scholarly journals A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5049
Author(s):  
Xiaojian Li ◽  
Yijia Zhao ◽  
Huadong Yao ◽  
Ming Zhao ◽  
Zhengxian Liu
Keyword(s):  
Design Method ◽  
Operating Conditions ◽  
Low Flow ◽  
Working Fluid ◽  
Centrifugal Compressors ◽  
Flow Angle ◽  
Real Gas ◽  
Total Condition ◽  
Swallowing Capacity ◽  
Cycle Efficiency

Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.

A New Approach to The Design of Fan Volute Profiles

1996 ◽  
Vol 210 (3) ◽  
pp. 287-294 ◽  
Author(s):  
D T Qi ◽  
M J Pomfret ◽  
K Lam
Keyword(s):  
Design Method ◽  
Operating Conditions ◽  
Flow Angle ◽  
New Approach ◽  
One Dimensional ◽  
Distribution Form ◽  
Flow Parameters ◽  
Centrifugal Fans ◽  
Ultimate Objective ◽  
The One

In traditional volute design methods, the flow at the volute inlet is assumed to be uniform according to one-dimensional theory. However, many experimental results have shown that under the design operating conditions, the actual distributions of the flow parameters at the volute inlet are different from those predicted by the ideal assumption. This is because of the influence of the non-axisymmetrical volute geometry, especially due to the presence of the volute tongue. Based on this fact, a new method was considered whereby different volute profiles can be generated by varying the distributions of flow parameters at the volute inlet. The ultimate objective is to achieve the optimal volute profile design so that the performance of a centrifugal machine can be improved. In this paper, a two-dimensional inverse method has been used to redesign the original volute profiles of two centrifugal fans. The results show that the method presented provides effective improvement to the one-dimensional volute design method. The controlled distribution form of volute inlet flow angle α4 in the redesign is qualitatively discussed and can be used for reference in the volute design and further research.

Working Fluid Selection for Organic Rankine Cycles from a Molecular Structural Point of View

2013 ◽  
Vol 805-806 ◽  
pp. 649-653
Author(s):  
Bing Zhang ◽  
Shuang Yang ◽  
Jin Liang Xu ◽  
Guang Lin Liu
Keyword(s):  
Critical Temperature ◽  
Heat Source ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Point Of View ◽  
Operating Conditions ◽  
Working Fluid ◽  
Working Fluids ◽  
Organic Fluids ◽  
Cycle Efficiency

The optimum working conditions of 11 working fluids under different heat source temperatures for an organic Rankine cycle (ORC) were located in our previous work. In the current work, the system irreversibility of each candidate were calculated and compared at their optimal operating conditions. Obvious variation trends of both the cycle efficiency and irreversibility were found for different types of organic fluids. It is suggested, when selecting working fluid for our ORC system, the critical temperature should be as close as possible to the heat source temperature to achieve high cycle efficiency but avoid large irreversibility. The relationships between the structure of the molecules and the critical temperature of the working fluids are investigated qualitatively and potentially meaningful for the rational selection of proper organic fluids for certain ORCs.

The Influence of Real Gas Effects on ICE-ORC Turbine Flow Fields

2014 ◽  
Author(s):  
Lei Zhang ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Jie Peng
Keyword(s):  
Thermodynamic Parameters ◽  
Gas Flow ◽  
Combustion Engine ◽  
Incidence Angle ◽  
Flow Fields ◽  
Operating Conditions ◽  
Specific Power ◽  
Working Fluid ◽  
Perfect Gas ◽  
Real Gas

This paper presents a quantitative comparison of the flow fields of a radial turbine between real gas and perfect gas models for the internal combustion engine (ICE) organic Rankine Cycle (ORC) application. Three-dimensional turbulent Navier-Stokes simulations are carried out using CFD code NUMECA FINE™/TURBO, which is linked to an accurate thermodynamic model for organic working fluid R123 in the form of thermodynamic tables. Four turbine operating conditions including the design point and three part-load points, the inlet compressibility factors of which are 0.82–0.89, are analyzed to discuss the differences of flow fields. Obvious derivations of thermodynamic parameters are investigated in the turbine flow fields. The derivations of speed of sound and density at the nozzle inlet are about 15–20%. There exist about 10m/s value differences in the nozzle outlet velocity evaluation, and furthermore a difference of 10 degrees in the rotor inlet incidence angle comparison. The derivations of relative Mach number are about 20–35% in the rotor outlet near the shroud surface. More than 30% differences are shown in the comparison of turbine total temperature drops. Other thermodynamic parameters show much smaller derivations. The differences of thermodynamic parameters lead to a 1–3% larger in mas flow rate, 1–2% larger in isentropic efficiency and 6–8% smaller in specific power comparison. However, there do not exist obvious differences on thermodynamic parameters distributions in the flow fields. The similar flow fields provide a suggestion that perfect gas model may be an acceptable model for turbine preliminary design and one-dimensional analysis in this gas thermodynamic region, and also the real gas flow fields simulated can be used as a start point to refine the turbine design.

Thermodynamic Analysis of Part-Flow Cycle Supercritical CO2 Gas Turbines

2008 ◽  
Author(s):  
Motoaki Utamura
Keyword(s):  
Heat Exchanger ◽  
Gas Turbines ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Working Fluid ◽  
Pinch Point ◽  
Regenerative Heat ◽  
Regenerative Heat Exchanger ◽  
Flow Cycle ◽  
Cycle Efficiency

Cycle characteristics of closed gas turbines using super critical carbon dioxide as a working fluid are investigated. It is found an anomalous behavior of physical properties of CO2 at pseudo-critical point may limit heat exchange rate of a regenerative heat exchanger due to the presence of pinch point inside the regenerative heat exchanger. Taking such pinch problem into consideration, the cycle efficiency of Brayton cycle is assessed. Its value is found limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative a part flow cycle is investigated and its operable range has been identified. It is revealed that the part flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20MPa and 800K. Optimal combination of turbine expansion ratio and a part flow ratio is 2.5 and 0.68 respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency.

Influence of Molecular Complexity on Nozzle Design for an Organic Vapor Wind Tunnel

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Alberto Guardone ◽  
Andrea Spinelli ◽  
Vincenzo Dossena
Keyword(s):  
High Pressure ◽  
Wind Tunnel ◽  
Operating Conditions ◽  
Critical Conditions ◽  
Working Fluid ◽  
Saturation Curve ◽  
Blow Down ◽  
Real Gas ◽  
Molecular Complexity ◽  
Organic Fluids

A novel blow-down wind tunnel is currently being commissioned at the Politecnico di Milano, Italy, to investigate real-gas behavior of organic fluids operating at subsonic-supersonic speed in the proximity of the liquid-vapor critical point and the saturation curve. The working fluid is expanded from a high-pressure reservoir, where it is kept at controlled super-heated or super-critical conditions, into a low-pressure reservoir, where the vapor is condensed and pumped back into the high-pressure reservoir. Expansion to supersonic speeds occurs through a converging-diverging Laval nozzle. Siloxane fluid MDM (octamethyltrisiloxane-C8H24O2Si3) is to be tested during the first experimental trials. A standard method of characteristics is used here to assess the influence of the molecular complexity of the working fluid on the design of the supersonic portion of the nozzle by considering different fluids at the same real-gas operating conditions, including linear and cyclic siloxanes, refrigerant R245fa, toluene, and ammonia. The thermodynamic properties of these fluids are described by state-of-the-art thermodynamic models. The nozzle length and exit area are found to increase with increasing molecular complexity due to the nonideal dependence of the speed of sound on density along isentropic expansion of organic fluids.

Thermodynamic Analysis of Part-Flow Cycle Supercritical CO2 Gas Turbines

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Motoaki Utamura
Keyword(s):  
Heat Exchanger ◽  
Gas Turbines ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Working Fluid ◽  
Pinch Point ◽  
Regenerative Heat ◽  
Regenerative Heat Exchanger ◽  
Flow Cycle ◽  
Cycle Efficiency

Cycle characteristics of closed gas turbines using supercritical carbon dioxide as a working fluid are investigated. It is found that an anomalous behavior of the physical properties of CO2 at the pseudocritical point may limit the heat exchange rate of a regenerative heat exchanger due to the presence of a pinch point inside the regenerative heat exchanger. Taking such a pinch problem into consideration, the cycle efficiency of the Brayton cycle is assessed. Its value is found to be limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative, a part-flow cycle is investigated and its operable range has been identified. It is revealed that the part-flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20 MPa and 800 K. Optimal combination of turbine expansion ratio and a part-flow ratio is 2.5 and 0.68, respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency.

scholarly journals Parametric Study of Various Thermodynamic Cycles for the Use of Unconventional Blends

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4656
Author(s):  
Odi Fawwaz Alrebei ◽  
Philip Bowen ◽  
Agustin Valera Medina
Keyword(s):  
Working Conditions ◽  
Parametric Study ◽  
Gas Turbines ◽  
Carbon Capture ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Simple Cycle ◽  
Working Fluid ◽  
Specific Work ◽  
Cycle Efficiency

This paper aims to conduct a parametric study for five gas turbine cycles (namely, simple, heat exchanged, free turbine and simple cycle, evaporative, and humidified) using a CO2-argon-steam-oxyfuel (CARSOXY) mixture as a working fluid to identify their optimal working conditions with respect to cycle efficiency and specific work output. The performance of the five cycles using CARSOXY is estimated for wet and dry compression, and a cycle is suggested for each range of working conditions. The results of this paper are based on MATLAB codes, which have been developed to conduct the cycle analysis for CARSOXY gas turbines, assuming a stoichiometric condition with an equivalence ratio of 1.0. Analyses are based on the higher heating value (HHV) of methane as fuel. This paper also identifies domains of operating conditions for each cycle, where the efficiency of CARSOXY cycles can be increased by up to 12% compared to air-driven cycles. The CARSOXY heat exchanged cycle has the highest efficiency among the other CARSOXY cycles in the compressor pressure ratio domain of 2–3 and 6–10, whereas, at 3–6, the humidified cycle has the highest efficiency. The evaporative cycle has intermediate efficiency values, while the simple cycle and the free turbine-simple cycle have the lowest efficiencies amongst the five cycles. Additionally, a 10% increase in the cycle efficiency can be theoretically achieved by using the newly suggested CARSOXY blend that has the molar fractions of 47% argon, 10% carbon dioxide, 10% H2O, and 33% oxyfuel at low compressor inlet temperatures, thus theoretically enabling the use of carbon capture technologies.

ASME PTC-10 Performance Testing of Centrifugal Compressors — The Real Gas Calculation Method

2014 ◽  
Author(s):  
Matt Taher
Keyword(s):  
Test Procedure ◽  
Performance Testing ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Centrifugal Compressors ◽  
Reduced Pressure ◽  
Real Gas ◽  
Test Gas ◽  
Wide Range ◽  
Compressibility Factors

ASME PTC-10 (2009) provides a test procedure to determine the thermodynamic performance of centrifugal compressors for gases conforming to ideal gas laws and for real gases. It requires using real gas calculation methods where the compressibility values depart from the specified limits. ASME PTC-10 employs Schultz X and Y compressibility factors to calculate the polytropic exponent for real gas compression. Specific values of X and Y for the test gas at the test condition may be different from the values provided in ASME PTC-10 generalized charts. Therefore, special care should be taken to properly calculate X and Y factors for a test gas at specified conditions. In this paper, Schultz compressibility factors X and Y are derived as functions of reduced properties. These functions can be used with any equation of state to precisely calculate X and Y values for any gas composition at the specified operating conditions. By using the proposed method, Schultz X and Y compressibility factors for propane are graphically represented covering a reduced pressure range of 0.1 to 3 and a reduced temperature range of 1.05 to 2. Also, the rate of change of polytropic exponents for propane over a wide range of pressures and temperatures is graphically demonstrated.

Working Fluid Selection for an Organic Rankine Cycle for Waste Heat Recovery under Different Heat Source Temperatures

2013 ◽  
Vol 732-733 ◽  
pp. 213-217 ◽  
Author(s):  
Shuang Yang ◽  
Bing Zhang ◽  
Jin Liang Xu ◽  
Wei Zhang ◽  
Chao Xian Wang
Keyword(s):  
Heat Source ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Working Fluids ◽  
Working Fluid Selection ◽  
Cycle Efficiency ◽  
Optimum Working

Optimum working conditions of 11 working fluids under different heat source temperatures in an organic Rankine cycle were systematically investigated. Cycle efficiency of each fluid was compared at their optimal operating conditions were then analyzed. R141b appears to be the best choice when the heat source temperature is around 200oC. Heptane is suggested the suitable working fluids for the ORC system when the heat source is 300oC.

Second-Law Analysis in a Steam Power Plant for Minimization of Avoidable Exergy Destruction

2010 ◽  
Author(s):  
Tapan K. Ray ◽  
Pankaj Ekbote ◽  
Ranjan Ganguly ◽  
Amitava Gupta
Keyword(s):  
Work Performance ◽  
Operating Conditions ◽  
Performance Criteria ◽  
Second Law ◽  
Feed Water ◽  
Exergy Destruction ◽  
Actual Performance ◽  
Time Operation ◽  
Major Equipment ◽  
Cycle Efficiency

Performance analysis of a 500 MWe steam turbine cycle is performed combining the thermodynamic first and second-law constraints to identify the potential avenues for significant enhancement in efficiency. The efficiency of certain plant components, e.g. condenser, feed water heaters etc., is not readily defined in the gamut of the first law, since their output do not involve any thermodynamic work. Performance criteria for such components are defined in a way which can easily be translated to the overall influence of the cycle input and output, and can be used to assess performances under different operating conditions. A performance calculation software has been developed that computes the energy and exergy flows using thermodynamic property values with the real time operation parameters at the terminal points of each system/equipment and evaluates the relevant rational performance parameters for them. Exergy-based analysis of the turbine cycle under different strategic conditions with different degrees of superheat and reheat sprays exhibit the extent of performance deterioration of the major equipment and its impact to the overall cycle efficiency. For example, during a unit operation with attemperation flow, a traditional energy analysis alone would wrongly indicate an improved thermal performance of HP heater 5, since the feed water temperature rise across it increases. However, the actual performance degradation is reflected as an exergy analysis indicates an increased exergy destruction within the HP heater 5 under reheat spray. These results corroborate to the deterioration of overall cycle efficiency and rightly assist operational optimization. The exergy-based analysis is found to offer a more direct tool for evaluating the commercial implication of the off-design operation of an individual component of a turbine cycle. The exergy destruction is also translated in terms of its environmental impact, since the irretrievable loss of useful work eventually leads to thermal pollution. The technique can be effectively used by practicing engineers in order to improve efficiency by reducing the avoidable exergy destruction, directly assisting the saving of energy resources and decreasing environmental pollution.

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