Transient analysis of hybrid rocket combustion by the zeldovich-novozhilov method

Hybrid rocket combustion has a manifestation of stable response to the perturbations compared to solid propellant combustion. Recently, it has revealed that the low frequency combustion instability about 10 Hz was occurred mainly due to thermal inertia of solid fuel. In this paper. the combustion response function was theoretically derived by use of ZN (Zeldovich-Novozhilov) method. The result with HTPB/LOX combination showed a quite good agreement in response function with previous works and could predict the low frequency oscillations with a peak around 10 Hz which was observed experimentally. Also, it was found that the amplification region in the frequency domain is independent of the regression rate exponentn but showed the dependence of activation energy. Moreover, the response function has shown that the hybrid combustion system was stable due to negative heat release of solid fuel for vaporization, even though the addition of energetic ingredients such as AP and Al could lead to increase heat release at the fuel surface.     

Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo₅SiB₂ and Mo₃Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.     

Development of the zone method for inhomogeneous non-isothermal participating plane layer media

The purpose of this paper is to present the first step in developing the zone method for inhomogeneous media that has never been published in the literature. It was derived and formulated using matrix relations for a plane layer system enclosing a non-isothermal and inhomogeneous gray and absorbing, emitting and isotropically scattering media. The media are enclosed by two infinite parallel plates that are opaque, diffuse, and gray, but the formulations allow transparent plate. The formulations recover homogeneous cases and satisfy the conservation relations. The accuracy of the zone method is verified by comparing with available exact solutions. Through the accuracy check, validity of the zone method is also shown. Thus, formulations presented can be used to test the accuracy of the works by others for the problem in the study that has many applications in engineering and science.

     

An unconventional route to high-efficiency dye-sensitized solar cells via embedding graphitic thin films into TiO2 nanoparticle photoanode

Graphitic thin films embedded with highly dispersed titanium dioxide (TiO(2)) nanoparticles were incorporated for the first time into the conventional dye-sensitized solar cells (DSSCs), resulting in a remarkably improved cell efficiency due to its superior electron conductivity. Massively ordered arrays of TiO(2) dots embedded in carbon matrix were fabricated via UV-stabilization of polystyrene-block-poly(4-vinylpyridine) films containing TiO(2) precursors followed by direct carbonization. For dye-sensitized TiO(2) based solar cells containing carbon/TiO(2) thin layers at both sides of pristine TiO(2) layer, an increase of 62.3% [corrected] in overall power conversion efficiency was achieved compared with neat TiO(2)-based DSSCs. Such a remarkably improved cell efficiency was ascribed to the superior electron conductivity and extended electron lifetime elucidated by cyclic voltammetry and impedance spectroscopy.     

Evaluation of the Fracture Strength for Silicon Carbide Layers in the Tri-Isotropic-Coated Fuel Particle

A program to develop new methods to measure the fracture strength of the chemical vapor deposition SiC coatings in nuclear fuel particles has been carried out. Internal pressurization and crush test techniques were developed and applied to prototype-sized tubular and hemispherical shell specimens. The fracture strength measured from each test method applying the Weibull two-parameter distribution, and Weibull parameters were measured. It was shown that data generated with each test technique were independent of the test technique applied. This implies that the developed test methods are reliable and provide reasonable strength data. For the same material, fracture strength varied with the specimen geometry and loading configuration. These size and loading configuration effects on the fracture strength are explained with the concept of effective surface.