This study focuses on the convective heat transfer characteristics of supercritical carbon dioxide flowing in a horizontal circular tube under high heat flux and low mass flux conditions. The ...influences of thermophysical property, buoyancy effect, and thermal acceleration on the heat transfer characteristics are discussed. The parameters are as follows: system pressure is 7.6–8.4 MPa, mass flux is 400–500 kg/m2 s, heat flux is 30–200 kW/m2, fluid temperature is 20°C −62°C, and Reynolds number is 1.23 × 104 to 4.3 × 104. The wall temperature and heat transfer coefficient of supercritical carbon dioxide are obtained. The results show that, under the condition of high heat flux and low mass flux, heat transfer deterioration would happen, in which thermophysical property and buoyancy effect are the main factors. When the pressure is 7.6 MPa, the buoyancy factor is greater than 10−3 in the whole heat transfer area, and the buoyancy effect cannot be ignored, while the thermal acceleration factor is 9.5 × 10−8 to 4 × 10−6 and the effect of thermal acceleration can be negligible. The experimental data are compared with the predictions using seven empirical correlations, in which the Liao–Zhao correlation shows the best performance.
A two-phase hydraulic turbine’s performance and flow field were predicted under different Inlet Gas Volume Fractions (IGVF) with incompressible and compressible models, respectively. The calculation ...equation of equivalent head, hydraulic efficiency, and flow loss considering the expanding work of compressible gas were deduced based on the energy conservation equations. Then, the incompressible and compressible results, including the output power and flow fields, are compared and analyzed. The compressible gas model’s equivalent head, output power, and flow loss are higher than the incompressible model, but the hydraulic efficiency is lower. As the IGVF increases, the gas gradually diffuses from the blade’s working surface to its suction surface. The gas–liquid separation happens at the runner outlet in the compressible results due to the gas expansion. The area of the low-pressure zone in the incompressible results increases with the IGVF. However, it decreases with the IGVF in the compressible results. As the gas expands in the blade passage, it takes up more flow area, causing the high liquid velocity in the same passage. The runner’s inlet gas distribution affects the liquid flow angle, causing the inlet shock and high TKE areas, especially in the blade passage near the volute tongue. The high TKE area in the compressible results is larger than the incompressible results because the inlet impact loss and the liquid velocity in the blade passage are higher. This paper provides a reference for selecting gas models in the numerical simulation of two-phase hydraulic turbines.
When range high-resolution radar is applied to target recognition,it is quite possible for the high-resolution range pro-files (HRRPs) of group targets in a beam to overlap,which re-duces the target ...recognition performance of the radar.In this pa-per,we propose a group target recognition method based on a weighted mean shift (weighted-MS) clustering method.During the training phase,subtarget features are extracted based on the template database,which is established through simulation or data acquisition,and the features are fed to the support vector machine (SVM) classifier to obtain the classifier parameters.In the test phase,the weighted-MS algorithm is exploited to ex-tract the HRRP of each subtarget.Then,the features of the sub-target HRRP are extracted and used as input in the SVM classifi-er to be recognized.Compared to the traditional group target re-cognition method,the proposed method has the advantages of requiring only a small amount of computation,setting paramet-ers automatically,and having no requirement for target motion.The experimental results based on the measured data show that the method proposed in this paper has better recognition per-formance and is more robust against noise than other recogni-tion methods.
The dependence of low cycle fatigue (LCF) behavior and microstructure evolution of Fe–22Mn-0.6C twinning-induced plasticity (TWIP) steel on the alloying element Al has been investigated under fully ...reversed total strain amplitude control with a nominal strain rate of 0.006 s−1 and strain amplitudes ranging from 0.002 to 0.010 at room temperature. The results indicate a strong dependence of LCF response and evolved microstructure on the addition of Al, owing to its effect on the stacking fault energy (SFE). At all strain amplitudes, the 3Al steel with a higher SFE exhibits a visibly lower cyclic hardening and a higher cyclic softening, resulting in a lower cyclic yield strength than the 0Al steel. As compared with the 0Al steel, the relatively higher SFE of the 3Al steel causes higher accumulated plastic strain, decreased slip planarity and weaker reversibility of dislocations, thereby decreasing the fatigue life. The optical microstructure is featured by increase in slip band density with increasing strain amplitude for both steels. However, the slip band density of the 3Al steel is higher than that of the 0Al steel. Moreover, cyclic loading promotes the formation of dislocation cells, rough labyrinths as well as planar dislocation arrays. Deformation twins are observed only in the 0Al steel with a visible lower critical twinning stress due to its low SFE as compared to the 3Al steel.
MADS-box transcription factors are important for plant growth and development, and hundreds of MADS-box genes have been functionally characterized in plants. However, less is known about the ...functions of these genes in the economically important allopolyploid oil crop, Brassica napus. We identified 307 potential MADS-box genes (BnMADSs) in the B. napus genome and categorized them into type I (Mα, Mβ, and Mγ) and type II (MADS DNA-binding domain, intervening domain, keratin-like domain, and C-terminal domain MIKCc and MIKC*) based on phylogeny, protein motif structure, and exon-intron organization. We identified one conserved intron pattern in the MADS-box domain and seven conserved intron patterns in the K-box domain of the MIKCc genes that were previously ignored and may be associated with function. Chromosome distribution and synteny analysis revealed that hybridization between Brassica rapa and Brassica oleracea, segmental duplication, and homologous exchange (HE) in B. napus were the main BnMADSs expansion mechanisms. Promoter cis-element analyses indicated that BnMADSs may respond to various stressors (drought, heat, hormones) and light. Expression analyses showed that homologous genes in a given subfamily or sister pair are highly conserved, indicating widespread functional conservation and redundancy. Analyses of BnMADSs provide a basis for understanding their functional roles in plant development.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this paper, a transcritical carbon dioxide power generation system based on a vortex tube is studied, which has the advantage of the self-condensation of carbon dioxide. The thermodynamic ...performance of the system was investigated by establishing a mathematical model. The results showed that under fundamental working conditions, the system could output a net power of 271.72 kW, and the thermal efficiency as well as the exergy efficiency of the system could reach 7.38% and 27.09%, respectively. Exergy analysis showed that the turbine had the greatest exergy loss among the system’s components, followed by the vortex tube, pump, heater and cooler. Parameter analysis showed that increasing the outlet pressure and inlet temperature of the vortex tube can improve the thermal efficiency and exergy efficiency of the system. In addition, the improvement in the turbine component’s efficiency is the most beneficial to the system’s performance, among which the turbine’s efficiency has the greatest impact. Carbon dioxide can be effectively liquified by expanding it in the vortex tube, and its liquefaction ratio increases with the decrease in the vortex tube’s inlet temperature and the increase in the vortex tube’s inlet pressure.
Heat transfer of supercritical-pressure kerosene is crucial for regenerative cooling systems in rocket engines. In this study, experiments were devoted to measure the heat transfer of ...supercritical-pressure kerosene under ultra-high heat fluxes. The kerosene flowed horizontally in a mini circular tube with a 1.0 mm inner diameter and was heated uniformly under pressures of 10–25 MPa, mass fluxes of 8600–51,600 kg/m2 s, and a maximum heat flux of up to 33.6 MW/m2. The effects of the operating parameters on the heat transfer of supercritical-pressure kerosene were discussed. It was observed that the heat transfer coefficient of kerosene increases at a higher mass flux and inlet bulk temperature, but is little affected by pressure. The heat transfer of supercritical-pressure kerosene is classified into two regions: normal heat transfer and enhanced heat transfer. When the wall temperature exceeds a certain value, heat transfer is enhanced, which could be attributed to pseudo boiling. This phenomenon is more likely to occur under higher heat flux and lower mass flux conditions. In addition, the experimental data were compared with several existing heat transfer correlations, in which one of these correlations can relatively well predict the heat transfer of supercritical-pressure kerosene. The results drawn from this study could be beneficial to the regenerative cooling technology for rocket engines.
Arsenic trioxide (ATO) has a significant effect on the treatment of acute promyelocytic leukemia (APL) and advanced primary liver cancer, but it still faces severe side effects. Considering these ...problems, red blood cell membrane-camouflaged ATO-loaded sodium alginate nanoparticles (RBCM-SA-ATO-NPs, RSANs) were developed to relieve the toxicity of ATO while maintaining its efficacy. ATO-loaded sodium alginate nanoparticles (SA-ATO-NPs, SANs) were prepared by the ion crosslinking method, and then RBCM was extruded onto the surface to obtain RSANs. The average particle size of RSANs was found to be 163.2 nm with a complete shell-core bilayer structure, and the average encapsulation efficiency was 14.31%. Compared with SANs, RAW 264.7 macrophages reduced the phagocytosis of RSANs by 51%, and the in vitro cumulative release rate of RSANs was 95% at 84 h, which revealed a prominent sustained release. Furthermore, it demonstrated that RSANs had lower cytotoxicity as compared to normal 293 cells and exhibited anti-tumor effects on both NB4 cells and 7721 cells. In vivo studies further showed that ATO could cause mild lesions of main organs while RSANs could reduce the toxicity and improve the anti-tumor effects. In brief, the developed RSANs system provides a promising alternative for ATO treatment safely and effectively.
•The cast 6063 alloy under solution treated (ST) and artificial aged (AA) were impacted at strain rates in the range of 1 × 10−3 to 3.5 × 103 s−1.•The AA alloy exhibits an obvious positive strain ...rate sensitivity under dynamic compression. For the ST alloy, slight strain rate sensitivity is detected.•The microstructure evolution during impact deformation resulted in different flow behaviors has been discussed in detail.•The modified constitutive equation seems to be consistent with the experimental results.
The compression deformation behavior of an as-casting 6063 aluminum alloy has been studied under quasi-static and impact loading conditions at strain rate ranges from 1 × 10−3 to 3.5 × 103 s−1 and a constant strain of 0.2. The results showed that the flow stress response of the as-casting 6063 alloy was sensitive to the aging treatment as well as strain rate. For the solution treated (ST) alloy, slight strain rate sensitivity was detected both under quasi-static and dynamic loading. However, the artificial aging (AA) alloy exhibits an obvious positive strain rate sensitivity under dynamic compression, while the sensitivity under quasi-static compression is low. The constants of the modified Johnson–Cook constitutive model were determined by using the measured flow stress data, which was consistent with the experimental results. Dislocations in the form of vein or cell structures with thick walls containing many parallel dislocation lines were observed in the ST alloy under high strain rate loading. By contrast, a relative high density of dislocations and a large number of homogeneous distributed needle-like β′′ precipitates were detected in the matrix of deformed AA samples. As compared with the AA alloy, the strain hardening and strain rate hardening of ST alloy are balanced by the thermal softening, which results from the adiabatic temperature rise during dynamic deformation. The interactions among them are related to the initial and corresponding evolved microstructure, which leads to its insensitivity to the applied strain rate.
The serrated flow behavior of a Fe–Mn–C twin-induced plasticity steel was investigated at room temperature. Tensile tests were performed at various strain rates under extensometer-measured strain ...control, as compared to conventional crosshead displacement-controlled tests. Different types of serrations were observed with type C ones identified for the first time.
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