| 82321. |
- Lin, Qianjin, et al.
(författare)
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Measurements of laminar burning velocities and an improved kinetic model of methyl isopropyl ketone
- 2023
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Ingår i: Combustion and Flame. - 0010-2180. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- Methyl isopropyl ketone (MIPK) is the simplest branched ketone and a promising biofuel. In this work, laminar burning velocities (SL) of MIPK + air flames were measured using the heat flux method at atmospheric pressure, over initial mixture temperatures of 298–358 K and equivalence ratios of 0.7–1.4. With the help of the temperature dependence of the SL, data inconsistency between the present measurements and the experimental data reported by Li et al. (Proc. Combust. Inst. 38 (2021) 2135) was demonstrated. Moreover, existing kinetic models for MIPK combustion notably deviate from the present SL measurements. Therefore, the MIPK model suggested by Lin et al. (Proc. Combust. Inst. 39 (2023) 315) was updated by revisiting the MIPK H-abstraction reactions and methyl isopropenyl ketone sub-model. Furthermore, a new di-methyl ketene (critical intermediate during MIPK oxidation) sub-model was constructed and integrated into the MIPK model. Flux and sensitivity analyses revealed that integration of the new di-methyl ketene model improves predictions of the laminar burning velocities as well as shock tube ignition delay times over the pressures of 1–40 bar due to converting di-methyl ketene into C3H5-T (CH2 = C˙CH3) rather than C3H6 or C3H5-S (C˙H = CHCH3) predicted by other MIPK models from the literature. Updates of the MIPK H-abstraction reactions yield more reasonable products branching ratios of formation of the primary fuel radicals, and improve prediction of the SL. It was also found that the rate constants of the MIPK decomposition reaction (MIPK (+M) = CH3CO + IC3H7 (+M)) in the model proposed by Li et al. (Proc. Combust. Inst. 38 (2021) 2135) are significantly underestimated, resulting in underestimation of the present SL measurements and significant overprediction of the ignition delay times.
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| 82322. |
- Lin, Ruiyu, et al.
(författare)
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Kinetic Influence of Siliceous Reactions on Structure Formation of Mesoporous Silica Formed via the Co-Structure Directing Agent Route
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:7, s. 3814-3821
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mechanism responsible for the formation of mesoporous silica formed with the so-called costructure directing agent (CSDA) route. The synthesis relies on the interaction between silica source (tetraethylorthosilicate), cationic surfactant (C18H37N+(CH3)2(CH2)3N+(CH3)3Br2), and CSDA (carboxyethylsilanetriol), which results in a material functionalized with carboxylic groups. Depending on the concentration of HCl in the synthesis, the structure is defined by Fm3¯m (at high pH) and by Fd3¯m (at low pH), with a gradual transition in the intermediate pH range. Here, we aim at finding the origin for the structural change triggered by pH and investigate the effects of the hydrolysis of the silica source on the overall kinetics of the synthesis. A fast process results in Fm3¯m, regardless of pH, and a slow process results in Fd3¯m. The hydrolysis step is the important structural control parameter. We studied the cross-linking of silica and CSDA using 29Si NMR. The cross-linking is similar for the two structures, and possibly the Fd3¯m structure contains slightly more CSDA. 13C PT ssNMR was used to investigate the surfactant mobility/rigidity during the synthesis. The rigidity of the Fm3¯m is established much faster than that of the Fd3¯m.
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| 82323. |
- Lin, Shangrong, et al.
(författare)
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Underestimated Interannual Variability of Terrestrial Vegetation Production by Terrestrial Ecosystem Models
- 2023
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 37:4
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Tidskriftsartikel (refereegranskat)abstract
- Vegetation gross primary production (GPP) is the largest terrestrial carbon flux and plays an important role in regulating the carbon sink. Current terrestrial ecosystem models (TEMs) are indispensable tools for evaluating and predicting GPP. However, to which degree the TEMs can capture the interannual variability (IAV) of GPP remains unclear. With large data sets of remote sensing, in situ observations, and predictions of TEMs at a global scale, this study found that the current TEMs substantially underestimate the GPP IAV in comparison to observations at global flux towers. Our results also showed the larger underestimations of IAV in GPP at nonforest ecosystem types than forest types, especially in arid and semiarid grassland and shrubland. One cause of the underestimation is that the IAV in GPP predicted by models is strongly dependent on canopy structure, that is, leaf area index (LAI), and the models underestimate the changes of canopy physiology responding to climate change. On the other hand, the simulated interannual variations of LAI are much less than the observed. Our results highlight the importance of improving TEMs by precisely characterizing the contribution of canopy physiological changes on the IAV in GPP and of clarifying the reason for the underestimated IAV in LAI. With these efforts, it may be possible to accurately predict the IAV in GPP and the stability of the global carbon sink in the context of global climate change.
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| 82324. |
- Lin, Wamei, et al.
(författare)
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A performance analysis of porous graphite foam heat exchangers in vehicles
- 2013
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 50:1, s. 1201-1210
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Tidskriftsartikel (refereegranskat)abstract
- Due to the increasing cooling power and space limitation in vehicles, a new compact heat exchanger graphite foam heat exchanger is proposed for vehicle cooling application. The graphite foam has high thermal conductivity (the effective thermal conductivity is 40-150 W/m K) and low density (0.2-0.6 g/cm(3)), but it has high flow resistance which is a problem in heat exchanger applications. In order to find a graphite foam heat exchanger with low flow resistance, four different configurations (baffle, pin-finned, corrugated, and wavy corrugated) of graphite foam fins are analyzed in terms of thermal performance and pressure drop by using a computational fluid dynamics approach. The simulation results show that the wavy corrugated foam presents high thermal performance and low pressure drop. Moreover, a comparative study between the wavy corrugated foam heat exchanger and a conventional aluminum louver fin heat exchanger is carried out to evaluate the performance of graphite foam heat exchangers in terms of coefficient of performance (removed heat/air pumping loss), power density (removed heat/mass of heat exchangers), and compactness factor (removed heat/volume of heat exchangers). Finally, this paper concludes that graphite foam heat exchangers should be further developed in vehicles, and presents several recommendations for how such development can be promoted. (C) 2012 Elsevier Ltd. All rights reserved.
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| 82325. |
- Lin, Wamei, et al.
(författare)
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A Review of Cooling Systems in Electric/Hybrid Vehicles
- 2012
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Ingår i: Proceedings Of The ASME International Mechanical Engineering Congress And Exposition - 2010, Vol 5, Pts A And B. ; , s. 1347-1356
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Konferensbidrag (refereegranskat)abstract
- Due to increasing oil demand and serious global warming, a green power generation system is urgently requested in transportation. Electric/hybrid vehicles (EV/HEV) have been considered as a potential solution with great promise in achieving high energy/power efficiency and a low environmental impact. The important electric and electronic equipment in EV/HEV are the battery, inverter and motor. However, because of the high power density in the inverters or the low working temperature of batteries, the cooling problems affect significantly the working performance or the lifetime of electric and electronic equipment in EV/HEV. This paper views different cooling systems including the battery cooling system, inverter cooling system and motor cooling system. A general introduction to the EV/HEV and the electric and electronic equipment working processes are briefly presented at first. Then different methods for the battery cooling system, the inverter cooling system and the motor cooling system are outlined and discussed in this paper. Among other things, the means of using phase change material, or electro-thermal modules are significant for the battery cooling system. Finally, some conclusions or recommendations are presented for the cooling systems, in order to promote the EV/HEV development.
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| 82326. |
- Lin, Wei Cheng, et al.
(författare)
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Effect of energy bandgap and sacrificial agents of cyclopentadithiophene-based polymers for enhanced photocatalytic hydrogen evolution
- 2021
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 298
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Tidskriftsartikel (refereegranskat)abstract
- A library of donor-acceptor system consisting of cyclopentadithiophene-based polymer photocatalysts have been designed and synthesized. Among all photocatalysts, the active PCPDTBSO achieved hydrogen evolution rates of 24.6 mmol h–1 g–1 with apparent quantum yields of 8.7 % at 500 nm. More importantly, combined the results of photocatalytic efficiency, apparent quantum yield, the time-resolved fluorescence decay spectra, the steady-state photoluminescence spectra, and the transient absorption spectroscopy, and the oxidation potentials of sacrificial donors and protons reduction potentials in different pH values, we confirmed the concept that ascorbic acid is a suitable sacrificial donor for narrow bandgap polymers and triethylamine is a suitable sacrificial donor for wide bandgap polymers owing to the existence of the optimal thermodynamic driving force. We believed this study would be advantageous for the selection of photocatalysts and sacrificial donors for hydrogen production.
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| 82327. |
- Lin, Weihua, et al.
(författare)
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Carrier Cooling in Lead Halide Perovskites : A Perspective on Hot Carrier Solar Cells
- 2024
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Ingår i: ACS Energy Letters. - 2380-8195. ; 9:1, s. 298-307
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Forskningsöversikt (refereegranskat)abstract
- The concept of hot carrier solar cells (HCSCs) has been proposed as a promising yet elusive path toward high-performance photovoltaics (PV), capable of surpassing the Shockley-Queisser limit by recycling energy that would otherwise be lost during thermalization. Lead halide perovskites (LHPs) have emerged as highly promising materials for PV applications. The reports of slow hot carrier (HC) cooling in these materials have ignited discussions of their potential in realizing HCSCs. Here we summarize the key findings regarding HC dynamics in LHPs, as revealed by numerous studies using advanced time-resolved spectroscopies. We also emphasize the interconnected mechanisms involved in HC cooling. In addition, we discuss the influence of nanostructuring on HC cooling dynamics in LHPs and suggest that two-dimensional LHPs, with their inherent quantum well structure, might exhibit modified phononic features and altered carrier-phonon coupling strength. We conclude by critically discussing the prospects for HCSCs, taking into account our current understanding of HC cooling and excitation conditions under sunlight.
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| 82328. |
- Lin, Weihua, et al.
(författare)
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Combining two-photon photoemission and transient absorption spectroscopy to resolve hot carrier cooling in 2D perovskite single crystals : the effect of surface layer
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 10:44, s. 16751-16760
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Tidskriftsartikel (refereegranskat)abstract
- We investigate hot carrier (HC) cooling in two-dimensional (2D) perovskite single crystals by applying two complementary ultrafast spectroscopy techniques - transient absorption (TA) and time-resolved two-photon photoemission (TR-2PPE) spectroscopies. TR-2PPE directly maps the hot electron distribution and its dynamics in the conduction band to the detected photoelectron distribution. While TR-2PPE selectively probes the upper layer of the material, TA provides information on the whole bulk. Two cooling regimes are resolved in both techniques. The fast timescale of 100-200 fs is related to the electron scattering by longitudinal optical (LO) phonons and the slow timescale of 3-4 ps corresponds to the LO phonon relaxation. The HC cooling dynamic of TA measurement has faster initial stage and higher starting temperature for the slower stage than in TR-2PPE measurements. Conclusions about spatial sensitivity of the cooling dynamics across the 2D perovskite single crystals constitute valuable information that can guide the future development of HC solar cells and thermoelectric applications based on 2D perovskites.
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| 82329. |
- Lin, Wamei, et al.
(författare)
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Comparison and Analysis of Heat Transfer in Aluminum Foam Using Local Thermal Equilibrium or Nonequilibrium Model
- 2016
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 1521-0537 .- 0145-7632. ; 37:3-4, s. 314-322
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Tidskriftsartikel (refereegranskat)abstract
- Aluminum foams are favorable in modern thermal engineering applications because of the high thermal conductivity and the large specific surface area. The present study aims to investigate an application of porous aluminum foam by using the local thermal equilibrium (LTE) and local thermal nonequilibrium (LTNE) heat transfer models. Three-dimensional simulations of laminar flow (porous foam zone), turbulent flow (open zone), and heat transfer are performed by a computational fluid dynamics approach. In addition, the Forchheimer extended Darcy's law is employed to evaluate the fluid characteristics. By comparing and analyzing the average and local Nusselt numbers, it is found that the LTNE and LTE models can reach the same Nusselt numbers inside the aluminum foam when the air velocity is high, meaning that the aluminum foam is in a thermal equilibrium state. Besides, a high interfacial heat transfer coefficient is required for the aluminum foam to reach a thermal equilibrium state as the height of the aluminum foam is reduced. This study suggests that the LTE model can be applied to predict the thermal performance at high fluid velocities or for the case with a large height.
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| 82330. |
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