One-Dimensional and Three-Dimensional Numerical Optimization and Comparison of Single-Stage Supersonic and Dual-Stage Transonic Radial Inflow Turbines for the ORC

2016 ◽  
Author(s):  
K. Rahbar ◽  
S. Mahmoud ◽  
R. K. Al-Dadah ◽  
N. Moazami
Keyword(s):  
Shock Waves ◽  
Thermal Efficiency ◽  
Numerical Optimization ◽  
Optimization Technique ◽  
Expansion Ratio ◽  
Single Stage ◽  
Cycle Performance ◽  
Turbine Efficiency ◽  
Dual Stage ◽  
Isentropic Efficiency

Organic Rankine cycle is one of the most efficient technologies that can utilize low-to-medium grade heat sources and generate useful power. Radial inflow turbine (RIT) is the key component of the ORC and its efficiency has significant effect on the overall cycle performance. Obtaining high cycle thermal efficiency requires large pressure difference (expansion ratio) across the cycle. With the low speed of sound of organic fluids and the high expansion ratios, RIT becomes chocked with supersonic flow regime and shock waves that deteriorate the turbine efficiency and hence reduce the cycle performance. Therefore, developing highly efficient RIT that can both preserve the high expansion ratio requirements of the ORC and maintain the turbine isentropic efficiency is crucial. This paper proposed the complete 1-D and 3-D numerical optimization of two different configurations as single-stage supersonic and dual-stage transonic RITs. Initially, the integrated 1-D modelling of the ORC with RIT coupled with genetic algorithm optimization technique was conducted to maximize the cycle thermal efficiency. The results showed that the dual-stage RIT exhibited considerably higher turbine efficiency in both stages and hence higher cycle efficiency compared to the single-stage supersonic one. Both configurations were further optimized using the 3-D CFD optimization procedure to maximize the turbine efficiency. The CFD results showed that the optimization of each stage individually was successful as the turbine performance increased significantly. The results revealed that the optimizations were more effective for the dual-stage transonic turbine compared to the single-stage supersonic due to the presence of shock waves. Comparison of the optimized single-stage supersonic RIT and complete dual-stage transonic RIT showed that about 15.7%, 10.63kW and 16.08% higher turbine isentropic efficiency, turbine power and cycle thermal efficiency were achieved respectively with the latter configuration.

scholarly journals Carnot cycle in practice: compensating inefficiencies of ORC expanders through thermal regeneration

2021 ◽  
Vol 238 ◽  
pp. 10005
Author(s):  
Lucie Lefebvre ◽  
Ward De Paepe ◽  
Mario L. Ferrari ◽  
Alberto Traverso
Keyword(s):  
Heat Extraction ◽  
Cycle Performance ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Small Scale ◽  
Low Grade ◽  
Expansion Process ◽  
Turbine Efficiency ◽  
Wide Range ◽  
Isentropic Efficiency

The Organic Rankine Cycle (ORC) is a thermodynamic cycle that can operate with a hot source over a wide range of temperatures, especially with low-grade heat (below 200°C). One of the main limitations for the success of small-scale ORC cycles (few to 100 kWe) is the relatively low isentropic efficiency of the typically used turbomachinery. Low turbine efficiency leads to low ORC cycle performance. To increase the performance of the cycle, the turbine efficiency must be increase, however, this significantly increases the cost of the machinery, making the cycle less profitable. In this work, the performance evaluation of low-temperature ORC cycles (100-150°C) with heat extraction along the expansion process is investigated, in an attempt to overcome this limitation. The studied cycle works in the same way as a conventional ORC, except that during the expansion process, heat is extracted. This heat is re-used later in the cycle, just before the hot source, allowing to reduce its load. The different cycles presented in this paper, using pentane as working fluid, are compared based on their exergetic and energetic efficiencies. The influence of three parameters on the cycle performance is studied: the regeneration ratio, the maximum temperature of the cycle and the turbine isentropic efficiency. In the case of a cycle using pentane with a maximum temperature of 150 °C and an turbine isentropic efficiency of 65%, the energy efficiency increases from 6.2% to 16.3% when going from no regeneration to full regeneration, and the exergy efficiency increases from 21.1 to 45.8%.. Secondly, the influence of the maximum temperature of the cycle is studied. Using pentane as the working fluid, the higher the maximum temperature is, the larger the benefits of heat extraction. However, this temperature cannot exceed the critical temperature of the organic fluid to stay in the case of a subcritical cycle. Finally, considering the turbine isentropic efficiency, it is possible to demonstrate that using a less efficient turbine, for example in small ORC systems, the performance of a cycle with an ideal turbine isentropic efficiency (100%) can be achieved compensating at cycle level the turbine losses with the heat extraction along the expansion process.

Integrated Modelling and Multi-Objective Optimization of Organic Rankine Cycle Based on Radial Inflow Turbine

2015 ◽  
Author(s):  
K. Rahbar ◽  
S. Mahmoud ◽  
R. K. Al-Dadah ◽  
N. Moazami
Keyword(s):  
Thermal Efficiency ◽  
Organic Rankine Cycle ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Integrated Modelling ◽  
Working Fluid ◽  
Multi Objective Optimization ◽  
Multi Objective ◽  
Turbine Efficiency ◽  
Radial Inflow Turbine

This paper presents the integrated modelling and multi-objective optimization of ORC based on radial inflow turbine. With this approach it is possible to replace the constant turbine efficiency with a dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. This allows overcoming any arbitrary assumption of the turbine efficiency, unlike the previous literature, and providing a more realistic estimation of the cycle performance. Parametric studies were conducted utilizing the developed model to identify the key input variables that have significant effects on the critical turbine-ORC performance indicators. These variables were then included in the optimization process using DIRECT algorithm to optimize two objective functions as the cycle thermal efficiency and the turbine overall size for five organic fluids. Optimization results predicted that isobutane exhibited the best performance with the maximum cycle thermal efficiency of 13.21% and turbine overall size of 0.1434m while having relatively high turbine isentropic efficiency of 77.03%.

scholarly journals Performance Analysis of Organic Rankine Cycle with the Turbine Embedded in a Generator (TEG)

Energies ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 309
Author(s):  
Jung-Bo Sim ◽  
Se-Jin Yook ◽  
Young Won Kim
Keyword(s):  
Thermal Efficiency ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Turbine Rotor ◽  
Loss Coefficient ◽  
Tip Clearance ◽  
Working Fluid ◽  
Turbine Generator ◽  
Turbine Efficiency ◽  
Isentropic Efficiency

The organic Rankine cycle (ORC) is a thermodynamic cycle in which electrical power is generated using an organic refrigerant as a working fluid at low temperatures with low-grade enthalpy. We propose a turbine embedded in a generator (TEG), wherein the turbine rotor is embedded inside the generator rotor, thus simplifying turbine generator structure using only one bearing. The absence of tip clearance between the turbine rotor blade and casing wall in the TEG eliminates tip clearance loss, enhancing turbine efficiency. A single-stage axial-flow turbine was designed using mean-line analysis based on physical properties, and we conducted a parametric study of turbine performance, and predicted turbine efficiency and power using the tip clearance loss coefficient. When the tip clearance loss coefficient was applied, turbine isentropic efficiency and power were 0.89 and 20.42 kW, respectively, and ORC thermal efficiency was 4.81%. Conversely, the isentropic efficiency and power of the turbine without the tip clearance loss coefficient were 0.94 and 22.03 kW, respectively, and the thermal efficiency of the ORC was 5.08%. Therefore, applying the proposed TEG to the ORC system simplifies the turbine generator, while improving ORC thermal efficiency. A 3D turbine generator assembly with proposed TEG structure was also proposed.

scholarly journals A gas turbine cooled-stage expansion model for the simulation of blade cooling effects on cycle performance

2019 ◽  
Author(s):  
Roberta Masci ◽  
Enrico Sciubba
Keyword(s):  
Gas Turbine ◽  
Thermal Efficiency ◽  
Gas Turbines ◽  
Numerical Procedure ◽  
Expansion Ratio ◽  
Cycle Performance ◽  
Inlet Temperature ◽  
Cooling Effects ◽  
Cooling Air ◽  
Cycle Efficiency

Modern gas turbines firing temperatures (1500-2000K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages -nozzle vanes and rotor blades- with a portion of the compressor discharge air, a practice that induces a penalty on the cycle thermal efficiency. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different TIT (turbine inlet temperature) and max (total turbine expansion ratio) with a realistically acceptable degree of approximation.. The calculations suggest that, at a given max, the TIT can be increased in order to reach higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher max and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at lower rather than higher max. The small penalty on cycle efficiency is compensated by lower plant cost. The results of our model agree with those of some previous much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate and low resource intensity of the corresponding numerical procedure: all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic, with no investigation on the effects of the different configurations on plant costs, so that future work addressing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.

scholarly journals A Gas Turbine Cooled-Stage Expansion Model for the Simulation of Blade Cooling Effects on Cycle Performance

2019 ◽  
Vol 4 (4) ◽  
pp. 36
Author(s):  
Masci ◽  
Sciubba
Keyword(s):  
Gas Turbine ◽  
Thermal Efficiency ◽  
Numerical Procedure ◽  
Degree Of Approximation ◽  
Expansion Ratio ◽  
Original Method ◽  
Cycle Performance ◽  
Cooling Effects ◽  
Cooling Air ◽  
Cycle Efficiency

Modern gas turbine firing temperatures (1500–2000 K) are well beyond the maximum allowable blade material temperatures. Continuous safe operation is made possible by cooling the HP turbine first stages, nozzle vanes and rotor blades, with a portion of the compressor discharge air, a practice that induces a penalty on the thermal efficiency cycle. Therefore, a current issue is to investigate the real advantage, technical and economical, of raising maximum temperatures much further beyond current values. In this paper, process simulations of a gas turbine are performed to assess HP turbine first-stage cooling effects on cycle performance. A new simplified and properly streamlined model is proposed for the non-adiabatic expansion of the hot gas mixed with the cooling air within the blade passage, which allows for a comparison of several cycle configurations at different turbine inlet temperatures (TIT) and total turbine expansion ratio (PR) with a realistically acceptable degree of approximation. The calculations suggest that, at a given PR, the TIT can be increased in order to reach a higher cycle efficiency up to a limit imposed by the required amount and temperature of the cooling air. Beyond this limit, no significant gains in thermal efficiency are obtained by adopting higher PR and/or increasing the TIT, so that it is convenient in terms of cycle performance to design at a lower rather than higher PR. The small penalty on cycle efficiency is compensated by the lower plant cost. The results of our model agree with those of some previous and much more complex and computationally expensive studies, so that the novelty of this paper lies in the original method adopted on which the proposed model is based, and in the fast, accurate, and low resource intensity of the corresponding numerical procedure, all advantages that can be crucial for industry needs. The presented analysis is purely thermodynamic and it includes no investigation on the effects of the different configurations on plant costs. Therefore, performing a thermo-economic analysis of the air-cooled gas turbine power plant is the next logical step.

scholarly journals A Theoretical Study on the Thermodynamic Cycle of Concept Engine with Miller Cycle

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1051
Author(s):  
Jungmo Oh ◽  
Kichol Noh ◽  
Changhee Lee
Keyword(s):  
Compression Ratio ◽  
Thermal Efficiency ◽  
Engine Performance ◽  
Thermodynamic Cycle ◽  
Expansion Ratio ◽  
Boost Pressure ◽  
Miller Cycle ◽  
Compression Pressure ◽  
Air Mass ◽  
Atkinson Cycle

The Atkinson cycle, where expansion ratio is higher than the compression ratio, is one of the methods used to improve thermal efficiency of engines. Miller improved the Atkinson cycle by controlling the intake- or exhaust-valve closing timing, a technique which is called the Miller cycle. The Otto–Miller cycle can improve thermal efficiency and reduce NOx emission by reducing compression work; however, it must compensate for the compression pressure and maintain the intake air mass through an effective compression ratio or turbocharge. Hence, we performed thermodynamic cycle analysis with changes in the intake-valve closing timing for the Otto–Miller cycle and evaluated the engine performance and Miller timing through the resulting problems and solutions. When only the compression ratio was compensated, the theoretical thermal efficiency of the Otto–Miller cycle improved by approximately 18.8% compared to that of the Otto cycle. In terms of thermal efficiency, it is more advantageous to compensate only the compression ratio; however, when considering the output of the engine, it is advantageous to also compensate the boost pressure to maintain the intake air mass flow rate.

Improving Efficiency of a High Work Turbine Using Non-Axisymmetric Endwalls: Part I—Endwall Design and Performance

2008 ◽  
Author(s):  
T. Germain ◽  
M. Nagel ◽  
I. Raab ◽  
P. Schuepbach ◽  
R. S. Abhari ◽  
...  
Keyword(s):  
Numerical Optimization ◽  
Axial Flow ◽  
Loss Reduction ◽  
Numerical Investigations ◽  
Turbine Efficiency ◽  
Transition Modeling ◽  
And Performance ◽  
High Work ◽  
Stage Efficiency ◽  
Probe Measurements

This paper is the first part of a two part paper reporting the improvement of efficiency of a one-and-half stage high work axial flow turbine by non-axisymmetric endwall contouring. In this first paper the design of the endwall contours is described and the CFD flow predictions are compared to five-hole-probe measurements. The endwalls have been designed using automatic numerical optimization by means of an Sequential Quadratic Programming (SQP) algorithm, the flow being computed with the 3D RANS solver TRACE. The aim of the design was to reduce the secondary kinetic energy and secondary losses. The experimental results confirm the improvement of turbine efficiency, showing a stage efficiency benefit of 1%±0.4%, revealing that the improvement is underestimated by CFD. The secondary flow and loss have been significantly reduced in the vane, but improvement of the midspan flow is also observed. Mainly this loss reduction in the first row and the more homogeneous flow is responsible for the overall improvement. Numerical investigations indicate that the transition modeling on the airfoil strongly influences the secondary loss predictions. The results confirm that non-axisymmetric endwall profiling is an effective method to improve turbine efficiency, but that further modeling work is needed to achieve a good predictability.

Single vs. Dual Stage Actuators: Why and When

2002 ◽  
Author(s):  
Fu-Ying Huang ◽  
Tetsuo Semba ◽  
Matthew White
Keyword(s):  
System Dynamics ◽  
Single Stage ◽  
Actuator Dynamics ◽  
Dual Stage ◽  
Dual Stage Actuator

Higher TPI HDD requires lower disturbance and higher error rejection capability. One of the limitations to achieve high error rejection capability is the dynamics of the actuator. Dual stage actuator (DSA) has been considered to replace single stage actuator (SSA) someday because of system dynamics difference and more freedom in servo design that may avoid the constraint of single stage actuator dynamics on servo. SSA and DSA were compared based on their dynamics, servo designs, and TMR benefits. The extendibility and limitations of both systems were studied. The criteria on when DSA would be implemented are also discussed.

A Numerical Optimization Technique Applied to the Design of Two-Dimensional Cavitating Hydrofoil Sections

1996 ◽  
Vol 40 (01) ◽  
pp. 28-38
Author(s):  
Shigenori Mishima ◽  
Spyros A. Kinnas
Keyword(s):  
Numerical Optimization ◽  
Cavity Length ◽  
Optimization Technique ◽  
Cavitation Number ◽  
Quadratic Functions ◽  
Two Dimensional ◽  
Systematic Design ◽  
Hydrodynamic Analysis ◽  
Total Drag ◽  
Cavitating Hydrofoil

A numerical nonlinear optimization technique is applied to the systematic design of two-dimensional partially or supercavitating hydrofoil sections. The design objective is to minimize the hydrofoil drag for given lift and cavitation number. The hydrodynamic analysis of the cavitating hydrofoil is performed in nonlinear theory, via a low-order potential-based panel method. The effects of viscosity are taken into account via a uniform friction coefficient applied on the wetted foil surface. The total drag, lift, cavitation number, and other quantities involved in the imposed constraints, are expressed in terms of quadratic functions of the main parameters of the hydrofoil geometry, angle of attack, and the cavity length. The optimization is based on the method of multipliers by coupling the Lagrange multiplier terms and the penalty function terms. The robustness and convergence of the method are extensively investigated, and the results are compared with those from applying other design methods.

Efficient Structural Design Using a Numerical Optimization Technique

2019 ◽  
Author(s):  
Qian Wang ◽  
Lucas Schmotzer ◽  
Yongwook Kim
Keyword(s):  
Structural Design ◽  
Numerical Optimization ◽  
Optimization Technique ◽  
Optimization Method ◽  
Optimization Techniques ◽  
Convergence Criteria ◽  
Efficient Design ◽  
Concrete Building ◽  
Gradient Based ◽  
Structural Responses

<p>Structural designs of complex buildings and infrastructures have long been based on engineering experience and a trial-and-error approach. The structural performance is checked each time when a design is determined. An alternative strategy based on numerical optimization techniques can provide engineers an effective and efficient design approach. To achieve an optimal design, a finite element (FE) program is employed to calculate structural responses including forces and deformations. A gradient-based or gradient-free optimization method can be integrated with the FE program to guide the design iterations, until certain convergence criteria are met. Due to the iterative nature of the numerical optimization, a user programming is required to repeatedly access and modify input data and to collect output data of the FE program. In this study, an approximation method was developed so that the structural responses could be expressed as approximate functions, and that the accuracy of the functions could be adaptively improved. In the method, the FE program was not required to be directly looped in the optimization iterations. As a practical illustrative example, a 3D reinforced concrete building structure was optimized. The proposed method worked very well and optimal designs were found to reduce the torsional responses of the building.</p>

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