Browsing by Author "Lund, Peter D."
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- A-site deficient semiconductor electrolyte Sr1−xCoxFeO3−δ for low-temperature (450-550 °C) solid oxide fuel cells
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-08-30) Lu, Yuzheng; Yousaf Shah, M. A.K.; Mushtaq, Naveed; Yousaf, Muhammad; Lund, Peter D.; Zhu, Bin; Asghar, Muhammad ImranFast ionic conduction at low operating temperatures is a key factor for the high electrochemical performance of solid oxide fuel cells (SOFCs). Here an A-site deficient semiconductor electrolyte Sr1−xCoxFeO3−δ is proposed for low-temperature solid oxide fuel cells (LT-SOFCs). A fuel cell with a structure of Ni/NCAL-Sr0.7Co0.3FeO3−δ-NCAL/Ni reached a promising performance of 771 mW cm−2 at 550 °C. Moreover, appropriate doping of cobalt at the A-site resulted in enhanced charge carrier transportation yielding an ionic conductivity of >0.1 S cm−1 at 550 °C. A high OCV of 1.05 V confirmed that neither short-circuiting nor power loss occurred during the operation of the prepared SOFC device. A modified composition of Sr0.5Co0.5FeO3−δ and Sr0.3Co0.7FeO3−δ also reached good fuel cell performance of 542 and 345 mW cm−2, respectively. The energy bandgap analysis confirmed optimal cobalt doping into the A-site of the prepared perovskite structure improved the charge transportation effect. Moreover, XPS spectra showed how the Co-doping into the A-site enhanced O-vacancies, which improve the transport of oxide ions. The present work shows that Sr0.7Co0.3FeO3−δ is a promising electrolyte for LT-SOFCs. Its performance can be boosted with Co-doping to tune the energy band structure. - Adhesion of Single-Walled Carbon Nanotube Thin Films with Different Materials
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-01-16) M Rajanna, Pramod; Luchkin, Sergey; Larionov, Konstantin V.; Grebenko, Artem; Popov, Zakhar I.; Sorokin, Pavel B.; Danilson, Mati; Bereznev, Sergei; Lund, Peter D.; Nasibulin, Albert G.Single-walled carbon nanotubes (SWCNTs) possess extraordinary physical and chemical properties. Thin films of randomly oriented SWCNTs have great potential in many opto-electro-mechanical applications. However, good adhesion of SWCNT films with a substrate material is pivotal for their practical use. Here, for the first time, we systematically investigate the adhesion properties of SWCNT thin films with commonly used substrates such as glass (SiO2), indium tin oxide (ITO), crystalline silicon (C-Si), amorphous silicon (a-Si:H), zirconium oxide (ZrO2), platinum (Pt), polydimethylsiloxane (PDMS), and SWCNTs for self-adhesion using atomic force microscopy. By comparing the results obtained in air and inert Ar atmospheres, we observed that the surface state of the materials greatly contributes to their adhesion properties. We found that the SWCNT thin films have stronger adhesion in an inert atmosphere. The adhesion in the air can be greatly improved by a fluorination process. Experimental and theoretical analyses suggest that adhesion depends on the atmospheric conditions and surface functionalization. - Advanced LT-SOFC Based on Reconstruction of the Energy Band Structure of the LiNi0.8Co0.15Al0.05O2-Sm0.2Ce0.8O2-δHeterostructure for Fast Ionic Transport
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-09-27) Tayyab, Zuhra; Rauf, Sajid; Xia, Chen; Wang, Baoyuan; Shah, M. A.K.Yousaf; Mushtaq, Naveed; Liang, Shi Heng; Yang, Changping; Lund, Peter D.; Asghar, Muhammad ImranFormation of a heterostructure of semiconductor materials is a promising method to develop an electrolyte with high ionic conductivity at low operational temperature of solid oxide fuel cells (LT-SOFCs). Herein, we develop various heterostructure composites by introducing a pure ionic conductor Sm0.2Ce0.8O2-δ (SDC) into a semiconductor LiNi0.8Co0.15Al0.05O2 (LNCA) for LT-SOFCs electrolyte. The morphology, crystal structure, elemental distribution, micro-structure, and oxidation states of the composite of LNCA-SDC are analyzed and studied via X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HR-TEM), high energy dispersive spectrometry, and X-ray photoelectron spectroscopy (XPS). Electrochemical studies found that the optimal weight ratio of 0.5 LNCA-1.5 SDC heterostructure composite exhibits relatively high ionic conductivity (0.12 S cm-1 at 520 °C), which is much higher than that of SDC. The designed composite of LNCA-SDC heterostructures with optimal weight ratio (0.5:1.5) delivers a remarkable fuel cell power output of 0.735 W cm-2 at 520 °C. The formation of the heterostructure and reconstruction of energy bands at the interface play the crucial roles in enhancing ionic conduction to improve electrochemical performance. The prepared composite heterostructure delivers a unique and insightful strategy of electrolyte in advanced LT-SOFCs. - An analytical model of hydrogen evolution and oxidation reactions on electrodes partially covered with a catalyst
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016) Kemppainen, Erno; Halme, Janne; Lund, Peter D.Our previous theoretical study on the performance limits of the platinum (Pt) nanoparticle catalyst for the hydrogen evolution reaction (HER) had shown that the mass transport losses at a partially catalyst-covered planar electrode are independent of the catalyst loading. This suggests that the two-dimensional (2D) numerical model used could be simplified to a one-dimensional (1D) model to provide an easier but equally accurate description of the operation of these HER electrodes. In this article, we derive an analytical 1D model and show that it indeed gives results that are practically identical to the 2D numerical simulations. We discuss the general principles of the model and how it can be used to extend the applicability of existing electrochemical models of planar electrodes to low catalyst loadings suitable for operating photoelectrochemical devices under unconcentrated sunlight. Since the mass transport losses of the HER are often very sensitive to the H2 concentration, we also discuss the limiting current density of the hydrogen oxidation reaction (HOR) and how it is not necessarily independent of the reaction kinetics. The results give insight into the interplay of kinetic and mass-transport limitations at HER/HOR electrodes with implications for the design of kinetic experiments and the optimization of catalyst loadings in the photoelectrochemical cells. - Analyzing national and local pathways to carbon-neutrality from technology, emissions, and resilience perspectives—Case of Finland
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-01-01) Pilpola, Sannamari; Arabzadeh, Vahid; Mikkola, Jani; Lund, Peter D.The Paris Climate Accord calls for urgent CO 2 reductions. Here we investigate low and zero carbon pathways based on clean electricity and sector coupling. Effects from different spatialities are considered through city and national cases (Helsinki and Finland). The methodology employs techno-economic energy system optimization, including resilience aspects. In the Finnish case, wind, nuclear, and biomass coupled to power-to-heat and other flexibility measures could provide a cost-effective carbon-neutral pathway (annual costs −18%), but nuclear and wind are, to some extent, exclusionary. A (near) carbon-neutral energy system seems possible even without nuclear (−94% CO 2 ). Zero-carbon energy production benefits from a stronger link to the broader electricity market albeit flexibility measures. On the city level, wind would not easily replace local combined heat and power (CHP), but may increase electricity export. In the Helsinki case, a business-as-usual approach could halve emissions and annual costs, while in a comprehensive zero-emission approach, the operating costs (OPEX) could decrease by 87%. Generally, electrification of heat production could be effective to reduce CO 2 . Low or zero carbon solutions have a positive impact on resilience, but in the heating sector this is more problematic, e.g., power outage and adequacy of supply during peak demand will require more attention when planning future carbon-free energy systems. - Beyond hydrophobicity: how F4-TCNQ doping of the hole transport material improves stability of mesoporous triple-cation perovskite solar cells
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-06-07) Liu, Maning; Dahlström, Staffan; Ahläng, Christian; Wilken, Sebastian; Degterev, Aleksandr; Matuhina, Anastasia; Hadadian, Mahboubeh; Markkanen, Magnus; Aitola, Kerttu; Kamppinen, Aleksi; Deska, Jan; Mangs, Oliver; Nyman, Mathias; Lund, Peter D.; Smått, Jan Henrik; Österbacka, Ronald; Vivo, PaolaDespite the outstanding power conversion efficiency of triple-cation perovskite solar cells (PSCs), their low long-term stability in the air is still a major bottleneck for practical applications. The hygroscopic dopants traditionally used in hole transport materials (HTMs) severely degrade the perovskite film. The p-type F4-TCNQ doping of the well-known spiro-OMeTAD HTM enables hydrophobicity-induced protection of the perovskite layer underneath. Nevertheless, the mechanism of F4-TCNQ doping in stabilizing PSCs is still rather unclear. Herein, when F4-TCNQ was adopted as the sole dopant of spiro-OMeTAD, highly stable mesoporous triple-cation PSCs were developed, with a very long T80 lifetime of more than 1 year (∼380 days) for devices stored in air (RH ∼ 40%). The present comprehensive experimental and theoretical studies on F4-TCNQ-doped spiro-OMeTAD reveal that the hydrophobic protection of the perovskite layer underneath is not the only reason for the increased long-term stability of the devices. The high uniformity of F4-TCNQ doping in the spiro-OMeTAD layer and less dopant aggregation and dopant migration towards the anode are key factors responsible for the increased stability of the perovskite solar cells when compared to conventional hygroscopic dopants. This work paves the way for future doping engineering of HTMs for PSCs with competitive stability. - Black titanium oxide : synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability
A2 Katsausartikkeli tieteellisessä aikakauslehdessä(2024-09-13) Hou, Xuelan; Li, Yiyang; Zhang, Hang; Lund, Peter D.; Kwan, James; Tsang, Shik Chi EdmanSince its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives. - Case beyond historical severity : Winds, faults, outages, and costs for electric grid
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-11-01) Jasiūnas, Justinas; Láng-Ritter, Ilona; Heikkinen, Tatu; Lund, Peter D.In recent years, global energy systems have experienced multiple disruptions from known threats at unprecedented severity, causing costly impacts in broader and unexpected domains. This work attempts to improve the understanding of such severity-dependent impact change for the historically unprecedented but meteorologically plausible windstorm on the present Finnish electricity grid. The wind gust speed field of the unprecedented windstorm is obtained by scaling the field of the historically most impactful windstorm upwards by 24%, a value obtained with the extreme-value-theory-based method. Windstorm impacts on the electricity supply are computed with a fragility-based electricity grid impact model, accounting for medium voltage line faults and repairs throughout the country. The lost load from 24% higher wind gust speeds increases tenfold. Impacts are limited by the significant cabling of powerlines done since 2011. The obtained spatiotemporal lost load profile provides a basis for the identification and quantification of extreme windstorm costs as well as a realistic case for broader emergency preparedness exercises. The former application is illustrated by the preliminary cost-benefit assessment for cabling in the case of an unprecedented windstorm. Finally, the reevaluation of currently used cost rates calls for an account of time dependency, critical services, and impacts on smaller economic and population segments. - 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. - Climate-friendly but socially rejected energy-transition pathways
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-09) Bolwig, Simon; Bolkesjø, Torjus Folsland; Klitkou, Antje; Lund, Peter D.; Bergaentzlé, Claire; Borch, Kristian; Olsen, Ole Jess; Kirkerud, Jon Gustav; Chen, Yi kuang; Gunkel, Philip Andreas; Skytte, KlausA framework to account for social acceptance in the modelling of energy-transition pathways is outlined. The geographical focus is on the Nordic-Baltic energy region and the technological focus is on onshore wind power and power transmission, which are considered key technologies in achieving carbon-neutral energy systems in northern Europe. We combine qualitative analysis of social acceptance with quantitative assessments of scenarios using techno-economic energy-system modelling. Key factors in and consequences of social acceptance are identified, especially environmental, health, and distributional factors, as well as costs for developers and society. The energy system analysis includes four scenarios illustrating the system effects and costs of low social acceptance. The results indicate that if low social acceptance were to restrict investments in onshore wind power, costlier solar photovoltaics and offshore wind power would step in. Greater social acceptance cost for onshore wind and transmission lines favours local solutions and a more balanced renewable energy mix. There are important distributional effects: no restrictions on transmission line investments benefit power producers while raising consumer prices in the Nordic-Baltic energy region, while very low social acceptance of onshore wind power would lead to 12% higher consumer costs. The results imply that socio-technical and political factors such as social acceptance may significantly affect transition pathway scenarios based on techno-economic variables alone. Therefore, the techno-economic, socio-technical and political layers of co-evolution of energy systems should be considered when analysing long-term energy transitions. It is important to link energy-system models with a consideration of the dynamics of socio-technical factors. - 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. - Coking resistant Ni–La0.8Sr0.2FeO3 composite anode improves the stability of syngas-fueled SOFC
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-02-26) Yao, Xueli; Asghar, Muhammad Imran; Zhao, Yicheng; Li, Yongdan; Lund, Peter D.An improved SOFC anode with excellent stability against carbon deposition with syngas as fuel is reported. The anode material is Ni–La0.8Sr0.2FeO3 (LSF) composite synthesized by anhydrous impregnation. After reduction in wet H2 (3% H2O), the material partially decomposes to SrLaFeO4 and exsolved Fe. The exsolved Fe forms Ni–Fe alloy with impregnated Ni. The particle size of Ni–Fe alloy is about 20–50 nm. The Ni–Fe alloy nanoparticles disperse on the surface of the La0.8Sr0.2FeO3 and SrLaFeO4 oxides. The increase of Ni content promotes the exsolution of Fe and increases the reaction sites of Ni–Fe alloy. With the increase of the Ni content, the electrical conductivity and catalytic activity are enhanced, which improves the electrochemical performance of the single cell. The cell with 10 mol.% Ni impregnated Ni-LSF as anode achieves a maximum power density of 550 mW cm−2 at 700 °C fueled with syngas. The strong interaction of the nano-sized Ni–Fe alloy with the LaxSryFeOz (La0.8Sr0.2FeO3 or SrLaFeO4) oxide substrate efficiently suppresses carbon deposition with high graphitization degree. Besides, the SrLaFeO4 phase which can accommodate interstitial oxygen facilitates the removal of the deposited carbon. - 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. - Comment on “How green is blue hydrogen?”
Comment/debate(2022-07) Romano, Matteo C.; Antonini, Cristina; Bardow, André; Bertsch, Valentin; Brandon, Nigel P.; Brouwer, Jack; Campanari, Stefano; Crema, Luigi; Dodds, Paul E.; Gardarsdottir, Stefania; Gazzani, Matteo; Jan Kramer, Gert; Lund, Peter D.; Mac Dowell, Niall; Martelli, Emanuele; Mastropasqua, Luca; McKenna, Russell C.; Monteiro, Juliana Garcia Moretz Sohn; Paltrinieri, Nicola; Pollet, Bruno G.; Reed, Jeffrey G.; Schmidt, Thomas J.; Vente, Jaap; Wiley, DianneThis paper is written in response to the paper “How green is blue hydrogen?” by R. W. Howarth and M. Z. Jacobson. It aims at highlighting and discussing the method and assumptions of that paper, and thereby providing a more balanced perspective on blue hydrogen, which is in line with current best available practices and future plant specifications aiming at low CO2 emissions. More specifically, in this paper, we show that: (i) the simplified method that Howarth and Jacobson used to compute the energy balance of blue hydrogen plants leads to significant overestimation of CO2 emissions and natural gas (NG) consumption and (ii) the assumed methane leakage rate is at the high end of the estimated emissions from current NG production in the United States and cannot be considered representative of all-NG and blue hydrogen value chains globally. By starting from the detailed and rigorously calculated mass and energy balances of two blue hydrogen plants in the literature, we show the impact that methane leakage rate has on the equivalent CO2 emissions of blue hydrogen. On the basis of our analysis, we show that it is possible for blue hydrogen to have significantly lower equivalent CO2 emissions than the direct use of NG, provided that hydrogen production processes and CO2 capture technologies are implemented that ensure a high CO2 capture rate, preferably above 90%, and a low-emission NG supply chain. - Comparative analysis of ceramic-carbonate nanocomposite fuel cells using composite GDC/NLC electrolyte with different perovskite structured cathode materials
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018) Asghar, Imran; Lepikko, Sakari; Patakangas, Janne; Halme, Janne; Lund, Peter D.A comparative analysis of perovskite structured cathode materials, La0.65Sr0.35MnO3 (LSM), La0.8Sr0.2CoO3 (LSC), La0.6Sr0.4FeO3 (LSF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), was performed for a ceramic-carbonate nanocomposite fuel cell using composite electrolyte consisting of Gd0.1Ce0.9O1.95 (GDC) and a eutectic mixture of Na2CO3 and Li2CO3. The compatibility of these nanocomposite electrode powder materials was investigated under air, CO2 and air/CO2 atmospheres at 550 °C. Microscopy measurements together with energy dispersive X-ray spectroscopy (EDS) elementary analysis revealed few spots with higher counts of manganese relative to lanthanum and strontium under pure CO2 atmosphere. Furthermore, electrochemical impedance (EIS) analysis showed that LSC had the lowest resistance to oxygen reduction reaction (ORR) (14.12 Ω∙cm2) followed by LSF (15.23 Ω∙cm2), LSCF (19.38 Ω∙cm2) and LSM (>300 Ω∙cm2). In addition, low frequency EIS measurements (down to 50 μHz) revealed two additional semi-circles at frequencies around 1 Hz. These semicircles can yield additional information about electrochemical reactions in the device. Finally, a fuel cell was fabricated using GDC/NLC nanocomposite electrolyte and its composite with NiO and LSCF as anode and cathode, respectively. The cell produced an excellent power density of 1.06 W/cm2 at 550 °C under fuel cell conditions. [Figure not available: see fulltext.] - A comparative assessment of air quality across European countries using an integrated decision support model
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-06) Torkayesh, Ali Ebadi; Alizadeh, Reza; Soltanisehat, Leili; Torkayesh, Sajjad Ebadi; Lund, Peter D.Reducing air pollution including greenhouse gas emissions originating from extensive use of fossil fuels is critical for European countries aiming at improving their environment and at carbon neutrality by the middle of this century. To optimally reduce the air pollutants and mitigate the climate change, not only national or European Union level regulation need to be considered, but also international agreements such as the Sustainable Development Goals, Kyoto Protocol, and Paris Climate Agreement need to be included in these strategies. Managing such a complex framework would benefit from reliable multi-criteria decision-making approaches. Current models to enhance air quality often concentrate on one criterion at a time and focus on momentary improvements only, unable to offer longstanding enhancement. Therefore, comparative analysis of emissions of several air pollutants simultaneously is highly relevant empowering decision-makers with better tools for policy development. The focus of this study is on a decision support model based on the Best-Worst Method and the Measurement of Alternatives and Ranking According to Compromise Solution method to comparatively analyze air pollutants of 22 European countries. This study is the first in its kind to develop an integrated decision model for air quality assessment considering six air pollutants. Extensive sensitivity analyses were performed to highlight the impacts from different scenarios on the decision-making. The results indicate that Sweden, Latvia, France, Lithuania, Hungary, and Italy ranked as the top six countries with the lowest emission. However, Finland, Poland, the Czech Republic, Luxembourg, and Estonia had the lowest overall ranking and the highest per capita emissions. The proposed methodology and evaluation framework can provide a helpful tool for developing regional and national strategies to minimize air pollutants and to improve environmental sustainability. - 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. - 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%. - Controlling anodization time to monitor film thickness, phase composition and crystal orientation during anodic growth of TiO2 nanotubes
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-01) Hou, Xuelan; Lund, Peter D.; Li, YongdanAnodic TiO2 nanotube (TNT) films show promises for photon-driven catalytic, electricity storage and chemical processes. The film thickness of anodic TNT is known to affect its performance in optical and electronic applications. Also, factors affecting the morphology and dimensions of anodic TNT films are rather well-known. However, the knowledge on phase transition and composition in the growth of anodic TiO2 from the titanium metal is very limited. In this work, the anodization time is controlled in intervals of 10, 60, 300, 1000, 2000 and 5000 s to investigate its effect on phase composition and transition, and the morphology of the anodic TNT during the growth process. Even though the mechanism of anodic TNT formation is still under debate, the scanning electron microscope results support bottom-up tube growth with evidence of a compact layer. It was also found that the Richards growth model is applicable to correlate growth time and film thickness. Finally, the phase transition, crystal orientation and pore formation during the anodic process are further discussed.