Simple Recuperated s-CO2 Cycle Revisited: Optimization of Operating Parameters for Maximum Cycle Efficiency

2019 ◽  
Author(s):  
Anchit Dutta ◽  
Adhip Gupta ◽  
Sharath Sathish ◽  
Aman Bandooni ◽  
Pramod Kumar
Keyword(s):  
Design Of Experiments ◽  
Design Space ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Maximum Temperature ◽  
Brayton Cycle ◽  
High Side ◽  
Side Pressure ◽  
Cycle Efficiency ◽  
The Impact

Abstract The paper presents modeling and Design of Experiments (DOE) analysis for a simple recuperated s-CO2 closed loop Brayton cycle operating at a maximum temperature of 600°C and a compressor inlet temperature of 45°C. The analysis highlights the impact of isentropic efficiencies of the turbine and compressor, decoupled in this case, on other equipment such as recuperator, gas cooler and heater, all of which have a bearing on the overall performance of the s-CO2 Brayton cycle. A MATLAB program coupled with REFPROP is used to perform the thermodynamic analysis of the cycle. A design space exploration with a Design of Experiments (DOE) study is undertaken using I-sight™ (multi-objective optimization software), which is coupled with the MATLAB code. The outcome of the DOE study provides the optimal pressure ratios and high side pressures for maximum cycle efficiency in the design space. By varying pressure ratios along with a floating high side pressure, the analysis reveals that the cycle performance exhibits a peak around a pressure ratio of 2.5, with cycle efficiency being the objective function. A further interesting outcome of the DOE study reveals that the isentropic efficiencies of the compressor and turbine have a strong influence not only on the overall cycle efficiency, but also the optimum pressure ratio as well as the threshold pressures (low as well as high side pressure). An important outcome of this exercise shows that the isentropic efficiency of the turbine has a much greater impact on the overall cycle performance as compared to that of the compressor.

A Methodology for Quantifying Distortion Impacts Using a Modified Parallel Compressor Theory

2018 ◽  
Author(s):  
Manish Pokhrel ◽  
Jonathan Gladin ◽  
Elena Garcia ◽  
Dimitri N. Mavris
Keyword(s):  
Boundary Condition ◽  
Design Space ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Interface Plane ◽  
Design And Optimization ◽  
Fan Performance ◽  
Fuel Burn ◽  
Distributed Propulsion ◽  
The Impact

Efforts to achieve NASA’s N+2 and N+3 fuel burn goals have led to various future aircraft concepts. A commonality in all these concepts is the presence of a high degree of interaction among the various disciplines involved. A tightly integrated propulsion/airframe results in distortion in the flow field around the engine annulus. Although beneficial in terms of propulsive efficiency (due to boundary layer ingestion), the impact of distortion on fan performance and operability remains in question for these concepts. As such, rapid evaluation of the impacts of distortion during the conceptual design phase is necessary to assess various concepts. This is especially important given the expansion of the design space afforded by turbo-electric and hybrid-electric distributed propulsion concepts, in which the gas turbine generator and propulsive devices can be decoupled in space. A simple and rapid methodology to assess operability of compressors is the theory of Parallel Compressors (PC). PC theory views the compressor as two compressors in parallel, one with a uniform high Pt and the other with a uniform low Pt, both operating at the same speed and exiting to a common static pressure. The assumption of two compressors exiting at the common static pressure is not entirely true, especially when the distortion is high. In this paper, the development of a modified parallel compressor model with parametric boundary condition that can capture the impact of non-uniform inflow on fan performance is introduced and validated. Unlike classical PC model, the modified approach introduces a boundary condition dependent on the intensity of distortion (DPCP) at the Aerodynamic Interface Plane (AIP). Additionally, the concept of PC is also extended to Multi-Per Revolution (MPR) distortion. A modeling environment which follows this methodology is created in PROOSIS, an object oriented 0-D cycle code. The model was created using the “compressor” components acting in parallel and a procedure for implementing both design mode and off-design mode solutions was created using the PROOSIS toolset. The example problem was implemented to demonstrate two capabilities — i) the ability of quantifying impacts on thrust and performance of a ducted fan propulsion system, and ii) the ability of predicting loss in stability pressure ratio. The results clearly show the ability of the tool to quantify distortion related losses. The work described in this paper can be integrated to a Multi-Disciplinary Design and Optimization (MDAO) framework along with other disciplines and can be used to evaluate the viability of design space offered by novel aircraft configurations.

A Methodology for Variable Geometry Optimization of Multistage Axial Compressors

2017 ◽  
Author(s):  
M. Eric Lyall ◽  
Fred J. Eisert ◽  
Douglas C. Rabe ◽  
Patrick M. Fleisher
Keyword(s):  
Design Of Experiments ◽  
Pressure Ratio ◽  
Geometry Optimization ◽  
Axial Compressor ◽  
Optimization Method ◽  
Variable Geometry ◽  
Factorial Design Of Experiments ◽  
Stage Matching ◽  
The Impact ◽  
Corrected Flow

This paper presents a procedure for experimentally optimizing a multistage axial compressor. Due to the usual proprietary nature of such tests, a mean-line model of a nine-stage compressor with three rows of variable geometry is used instead of a real machine as a testbed for explaining the optimization method. The compressor is optimized to achieve design-intent corrected flow and pressure ratio while achieving acceptable efficiency and stage matching. The optimization is performed using a response surface methodology that leverages a full factorial design of experiments approach. The resulting empirical models of compressor performance are of high quality, with coefficients of determination exceeding 0.99. An important finding of the work is that stage interactions are important for modeling both efficiency and stage matching, much more than for corrected flow and pressure ratio. Additionally the empirical equations resulting from the design of experiments analysis provide sensitivities due to changes in the variable geometry. These sensitivities can be applied to understanding the impact of uncertainties related to rigging the variable geometry and for assessing potential new or upgraded compressor designs.

scholarly journals Influence of selected cycle components parameters on the supercritical CO2 power unit performance

2018 ◽  
Vol 240 ◽  
pp. 05035
Author(s):  
Marcin Wołowicz ◽  
Jarosław Milewski ◽  
Gabriel Ziembicki
Keyword(s):  
Power Unit ◽  
Cycle Performance ◽  
Brayton Cycle ◽  
Split Ratio ◽  
Compressor Inlet ◽  
Set Up ◽  
Cycle Efficiency ◽  
Unit Performance ◽  
Isentropic Efficiency

The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.

scholarly journals Investigation of the Pressure Gain Characteristics and Cycle Performance in Gas Turbines Based on Interstage Bleeding Rotating Detonation Combustion

Entropy ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 265 ◽  
Author(s):  
Lei Qi ◽  
Zhitao Wang ◽  
Ningbo Zhao ◽  
Yongqiang Dai ◽  
Hongtao Zheng ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Efficiency Enhancement ◽  
Compressor Pressure Ratio ◽  
Detonation Combustion ◽  
Gas Turbine Cycle ◽  
Cycle Efficiency ◽  
Rotating Detonation

To further improve the cycle performance of gas turbines, a gas turbine cycle model based on interstage bleeding rotating detonation combustion was established using methane as fuel. Combined with a series of two-dimensional numerical simulations of a rotating detonation combustor (RDC) and calculations of cycle parameters, the pressure gain characteristics and cycle performance were investigated at different compressor pressure ratios in the study. The results showed that pressure gain characteristic of interstage bleeding RDC contributed to an obvious performance improvement in the rotating detonation gas turbine cycle compared with the conventional gas turbine cycle. The decrease of compressor pressure ratio had a positive influence on the performance improvement in the rotating detonation gas turbine cycle. With the decrease of compressor pressure ratio, the pressurization ratio of the RDC increased and finally made the power generation and cycle efficiency enhancement rates display uptrends. Under the calculated conditions, the pressurization ratios of RDC were all higher than 1.77, the decreases of turbine inlet total temperature were all more than 19 K, the power generation enhancements were all beyond 400 kW and the cycle efficiency enhancement rates were all greater than 6.72%.

Performance Evaluation of Space Solar Brayton Cycle Power Systems

1992 ◽  
Author(s):  
Zheng-Gang Diao
Keyword(s):  
Life Cycle ◽  
Power Systems ◽  
Power System ◽  
Life Cycle Cost ◽  
Pressure Ratio ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Compressor Inlet ◽  
Cycle Efficiency ◽  
System Characteristics

Unlike gas turbine power systems which consume chemical or nuclear energy, the energy consumption and/or cycle efficiency should not be a suitable criterion for evaluating the performance of space solar Brayton cycle power. A new design goal, life cycle cost, can combine all the power system characteristics, such as mass, area, and station-keeping propellant, into a unified criterion. Effects of pressure ratio, recuperator effectiveness, and compressor inlet temperature on life cycle cost were examined. This method would aid in making design choices for a space power system.

High Efficiency Cavity Winglets for High Pressure Turbines

2014 ◽  
Author(s):  
John D. Coull ◽  
Nicholas R. Atkins ◽  
Howard P. Hodson
Keyword(s):  
High Pressure ◽  
Discharge Coefficient ◽  
Design Space ◽  
High Efficiency ◽  
Pressure Ratio ◽  
Loss Reduction ◽  
Lower Stress ◽  
Flow Angle ◽  
Reduction Mechanisms ◽  
The Impact

The flow leaking over the tip of a high pressure turbine blade generates significant aerodynamic losses as it mixes with the freestream flow. This paper examines the potential for reducing these losses using winglets with recessed cavities on the tip. These features combine the loss-reduction mechanisms of cavity tips, which reduce the discharge coefficient, and winglet overhangs, which reduce the mixing Mach number, leakage flow angle mismatch, and the driving pressure ratio. RANS calculations are performed for an un-cooled HP rotor blade to explore the cavity-winglet design space and examine the impact on the aerothermal performance of the blade. Relative to a plain-tip design, a cavity tip can reduce the sensitivity to clearance by around 30%. Similar performance can be achieved using a flat-tip winglet with an overhang around the whole blade perimeter. However, by adding a cavity to this winglet it is possible to out-perform the cavity tip at all clearances, and reduce the sensitivity to clearance by 46% relative to the plain tip. This sensitivity is equivalent to a two-fin attached shroud, but the winglet blade will exhibit lower stress and require less coolant flow. Furthermore this cavity-winglet may offer some cooling advantages over the cavity tip.

Gas Properties as a Limit to Gas Turbine Performance

2002 ◽  
Author(s):  
R. C. Wilcock ◽  
J. B. Young ◽  
J. H. Horlock
Keyword(s):  
Gas Turbines ◽  
Industrial Development ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Cycle Efficiency ◽  
Gas Properties

Although increasing the turbine inlet temperature has traditionally proved the surest way to increase cycle efficiency, recent work suggests that the performance of future gas turbines may be limited by increased cooling flows and losses. Another limiting scenario concerns the effect on cycle performance of real gas properties at high temperatures. Cycle calculations of uncooled gas turbines show that when gas properties are modelled accurately, the variation of cycle efficiency with turbine inlet temperature at constant pressure ratio exhibits a maximum at temperatures well below the stoichiometric limit. Furthermore, the temperature at the maximum decreases with increasing compressor and turbine polytropic efficiency. This behaviour is examined in the context of a two-component model of the working fluid. The dominant influences come from the change of composition of the combustion products with varying air/fuel ratio (particularly the contribution from the water vapour) together with the temperature variation of the specific heat capacity of air. There are implications for future industrial development programmes, particularly in the context of advanced mixed gas-steam cycles.

scholarly journals First and Second Law Analysis of Supercritical CO2 Recompression Brayton Cycle

2020 ◽  
Vol 13 (1) ◽  
pp. 21-27
Author(s):  
Muhammad Sajid Khan ◽  
Ugur Atikol
Keyword(s):  
Pressure Ratio ◽  
Cycle Performance ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Optimum Pressure ◽  
Environment Temperature ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
The Individual ◽  
Cycle Temperature

The present research concentrates on the energy and exergy analysis of the S-CO2 recompression Brayton cycle and the individual components irreversibilities by varying the different operating parameters. Results show that the cycle efficiencies and LTR effectiveness reduce by increasing minimum cycle temperature, but HTR increases. The effect of minimum cycle temperature is more critical on cycle performance than maximum cycle temperature. The reactor has the highest irreversibility followed by recuperators and pre-cooler. Exergy efficiency shows a downward trend as environment temperature enhances. However, the effect of turbine inlet temperature is very low on-cycle efficiency and optimum pressure ratio for lower compressor outlet pressure values, which is more significant by increasing this parameter.

scholarly journals Power, Efficiency, Power Density and Ecological Function Optimization for an Irreversible Modified Closed Variable-Temperature Reservoir Regenerative Brayton Cycle with One Isothermal Heating Process

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5133 ◽  
Author(s):  
Lingen Chen ◽  
Chenqi Tang ◽  
Huijun Feng ◽  
Yanlin Ge
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Variable Temperature ◽  
Pressure Ratio ◽  
Ecological Function ◽  
Function Optimization ◽  
Cycle Performance ◽  
Heating Process ◽  
Brayton Cycle ◽  
Isothermal Heating

One or more isothermal heating process was introduced to modify single and regenerative Brayton cycles by some scholars, which effectively improved the thermal efficiency and significantly reduced the emissions. To analyze and optimize the performance of this type of Brayton cycle, a regenerative modified Brayton cycle with an isothermal heating process is established in this paper based on finite time thermodynamics. The isothermal pressure drop ratio is variable. The irreversibilities of the compressor, turbine and all heat exchangers are considered in the cycle, and the heat reservoirs are variable-temperature ones. The function expressions of four performance indexes; that is, dimensionless power output, thermal efficiency, dimensionless power density and dimensionless ecological function are obtained. With the dimensionless power density as the optimization objective, the heat conductance distributions among all heat exchangers and the thermal capacitance rate matching among the working fluid and heat reservoir are optimized. Based on the NSGA-II algorithm, the cycle’s double-, triple- and quadruple-objective optimization are conducted with the total pressure ratio and the heat conductance distributions among heat exchangers as design variables. The optimal value is chosen from the Pareto frontier by applying the LINMAP, TOPSIS and Shannon entropy methods. The results show that when the pressure ratio in the compressor is less than 12.0, it is beneficial to add the regenerator to improve the cycle performance; when the pressure ratio is greater than 12.0, adding the regenerator will reduce the cycle performance. For single-objective optimization, the four performance indexes could be maximized under the optimal pressure ratios, respectively. When the pressure ratio is greater than 9.2, the cycle is simplified to a closed irreversible simple modified Brayton cycle with one isothermal heating process and coupled to variable-temperature heat reservoirs. Therefore, when the regenerator is used, the range of pressure ratio is limited, and a suitable pressure ratio should be selected. The triple objective (dimensionless power output, dimensionless power density and dimensionless ecological function) optimization’ deviation index gained by LINMAP or TOPSIS method is the smallest. The optimization results gained in this paper could offer some new pointers for the regenerative Brayton cycles’ optimal designs.

Aspects of Cooled Gas Turbine Modelling for the Semi-Closed O2/CO2 Cycle With CO2 Capture

2003 ◽  
Author(s):  
Kristin Jordal ◽  
Olav Bolland ◽  
A˚ke Klang
Keyword(s):  
Gas Turbine ◽  
Rotational Speed ◽  
Pressure Ratio ◽  
Continuous Process ◽  
Cycle Performance ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Stage Model ◽  
Detailed Model ◽  
The Impact

In order to capture the behaviour of the oxyfuel cycle operating with high combustor-outlet temperature, the impact of blade and vane cooling on cycle performance must be included in the thermodynamic model. As a basis for a future transient model, three thermodynamic models for the cooled gas turbine are described and compared. The first model, known previously from the literature, models expansion as a continuous process with simultaneous heat and work extraction. The second model is a simple stage-by-stage model and the third is a more detailed stage-by-stage model that includes velocity triangles and enables the use of advanced loss correlations. An airbreathing aeroderivative gas turbine is modelled, and the same gas turbine operating in an oxyfuel cycle is studied. The two simple models show very similar performance trends in terms of variation of pressure ratio and turbine inlet temperature in both cases. With the more detailed model, it was found that, without any change of geometry, the turbine rotational speed increases significantly and performance drops for the maintained geometry and pressure ratio. A tentative increase of blade angles or compressor pressure ratio is found to increase turbine performance and decrease rotational speed. This indicates that a turbine will require re-design for operation in the oxyfuel cycle.

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