Browsing by Author "Wang, Jun"
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- A-site ordered double perovskite with in situ exsolved core-shell nanoparticles as anode for solid oxide fuel cells
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-02-20) Hou, Nianjun; Yao, Tongtong; Li, Ping; Yao, Xueli; Gan, Tian; Fan, Lijun; Wang, Jun; Zhi, Xiaojing; Zhao, Yicheng; Li, YongdanA highly active anode material for solid oxide fuel cells resistant to carbon deposition is developed. Co-Fe co-doped La 0.5 Ba 0.5 MnO 3- with a cubic-hexagonal heterogeneous stucture is synthesized through the Pechini method. An A-site ordered double perovskite with Co 0.94 Fe 0.06 alloy-oxide core-shell nanoparticles on its surface is formed after reduction. The phase transition and the exsolution of the nanoparticles are investigated with X-ray diffraction, thermogravimetric analysis, and high-resolution transmission electron microscope. The exsolved nanoparticles with the layered double-perovskite supporter show a high catalytic activity. A single cell with that anode and a 300 μm thick La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3 electrolyte layer exhibits maximum power densities of 1479 and 503 mW cm -2 at 850 °C with wet hydrogen and wet methane fuels, respectively. Moreover, the single cell fed with wet methane exhibits a stable power output at 850 °C for 200 h, demonstrating a high resistance to carbon deposition of the anode due to the strong anchor of the exsolved nanoparticles on the perovskite parent. The oxide shell also preserves the metal particles from coking. - Characteristics of natural convection in n-eicosane in a square cavity with discrete heat source
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-10) Yang, Shimi; Huang, Bingkun; Wang, Jun; Lund, Peter D.The natural convection of phase change material (PCM) in a two-dimensional square cavity is numerically analyzed. The cavity consists of heat surface with a constant total heated area and adiabatic wall. The Grashof and Prandtl numbers for the PCM (n-eicosane with the melting temperature, Tmelt=36°C) in basic LHS system are 9 × 10^5 and 62.7, respectively, at 350.15K. The mass, momentum and energy balance equations of the system were considered. Three basic heating surface strategies were considered (discrete heat sources): single, side-side and side-bottom heating surface. The results show that the transient Nusselt number, mean kinetic energy at the surface and energy storage rate of the fluid are effectively enhanced by proper arrangement of the discrete heat source location and heating from the bottom half of the left and right sides requires the least time for 300 kJ energy storage. The results indicate that optimally placed discrete heat sources in PCM could be a promising alternative for high-efficient thermal energy storage. - Co-estimating the state of charge and health of lithium batteries through combining a minimalist electrochemical model and an equivalent circuit model
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-02-01) Xu, Zhicheng; Wang, Jun; Lund, Peter D.; Zhang, YaomingAccurate estimation of the state of charge (SOC) and state of health (SOH) is a fundamental requirement for the management system of a lithium-ion battery, but also important to the safety and operational effectiveness of electric vehicles and energy storage systems. Here a model-based method is implemented to assess the SOC and SOH simultaneously. An equivalent circuit model is employed to describe the battery dynamics with recursive least squares online identifying model parameters and unscented Kalman filter estimating battery state. A minimalist electrochemical model is proposed to describe the distribution of the lithium content inside the battery relating the SOH to the capacity fading due to irreversible loss of Li. Based on the real-time capacity value, the state of charge could further be estimated. Comparing the experimental results shows that the battery capacity, i.e., SOH could be predicted timely with a mean error around 2%, which confirms the validity of the proposed co-estimation method for SOC and SOH. - Combining CFD and artificial neural network techniques to predict the thermal performance of all-glass straight evacuated tube solar collector
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-04-01) Du, Bin; Lund, Peter D.; Wang, JunThermal performance modelling and performance prediction of a novel all-glass straight-through evacuated tube collector is analyzed here. A mathematical model of the tube was developed and incorporated into CFD software for numerical performance simulation. To improve the thermal performance prediction of the collector, different artificial neural network (ANN) models were considered. A comprehensive experimental dataset with more than 200 samples were employed for testing of the models. Integrating the thermal simulation model with the ANN models by using modelled collector output as one of the input models, significantly improved the prediction accuracy of the ANN models. The predictions based on the CFD model alone gave the poorest accuracy compared to the ANN models. The convolutional neural network (CNN) model proved to be the best ANN model in terms of prediction accuracy. - Comparative study of heat transfer enhancement using different fins in semi-circular absorber tube for large-aperture trough solar concentrator
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-05) Gong, Jing hu; Wang, Jun; Lund, Peter D.; Zhao, Dan dan; Xu, Jing wen; Jin, Yi haoAn improved evacuated absorber tube (AT) design consisting of a semi-circular tube is proposed for large-aperture parabolic trough concentrator. The absorber tube also contains a flat-plate radiation shield in the vacuum part of the tube in the glass cover. To enhance the heat transfer in the AT, different fins geometries added to the bottom of the AT were analyzed here. Compared to an AT without fins, the thermal efficiency of the tube could be increased from 75.7% to 76.9% with a short and thick fin and to 77.3% with a long and thin fin in the flow velocity range of 0.4–1.5 m/s. The long and thin finned AT shows better enhancement of heat transfer, but the heat transfer performance factor also accounting for frictional losses is higher for short and thick fin. Simultaneously, increasing the number of long and thin fins in the AT would not improve much the heat transfer performance. - Comparative study of optical and thermal model for a large-aperture parabolic trough concentrator with smaller diameter absorber tube bundle
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-11) Gong, Jing hu; Yang, Chi; Wang, Jun; Lund, Peter D.Improving efficiency has always been the purpose of study on large-aperture parabolic trough solar concentrating power. This paper presents a novel design idea for absorber tube to improve efficiency, that is, a large diameter absorber tube was divided into smaller diameter absorber tube bundles, which was arranged in area of high solar flux density and used solar salt (60% KNO3 +40% NaNO3) as working fluid. Yield a 78.4%-optical and 74.8%-thermal efficiency at condition of and temperature= 400 ℃, and 7% and 8.5–9% higher than the traditional 80 mm diameter absorber tube system at temperature of 400–550 ℃, respectively. Moreover, the average surface temperature and max temperature of the smaller diameter absorber tube bundles decreases by 2 ℃ and 4 ℃ compared to traditional absorber tube, respectively. The use of new absorber tube bundle improves flow rate by reducing the hydraulic diameter, achieving the goal of improving transfer heat coefficient, reducing absorber tube surface temperature and improving thermal efficiency. But at the cost of improving the friction coefficient and pump consumption. - Comparisons and optimization of two absorption chiller types by considering heat transfer area, exergy, and economy as single objective functions
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-01-06) Qiu, Yida; Wang, Jingkun; Han, Jing; Chen, Yuzhu; Wang, Jun; Lund, PeterAbsorption cooling technology is an environmentally friendly method to generate continuous chilled water making use of multiple thermal sources, such as waste heat and renewable thermal energy. In this study, two absorption chillers (nominal capacity of 400 kW) with series and parallel connections are evaluated. To research the ideal configuration of chillers after thermodynamic analysis, the structures of the chillers are optimized using the particle swarm optimization algorithm by considering the heat transfer area (HTA), exergy efficiency and total annual cost as single-objective functions. The impact of temperature differences between external and internal flows, heat exchanger efficiencies and the solution allocation ratio is estimated. The optimized HTA, coefficient of performance, exergy efficiency and total annual cost are 149.0 m2, 1.56, 29.44% and $229 119 for the series-connected chiller, and 146.7 m2, 1.59, 31.45% and $234 562 for the parallel-connected type, respectively. Under the lowest HTA condition, compared with the reference simulation results, the energy and exergy performances are improved, while the annual total cost is higher. The annual total cost is highest when maximizing the exergy efficiency, which is attributed to the increase in the HTA. The operating cost accounts for 27.42% (series type) and 26.54% (parallel type) when the annual cost is the lowest. - Comprehensive performance analysis of an advanced power generation cycle for liquid hydrogen cold energy recovery
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2025) Xia, Rui; Wang, Jun; Lund, Peter D.Liquid hydrogen is one of the most efficient ways to store hydrogen. To reduce the energy loss in the liquid hydrogen cycle, the cold energy released at ultra-low temperature in hydrogen regasification should be utilized. Here, an integrated two-stage organic Rankine cycle power generation system for cold energy recovery from liquid hydrogen regasification is proposed. The designed system could recover some 15.3% of the cold energy and increasing the hydrogen cycle exergy efficiency to 71.8%. The working fluid pair R41/R1270 gave the best results and improved the net present value by 2.3%. - Coral-shaped porous LiFePO4/graphene hybrids for high rate and all-climate battery applications
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-01-01) Fan, Qi; Zhang, Yuanjian; Xu, Qingyu; Wang, Jun; Lei, Lixu; Sun, Yueming; Lund, Peter D.Tailor-designed cathode materials are essential for Li-ion batteries with both high energy density and outstanding capacity retention. Here we have designed and fabricated coral-shaped hierarchical porous LiFePO4/graphene hybrids for lithium-ion batteries. These novel hybrid materials exhibit excellent electrochemical performance over a wide temperature range from −40 °C to +60 °C. Even at −40 °C, the hybrid cathode can deliver a high initial capacity of 120 mAhg−1 and still maintain a discharge capacity of 80 mAhg−1 after 500 cycles with a very low capacity loss of 0.066% per cycle. The excellent wide-temperature performance can be ascribed to the porous structure and fast ion/electronic transport kinetics of the high conductive framework. - Design and performance evaluation of a high-temperature cavity receiver for a 2-stage dish concentrator
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-11-01) Yang, Song; Wang, Jun; Lund, Peter D.; Jiang, Chuan; Huang, BingkunHere a new design of a cavity heat-pipe receiver for a 2-stage dish concentrator is proposed. Both optical and thermal simulations are used for the design and for performance evaluation of the cavity. The receiver was fitted to a conventional 2-stage and an improved (overlapped) 2-stage dish. The latter system configuration shows superior performance compared to the conventional one, in particular in terms of compact structure, uniformity of the incident flux and temperature distribution, and solar-to-thermal efficiency. The variance of the irradiation distribution at the cavity decreased by 25% and the largest adjacent temperature difference decreased by 54%. In total, the conversion efficiency increased from 61.3% to 68.6%. Moreover, the new receiver with the improved 2-stage dish concentrating system has less limits of scales (e.g. weight and volume) compared to the traditional single dish design. - Energy, environmental-based cost, and solar share comparisons of a solar driven cooling and heating system with different types of building
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-07-05) Chen, Yuzhu; Hua, Huilian; Xu, Jinzhao; Wang, Jun; Lund, Peter D.; Han, Yifeng; Cheng, TanghuaTo reduce fossil fuel consumption and carbon emissions from building energy systems, a solar-based cooling and heating system is proposed here employing solar concentrating collectors, photovoltaics, double-effect absorption heat pump and thermal storage. The system is applied to five building types in a region with cold winter and hot summer. The system configuration is optimized using energy, environmental cost, and solar fraction as criteria. The results demonstrate that the solar system could produce at least 31.1% of the cooling/heating loads resulting in 73.3% and 64.2% energy and cost savings in a hospital. The coefficient of performance of the hybrid system ranges from 5.87 to 7.56 in cooling mode, and 1.22 to 1.65 for heating. The cost of devices is the most sensitive factor, and followed by the price of grid electricity. Increasing the renewable energy penetration rate could improve the energy performance, but decrease the cost saving ratio due to the lower carbon emissions. - Enhanced activity and stability of Sr 2 FeMo 0.65 Ni 0.35 O 6-δ anode for solid oxide fuel cells with Na doping
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-06-15) Yao, Tongtong; Hou, Nianjun; Gan, Juanjuan; Wang, Jun; Zhi, Xiaojing; Fan, Lijun; Gan, Tian; Zhao, Yicheng; Li, YongdanSr 2-x Na x FeMo 0.65 Ni 0.35 O 6-δ is synthesized as an anode material for solid oxide fuel cells. The effects of Na on the crystalline phase and electrical properties are investigated. The main perovskite phase changes into a Ruddlesden-Popper structure after reduction when x is less than 0.1, while the material with a higher amount of Na keeps the perovskite structure. FeNi x alloy nanoparticles are exsolved during reduction, in which the content of Ni increases with the rise of Na amount. The surface oxygen vacancy concentration is also influenced by the doping of Na, and the highest value is reached when x is 0.1. Sr 1.9 Na 0.1 FeMo 0.65 Ni 0.35 O 6-δ anode exhibits the highest activity, and a single cell supported by a 300-μm-thick La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ electrolyte layer shows maximum power densities of 1495 and 627 mW cm −2 at 850 °C with H 2 and wet CH 4 as fuels, respectively. The coking resistance of the anode is also improved with Na doping. - Enhancement of the electrocatalytic activity of La0.6Sr0.4Co0.2Fe0.8O3-δ through surface modification by acid etching
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-03-15) Fan, Lijun; Wang, Jun; Huang, Zhiyong; Yao, Xueli; Hou, Nianjun; Gan, Tian; Gan, Juanjuan; Zhao, Yicheng; Li, YongdanThe surface properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite electrode are modified with HNO3 treatment to improve its catalytic activity towards oxygen reduction reaction between 500–650 °C. The surface concentrations of A-site cations are reduced after the acid etching. After the calcination at 1150 °C, severe segregation of Sr is observed on the surface of untreated LSCF powder, which is suppressed remarkably with the HNO3 pretreatment. Highly reactive oxygen species and Fe4+ species are formed on the surface of LSCF after the HNO3 treatment, which are beneficial to oxygen reduction reaction. The reduction of oxygen species adsorbed on the LSCF surface, the rate-determining step of the electrode process, is accelerated significantly with the acid etching. - Estimation and prediction of state of health of electric vehicle batteries using discrete incremental capacity analysis based on real driving data
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-06-15) Xu, Zhicheng; Wang, Jun; Lund, Peter D.; Zhang, YaomingThe accuracy of the state of health (SoH) estimation and prediction is of great importance to the operational effectiveness and safety of electric vehicles. Present approaches mostly employ data-driven analysis with laboratory measurements to determine these parameters. Here a novel method is proposed using discrete incremental capacity analysis based on real-life driving data, which enables to estimate the battery SoH without any prior detailed knowledge of battery internal specifics such as current capacity/resistance information. The method accounts for the battery characteristics. It is robust, highly compatible, and has a short computing time and low memory requirement. It's capable to evaluate the SoH of various type of electric vehicles under different charging strategies. The short computing time and low memory needed for the SoH estimation also demonstrates its potential for practical use. Moreover, the clustering analysis is presented, which provides SoH comparison information of certain EV to that of EVs belonging to same type. - Exergo-economic assessment and sensitivity analysis of a solar-driven combined cooling, heating and power system with organic Rankine cycle and absorption heat pump
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-09-01) Chen, Yuzhu; Xu, Jinzhao; Zhao, Dandan; Wang, Jun; Lund, Peter D.District energy systems based on renewable resources help to reduce greenhouse-gas emissions and fossil-fuel use. Here, a multi-generation energy system combining cooling, heating, and power is realized by employing organic Rankine cycle (ORC) and absorption heat pump (AHP) technologies, which enable cascading the utilization of solar heat. The AHP can operate steadily providing cooling, heating and hot water from solar thermal and geothermal sources. A modelling approach presented to evaluate the energy, exergy, economic, and exergo-economic performance of the above system. The results show that the AHP could reach a coefficient of performance (COP) between 1.38 and 2.37 depending on the mode of operation. The yearly energy and exergy efficiency of the tri-generation system is 56.5% and 9.6%, respectively. Compared to a separate system, the simple economic payback time of the tri-generation system is 3.5 years. The specific exergo-economic cost of electricity produced is 0.12 $/kWh, whereas the cost of hot water is much higher, or 0.31 $/kWh. The sensitivity analysis performed shows that the inlet and outlet temperatures of the AHP together with the yearly solar irradiance have the highest impact on the performance. This study provides a new direction on cost-effective utilization of renewable sources in district energy systems. - Exergo-environmental cost optimization of a combined cooling, heating and power system using the emergy concept and equivalent emissions as ecological boundary
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-10-15) Chen, Yuzhu; Xu, Jinzhao; Wang, Jun; Lund, Peter D.District energy systems, in particular combined cooling, heating and power (CCHP) systems, can provide cost-effective energy products, reduce fossil fuel consumption and emissions. A gas-fired CCHP system is considered here employing an internal combustion engine, whose exhaust gas is split between an organic Rankine cycle unit and absorption heat pump. A simulation model of the system is constructed and validated. An emergy based exergo-environmental cost method is proposed here to optimize the exhaust gas allocation ratio based on specific working conditions considering the equivalent emissions of the whole life-cycle chain from an ecological view. The emergy consumption in each process stage is evaluated accompanied with a sensitivity analysis. The results show that the minimize specific system cost is 310050 seJ/J when 63% of the exhaust gas flows to the ORC-unit. The ICE and AHP are responsible for >98% of the emergy consumption, dominated by the operation of the system. The sensitivity analysis shows that heating is the most sensitive of all products against key parameter variations, while electricity is the least. Increasing the service period and the operating hours, the economic performance could be improved, while the transformity of emission enlarges the cost. - Exergo-environmental cost optimization of a solar-based cooling and heating system considering equivalent emissions of life-cycle chain
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-04-15) Chen, Yuzhu; Li, Xiuxiu; Hua, Huilian; Lund, Peter D.; Wang, JunSolar-driven energy systems can effectively reduce the fossil fuel use and pollutant emissions in the built environment. A solar-based cooling and heating (SCH) system employing solar thermal collectors, photovoltaics, a double-effect absorption heat pump, and an electric boiler/chiller is proposed to meet the energy demand of a community. The system and its components are optimized by simultaneously minimizing the specific exergo-environmental cooling/heating costs over the life-cycle and maximizing the cost saving ratio. Compared to the conventional exergo-economic and exergo-environmental optimization methods without life-cycle equivalent emissions, the results show that the system resulting from the proposed method has higher specific costs, or, 1.10 $/kWh for cooling and 2.77 $/kWh for heating, and the corresponding cost saving ratio is >0.02%-unit lower. The coefficient of performance of the hybrid system in the cooling and heating modes are 4.5 and 1.04, respectively. The specific heating cost shows the highest sensitivity against parameter changes. Increasing the capacity of the heat storage and price of grid power would increase the cost saving benefit, while increasing other parameters such as investment cost would decrease the saving ratio. - High performance integrated receiver-storage system for concentrating solar power beam-down system
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-07-15) Yang, Song; Wang, Jun; Lund, Peter D.; Jiang, Chuan; Li, XiuxiuConcentrating solar power systems (CSP) with thermal storage units can provide dispatchable power. Here we propose a modified design of a cavity receiver combined with a thermocline heat storage unit for the beam-down CSP. Instead of using a separate receiver and heat storage unit, an integrated unit consisting of an extended cylindrical cavity with a packed bed storage is proposed. The new approach was designed using validated cavity radiation and quasi-1D 2-phase numerical heat transfer models. As the concentrated irradiation can be directly absorbed in such a system, the structure used can be simplified and operation of the unit is more effective. A high solar-to-exergy conversion ratio of 0.52 was reached with an optimized design, charging and discharging efficiencies being well beyond 99% and 92% at 770 °C. An important detail in the integrated receiver-storage design was the use of a circulation air flow fan, which enhanced the heat transfer inside the packed bed storage. The proposed design is promising for improving the efficiency and economics of beam down CSP. - A High-Performance direct carbon fuel cell with reed rod Biochar as Fuel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-02-15) Wang, Jun; Fan, Lijun; Yao, Tongtong; Gan, Juanjuan; Zhi, Xiaojing; Hou, Nianjun; Gan, Tian; Zhao, Yicheng; Li, YongdanReed biochar is used as fuel of direct carbon fuel cells. KCl is the main impurity in raw reeds, which decreases the graphitization degree of biochar obtained from the pyrolysis of reeds, resulting in a high oxidation activity of the biochar. The reed char exhibits a straight hollow tubular structure, bringing about a high electronic conductivity of the anode. A single cell supported by a 610 ìm-thick Ce 0.8 Sm 0.2 O 1.9 -carbonate composite electrolyte layer with the reed char as fuel achieves a maximum power density of 378 mW cm -2 at 750°C. The cell with 0.04 g carbon fuel exhibits a discharge current density of 30 mA cm -2 for 3 h. The producing rates of CO and CO 2 in the anode under various discharge currents are examined. - High-temperature two-layer integrated receiver storage for concentrating solar power systems
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023) Li, Xiuxiu; Yang, Song; Wang, Jun; Lund, PeterAn integrated receiver storage for a beam-down concentrating solar power (CSP) plant enables simplifying the system layout and reducing the costs. Here a two-layer integrated receiver storage (TLIRS) system design is proposed consisting of a cavity receiver and a two-layer packed-bed storage. The first layer is a porous ceramic and the second one is rocks. To enable performance optimization of the system, models for cavity radiation, two-phase transient heat transfer and local thermal nonequilibrium were derived and validated. The thermal performance of the TLIRS system was assessed and characterized by the absorbing, charging, discharging and overall efficiencies and by the solar-to-exergy conversion ratio. The results indicate that the porous ceramic layer significantly enhances the absorption of solar irradiance and thus improves the thermal efficiencies. For CSP applications, the TLIRS system potentially achieves high thermal performance in repetitive charging and discharging cycles.
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