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[en] In order to monitor the influence of hydrogen on the coupled evolution of dislocation velocity and mobile dislocation density, we applied repeated transients to pure iron under simultaneous hydrogen cathodic charging conditions. The effective activation volume and the thermal stress were determined at different hydrogen concentrations. The effective activation volume decreases immediately with cathodic charging. At high hydrogen concentrations, the activation volume decreases and the thermal stress increases rapidly. The density of mobile dislocations in the hydrogen-charged iron has a lower rate of exhaustion than the hydrogen-free one. The thermal activation energy decreases and the average dislocation velocity increases as a function of hydrogen concentration. Transmission electron microscopy reveals hydrogen-induced tangled dislocations, which indicates a weakening of the repulsive stress field between dislocations
[en] Highlights: • The contact areas, thermal radiation and other influences were considered in this theoretical model. • Two experimental platforms were respectively built up, one is based on transient thermal probe method and the other is based on transient plane source method. • The effective thermal conductivity of Li4SiO4 pebble bed has been obtained. • The comparison between the experimental results and calculation results showing a great agreement. - Abstract: The effective thermal conductivity of breeder pebble bed as an important thermal physical parameter directly affects the thermal and mechanical properties of solid blanket. Theoretical and experimental studies on effective thermal conductivity of Li4SiO4 pebble bed were introduced in this paper. First, a theoretical model coupling the contact areas with bed strains was presented to predict the effective thermal conductivity of mono-sized pebble bed. Taken into account in this theoretical model is the influence of factors, such as properties of pebbles and gas, bed porosity, pebble size, gas flow, contact areas, thermal radiation and contact resistance. Second, experimental platforms were built up to measure the effective thermal conductivity of Li4SiO4 pebble bed. One is based on transient thermal probe method and the other is based on transient plane source method. The effective thermal conductivity of Li4SiO4 pebble bed with pebbles in a diameter of around 1 mm were measured in the temperature range of RT ∼ 550 °C. The helium at 0.1 MPa and air at atmospheric pressure were used as filling gas respectively to assess the influence on effective thermal conductivity of pebble bed. The comparison between the experimental results and calculation results by theoretical model was also discussed.
[en] Highlights: • Numerical simulations of helium flow in the manifolds were carried out. • Full-scaled computational models were built. • The flow distributions were optimized by changing the location of inlet/outlet or adding fluid guides. - Abstract: As a candidate of tritium breeding blanket for Chinese Fusion Engineering Test Reactor (CFETR), a helium cooled solid breeder blanket was proposed. The heat deposited on the blanket is cooled by the helium distributing from the manifolds and flowing in the internal channels of cooling components. To make the temperature of the various blanket components within allowable limits, accurate flow control of helium for the coolant channels should be guaranteed. In this paper, the mass flow rates of helium feeding into the coolant channels were obtained by numerical simulation. The results showed that the helium can be distributed relatively uniform into the first wall channels. However, the mass flow rates of some channel inlets of the other components greatly deviated from the theoretical values. Based on structural improvement of the manifolds, the maximum deviations of flow rate were decreased by almost an order of magnitude.
[en] Highlights: • Compare three models of heat recovery and power generation for industrial waste gas. • Pinch method is used in thermodynamic analysis. • Parameter optimization increases power generation by 15% for single-pressure systems. • Parameter optimization increases power generation by 17% for dual-pressure systems. • Energy integration doubles the improving effect of power generation with fuel saving. - Abstract: A large quantity of waste gas from industrial processes can be used for steam and power generation. Thus, it is of great interest to define a strategy for these power generation systems to get improved performances and efficiency. Three detailed thermodynamic models of heat recovery and power generation from industrial waste gas specified as single-pressure, dual-pressure, and energy integration systems are presented; Meanwhile, impact factors such as steam parameters, pinch temperature difference, and fluctuation of waste gas source on power generating capacity and total site efficiency are comparable analyzed by adopting a thermodynamic analysis combined with pinch method. Also, a case study of energy integration which doubles the improving effect of power generation accompanied with considerable energy saving is performed on basis of fuel efficiency and exergy calculation. In particular, the hierarchical strategy of energy integration of the total site is proposed and exampled.
[en] We investigated the reduction leaching process of manganese dioxide ore using black locust as reductant in sulfuric acid solution. The effect of parameters on the leaching efficiency of manganese was the primary focus. Experimental results indicate that manganese leaching efficiency of 97.57% was achieved under the optimal conditions: weight ratio of black locust to manganese dioxide ore (WT) of 4:10, ore particle size of 63 μm, 1.7 mol·L"-"1 H_2SO_4, liquid to solid ratio (L/S) of 5:1, leaching time of 8 h, leaching temperature of 368 K and agitation rate of 400 r·min"-"1. The leaching rate of manganese, based on the shrinking core model, was found to be controlled by inner diffusion through the ash/inert layer composed of associated minerals. The activation energy of reductive leaching is 17.81 kJ·mol"-"1. To conclude the reaction mechanism, XRD analysis of leached ore residue indicates manganese compounds disappear; FTIR characterization of leached residue of black locust sawdust shows hemicellulose and cellulose disappear after the leaching process.
[en] Highlights: • A trapezoidal U-shaped FW was adopted to decrease the gaps between blankets. • The FW thermo-mechanical performance was assessed by 3D fluid–solid coupled numerical simulation. • The influence of different FW geometrical configurations on temperature and stress was investigated. • A new dimensions of the coolant channel were suggested. - Abstract: Recently a conceptual structure design of helium-cooled solid breeder blanket was proposed as one of the candidates for the Chinese Fusion Engineering Test Reactor (CFETR). In the blanket, a trapezoidal U-shaped FW was adopted to decrease gaps between blanket modules. Due to high heat flux from plasma and intense irradiation by high-energy neutrons, thermal–mechanical analysis of the FW was carried out to ensure reasonable FW temperature and stress under normal load condition. A fluid–solid coupled code ANSYS was used to verify that the mechanical behavior conforms to the criteria of design codes and standards. The calculations showed that the FW material temperature limit was satisfied when the inner surface of the coolant channel was artificially roughened to 0.5 mm in height. Furthermore, the influence of different FW geometrical configurations on the temperature field and stress distribution was investigated. The results led to improvements to the FW design that can reduce the maximum temperature and stress of FW structural material
[en] As for the vibration fatigue problems existed in branch pipes used for domestic 2rd+ generation two-loop nuclear power plant testing, a measurement and calculation analysis method for identifying fatigue vibration is proposed, which is applied to carry out conditions analysis, vibration measurement and maximum effective vibration speed calculation for small branch pipes of a domestic two-loop nuclear power plant. At the same time, the structural mechanics finite element application program ANSYS is used to analyze the vibration fatigue stress of small branch pipes. The result shows, this method can diagnose the first type of sensitive pipes and the second type of sensitive pipes existed in small branch pipes, thus, it can provide theoretical basis for determining whether there are sensitive pipes in the branch pipes used for two-loop nuclear power plant testing. (authors)
[en] In this research, considering the structural parameters and operating conditions for NP reactors, a numerical simulation of downward sub-cooled boiling flow in a vertical rectangular channel under atmospheric pressure was carried out by VOF model of the FLUENT. The Lee model of FLUENT was used to realize the phase transition process of water liquid and water vapor. And CSF (Continuum Surface Force) model was adopted to handle surface tension. The wall super-heat at the Onset of Boiling (ONB) was calculated under different conditions. The simulation results were consistent with experimental data. The impact of different parameters on ONB was analyzed which showed that the distance from the entrance to ONB obviously increases with increasing inlet velocity and subcooled temperature. The increase of heat flux improved the wall super-heat at ONB, but no significant effect of inlet subcooled temperature and inlet velocity was found. In addition, the heat transfer coefficient along the direction of flow was calculated and analyzed. The results showed that the heat transfer coefficient increased significantly with increasing heat flux. However, it was not a simple monotonic relationship between heat transfer coefficient and the inlet velocity or inlet temperature. Moreover, the ONB and the heat transfer coefficient of present work were compared with the case of single-heated. (author)
[en] As for the vibration fatigue problems existed in branch pipesused for test of domestic generation Ⅱ+ two-loop nuclear power plant, a measurement and calculation analysis method for identifying fatigue vibration is proposed, which is applied to carry out condition analysis, vibration measurement and maximum effective vibration speed calculation for small branch pipes of a domestic two-loop nuclear power plant. At the same time, the structural mechanics finite element application program ANSYS is used to analyze the vibration fatigue stress of small branch pipes. The result shows that this method can diagnose the first type and the second type of sensitive pipes existed in small branch pipes. Thus, it can provide the theoretical basis for determining whether there are sensitive pipes in the branch pipes used for test of two-loop nuclear power plant. (authors)
[en] Objective: To explore the feasibility of dual-source CT coronary angiography (CTCA) using 80 kV tube voltage setting in patients with low body mass index (BMI). Methods: A total of 240 patients with suspected coronary artery disease (BMI range 18.6-21.5 kg/m"2) underwent dual-source CTCA. They were randomly assigned to group A (120 kV tube voltage), B (100 kV tube voltage) and C (80 kV tube voltage) based on a random number table. The contrast media dose, volume CT dose index (CTDIvol), dose length product (DLP), and effective dose (ED) were evaluated for each patient. Image noise, CT value, contrast, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and figure of merit (FOM) of coronary artery were all evaluated. Tie image quality of coronary artery was assessed with a three point scale (3 points: excellent, 2 points: general, 1 point: poor). Scan length, CTDIvol, DLP, ED, and contrast media dose for patients, image noise, CT value, contrast, SNR, CNR, and FOM of coronary artery were all analyzed using one-way ANOVA analysis for 3 groups. Time windows of ECG-pulsing protocol were analyzed using χ"2 test, and the image quality scores of coronary artery were analyzed using Kruskal-Wallis test. Results: There were no differences in scan length and Time windows of ECG-pulsing protocol among 3 groups (scan length F = 2.58, P > 0.05, Time windows of ECG-pulsing protocol χ"2 = 0.77, P > 0.05). The average contrast media doses were (82.0 ± 6.4), (76.8 ± 6.1), and (59.1 ± 3.5) ml, the average CTDIvol were (27.5 ± 6.2), (18.7 ± 4.4), and(11.4 ± 2.4) mGy, the average DLPs were (427.7 ± 92.4), (295.4 ± 77.1), and (183.9 ± 41.3) mGy · cm, and the average EDs were (6.1 ± 1.3), (4.1 ± 1.1), and (2.6 ± 0.6) mSv for group A, B and C, respectively. There were statistical differences in contrast media dose, CTDIvol, DLP, and ED among 3 groups (the F values for contrast media dose, CTDIvol, DLP, and ED were 383.08, 248.13, 221.05, and 234.81, respectively, all P < 0.01). Compared to group A and B, the contrast media dose in group C decreased 27.9% and 23.0%, and the ED decreased 57.4% and 36.65, respectively. The average image noise was (22.6 ± 2.2), (26.1 ± 3.0), and(29.1 ± 3.4)HU for group A, B and C, respectively, and there was statistical difference in image noise among 3 groups (F = 101.32, P < 0.01). The average CT value,contrast, SNR, CNR and FOM were (438.3 ± 66.3) HU, (517.3 ± 67.8) HU, 19.5 ± 2.8, 23.0 ± 3.0, and 92.9 ± 31.0 in proximal RCA and (440.2 ± 59.9) HU, (509.5 ± 62.6) HU, 19.6 ± 2.6, 22.7 ± 2.9, and 90.1 ± 29.7 in LMA for group A, (534.2 ± 68.8) HU, (628.9 ± 70.0) HU, 20.7 ± 3.2, 24.3 ± 3.6, and 157.6 ± 59.8 in proximal RCA and (528.4 ± 61.2) HU, (607.9 ± 71.2) HU, 20.4 ± 3.0, 23.5 ± 3.4, and 147.6 ± 57.6 in LMA for group B, and (602.1 ± 78.8) HU, (696.8 ± 83.3) HU, 20.8 ± 2.9, 24.1 ± 3.2, and 239.3 ± 74.8 in proximal RCA and (592.5 ± 72.3) HU, (671.8 ± 82.5) HU, 20.5 ± 2.5, 23.2 ± 3.0, and 221.8 ± 65.7 in LMA for group C, respectively. The CT value, contrast, SNR, CNR and FOM of coronary artery for group C did not decrease (the F values for CT value, contrast, SNR, CNR and FOM were 106.06, 119.90, 4.69, 3.70, and 127.50 in proximal RCA, and 111.79, 101.57, 2.68, 1.39, and 123.00 in LMA, and the P values were < 0.01, <0.01, <0.05, <0.05, and <0.01, in proximal RCA, and <0.01, <0.01, > 0.05, > 0.05, and < 0.01, in LMA, respectively). Image quality was rated as excellent, general and bad for 631, 330, and 37 segments in group A, 640, 323, and 41 segments in group B, and 615, 348, and 45 segments in group C, respectively, there was no significant difference in image quality scores among 3 groups (χ"2 = 1.90, P > 0.05). Conclusion: For the patient with BMI ≤ 21.5 kg/m"2, dual-source CTCA with 80 kV tube voltage setting can be used to diagnose coronary artery disease and the contrast media lose and radiation dosage can be reduced obviously. (authors)