Thermodynamic optimization for an air-standard irreversible Dual-Miller cycle with linearly variable specific heat ratio of working fluid

2018 ◽  
Vol 124 ◽  
pp. 46-57 ◽  
Author(s):  
Zhixiang Wu ◽  
Lingen Chen ◽  
Yanlin Ge ◽  
Fengrui Sun
Keyword(s):  
Specific Heat ◽  
Working Fluid ◽  
Thermodynamic Optimization ◽  
Miller Cycle ◽  
Specific Heat Ratio

Modelling and Simulation of Transient Performance of the Semi-Closed O2/CO2 Gas Turbine Cycle for CO2-Capture

2003 ◽  
Author(s):  
Ragnhild E. Ulfsnes ◽  
Olav Bolland ◽  
Kristin Jordal
Keyword(s):  
Water Vapor ◽  
Specific Heat ◽  
Gas Turbine ◽  
Transient Behavior ◽  
Cycle Performance ◽  
Working Fluid ◽  
Transient Event ◽  
Co2 Gas ◽  
Specific Heat Ratio ◽  
Gas Turbine Cycle

One of the concepts proposed for capture of CO2 in power production from gaseous fossil fuels is the semi-closed O2/CO2 gas turbine cycle. The semi-closed O2/CO2 gas turbine cycle has a near to stoichiometric combustion with oxygen, producing CO2 and water vapor as the combustion products. The water vapor is condensed and removed from the process, the remaining gas, primarily CO2, is mainly recycled to keep turbine inlet temperature at a permissible level. A model for predicting transient behavior of the semi-closed O2/CO2 gas turbine cycle is presented. The model is implemented in the simulation tool gPROMS (Process System Enterprise Ltd.), and simulations are performed to investigate two different issues. The first issue is to see how different cycle performance variables interact during transient behavior; the second is to investigate how cycle calculations are affected when including the gas constant and the specific heat ratio in compressor characteristics. The simulations show that the near to stoichiometric combustion and the working fluid recycle introduce a high interaction between the different cycle components and variables. This makes it very difficult to analytically predict the cycle performance during a transient event, i.e. simulations are necessary. It is also found that, except for the shaft speed calculation, the introduction of gas constant and specific heat ratio dependence on the compressor performance map will have only a minor influence on the process performance.

The Influence of Working Fluid Characteristic Parameters on Turbine Performance for the Small Scale ORC System

2013 ◽  
Author(s):  
Lei Zhang ◽  
Weilin Zhuge ◽  
Xinqian Zheng ◽  
Yangjun Zhang
Keyword(s):  
Specific Heat ◽  
Similarity Criterion ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Working Fluid ◽  
Small Scale ◽  
Characteristic Parameters ◽  
Operating Condition ◽  
Specific Heat Ratio ◽  
Turbine Performance

The small scale Organic Rankine Cycle (ORC) using a turbine as expanders is considered as one of the most efficient ways to convert the waste heat energies of automobile engine into electrical energy, in the power range from several kW up to dozens of kW. In general, two important factors must be taken into account when designing the ORC turbine: the real gas effects of the organic fluid and the high expansion ratio presented in the machinery due to thermodynamic and efficiency factors. The characteristic parameters of R245fa have great difference compared with air. When designing an ORC turbine, the initial problem is the influence of the working fluid characteristic parameters on the turbine performance. Similarity analysis method is used to analyze this problem. When using the similarity theory to design two similar operating conditions, gas constant R and dynamic viscosity μ are easy to be taken into account as they have a dimension; specific heat ratio κ is hard to be taken into consideration. In this paper, a high expansion ratio ORC turbine is generated for a small scale ORC system working with the organic fluid R245fa, and the influence of κ on the turbine performance parameters analyzed. Firstly, the turbine geometry is designed in an iterative process using the commercial design tool Concepts-NREC Rital program, and the designed operating condition is determined. Secondly, the similarity criterion numbers are deduced with no consideration of the specific heat ratio κ, and the similar operating condition is calculated by the deduced similarity criterion numbers. The results achieved by the one-dimensional design software Rital shows that the deviation of similarity criterion numbers is small, which indicates that the two operating conditions are similar. Then, to verify the conclusion above, the flow field simulation using one channel model is conducted based on the R245fa operating condition and air operating condition using the computational fluid dynamics (CFD) code NUMECA-FineTurbo. However, deviations of the similarity criterion numbers from the CFD results are more than twice to those from the one-dimensional results. The larger deviation may indicate that the influence of the specific heat ratio κ cannot be ignored. After that, the distributions of the total pressure, total temperature, the relative Ma number and entropy in the nozzle and rotor channel are compared. These results show that except the total temperature the distributions of the other three parameters are very similar. The similar distribution may indicate that the specific heat ratio κ has little influence on the efficiency and expansion ratio, but κ has greater influence on the temperature and output power. All of these conclusions are made according to the simulation results, the accuracy should be verified through the test results.

Performance Analysis and Comparison of Air Standard Diesel and Diesel-Atkinson Cycles

2013 ◽  
Vol 9 ◽  
pp. 57-65
Author(s):  
Mojtaba Beigzad Abbassi ◽  
Mohamad Hashemi Gahruei ◽  
Saeed Vahidi ◽  
Hamed Shahmirzae Jeshvaghani
Keyword(s):  
Heat Transfer ◽  
Performance Analysis ◽  
Specific Heat ◽  
Output Power ◽  
Compression Ratio ◽  
Thermal Efficiency ◽  
Working Fluid ◽  
Maximum Output ◽  
Specific Heat Ratio ◽  
Atkinson Cycle

This study is concerned with the performance analysis and comparison of air standard Diesel and Diesel-Atkinson cycles with heat-transfer loss, friction like term loss and variable specific-heat ratio of the working fluid based on finite-time thermodynamics. Also numerical examples are detailed to show the relations between the output power and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the output power and the thermal efficiency of both cycles. Furthermore, the effects of variable specific-heat ratio of the working fluid, heat transfer and the friction-like term loss on the performance of both irreversible cycles are analyzed. Comparison of the performance of cycles shows that the heat efficiency and the output power of an air standard Diesel-Atkinson are higher than the Diesel ones and the points of maximum output power and thermal efficiency of Diesel-Atkinson cycle occur at the lower compression ratio. Reduction of Noxis another advantage of Diesel-Atkinson cycle. The results obtained in this paper provide guidance for the design of Diesel and Diesel-Atkinson engines.

Effect of the Specific Heat Ratio on the Aerodynamic Performance of Turbomachinery

2002 ◽  
Vol 127 (4) ◽  
pp. 773-780 ◽  
Author(s):  
Stephen K. Roberts ◽  
Steen A. Sjolander
Keyword(s):  
Specific Heat ◽  
Pressure Ratio ◽  
Working Fluid ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Working Fluids ◽  
Specific Heat Ratio ◽  
Flow Parameters ◽  
Isentropic Flow ◽  
Compressor Map

Many gases, including carbon dioxide and argon, have been considered as alternative working fluids to air in a number of design studies for closed and semi-closed gas turbine engines. In many of these studies, it has been assumed that if the gas constant R and specific heat ratio γ are included in the speed and flow parameters, the compressor map or turbine characteristic is applicable to other working fluids. However, similarity arguments show that the isentropic exponent itself is a criterion of similarity and that the turbomachinery characteristics, even when appropriately nondimensionalized, will, in principle, vary as the γ of the working fluid varies. This paper examines the effect of γ on turbomachinery characteristics, mainly in terms of compressors. The performance of a centrifugal compressor stage was measured using air (γ=1.4), CO2(γ=1.29), and argon (γ=1.67). For the same values of the nondimensional speed, the pressure ratio, efficiency, and choking mass flow were found to be significantly different for the three test gases. The experimental results have been found to be consistent with a CFD analysis of the impeller. Finally, it is shown that the changes in performance can be predicted reasonably well with simple arguments based mainly on one-dimensional isentropic flow. These arguments form the basis for correction procedures that can be used to project compressor characteristics measured for one value of γ to those for a gas with a different value.

scholarly journals The Effect of Heavy Working Fluids on Hydrogen Combustion

2017 ◽  
Author(s):  
Martia Shahsavan ◽  
John Hunter Mack
Keyword(s):  
Specific Heat ◽  
Internal Combustion Engines ◽  
Fuel Injection ◽  
Working Fluid ◽  
Scalar Dissipation ◽  
Injection Velocity ◽  
Thermodynamic Efficiency ◽  
Mixing Rate ◽  
Penetration Length ◽  
Specific Heat Ratio

The thermodynamic efficiency of internal combustion engines is dependent on the compression ratio and specific heat ratio of the working fluid. Using a mixture of oxygen and noble gases instead of air can increase the thermal efficiency due to their higher specific heat ratio. It also has advantage of eliminating NOx caused by lack of nitrogen. In this study, the three dimensional turbulent injection of hydrogen into a constant volume combustion chamber has been modeled and compared to mixtures of oxygen with nitrogen, argon and xenon. All conditions including the mass flow rate of the injected fuel, injection velocity, and initial temperature and pressure of the chamber were kept constant. The results indicate that the hydrogen jet has more penetration length in nitrogen compared to argon and xenon. However, the smaller penetration lengths lead to more complex jet shapes and larger cone angles. In combination with the higher specific heat ratio, combustion in a noble gas environment results in higher temperatures and OH radical concentrations. Furthermore, mixedness is investigated using mean spatial variation and mean scalar dissipation. Hydrogen in argon shows a better mixing rate compared to nitrogen and xenon due to higher diffusivity.

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