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[en] Heat transfer by natural convection and radiation in participating fluids enclosed in a square enclosure is numerically simulated. The continuity, momentum and energy equations are solved by the control volume method while the thermal radiative transfer is analyzed by the Monte Carlo simulation. In this study the WSGG (Weighted-Sum-of-Gray-Gases) model is incorporated for handling the complicated radiative properties of non-gray gas with temperature and wavelength dependency. All variables such as U, V, and T are solved each time the radiative heat flux is updated. Both the nongray gas analysis and the conventional gray gas assumption based analysis are carried out. As the result, the influences of thermal radiation on the flow and temperature field are found significant. In areas close to the insulated walls, unstable temperature stratification is observed. The mechanism for this distinct phenomenon is discussed. It is found that the non-gray gas solutions differ widely from the conventional gray gas results which overestimate the flow strength and underestimate the unstable temperature stratification. (author)
[en] Heat transfer by natural convection and radiation in participating fluids enclosed in a square enclosure is numerically simulated. The continuity, momentum and energy equations are solved by the control volume method while the radiative heat transfer is analyzed by the Monte Carlo simulation. The Monte Carlo simulation is linked with the SIMPLE algorithm for solving the Navier-Stokes equations, therefore all variables such as U, V, and T are solved each time the radiative heat flux is updated. As the result, the influences of thermal radiation on the flow and temperature fields are found significant. The radiative heat transfer is dominant. The convection is also strengthened. These features become clear with higher optical thickness. (author)
[en] The paper describes design techniques of the Model GZC γ camera data acquisition system. There are three parts description within this paper: 1) GZC γ camera acquisition system structures; 2) Acquisition and control flow chart; 3) Acquisition Monitor
[en] The goal of the paper is to study the optimal design problem for nonlinear diffraction gratings. The problem arises in the study of surface enhanced nonlinear optical effects of second harmonic generation. In order to apply certain gradient based optimization methods, an explicit formula for the partial derivatives of the Rayleigh coefficients with respect to the parameters of the grating profile is derived. Using the formula, numerical results are presented on an optimal design problem of nonlinear binary gratings
[en] The hexagonal ferrite Sr0.80La0.20FexZn0.15O19 (10.65≤x≤12.05) magnetic powder and magnets were synthesized by the ceramics process. The phase components of the hexagonal ferrite magnetic powder were studied using X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to investigate the morphology of the sintered magnets. The effects of the iron content on magnetic properties of the magnets were studied systematically. The remanence (Br) and maximum energy product [(BH)max] for the magnets at x=11.25 reached the maximum value of 414.5 mT and 32.24 kJ/m3, respectively. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) for the magnets at x=11.65 reached the maximum value of 265.8 kA/m and 257.8 kA/m, respectively. - Highlights: • Sr0.80La0.20FexZn0.15O19 hexaferrites were synthesized by the ceramics process. • The iron content greatly influences magnetic properties of the hexaferrites. • When x=11.25, higher Br and larger (BH)max were obtained. • Hcj and Hcb reached the maximum values at x=11.65
[en] The collective behavior of a two-dimensional wet granular cluster under horizontal swirling motions is investigated experimentally. Depending on the balance between the energy injection and dissipation, the cluster evolves into various nonequilibrium stationary states with strong internal structure fluctuations with time. Quantitative characterizations of the fluctuations with the bond orientational order parameter reveal power spectra of the form with the exponent α closely related to the stationary states of the system. In particular, type of noise with emerges as melting starts from the free surface of the cluster, suggesting the possibility of using noise as an indicator for phase transitions in systems driven far from thermodynamic equilibrium. (paper)
[en] In strong field above threshold ionization, we reproduce the “plateau structure” of the photoelectron spectra by using some important rescattering points. The corrected result is in good agreement with the semiclassical simulation which takes the full Coulomb influence into consideration. This indicates that the Coulomb influence in the rescattering process mainly functions in the area where the electron kicks the parent ion. A chaotic channel caused by the rescattering points appears when the initial transverse velocity of the electron can nearly counteract the drift velocity induced by the laser field. It is also found that the different order rescattering points play a different role in the formation of the chaotic channel and that the rescattering number is very important in determining the final energy of electron. Graphical abstract: .
[en] Highlights: • Heat removal capacity of the FW is evaluated under BWR, PWR and He coolant inlet conditions. • Heat transfer property of the gas–liquid two phase and the two boiling crises are analyzed. • Heat removal capacity of water is larger than helium coolant. - Abstract: The water cooled ceramic breeder blanket (WCCB) is being researched for Chinese Fusion Engineering Test Reactor (CFETR). As an important component of the blanket, the FW should satisfy with the thermal requirements in any case. In this paper, three parameters including the heat removal capacity, coolant pressure drop as well as the temperature rise of the FW were investigated under different coolant velocity and heat flux from the plasma. Using the same first wall structure, two main water cooled schemes including Boiling Water Reactor (BWR, 7 MPa pressure and 265 °C temperature inlet) and Pressurized Water Reactor (PWR, 15 MPa pressure and 285 °C temperature inlet) conditions are discussed in the thermal hydraulic calculation. For further research, the thermal hydraulic characteristics of using helium as coolant (8 MPa pressure, 300 °C temperature inlet) are also explored to provide CFETR blanket design with more useful data supports. Without regard to the outlet coolant condition requirements of the blanket, the results indicate that the ultimate heat flux that the FW can resist is 2.2 MW/m"2 at velocity of 5 m/s for BWR, 2.0 MW/m"2 at velocity of 5 m/s for PWR and 0.87 MW/m"2 for helium at velocity 100 m/s under the chosen operation condition. The detrimental departure from nucleate boiling (DNB) crisis would occur at the velocity of 1 m/s under the heat flux of 3 MW/m"2 and dry out crisis appears at the velocity of less than 0.2 m/s with the heat flux of more than 1 MW/m"2 for BWR. The further blanket/FW optimization design is provided with more useful data references according to the abundant calculation results.
[en] The structural stability of β-TiO with FCC NaCl structure was investigated via the first-principles method based on density functional theory. It found that the β-TiO with certain content vacancies was the most stable structure determined by calculation using GGA density functional with the continuously increasing vacancies. The electronic properties of β-TiO such as DOS, PDOS, bond population and charge density, were also calculated which demonstrated that Ti–Ti bond forms around O-vacancy due to the weaker O–Ti bond. The calculating results about thermodynamic and elastics properties are given and compared with the actual β-TiO. Based on the above calculation results, the relaxation structure of β-TiO with vacancies is found to be consistent with the actual structures having a disordered array of stoichiometric vacancies about 15% at both oxygen and titanium sites. All of these validate the advantages of our investigations with GGA method for predicting physical properties in β-TiO
[en] To fluidize wet granulates by vertical vibration, extra force is necessary to overcome the capillary force. We explore experimentally the fluidization of a granulate wetted by liquid Helium, because of its special liquid properties. By varying temperature around the γ point, we study how liquid Helium changes the dynamic properties of granulates. For superfluid wetting, the critical acceleration for fluidization increases almost linearly with film thickness. This indicates that superfluid starts to flow and forms liquid bridges. For wetting by normal fluid Helium, the critical acceleration shows a relatively steep increase close to saturation. Above saturation, both superfluid and normal fluid give rise to a plateau of the critical acceleration, because the capillary force depends only weakly on the volume of the bridge. The plateau value is found to vary with temperature and shows a peak around the γ point, which indicates the influence of the specific heat of liquid Helium