
Nuno Couto
Keyword(s):  
Mass Fraction ◽  
Exergy Analysis ◽  
Fluid Dynamic ◽  
Time Discretization ◽  
Euler System ◽  
Total Enthalpy ◽  
Finite Volume Discretization ◽  
System Equations ◽  
Hydrogen Mass ◽  
Exergy Losses

The main goal of this paper is to analyze the exergy losses during the shock and rarefaction wave of hydrogen-air mixture. First, detonation parameters (pressure, temperature, density, and species mass fraction) are calculated for three cases where the hydrogen mass fraction in air is 1.5%, 2.5%, and 5%. Then, exergy efficiency is used as objective criteria of performance evaluation. A two-dimensional computational fluid dynamic code is developed using Finite volume discretization method coupled with implicit scheme for the time discretization (Euler system equations). A seven-species and five-step global reactions mechanism is used. Implicit total variation diminishing (TVD) algorithm, based on Riemann solver, is solved. The typical diagrams of exergy balances of hydrogen detonation in air are calculated for each case. The energy balance shows a successive conversion of kinetic energy, and total enthalpy, however, does not indicate consequent losses. On the other hand, exergy losses increase with the augment of hydrogen concentration in air. It obtained an exergetic efficiency of 77.2%, 73.4% and 69.7% for the hydrogen concentrations of 1.5%, 2.5%, and 5%, respectively.

scholarly journals The Finite Volume WENO with Lax–Wendroff Scheme for Nonlinear System of Euler Equations

Mathematics ◽  
2018 ◽  
Vol 6 (10) ◽  
pp. 211 ◽  
Author(s):  
Haoyu Dong ◽  
Changna Lu ◽  
Hongwei Yang
Keyword(s):  
Finite Volume ◽  
Time Discretization ◽  
Euler System ◽  
Weno Scheme ◽  
Local Characteristic ◽  
Finite Volume Scheme ◽  
Mesh Structure ◽  
Hyperbolic Conservation Law ◽  
Higher Derivative ◽  
Accuracy Order

We develop a Lax–Wendroff scheme on time discretization procedure for finite volume weighted essentially non-oscillatory schemes, which is used to simulate hyperbolic conservation law. We put more focus on the implementation of one-dimensional and two-dimensional nonlinear systems of Euler functions. The scheme can keep avoiding the local characteristic decompositions for higher derivative terms in Taylor expansion, even omit partly procedure of the nonlinear weights. Extensive simulations are performed, which show that the fifth order finite volume WENO (Weighted Essentially Non-oscillatory) schemes based on Lax–Wendroff-type time discretization provide a higher accuracy order, non-oscillatory properties and more cost efficiency than WENO scheme based on Runge–Kutta time discretization for certain problems. Those conclusions almost agree with that of finite difference WENO schemes based on Lax–Wendroff time discretization for Euler system, while finite volume scheme has more flexible mesh structure, especially for unstructured meshes.

Impact on Overall Efficiency of Component Efficiency Increases for an Existing Thermal Electrical Generating Station

2002 ◽  
Author(s):  
Marc A. Rosen
Keyword(s):  
Exergy Analysis ◽  
Large Temperature ◽  
Efficiency Improvement ◽  
Combustion Heat ◽  
Component Efficiency ◽  
Pertinent Information ◽  
Electrical Generator ◽  
Overall Efficiency ◽  
Exergy Analyses ◽  
Exergy Losses

Most electrical generating utilities are striving to improve the efficiencies of their existing thermal electric generating stations, many of which are old. Exergy methods have been shown to provide meaningful insights that can assist in increasing the efficiency of conventional coal-to-electricity technologies. Here, exergy analysis is used to assess measures for improving the efficiencies of coal-fired electrical generating stations. This scope of the study is limited to minor practical improvements, which can be undertaken with limited effort and cost and are not overly complex. The plant considered is the coal-fired Nanticoke Generating Station (GS) in Ontario, Canada. The findings suggest that the results of exergy analyses should be used, along with other pertinent information, to guide efficiency improvement efforts for thermal generating stations. Also, efficiency improvement efforts should focus on plant components responsible for the largest exergy losses: the steam generator (where large losses occur from combustion heat transfer across large temperature differences), the turbines, the electrical generator and the transformer. Possible improvements in these areas should be assessed in conjunction with other criteria, and other components should be considered where economically beneficial improvements can be identified.

scholarly journals CFD-Exergy analysis of the flow in a small-sized Venturi

2020 ◽  
Vol 307 ◽  
pp. 01037
Author(s):  
Ahmed Razali ◽  
Mohammed Baghdad ◽  
Ahmed Ouadha
Keyword(s):  
Exergy Analysis ◽  
Velocity Gradients ◽  
Exergy Losses ◽  
Different Parts

The present study aims to compare cavitation models in predicting the flow in small-sized cavitating venturis. Three cavitation models, namely Schnerr and Sauer model, Zwart et al. Model and Singhal et al. Model have been compared under the mixture approach. Furthermore, the performance of this device has been assessed using the concept of exergy by quantifying the exergy losses accuring in its different parts. It is found that all models are capable of reproducing the physics of cavitation phenomena within the cavitating venturi. However, the Schnerr and Sauer model return higher values than the others model. It is also observed that most of the exergy losses occur in the converging and diverging parts of the venturi due to higher pressure and velocity gradients in these regions.

scholarly journals Exergy Analysis for Utilizing Latent Energy of Thermal Energy Storage System in District Heating

Energies ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1391 ◽  
Author(s):  
Joong Yong Yi ◽  
Kyung Min Kim ◽  
Jongjun Lee ◽  
Mun Sei Oh
Keyword(s):  
Power Generation ◽  
Energy Storage ◽  
Thermal Energy ◽  
Exergy Analysis ◽  
Heat Storage ◽  
Storage System ◽  
District Heating ◽  
Hydraulic Turbine ◽  
Storage Process ◽  
Exergy Losses

The thermal energy storage (TES) system stores the district heating (DH) water when the heating load is low. Since a TES system stores heat at atmospheric pressure, the DH water temperature of 115 °C has to be lowered to less than 100 °C. Therefore, the temperature drop of the DH water results in thermal loss during storage. In addition, the DH water must have high pressure to supply heat to DH users a long distance from the CHP plant. If heat is to be stored in the TES system, a pressure drop in the throttling valve occurs. These exergy losses, which occur in the thermal storage process of the general TES system, can be analyzed by exergy analysis to identify the location, cause and the amount of loss. This study evaluated the efficiency improvement of a TES system through exergy calculation in the heat storage process. The method involves power generation technology using the organic Rankine cycle (ORC) and a hydraulic turbine. As a result, the 930 kW capacity ORC and the 270 kW capacity hydraulic turbine were considered suitable for a heat storage system that stores 3000 m3/h. In this case, each power generation facility was 50% of the thermal storage capacity, which was attributed to the variation of actual heat storage from the annual operating pattern analysis. Therefore, it was possible to produce 1200 kW of power by recovering the exergy losses. The payback period of the ORC and the hydraulic turbine will be 3.5 and 7.13 years, respectively.

Hydrogen Storage in Small Size Hollow Microspheres

2012 ◽  
Vol 512-515 ◽  
pp. 1395-1399 ◽  
Author(s):  
Zhan Wen Zhang ◽  
Su Fen Chen ◽  
Yi Yang Liu ◽  
Lin Su ◽  
Mei Fang Liu ◽  
...  
Keyword(s):  
High Pressure ◽  
Elevated Temperature ◽  
Hydrogen Storage ◽  
Vapor Deposition ◽  
Mass Fraction ◽  
Hoop Stress ◽  
Hydrogen Gas ◽  
Hollow Microspheres ◽  
Hydrogen Mass ◽  
Pressure Hydrogen

Hollow microspheres with less than 1 millimeter in diameter and several micrometers in wall thickness are attractive for hydrogen storage and transportation. The hollow microspheres can be made by drop tower technique, microencapsulation and vapor deposition methods. By immersion in high pressure hydrogen for a period of time at elevated temperature, the hollow microspheres can be filed with hydrogen gas at pressures up to one hundred MPa. The hydrogen mass fraction can be varied from 1% to 10% for hollow microspheres with different membrane hoop stress at failure.

Exergy Analysis on a Split-Type Conditioner Using Ejector as an Expansion Device

2014 ◽  
Vol 699 ◽  
pp. 828-833 ◽  
Author(s):  
Sumeru ◽  
Markus ◽  
Farid Nasir Ani ◽  
Henry Nasution
Keyword(s):  
Performance Improvement ◽  
System Performance ◽  
Air Conditioning ◽  
Exergy Analysis ◽  
Energy Savings ◽  
Air Conditioner ◽  
Total Energy Consumption ◽  
Air Conditioning System ◽  
Air Conditioners ◽  
Exergy Losses

Air conditioning system consumes approximately 50% of the total energy consumption of buildings. Split-type air conditioner is the most widely used in residential and commercial buildings. As a result, enhancement on the performance of the air conditioners will yield a significant energy savings. The use of ejector as an expansion device on the split-type air conditioners is one method to increase the system performance. Exergy analysis on a split-type air conditioner uses an ejector as an expansion device at room and outdoor temperatures of 24 °C and 34 °C, respectively, yielded the percentage of exergy reduction up to 40.6%. Also, the exergy losses on in the compressor had the highest impact on the performance improvement of the split-type air conditioner.

Effect of Sand Containing Conditions on Wear of Nano Ceramic Coating on Downhole Cyclone

2018 ◽  
Vol 13 (10) ◽  
pp. 1514-1521
Author(s):  
Yong Zhang ◽  
Cunxiao Yin ◽  
Lei Xing ◽  
Wei Liu ◽  
Zhihong Cao
Keyword(s):  
Particle Size ◽  
Wear Rate ◽  
Mass Fraction ◽  
Ceramic Coating ◽  
Fluid Dynamic ◽  
Wear Properties ◽  
Spiral Flow ◽  
Water Separator ◽  
Discrete Phase ◽  
Oil Water

Based on the discrete phase mode (DPM) in Computational Fluid Dynamic (CFD) software Fluent, the numerical simulation and experimental study on erosion wear properties of a new nano ceramic coating for downhole cyclone were carried out under sand containing conditions of the produced liquid. The results showed that the maximum wear position of nano ceramic coating in the spiral flow channel in downhole oil-water separator was in the range of azimuth 108°∼144°, and the coating wear rate increased with the increase of inlet flow velocity. When the particle size of sand phase was less than 0.3 mm, the wear rate of nano ceramic coating on cyclone was greatly affected by the particle size. The wear rate decreased with the increase of particle size. When the particle size of sand phase was larger than 0.3 mm, the wear rate of nano ceramic coating was less affected by the particle size. At the same time, the sand phase mass fraction was in the range of 0.1%∼3%. With the increase of sand content in the produced liquid, the wear rate of the cyclone coating increased gradually.

scholarly journals CFD simulation of the laminar flow in stirred tanks generated by double helical ribbons and double helical screw ribbons impellers

2011 ◽  
Vol 1 (4) ◽  
Author(s):  
Zied Driss ◽  
Sarhan Karray ◽  
Hedi Kchaou ◽  
Mohamed Abid
Keyword(s):  
Laminar Flow ◽  
Viscous Dissipation ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Numerical Results ◽  
Stirred Tanks ◽  
Mixing Performance ◽  
Finite Volume Discretization ◽  
Field Velocity

AbstractIn this paper, the mixing performance of double helical ribbons and double helical screw ribbons impellers mounted on stirred tanks is numerical investigated. The computer simulations are conducted within a specific computational fluid dynamic (CFD) code, based on resolution of the Naviers-Stokes equations in the laminar flow with a finite volume discretization. The field velocity and the viscous dissipation rate are presented in different vessel planes. The global characteristics and the power consumption of these impellers are also studied. The numerical results showed that the velocity field is more active with the double helical screw ribbons impeller. In this case, the effectiveness of the viscous dissipation and the pumping flow has been obviously noted. Also, the pumping and the energy efficiency reach the highest values at the same Reynolds number. The good agreement between the numerical results and the experimental data quietly confirmed the analysed method.

scholarly journals EXERGIC EFFICIENCY OF THE HEAT RECOVERY UNIT FOR WASTE GASES OF A HEAT ENGINE OF A COGENERATION PLANT

2020 ◽  
Vol 42 (3) ◽  
pp. 56-60
Author(s):  
N. Fialko ◽  
A. Stepanova ◽  
R. Navrodskaya ◽  
S. Shevchuk
Keyword(s):  
Heat Exchanger ◽  
Heat Recovery ◽  
Exergy Analysis ◽  
Heat Engine ◽  
Cogeneration Plant ◽  
Advantages And Disadvantages ◽  
Recovery Unit ◽  
Recovery Schemes ◽  
Exergy Losses ◽  
Complex Methods

The paper presents the results of a study of the efficiency of a heat recovery unit for waste gases of a heat engine of a cogeneration plant. The possibilities of using for this purpose the discrete-modular principle and complex methods of analyzing the efficiency of heat recovery systems, which are based on the methods of exergo-dissipative functions and exergic balances, are analyzed. The design features of the heat exchanger are considered and a conclusion is made about the possibility of presenting it as a system of eight discrete modules. The results of calculating the exergy characteristics for each of the eight heat exchanger modules, performed within the framework of the indicated methods, are presented. A regular decrease in exergy losses and heat-exergy criterion of efficiency is observed during the transition from the first to the eighth module of the heat recovery unit. However, exergy characteristics for the third and fourth modules of the heat exchanger are somewhat higher than the indicated dependence suggests. This indicates the thermodynamic imperfection of these modules. The main exergy losses in all heat exchanger modules are associated with losses due to heat transfer from flue gases to the wall. An insignificant discrepancy between the values ​​of the total exergy losses calculated within the framework of the methods used indicates that both methods can be used in various heat recovery schemes. However, in each specific case, it is necessary to choose a methodology with which it is possible to identify individual elements that need optimization or constructive improvement. Particular attention is paid to the comparative analysis of the selected techniques and consideration of the advantages and disadvantages of their use in various cases. It is noted that the technique based on the integral balance method of exergy analysis can be considered effective due to the small number of initial parameters and the simplicity of the analytical and calculation methods. The advantage of the technique using exergo-dissipative functions is that it allows one to differentiate exergy losses in a heat exchanger and establish the causes and areas of their localization.

scholarly journals Turbulence Enhancement and Mixing Analysis for Multi-Inlet Vortex Photoreactor for CO2 Reduction

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2237
Author(s):  
Jesús Valdés ◽  
Jorge Luis Domínguez-Juárez ◽  
Rufino Nava ◽  
Ángeles Cuán ◽  
Carlos M. Cortés-Romero
Keyword(s):  
Residence Time ◽  
Turbulence Intensity ◽  
Mass Fraction ◽  
Fluid Dynamic ◽  
Co2 Reduction ◽  
Point Of View ◽  
Molar Ratio ◽  
Cylindrical Shape ◽  
Turbulent Regime ◽  
Computational Fluid Dynamics Cfd

In this article, we describe a prototype photoreactor of which the geometrical configuration was obtained by Genetic Algorithms to maximize the residence time of the reactant gases. A gas reaction mixture of CO2:H2O (1:2 molar ratio) was studied from the fluid dynamic point of view. The two main features of this prototype reactor are the conical shape, which enhances the residence time as compared to a cylindrical shape reference reactor, and the inlet heights and position around the main chamber that enables turbulence and mass transfer control. Turbulence intensity, mixing capability, and residence time attributes for the optimized prototype reactor were calculated with Computational Fluid Dynamics (CFD) software and compared with those from a reference reactor. Turbulence intensity near the envisioned catalytic bed was one percentage point higher in the reference than in the optimized prototype reactor. Finally, the homogeneity of the mixture was guaranteed since both types of reactors had a turbulent regime, but for the prototype the CO2 mass fraction was found to be better distributed.

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