Natural convection heat transfer of high temperature gas in an annulus between two vertical concentric cylinders

Water cooling panels have been adopted as the vessel cooling system of the High Temperature Engineering Test Reactor (HTTR) to cool the reactor core indirectly by natural convection and thermal radiation. In order to investigate the heat transfer characteristics of high temperature gas in a vertical annular space between the reactor pressure vessel and cooling panels of the HTTR, we carried out experiments and numerical analyses on natural convection heat transfer coupled with thermal radiation heat transfer in an annulus between two vertical concentric cylinders with the inner cylinder heated and the outer cylinder cooled. In the present experiments, Rayleigh number based on the height of the annulus ranged from 2.0 × 10⁷ to 5.4 × 10⁷ for helium gas and from 1.2 × 10⁹ to 3.5 × 10⁹ for nitrogen gas. The numerical results were in good agreement with the experimental ones regarding the surface temperatures of the heating and cooling walls. As a result of the experiments and the numerical analyses, the heat transfer coefficient of natural convection coupled with thermal radiation was obtained as functions of Rayleigh number, radius ratio, and the temperatures and emissivities of the heating and cooling wall surfaces. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 293–308, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20070     

Green Fabrication of Porous Ceramics Using an Aqueous Electrophoretic Deposition Process

We prepared porous ceramic depositions using gas generation in an aqueous electrophoretic deposition (EPD) process. Especially, this aqueous EPD process in combination with a sintering step could advantageously result in unique porous deposition containing many unidirectionally aligned continuous pores. The aqueous EPD process has environmental and cost reduction advantages.     

Drainage phenomenon of pastes during extrusion

The effects of elemental powder characteristics, binder content and its composition, as well as some additives on pressure change and drainage phenomenon of pastes during extrusion have been mainly investigated. The pastes consisted of a powder, zirconia or stainless steel, and a water-based binder, an aqueous solution of water-soluble polymer (hydroxypropyl methylcellulose). The drainage phenomenon has been found in extrusion of the stainless steel pastes with lower binder contents, while the zirconia pastes show a small probability of drainage in the range of the binder contents used in this investigation. It is shown that broadening particle size distribution by mixing powders with different average particle sizes has a significant effect on decreasing extrusion pressure and restraining occurrence of the drainage phenomenon, thus improving the extrudability of pastes. It is effective to increase the binder content in pastes, raise the mixing fraction of HPMC in binder and add plasticizer like glycerol, in order to reduce occurrence of the drainage phenomenon during extrusion of the stainless steel pastes.     

Suppression of carbon buildup and lifetime improvement by heating carbon stripper foils

We have successfully developed a new method to reduce the amount of carbon buildup on thin cluster (less than 3.5 μg/cm²) carbon stripper foils by heating them with infrared radiation during beam bombardment. We studied the carbon buildup and the foil temperature on foil lifetime using a 2.0 ± 0.5 μA beam of 3.2-MeV Ne⁺ ions. It was found that the carbon buildup begins to rapidly suppress at 460 °C; further, at a foil temperature higher than approximately 820 °C, the initial foil thickness did not change until the foil ruptured. We also found that the carbon buildup shortens the lifetime of stripper foils.The foils treated by the newly developed present method could withstand the maximum and average total beam charges of 530 mC/cm² and 340 mC/cm², respectively, which are approximately 18 and 11 times larger than the values for the best commercially available foils and approximately 3 and 2 times greater than the values for the cluster foils that are not treated by this method.     

Genetic correlations between the cumulative pseudo-survival rate,milk yield,and somatic cell score during lactation in Holstein cattle in Japan using a random regression model

Trends in genetic correlations between longevity, milk yield, and somatic cell score (SCS) during lactation in cows are difficult to trace. In this study, changes in the genetic correlations between milk yield, SCS, and cumulative pseudo-survival rate (PSR) during lactation were examined, and the effect of milk yield and SCS information on the reliability of estimated breeding value (EBV) of PSR were determined. Test day milk yield, SCS, and PSR records were obtained for Holstein cows in Japan from 2004 to 2013. A random subset of the data was used for the analysis (825 herds, 205,383 cows). This data set was randomly divided into 5 subsets (162–168 herds, 83,389–95,854 cows), and genetic parameters were estimated in each subset independently. Data were analyzed using multiple-trait random regression animal models including either the residual effect for the whole lactation period (H0), the residual effects for 5 lactation stages (H5), or both of these residual effects (HD). Milk yield heritability increased until 310 to 351 d in milk (DIM) and SCS heritability increased until 330 to 344 DIM. Heritability estimates for PSR increased with DIM from 0.00 to 0.05. The genetic correlation between milk yield and SCS increased negatively to under ?0.60 at 455 DIM. The genetic correlation between milk yield and PSR increased until 342 to 355 DIM (0.53–0.57). The genetic correlation between the SCS and PSR was ?0.82 to ?0.83 at around 180 DIM, and decreased to ?0.65 to ?0.71 at 455 DIM. The reliability of EBV of PSR for sires with 30 or more recorded daughters was 0.17 to 0.45 when the effects of correlated traits were ignored. The maximum reliability of EBV was observed at 257 (H0) or 322 (HD) DIM. When the correlations of PSR with milk yield and SCS were considered, the reliabilities of PSR estimates increased to 0.31–0.76. The genetic parameter estimates of H5 were the same as those for HD. The rank correlation coefficients of the EBV of PSR between H0 and H5 or HD were greater than 0.9. Additionally, the reliabilities of EBV of PSR of H0 were similar to those for H5 and HD. Therefore, the genetic parameter estimates in H0 were not substantially different from those in H5 and HD. When milk yield and SCS, which were genetically correlated with PSR, were used, the reliability of PSR increased. Estimates of the genetic correlations between PSR and milk yield and between PSR and SCS are useful for management and breeding decisions to extend the herd life of cows.     

Stress-strain behavior of multi-walled carbon nanotube/PEEK composites

This study examined the effects of multi-walled carbon nanotube (CNT) dispersion on stress-strain behaviors of poly-ether-ether-ketone (PEEK) at room temperature. Tensile test specimens containing 9 wt.% and 15 wt.% of CNT were fabricated using injection molding. Results of focused ion beam (FIB) observations show that many CNTs in the CNT/PEEK composite are aligned longitudinally. Although the PEEK stress-strain behavior is almost linear up to 1.5% strain, the stress-strain curves of CNT/PEEK composites exhibit considerable nonlinear and hysteretic behaviors from extremely low strain (<0.1%) under both tensile and compressive loading. The experimental results suggest that the viscoelastic deformation effects on nonlinear and hysteresis behaviors are not strong below 1.5% strain. Presumably, the slippage at the CNT-PEEK interface occurs with increasing applied stress because of poor interfacial load-transfer capability.     

Strength of a Hi-Nicalon™/Silicon-Carbide-Matrix Composite Fabricated by the Multiple Polymer Infiltration-Pyrolysis Process

A woven-fabric Hi-Nicalon™-fiber reinforced SiC-matrix composite has been fabricated by using a multiple polymer infiltration-pyrolysis (PIP) process. The three-point bend strength, at room temperature, of the composite is examined as a function of total porosity of the composite. The porosity of the composite decreases as the number of PIP cycles ( N ) increases. Both the proportional-limit load and the maximum load in the three-point bend test increase as N increases. A compressive fracture mode is observed for N < 10 (total porosity of >10%), and a tensile fracture mode is observed for N greaterthan equal to 10 (total porosity of lessthan equal to10%). For the composite with N = 14, with a total porosity of 8 vol%, a proportional-limit stress of 410 MPa and a maximum stress of 600 MPa are achieved.     

Development of Stress-Induced Martensitic Transformation in TiNi Shape Memory Alloy

TiNi shape memory alloy (SMA) was subjected to tension at strain-controlled test on quasistatic testing machine. The nucleation, development, and saturation of the stress-induced martensitic transformation were investigated, taking into account the obtained dependency of mechanical parameters and the specimen temperature changes measured by an infrared camera (IR). Three kinds of data obtained by the IR system were analyzed: the temperature distribution on the SMA sample surface, the temperature changes derived as average from the chosen sample area, and the temperature profiles obtained along the sample length. The temperature distribution shows nucleation of the transformation process and a creation of the transformation bands. The average temperature reflects the effects of thermomechanical coupling, accompanying exothermic martensitic forward and endothermic reverse transformation. The temperature profiles revealed the temperature difference between the band and the rest of the sample. The experimental results were supported with finite element method numerical analysis (FEM). The FEM software components for structural and heat transfer problems, coupled in partitioned approach, were used for thermomechanical analysis.