Optimal Cycle Parameters Research Articles

Thermo-economic analysis of regenerative supercritical CO2 Brayton cycle considering turbomachinery leakage flow

The regenerative supercritical CO2 Brayton cycle (RSCBC) has great potential to improve the energy utilization efficiency and reduce greenhouse gas emissions. The leakage of supercritical CO2 into rotor cavity through labyrinth seals in turbomachinery including turbine and compressor inevitably reduces the cycle efficiency. Here, we propose a numerical method coupling the thermodynamic model with the labyrinth seal leakage model. The variations of turbomachinery leakage flow with cycle parameters and its effect on cycle thermo-economic performance are investigated. The optimal cycle parameters and thermo-economic performance are obtained by the multi-objective optimization. We find the cycle maximum pressure benefits the thermo-economic performance, while penalizes the sealing performance of turbomachinery labyrinth seal. Compared with ignoring the turbomachinery leakage, the optimal inlet state of the compressor vicinity of the pseudo-critical point that is adjacent to critical point when considering turbomachinery leakage. Furthermore, the turbomachinery leakage flow accounted for 2.5 % of the total flow under the optimized working condition, causing the thermal efficiency and exergy efficiency decrease 1.38 % and 3.52 % respectively, the heat exchanger area per unit power output and levelized energy cost increase 3.8 % and 3.83 % respectively. The proposed method and obtained results can provide some guidance for the optimal design of RSCBC system.

Optimization of the isolation of biologically active complexes from buds and shoots of birch and poplar buds for their further use in cosmeceutical compositions

The aim is to optimize the isolation of biologically active birch and poplar complexes based on woodworking industry waste to study their biological activity to create cosmeceutical compositions that have cosmetic and pharmaceutical effects.
 Materials and methods. The object of research is the vegetative organs of birch (buds and shoots) and poplar (buds). In the process of work, experimental studies were carried out on the extraction and separation of natural compounds, development of biological complexes of vegetative organs of birch and poplar, study of the chemical composition and standardization of biologically active complexes of birch and preparations based on them.
 Results. The optimal methods for extracting natural complexes were determined. Created as a semi-industrial installation for producing biologically active complexes by barothermal method, combining two processes - high pressure and hydrodistillation. The optimal operating cycle and plant parameters were determined. The optimal solvents for the extraction of biologically active complexes from the vegetative organs of birch and poplar have been determined. Petroleum ether (33.60 %) extracted the most compounds from birch buds, in birch shoots - ethanol (8.34 %). Qualitative and quantitative indicators of biologically active complexes are determined, and projects for examining the obtained biologically active complexes are proposed. We determined the yield of essential oil depending on the time of collection of raw materials and determined that the largest amount of essential oil is contained in spring buds (0.21 % of dry raw materials) and shoots (0.08 %).
 Conclusions. Biological complexes created from timber processing waste with high activity are the basis for the creation of cosmetic products. The created semi-industrial plant will provide the basis for creating new original products in industrial volumes.

Selecting working fluids in organic Rankine cycle (ORC) for waste heat applications and optimal cycle parameters for different hot source temperatures

Selecting working fluids in organic Rankine cycle (ORC) for waste heat applications and optimal cycle parameters for different hot source temperatures

A Machine Learning Framework With an Intelligent Algorithm for Predicting the Isentropic Efficiency of a Hydraulic Diaphragm Metering Pump in the Organic Rankine Cycle System

The pump provides the necessary pressure and flow for the organic Rankine cycle (ORC) system. The traditional methods have obvious limitations when analyzing the time-varying characteristics of the key operating parameters of the pump. This study first introduces the scatter plot analysis method to analyze and evaluate the time-varying and coupling characteristics of the hydraulic diaphragm metering pump. Then, a machine learning-fitting algorithm hybrid model is constructed to solve and verify the actual matching correlation equation of the key operating parameters. In addition, the complicated non-linear relationship brings great challenges to obtaining the limit value of the pump isentropic efficiency. This study introduces the bilinear interpolation algorithm to systematically analyze the change trend between operating parameters and isentropic efficiency. Based on the wavelet neural network (WNN) with momentum term and particle swarm optimization-adaptive inertia weight adjusting (PSO-AIWA), a machine learning framework with an intelligent algorithm is constructed. Under this framework, the maximum isentropic efficiency of the pump can be stabilized at 70.22–74.67% under all working conditions. Through the theoretical analysis model, the effectiveness of this framework is evaluated. Finally, the optimal cycle parameters are evaluated. This study can provide direct significance for the analysis and optimization of the actual performance of the ORC system.

Analysis of a 10 MW recompression supercritical carbon dioxide cycle for tropical climatic conditions

Recompression supercritical CO2 (sCO2) power cycles offer higher efficiencies over other sCO2 cycle configurations. This paper addresses the design of a 10 MW sCO2 recompression cycle suitable for tropical climates with a compressor inlet temperature of 45 °C and a maximum turbine inlet temperature of 565 °C to facilitate the use of conventional steel alloys. A design space analysis is carried out by incorporating individual component performance under various operating conditions. The proposed cycle uses a single two-stage axial turbine and two single-stage centrifugal compressors. The results are presented on an efficiency-net-specific work diagram showing the Pareto optimal curves for a range of recompression fractions. The optimum cycle parameters, pressure ratio, and recompression fraction are found to be 2.0 and 0.25, respectively, yielding a design point efficiency of 35%. The paper brings forth the effect of turbomachinery and heat exchangers sized for 45 °C compressor inlet temperature and 565 °C turbine inlet temperature on off-design cycle performance. The analysis is applied to develop strategies for optimally operating the recompression cycle at part load and off-design conditions.

A Study on Aeroengine Conceptual Design Considering Multi-Mission Performance Reliability

Owing to the realization of multi-mission adaptability requires more complex mechanical structure, the candidates of future aviation propulsion are confronted with more overall reliability problems than that of the conventional gas turbine engine. This situation is challenging to a traditional aeroengine deterministic design method. To overcome this challenge, the Reliability-based Multi-Design Point Methodology is proposed for aeroengine conceptual design. The presented methodology adopted an unconventional approach of engaging the reliability prediction by artificial neural network (ANN) surrogate models rather than the time-consuming Monte Carlo (MC) simulation. Based on the Adaptive Particle swarm optimization, the utilization of the pre-training technique optimizes the initial network parameters to acquire better-conditioned initial network, which is sited closer to designated optimum so that contributes to the convergence property. Moreover, a new hybrid algorithm is presented to integrate the pre-training technique into neural network training procedure in order to enhance the ANN performance. The proposed methodology is applied to the cycle design of a turbofan engine with uncertainty component performance. The testing results certify that the prediction accuracy of pre-trained ANN is improved with negligible computational cost, which only spent nearly one-millionth as much time as the MC-based probabilistic analysis (0.1267 s vs. 95,262 s, for 20 testing samples). The MC simulation results substantiate that optimal cycle parameters precisely improve the engine overall performance to simultaneously reach expected reliability (≥98.9%) in multiple operating conditions without unnecessary performance redundancy, which verifies the efficiency of the presented methodology. The presented efforts provide a novel approach for aeroengine cycle design, and enrich reliability design theory as well.

Organic Rankine Cycle Optimization With Explicit Designs of Evaporator and Radial Inflow Turbine

Abstract Although there are studies on optimizing organic Rankine cycles (ORCs) through individual components, in this study, for the first time, both evaporator and turbine designs are included in a multiobjective optimization. Twenty-eight working fluids are used to find optimum cycle parameters for three source temperatures (90, 120, and 150 °C). A mean-line radial inflow turbine model is used. Nondominated Sorting Genetic Algorithm II is utilized to minimize total evaporator area per net power output and maximize performance factor simultaneously. The technique for Order Preference by Similarity to Ideal Situation (TOPSIS) procedure is followed to obtain ideal solutions. A group of working fluids with highest net power output is determined for each heat source temperature. Optimized geometric parameters of the evaporator vary in a narrow range independent of the working fluid and the source temperature, but evaporator PPTD and degree of superheating depend on the working fluid. The specific speed, the pressure ratio through the turbine, and the nozzle inlet-to-outlet radius ratio do not change significantly with cycle conditions.

Environmental impact and cost analysis of gas turbine cycles with steam injection and inter-stage turbine reheat

Inter-stage turbine reheat is an effective gas turbine retrofit which can easily be used with simple and steam injected gas turbines as well. Owing to the uncertainties relating to an efficiency comparison of steam injected and no-injection cycle designs, thermoeconomics and environmental impacts have been considered to evaluate reheat and steam injection which regards pollutant emissions and environmental costs together. Being the complemental of the authors previous studies on steam injected gas turbines, simple, reheat, steam injected (STIG) and reheat steam injected (RHSTIG) gas turbine cycles are compared. Economic feasibility of steam injection as well as inter-stage turbine reheat are discussed according to 2018 plant cost data. Optimal cycle parameters are determined using a new comprehensive cycle model which permits to work with realistic working fluids, simulates the combustion process regarding 14 exhaust species and determines NOx and CO emissions.

Environmental impact and cost analysis of gas turbine cycles with steam injection and inter-stage turbine reheat

Inter-stage turbine reheat is an effective gas turbine retrofit which can easily be used with simple and steam injected gas turbines as well. Owing to the uncertainties relating to an efficiency comparison of steam injected and no-injection cycle designs, thermoeconomics and environmental impacts have been considered to evaluate reheat and steam injection which regards pollutant emissions and environmental costs together. Being the complemental of the authors previous studies on steam injected gas turbines, simple, reheat, steam injected (STIG) and reheat steam injected (RHSTIG) gas turbine cycles are compared. Economic feasibility of steam injection as well as inter-stage turbine reheat are discussed according to 2018 plant cost data. Optimal cycle parameters are determined using a new comprehensive cycle model which permits to work with realistic working fluids, simulates the combustion process regarding 14 exhaust species and determines NOx and CO emissions.

The investigation of thermo-economic performance and conceptual design for the miniaturized lead-cooled fast reactor composing supercritical CO2 power cycle

A comprehensive study of thermo-economic analysis and practical conceptual design of miniaturized lead-cooled fast reactor (LFR) composing supercritical CO2 power cycle is proposed in order to promote the real application in the market. The thermodynamic model and economic model are established based on the following five supercritical CO2 (S-CO2) Brayton cycles integrating with the miniaturized LFR, separately. Moreover, the optimization algorithm is adopted to optimize the key parameters of five power cycles with the objectives of maximizing the system thermoelectric conversion efficiency and electricity production costs (EPC) simultaneously. The optimal cycle and optimum parameters are obtained for the integrated system. Furthermore, the structural parameters of key components are confirmed based on the above results. The main subsidiary systems are designed. Finally, the practical design of LFR composing S-CO2 power cycle is carried out. The results shown that various parameters have different effects on the thermodynamic-economic performance of the system. The higher inlet temperature of turbine is beneficial to improve both thermodynamic and economic performance of the system. With the ƞt,sys-EPC analyzed simultaneously, the recompression cycle is the optimal to operate with more working conditions. Its ƞt,sys is from 36.68% to 44.46%, and EPC is from 0.050 $·kW−1·h−1 to 0.055 $·kW−1·h−1).

Thermoenvironomic evaluation of simple, intercooled, STIG, and ISTIG cycles

Low-technology cycle modifications available for improving gas turbine performance are still largely unexploited. Among those proven modifications, steam injection is found to be the most effective in boosting both the output capacity and thermal efficiency while reducing NOx emissions. It further improves part load performance under varying ambient conditions. Intercooling is another low-technology modification which can improve performance of simple and steam injected gas turbine cycles. Because of the uncertainties relating to an efficiency comparison of steam injected and simple cycle designs, the decision as to whether it is worthwhile to give more emphasis to steam injected cycles should be made on grounds other than efficiency alone. Therefore, this study comparatively evaluates simple, intercooled, steam injected (STIG), and intercooled steam injected (ISTIG) gas turbine cycles from the points of efficiency, network output, economics, and pollutant emissions using an advanced validated thermoenvironomic model. Optimum cycle parameters are investigated. Economic feasibility of steam injection and intercooling on simple and intercooled cycles are evaluated using an updated plant cost data. Total and environmental costs as well as profit of the plant owner are estimated for varying fuel costs and varying cycle parameters such as pressure, steam injection, and equivalence ratio. Results of our analysis based on the characteristic cycle parameters show that network output increases up to 22.2% and 14% respectively, when steam injection is implemented on simple and intercooled gas turbine cycles which correspond to up to 6.7% and 4.4% decrease in specific fuel consumption. Steam injection decreases NOx emissions of simple and intercooled cycles up to 67.2% and 65.2% respectively, and provides up to approximately 126.3% increase in net profit of intercooled cycle at the expense of an increase in total cost by 3.3%.

Parametric optimization and thermodynamic performance comparison of single-pressure and dual-pressure evaporation organic Rankine cycles

Dual-pressure evaporation organic Rankine cycle (ORC) involves two evaporation processes with different pressures, and can significantly reduce the exergy loss in the heat absorption process compared with conventional single-pressure evaporation ORCs. However, the applicable heat source temperatures of dual-pressure evaporation ORCs and the effects of the working fluid thermophysical properties on the applicable conditions remain indeterminate. Optimal cycle parameters for various heat source temperatures also need to be studied. Solving these questions is crucial for the application and promotion of dual-pressure evaporation ORCs. This study focuses on a typical dual-pressure evaporation ORC driven by the 100–200 °C heat sources without a limit on the outlet temperature. Nine pure organic fluids were selected as working fluids. Evaporation pressures and evaporator outlet temperatures of the single-pressure and dual-pressure evaporation ORCs were optimized, and their optimized system thermodynamic performance was compared. Results show that the applicable heat source temperature range of the dual-pressure evaporation ORC (Wnet,dual>Wnet,single) generally increases as the working fluid critical temperature increases. The upper limit of the applicable heat source temperatures (THS,in_TP), working fluid critical temperature and pinch point temperature difference generally conform to a linear relation. For the heat source temperature below THS,in_TP, the maximized net power output of the dual-pressure evaporation ORC is larger than that of the single-pressure evaporation ORC. Furthermore, the increment generally increases as the heat source temperature decreases, and the maximum increments are 21.4–26.7% for nine working fluids. For the heat source temperature above THS,in_TP, the dual-pressure evaporation ORC is unbefitting.

Study on off-design performance of transcritical CO2 power cycle for the utilization of geothermal energy

Exploiting renewable energy could greatly alleviate current severe energy situation. Transcritical CO2 (tCO2) cycle system as a type of competitive and promising energy converter could utilize low temperature geothermal energy effectively. In this paper, the methodology for the off-design operation of tCO2 system has been proposed and the quantitative performance analysis is carried out for the utilization of geothermal energy. With the aim at obtaining better thermodynamic and economic performance, the optimal power cycle parameters can be determined by the non-dominated sorting genetic algorithm-II (NSGA-II) in the design stage. The models of exergoeconomic analysis and main system components including turbine, pump and heat exchangers are established. The sliding pressure control strategy is applied to respond to the varieties of heat source and heat sink conditions in the off-design stage. Results show that there exists an optimal value of geothermal resource mass flow rate to maximum the thermal efficiency. The pump rotational speed increases linearly with the increasing geothermal resource temperature and geothermal resource mass flow rate while the pump rotational speed is gradually sensitive to the increase of heat sink temperature. The guideline listed in the table for pump could provide effective reference for practical operation.

A New Criterion to Optimize ORC Design Performance using Efficiency Correlations for Axial and Radial Turbines

Several studies on Organic Rankine Cycles (ORCs) in the literature search for the optimal cycle parameters and working fluids that maximize the net power output. Only few studies carry out a preliminary turbine design to calculate an accurate value of turbine efficiency, but this is done only after the cycle thermodynamic optimization is performed assuming a fixed and somewhat arbitrary value of turbine efficiency. Instead, a new design optimization procedure of ORCs is proposed here which embeds correlations for the design efficiency of both axial and radial turbines. The correlations are obtained from published data in the literature and use the volumetric expansion ratio (VR) and the size parameter (VH) as performance predictors. While been applied to a selected number of working fluids and single stage turbines, the procedure has a general validity being the correlations applicable to any fluid and turbine type. Results show how the turbine efficiency, and in turn the optimum cycle parameters, are influenced by the fluid properties through the turbine VH and VR values, highlighting that the procedure for working fluid selection cannot ignore the real turbine behaviour. So, the optimum design that is obtained is expected to give a behaviour much closer to reality.

Minimum power requirement for a propeller-driven aircraft and optimum cycle parameters of turboprop engines

This article presents a methodology to design for optimal performance of turboprop engines matching the power requirements for propeller-driven aircrafts. First, the flight performance analyses were used to assess the relatively significant constraints, and then identify the feasible design space and the ideal design point by adopting KSOPT optimizing technique. Second, a multi-objective deterministic algorithm modified method of feasible direction was used for the Pareto approach optimization of the propulsion cycle for three configurations of turboprops. In this optimization problem the maximum specific power and the minimum power specific fuel consumption are the principal figures of merit. The obtained results were based on a created model from the published data of a particular aircraft. This methodology used in the preliminary design phase has shown its effectiveness in rapidly searching for the ideal match point and identifying a candidate turboprop engine, as well as in the development of a derivative engine.

Thermodynamic optimization for a scramjet with Re-cooled Cycle

A new Re-cooled Cycle has been proposed for a regeneratively cooled scramjet to reduce the fuel flow for cooling, fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. Parametric analysis of the Re-cooled Cycle carried out in previous study shows the potential for the cycle to be optimized. A thermodynamic optimization analysis of Re-cooled Cycle for a scramjet is obtained by satisfying hydrodynamic, thermal, and Mach number constraints. The optimal cycle parameters and length allocation between the first and second cooling passages are obtained.

MODELING AND OPTIMIZATION OF AN AMMONIA-WATER COMPRESSION-RESORPTION HEAT PUMPS WITH WET COMPRESSION

Wet ammonia-water compression-resorption heat pumps constitute an attractive alternative to the commonly known heat pumps based on Osenbrück cycle because they eliminate the necessity of oil-liquid refrigerant separation. In this respect, a special designed oil-free compressor operating under wet (two-phase) conditions equips the heat pump. The compressor is lubricated by the liquid refrigerant which is carried-out while compressing the vapor. The thermodynamic cycle is located completely inside the two-phase region. In this paper are demonstrated two procedures to optimize the design for COP maximization. It is shown that there is: (i) an optimal choice of the vapor quality at suction, and (ii) an optimal distribution of heat transfer surface between the resorber and the desorber (the total amount of heat transfer surface, being an expression of investment cost, is fixed). The circulating concentration of ammonia has to be chosen such that the minimum pressure in the system is over one bar (to avoid air penetration from the atmosphere) and the maximum pressure is bounded by a technical-economical maximal limit. A general procedure for calculation of the optimal cycle parameters is presented and exemplified for a case with practical relevance. The paper presents only the trends and rough quantitative estimations because the analyzed case is restricted to the ideal isentropic compression. Further research is needed to quantify in detail the effect of compression irreversibility.

Rapid determination of dry layer mass transfer resistance for various pharmaceutical formulations during primary drying using product temperature profiles

Mass transfer resistance of the dry layer during the primary drying phase of a lyophilizaton cycle is probably the most important factor affecting maximum product temperature and drying time. Product resistance parameters should be determined for each formulation because of their dependence of formulation composition and concentration. The purpose of this study was to determine the dry layer mass transfer resistance, using a simple and rapid method, for various pharmaceutical formulations during primary drying in a laboratory dryer, using monitored product temperature profiles. The mathematical tools used for the determination were a primary drying simulation program in conjunction with Powell's optimization algorithm. For each formulation studied, primary drying was performed using a shelf temperature of −15 or −20 °C and the chamber pressure controlled at 100 mTorr (0.1 Torr). The product temperature profiles ( T b) during primary drying were recorded and became the input data for the parameter estimation. The normalized product resistance, R pN, as a function of the dry layer thickness, ℓ , can be described by: R pN = R 0 + A 1 ℓ / ( 1 + A 2 ℓ ) , where the constants R 0, A 1 and A 2 are product resistance parameters of water vapor through the dry layer. Even when the parameter A 1 was negative, indicating that product temperature atypically decreased over time, the dry layer product resistance parameters of the various pharmaceutical formulations could be rapidly and successfully determined using the proposed approach. The product resistance equation obtained in this work for 5% marmitol, expressed as R pN = 0.0002025 + 20.23 ℓ , is similar to that obtained by Pikal [Pikal, M.J., 1985. Use of laboratory data in freeze drying process design: heat and product resistance parameters and the compute simulation of freeze drying. J. Parent. Sci. Technol. 39, 115–138.] using the microbalance method, expressed as R pN = 1.40 + 16.0 ℓ . The product resistance values obtained for the 3% lactose–LDH formulation are also very close to those obtained by (Milton, N., Pikal, M.J., Roy, M.L., Nail, S.L., 1997. Evaluation of manometric temperature measurement as a method of monitoring product temperature during lyophilization. PDA J. Pharm. Sci. Technol. 51, 7–16.) for 5% lactose using the MTM (manometric temperature measurement) method. With the obtained values of the parameters R 0, A 1, and A 2, simulations can be performed to determine the maximum product temperature and the drying time during primary drying. As such, optimum cycle parameters can be determined to avoid collapse of the product. The proposed approach requires only accurately measured product temperature profiles, easily obtained in a laboratory dryer.

Optimization of a transcritical CO 2 heat pump cycle for simultaneous cooling and heating applications

Energetic and exergetic analyses as well as optimization studies of a transcritical carbon dioxide heat pump system are presented in this article. A computer code has been developed to obtain sub-critical and super-critical thermodynamic and transport properties of carbon dioxide. Estimates for irreversibilities of individual components of the system lead to possible measures for performance improvement. The COP trends indicate that such a system is more suitable for high heating end temperatures and modest cold end temperatures. Expressions for optimum cycle parameters have been developed and these correlations offer useful guidelines for optimal system design and for selecting appropriate operating conditions.

Gas Turbine Cycles With Solid Oxide Fuel Cells—Part II: A Detailed Study of a Gas Turbine Cycle With an Integrated Internal Reforming Solid Oxide Fuel Cell

In conventional energy conversion processes, the fuel combustion is usually highly irreversible, and is thus responsible for the low overall efficiency of the power generation process. The energy conversion efficiency can be improved if immediate contact of air and fuel is prevented. One means to prevent this immediate contact is the use of fuel cell technology. Significant research is currently being undertaken to develop fuel cells for large-scale power production. High-temperature solid oxide fuel cells (SOFC) have many features that make them attractive for utility and industrial applications. However, in view of their high operating temperatures and the incomplete nature of the fuel oxidation process, such fuel cells must be combined with conventional power generation technology to develop power plant configurations that are both functional and efficient. Most fuel cell cycles proposed in the literature use a high-temperature fuel cell running at ambient pressure and a steam bottoming cycle to recover the waste heat generated by the fuel cell. With such cycles, the inherent flexibility and shorter start-up time characteristics of the fuel cell are lost. In Part I of this paper (Harvey and Richter, 1994), a pressurized cycle using a solid oxide fuel cell and an integrated gas turbine bottoming cycle was presented. The cycle is simpler than most cycles with steam bottoming cycles and more suited to flexible power generation. In this paper, we will discuss this cycle in more detail, with an in-depth discussion of all cycle component characteristics and losses. In particular, we will make use of the fuel cell’s internal fuel reforming capability. The optimal cycle parameters were obtained based on calculations performed using Aspen Technology’s ASPEN PLUS process simulation software and a fuel cell simulator developed by Argonne National Laboratory (Ahmed et al., 1991). The efficiency of the proposed cycle is 68.1 percent. A preliminary economic assessment of the cycle shows that it should compare favorably with a state-of-the-art combined cycle plant on a cost per MWe basis.