A novel approach of manufacturing Nickel Wicks for loop heat pipes using Metal Injection Moulding (MIM)

Sintered nickel powder is proposed to be used as porous wicks in loop heat pipes used for space applications such as satellites and space crafts. In this work, the manufacturing procedure for tubular wicks through novel Metal Injection Moulding (MIM) route is discussed. Nickel powder, Polypropylene powder and thermoplastic binder are used to produce feedstock for injection moulding. Ideal sintering condition identified as 900°C and 60 minutes. Porosity, pore diameter of the wicks are evaluated by geometric measurements using an electronic weight measuring machine and a micrometer and extrusion flow Porosimeter, respectively. Permeability was calculated according to the Carmen–Kozeny equation. Experimental finding shows that porosity level of 55 vol%, average pore diameter of 2.6 μm, permeability of 1.94 × 10^???12 m² and roundness of 5% have been achieved in the porous wick. SEM investigation of pore structures shows the presence of large pores which leads to enhanced porosity and interconnected fine pore network responsible for generation of required capillary pumping pressure.     

Dielectric response of PLZT ceramics <Emphasis Type="Italic">x</Emphasis>/57/43 across ferroelectric–paraelectric phase transition

The dielectric properties of lead lanthanum zirconate titanate (PLZT) ceramics [Pb(Zr_0·57Ti_0·43)O₃ + x at% of La, x = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz–1 MHz using the vector impedance spectroscopy (VIS) at different temperatures. All the compositions show both non-dispersive and dispersive dielectric responses in different temperature regions. The non-dispersive region obeys the universal dielectric response. A low frequency (<1 kHz) relaxation phenomenon with a high value of distribution parameter ‘h’ (~0·4 to 0·6) has been observed in all the compositions around the temperature corresponding to the maximum dielectric constant (T _m). The activation energies as calculated from the relaxation and d.c. conduction processes are comparable. The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content.     

Reaction of Dehydrated Surface of Partially Leached Glass with Water

Glasses containing sodium and potassium were leached with water and the alkali was extracted by a linear relation with square root of time. The leached surfaces were then dried by different techniques, heat-treated at various temperatures, and again attacked by water. For glasses containing Na₂O, the heat-treated preleached grains showed neither extraction behavior having a linear relation with time nor extraction by a square root-time relation. For glasses containing K₂O, the heat-treated preleached glass grains showed a linear relation of extraction. The results were explained by a structural transformation for the sodium glasses, in which an S-shaped sodium ion distribution at the surface layer was greatly affected by the heat treatment. For the potassium glasses no such transformation could occur since the alkali ion distribution was exponential and unaffected by temperature.     

Effect of MoO3 Addition on the Grain Growth Kinetics of a Manganese Zinc Ferrite

The effect of MoO₃ addition on the grain growth and densification kinetics of a high permeability manganese zinc ferrite was studied. Grain growth in the presence of a small amount of MoO₃ occurs in two main stages characterized by a faster rate of grain growth accompanied by rapid densification and pore coalescence in the first stage, when the MoO₃ is present as a liquid phase along the grain boundaries, and comparatively slower rates of grain growth and densification than those for the basic composition in the second stage, when MoO₃ evaporates from the matrix. The activation energies for grain growth in these stages suggested that surface and volume diffusion mechanisms were operating in the first and second stages respectively.     

A new look at the effect of bandwidth and non-normality on fatigue damage

A new attempt is made in this paper to quantify the effect of bandwidth and non‐normality in fatigue damage analysis. For the lack of actual stress history, a series of non‐Gaussian and homogeneous random processes are generated with fast Fourier transform (FFT) acceleration. A factor is defined on the basis of rain‐flow counting and Palmgren–Miner rule to correct the narrow band and normality assumption. It is revealed that the fatigue damage evaluated through the traditional method may be either conservative or rather unconservative. The upper and lower bounds of the correction factor are studied with respect to kurtosis and skewness of the generated random process and the slope of S–N curve.     

Morphological and optical properties of n-type porous silicon: effect of etching current density

Morphological and optical properties of porous silicon (PS) layer fabricated on n-type silicon wafer have been reported in the present article. Method of PS fabrication is by photo-assisted electrochemical etching with different etching current densities (J). Porosity and PS layer thickness, obtained by the gravimetric method, increase with increasing J. Pore morphology observed by FESEM shows the presence of randomly distributed pores with mostly spherical shape. Calculated pore size is also seen to increase with increasing value of J. XRD gives the characteristic amorphous peak of PS along with some peaks corresponding to crystalline silicon (c-Si). Calculated crystallite size shows decreasing trend with increasing J value. The optical properties of these samples have been investigated by UV–visible reflectance, Raman spectroscopy and photoluminescence (PL) spectra. Reflectance measurement shows blue-shift of the spectrum with increased reflectivity for increasing J. Raman spectra show remarkable blue-shift with respect to the c-Si peak. PL spectra give the luminescence energy in the orange–red region of the visible spectrum and little change with variation of J.     

Fabrication of macroscopic solid models of three-dimensional microscopic data by selective laser sintering

We discuss and give examples of the use of selective laser sintering to fabricate solid macroscopic models of microscopic specimens that have been imaged with a confocal microscope. The digital image processing necessary to create structurally sound models of both translucent and opaque specimens is presented. The fabricated models offer the ultimate in data visualization since they can be physically handled and manipulated to investigate the shape and features of the specimen. Such a powerful visualization tool is useful in both research and educational environments.     

Circulation characteristics of horseshoe vortex in scour region around circular piers

This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter (ADV). Velocity vector plots and vorticity contours of the flow field on the upstream plane of symmetry (y = 0 cm) and on the planes ±3 cm away from the plane of symmetry (y = ±3 cm) are presented. The vorticity and circulation of the horseshoe vortices were determined using the forward difference technique and Stokes theorem, respectively. The results show that the magnitudes of circulations are similar on the planes y = 3 cm and y = -3 cm, which are less than those on the plane y = 0 cm. The circulation decreases with the increase of flow shallowness, and increases with the densimetric Froude number. It also increases with the pier Reynolds number at a constant densimetric Froude number, or at a constant flow shallowness. The relative vortex strength (dimensionless circulation) decreases with the increase of the pier Reynolds number. Some empirical equations are proposed based on the results. The predicted circulation values with these equations match the measured data, which indicates that these equations can be used to estimate the circulation in future studies.     

The use of field programmable gate array （FPGA） in direct torque control of induction motor

In this paper, the feasibility of embedding the direct torque control （DTC） of an induction machine into field programmable gate arrays （FPGA） is investigated. DTC of an induction machine is simulated in a MATLAB/Simulink environment using a Xilinx system generator. The resulting design has a flexible and modular structure where the designer can customize the hardware blocks by changing the number of inputs, outputs, and algorithm when it is compared to the designs implemented using classical microcontrollers and digital signal processors. With its flexibility, other control algorithms can easily be programmed and embedded into the FPGA. The above system has been implemented on Xilinx Spartan 3A DSP FPGA controller. Simulation and experimentation have been performed to prove the validity of the proposed methodology.     

Soft chemistry based sponge-like indium tin oxide (ITO) ---- a prospective component of photoanode for solar cell application

Previously we reported the synthesis of novel organic-inorganic composite indium tin oxide (ITO) foam precursor leading to the formation of “sponge-like” ITO by burning away the organics. This newly made sponge-like ITO possesses relatively high electrical conductivity due to phonon confinement with reasonable pore structure and may have potential application as functional materials in semiconducting dye absorbing layer in dye-sensitized solar cell (DSSC) and also as the receptor of electrons injected from the quantum dots (QDs) of organic--inorganic hybrid QD based solar cell. This report is a short review of “sponge-like” ITO described as a lecture note on its future use as an alternative new prospective material for photoanode of solar cell in the domain of sustainable energy.