| 1. |
- Yaning, Li, et al.
(author)
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Situations and challenges of road safety in China
- 2013
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In: Proceedings of the 16th International Conference Road Safety on Four Continents. - Linköping : Statens väg- och transportforskningsinstitut.
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Conference paper (other academic/artistic)abstract
- Although the road safety in China has made great achievement, the current situation is still not optimistic. The new situations and challenges of road safety in China are analyzed. There are still many factors affecting road traffic safety, and the foundation of road safety is still weak. Currently, the accidents are likely to relapse, the accident rate and lethality rate are very high, the road safety in rural areas is not optimistic, the accidents caused by commercial vehicles frequently happened, and the devastating accidents with group deaths and injuries are still very frequent. The challenges include: the hidden dangers are prominent, the safety awareness of citizens is very poor, and the management, enforcement of road safety and emergency rescue skills are low.With a series of policies and measures gradually taking effect, road traffic accidents in China went down quickly. China has successfully achieved the objectives of curbing high incidence and gradually reducing accidents, gradually improving road safety year on year. Although the road traffic safety has been keeping a relatively stable level, there are still many factors affecting road traffic safety, and the foundation of road safety is still weak.
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| 2. |
- Cui, Yalin, et al.
(author)
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Unified formula for the field synergy principle
- 2020
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In: Numerical Heat Transfer, Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 77:4, s. 287-298
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Journal article (peer-reviewed)abstract
- The field synergy principle has three criteria to qualitatively describe the essence of single-phase convective heat transfer enhancement. However, in practice these criteria are difficult to be applied to convective heat transfer analysis, because there are no corresponding indicators available to quantitatively describe them. Therefore, a unified formula for the field synergy principle was developed based on these three criteria using probabilistic techniques in this study to overcome these defects. The formula is applicable to incompressible flows with constant properties in both laminar and turbulent flow regimes. The formula contains three categories of non-dimensional indicators corresponding to the three criteria of the field synergy principle, respectively, including domain-averaged cosine of synergy angle, the Pearson linear correlation coefficients between the scalar functions contained in the energy governing equation of convective heat transfer, and the variation coefficients of these functions. The physical meanings of these indicators for the field synergy principle and their connections with the known heat transfer enhancing mechanisms were then discussed. Based on this formula, an improved analytical system for the field synergy principle was proposed. It allows an efficient and quantitative analysis of all single-phase constant-property convective heat transfer phenomena. This new system overcomes the limitation of the conventional field synergy analytical system that mainly analyzes convective heat transfer mechanism from the perspective of synergy angle.
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| 3. |
- Wang, Sifan, et al.
(author)
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Fire carbon emissions over Equatorial Asia reduced by shortened dry seasons
- 2023
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In: npj Climate and Atmospheric Science. - 2397-3722. ; 6:1
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Journal article (peer-reviewed)abstract
- Fire carbon emissions over Equatorial Asia (EQAS) play a critical role in the global carbon cycle. Most regional fire emissions (89.0%) occur in the dry season, but how changes in the dry-season length affect the fire emissions remains poorly understood. Here we show that, the length of the EQAS dry season has decreased significantly during 1979–2021, and the delayed dry season onset (5.4 ± 1.6 (± one standard error) days decade−1) due to increased precipitation (36.4 ± 9.1 mm decade−1) in the early dry season is the main reason. The dry season length is strongly correlated with the length of the fire season. Increased precipitation during the early dry season led to a significant reduction (May: −0.7 ± 0.4 Tg C decade−1; August: −12.9 ± 6.7 Tg C decade−1) in fire carbon emissions during the early and peak fire season. Climate models from the Coupled Model Intercomparison Project Phase 6 project a continued decline in future dry season length in EQAS under medium and high-emission scenarios, implying further reductions in fire carbon emissions.
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| 4. |
- Wang, Wei, et al.
(author)
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Analysis of laminar flow and heat transfer in an interrupted microchannel heat sink with different shaped ribs
- 2019
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In: Journal of Thermal Analysis and Calorimetry. - : Springer Science and Business Media LLC. - 1388-6150 .- 1588-2926.
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Journal article (peer-reviewed)abstract
- A numerical study was conducted to investigate the mechanism of laminar flow and heat transfer enhancement in an interrupted microchannel heat sink (IMCHS) with different shaped ribs at Reynolds number ranging from 100 to 900. The global flow features, heat transfer and friction for IMCHS with no ribs, rectangle ribs, triangle ribs and trapezoid ribs are detailed compared. The results show that the local heat transfer and friction performance of IMCHS with ribs show significant increase at the windward side of the ribs. Additionally, the smaller the chamfer of ribs, the larger average heat transfer and friction performance. For IMCHS with rectangle ribs, the maximum increment of Nu and f can reach to 1.81 and 2.59, respectively. Concerning the overall heat transfer performance (PEC), the trapezoid ribs show the best behavior with PEC = 1.65–1.38 at Re = 100–900.
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| 5. |
- Wang, Wei, et al.
(author)
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Entropy generation analysis of fully-developed turbulent heat transfer flow in inward helically corrugated tubes
- 2018
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In: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 73:11, s. 788-805
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Journal article (peer-reviewed)abstract
- The entropy generation analysis of fully-developed turbulent heat transfer flow in inward helically corrugated tubes was numerically performed by using a Reynolds stress model. The simulations were conducted for a smooth tube and five cases of corrugated tubes with Reynolds number (Re) ranging from 10,020 to 40,060 at a constant wall temperature condition. The effects of corrugation pitch and height on the flow patterns as well as local thermal and frictional entropy generation are detailed in the near wall region. The results indicate that the local heat transfer entropy generation is significantly evident at the sub-layer region and the detached vortex region, and the local thermal entropy is improved with increases in the secondary flow. Local friction entropy generation is mainly located at the windward of the corrugation and the severely turbulent fluctuation region and is mainly induced by the velocity gradient. The average friction entropy generation exhibits an exponential growth, while the average heat transfer and the total entropy generation display a linear growth trend with increased Re. The average Bejan number (Be) exhibits an exponential decline, and the minimum value can reach 0.69. From a comprehensive viewpoint, it is optimal for the Re to be lower than 30,050. When Re <20,030, higher and dense corrugations are beneficial. When 20,030 < Re <30,050, low and spare corrugations are more optimal. Besides, the case with Hl/D = 0.08 is not recommended.
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| 6. |
- Wang, Wei, et al.
(author)
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Entropy Study on the Enhanced Heat Transfer Mechanism of the Coupling of Detached and Spiral Vortex Fields in Spirally Corrugated Tubes
- 2021
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In: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 42:17, s. 1417-1431
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Journal article (peer-reviewed)abstract
- The present work numerically studied the enhanced heat transfer mechanism of the coupled fields of detached and spiral vortices in symmetrical and asymmetrical spirally corrugated tubes. The heat transfer and viscous dissipation were analyzed by evaluating the entropy combined with the flow patterns, and the global entropy generation rate was analyzed by considering the local Nusselt number and friction factor. The results indicated that, both the leeside and windward corrugation angles had obvious effects on the strength of detached vortex and spiral flow, and also the location of the vortex. The maximum values of the heat transfer entropy were located at the boundary layers, and the heat transfer entropy of the secondary flow region was more distinguished than in other parts of the main flow region. The maximum values of friction entropy generation were located at both the boundary layers and the core of detached vortex. The performance evaluation criterion (PEC) presents nearly the same values for the four cases, when the Reynolds number (Re) is less than 6,300. In addition, the PEC of symmetrical spirally corrugated tube with corrugation angle equal to 25° showed the best performance, when Re is greater than 6,300. To keep the PEC above 1, Re should not exceed 33,000.
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| 7. |
- Wang, Wei, et al.
(author)
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Large eddy simulation of turbulent flow and heat transfer in outward transverse and helically corrugated tubes
- 2019
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In: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 75:7, s. 456-468
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Journal article (peer-reviewed)abstract
- Turbulent flow and heat transfer in outward transverse and helically corrugated tubes are performed with large eddy simulation by the ANSYS Fluent software. The prediction accuracy is validated by comparison with experimental data and empirical correlations for a wavy surface wall and smooth tube, respectively. The turbulent flow patterns, local heat transfer, and friction factor are discussed. The results show that the secondary and turbulent eddies are inhibited by the spiral flow. Otherwise, the flow impact of the wall is the key factor for heat transfer enhancement, and the spiral flow has of small effect on heat transfer performance, however it can decrease the flow resistance significantly. The overall heat transfer performance for the helical corrugated tube is 1.23, which is superior to the value of 1.18 for the transverse corrugated tube.
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| 8. |
- Wang, Wei, et al.
(author)
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Numerical investigation of entropy generation of turbulent flow in a novel outward corrugated tube
- 2018
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 126, s. 836-847
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Journal article (peer-reviewed)abstract
- The present study numerically investigates the second law analysis of turbulent flow in novel outward helical corrugated tubes by using a Reynolds Stress Model (RSM). A case of a transverse corrugated tube and five cases of helical corrugated tubes with different height-to-diameter ratios and pitch-to-diameter ratios are examined with Reynolds number ranging from 3800 to 43,800 at a constant wall temperature condition. The results indicate that the secondary flow significantly increases the thermal and viscous dissipation irreversibilities. However, the spiral flow inhibits the secondary flow and the production of local entropy. The heat transfer effective zone (Belocal > 0.5) is mainly located at the sub-layer and buffer-layer, and the ineffective zone (Belocal < 0.2) is located at the turbulent severe pulsation zone. A comprehensive consideration of the total entropy generation number (Ns-tot) and average Bejan number (Beave) indicates that the optimal Re is less than 31,000 for all the cases although Re does not exceed 18,800 in the case of Hl/D = 0.15, pl/D = 1.0 and Hl/D = 0.10, pl/D = 0.5. Additionally, the helical corrugated tube exhibits an overall advantage when compared with a transverse corrugated tube with the same geometrical parameters.
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| 9. |
- Wang, Wei, et al.
(author)
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Thermophysical properties and convection heat transfer behavior of ionic liquid [C4mim][NTf2] at medium temperature in helically corrugated tubes
- 2018
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 142, s. 457-465
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Journal article (peer-reviewed)abstract
- The thermophysical properties of the ionic liquid, 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C4mim][NTf2], at medium temperature, were predicted based on a summary of previous literature data. Furthermore, the heat transfer behavior in smooth and corrugated tubes was numerically studied, using different fluid temperatures and corrugation heights. A multi-objective optimization method was used to obtain the optimal solutions from a set of feasible solutions. The result show that the empirical formulas can well predict the density, heat capacity, and thermal conductivity conditions, yet show small errors on different viscosity conditions. The heat transfer performance for high-temperature fluids is quite superior to that in the low temperature condition, as well as on pressure drop. The growth rate of the heat transfer performance is significant for the cases of corrugation height to diameter ratio equal to 0.025 and 0.05. In addition, the overall heat transfer performance presents an interval optimum principle, where the Reynolds number is inversely proportional to the corrugation height, except for the case of corrugation height to diameter ratio equal to 0.15. The response values of the Pareto optimal solution correspond to Nusselt number = 724.6, Poiseuille number = 1519.8 and Overall heat transfer performance = 1.01, with the Reynolds number = 70,490 and ratio of corrugation height to diameter = 0.0252.
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