Exergy-entropy process of passive solar heating and global environmental systems

The mechanism of a passive solar heating system and its relation to the mechanism of the global environmental system are discussed using the concepts of entropy and exergy. The reason that we use both of these concepts is to make it clearer how the systems work and hence why the passive solar heating system is called environmentally friendly. The mechanism of the systems is described as a process in which exergy is supplied, its portion consumed, and the resultant generated entropy is finally given off. We call this process “exergy-entropy process”. A numerical example of the exergy-entropy process of the passive solar heating system and the global environmental system revealed the following. Generated entropy within the passive solar heated room is discarded into the outdoor environment through glass windows and concrete floors. The global environmental system has a mechanism that disposes of all the generated entropy resulting from the solar exergy consumption on the Earth's surface into the universe. Passive solar heating systems therefore fit inside the global environmental system, on which they impose almost no burden.     

Effects of starting carbon and solvent-catalyst on the reaction sintering of diamond

Polycrystalline diamond sintered compact was prepared under high pressure and temperature conditions (7 GPa, 1700° C, 10 to 15 min) from purified natural graphite (NG) or graphitized pitch coke (GPC) using iron, cobalt or nickel as the catalytic active metal and titanium or zirconium as the solvent metal. The effects of the combinations of starting carbon and solvent-catalyst on the transformation behaviour and morphology of the converted diamond were investigated in relation to the starting powder compositions. Diamond crystals converted from NG tended to have euhedral habits, when twin crystals were occasionally found due to a relatively rapid conversion and growth rate of diamond. On the other hand, a skeletal structure of diamond was easily formed by a mild conversion from GPC in the 15 to 30 vol% ( 40 to 60 wt%) nickel solvent-catalyst. The degree of catalytic action in the 8A group of 3d transition metals for the GPC system was in the order: Ni Co > Fe. The grain growth of the converted diamond was depressed by the addition of 4A transition metals (titanium or zirconium) which results in the fine-grained and homogeneous sintered microstructure.     

An Energy-Efficient Model of Random Cognitive Radio Network: Rayleigh-Lognormal Environment

Wireless Personal Communications - Motivated by the current demand for improvements in transmission rate and energy efficiency of random wireless cellular networks, we investigate the theoretical...     

Synthesis of surfactants from 1-olefins wo bromoalkoxylation reaction

Alkyl β-bromoalkyl ether derivatives (I) (isomeric mixture) were prepared by the bromoalkoxylation reaction of olefins withN-bromosuccinimide (NBS) and appropriate alcohols. A series of nonionic surfactants was obtained by the reaction of I with glycols or ethanolamines. The distribution of two isomers (Markovnikov-type and anti-Markovnikov-type) in products was found to be slightly different from that in the starting material (I). Surface properties of several nonionic surfactants, which were prepared from I, were presented and discussed based on the difference in the structures.     

Effect of Neutron Irradiation on Knoop Microhardness Anisotropy in MgO·3Al2O3 Single Crystals

MgO·3Al₂O₃ single crystals were irradiated with neutron fluences of 8.3 × 10²² n/m² at 100°C and 2.4 × 10²⁴ n/m² at 470°C ( E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness profile of the crystals was almost the same after the two irradiation conditions. The hardness increased by 4–15% because of the irradiations depending on the crystallographic orientation, the larger change being observed at orientations between the (001) and (011) directions. While both the {111}     and {110}     slip systems are simultaneously active in the unirradiated MgO·3Al₂O₃, the {111}     system may be the dominant slip system in the neutron-irradiated crystals. It is concluded that the restriction of the {110}     slip system is caused by irradiation-induced interstitial ions.     

Direct Formation and Photocatalytic Performance of Anatase (TiO2)/Silica (SiO2) Composite Nanoparticles

Anatase (TiO₂)/silica (SiO₂: 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO₄) and sodium metasilicate (Na₂SiO₃) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO₄ and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as-prepared TiO₂/SiO₂ composite nanoparticles showed far more improved photocatalytic activity than the pure anatase-type TiO₂. The composite nanoparticles formed from (i) TiOSO₄ and Na₂SiO₃ as well as those from (ii) TiOSO₄ and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.     

In situ conversion electron Mössbauer spectrometry (CEMS) studies on α- and γ-Fe2O3 gas sensors

Clarification of the sensing mechanism of-Fe₂O₃ and -Fe₂O₃ gas sensors was attempted. The information on the surface states of iron oxides at working temperature (400° C for-Fe₂O₃ and 250° C for-Fe₂O₃) was obtainedin situ by applying thein situ CEMS. The-Fe₂O₃ gas sensor, prepared by the precipitation of Fe(OH)₃ from a solution of iron (III) sulphate and tin (IV) chloride, was composed of fine particles (–15 nm) and was superior in sensitivity to other-Fe₂O₃. The gas sensitivity was found to depend on the amounts of remaining sulphate ion, the microstructure and a small amount of iron (II) species generated through the reduction of-Fe₂O₃. The sensing mechanism of-Fe₂O₃ gas sensor was confirmed to be due to the reduction of-Fe₂O₃ to the low resistive Fe_3-x O₄ by combustible gas and to depend on the crystal structure.     

Detailed analyses of key phenomena in core disruptive accidents of sodium-cooled fast reactors by the COMPASS code

A five-year research project has been initiated in 2005 to develop a code based on the MPS (Moving Particle Semi-implicit) method for detailed analysis of key phenomena in core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). The code is named COMPASS (Computer Code with Moving Particle Semi-implicit for Reactor Safety Analysis). The key phenomena include (1) fuel pin failure and disruption, (2) molten pool boiling, (3) melt freezing and blockage formation, (4) duct wall failure, (5) low-energy disruptive core motion, (6) debris-bed coolability, and (7) metal–fuel pin failure. Validation study of COMPASS is progressing for these key phenomena. In this paper, recent COMPASS results of detailed analyses for the several key phenomena are summarized. Simulations of GEYSER and THEFIS experiments were performed for dispersion and freezing behaviors of molten materials in narrow flow channels. In particular, the latter experiment using melt–solid mixture is also related to fundamental behavior of low energy disruptive core. CABRI-TPA2 experiment was simulated for boiling behavior of molten core pool. Expected mechanism of heat transfer between molten fuel and steel mixture was reproduced by the simulation. Analyses of structural dynamics using elastoplastic mechanics and fracture criteria were performed for SCARABEE BE+3 and CABRI E7 experiments. These two analyses are especially focused on thermal and mechanical failure of steel duct wall and fuel pin, respectively. The present results demonstrate COMPASS will be useful to understand and clarify the key phenomena of CDAs in SFRs in details.     

Bubble behavior and heat transfer during pool boiling of binary mixtures

Heat transfer coefficients were measured during pool boiling of binary mixtures on a heated wire hung horizontally and bubble behavior was simultaneously captured with a high‐speed video camera. The experiment was carried out at a pressure of 0.4 and 0.7 MPa for the whole range of mass fractions in a binary mixture of R22/R11. We clarified the change in bubble behavior and heat transfer by measuring the bubble departure diameter, frequency and growth rate on the basis of the video images. Furthermore, we discussed the relationship between the bubble behavior and the boiling heat transfer coefficient in the binary mixtures. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 449–459, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20087     

CFD analysis of heat transfer in subchannels of a Super Fast Reactor

This paper presents CFD analyses of heat transfer in subchannels of a Super Fast Reactor fuel assembly. Analyses are concentrated on the circumferential temperature distribution on the cladding outer surface because the Maximum Cladding Surface Temperature (MCST) has been a crucial design parameter to evaluate fuel cladding integrity of the Super Fast Reactor. Speziale non-linear high Re k-? model, which can reproduce the anisotropic turbulence flow in non-circular flow channels, with two-layer near-wall treatment is adopted. The results show that heat conduction in the cladding should be considered in the CFD analyses. Larger circumferential temperature gradient occurs on the cladding surface in the edge and corner subchannels than that in the ordinary subchannel because of their special geometries causing larger heterogeneity of mass flow rate distribution inside the subchannels. Improved subchannel configurations to reduce the circumferential temperature gradient are proposed. This study will be a good guideline to the future core design improvement.