Mass Flow Ratio Research Articles

Topological transitions of Jet A-1 lean azimuthal flames (LEAF)

Prior studies about liquid fuel combustion in a vitiated air environment have shown increased combustion efficiency with reduced NOx, CO, and soot emissions. The concept of lean azimuthal flame (LEAF), which can be associated to the latter combustion mode, is based on opposed injections of air and liquid fuel sprays in an axisymmetric chamber with a central outlet, which can result in a highly turbulent toroidal reaction zone. The mixture of fresh air and hot combustion products of each spray provides a vitiated cross-flow configuration to the next spray distributed along the chamber circumference, leading to ignition and sequential combustion of the sprays by the others. The present paper deals with a LEAF combustor with air-assisted spray atomization, which has not been investigated so far. The combustor is fueled with Jet A-1 and operated from 15 to 25 kW with variations in the atomization-air to liquid mass flow ratio (ALR). This study focuses on the flame topology transitions as a function of atomizer ALR. Experimental results based on flame chemiluminescence and OH planar laser-induced fluorescence show two flame topologies: tubular and LEAF topology for ratio of 2 and 4, respectively (denoted ALR2 and ALR4). The spray Mie scattering indicates a significant presence of unburnt droplets for ALR2, whereas quick evaporation is observed for ALR4 cases. In this paper, we propose and validate a basic model based on the spray droplet size distribution, and the evaporation and convection timescales, which are the prominent factors governing the flame topology. Indeed, for ALR2, the evaporation timescale is longer than the convective timescale, which causes incomplete spray evaporation and insufficient vitiated environment, leading to a tubular flame topology and preventing a LEAF to develop. In contrast, for ALR4, the spray evaporation timescales are smaller than the convective timescales, which aids the LEAF topology.

New regulation strategies study of solar aided liquid air energy storage system under off-design conditions

Liquid air energy storage (LAES) is a large-scale physical energy storage system with high energy storage density. At present, the coupling matching regulation mechanism of the cold and thermal cycles is unclear under off-design conditions, which makes the stable and efficient operation of the LAES system difficult. New multivariable control strategies for cold and thermal cycles are proposed based on the solar aided liquid air energy storage (SA-LAES) system. The study results show the “equal proportion cold recovery” strategy is superior to other strategies, improving the system performance and meeting the demand of the maximum capacity of the charging process. When the liquid air mass flow ratios are 0.7 and 0.4, the air liquefaction ratios increase by 20.20% and 86.43%, and the round-trip efficiency (RTE) values increase by 19.44% and 84.86%, respectively. The new thermal cycle control strategy achieves a good heat coupling matching and maximizes the discharging time and RTE in the zero-carbon environment. Under 70% load and 40% load, the discharging time increase by 16.26% and 53.83%. RTE values increase by 16.28% and 53.84%, respectively. Finally, the operation domains of SA-LAES at different molten salt temperatures are obtained with the optimal cold and thermal cycle strategies. The achievements in this paper will provide valuable reference for the stable operation of SA-LAES under off-design conditions.

Soot-free and low-NO combustion of Jet A-1 in a lean azimuthal flame (LEAF) combustor with hydrogen injection

The quest for aeroengine technologies capable of reducing soot and NOx emissions motivates the development of novel burner concepts. The present work contributes to this line of research by presenting and characterizing a low emissions LEAF combustor fuelled with Jet A-1 and hydrogen at atmospheric condition. The inclined air injection from the top manifold creates an azimuthal flow entraining the Jet A-1 sprays from the bottom manifold and produces, under favorable conditions, a toroidal distributed reaction zone which we call LEAF. In this LEAF, the combustion of the fuel from one atomizer provides a vitiated environment to the spray of the next atomizer. The flame topology and spray characteristics are analysed by means of OH* and CH* chemiluminescence, Mie scattering and soot luminescence. The burner is operated at a constant equivalence ratio with varying thermal power and air-to-liquid massflow ratio (ALR) of the air-blast atomizers. The flame topology is significantly influenced by the atomization air, through its simultaneous effect on the spray characteristics and the flow field. At low atomization air mass flow rates, the combination of lower mixing and larger spray Sauter Mean Diameter (SMD) results in localized droplet and non-uniform spray combustion. Consequently, these inhomogeneities in the combustion process prevent the formation of a LEAF and lead to topological transition of the flame to a tubular shape. In this study, we show that by injecting hydrogen into the combustor we can stabilise a LEAF topology at low ALR. At higher ALR, smaller spray SMD and higher mixing results in a spread-out reaction of hot oxidisers and evaporated fuel, which are characteristics of flameless oxidation. Measurements of soot and NO at the combustor exhaust show very low emission of NO and unburnt fuel and no soot emission, even in absence of preheating of the combustor air.

Techno-economic assessment on a multi-stage compressed carbon dioxide energy storage system with liquid storage

Energy storage system is capable of solving the intermittent and volatility problems of renewable energy and can also perform peak-shaving and valley-filling of the grid. A compressed gas energy storage by storing liquid carbon dioxide possesses the merits of high energy density and competitive efficiency, which makes it a promising overground energy storage technology. However, the problems this technology faced with are narrow compression/expansion processes, high storage pressure and liquefying the gaseous carbon dioxide. Therefore, a liquid carbon dioxide storage system with low-pressure storage and extended working process is suggested in this work. Furthermore, a comprehensive evaluation is conducted on the system from both thermodynamic and economic aspects. The effects of charge and discharge pressures, CO2 mass flow ratio, system operation years, annual cycle times, discount rate, inflation rate and electricity price in different cities on system performance are analyzed. The results indicate that by increasing the charge and discharge pressures there is a maximum round trip efficiency of 56.23% and a peak energy density of 19.90 kWh/m3, respectively. In addition, the analysis of the electricity prices in four different cities on the economic action over the system shows that Shenzhen has the lowest levelized cost of energy (0.0907 $/kWh), Beijing can obtain the highest net present value of 35.314 million dollars and complete cost recovery in the shortest time of 4.84 years.

Performance evaluation and multi-objective optimization of an innovative solar-assisted multigeneration energy storage system for freshwater/O2/H2 generation

A novel multigeneration energy system encompassing a two-stage water purification unit, high-temperature solid oxide electrolysis cell (SOEC), heliostat solar field, and power generation cycles including organic and two-stage steam Rankine cycles is introduced in this study. The two-stage desalination system comprises humidification, dehumidification, and reverse osmosis units. A thermoelectric generator is also utilized to convert dissipated heat into electricity. The proposed system is comprehensively analyzed from energy, exergy, economic, and sustainability standpoints. The effect of design parameters such as heliostat concentration ratio, view factor, desalination mass flow ratio, SOEC operating temperature, and current density on the hydrogen, oxygen and freshwater generation rate, sustainability index, total cost rate, and overall performance of the energy system are discussed. Further, multi-objective optimization based on non-dominated sorting genetic algorithm (NSGA-II) is implemented to identify the optimal operating state of the system. Comparative assessment of the system in the actual condition in the Middle East region showed that the plant has higher performance in June compared to December. Also, optimization revealed that by choosing C = 988, P7 = 1500 kPa, P8 = 300 kPa, MFD = 2.5 and Tcell = 1250 K, the highest obtainable exergy efficiency and minimum total cost rate in the optimal operating state would be 11.32 % and 78.18 $/h, respectively.

MAINTAINING DECLARED PERFORMANCE IN GAS TURBINES DURING INCREASED AMBIENT TEMPERATURES

The classical gas turbine process is characterised by air compression from its surroundings, heating fuel in the combustion chambers, hence causing the created flue gases to expand in the turbine and thus induce mechanical action. The performance of gas turbine depends on anything that affects the airflow density and/or mass at the compressor inlet. The most obvious changes in gas turbine performance is a reduction in power and an increase in specific fuel consumption following an increase in the ambient temperature, resulting in significant deviations of the guaranteed (and achieved) values at ISO conditions. In cooling air at the compressor inlet at increased ambient temperatures, an increase in the mass flow and compression ratio is achieved, thus preventing a reduction in power and an increase in specific fuel consumption. When using gas turbines in combined cycle cogeneration power plants for the production of electrical and thermal power, increasing mass flow through gas turbines leads to an increase in power transferred by the flue gases to the turbine exhaust, and which in the waste heat recovery boiler at the combined cycle plant transfers to the steam turbine cycle. Consequently, the effect at the combined cycle plant is a more significant reduction in specific fuel consumption. The work has used the example of the GE-PG610FA turbine to show the dependency on surrounding climatic conditions, and the manner in which this dependency can be reduced or removed.

Effect of bubble cutting on spray characteristics and dust control performance in the effervescent atomization

Effervescent atomization performance depends on the bubble size inside the mixing chamber, consequently influencing the spray dust control performance. This paper proposes an optimization of atomization quality and dust control performance by incorporating a bubble cutter in the atomizer mixing chamber. The effects of the bubble cutter aperture on spray characteristics and flow characteristics were experimentally investigated under different operating conditions. Experimental results showed that Sauter means diameter (SMD) decreases with increasing injection pressure and gas-liquid mass flow ratio (GLR). Furthermore, SMD initially increased and then decreased by reducing the aperture of the bubble cutter from 500 µm to 80 µm. In particular, high injection pressure (Pi =0.6 MPa) and low gas-liquid mass flow ratio (GLR=0.09) strengthened the effects of the bubble cutter aperture on SMD. Moreover, bubble cutter causes a contiguous concentrated droplet size distribution, but it has little effect on droplet velocity. Ultimately, the optimal bubble cutter aperture on the efficiency of respirable dust control efficiencies was theoretically calculated. The dust control efficiency is a maximum at the bubble cutter with an aperture of 230 µm for the effervescent atomizer in this paper. Spray dust control efficiency reaches 93.15 %, which effectively solves the problem of high dust concentration pollution in the mechanized working environment.

Large Eddy Simulation of a Reacting Kerosene Spray in Hot Vitiated Cross-Flow

The evaporation and combustion characteristics of a kerosene spray injected perpendicularly into a cross-flow of high-temperature vitiated air is investigated. This fundamental flow configuration has wider implications for the future development of ultra-low emission aeronautical combustors, particularly with respect to technologies involving MILD combustion. Large eddy simulations with a Eulerian–Lagrangian framework are performed to investigate the spray evolution and the characteristics of the reaction zone for a range of conditions. For the closure of turbulence-chemistry interactions at the sub-grid scales, a transported probability density function approach solved by the Eulerian stochastic fields method is applied. A configuration based on the use of airblast atomisation is assessed first and compared with experimental observations. The effect of the atomiser air-to-liquid mass flow ratio is studied in greater detail, both in terms of the resulting gas-phase properties and the droplet evaporation process. Then, the effect of ambient pressure on the global spray flame behaviour is examined. For this part of the study, no atomising air is included in the simulation to separate the effects of ambient pressure on the spray from the interaction with the air jet. Analysis of the flame and spray properties at cross-flow operating pressures of 1 atm, 2 bar and 4 bar highlights the strong coupling between the reacting flow and droplet evaporation characteristics, which are highly affected by the penetration of the spray into a flow field characterised by relatively large gradients of temperature. The results reported in this work provide fundamental understanding for the development of novel low-emission combustion technologies and demonstrate the feasibility of applying large eddy simulation with detailed chemistry for the investigation of reacting aviation fuel sprays in hot vitiated cross-flow.

Critical evaluation of the thermal performance analysis of a new cooling tower prototype

This paper presents a critical evaluation of the thermal performance analysis of the inverted cooling tower, which was conceived as a new cooling tower prototype that prevents the dispersion of pollutants to the atmosphere during its operation. The device can be classified as a mechanical forced draft, counterflow-parallel flow cooling tower. The combination of the Merkel and Poppe methods of analysis and the counterflow, parallel and counterflow/parallel flow arrangements has been discussed, for a total of 5 different approaches. The Poppe method for thermal performance prediction reports higher Merkel numbers than the Merkel method: from 3.84% to 6.64%. A higher Merkel number is obtained for the parallel arrangement compared to counterflow to achieve the same cooling. Differences from 1.12% to 12.19% are observed for the range of tested water-to-air mass flow ratios. The rigorous method that uses the Poppe theory and combines counterflow and parallel flow arrangements (main novelty of this paper) is recommended to evaluate the thermal performance. Not only it provides the best predictions for the outlet water and air temperatures (0.44 °C difference for the water prediction and 0.74 °C difference for the air) but it is a good approximation of the complex underlying physics of the problem and the state of the outlet air is accurately determined. • A critical evaluation of the performance of a novel cooling tower was conducted. • The Poppe theory combining parallel/countercurrent flow arrangements is suggested. • The method predictions are confident: less than 2% for water and air temperatures. • The Poppe theory reports results 3.76% and 6.67% higher than the Merkel theory. • Parallel configuration provides up to 12.26% higher Merkel number than counterflow.

Evaluation of mist/air film cooling of C3X vane with serrate-type trenched holes

• Film cooling of C3X vane with serrate-type trenched holes using mist/air mixture under practical conditions is evaluated. • Both serrated transverse trench structure and addition of mist to air can significantly improve film cooling performance. • Replacing the trench edge by a double-curvature lip structure can further improve the film cooling effectiveness. • Film cooling effectiveness of the vane is reduced when the angle of the serrated trench is too large. • Vortex for the six trenched holes intensifies with the increase in the mass flow rate . Serrate-type trenched cooling holes have shown good film cooling performance for the cooling of turbine vanes using coolant air. Mist-assisted film cooling has also exhibited great potential for efficient cooling of a turbine vane. The combination of them may create a substantial improvement of cooling performance, which is explored in this simulation. This work studies the influence of serrate structure on the cooling performance of trenched holes for the C3X turbine vane under practical conditions by examining the flow and heat transfer characteristics of the mist/air mixture. The results prove the concept proposed for significantly improving the cooling performance. At the mass flow ratio R c = 0.25% ( M = 0.5) and R c = 0.50% ( M = 1.0), replacing the trench edge by a double-curvature lip structure can further improve the film cooling effectiveness. The film cooling effectiveness of the vane is reduced when the angle of the serrated trench is too large and the vortex for the six trenched holes intensifies with increasing mass flow ratio. The comparison of streamlines distribution and vortex structures at different blowing ratios by the Q criterion for the trenched holes in the flat plate reveals why the serrated trench structure can improve the cooling effectiveness: it can generate anti-counter-rotating vortices, making it difficult for the coolant film to separate from the wall. Although it is worth of further study on this novel design of serrated trench with mist/air film cooling under engine-representative conditions, this work provide heuristic guidance for the cooling of turbine vanes.

A Novel Control Algorithm of the Air Supply Subsystem: Based on Dynamic Modeling of Proton Exchange Membrane Fuel Cell

In this paper, a novel second-order active disturbance rejection control (2-ADRC) algorithm is proposed to optimize the control of the air supply subsystem for Proton Exchange Membrane Fuel Cell (PEMFC). To improve the optimal control effect of the air supply subsystem for PEMFC, the modeling theory of the air supply subsystem considering dynamic characteristics of the PEMFC system is first studied, and the dynamic Simulink model of the PEMFC system is established and verified. Then, the optimal oxygen excess ratio (OER) parameters under different load currents are obtained, and the optimal OER parameters are also used as the OER control reference for the designed algorithms. In addition, a 2-ADRC algorithm is designed and proposed to make the actual OER parameters close to the optimal OER in real time. Furthermore, compared with PID and MPC algorithms, the 2-ADRC algorithm can comprehensively consider the two parameters of mass flow and pressure ratio to make the compressor work in the high-efficiency zone and improve the net power and efficiency of the PEMFC system.

(Digital Presentation) Fabrication and Characterization for Vanadium Oxynitride Thin Films By Magnetron Sputtering

Vanadium oxynitride (VNxOy, x+y=1) is a metallic compound between vanadium oxides (VO, V2O3, V2O5) and vanadium nitride (VN) which would have interesting properties and functions that potentially can be supplied for different applications. In this study, vanadium nitride and oxynitride thin films were obtained by reactive magnetron sputtering using vanadium targets, Ar as plasma carrier, and a mix of N2 and O2 as reactive gas. The ratio of mass flow between the two gases is maintained around O2:N2=1:20 during the process. To obtain crystalline phases of oxynitrides a post rapid thermal annealing (RTP) in Ar atmosphere at 600ºC and 700ºC for 5 minutes was done. The purpose of the study is to define the effect of the magnetron sputtering parameters, such as reactive gas flow rates, and annealing temperature on the composition, microstructure, and optical properties of the obtained vanadium oxynitride thin films. The characterization of obtained films includes the examination of thickness and morphology by the surface profiler and SEM; identifying crystal structures and further microstructural vibration modes of molecular polarizability by X-ray diffraction and Raman spectroscopy, respectively; evaluation of the chemical composition of films by XPS analysis; assessing of optical transmittance, reflectance, and absorbance by the UV-visible- NIR spectrometer. Experimental data reveal that the annealed films can be oxynitrides when the oxygen flow rate is below 0.25 sccm and the ratio of oxygen/nitrogen ≤1/20. The annealed vanadium oxynitride films in terms of their properties are closer to vanadium nitrides than to oxides: more metallic than semi-conductive with dark appurtenance and high optical absorbance across the spectrum between 200 and 900 nm. The optical absorbance reaches almost 90% around 300 nm and then slowly reduces to 70% at 900 nm. Thus, these films could be good optical shields. For practical usage, the deposition of O2:N2=1/20, O2<0.25 sccm, and 600ºC annealing are recommended because of the truly low transmittance (<10%) through films.

Effect of rotor blade loading distribution on flow stability of transonic compressor

The stall inception prediction method based on eigenvalue theory is established to analyze the effect of rotor blade loading distribution on the flow stability of transonic compressors. The parameterization is implemented to describe the blade geometry with a number of control parameters. Four designs with different blade loading distributions are achieved by modifying the maximum thickness position of each element profile. The steady simulations show that the variation of rotor blade loading distribution leads to significant change of the steady performance incorporating pressure ratio and efficiency at all mass flow conditions. When the blade loading is located further downstream, the pressure rise curve moves towards smaller mass flow and higher pressure ratio, while there exists an optimal blade loading distribution that maximizes the rotor peak efficiency. According to the theoretical prediction, moving the blade loading downstream leads to a smaller stall inception mass flow rate. The rotor work, entropy generation and diffusion factor of the four rotors are analyzed to explain the performance difference. And the relative positions of passage shock and unsteady tip clearance flow at design and near-stall operating conditions are compared in detail to explain the stall onset distinction.

Investigations of bubble size distribution on swirl effervescent atomizer flotation

Atomizer flotation has the advantages of low cost, low energy consumption, adjustable, and long cycle life in industrial applications. The bubble diameter is an important parameter for floatation. The smaller the bubble diameter, the better the flotation effect. However, the bubble diameter produced by the atomizer during flotation separation is large at present. In this paper, a swirl effervescent atomizer is designed and experimental diagnosis through a spray measurement system and submerged spray visualization system. The diameter and size distribution of bubbles in 5 mm from the atomizer outlet to the jet cross-section spray were discussed. The results showed that the swirl effervescent atomizer obtained a fine Sauter mean diameter (SMD is 13–25 μm) compared with the traditional atomizer. Three flow patterns were observed at the submerged spray system: large bubbly flow, discrete bubbly flow, and slug flow. A statistical method of bubbles under high injection pressure was proposed. The effects of the operating conditions of the effervescent atomizer on the bubble diameter were investigated. The average bubble diameter decreased with the increase in injection pressure and gas–liquid mass flow ratios (GLR). However, with the GLR being increased to 0.15, the influence of injection pressure on bubble diameter was reduced. The backpressures (Liquid level heights) have less effect on bubbles compared with injection pressure and GLR. This paper has great significance for the sustainable development of the atomizer in the flotation separation application.

Numerical studies on the combustion of ultra-low calorific gas in a divergent porous burner with heat recovery

This study presents the idea of heat recovery through recirculating walls to enhance the combustion stability for ultra-low calorific gas in a porous burner. Numerical studies on the combustion of ultra-low calorific gas of CO/H2 with CO2 and N2 in a developed divergent porous burner with annular channel is conducted using two-dimensional axis symmetrical model with detailed kinetics. The heat recovery efficiency is defined as the ratio of heat recovery by the fresh mixture in the annular channel to burner power. It is shown that the heat recovery has significant effect on the minimal inlet gas temperature (MIGT) for stable combustion. It is confirmed that the heat recovery enhances the combustion and the stability limits are enlarged by preheating the fresh mixture, but it also leads to an extra pressure loss across the burner compared to that without heat recovery. Results show that heat recovery efficiency reaches up to 0.18 for all the investigated parameters and it reduces linearly from 0.32 to 0.18 as the mass flow ratio increases from 0.8 to 1.5. The MIGT for the burner with heat recirculating channel is always smaller than that without heat recovery. As a result, the combustion is greatly improved by the heat recovery in the divergent burner. Meanwhile, it is shown that pressure loss is increased significantly when the heat recirculating annular channel is added.

Detached Eddy Simulation of the Unsteady Flow and Film Cooling Characteristics of an Endwall With an Interrupted Slot

Abstract The flows close to a high-pressure turbine endwall are highly three-dimensional and unsteady. These flows increase the aerodynamic loss and augment the heat transfer. In this paper, the unsteady flows and film cooling characteristics of an endwall were studied by using the Detached eddy simulation (DES). First, the unsteady flows and film cooling characteristics of a slot on a flat plate were studied at three different coolant mass flow ratios. A comparison of the experimental and numerical results showed that the DES offered an improved ability to capture the distribution of film cooling effectiveness. The aerothermal characteristics of the interrupted slot on a vane endwall were then studied. By analyzing the unsteady flow as well as the mixing process, it was found that the shedding vortices produced by the step lip played a dominant role in the film cooling distribution and the formation of the horseshoe vortex. The coupling of the shedding vortices with the horseshoe vortex had an important influence on the film effectiveness on the endwall. Finally, the effect of the axial distance between the interrupted slot and the vane leading edge on the formation of the horseshoe vortex was further studied. The instantaneous vorticity contours showed that varying the axial position of the interrupted slot affected the development of the horseshoe vortex. As the axial distance increased, the horseshoe vortex disappeared periodically and then reappeared. As the axial distance decreased, the horseshoe vortex retained a steady pattern upstream of the vane leading edge.

Active Flow Control of Supersonic Jet Using Streamwise Pulsed Blowing

The present study investigates a novel control strategy to create a sweeping oscillatory jet using fluidic actuation principle. A supersonic underexpanded primary jet issued into a suddenly expanding duct is oscillated by giving cyclic pulsed secondary jet blowing in the top and bottom step regions of the suddenly expanding duct. The current study employs the bistable nature of jet expansion seen in a suddenly expanding duct for the jet oscillation. The cyclic perturbations (pulsed secondary jet blowing) given in the streamwise direction switch the direction of the asymmetric jet expansion of the underexpanded primary supersonic jet to the top and bottom wall alternatively, thereby creating an oscillatory supersonic jet. It is found that the switching of the direction of the primary jet to any one wall is caused by the Coanda effect produced by the secondary jet issued in the corresponding wall side. The results show that the primary jet quickly responds to the secondary jet perturbations and that the supersonic primary jet oscillation frequency nearly matches secondary jet perturbation frequency. A parametric study to investigate the jet oscillation characteristics with various secondary jet oscillation frequencies and mass flow rate ratios are also being carried out in the present study. It is found that the jet oscillation frequency increases with increase in the secondary jet pulsation frequency. The jet deflection is found to increase with increase in the secondary jet to primary jet mass flow ratio (blowing ratio) up to a critical limit, after which the increment in jet deflection ceases due to the restrictions imposed by the duct geometry.

Numerical study of kerosene spray and combustion characteristics using an air-blast atomizer

In this study, a computational model for a cylindrical combustor with an air-blast atomizer was created to investigate the effect of changing air to liquid mass ratio (ALR) on spray characteristics without combustion and the effect of changing ALR on combustion characteristics under different swirl numbers with constant kerosene fuel mass flow rate using computational fluid dynamics (CFD) code. The study aim is to define the ALR at which the pollutants concentrations at combustion exhaust will be the least. Eight values of ALR were considered and these include 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4 and 1.5. The cold spray characteristics including the number of droplets, Sauter Mean Diameter, droplets penetration length and droplets contours were obtained in addition to combustion characteristics that were studied by describing the reverse flow zone (RFZ) boundary, flow pathlines, temperatures maps, outlet temperatures at combustor exit and species concentrations. The results indicate that increasing ALR and consequently spray droplet diameter decrease does not always translate into superior emissions performance and it depends on several parameters including swirling intensity where the modernistic capabilities of CFD code including flow visualization and calculated recirculated mass flow ratio are used to justify the reasons behind this exceptional behavior. In addition, the results show that the spray Sauter Mean Diameter decreases by increasing ALR but the droplet diameter reduction effect was steeper at lower ALR than higher ones. The length of the RFZ is decreasing with the increase of ALR and shifts upstream closer to the combustor swirler. The recirculated flow mass ratio and the outlet average temperature are decreasing with the increase of ALR.

Analysis and Performance Optimization of Supercritical CO2 Recompression Brayton Cycle Coupled Organic Rankine Cycle Based on Solar Tower

Abstract Supercritical carbon dioxide (SCO2) Brayton cycle has been proved to be an efficient power cycle to replace the traditional steam Rankine cycle. The thermal efficiency of SCO2 cycle can be further improved by coupling another type of cycle (the bottom cycle) at the waste heat end. A supercritical carbon dioxide recompression Brayton cycle (SCRBC) coupled organic Rankine cycle (ORC) based on solar tower is designed and established. According to the requirements of the waste heat temperature range of the top cycle, R600 is selected as the working medium of ORC. Under the design conditions, the effects of split ratio on the net power, the thermal efficiency, and the exergy loss of the combined cycle are studied. The variation of thermal efficiency of each part of the system with split ratio under different turbine inlet pressures and temperatures is further analyzed, and the influence of turbine inlet pressure and working fluid mass flow ratio ε (mass flow ratio of CO2 to R600) on the system performance is analyzed. Genetic algorithm-based multiobjective optimization is used to obtain the Pareto solution set for the thermal performance and unit investment cost of the system. The results show that the thermal efficiency of the combined cycle can be increased by more than 2% compared with that of a single top cycle. There is an optimal split ratio to maximize the thermal efficiency of the combined cycle, and the positions of the optimal split ratio are different for different turbine inlet pressures. Finally, through the multiobjective optimization method, several groups of Pareto solutions can be found, which can provide some reference for engineering design.

Investigation of cooling performance degradation of impingement/effusion structure on pressure side of nozzle guide vane

The cooling performance of the impingent/effusion structure on the pressure side of nozzle guide vanes tested in an engine operating for the various duration of 100 h, 300 h, and 500 h was evaluated in this study via infrared thermal imaging. The original vane was also examined as a comparison. The examined impingement/effusion structure consisted of 4 rows of impinging hole and 5 rows of film hole. The tested coolant-to-mainstream mass flow ratios was 0.0392–0.0784. Reynolds number was 624000 based on the vane chord and cascade inlet velocity. Cooling performance degradation in the impingent/effusion structure was investigated as it relates to oxidation and dust deposition after various durations of engine operation. The two-dimensional temperature distributions in the vane wall became nonuniform over time. The cooling performance quickly degraded after the vane was tested for 100 h in the engine; this degradation grew less intense as operation duration continually increased. The surface-averaged values of the overall cooling effectiveness of the impingent/effusion structure decreased by 9%–11% dependent on the mass flow ratio after the vane was tested for 500 h of engine operation. The coolant flow resistance increased with engine operation time as well.