Turbine Isentropic Efficiency Research Articles

Experimental Study of Low-temperature Organic Rankine Cycle with Axial Flow Turbine

We build a low temperature heat recovery ORC experimental system, in which R245fa is used as working fluids, a single-stage axial flow turbine is used to generate work, and the brazed plate heat exchangers are used as evaporator and condenser. The hot water is used to simulate the low-temperature heat source with temperature in the range of 320-370K, and cooling water at ambient temperature used as heat sink. Overall performance of the low-temperature ORC system is investigated. The results show that the axial flow turbine's isentropic efficiency is near of 0.6 under different evaporating temperature, and the fluctuated characteristics of the turbine appears at evaporating temperature of near 350K, and causes the stable overall performance of the ORC system at that temperature range. Moreover, overall net power output of the ORC system is over zero when evaporating temperature exceeds 350K in this research.

Analyses and optimization of a supercritical N2O Rankine cycle for low-grade heat conversion

Analyses and operating pressure optimization of the supercritical Rankine cycles with and without regenerator and reheating for low-grade heat conversion have been conducted using N2O as a working fluid and compared with its counterpart CO2 based on various performance indicators. N2O is better in terms of net power output, thermal efficiency and exergetic efficiency and N2O works at much lower pressures at optimum operation; whereas, CO2 is advantageous in terms of turbine size, expansion ratio and heat transfer requirement. The choice of optimum operating conditions will differ depending on the chosen performance indicator. Hence, there is a need of trade-off between various indicators. Component wise irreversibility distribution shows the similar trends for both working fluids. With the increase in cycle temperature lift, both turbine shape parameter and heat transfer requirement decrease, leading to more compactness. Higher pump and turbine isentropic efficiencies yield higher optimum turbine inlet pressure, and lower heat transfer requirement and turbine size. Uses of internal heat exchanger and reheating in the supercritical Rankine cycle not only improve the performances, it also constitutes an excellent compromise between various performance indicators based optimizations. Present study reveals that N2O is a potential option for the supercritical Rankine cycle.

Parametric optimization and range analysis of Organic Rankine Cycle for binary-cycle geothermal plant

In this study, a thermodynamic model of Organic Rankine Cycle (ORC) system combined with orthogonal design is proposed. The comprehensive scoring method was adopted to obtain a comprehensive index to evaluate both of the thermodynamic performance and economic performance. The optimal level constitution of system parameters which improves the thermodynamic and economic performance of ORC system is provided by analyzing the result of orthogonal design. The range analysis based on orthogonal design is adopted to determine the sensitivity of system parameters to the net power output of ORC system, thermal efficiency, the SP factor of radial inflow turbine, the power decrease factor of the pump and the total heat transfer capacity. The results show that the optimal level constitution of system parameters is determined as the working fluid of R245fa, the super heating temperature of 10°C, the pinch temperature difference in evaporator and condenser of 5°C, the evaporating temperature of 65°C, the isentropic efficiency for the pump of 0.75 and the isentropic efficiency of radial inflow turbine of 0.85. The order of system parameters’ sensitivity to the comprehensive index of orthogonal design is evaporating temperature>isentropic efficiency of radial inflow turbine>the working fluid>the pinch temperature difference of the evaporator and the condenser>isentropic efficiency of cycle pump>the super heating temperature. This study provides useful references for selecting main controlled parameters in the optimal design of ORC system.

Detailed analysis of the effect of the turbine and compressor isentropic efficiency on the thermal and exergy efficiency of a Brayton cycle

Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The irreversibility of the adiabatic processes in turbine and compressor is taken into account through their isentropic efficiencies. The net work per cycle, the thermal efficiency and the two exergy efficiencies are expressed as functions of the four dimensionless variables: the isentropic efficiencies of turbine and compressor, the pressure ratio, and the temperature ratio. It is shown that the maximal values of the net work per cycle, the thermal and the exergy efficiency are achieved when the isentropic efficiencies and temperature ratio are as high as possible, while the different values of pressure ratio that maximize the net work per cycle, the thermal and the exergy efficiencies exist. These pressure ratios increase with the increase of the temperature ratio and the isentropic efficiency of compressor and turbine. The increase of the turbine isentropic efficiency has a greater impact on the increase of the net work per cycle and the thermal efficiency of a Brayton cycle than the same increase of compressor isentropic efficiency. Finally, two goal functions are proposed for thermodynamic optimization of a Brayton cycle for given values of the temperature ratio and the compressor and turbine isentropic efficiencies. The first maximizes the sum of the net work per cycle and thermal efficiency while the second the net work per cycle and exergy efficiency. In both cases the optimal pressure ratio is closer to the pressure ratio that maximizes the net work per cycle.

Organic Rankine Cycle as Bottoming Cycle to a Combined Brayton and Clausius - Rankine Cycle

A preliminary evaluation has been made of a possibility of bottoming of a conventional Brayton cycle cooperating with the CHP power plant with the organic Rankine cycle installation. Such solution contributes to the possibility of annual operation of that power plant, except of operation only in periods when there is a demand for the heat. Additional benefit would be the fact that an optimized backpressure steam cycle has the advantage of a smaller pressure ratio and therefore a less complex turbine design with smaller final diameter. In addition, a lower superheating temperature is required compared to a condensing steam cycle with the same evaporation pressure. Bottoming ORCs have previously been considered by Chacartegui et al. for combined cycle power plants [ Their main conclusion was that challenges are for the development of this technology in medium and large scale power generation are the development of reliable axial vapour turbines for organic fluids. Another study was made by Angelino et al. to improve the performance of steam power stations [. This paper presents an enhanced approach, as it will be considered here that the ORC installation could be extra-heated with the bleed steam, a concept presented by the authors in [. In such way the efficiency of the bottoming cycle can be increased and an amount of electricity generated increases. A thermodynamic analysis and a comparative study of the cycle efficiency for a simplified steam cycle cooperating with ORC cycle will be presented. The most commonly used organic fluids will be considered, namely R245fa, R134a, toluene, and 2 silicone oils (MM and MDM). Working fluid selection and its application area is being discussed based on fluid properties. The thermal efficiency is mainly determined by the temperature level of the heat source and the condenser conditions. The influence of several process parameters such as turbine inlet and condenser temperature, turbine isentropic efficiency, vapour quality and pressure, use of a regenerator (ORC) will be presented. Finally, some general and economic considerations related to the choice between a steam cycle and ORC are discussed.

Additional Power Generation From Waste Energy of Diesel Engine Using Parallel Flow Shell and Tube Heat Exchanger

High temperature diesel engine exhaust gas can be an important source of heat to operate a bottoming Rankine cycle to produce additional power. In this research, an experiment was performed to calculate the available energy in the exhaust gas of an automotive diesel engine. A shell and tube heat exchanger was used to extract heat from the exhaust gas, and the performance of two shell and tube heat exchangers was investigated with parallel flow arrangement using water as the working fluid. The heat exchangers were purchased from the market. As the design of these heat exchangers was not optimal, the effectiveness was found to be 0.52, which is much lower than the ideal one for this type of application. Therefore, with the available experimental data, the important geometric aspects of the heat exchanger, such as the number and diameter of the tubes and the length and diameter of the shell, were optimized using computational fluid dynamics (CFD) simulation. The optimized heat exchanger effectiveness was found to be 0.74. Using the optimized heat exchangers, simulation was conducted to estimate the possible additional power generation considering 70% isentropic turbine efficiency. The proposed optimized heat exchanger was able to generate 20.6% additional power, which resulted in improvement of overall efficiency from 30% to 39%. Upon investigation of the effect of the working pressure on additional power generation, it was found that higher additional power can be achieved at higher working pressure. For this particular application, 30 bar was found to be the optimum working pressure at rated load. The working pressure was also optimized at part load and found that 2 and 20 were the optimized working pressures for 25% and 83% load. As a result 1.8% and 13.3% additional power were developed, respectively. Thus, waste heat recovery technology has a great potential for saving energy, improving overall engine efficiency, and reducing toxic emission per kilowatt of power generation.

Experimental Study and Numerical Simulation of a Regenerative ORC Utilizing Low-Grade Heat Source

In this paper, the performance of the regenerative organic rankine cycle (ORC) working with R123 is experimentally analyzed at different heat source temperatures of approximately 85, 95, 110, and 130°C. The higher heat source temperature leads to higher turbine inlet temperature, turbine inlet pressure, and turbine rotation speed. The regenerator and the increment of turbine inlet temperature can both increase the efficiency of the system. The experimental data of ORC are compared with that of the conventional Rankine cycle (CRC), which employs water as the working fluid. The results indicate that the thermal efficiency and the turbine isentropic efficiency of the ORC are higher than that of the CRC by approximately 5.9 and 24%, respectively. A numerical model is built by interconnecting different submodels: a turbine model, a volumetric pump model, and the heat exchanger models. The numerical results show a good agreement with the experimental data in terms of system efficiency. The model is finally used to calculate the pressure drop and pump power of the system.

Waste heat recovery from the exhaust of a diesel generator using Rankine Cycle

Exhaust heat from diesel engines can be an important heat source to provide additional power using a separate Rankine Cycle (RC). In this research, experiments were conducted to measure the available exhaust heat from a 40kW diesel generator using two ‘off-the-shelf’ heat exchangers. The effectiveness of the heat exchangers using water as the working fluid was found to be 0.44 which seems to be lower than a standard one. This lower performance of the existing heat exchangers indicates the necessity of optimization of the design of the heat exchangers for this particular application. With the available experimental data, computer simulations were carried out to optimize the design of the heat exchangers. Two heat exchangers were used to generate super-heated steam to expand in the turbine using two orientations: series and parallel. The optimized heat exchangers were then used to estimate additional power considering actual turbine isentropic efficiency. The proposed heat exchanger was able to produce 11% additional power using water as the working fluid at a pressure of 15bar at rated engine load. This additional power resulted into 12% improvement in brake-specific fuel consumption (bsfc). The effects of the working fluid pressure were also investigated to maximize the additional power production. The pressure was limited to 15bar which was constrained by the exhaust gas temperature. However, higher pressure is possible for higher exhaust gas temperatures from higher capacity engines. This would yield more additional power with further improvements in bsfc. At 40% part load, the additional power developed was 3.4% which resulted in 3.3% reduction in bsfc.

English

Owing to their numerous advantages, gas turbine (GT) power plants have become an important technology for power generation. This paper presents a parametric analysis for different configurations of GT plants, considering the effects of isentropic compressor and turbine efficiency, which allows the selection of the optimum GT configuration for the optimum performance of a GT power plant. The computational model was developed utilizing MATLAB software. The simulated results show that the reheat GT configuration has higher power output, whereas the regenerative GT configuration has higher thermal efficiency, when considering the effects of isentropic compressor and turbine efficiency. The maximum thermal efficiency of 52.4% and the maximum power output of 268 MW are obtained with isentropic turbine efficiency. The result reveals that isentropic compressor and turbine efficiency influence significantly the performance of GTs.

Thermo‐economic Optimization of Gas Turbine Power Plant with Details in Intercooler

AbstractIn this paper a gas turbine power plant with intercooler is modeled and optimized. The intercooler is modeled in details using the ε − NTU method. Air compressor pressure ratio, compressor isentropic efficiency, gas turbine isentropic efficiency, turbine inlet temperature, cooling capacity of the absorption chiller, recuperator effectiveness as well as eight parameters for configuration of the intercooler are selected as design variables. Multi‐objective genetic algorithm is applied to optimize the total cost rate and total cycle efficiency simultaneously. Two plants including an intercooler and with/without air preheater are studied separately. It is observed that the air compressor pressure ratio in the HP compressor is higher than the LP compressor in both cases and its differences are higher for a plant without an air preheater. Actually the air compressor pressure ratio is found to be about 8.5% lower than the ideal value and 9.5% higher than the ideal value in the LP compressor and HP compressor, respectively, in the case with an air preheater. Moreover, a correlation for intercooler pressure drop in terms of its effectiveness was derived in the optimum situation for each case. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 704–723, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21051

Modelling and exergoeconomic based design optimisation of combined power plants

In this research a Combined Cycle Power Plant (CCPP) which can provide 80 MW of electrical power has been studied. The design parameters of the plant were chosen as: compressor pressure ratio, compressor isentropic efficiency, gas turbine isentropic efficiency, and turbine inlet temperature, pinch difference temperature, steam turbine inlet temperature, steam turbine isentropic efficiency, condenser pressure, and pump isentropic efficiency. In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function representing the total cost of the plant in terms of dollar per second was defined as the sum of the operating cost related to the fuel consumption, and the capital investment for equipment purchase and maintenance costs. Finally, the optimal values of decision variables were obtained by minimising the objective function using Sequential Quadratic Programming (SQP) for, 50, 60, 70, and 80 MW of net power output.

Exergo-environmental analysis of an integrated organic Rankine cycle for trigeneration

A comprehensive thermodynamic modelling is reported of a trigeneration system for cooling, heating (and/or hot water) and electricity generation. This trigeneration system consists of a gas turbine cycle, an organic Rankine cycle (ORC), a single-effect absorption chiller and a domestic water heater. Energy and exergy analyses, environmental impact assessments and related parametric studies are carried out, and parameters that measure environmental impact and sustainability are evaluated. The exergy efficiency of the trigeneration system is found to be higher than that of typical combined heat and power systems or gas turbine cycles. The results also indicate that carbon dioxide emissions for the trigeneration system are less than for the aforementioned systems. The exergy results show that combustion chamber has the largest exergy destruction of the cycle components, due to the irreversible nature of its chemical reactions and the high temperature difference between the working fluid and flame temperature. The parametric investigations show that the compressor pressure ratio, the gas turbine inlet temperature and the gas turbine isentropic efficiency significantly affect the exergy efficiency and environmental impact of the trigeneration system. Also, increasing the turbine inlet temperature decreases the cost of environmental impact, primarily by reducing the combustion chamber mass flow rate.

Exergoeconomic analysis of a combined cycle system utilizing associated gases from steel production process based on structural theory of thermoeconomics

Exergoeconomic analysis plays an important role in finding ways to improve the performance of a complex thermal system. In this article, exergoeconomic analysis had been performed for a combined cycle system, which was proposed by authors, utilizing associated gases (blast-furnace gas, coke oven gas and sintering waste gas) from steel production process based on structural theory of thermoeconomics. Three exergoeconomic indexes (the cost difference, the relative cost difference and the exergoeconomic factor) were calculated to evaluate the thermoeconomic performance of each component. Moreover, the influences of the decision variables (the pressure ratios and the isentropic efficiencies of air compressor and blast-furnace-gas compressor, the temperature of combustion products entering gas turbine, and the isentropic efficiencies of gas turbine and steam turbine) and the capital costs (equipment purchase and fuel) on the unitary exergetic and monetary costs of production were also investigated. The analysis shows the deep relations of the unitary costs to the changes in these parameters and the superiorities of the proposed system emerging gradually through comparing with other systems (the combined cycle system with afterburning chamber in heat recovery steam generator, the combined cycle system without afterburning combustion, and the power generation system of steam turbine).

Contribution to the Modeling and Understanding of Cold Pulsating Flow Influence in the Efficiency of Small Radial Turbines for Turbochargers

In the present paper, an unsteady approach to determine the performance of a small radial inflow turbine working under cold pulsating flow is presented. It has been concluded that a reasonably good characterization of turbine behavior working with pulsating flow can be obtained using, in a quasi-steady way, models of the turbine isentropic efficiency and turbocharger mechanical efficiency. Both models have been fitted using data obtained from a steady flow characterization procedure. Turbocharger-measured parameters from the cold pulsating flow campaign have been compared with the ones obtained from one-dimensional gas dynamics computational modeling. The modeling approach is based on quasi-steady isentropic and mechanical efficiency models. Reasonably good accuracy in compressor and turbine variables prediction has been obtained for most of the operative conditions. Influence of amplitude and frequency of the pulsating flow over the instantaneous and average turbine efficiency has been studied to put some light on the analysis of the involved physical phenomena. The main conclusion is that the biggest effect of unsteady flow on turbine efficiency is through the influence on blade jet to speed ratio. It has been also concluded that, for the same average blade jet to speed ratio, pulses’ amplitude does not influence turbine efficiency when it is closed, but does at other variable geometry turbine (VGT) positions. The effect of pulses’ frequency is less evident and only influences VGT performance at the highest VGT openings.

Energetic and exergetic investigation of an organic Rankine cycle at different heat source temperatures

The energetic and exergetic performance of an updated ORC (organic Rankine cycle) is investigated. The thermal efficiencies of the ORC at different heat source temperatures of about 100, 90, 80, and 70 °C are explored. The thermodynamic irreversibility that takes place in the evaporator, condenser, turbine, pump, and separator is revealed. The ORC feasibility for low-temperature applications is demonstrated. With a hot side temperature of around 80 °C, a thermal efficiency of 7.4% and a turbine isentropic efficiency of 0.68 can be achieved. The present research further indicates that exergy destruction caused by heat transfer through an appreciable temperature difference in the evaporator is the largest in the energy conversion process, followed by that in the condenser. The exergy destroyed in the heat exchangers amounts to 74% of the overall exergy loss. The total system exergy efficiency is approximately 40%; thus, ways to improve exergy efficiency are required. HCFC-123, a dry fluid, is experimentally confirmed to be highly superheated after expansion in this study. A regenerator should be used to preheat HCFC-123 prior to entering the evaporator. Meanwhile the heat-transfer configuration with two oil cycles can be a good solution to overcome the thermodynamic disadvantage of a one-stage evaporator.

Modelling and exergoeconomic optimisation of a gas turbine with absorption chiller using evolutionary algorithm

In this paper, thermodynamic modelling of a gas turbine cycle with absorption chiller is performed. A thermoeconomic approach is utilised to find the most optimal values of design parameters for practical applications. Some design parameters considered are compressor pressure ratio, compressor isentropic efficiency, gas turbine isentropic efficiency, gas turbine inlet temperature, HRSG pressure, pinch point temperature, absorption generator temperature, absorption evaporator temperature and absorption condenser temperature. The objective function considered for the optimisation purpose is the summation of the fuel cost, purchase cost of each component and the total cost rate of exergy destruction. A sensitivity analysis of the changes in the design parameters with respect to the unit cost of fuel and gas turbine output power is also performed. The results show that increase in the unit cost of fuel tends to decrease in other term of objective function. Moreover, increase of the unit cost of fuel leads to elect the equipment in the way their cost of exergy destruction reduces.

Multi-Objective Approach in Exergoeconomic and Environmental Optimization of the Gas Turbine Cycle

The gas turbine cycle either as an individual power production cycle or as a part of yet another cycle, is one of the most common industrials till now which, has been ever evaluated and analyzed. In the present research, this cycle has been modeled individually along with a pre-heater and a compressor at two stages with the objective to maximize the exergic efficiency and in the meantime decreasing the costs and environmental pollution. In addition, the isentropic turbine efficiency, the isentropic compressor efficiency, the ratio of the total pressure of the cycle, and the percentage of extra air has been defined as the design variables. Two objective functions are evaluated to be optimized by the genetic algorithm using the Pareto fitness approach as the determining comparison function. Finally, the exergo-economic coefficient of the related components and the amount of their exergy destruction and cost, at the optimum point, has been compared.

베인노즐 출구각도에 따른 100kW급 구심터빈의 성능 및 내부유동의 영향

In this study, we analysed the influence of the performance and inflow flow of a radial inflow turbine with the variation of vane nozzle exit angles for a 100kW class turbine applicable in the waste heat recovery system. For this, three-dimensional CFD analysis was performed using commercial code called ANSYS Fluent 12.1. As the vane nozzle exit angle was more increased the reattachment region near blades of the vane nozzle got smaller, and also the Mach number at vane nozzle exit was observed to be 1 due to the effect of the cross section reduction. Through this study, we expect that the analysed results will be used as the design material for the composition of the turbine optimal design parameters corresponding to the target output power. Key w ords: Radial inflow turbine, Computational fluid dynamics, Vane nozzle exit angle, Mach number, Isentropic turbine efficiency, Mechanical power

Greenhouse gas emission and exergo-environmental analyses of a trigeneration energy system

A comprehensive thermodynamic modeling is reported of a trigeneration system for cooling, heating and electricity purposes. This trigeneration system consists of a gas turbine cycle, a steam turbine cycle and a single-effect absorption chiller. Energy and exergy analyses, environmental impact assessments and related parametric studies are carried out, and parameters that measure environmental impact and sustainability are evaluated. The exergy efficiency of the trigeneration system is found to be higher than that for typical combined heat and power systems or gas turbine cycles. The results also indicate that the carbon dioxide emissions for the trigeneration system are less than those for the compared systems. The parametric investigations show that compressor pressure ratio, the gas turbine inlet temperature, the gas turbine isentropic efficiency and the heat recovery steam generator pressure significantly affect the exergy efficiency and environmental impact of the trigeneration system. The results also show that compressor pressure ratio and turbine inlet temperature decreases the cost of environmental impact, primarily by reducing the combustion chamber mass flow rate. The evaluation of the exergy efficiency, exergy destruction, carbon dioxide emission and cost of environmental impacts for each case and the overall cycle demonstrate that the combustion chamber has the highest exergy destruction of all system components, due to the high temperature difference between the working fluid and the flame temperature.

Thermodynamic and exergoenvironmental analyses, and multi-objective optimization of a gas turbine power plant

Abstract The present study deals with a comprehensive thermodynamic and exergoeconomic modeling of a Gas Turbine (GT) power plant. In order to validate the thermodynamic model, the results are compared with one of the largest gas turbine power plants in Iran (known as Shahid Salimi Gas Turbine power plant). Moreover, a multi-objective optimization is performed to find the best design variables. The design parameters considered here are air compressor pressure ratio ( r AC ), compressor isentropic efficiency ( η AC ), gas turbine isentropic efficiency ( η GT ), combustion chamber inlet temperature ( T 3 ) and gas turbine inlet temperature (TIT). In the multi-objective optimization approach, certain exergetic, economic and environmental parameters are considered through two objective functions, including the gas turbine exergy efficiency, total cost rate of the system production including cost rate of environmental impact. In addition, fast and effective non-dominated sorting genetic algorithm (NSGA-II) is applied for the optimization purpose. The thermoenviroeconomic objective function is minimized while power plant exergy efficiency is maximized using a power full developed genetic algorithm. The results of optimal designs are obtained as a set of multiple optimum solutions, called ‘the Pareto optimal solutions’. Moreover, the optimized results are compared with the working data from the case study. These show that by selecting the optimized data 50.50% reduction in environmental impacts is obtained. Finally, sensitivity analysis of change in objective functions, when the optimum design parameters vary, is performed and the degree of each parameter on conflicting objective functions has been determined.