Forced Convective Heat Transfer Experiment of Supercritical Water in Different Diameter of Tubes

Forced convective experiment of supercritical water was performed in Inconel-625 tubes of 4.62 mm, 7.98 mm and 10.89 mm in diameter. The water flowed upward, covering the ranges of pressure of 23.4 MPa to 25.8 MPa, mass flux of 90 kg/m^2s to 3,281 kg/m^2s, local bulk temperature of 102-384 ℃, inner wall temperature of 167-669℃ and heat flux of up to 2.41 MW/m^2. The results exhibited severe deteriorated and enhancement heat transfer. The experimental results can be calculated by the Jackson＇s correlation and the Bishop＇s correlation mostly. But some data with strong effects of the buoyancy force and the variations of flow regimes can not be predicted properly.

A General Thermal Equilibrium Discharge Flow Model

Based on isentropic flow and thermal equilibrium assumptions, a model was derived to calculate discharge flow rate, which unified the rules of room temperature water discharge, high temperature and high pressure water discharge, two-phase critical flow, saturated steam and superheated steam critical flow, and gave a method to calculate critical condition. Because of the influence of friction, the entropy is increased in the actual discharge process, and the discharge flow rate in thermal equilibrium condition can be obtained by the original model multiplied by an appropriate correction coefficient. The model calculated results agreed well with the experiment data of long nozzle critical flow.

Critical Heat Flux with Subcooled Flowing Water in Tubes for Pressures from Atmosphere to Near-Critical Point

During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.

Microstructure characteristics of 12Cr ferritic/martensitic steels with various yttrium

12Cr ferritic/martensitic steels with 0, 0.1 wt%, 0.2 wt% and 0.3 wt% theoretical yttrium(Y) additions were fabricated by vacuum inducting melting and casting method. Solubilities of Y in the 12Cr steels are0.027, 0.078 and 0.17 for 12Cr-0.1 Y, 12Cr-0.2 Y and 12Cr-0.3 Y, respectively. Phase transformations and microstructure characteristics under different heat-treatment schedules were investigated. The starting temperature of ferrite-to-austenite transformation A^(c1) are maintained about 850℃, but the finishing temperature of ferrite-to-austenite transformation A^(c3) are about 950, 970, 980 and 1000℃ for 12Cr-0 Y,12Cr-0.1 Y, 12Cr-0.2 Y and 12Cr-0.3 Y, respectively, which indicates that A^(c3) increases gradually with the addition of Y. Martensite accompanied with a few δ-ferrite is the dominant structure in all the steels. The amount of δ-ferrite shows a strong dependence with the Y content and austenitizing temperature. Area fraction of δ-ferrite increases with the content of Y, which is the ferrite favouring element. The minimum amount of δ-ferrite are achieved at 950℃ for 12Cr-0 Y, 12Cr-0.1 Y, 12Cr-0.2 Y and 1000℃ for 12Cr-0.3 Y.Besides, more carbides precipitate along the martensite laths and grain boundaries in the Y-bearing steel due to the redistribution of carbon between austenite and ferrite resulting from the ferrite favouring element of Y.

Effects of Nb Addition on Charpy Impact Properties of TiVTa Refractory High‑Entropy Alloy

In the present study,the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy impact testing machine.The experimental results showed that the impact toughness was remarkably improved by Nb addition in TiVTa to form TiVTaNb alloy.The crack initiation energy and propagation energy of TiVTaNb were 67.3%and 24.9%higher than that of TiVTa,indicating that Nb addition simultaneously reinforced the resistance to crack initiation and propagation.The impact fracture of TiVTaNb exhibited larger bending degree of shear lips,deeper dimples and more secondary cracks which effectively dissipated more impact energy.The deformation mechanism of TiVTa alloy was dominated by dislocation activities.While in TiVTaNb,the deformation mechanism was synergized by dislocation activities and deformation twinning,which were the main contributors for the improved impact properties and the stronger crack resistance of TiVTaNb alloy under impact loading.

Morphology,microstructure and tribological properties of anodic films formed on Ti10V2Fe3Al alloy in different electrolytes

This study investigated the morphology, structure and tribological properties of the three samples produced by anodic oxidation of Ti10 V2 Fe3 Al in a sulfuric/phosphoric acid electrolyte(SPA), a near-neutral sodium tartrate electrolyte without nanoparticles(STA) and a nearneutral sodium tartrate electrolyte with polytetrafluoroethylene(PTFE) nanoparticles(CA) in suspension. The STA film had a surface full of bulges and cracks, the SPA film was porous, and the CA film was nanoporous. The SPA film was mainly composed of anatase TiO2, whereas the STA and CA films were mainly amorphous TiO2 with little anatase. The tribological tests indicated that the SPA sample had a lower wear resistance than the titanium alloy substrate, which was attributed to the shedding of abrasive debris, leading to rapid wear. Both STA and CA samples exhibited much lower wear rates than the titanium alloy substrate, and CA sample displayed the lowest wear rate attributed to the formation of a lubricating layer by PTFE nanoparticles. The wear mechanisms are proposed.

Porous SiC/melamine-derived carbon foam frameworks with excellent electromagnetic wave absorbing capacity

Porous three-dimensional Si C/melamine-derived carbon foam(3 D-Si C/MDCF)composite with an original open pore structure was fabricated by the heat treatment of the commercial melamine foam(MF),carbonization of the stable MF,and chemical vapor deposition of the ultra-thin Si C coating.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)were employed to detect the microstructure and morphology of the as-prepared composites.The results indicated that the 3 D-Si C/MDCF composites with the coating structure were prepared successfully.The obtained minimum reflection loss was–29.50 d B when the frequency and absorption thickness were 11.36 GHz and 1.75 mm,respectively.Further,a novel strategy was put forward to state that the best microwave absorption property with a thin thickness of 1.65 mm was gained,where the minimum reflection loss was–24.51 d B and the frequency bandwidth was 3.08 GHz.The excellent electromagnetic wave absorption ability resulted from the specific cladding structure,which could change the raw dielectric property to acquire excellent impedance matching.This present work had a certain extend reference meaning for the potential applications of the lightweight wave absorption materials with target functionalities.