[en] Experiments of natural circulation under different rolling conditions are performed in order to investigate the effect of rolling motion on flow resistance. The results reveal that the flux under rolling condition is less than that under non-rolling condition when heating power is the same. The shorter the rolling period or the larger the rolling amplitude, the smaller the flux of natural circulation. According to experimental phenomena and velocity distribution of the flow, some theoretical analyses are performed in order to explain the profile of fluid flow in vertical channel especially the flow in radial direction. The analyses figure out that rolling motion would bring about cross-mixed flow in radial direction, which makes the flow more turbulent, leads to the increase of viscous dissipation. Rolling motion would make a part of fluid deviate from the mainstream to impact the wall of channel, which causes impact dissipation. At the same time, the flow deviating from the mainstream brings about secondary flow near the wall which increases the viscous dissipation further. The increase of the impact dissipation and the viscous dissipation result in the increase of flow resistance, consequently the flux decreases

[en] Highlights: • Pressure drop fluctuation is enhanced with increasing rolling amplitude and period. • The phase difference between flow rate and pressure drop fluctuation is 1/4 period. • Amplitude of boiling heat transfer coefficient increases with increasing heat flux. • The curve of boiling heat transfer coefficient fluctuations is close to sine curve. - Abstract: Experimental investigations on thermal–hydraulic characteristics of boiling flow in a rectangular narrow channel under rolling motion conditions are carried out. This experiment is designed to elucidate the phenomena of boiling flow under rolling motion and to give the corresponding rational explanations. The results show that the amplitudes of fluctuations of pressure drop, flow rate, fluid and wall temperatures, and boiling heat transfer coefficient increase with the increasing of rolling amplitude and rolling period. The phase difference of flow rate fluctuation and pressure drop fluctuation is 1/4 period, and the saturated water temperature fluctuations of the test section delay 2–3 s behind the pressure drop fluctuations. The time average boiling heat transfer coefficients of the rectangular narrow channel under rolling motion are equal to those under static conditions. The amplitude of boiling heat transfer coefficient of test section increases with increasing heat flux and flow rate, while decreases with increasing system pressure

[en] The reaction of uranium and its alloy with oxygen and water vapor has attracted widely attention as an important nuclear material. The oxidation process, reaction rate and products of uranium and its alloy with oxygen, water vapor and humid oxygen has been summarized and discussed. The process of uranium-oxygen systematic reaction includes the adsorption, solution of oxygen on the surface, diffuseness in the crystal lattice which is the determinative step and reaction at the interface of the metal and the oxide. However, the reaction mechanism of uranium-water system was dispersive on the diffuse ion. The uranium-oxygen-water systematic reaction is the result combines the uranium-oxygen and uranium-water reaction. (authors)

[en] A series of experimental studies of frictional pressure drop for single phase and two-phase bubble flow in smooth rolling tubes were carried out. The tube inside diameters were 15 mm, 25 mm and 34.5 mm respectively, the rolling angles of tubes could be set as 10 deg. and 20 deg., and the rolling periods could be set as 5 s, 10 s and 15 s. Combining with the analysis of single-phase water motion, it was found that the traditional correlations for calculating single-phase frictional coefficient were not suitable for the rolling condition. Based on the experimental data, a new correlation for calculating single-phase frictional coefficient under rolling condition was presented, and the calculations not only agreed well with the experimental data, but also could display the periodically dynamic characteristics of frictional coefficients. Applying the new correlation to homogeneous flow model, two-phase frictional pressure drop of bubble flow in rolling tubes could be calculated, the results showed that the relative error between calculation and experimental data was less than ± 25%. (authors)

[en] Experimental studies of single-phase natural circulation flow and heat transfer under a rolling motion condition are performed. Experiments with and without rolling motions are conducted so the effects of rolling motion on natural circulation heat transfer are obtained. The experimental results show rolling motion enhances the heat transfer, and the heat transfer coefficient of natural circulation flow increases with the rolling amplitude and frequency. Analyses of data show that the effect of heat capacity of heated tube can not be neglected and Reynold number of acceleration is introduced to employ the effect of heat capacity. Based on the experimental data, an empirical equation for the heat transfer coefficient under rolling motion is achieved. The calculated results agree well with experimental data

[en] Highlights: •The Volta potential differences relative to the matrix are positive for both types of inclusions. •Both types of inclusions are cathodic in the “inclusion/matrix” microgalvanic couples. •The oxide-rich inclusions show a larger Volta potential value of about 115 mV than the carbo-nitride-rich inclusions. •The oxide-rich inclusions give stronger local galvanic coupling with the matrix. •The oxide-rich inclusions are more predisposed to initiate pitting corrosion. -- Abstract: The effects of carbo-nitride-rich and oxide-rich inclusions on the pitting susceptibility of depleted uranium were investigated by electrochemical corrosion measurements, optical microscopy, scanning Kelvin probe force microscopy (SKPFM), and SEM. The results of the potentiodynamic polarization tests suggest that oxide-rich inclusions are more likely to induce pitting corrosion than carbo-nitride-rich inclusions. This enhanced corrosion may be explained by the strong local galvanic coupling between the oxide-rich inclusion and the surrounding matrix, which, from the sight of SKPFM analysis, exhibits a 115 V higher Volta potential than the coupling between the carbo-nitride-rich inclusions and the matrix, respectively.

[en] Highlights: • Chen correlation cannot well predict the coefficient of rectangular channel. • Kim and Mudawar correlation is the best one among the Chen type correlations. • Lazarek and Black correlation predicted 7.0% of data within the ±30% error band. • The new correlation can well predict the coefficient with a small MAE of 14.4%. - Abstract: In order to research the characteristics of boiling flows in a vertical rectangular narrow channel, a series of convective boiling heat transfer experiments are performed. The test section is made of stainless steel with an inner diameter of 2 × 40 mm and heated length of 1100 mm. The 3194 experimental data points are obtained for a heat flux range of 10–700 kW/m"2, a mass flux range of 200–2400 kg/m"2 s, a system pressure range of 0.1–2.5 MPa, and a quality range of 0–0.8. Eighteen prediction models are used to predict the flow boiling heat transfer coefficient of the rectangular narrow channel and the predicted value is compared against the database including 3194 data points, the results show that Chen type correlations and Lazarek and Black type correlations are not suitable for the rectangular channel very much. The Kim and Mudawar correlation is the best one among the 18 models. A new correlation is developed based on the superposition concept of nucleate boiling and convective boiling. the new correlation is shown to provide a good prediction against the database, evidenced by an overall MAE of 14.4%, with 95.2% and 98.6% of the data falling within ±30% and ±35% error bands, respectively

[en] Highlights: • Annular flow model can well predict pressure gradient and heat transfer coefficient. • Effect of heat flux on liquid film thickness is bigger than that of mass flow rate. • The velocity profile in the liquid film is not linear. • The velocity of liquid film increases with increasing heat flux. • The velocity gradient increases noticeably near the liquid/vapor interface. - Abstract: A mathematical separated flow model has been developed that is applicable to the annular two-phase flow in the rectangular narrow channels with peripheral heating. The theoretical annular flow model is based on the fundamental conservation principles: the mass, momentum and energy conservation equations of liquid film, and the momentum conservation equation of the vapor core. Through numerically solving the closed equations, boiling heat transfer coefficient, axial pressure gradient, liquid film thickness and velocity profiles in the liquid film are obtained. A good agreement has been found through comparing the experimental data and theoretically predicted results. The liquid film thickness will decrease with the increase of heat flux and channel width, while increases with increasing flow rate and channel height. The velocity profile in the liquid film is not linear when the thickness of the liquid film is not very thin and it increases with increasing heat flux, while decreases with the increase of mass flow rate and channel size. The effects of heat flux and channel width on velocity in the liquid film are larger than that of mass flow rate. The velocity in liquid film tends towards linear, when the liquid film is mainly in the laminar boundary layer

[en] Luminescence sensing is an attractive approach for in-situ monitoring the health and integrity of multilayered surface protective coatings on highly active metals. In this work, we demonstrate the potential of erbium (Er) doped aluminum nitride (AlN) films to be applied as luminescence sensing layer in the Al/AlN multilayered coating system. The AlN:Er films were prepared by radio-frequency magnetron sputtering from Al targets doped with varied concentrations (from 0.5 at.% to 2.5 at.%) of Er. The chemical composition, surface morphology, crystal structure, chemical state and optical properties of the deposited AlN:Er films were investigated. We found that the crystal structure, surface roughness and optical properties of the AlN:Er films have strong correlations with the Er doping level. The as-deposited AlN:Er films showed the characteristic photoluminescence emission lines of the trivalent Er ions in the visible frequency range and quenching was observed when the Er doping level increased to 2.5 at.%. This work signifies the viability of AlN:Er film as luminescence sensing layer and the optimal Er doping concentration of the Al sputtering target is 2.0 at.% for practical applications. - Highlights: • AlN:Er film for luminescence sensing of multilayer Al/AlN coating health is proposed. • The properties of the AlN:Er films have strong correlations with the Er doping level. • The as-deposited AlN:Er films showed strong visible photoluminescence emission. • The optimal Er doping level of the Al target is 2.0 at.% for luminescence sensing.

[en] Depleted uranium (DU) has many military and civilian uses. However, its high chemical reactivity limits its application. The effect of Nb content on corrosion behavior of DU is evaluated by scanning Kelvin probe and electrochemical corrosion measurements. The Volta potential value of DU and U-2.5 wt% Nb is about the same level, the Volta potential value of U-5.7 wt% Nb has a rise of 370mV_S_H_E in comparison with DU. The polarization current of U-5.7 wt% Nb alloy is about an order of magnitude of that of DU. The Nb_2O_5 is the protective layer for the U-Nb alloys. The negative potential of Nb-depleted α phase is the main reason of the poor corrosion resistance of DU and U-2.5 wt% Nb alloy. - Highlights: • New method (scanning Kelvin probe) was used to study the corrosion property. • Three types of corrosion morphologies were found after potentiodynamic polarization. • The effect of impurity elements on corrosion property was mentioned. • The corrosion mechanism of DU and U-Nb alloys was discussed.