Net Power Research Articles

Sintering parameter optimization by inverse analysis in direct metal deposition of Inconel 718

PurposeThe net power delivered to the surface of parts (i.e. the actual heat flux) is a key parameter in the laser melting process and its exact control has a great impact on the numerical solutions. In this paper, the impact of laser additive manufacturing parameters including laser power, scanning speed and powder injection rate on thermal efficiency, net power delivered to the part and power loss due to powder flow has been investigated.Design/methodology/approachThe response surface method was applied to measure the net laser power in laser deposited Inconel 718 using k-type thermocouples. The temperature history obtained by thermocouples was used to calculate the net power delivered by inverse analysis method. The applied model is Rosenthal's optimized model, in which all the thermal properties of the material are considered to vary with temperature.FindingsThe results indicated that the thermal efficiency, power delivered to the part and power loss can be optimized simultaneously at laser power of 400 W, scanning speed of 2 mm/s and powder injection rate of 200 mg/s. The microstructure analysis indicated that a high-quality sample without microstructural defects was formed under optimal condition of parameters. Moreover, the primary dendrite arm spacing for the optimal sample was higher than that obtained for other samples.Originality/valueThe novelty of this research summarized as follows: Prediction of the thermal efficiency and power loss during the laser metal deposition of Inconel 718 superalloy using the inverse analysis. Finding the optimal values of thermal efficiency, power delivered to the surface and power loss in the laser metal deposition of Inconel 718 superalloy. Investigating the effect of laser power, powder injection rate and scanning speed on the thermal efficiency and power loss of Inconel 718 superalloy during the laser metal deposition.

Numerical simulation analysis of composite flow field design on mass transfer in proton exchange membrane fuel cell

Bipolar plate flow field design is crucial for optimizing Proton Exchange Membrane Fuel Cell (PEMFC) performance. This study employs three-dimensional simulations and Computational Fluid Dynamics (CFD) methods to analyze and compare traditional Straight Parallel Flow Field (SPFF), Block Incorporated Flow Field (BIFF), Sub-channel Ribbed Flow Field (SRFF), and Combined Block and Sub-channel Flow Field (CBSFF). The findings indicate that CBSFF not only demonstrates superior oxygen distribution characteristics at high current densities but also shows improved uniformity in moisture and temperature distribution. In addition, the effect of the structural parameters of the CBSFF flow field on its performance has been investigated. In particular, at a voltage of 0.5 V, the net power of the CBSFF is increased by 18 percent compared with that of the SPFF when the height of the block, hb=0.5, and the height of the subchannel, hs=0.3, are used.

A simulation of diesel and biodiesel blending for energy generation

This study is to simulate bioenergy in the Saudi energy sector. The methodologies used in this study include the simulation of biodiesel blends in power plants. GIS software was used to calculate the area of Jatropha plants cultivated (228.5 km2) to produce 1.62 kg/s Jatropha oil. The results showed that the validation was done by comparing the net power output (72.3 MW) and efficiency of 30.44% of the real energy plant with the simulation net power output of 69.15 MW and efficiency of 30.67%. The efficiency was increased to 51.1% after the simple cycle was modified to the combined cycle. Biodiesel (1.534 kg/s) was blended with diesel. The blended diesel and biodiesel were examined and the effect of the blends on the combined cycle power plant performance was inspected. The overall result revealed that the energy from biodiesel can be an alternative to support the Saudi Arabia Vision 2030.

Experimental study on the comparative performance of R1233zd(E) and R123 for organic rankine cycle for engine waste heat recovery

ABSTRACT The organic Rankine cycle (ORC) is an effective way for engine waste heat recover (WHR). The selection of the working fluid is crucial. In recent years, low GWP and ODP working fluid have been invented. For R123, which is commonly used in engine ORC-WHR system, the alternative working fluid is R1233zd(E). In order to explore the performance of R123 and R1233zd(E) when applied to ORC-WHR system, this study conducted experimental studies of R123 and R1233zd(E) under a wide range of engine working conditions. The experiments were carried out under seven sets of engine working conditions with gradually increasing loads. Variable operating parameter experiments were carried out for R123 and R1233zd(E) at each engine load. The selected operating parameters include expander speed and superheat degree. The experimental results show that R123 has higher output power and thermal efficiency compared to R1233zd(E) at all engine conditions.The maximum output power and thermal efficiency of R123 are 1.55 kw and 5.81% respectively.The maximum output power and thermal efficiency of R1233zd(E) are 1.43 kw and 5.29% respectively. Taking the net output power as the evaluation index, the optimal expander speed of R123 is higher than that of R1233zd(E) under the same engine working condition, and the superheat degree has little effect on the net output power.

Thermodynamic analysis of waste heat in a combined super-critical CO2 Brayton cycle for power and hydrogen production

The current investigation aims to propose a novel cycle to generate power and hydrogen using waste heat. For this purpose, super-critical carbon dioxide Brayton cycle, Organic Rankine Cycle (ORC) and proton exchange membrane (PEM) electrolyser systems are consideredin the cycle. Energy, exergy analyses along with parametric study are performed in the research. The best organic working fluid is selected for ORC based on the obtained results. Zero-dimensional modeling for components is performed and results are presented. Results show that the net power generation is 245.5 MW, thermal efficiency is 40.97 %, exergy efficiency is 56.73 %, and hydrogen and oxygen production is 9.04 kg/h and 74.2 kg/h, respectively. The optimum working pressure ratio and evaporator temperature are calculated. The effect of different working parameters on the system performance is obtained. It is shown that increasing the isentropic efficiency of the main and recompression compressors increases power generation, hydrogen production and system efficiency. Furthermore, increasing the turbine’s inlet temperature increases the power generation of the system.

Energy, exergy, exergoeconomic, economic, and environmental analyses and multi-objective optimization of a novel combined cooling and power system with dual-pressure Kalina cycle-absorption refrigeration

A novel combined cooling and power system, the dual-pressure Kalina cycle-absorption refrigeration (DPKC-AR-CCP), is proposed for the cascade utilization of waste heat from high-temperature flue gas and jacket water from internal combustion engines. A pneumatic booster pump unit is employed to increase the inlet pressure of the low-pressure expander, with heat generated during the compression process utilized for preheating the ammonia/water mixture, and exhaust gas from the low-pressure expander is combined with driving gas for absorption refrigeration. By integrating the first and second laws of thermodynamics with the SPECO Methodology, models for energy, exergy, exergoeconomy, economy, and environment of the DPKC-AR-CCP system are developed. A multi-objective optimization model is formulated with maximum exergy efficiency, minimum total exergy cost rate, and maximum annual equivalent carbon dioxide (CO2) emission reduction as objective functions. MATLAB software (combined with REFPROP software) is utilized for simulation and multi-objective optimization. The performance of each component under specific conditions is assessed, and a comparison with the simple absorption refrigeration/Kalina cogeneration system (AR/KC) highlights the advantages of the DPKC-AR-CCP system; an investigation into the effects of different operating parameters on performance is conducted. The results indicate that, under identical operational parameters, the DPKC-AR-CCP system exhibits a substantial increase in net output power (230.2 %), cooling capacity (98.7 %), and exergy efficiency (148.8 %) compared to the simple AR/KC system; payback period is reduced by 64.8 %; and annual equivalent CO2 emissions are decreased by 202.2 %. However, there is an increase in the total exergy cost rate by 90.5 %. The optimal concentration of ammonia/water is determined to be 0.816/0.184, with a heat exchanger outlet temperature of 341.07 K, driving pressure of 0.654 MPa, and low-pressure expander inlet pressure of 5.064 MPa. Correspondingly, the optimal exergy efficiency is 87.2 %, the annual reduction in CO2 emissions is 5.53 × 107 kg, and the total exergy cost rate is 288.48$/h.

Performance optimization study on the thermal management system of proton exchange membrane fuel cell based on metal hydride hydrogen storage

To compare the performance differences between proton exchange membrane fuel cell (PEMFC), metal hydride tank (MHT) and heat exchanger (HX) coupling configurations and optimize thermal management methods, this study investigates and compares three coupling systems, PEMFC-MHT-HX series, PEMFC-HX-MHT series, and PEMFC-MHT|HX parallel system. Results reveal that, under controlled load variables, all three systems achieve an energy efficiency of 48.1 % at the maximum net power of 41.99 kW, increased by 16.93 % compared to standalone PEMFC. Exergy efficiencies of the systems show little differences, with values of 43.65 %, 43.38 %, and 43.51 %, respectively. The PEMFC-MHT-HX system exhibits the highest hydrogen outlet pressure, which is suitable for high-pressure applications. Conversely, the PEMFC-MHT|HX system enables flexible hydrogen supply regulation through decoupled control of hydrogen outlet pressure and flow. Increasing the MHT heat transfer coefficient can enhance the outlet pressure, but this effect diminishes beyond 1500 W/(m2·K). Sensitivity analysis identifies current and stack temperature as pivotal factors, emphasizing the necessity of precise current regulation and effective thermal management strategies. Additionally, the proportion of PEMFC waste heat recovered by the MHT decreases from 36.8 % to 29.0 % as the current load rises from 100 A to 400 A, indicating potential for alternative waste heat recovery devices over HX.

Proposal and performance analysis of a novel hydrogen and power cogeneration system with CO2 capture based on coal supercritical water gasification

To establish a sustainable energy system, it is essential to achieve low-carbon and clean utilization of coal. In this study, a novel hydrogen and power cogeneration system with full CO2 capture that based on coal supercritical water gasification (SCWG) is proposed. Hydrogen is separated from syngas produced by coal SCWG, and the remaining combustible gas is burned to generate power. Moreover, supercritical CO2 cycle is integrated within the cogeneration system to recover the waste heat with high exergy efficiency. Thermodynamic performances, effects of key operation parameters and off-design performances under part-load conditions of the cogeneration system are analyzed. Under the design condition, the cogeneration system produces 20.26 mol kg−1 hydrogen and generates 8746 kJ kg−1 net power, achieving the high energy efficiency and exergy efficiency of 54.77 % and 52.54 %. The exergy efficiency of cogeneration system can be enhanced by optimizing the operation parameters, which is increased by 0.42 %, 4.03 % and 1.10 % with the optimal coal water slurry concentration (17.5 %), higher gasification temperature (750 °C) and higher gas turbine inlet parameters (1500 °C/3 MPa), respectively. The cogeneration system performance decreases with the power load, and the exergy efficiency decreases by 9.61 % when the system power load reduces from 100 % to 30 %.

Proposal of a novel multi-generation system based on dual-loop absorption power and compression refrigeration cycle

One of the promising approaches to compensate for imminent depletion of fossil energy resources and their adverse global impacts is enhancing the efficiency of systems utilizing low-temperature heat sources. The initial target of the research is to present a promising system for simultaneous production of power, refrigeration, heat, and hydrogen utilizing a combination of the absorption power cycle, the vapor compression refrigeration cycle, and a proton exchange membrane electrolyzer. On this subject, a comprehensive modeling of the energy and exergy of the proposed set-up is presented, and its thermodynamic performance is scrutinized. Furthermore, a comprehensive study of various parameters is performed to evaluate their impacts on system performance. The research aims to enhance and optimize the use of energy and various resources, contributing to the development of more sustainable efficient energy systems. Thermodynamic analysis of the multiple generation system shows that under baseline conditions and initial design, the system has the capability to produce net electrical power of approximately 17.12 kW, cooling power of about 201.5 kW, heating power of around 697.1 kW, and produce pure hydrogen at a rate of 0.153 kilograms per hour. The system exhibits an energy efficiency ratio of 1.364 and an exergy efficiency of 36.58 %. Moreover, optimization with single and multiple objectives with different weighting coefficients reveals that higher values of these parameters can be obtained. In other words, in the MOOM optimization mode, exergy efficiency increases to 7.16 %, and the energy performance ratio rises to 85.73 % compared to the BM mode. Additionally, through a parametric assessment to define the effect of input parameters on system performance, it demonstrates that increasing the temperature of the heat source may simultaneously increase the exergy efficiency and energy performance ratio of the system. The Grassmann diagram also indicates that the total exergy of the input fuel is about 196.9 kW. From this amount, approximately 121.5 kW are destroyed through the components of the system. Furthermore, about 3.39 kW are lost through the absorber coolant and waste from the hydrogen production unit. About 72.4 kW are attributed to products.

An integrated approach to green power, cooling, and freshwater production from geothermal and solar energy sources; case study of Jiangsu, China

This paper introduces an innovative integration of geothermal and solar energies to assess the production of power, cooling, and freshwater. These products are achieved through a modified absorption refrigeration cycle, a modified organic Rankine cycle, and humidification-dehumidification subsystems driven by a flash-binary configuration. The performance of the setup is evaluated using both thermodynamic and economic approaches. Additionally, three multi-objective optimizations are applied to determine a suitable optimal state. The approaches reveal net power, cooling, and freshwater production rates of 807.3 kW, 1345 kW, and 7.96 kg/s, respectively. The designed setup requires a total capital investment cost of $2,490,310 and has a payback period of 5.76 years in the base mode. The study highlights that the temperature difference of superheating significantly impacts the total capital investment cost and exergy efficiency, while the cooling production is mainly influenced by the evaporator temperature. The final optimal state achieved an exergy efficiency of 15.98 % and a net present value of $1,999,864. Overall, this innovative hybrid geothermal-solar setup demonstrates a viable solution for sustainable energy production, combining power generation, cooling, and freshwater production in a single integrated system. The findings support the system's potential for real-world applications, particularly in regions with suitable geothermal and solar resources.

Energy, economic, and environmental analysis of a novel combined cooling, heating, and power (CCHP) from infectious medical waste

The outbreak of coronavirus disease 2019 (COVID-19) has led to an increase in infectious medical waste (IMW). Waste-to-energy (WtE) technologies are considered to manage IMW in the context of the COVID-19 situation and to reduce illegal dumping and landfill problems. This study focuses on managing IMW by using WtE technology. Energy, economic, and environmental (3E) impacts are considered as a single implication value of WtE technology. Combined cooling, heating, and power (CCHP) is a novel system for generating energy from a treated IMW by using a steam sterilization system. The moisture from sterilization waste is extracted by a drying process to create refuse-derived fuel type 3 (RDF-3). An RDF-3 of 81.98 kg/h at a low heating value of 26.29 MJ/kg is used for a combustion–incineration process of 236.56 kW. A net power from an organic Rankine cycle of 15.80 kWe, an absorption cooling capacity of 4.62 kW, and a drying room unit of 13.21 kW are found from the combined CCHP system. The energy index is calculated at an overall energy efficiency of approximately 13.40 %. The energy–environmental impact is summarized by a single score of 5.63E-04 Pt. The energy–economic impact is summarized by a levelized energy cost of 0.35 USD/kWh. The economic-environmental perspective is an energy costing per life cycle assessment of 0.73 USD/kg emission-eq. The 3E analysis reveals a single indicator of 1.95E-04 USD·Pt/kWh2, which is used in the decision to compare with other energy systems. The CCHP system shows advantages in terms of sustainability, quality, and efficiency. Consequently, a novel in this study promotes the sustainability of energy, avoiding environmental impact, and IMW management.

Techno-economic comparison of organic fluid between single- and dual-flash for geothermal power generation enhancement

The geothermal energy has become a research focus due to its unique advantages as the renewable energy source. Organic Rankine cycle (ORC) is one of the important technologies for geothermal power generation, but ORC has a large irreversible loss and a low overall efficiency. The organic Rankine single-stage flash cycle (ORSFC) and organic Rankine dual-stage flash cycle (ORDFC) are proposed in this paper, and the corresponding mathematical models are established. The influence of operating parameters on techno-economic performance of three power generation systems is studied. Additionally, the comparison of the techno-economic performance of three power generation systems is conducted. The results show that the lower condensation temperature and pinch point temperature difference of heat exchangers improve the power generation performance. The evaporation temperature and flash temperature can be regarded as equivalent temperatures. Compared with the ORC system, the average increase in net output power of ORSFC and ORDFC systems is 22.87 % and 31.71 %, respectively, while the economic performance decreased by 0.98 % and 6.48 %, respectively. Therefore, it is recommended to use ORSFC as the incomplete evaporation power generation system. The R245fa is the optimal choice for ORC system, while the R601 and R601a are more suitable for ORSFC and ORDFC systems.

Evaluation of Different Corneal Powers Measured by Corneal Tomography in Intraocular Lens Power Calculation

Abstract Background Corneal power measurement is essential for IOL power calculation. Conventional keratometry measures the anterior corneal surface using a standard keratometric index without measuring the posterior corneal surface. Schiempflug imaging have added the ability to measure posterior corneal surface which may affect IOL power calculation and postoperative refraction. Purpose To evaluate different keratometric measurements including Simulated keratometry (SimK), true net power (TNP), total corneal refractive power (TCRP) and equivalent K reading (EKR) obtained from corneal tomography in IOL power calculation and compare the predicted refraction of calculated IOL power with postoperative subjective refraction. Materials and Methods Sixty-five cataractous eyes were included in this prospective interventional case series. Four corneal power measurements using Pentacam AXL were analyzed: SimK over 3mm, TNP over 4mm, TCRP over 3mm and EKR over 4.5mm. The IOL power was calculated using Barrett Universal II formula. Results No statistically significant difference between SimK and EKR (p- value=1.000) while TNP and TCRP were statistically significantly higher than SimK (p-value<0.001) with mean difference 1.2+/-0.2D and 0.67+/-0.34D respectively. The mean prediction error of refractive outcome was -0.006+/-0.32D for SimK, -0.02+/- 0.5D for EKR, 1.08+/-0.4D for TNP and 0.56+/-0.46D for TCRP. Conclusion Corneal power measurements using SimK and EKR displayed comparable accuracy in IOL power calculation and postoperative refraction while TNP and TCRP were far away.

Effects of prosthetic stiffness and added mass on metabolic power and asymmetry in female runners with a leg amputation.

Similar to nonamputees, female athletes with unilateral transtibial amputation (TTA) using running-specific leg prostheses (RSPs) may have worse running economy and higher rates of running-related injury than male athletes. Optimizing RSP configuration for female athletes could improve running economy and minimize biomechanical asymmetry, which has been associated with running-related injury. Nine females with a TTA ran at 2.5 m/s while we measured metabolic rates and ground reaction forces. Subjects used an RSP with a manufacturer-recommended stiffness category, one category less stiff and two categories less stiff than recommended. Use of an RSP two categories less stiff resulted in 3.0% lower net metabolic power (P = 0.04), 7.8% lower affected leg stiffness (P = 6.01 × 10-4), increased contact time asymmetry (P = 0.04), and decreased stance average vertical ground reaction force asymmetry (P = 0.04) compared with a recommended stiffness category RSP. Lower RSP stiffness (kN/m) values were associated with lower net metabolic power (P = 0.02), lower affected leg stiffness (P = 1.36 × 10-4), longer affected leg contact time (P = 1.46 × 10-4), and similar affected leg peak and stance-average vertical ground reaction force compared with higher RSP stiffness values. Subjects then used the RSP stiffness category that elicited the lowest net metabolic power with 100 g, 200 g, and 300 g added distally. We found no significant effects of added mass on net metabolic power, biomechanics, or asymmetry. These results suggest that female runners with a TTA could decrease metabolic power during running while minimizing biomechanical asymmetries, which have been associated with running-related injury, by using an RSP two categories less stiff than manufacturer recommended.NEW & NOTEWORTHY Females with unilateral transtibial amputation can improve running performance through reductions in net metabolic power by using a running-specific prosthesis (RSP) that is less stiff than manufacturer-recommended. Lower RSP stiffness values are associated with greater leg stiffness and contact time asymmetry, and lower stance-average vertical ground reaction force asymmetry. However, we found that adding mass to the RSP did not affect net metabolic power and stance-phase biomechanical asymmetries during running.

Performance analysis and optimization of a novel S-CO2 closed-Brayton-cycle-based thermal management system for scramjets

The thermal management system (TMS) based on closed-Brayton-cycle is a solution to solve the problems of thermal protection and electricity supply for long-endurance hypersonic vehicles. A novel TMS is proposed in this paper, and the system performance is simulated and analyzed based on a zero-dimensional thermodynamic cycle model and a quasi-one-dimensional heat transfer model. The results indicate that the heat transfer coefficients of the post-mixing method are significantly higher. As the split ratio of the bottom sub-cycle increases, net power first increases to a maximum value and then gradually decreases, but the fuel flow rate for cooling is the opposite. Moreover, the increase in turbine inlet temperature has a positive effect on both fuel flow rate and net power. The optimization results show that the minimum fuel flow rate for cooling is 0.3313 kg/s and net power reaches 162.37 kW when keeps wall temperature under the limit. Furthermore, if the maximum fuel temperature is 723 K, the fuel mass flow rate will further decrease to 0.2907 kg/s. This research provides a potential solution for enhancing the performance of the thermal management system for hypersonic vehicles powered by scramjets.

Performance evaluation and economic analysis of integrated solid oxide electrolyzer cell and proton exchange membrane fuel cell for power generation

In order to generate clean electricity from thermal energy, a hybrid electrochemical system is conceptually developed by coupling the proton exchange membrane fuel cell (PEMFC) and solid oxide electrolyzer cell (SOEC). For evaluating the proposed hybrid system, firstly, the two subsystems are modeled numerically and then they are merged into an integrated SOEC-PEMFC system. Moreover, the SOEC-PEMFC is analytically modeled for further evaluation. The effects of important operational parameters are examined. The outcomes show that when the SOEC operating temperature increases from 823 to 1273 K, the efficiency increases from 18.7 % to 38 % and the net output power improves about 36 % while cost per unit of power of hybrid system decreases about 80 %. Furthermore, by increasing the PEMFC operating temperature from 323 to 348 K, the system net output power and efficiency increase about 16.7 % and 10 %, respectively, whilst the cost per unit of electricity decreases about 19 %. In addition by increasing operating pressure of system, the net output power and efficiency are also improved. The proposed system has maximum output power density of 3.9 kW.m−2 and maximum efficiency of 38 %. In addition, the SOEC-PEMFC system is compared with the previously studied proton exchange membrane electrolyzer cell-proton exchange membrane fuel cell (PEMEC-PEMFC) system. In comparison with the previous PEMEC-PEMFC system, the present system's cost per unit of power and efficiency are about 16 % and 17 % higher, respectively; while the output power density is about double that of the PEMEC-PEMFC system. Generally, because hydrogen-powered systems offer reliable operation from an economic and energetic perspective, the SOEC-PEMFC system represents a promising technological solution to the clean energy demands.

Improving the thermodynamic efficiency and turboexpander design in bottoming organic Rankine cycles: The impact of working fluid selection

In the contemporary context, significant importance is attributed to micro and small-scale Organic Rankine Cycle (ORC) units that are specifically designed for decentralized electricity generation. An essential component within each ORC system is the expander, available in both volumetric and turboexpander configurations. In the existing biogas plant with an Internal Combustion Engine (ICE), the ORC, functioning as a bottoming cycle (BORC) on ICE waste heat, is installed. The BORC utilizes the heat from exhaust gases and the cooling water of the ICE. The paper investigates the effects of various working fluids on both the thermodynamic efficiency of the BORC and the isentropic efficiency of the turboexpander, thus influencing the design parameters of the turboexpander (e.g., number of stages, stator and rotor blade heights, etc.). The BORC, employing the working fluid R141b, has exhibited superior thermodynamic performance, demonstrating a commendable 63.5 kW in net power with a thermodynamic efficiency of 13 %, and ultimately increased the power of the ICE (537 kW) by approx. 12 %. Regarding the turbine component, the turbine operating with the R141b working fluid demonstrated the highest power output and isentropic efficiency, achieving values of 64.14 kW and 67.4 %, respectively. A design was developed for the same turbine, with aerodynamically perfect profiles specially designed for the stator and rotor blades.

Two novel dual-tube photovoltaic-thermal collector designs with improved performance for liquid-cooled photovoltaic-thermal systems

Photovoltaic-thermal (PVT) collectors developed over the years have achieved reduced photovoltaic (PV) panel temperature and improved electrical efficiency mostly based on single-tube spiral and serpentine configurations of the cooling pipes. However, the design and analysis of PVT collector configurations incorporating multiple serpentine tubes, capable of simultaneously reducing both the average PV panel temperature and temperature non-uniformity within the panel, are rare. The present work introduces two novel designs PVT collector systems by incorporating dual-tube arrangements, namely, the Dual-Tube Uni-Directional (DTUD) and the Dual-Tube Opposite-Directional (DTOD) systems. The new collectors' performance is numerically analysed through three-dimensional (3D) simulations. The highest net powers are obtained with 32 cooling loops in both the DTUD and DTOD designs for the given flow rate and panel area. The DTUD-based PVT system yields up to 10.39 % and 10.36 % gains in electrical efficiency and net power, respectively. On the contrary, the DTOD system also results in gains of these parameters, albeit marginally less than the DTUD arrangement. However, the DTOD arrangement results in reduced maximum PV panel temperature, which can positively impact the panel's life span.

Multiple boundary layer suction slots technique for performance improvement of vertical-axis wind turbines: Conceptual design and parametric analysis

Vertical-axis wind turbines (VAWTs) are gaining attention for urban and offshore applications. However, their development is hindered by suboptimal power performance, primarily attributable to the complex aerodynamic characteristics of the blades. Flow control techniques are expected to regulate the flow on the blade surface and improve blade aerodynamics. In the present study, an effective active flow control technique, multiple boundary layer suction slots (MBLSS), is designed for VAWTs performance improvement. The impact of MBLSS on the aerodynamic performance of VAWTs is examined using high-fidelity computational fluid dynamics simulations. The response surface methodology is employed to identify the relatively optimal configuration of MBLSS. Three key parameters are considered, i.e., number of slots (n), distance between slots (d), and slot length (l), which vary from 2 to 4, 0.025c to 0.125c, and 0.025c to 0.075c, respectively. The results show that MBLSS positively affects the power performance and aerodynamics of VAWTs. Parameter n has the most significant effect on VAWT power performance and the importance of d and l is determined by tip speed ratios (TSRs). Tight and loose slot arrangements are recommended for high and low TSRs, respectively. The relatively optimal configuration (n = 2, d = 0.025c, l = 0.05c) results in a remarkable 31.02% increase in the average net power output of the studied TSRs. The flow control mechanism of MBLSS for VAWT blade boundary layer flow has also been further complemented. MBLSS can prevent the bursting of laminar separation bubbles and avoid the formation of dynamic stall vortices. This increases the blade lift-to-drag ratio and mitigates aerodynamic load fluctuations. The wake profiles of VAWTs with MBLSS are also investigated. This study would add value to the application of active flow control techniques for VAWTs.

Investigation of low-GWP working fluids as substitutes for R245fa in organic Rankine cycle application

This study presents a thermo-economic assessment of three low-global-warming-potential (GWP) substitutes, R1233zd(E), R1234ze(Z) and R1234ze(E), for R245fa used in organic Rankine cycle (ORC) systems, considering two models with different heat sources. The exhaust heat from a diesel generator is served as heat source of Model I, while the waste heat of exhaust and jacket cooling water are used as heat source of Model II. It is noted that the working pressure of R1234ze(E) is much higher than that of R1233zd(E), R1234ze(Z) and R245fa in a fixed evaporation-temperature range. Furthermore, the system using R1234ze(E) has the minimum net power output for Model I, while it turns into the maximum net power output for Model II. In addition, both R1234ze(Z) and R1233zd(E) can be used as good alternative working fluids for R245fa because R1234ze(Z), R1233zd(E) and R245fa have close working pressures, maximum net power outputs, and minimum levelized energy costs. Compared to Model I, LECmin of R1233ed(E) and R1234ze(Z) are reduced by 10.8 % and 9.9 % and PBmin of R1233ed(E) and R1234ze(Z) are reduced by 11.5 % and 10.1 %, respectively, in Model II. However, R1233zd(E) has the highest minimum payback period for both Model I and Model II among the four working fluids investigated.