A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

Lifetime estimation of IGBT module using square-wave loss discretization and power cycling test

The insulated gate bipolar transistor(IGBT)module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety risks and unnecessary costs. The pulsed current pattern of the accelerator power supply is different from other converter applications;therefore, this study proposed a lifetime estimation method for IGBT modules in pulsed power supplies for accelerator magnets. The proposed methodology was based on junction temperature calculations using square-wave loss discretization and thermal modeling.Comparison results showed that the junction temperature error between the simulation and IR measurements was less than 3%. An AC power cycling test under real pulsed power supply applications was performed via offline wearout monitoring of the tested power IGBT module. After combining the IGBT4 PC curve and fitting the test results,a simple corrected lifetime model was developed to quantitatively evaluate the lifetime of the IGBT module,which can be employed for the accelerator pulsed power supply in engineering. This method can be applied to other IGBT modules and pulsed power supplies.

Progress in Research and Development of Molten Chloride Salt Technology for Next Generation Concentrated Solar Power Plants

Concentrated solar power(CSP)plants with thermal energy storage(TES)system are emerging as one kind of the most promising power plants in the future renewable energy system,since they can supply dispatchable and low-cost electricity with abundant but intermittent solar energy.In order to significantly reduce the levelized cost of electricity(LCOE)of the present commercial CSP plants,the next generation CSP technology with higher process temperature and energy efficiency is being developed.The TES system in the next generation CSP plants works with new TES materials at higher temperatures(>565℃)compared to that with the commercial nitrate salt mixtures.This paper reviews recent progressin research and development of the next generation CSP and TES technology.Emphasis is given on theadvanced'TES technology based on molten chloride salt mixtures such as MgCl_(2)/NaCl/KCl which hassimilar thermo-physical properties as the commercial nitrate salt mixtures,higher thermal stability(>800℃),and lower costs(<0.35USD·kg^(-1)).Recent progress in the selection/optimization of chloridesalts,determination of molten chloride salt properties,and corrosion control of construction materials(eg.,alloys)in molten chlorides is reviewed.

一种SATA固态硬盘Power Cycle功能自动化测试方法

提出了一种SATA固态硬盘Power Cycle功能自动化测试方法,用于验证SATA固态硬盘在上下电过程中数据完整性与安全性,保证SATA固态硬盘在多种应用场景中都可以保持正常且高效的运行状态.通过分析标准SATA协议与ATA命令集协议,针对SATA固态硬盘Power Cycle工作流程,在DriveMaster和ULink Power Hub软硬件平台基础上进行脚本编程,对SATA固态硬盘Power Cycle功能进行自动化测试.测试方法包含基于标准协议提炼出的测试流程图,软件平台DriveMaster脚本编程和DriveMaster平台与ULink Power Hub硬件组件联动设置,待测硬盘运行状况记录,发生异常时运行环境记录,测试结果汇总等内容.为满足用户对SATA固态硬盘使用需求,测试过程在经典用例"写入数据-下电-上电-读回比较"基础上,为SATA固态硬盘制造多种不同写入压力,模拟SATA固态硬盘真实使用场景,从厂商角度保证SATA固态硬盘中数据完整性以及正确性.

Performance and Stability of Supercapacitor Modules based on Porous Carbon Electrodes in Hybrid Powertrain

Hybrid power sources have attracted much attention in the electric vehicle area. Particularly, electric-electric hybrid powertrain system consisting of supercapacitor modules and lithium-ion batteries has been widely applied because of the high power density of supercapacitors. In this study, we design a hybrid powertrain system containing two porous carbon electrode-based supercapacitor modules in parallel and one lithium ion battery pack. With the construction of the testing station, the performance and stability of the used supercapacitor modules are investigated in correlation with the structure of the supercapacitor and the nature of the electrode materials applied. It has been shown that the responding time for voltage vibration from 20 V to 48.5 V during charging or discharging process decreases from about 490 s to 94 s with the increase in applied current from 20 A to 100 A. The capacitance of the capacitor modules is nearly independent on the applied current. With the designed setup, the energy efficiency can reach as high as 0.99. The results described here provide a guidance for material selection of supercapacitors and optimized controlling strategy for hybrid power system applied in electric vehicles.

Pedaling for a Cause A Chinese adventurer cycles through Africa to raise money to power a village in Benin

Yuan Jianglei has an amazing story to tell. The 27 year old is one of a handful of people who can say they have cycled through Africa - solo.Yuan began his epic adventure in the West African country of Benin, ending 10,544 km and 333 days later in his hometown of Ningbo, east China＇s Zhejiang Province.

Data-driven modeling of power generation for a coal power plant under cycling

Increased penetration of renewables for power generation has negatively impacted the dynamics of conventional fossil fuel-based power plants.The power plants operating on the base load are forced to cycle,to adjust to the fluctuating power demands.This results in an inefficient operation of the coal power plants,which leads up to higher operating losses.To overcome such operational challenge associated with cycling and to develop an optimal process control,this work analyzes a set of models for predicting power generation.Moreover,the power generation is intrinsically affected by the state of the power plant components,and therefore our model development also incorporates additional power plant process variables while forecasting the power generation.We present and compare multiple state-of-the-art forecasting data-driven methods for power generation to determine the most adequate and accurate model.We also develop an interpretable attention-based transformer model to explain the importance of process variables during training and forecasting.The trained deep neural network(DNN)LSTM model has good accuracy in predicting gross power generation under various prediction horizons with/without cycling events and outperforms the other models for long-term forecasting.The DNN memory-based models show significant superiority over other state-of-the-art machine learning models for short,medium and long range predictions.The transformer-based model with attention enhances the selection of historical data for multi-horizon forecasting,and also allows to interpret the significance of internal power plant components on the power generation.This newly gained insights can be used by operation engineers to anticipate and monitor the health of power plant equipment during high cycling periods.

The pulsed microwave damage trend of a bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwaves（HPMs）,and investigate the thermal accumulation effect as a function of pulse repetition frequency（PRF） and duty cycle.A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density.The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz.The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time.Adopting the fitting method,the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained.Moreover,the accumulation temperature decreases with duty cycle increasing for a certain mean power.

An Innovative Argon/Miller Power Cycle for Internal Combustion Engine: Thermodynamic Analysis of its Efficiency and Power Density

Increasing efficiency and reducing emissions are fundamental approaches to achieving peak carbon emissions and carbon neutrality for the transportation and power industries.The Argon power cycle(APC)is a novel concept for high efficiency and zero emissions.However,APC faces the challenges of severe knock and low power density at high efficiency.To elevate efficiency and power density simultaneously of APC,the Miller cycle is applied and combined with APC.The calculation method is based on a modification of the previous thermodynamic method.The mixture of hydrogen and oxygen is controlled in the stoichiometric ratio.The results indicate that to obtain a thermal conversion efficiency of 70%,in the Otto cycle,the compression ratio and the AR(argon molar ratio in the argon-oxygen mixture)could be 9 and 95%,respectively.In comparison,for the Miller cycle,these two parameters only need to be 7 and 91%.A lower compression ratio can reduce the negative effect of knock,and a reduced AR increases the power density by 66%with the same efficiency.The improvement effect is significant when the expansion-compression ratio is 1.5.Meanwhile,increasing the expansion-compression ratio is more effective in the argon-oxygen mixture than in the nitrogen–oxygen mixture.For the next-generation Argon/Miller power cycle engine,the feasible design to achieve the indicated thermal efficiency of 58.6%should be a compression ratio of 11,an expansion-compression ratio of 1.5,and an AR of 91%.

Development and assessment of a novel integrated system powered by parabolic trough collectors for combined power, heating and freshwater production

Hybrid solar-based integrated systems represent a viable solution for countries with abundant solar radiation,as they provide energy needs in an environmentally friendly way,offering a sustainable and economically advantageous energy solution that utilizes a free source of energy.Therefore,this research offers a thermodynamic evaluation of a novel integrated system driven by solar energy that aims to produce power,heating and freshwater.The integrated system consists of a parabolic trough collector that uses CO_(2) as its working fluid and implements the supercritical carbon dioxide cycle to generate power and heating.The integrated system also in-cludes an adsorption desalination system with heat recovery between the condenser and evaporator,which employs a cutting-edge material called an aluminium fumarate metal–organic framework to produce fresh water.For the modelling of a novel system,an en-gineering equation solver,which is considered a reliable tool for thermodynamic investigations,is employed.The effectiveness of an integrated system is evaluated using a mathematical model and different varying parameters are examined to ascertain their influence on thermal and exergy efficiency,specific daily water production and gained output ratio.The results revealed that the parabolic trough collector achieved a thermal efficiency of 67.2%and an exergy efficiency of 41.2%under certain conditions.Additionally,the thermal efficiencies for electrical and heating were obtained 24.68%and 9.85%,respectively.Finally,the specific daily water production was calculated,showing promising results and an increase from 7.1 to 12.5 m3/ton/day,while the gain output ratio increased from 0.395 to 0.62 when the temperature of hot water increased from 65°C to 85°C,under the selected conditions.

A goal-oriented Design Method of CO_(2) Power Cycle(CPC)System

The CO_(2)power cycle(CPC)system is an efficient and environmentally friendly method for waste heat recovery(WHR).However,the traditional design and optimization process of a CPC system is very complex and timeconsuming.This paper proposes a novel goal-oriented design method based on machine-learning methods for quickly designing an optimized CPC system with given performance indicators.And taking the design of the CO_(2)transcritical power cycle(CTPC)system for internal combustion engines(ICEs)as an example.Firstly,the net output power and the total cost of the system prediction models are trained by simulated data.Then the multiobjective optimization of the system is carried out by using the genetic algorithm coupled with the prediction models,and the optimization results are used to train a classification model.Finally,the given target indicators are input into the classification model for goal-oriented designing and getting the optimal configuration.The results of the goal-oriented design validation show that the goal-oriented design method can design the CTPC system well.And,once the classification model is trained,the CTPC system’s future goal-oriented design process only needs to be calculated once,significantly reducing design time.In conclusion,the goal-oriented design method based on machine-learning proposed is a novel and promising method.This is a technology that combines computer science and energy science and can provide users with a quick and reliable CPC system design method.

Life Cycle Assessment Analysis and Comparison of 1000 MW S-CO_(2)Coal Fired Power Plant and 1000 MW USC Water-Steam Coal-Fired Power Plant

The objective of this paper is to understand the benefits that one can achieve for large-scale supercritical CO_(2)(S-CO_(2))coal-fired power plants.The aspects of energy environment and economy of 1000 MW S-CO_(2)coal-fired power generation system and 1000 MW ultra-supercritical(USC)water-steam Rankine cycle coal-fired power generation system are analyzed and compared at the similar main vapor parameters,by adopting the neural network genetic algorithm and life cycle assessment(LCA)methodology.Multi-objective optimization of the 1000 MW S-CO_(2)coal-fired power generation system is further carried out.The power generation efficiency,environmental impact load,and investment recovery period are adopted as the objective functions.The main vapor parameters of temperature and pressure are set as the decision variables.The results are concluded as follows.First,the total energy consumption of the S-CO_(2)coal-fired power generation system is 10.48 MJ/k Wh and the energy payback ratio is 34.37%.The performance is superior to the USC coal-fired power generation system.Second,the resource depletion index of the S-CO_(2)coal-fired power generation system is 4.38μPRchina,90,which is lower than that of the USC coal-fired power generation system,and the resource consumption is less.Third,the environmental impact load of the S-CO_(2)coal-fired power generation system is 0.742 m PEchina,90,which is less than that of the USC coal-fired power generation system,0.783 m PEchina,90.Among all environmental impact types,human toxicity potential HTP and global warming potential GWP account for the most environmental impact.Finally,the investment cost of the S-CO_(2)coal-fired power generation system is generally less than that of the USC coal-fired power generation system because the cost of the S-CO_(2)turbine is only half of the cost of the steam turbine.The optimal turbine inlet temperature T_(5)becomes smaller,and the optimal turbine inlet pressure is unchanged at 622.082°C/30 MPa.

CO_(2) Reduction Request and Future High-Efficiency Zero-Emission Argon Power Cycle Engine

To meet the requirements of strict fuel consumption and emission limits,continuously increasing the thermal efficiency of an internal combustion engine and decreasing its exhaust emissions are the main challenges to its sustainable development within the automotive industry.Considering the competition with other zero-emission powertrain systems,such as vehicle batteries and fuel cells,the development of the internal combustion engine needs to focus on producing higher efficiency and zero emissions to meet the request of CO_(2) reduction.This paper introduces two novel concepts for an internal combustion engine featuring high efficiency and zero emissions.Referred to as the argon power cycle engine fueled with either hydrogen or natural gas within an oxygen–argon mixture,its fundamentals and characteristics are expounded.This includes a method necessary to absorb carbon dioxide when natural gas is used as fuel instead of hydrogen.

A review of cryogenic power generation cycles with liquefied natural gas cold energy utilization

Liquefied natural gas （LNG）, an increasingly widely applied clean fuel, releases a large number of cold energy in its regasification process. In the present paper, the existing power generation cycles utilizing LNG cold energy are introduced and summarized. The direction of cycle improvement can be divided into the key factors affecting basic power generation cycles and the structural enhancement of cycles utilizing LNG cold energy. The former includes the effects of LNG-side parameters, working fluids, and inlet and outlet thermodynamic parameters of equipment, while the latter is based on Rankine cycle, Brayton cycle, Kalina cycle and their compound cycles. In the present paper, the diversities of cryogenic power generation cycles utilizing LNG cold energy are discussed and analyzed. It is pointed out that further researches should focus on the selection and component matching of organic mixed working fluids and the combination of process simulation and experi- mental investigation, etc.

Identifying Critical Components of Combined Cycle Power Plants for Implementation of Reliability-centered Maintenance

Maintenance scheduling and asset management practices play an important role in power systems,specifically in power generating plants.This paper presents a novel riskbased framework for a criticality assessment of plant components as a means to conduct more focused maintenance activities.Critical components in power plants that influence overall system performance are identified by quantifying their failure impact on system reliability,electric safety,cost,and the environment.Prioritization of plant components according to the proposed risk-based method ensures that the most effective and techno-economic investment decisions are implemented.This,in turn,helps to initiate modern maintenance approaches,such as reliability-centered maintenance(RCM).The proposed method is applied to a real combined cycle power plant(CCPP)in Iran,composed of two gas turbine power plants(GTPP)and one steam turbine power plant(STPP).The results demonstrate the practicality and applicability of the presented approach in real world practices.

Preliminary experimental study of a supercritical CO2 power cycle test loop with a high-speed turbo-generator using R134a under similarity conditions

Research on applying a supercritical carbon dioxide power cycle （S-CO2） to concentrating solar power （CSP） instead of a steam Rankine cycle or an air Brayton cycle has been recently conducted. An S-CO2 system is suitable for CSP owing to its compactness, higher efficiency, and dry-cooling capability. At the Korea Institute of Energy Research （KIER）, to implement an S-CO2 system, a 10 kWe class test loop with a turbine- alternator-compressor （TAC） using gas foil bearings was developed. A basic sub-kWe class test loop with a high- speed radial type turbo-generator and a test loop with a capability of tens of kWe with an axial type turbo- generator were then developed. To solve the technical bottleneck of S-CO2 turbomachinery, a partial admission nozzle and oil-lubrication bearings were used in the turbo- generators. To experience the closed-power cycle and develop an operational strategy of S-CO2 operated at high pressure, an organic Rankine cycle （ORC） operating test using a refrigerant as the working fluid was conducted owing to its operational capability at relatively low- pressure conditions of approximately 30 to 40 bar. By operating the sub-kWe class test loop using R134a as the working fluid instead of CO2, an average turbine power of 400 W was obtained.

Real drive cycles analysis by ordered power methodology applied to fuel consumption,C0_(2),NO_(x) and PM emissions estimation

In this work three fuel consumption and exhaust emission models,ADVISOR,VT-MICRO and the European Environmental Agency Emission factors,have been used to obtain fuel consumption(FC)and exhaust emissions.These models have been used at micro-scale,using the two signal treatment methods presented.The manuscript presents:1)a methodology to collect data in real urban driving cycles,2)an estimation of FC and tailpipe emissions using some available models in literature,and 3)a novel analysis of the results based on delivered wheel power.The results include Fuel Consumption(FC),CO_(2),NO_(x) and PM_(10) emissions,which are derived from the three simulators.In the first part of the paper we present a new procedure for incomplete drive cycle data treatment,which is necessary for real drive cycle acquisition in high density cities.Then the models are used to obtain second by second FC and exhaust emissions.Finally,a new methodology named Cycle Analysis by Ordered Power(CAbOP)is presented and used to compare the results.This method consists in the re-ordering of time dependant data,considering the wheel mechanical power domain instead of the standard time domain.This new strategy allows the 5 situations in drive cycles to be clearly visualized:hard breaking zone,slowdowns,idle or stop zone,sustained speed zone and acceleration zone.The complete methodology is applied in two real drive cycles surveyed in Barcelona(Spain)and the results are compared with a standardized WLTC urban cycle.

Novel Matching Strategy for the Coupling of Heat Flux in Furnace Side and CO_(2)Temperature in Tube Side to Control the Cooling Wall Temperatures

Required by the supercritical carbon dioxide(s CO_(2))coal-fired power cycle,s CO_(2)entering a boiler has a high temperature and can cause overheating of tubes.To eliminate the pressure drop penalty effect,the s CO_(2)boiler consists of several modules,each having different heat flux received from the furnace side(q)and different CO_(2)temperature in the cooling wall tube(T_f).We aim to search for the best matching strategy coupling furnace side and tube side to obtain the lowest temperature of tubes.By theoretically analyzing the wall temperature influenced by q,T_f and a comprehensive thermal resistance C,two matching methods are introduced:the heat flux-temperature matching(HTM)which matches higher q with lower T_f,and the heat flux-heat flux matching(HHM)that matches higher q with higher allowable-heat-flux at the temperature limit of tubes.HTM is a conventional method but HHM is newly proposed here.We show that,if C is identical for different modules,the two methods coincide;otherwise,HHM is recommended.For a s CO_(2)boiler driving 1000 MWe power plant,smaller cooling wall temperatures are obtained by HHM than HTM.Based on HHM,the mid-partition wall,heat transfer enhancement,and downward flow are comprehensively used,decreasing the wall temperature significantly.

Combustion Characteristic and Mechanism of a Mixture Working Fluid C_(3)H_(8)/CO_(2)

In the CO_(2)transcritical power cycle,conventional cooling water can hardly condense subcritical CO_(2)because its critical temperature is as low as 30.98°C.In order to avoid this condensing problem,CO_(2)-based mixtures have been proposed as working fluids for transcritical power cycle.They can raise the critical temperature by mixing a little C_(3)H_(8)as the secondary component to CO_(2).However,the flammability of the mixture may limit its application.This article investigated laminar flame speed of C_(3)H_(8)/CO_(2)which represents the mixture’s combustion characteristic by a so-called heat flux method and studied the inhibition mechanism of CO_(2)on the combustion based on the Premixed Laminar Flame-Speed Calculation reactor of Chemkin-Pro.The experimental results showed that the laminar flame speed shows a peak value with changing the equivalence ratio and accelerates with raising the mole fraction of the organic gas.Additionally,a slight upwards trend was observed for the corresponding equivalence ratio of the peaks.The flammable range for the equivalence ratio extended with the mole fraction of C_(3)H_(8)increasing.With the mole fraction of C_(3)H_(8)of 0.15,the maximum laminar flame speed was 12.8 cm/s,31.7%of that of the pure C_(3)H_(8).The flammable range was from 0.41 to 1.33,decreasing by 23.3%compared with that of C_(3)H_(8).A flammable critical mixing ratio was also found as 0.08/0.92 for C_(3)H_(8)/CO_(2)at the normal condition.By simulating,it was found that the most key free radical and elementary reaction which determine the inhibition of CO_(2)on the combustion are OH and H+O_(2)=O+OH,respectively.

Cost effectiveness of new roadway lighting systems

Appropriate and adequate lighting at select locations on roadways is essential for roadway safety. As the lighting technologies advance, many Wpes of new lighting devices have been developed for roadway lightings. The most promising new lighting technologies for roadway lighting include light emitting diode, induction, plasma, and metal halide lighting systems. A study was conducted to compare the new systems with the conventional high pressure sodium systems that are currently used on the Indiana roadway systems. In this study, the engineering issues, were analyzed such as illuminance, color rendering, power usage, cost effectiveness, and approval procedures for new roadway lighting systems. This paper, however, presents only the study findings related to cost effectiveness of the evaluated roadway lighting systems. Illustrated in this paper are the main features of the roadway lighting systems under evaluations, installations of the new lighting systems, measurements of power consumptions, and life cycle cost analyses of the lighting systems. Through this study, experience and knowledge have been obtained on the installations, power measurements, and cost effectiveness of the new types of the roadway lighting devices. The actual power values of various luminaires were obtained by measuring the electric current with a multi-meter. It was found that the differences between the rated and measured power values could be significant. The results of the life cycle cost analysis indicate that the lower life cycle costs of some of the alternative lighting devices are attributed to their relatively lower electricity usages and longer lamp/emitter replacement cycles.