F. Díaz

Experimental study on a self-adapting Darrieus—Savonius wind machine

Abstract In the present paper a study of the starting torque and power coefficient of the Darrieus and Savonius machines have been realized. The results obtained were used to design a Darrieus-Savonius combined machine which is also fully analysed. Finally, a new design of the Darrieus-Savonius combined rotor is proposed and analysed.

Statistical and spectral analysis of the wind regime in the area of Catalonia

SummaryThis work presents a statistical study of the wind power potential of three stations in the Catalonia area (Spain) over the 1973–1982 period. These stations correspond to three airports (Barcelona, Palma de Mallorca and Girona), which obviously do not present a high wind power potential and are not the suitable locations for wind power utilization, but which have been chosen for the long record of data stored (10 years). The aim of this work is to provide a model of wind potential in terms of the speed and wind direction, which may be applied to other sites. The wind speed has been modelled by a Weibull distribution function and the wind direction by a normal two-dimensional function. A spectral analysis of both variables has also been carried out. The present study provides an evaluation of the local wind power in the geographic area of Catalonia.

Image processing of Czochralski bulk flow

Abstract A new experimental way for analyzing velocity fields in thermo-hydrodynamic processes like those produced in Czochralski crystal growth is presented. The flow patterns obtained by means of tracer particles are digitalized and processed in order to evaluate the dynamic field.

Optical spectroscopy of Ho3+ and Tm3+ ions in KTiOPO4 single crystals

Abstract KTiOPO 4 single crystals doped with Ho 3+ or Tm 3+ ions have been grown by the top seeded solution growth (TSSG) slow cooling technique using a 49.8K 2 O:33.2P 2 O 5 :16.32TiO 2 :0.68RE 2 O 3 (RE=Ho, Tm) flux. The holmium and thulium concentrations obtained in the crystal are [Ho]=340 ppm and [Tm]=500 ppm, and the corresponding distribution coefficients K Ho =2.7×10 −3 and K Tm =5.1×10 −3 . Sharp optical absorption bands corresponding to Ho 3+ and Tm 3+ ions have been measured at 4.2 K. For both ions the optical absorption shows a dichroic character, generally being more intense when the polarization of the light is parallel to the c -axis of the crystal and weakest when the light is polarized parallel to the a -axis. Photoluminescence has been excited at room temperature in KTP:Tm crystals by using the 476 nm light of an Ar laser.

High-temperature solutions of the (0.4Na2O-0.6B2O3)-BaO-((6 − x)Fe2O3 + xCoSnO3) system. Physical properties

Abstract In this paper the thermal dependences of the viscosity, density and surface tension of several solutions of the (0.4Na 2 O-0.6B 2 O 3 )-BaO-((6−x)Fe 2 O 3 + xCoSnO 3 ) system containig four different degrees of substitution of Fe 3+ by Co 2+ + Sn 4+ have been determined experimentally. On the basis of all these sets of results, the solution compositions with the highest solvent contents have been proposed for the growth of BaFe 12−(x+y) Co x Sn y O 19 using a TSSG/slow cooling methodology.

Experimental study of the hydrodynamics in a model crystal growth crucible

In this paper, image processing techniques are applied to the meridional visualizations of the bulk flow generated under different boundary conditions in a model crystal growth crucible. The steady forced convective patterns obtained by means of tracer particles are digitized and processed in order to characterize its hydrodynamic behaviour. This characterization is carried out based on the analysis of the resulting meridional velocity, streamfunction and vorticity distributions. Some comparisons between the present results and other available data are also made.

High-temperature solutions of the (0.4Na2O - 0.6B2O3) - BaO - ((6−x)Fe2O3 + xCoSnO3) system. Crystallization regions of BaFe12-(x+y)CoxSnyO19

In this work, high-temperature solutions of the (0.4Na2O-0.6B2O3)-BaO -((6 − x)Fe2O3 + xCoSnO3) system have been investigated. The concentration and temperature regions for the crystallization of BaFe12 − (x + y)CoxSnyO19 for four different degrees of cobalt and tin substitution −Fe(Co + Sn) = 120, 111, 102 and 93- have been established. Using six compositions for each one of the above mentioned cases, hexaferrite single crystals have been grown by spontaneous nucleation. The volatility and the creeping of these twenty four solutions as well as the habit and distribution coefficients of Co2+ and Sn4+ of the single crystals obtained were also discussed. On the basis of these results, suitable solution compositions for the growth of Co2+ + Sn4+ substituted barium M-hexaferrites have been proposed.

Density, surface tension and viscosity of some high temperature solutions of the BaFe12O19Na2O pseudo-binary system

Abstract In this paper, the thermal dependences of the density, surface tension and viscosity for a number of solutions of the BaFe 12 O 19 Na 2 O pseudo-binary system have been experimentally established. The thermal and concentrational expansion coefficients as well as the thermal and concentrational surface tension coefficients have also been numerically evaluated. All these results will provide useful data in order to analyze both experimentally and numerically the most idoneous boundary conditions for the growth of barium ferrite single crystals by using the TSSG method.

Influence of dynamic boundary conditions on the computed flow patterns inside a coaxial rotating disk-cylinder system

Abstract In this paper, numerical solutions for the steady axisymmetric flow of an isothermal viscous fluid driven by moderate disk and/or cylinder coaxial rotation are presented. The influence of the two possible types of dynamic boundary conditions for the solid walls on the meridional flow features is discussed in detail using the computed Stokes streamfunction, angular momentum and vorticity distributions. Results show a clear dependence between the computed-generated flow patterns and the boundary conditions used.

Solvents for the growth of BaFe12-(x+y)CoxSnyO10 bulk crystals from high-temperature solution

In the present work, the system Na 2 O-B 2 O 3 -BaO-Fe 2 O 3 -CoSO 3 has been analysed in order to find appropriate solvents for the growth of BaFe 12-(x+y) Co x Sn y O 19 from high temperature solutions. The concentration and temperature regions of crystallization of this phase have been determined and the viscosity, density. volatility and climbing of some solutions have also been established. On the basis of the experimental results a new suitable solvent was chosen. The advantages of this solvent are discused