Higher Turbine Inlet Temperature Research Articles

A numerical procedure to model heat transfer in radial turbines for automotive engines

The thermal condition of a turbocharger considerably differs between different applications, which makes it difficult to model the heat transfer. In this study, a general procedure to characterize the heat transfer model for a radial turbine was established using 3D Conjugate Heat Transfer (CHT) simulation. The external convective and radiation heat losses were modelled by an equivalent convection heat transfer coefficient and an equivalent metal emissivity, following an analysis of the heat transfer mechanisms. The established model was validated by measurements under adiabatic and diabatic conditions. The characterization procedure was further simplified to extend its applications. The number of required operating points for simulation and measurements were significantly reduced, which enabled it to be used under different operating conditions, e.g., engine test and in-vehicle operations, where a constant turbo speed line could hardly be regulated. Then a comparison was conducted with a reference model based on the geometric simplification. The proposed model was observed to give a slightly better result regarding turbine housing temperatures under low and high turbine inlet temperatures. In the end, an analysis of turbine heat flow was conducted, which indicated that on average 80.4% of the turbine internal heat transfer occurred at the volute and 17.3% at the diffuser. Besides, the external heat losses can be up to 2.511 times of the turbine mechanical power.

Effects of Gas Film Hole on Mechanical Property and Oxidative Damage of Turbine Blades

With the development of aero-engine with high specific flux, high thrus-weight ratio, and high turbine inlet temperature, it is an effective way to improve the cooling efficiency by designing dense gas film holes on the blade surface of the turbine blades, especially at the intake side. However, the introduction of gas film holes destroys the geometrical integrity of the blade structure, resulting in a multiaxial high stress state of the blade material around the small holes, which seriously affects the strength and life of the cooling blades. In addition, the geometry design of the gas film holes also directly affects the temperature and the oxidation rate of the turbine rotor blades. In this paper, the researches on the mechanical properties and oxidative damage of the gas film holes at home and abroad in recent years have been systematically introduced. The effects of gas film holes on the durability and fatigue properties, the high temperature oxidation behavior of single crystal superalloys, and the thin-walled effect of oxidative damage of gas film holes have been systematically described.

CFD Analysis and Experimental Validation of the Flow Field in a Rib Roughed Turbine Internal Cooling Channel

Abstract Advances in thermal science force us to develop more efficient systems. The efficiency of widely-used gas turbine engines, is highly dependent on turbine inlet temperature. However, a high turbine inlet temperature yields material deterioration and long term degradation of turbines. To prevent material deterioration, cooling the hot zones of gas turbine engines, particularly turbine components and blades, is a priority. In this way, long term degradation of the turbine is prevented, while the thermal efficiency of the gas turbine engine is boosted. In the current paper, a flow field within a rib roughed blade internal cooling channel is discussed. Within this scope, a computational fluid dynamics analysis is conducted using a Standard k-ω turbulence model. After this, the same case is experimentally investigated. Experimental results obtained from particle image velocimetry measurements are used to validate the results of the computational fluid dynamics analysis. At the end of the study, the flow field is fully mapped with the recirculation and separation zones being clearly pinpointed.

Modeling and experimental testing of periodic flow regenerators for sCO2 cycles

Supercritical CO2 cycles have the ability to reach high efficiency because of their high turbine inlet temperatures. However, high effectiveness recuperators (>90%) are needed to achieve high efficiencies. Periodic flow regenerators have been proposed as an alternative to conventional heat exchanger designs such as Printed Circuit Heat Exchangers (PCHEs) or micro-tube heat exchangers. Regenerators use a packed bed of spheres to alternatively store and release heat. Since the hot and cold fluid streams are not in direct contact, the design of the regenerator is much simpler and less expensive than a recuperator. A model of the regenerator has been created that can predict the effectiveness, pressure drop, and carryover when given the regenerator size and operating conditions. To verify this model, an experimental test facility has been constructed that is capable of testing regenerators at temperatures up to 550 °C and pressures up to 2400 psi at a heat transfer rate of approximately 10 kW. Experimental data was collected and compared to the model predictions. The model was able to predict effectiveness to within approximately 2% and pressure drop to within approximately 20%; both results are acceptable. However, it was necessary to develop a correction for carryover to account for the differences between the model predictions and experimental data. The final result of this work is a verified model of the regenerator that can be used to quickly and accurately design and optimize a regenerator for a sCO2 Brayton cycle.

Beyond Brayton Cycle: It is Time to Change the Paradigm

A detailed look at the gas turbine (GT) technology over the last three decades clearly shows that an asymptotic limit is reached in thermal efficiency in combined cycle (CC) configuration. There is little reason to expect a technology leap anytime soon to change this appreciably as long as the industry sticks to the classic Brayton cycle configuration and the brute force approach of ever higher turbine inlet temperatures (TITs). The changing landscape of electric power generation, especially integration of fossil fuel fired technologies with renewable generation and wide variation in natural gas prices, suggests that it is time to look at the direction of future development efforts differently. This paper looks at the need of a paradigm shift in GT CC technology using thermodynamic and economic arguments.

Ceramic-metal composites for heat exchangers in concentrated solar power plants.

The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heatexchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1-3, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage4-6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin9. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heatexchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost.

Preliminary conceptual exploration about performance improvement on supercritical CO2 power system via integrating with different absorption power generation systems

Supercritical CO2 (sCO2) power system has been investigated by many scholars due to its attractive advantages of higher efficiency, compact system structure and eco-friendly working fluid. In this paper, some preliminary conceptual exploration about performance improvement on sCO2 power system by integrating with two types of absorption power generation (APG) systems are conducted. Parameter analysis, genetic algorithm (GA) optimization and exergy analysis are carried out quantitatively for the proposed combined sCO2/APG systems based on the self-built simulation platform from the viewpoints of thermodynamics and economics. Parameter analysis results reveal that there exist optimal compressor pressure ratio to maximize the thermal efficiency or minimize the total product unit cost. Higher turbine inlet temperature and lower absorber temperature could contribute to the overall system performance. In addition, compared with the stand-alone sCO2 system, improvements of 5.98% and 5.07% in thermodynamics as well as promotion of 4.24% and 2.19% in economics can be obtained for sCO2/LiBr-H2O system and sCO2/ammonia water system, respectively. Furthermore, exergy analyses show that the main exergy destructions occur in the reactor and the cooler and the proposed combined sCO2/APG system could effectively reduce around half of the exergy destruction within the cooler of the stand-alone sCO2 system.

Performance investigation of a novel closed Brayton cycle using supercritical CO2-based mixture as working fluid integrated with a LiBr absorption chiller

A novel closed Brayton cycle using supercritical CO2–Kr mixture as working fluid integrated with an absorption chiller (CBC/AC) is proposed. The waste heat of the CO2–Kr in the cold end of the top closed Brayton cycle (CBC) is utilized to drive the absorption chiller, which further chills the CO2–Kr fluid exiting the precooler before it enters the main compressor. Compared with the stand-alone supercritical CO2 (S-CO2) CBC, the CBC/AC exploits the performance improvement potentials under low ambient temperature (T0) condition and alleviates the performance penalty under high T0 condition. The energy and exergy analyses of the CBC/AC in three typical T0 conditions (10 °C, 25 °C and 40 °C) show that the thermal efficiencies are improved by 3.12%, 0.40% and 6.86%, respectively, the exergy efficiencies are improved by 3.53%, 0.54% and 7.53%, respectively. The exergy loss from the precooler is significantly reduced in the CBC/AC relative to that in the stand-alone S-CO2 CBC. The comparisons between different working conditions for the CBC/AC indicate that the improvements of the thermal and exergy efficiencies are more apparent under water-cooling and high turbine inlet temperature conditions. The effects of the component performance on the CBC/AC are also evaluated.

Optimal design of supercritical CO2 power cycle for next generation nuclear power conversion systems

Most generation IV (Gen IV) nuclear reactors have high operating temperatures to increase power plant efficiency and to allow for hydrogen production. The widely used steam Rankine cycle is not suitable for Gen IV reactors because of high turbine inlet temperature with extremely high pressure by using ultra-supercritical (USC) steam cycle. The supercritical CO2 (S-CO2) recompression cycle can achieve a competitively high thermal efficiency with turbine inlet temperature at 500–600 °C and turbine inlet pressure at 20 MPa. However, the operating pressure of the heat source is still too high to promote its application and impede the licensing of using S-CO2 cycle for nuclear power plant. The aim of this work is to reduce the operating pressure of heat sources in the S-CO2 cycle, since the heat sources are usually accompanied by high radiation or high temperature environment. A combined recompression cycle and dual expansion turbine technology is first recommended to reduce the operating pressure of heat source for nuclear power plants and maintain high thermal efficiency. Additionally, sensitivity analysis is performed for three types of S-CO2 power cycles to compare the merits and faults. An optimization analysis is also presented. The results show that the combined recompression cycle and dual expansion turbine technology is effective and suitable for Gen IV reactors with a relatively low heat source operating pressure and high thermal efficiency. This kind of S-CO2 cycle can be coupled with different kinds of heat sources to reduce their operating pressure.

Energy and exergy evaluation of a 220MW thermal power plant

A component based energy and exergy evaluation was performed on a 220MW thermal power plant in Nigeria. The component based exergy analysis examines and compares the energetic and exergetic performances of each component by identifying the deficiencies of each component. Design and operating data were obtained from Egbin power plant in Nigeria. The result of the analysis showed that the total exergy that was destroyed in the power plant was 400.015 MW. The major contributors to the exergy destruction in the power plant were the boiler (87%), the three turbines (a combined total of 9%) and the condenser (2 %). The effect of increasing the High Pressure turbine (HPT) inlet temperature at constant boiler pressure incresses the exergy efficiency of the component as well as the second law efficiency of the power plant, thus reducing the exergy destruction of the component. At the variation of environmental or dead state temperature, there were no appreciable changes in the values of exergy efficiency of the boiler/steam generator. The outcomes of this work provide the exergy consumption and distribution profiles of the thermal power plant, making it possible to adopt effective energy-saving measures. http://dx.doi.org/10.4314/njt.v37i1.15

Technoeconomic and exergy analysis of a solar geothermal hybrid electric power plant using a novel combined cycle

A novel Solar Geothermal Hybrid Electric Power Plant (SGHEPP) based on the hybridization of an existing binary Geothermal Electric Power Plant by adding a solar-powered steam-Rankine topping cycle is proposed. The proposed SGHEPP has several benefits. First, the hybridization scheme does not require the binary bottoming cycle to be physically modified or operated outside its design conditions. Second, the proposed SGHEPP has a higher turbine inlet temperature, which results in higher solar-to-electricity conversion efficiencies. Third, the daily energy production for the SGHEPP peaks on sunny summer days when electricity prices are generally highest. And fourth, the design reduces the consumption of geothermal resources, which can extend the useful life of declining and marginal geothermal fields. Annual simulations are run for a representative plant in southwestern Turkey and used to assess the plant’s energetic, exergetic, and economic performance. The performance of four designs are compared that differ with respect to how the geothermal resources are managed and the size of the solar field. A representative design has an incremental solar efficiency of 12.2% and consumes up to 17% less brine than a similar stand-alone geothermal plant. The calculated solar based LCOE for each design is in the range of 163–172 USD MWh−1.

Experimental procedure for the characterization of turbocharger’s waste-gate discharge coefficient

Nowadays, the turbocharger has become one of the key components for automotive spark-ignition engine improvements (fed with both liquid and gaseous fuels), as a support for the boosting and downsizing concept to reduce fuel consumption and exhaust emission. In gasoline engines, the usage of the waste-gate valve typically regulates the maximum boost pressure in the turbocharger system, to protect the engine and the turbocharger at high engine speeds. To improve the transient response at low engine speeds, two-stage turbocharger is widely used. Two-stage systems are composed of several valves to regulate the flow to control the boosting of the system. Like a bypass valve between the turbines, a check valve is present between the compressor and a waste-gate valve for the low-pressure turbines. This article deals with a methodology for characterizing the discharge coefficient of an electronic waste-gate valve in the turbocharger. To estimate the gas flow over the same in one-dimensional models, an empirical model is correlated and validated. For this, a constant-stream experimental work has been carried out on a test rig at different valve position openings, with high turbine inlet temperatures. Finally, an optimal map of discharge coefficient has been drawn out through interpolation method, which can integrate into the full one-dimensional turbocharged engine model system, to calculate the actual mass flow through the waste-gate valve.

Benchmarking Reynolds Averaged Navier–Stokes Turbulence Models in Internal Pin Fin Channels

The performance of gas turbine engines increases with higher turbine inlet temperatures. To enable operation at temperatures beyond material limitations, turbine blades are often cooled using internal pin fin channels, which are used at the trailing-edge region. This study validates the accuracy of various Reynolds-averaged Navier–Stokes turbulence models in predicting the heat transfer rates and pressure distributions on the surface of the pins by comparing computational fluid dynamics simulation data against a valid set of experimental data obtained from literature. Considering the problem from an industrial design perspective, several commercially available, computationally efficient Reynolds-averaged Navier–Stokes turbulence models are used to predict the cooling performance of the pin fin channel. Turbulence models investigated are Menter’s shear stress transport, realizable , and a quadratic formulation of the realizable model. The geometry investigated is a staggered eight-row pin fin channel. Results show that the quadratic realizable and shear stress transport models predict pin surface heat transfer rates with the highest accuracy, with a dependency on Reynolds number and location within the channel. Comparisons have also shown that depending on Reynolds number, the realizable and quadratic realizable models match the pressure coefficient on the surface of the pin to within 8%.

Exergo-economic analysis of a 1-MW biomass-based combined cycle plant with externally fired gas turbine cycle and supercritical organic Rankine cycle

This paper deals with exergo-economic modeling and analysis of a 1-MW biomass integrated gasification combined cycle plant that couples an indirectly heated gas turbine (GT) cycle with a supercritical organic Rankine cycle (ORC). The GT produces a fixed net output of 500 kWe, and the organic vapor turbine produces the rest. Saw dust is considered as biomass feed for the gasifier, and toluene acts as ORC working fluid. GT cycle working fluid is heated through a combined combustor-heat exchanger (CHX) unit. Effects of plant parameters, viz. compressor pressure ratio (rp), gas turbine inlet temperature (TIT) and cold end temperature difference (CETD) of the CHX unit on the thermodynamic and economic performance of the plant are reported. Energy efficiency is maximized at a fixed value of rp (=6), for all TITs. Higher TIT yields in higher efficiency of the plant. Although increase in CETD lowers the plant efficiency but decreases the size of CHX unit, resulting in the lower capital cost of the unit. Exergo-economic analysis reveals that unit product cost (UPC) is lower at higher TITs and higher rp values. Levelized unit cost of electricity (LUCE) is also minimized at rp = 6 for all TITs. Higher TIT also yields lower UPC and LUCE values. Both UPC and LUCE decrease with increase in CETD. For rp = 6, TIT = 1100 °C and CETD = 300 °C, the plant offers minimum UPC and LUCE values.

A New Method for the Design of Optimal Control in the Transient State of a Gas Turbine Engine

To improve the control performance in the transient state of a gas turbine engine, a new method based on variable replacement method (VRM) and particle swarm optimization (PSO) algorithm is proposed. Above all, an acceleration schedule under the constraints of fuel air ratio ( $FAR$ ), high pressure turbine inlet temperature ( $T_{4}$ ) and high pressure compressor surge margin ( $SM$ ) could be obtained. Then PSO is employed to optimize the acceleration controller. At the same time, the deceleration controller is designed in consideration of minimum fuel ratio unit ( ${W_{f}}/{P_{s_{3}}}$ ) limiter. At last, a simulation is carried out to verify the performance of the proposed method and the results manifest that the optimized controller can track the acceleration command quickly and accurately, while accomplish the requirement of minimum fuel ratio unit (0.005) in deceleration.

Comparison of the performance of two different Dual-loop organic Rankine cycles (DORC) with nanofluid for engine waste heat recovery

To recover the heat from engine exhaust, coolant liquid and high-temperature loop, two different Dual-loop organic Rankine cycles (DORC) are studied in this paper. The two systems differ for the number of stages of heat recovery from engine exhaust, and both include high temperature loop and low temperature loop in each system. R123, R245fa, ethanol, R141b, and water are the candidate working fluids of HT loop, and R143a is the working fluid of LT loop. Because the coolant water in engines has lower temperature, it is more difficult to recover its heat. Therefore, in this study, graphene nanoparticles and carbon nanotubes are added to coolant water to enhance its heat transfer. Net output power, thermal efficiency, and exergy efficiency are selected as the objective functions. Results show that the single stage system (S1) is a little better than the other. Water-based S1 performs the best and the net output power, the thermal efficiency, and the exergy efficiency are 96.92kW, 14.13% and 64.04%, respectively. High evaporation pressure and turbine inlet temperature are better for performance optimization. And when the coolant water contains 0.5wt% carbon nanotubes, system reaches the max net output power increment of 3.84kW.

Energy and exergy analyses of a novel near zero emission plant: Combination of MATIANT cycle with gasification unit

A new combined near zero emission power producing system is proposed and analyzed in detail. The system is a combination of an oxy-fuel cycle, an externally biomass fired gas turbine cycle and an organic Rankine cycle (ORC). Energy and exergy analyses are performed to assess the system performance and identify the sources of inefficiencies in the system. The cycle efficiency is maximized at an optimum compressor pressure ratio the value of which depends on the ambient temperature, the high temperature turbine inlet temperature and the high pressure gas turbine inlet pressure. Energy and exergy efficiencies of 52.06% and 47.02%, respectively, are achieved for the proposed combined system for a temperature of 1400°C and a pressure of 40bar at the high temperature gas turbine inlet, a temperature of 700°C and a pressure of 300bar at the high pressure gas turbine inlet and a compressor pressure ratio of 19.59.

Lignite-fired air-blown IGCC systems with pre-combustion CO2capture

Detailed analyses based on mass and energy balances of lignite-fired air-blown gasification-based combined cycles with CO2 pre-combustion capture are presented and discussed in this work. The thermodynamic assessment is carried out with a proprietary code integrated with Aspen Plus® to carefully simulate the selective removal of both H2S and CO2 in the acid gas removal station. The work focuses on power plants with two combustion turbines, with lower and higher turbine inlet temperatures, respectively, as topping cycle. A high-moisture lignite, partially dried before feeding the air-blown gasification system, is used as fuel input. Because the raw lignite presents a very low amount of sulfur, a particular technique consisting of an acid gas recycle to the absorber, is adopted to fulfill the requirements related to the presence of H2S in the stream to the Claus plant and in the CO2-rich stream to storage. Despite the operation of the H2S removal section representing a significant issue, the impact on the performance of the power plant is limited. The calculations show that a significant lignite pre-drying is necessary to achieve higher efficiency in case of CO2 capture. In particular, considering a wide range (10–30 wt.%) of residual moisture in the dried lignite, higher heating value (HHV) efficiency presents a decreasing trend, with maximum values of 35.15% and 37.12% depending on the type of the combustion turbine, even though the higher the residual moisture in the dried coal, the lower the extraction of steam from the heat recovery steam cycle. On the other hand, introducing the specific primary energy consumption for CO2 avoided (SPECCA) as a measure of the energy cost related to CO2 capture, lower values were predicted when gasifying dried lignite with higher residual moisture content. In particular, a SPECCA value as low as 2.69 MJ/kgCO2 was calculated when gasifying lignite with the highest (30 wt.%) residual moisture content in a power plant with the advanced combustion turbine. Ultimately, focusing on the power plants with the advanced combustion turbine, air-blown gasification of lignite brings about a reduction in HHV efficiency equal to almost 1.5 to 2.8 percentage points, depending on the residual moisture in the dried lignite, if compared with similar cases where bituminous coal is used as fuel input. Copyright © 2016 John Wiley & Sons, Ltd.

서스펜션 플라즈마 용사법을 이용한 La2Zr2O7/YSZ 2층세라믹 열차폐코팅의 제조와 특성평가

Rare-earth zirconates, such as La2Zr2O7 and Gd2Zr2O7, have been investigated as one of the candidates for replacing conventional yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications at higher turbine inlet temperatures. In this study, double-ceramic-layer (DCL) TBCs of YSZ 1st layer and La2Zr2O7 top coat layer are fabricated by suspension plasma spray with serial liquid feeders. Microstructures, hardness profiles, and thermal durability of DCL-TBCs are also characterized. Fabricated DCL-TBCs of YSZ/ La2Zr2O7 exhibit excellent properties, such as adhesion strength (>25 MPa) and electrical thermal fatigue (~1429 cycles), which are comparable with TBCs fabricated by atmospheric plasma spray.

Exergy costing analysis and performance evaluation of selected gas turbine power plants

AbstractIn this study, exergy costing analysis and performance evaluation of selected gas turbine power plants in Nigeria are carried out. The results of exergy analysis confirmed that the combustion chamber is the most exergy destructive component compared to other cycle components. The exergetic efficiency of the plants was found to depend significantly on a change in gas turbine inlet temperature (GTIT). The increase in exergetic efficiency with the increase in turbine inlet temperature is limited by turbine material temperature limit. This was observed from the plant efficiency defect curve. As the turbine inlet temperature increases, the plant efficiency defect decreases to minimum value at certain GTIT (1,200 K), after which it increases with GTIT. This shows degradation in performance of gas turbine plant at high turbine inlet temperature. Exergy costing analysis shows that the combustion chamber has the greatest cost of exergy destruction compared to other components. Increasing the GTIT, both the...