Correlation Analysis of Wind Turbine Temperature Rise and Exergy Efficiency Based on Field-Path Coupling

To solve the problems of large losses and low productivity of permanent magnet synchronous generators used in wind power systems,the field-circuit coupling method is used to accurately solve the electromagnetic field and temperature field of the generator.The loss distribution of the motor is accurately obtained by considering the influence of external circuit characteristics on its internal physical field.By mapping the losses to the corresponding part of the three-dimensional finite element model of the motor,the temperature field is solved,and the global temperature distribution of the generator,considering the influence of end windings,is obtained.By changing the air gap length,permanent magnet thickness,and winding conductivity,the relationship between the loss,temperature rise,and exergy efficiency can be obtained.By optimizing the air gap length,permanent magnet thickness,and winding conductivity,the best configuration and material properties can improve the efficiency of the motor by up to 4%.

Energy and Exergy Efficiency Analysis of Advanced Adiabatic Compressed Air Energy Storage Based Trigeneration Energy Hub

With growing public awareness of decarbonization and increasing penetration of renewable generation,energy storage is in great need.Advanced adiabatic compressed air energy storage(AA-CAES)is capable of producing power,heating and cooling,making it an ideal choice of an environmental-friendly energy hub.This paper proposes an energy and exergy efficiency analysis for an AA-CAES based trigeneration energy hub.Impact of power storage and heat load supply rates on energy output efficiency and total exergy losses are analyzed.Based on the proposed model,optimal configuration of power storage and heat load supply rates can be determined under different purposes.According to basic thermodynamic principles,the proposed method calculates trigeneration capability estimates considering energy grade difference and multi-dimension energy distribution,which can demonstrate more energy conversion properties of the system.Case studies verify that the proposed method can provide various characteristic analyses for an energy hub and its application in actual systems proves computation accuracy.Integrative energy efficiency is improved compared to pursuing maximum electricity-to-electricity efficiency.

Energy and Exergy Analysis of a Finned-Plate Double Pass Solar Air Heater with Different Arrangement

The present work investigated the solar collector system with triangular longitudinal fins fixed to the absorber surface at different configuration. Four models of collectors were manufactured with different absorber plates made from aluminum material. The experiments were carried out at the winter session in the climate of Iraq—Ramadi city with longitude (43.268) and latitude (33.43). The experiments have used three values from (0.027 to 0.037) kg/s. The results showed that the temperature difference increases gradually until midday and begins decreasing gradually until it becomes zero at sunset. Maximum temperatures difference has been obtained at the fourth type which is (20.6 °C), and maximum efficiency and exergetic efficiency (99.9%), (43.08%) respectively. A comparison has been made with previous works for thermal and exergetic efficiency. The comparison showed good compatibility between results; the percentage of error does not exceed 3%. The results proved that the existence of fins was a good technique for enhancing the thermal performance of double pass solar collector with a non-effective increase in pressure drop.

Optimization of a Single Flash Geothermal Power Plant Powered by a Trans-Critical Carbon Dioxide Cycle Using Genetic Algorithm and Nelder-Mead Simplex Method

The usage of renewable energies,including geothermal energy,is expanding rapidly worldwide.The low efficiency of geothermal cycles has consistently highlighted the importance of recovering heat loss for these cycles.This paper proposes a combined power generation cycle(single flash geothermal cycle with trans-critical CO_(2) cycle)and simulates in the EES(Engineering Equation Solver)software.The results show that the design parameters of the proposed system are significantly improved compared to the BASIC single flash cycle.Then,the proposed approach is optimized using the genetic algorithm and the Nelder-Mead Simplex method.Separator pressure,steam turbine output pressure,and CO_(2) turbine inlet pressure are three assumed variable parameters,and exergy efficiency is the target parameter.In the default operating mode,the system exergy efficiency was 32%,increasing to 39%using the genetic algorithm and 37%using the Nelder-Mead method.

Exergy Analysis of Charge and Discharge Processes of Thermal Energy Storage System with Various Phase Change Materials:A Comprehensive Comparison

Thermal energy storage(TES) is of great importance in solving the mismatch between energy production and consumption.In this regard,choosing type of Phase Change Materials(PCMs) which are widely used to control heat in latent thermal energy storage systems,plays a vital role as a means of TES efficiency.However,this field suffers from lack of a comprehensive investigation on the impact of various PCMs in terms of exergy.To address this issue,in this study,in addition to indicating the melting temperature and latent heat of various PCMs,the exergy destruction and exergy efficiency of each material are estimated and compared with each other.Moreover,in the present work the impact of PCMs mass and ambient temperature on the exergy efficiency is evaluated.The results proved that higher latent heat does not necessarily lead to higher exergy efficiency.Furthermore,to obtain a suitable exergy efficiency,the specific heat capacity and melting temperature of the PCMs must also be considered.According to the results,LiF-CaF_(2)(80.5%:19.5%,mass ratio) mixture led to better performance with satisfactory exergy efficiency(98.84%) and notably lower required mass compared to other PCMs.Additionally,the highest and lowest exergy destruction are belonged to GR25 and LiF-CaF_(2)(80.5:19.5) mixture,respectively.

Optimization Study on Regenerative Organic Rankine Cycle(ORC) with Heat Source of Low-Grade Steam

Aiming at improving the performance of Organic Rankine Cycle(ORC)system with low-grade steam as heat source,this work studied and optimized the main operating parameters of the ORC system.The effects of evapo-ration temperature,superheat degree,condensation temperature and regenerator pinch temperature difference on the system performance were obtained.The optimization for the operating parameters is based on the indicators of specific net power output,waste heat pollution,cycle exergy efficiency,and total UA value(the product of overall heat transfer coefficient and heat transfer area of heat exchanger).The results show that the increase of the evaporation temperature and the superheat degree,and the decrease of the condensation temperature and regenerator pinch temperature difference can improve general system performance but lead to weaker economic performance.The optimal evaporation temperature,superheat degree,condensation temperature and regenerator pinch temperature difference are determined as 139℃,4°C,36°C and 8°C,respectively,reaching net power output of 114.73 kW,exergy efficiency of 37.10%.Besides,it is indicated that the regenerative ORC system can reach 13.6%additional net power output compared to the ORC system without the regenerator.

Study of Flow and Heat Transfer in an Ejector-Driven Swirl Anti-Icing Chamber

The formation of ice on the leading edge of aircraft engines is a serious issue,as it can have catastrophic consequences.The Swirl Anti-Icing(SAI)system,driven by ejection,circulates hot fluid within a 360°annular chamber to heat the engine inlet lip surface and prevent icing.This study employs a validated Computational Fluid Dynamics(CFD)approach to study the impact of key geometric parameters of this system on flow and heat transfer characteristics within the anti-icing chamber.Additionally,the entropy generation rate and exergy efficiency are analyzed to assess the energy utilization in the system.The research findings indicate that,within the considered flow range,reducing the nozzle specific areaφfrom 0.03061 to 0.01083 can enhance the ejection coefficient by over 60.7%.This enhancement increases the air circulating rate,thereby intensifying convective heat transfer within the SAI chamber.However,the reduction inφalso leads to a significant increase in the required bleed air pressure and a higher entropy generation rate,indicating lower exergy efficiency.The nozzle angleθnotably affects the distribution of hot and cold spots on the lip surface of the SAI chamber.Increasingθfrom 0°to 20°reduces the maximum temperature difference on the anti-icing chamber surface by 60 K.

A separate-type autothermal CH_(4) dry reforming system with exergy recuperation

Currently,CO_(2) conversion and utilization have become a key to mitigate the global warming.In this study,a novel separate-type autothermal dry reforming of methane(S-ATDRM)system is proposed and simulated,in which the methane dry reforming combined with methane partial oxidation is performed in a circulating fluidized bed with exergy recuperation to eliminate the negative effect of the products of CH_(4) partial oxidation on the DRM reaction and further improve the CO_(2) conversion efficiency.The results demonstrate that this S-ATDRM system can achieve an exergy efficiency of 84.7%,and about 1055.7 kW of exergy can be recuperated from the process for crude syngas cooling and reapplied for pre-heating of feedstocks of CO_(2),O2 and CH_(4).It is found that the largest exergy destruction in this system occurs in the partial oxidation reactor,which occupies ca.45.6%of the whole exergy loss.Comparing with the conventional ATDRM system,although the exergy of S-ATDRM system is decreased by approximately 0.3%,the CO_(2) conversion is substantially increased by about 11.3%.

Energy-and exergy-based performance evaluation of solar powered combined cycle(recompression supercritical carbon dioxide cycle/organic Rankine cycle)

Nowadays,the recompression supercritical carbon dioxide(R-SCO_(2))cycle has emerged as a promising option for power conversion systems because of its boundless potential to tackle energy and environmental issues.In this study,we examined the performance of the solar parabolic trough collector(SPTC)integrated combined cogeneration system for the purpose of power generation as well as recovery of waste exhaust heat from the R-SCO_(2) cycle with the help of the organic Rankine cycle(ORC).An exergy and energy analysis was performed for a combined recompression cycle(R-SCO_(2)-ORC)by varying the input variables such as intensity of solar irradiation(Gb),pressure at the inlet of SCO_(2) turbine(P_(5)),mass flow rate of SCO_(2)()&mSCO_(2) inlet temperature of SCO_(2) turbine(T5),inlet temperature of main compressor(T_(9))and effectiveness of the high-and low-temperature recuperator( HTR and LTR).Eight organic working fluids were considered for the ORC:R123,R290,isobutane,R1234yf,R1234ze,toluene,isopentane and cyclohexane.The study revealed that R123-based R-SCO_(2)-ORC demonstrates the highest thermal and exergy efficiency:~73.4 and 40.89%at G_(b)=0.5 kW/m^(2);78.8 and 43.9%at P_(5)=14 MPa;63.86 and 35.57%at T5=650 K;74.84 and 41.69%at&mSCO 7kg s;2=/85.83 and 47.82%at T_(9)=300 K;84.57 and 47.11%at HTR 65;=0.85.06 and 47.38%at LTR 65,=0.respectively.Alternatively,R290 showed the minimum value of exergy and thermal efficiency.As can be seen,the maximum amount of exergy destruction or exergy loss occurs in a solar collector field,~58.25%of the total exergy destruction rate(i.e.6703 kW)and 18.99%of the solar inlet exergy(i.e.20562 kJ).Moreover,R123 has the highest net work output,~4594 kJ at T5=650 K and 6176 kJ at T_(9)=300 K.

Numerical Simulation of Nanofluid-Based Parallel Cooling Photovoltaic Thermal Collectors

A novel hybrid cogeneration system based on a parallel-cooled photovoltaic/thermal(PV/T)module is presented in this paper.The temperature of the parallel-cooled PV/T module is more uniform due to the parallel cooling fluid of air mixed with water or nanofluids(SiO2,CuO,Ag,and Al_(2)O_(3)).The results show that the overall temperature of the PV cell in the parallel-cooled module is about 2 K lower than that in the single-cooled module,with a 9.01%improvement in thermal efficiency and a 0.09%enhancement in electrical efficiency.The PV/T module with nanofluid shows a significant improvement in thermal and electrical efficiency.The thermal and electrical efficiencies of the parallel-cooled PV/T module consisting of Al_(2)O_(3)nanofluid and air are 89.21%and 9.84%,respectively.Compared with the non-nanofluid parallel cooling scheme,the cooling method consisting of 1 wt%,3 wt%,or 5 wt%Al_(2)O_(3)and air,the thermal efficiency of PV/T was improved by 5.47%,5.30%,and 3.93%,respectively with the solar radiation of 800 W/m^(2)and the flow rate of 0.10 m/s,while the electrical efficiency was improved by 0.026%,0.027%,and 0.034%,respectively.In addition,when the solar radiation is 1000 W/m^(2)with a flow rate of 0.025 m/s,the air-water parallel cooling PV/T module achieves a maximum exergy efficiency of 11.74%.

Thermodynamic Performance Analysis of a Low-Cost,Recycled and Energy-Efficient Solar Air Heater with Waste Beverage Cans:An Experimental Research

Solar air heaters are at the centre of interest owing to their widespread use for various purposes.In the study,thermal performance analysis of a solar air heater that can be easily produced from daily waste materials is done.The system has a low-cost structure with both waste material use and a simple design.The proposed system is tested under different climatic conditions,and the energetic and the exergetic performance figures are obtained for the first time in literature.It is observed from the experimental tests that the results are stable and coherent as well as in good accordance with the similar attempts in literature with some cost reductions and performance improvements.Thermodynamic performance analyses indicate that the maximum energy efficiency of the system is about 21%,whereas the exergy efficiency is 1.8%.The energetic and exergetic outputs of the system are also determined to be 27 W and 3 W,respectively,which is promising.

Comparative study on the globally optimal performance of cryogenic energy storage systems with different working media

Cryogenic energy storage(CES)has garnered attention as a large-scale electric energy storage technology for the storage and regulation of intermittent renewable electric energy in power networks.Nitrogen and argon can be found in the air,whereas methane is the primary component of natural gas,an important clean energy resource.Most research on CES focuses on liquid air energy storage(LAES),with its typical round-trip efficiency(RTE)being approximately 50%(theoretical).This study aims to explore the feasibility of using different gases as working media in CES systems,and consequently,to achieve a high system efficiency by constructing four steady-state process models for the CES systems with air,nitrogen,argon,and methane as working media using Aspen HYSYS.A combined single-parameter analysis and multi-parameter global optimization method was used for system optimization.Further,a group of key independent variables were analysed carefully to determine their reasonable ranges to achieve the ideal system performance,that is,RTE and liquefaction ratio through a single-parameter analysis.Consequently,a multi-parameter genetic algorithm was adopted to globally optimize the CES systems with different working media,and the energy and exergy analyses were conducted for the CES systems under their optimal conditions.The results indicated the high cycle efficiency of methane and a low irreversible loss in the liquefaction cycle.Moreover,the Joule-Thomson valve inlet temperature and charging and discharging pressures considerably affected the system performance.However,exergy loss in the CES system occurred primarily in the compressor,turbine,and liquefaction processes.The maximum optimal RTE of 55.84%was achieved in the liquid methane energy storage(LMES)system.Therefore,the LMES system is expected to exhibit potential for application in the CES technology to realize the integration of natural gas pipelines with renewable power grids on a large scale.Moreover,the results of study have important theoretical significance for the innovation of the CES technology.

Simulation and experiments on cooling and power system driven a solid sorption combined by the exhaust waste heat

A solid sorption combined cooling and power system driven by exhaust waste heat is proposed, which consists of a MnCl2 sorption bed, a CaCl2 sorption bed, an evaporator, a condenser, an expansion valve, and a scroll expander, and ammonia is chosen as the working fluid. First, the theoretical model of the system is established, and the partitioning calculation method is proposed for sorption beds. Next, the experimental system is estab- lished, and experimental results show that the refrigerating capacity at the refrigerating temperature of-10℃ and the resorption time of 30 min is 1.95 kW, and the shaft power is 109.2 W. The system can provide approximately 60% of the power for the evaporator fan and the condenser fan. Finally, the performance of the system is compared with that of the solid sorption refrigeration system. The refrigerating capacity of two systems is almost the same at the same operational condition. Therefore, the power generation process does not influence the refrigeration process. The exergy efficiency of the two systems is 0.076 and 0.047, respectively. The feasibility of the system is determined, which proves that this system is especially suitable for the exhaust waste heat recovery.