Modifications to COBRA-TF to model dispersed flow film boiling with two flow,four field Eulerian–Eulerian approach – Part 2

In the first part of the paper, the modifications performed to improve the dispersed flow film boiling model in COBRA-TF have been described. The improvements were achieved by adding a small droplet field to the code’s solution scheme. The conservation equations, the source terms for the equations and the models developed were summarized. In this paper, the effects of spacer grids on the dispersed flow heat transfer and COBRA-TF modifications for the spacer grid models are presented. The results of the code predictions are presented by comparing the experimental data from Rod Bundle Heat Transfer experiments with the results of code simulations performed with original and modified code. Measurements and calculations for the spacer grid temperature have been compared. The results of the analysis performed with the modified code indicate the improvement in code predictions for the spacer grid temperature.     

Micro thermoelectric cooler: Planar multistage

A suspended, planar multistage micro thermoelectric (TE) cooler is designed using thermal network model to cool MEMS devices. Though the planar (two-dimensional) design is compatible with MEMS fabrication, its cooling performance is reduced compared to that of a pyramid (three-dimensional) design, due to a mechanically indispensable thin dielectric substrate (SiO₂) and technical limit on TE film thickness. We optimize the planar, six-stage TE cooler for maximum cooling, and predict ΔT_max = 51 K with power consumption of 68 mW using undoped, patterned 4–10 μm thick co-evaporated Bi₂Te₃ and Sb₂Te₃ films. Improvement steps of the planar design for achieving cooling performance of the ideal pyramid design are discussed. The predicted performance of a fabricated prototype is compared with experimental results with good agreements.     

Monolithically-integrated BiVO4/p+-n GaAs1-xPx tandem photoanodes capable of unassisted solar water splitting

Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs_1-xP_x (x ? 0.32) grown on n⁺-GaAs wafers. A p⁺-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs_0.68P_0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p⁺-GaAs_0.68P_0.32 surface layer. Transparent, conducting SnO₂:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO₄ photocatalyst layer. In some photoanodes, a WO₃ thin film was interposed between the SnO₂:F and BiVO₄. All oxide coatings were produced by ultrasonic spray pyrolysis except WO₃, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO₄ surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices.     

Reductive alkylation of illinois No. 6 coal. 1H and 13C n.m.r. spectra of the 13C-enriched alkylation products

The reductive alkylation of Illinois No. 6 coal has been carried out using potassium and naphthalene in tetrahydrofuran and methyl-¹³C and butyl-1 -¹³C iodides to alkylate the resultant polyanion. The soluble products of the reductive alkylation reaction were isolated by extraction and chromatography. Proton and carbon n.m.r. spectra were recorded. The intense resonance signal at δ3.95 which appears in the proton n.m.r. spectra of Illinois No. 6 coal butylated with unenriched butyl iodide is split into a doublet by the ¹³C nuclei. Similar results were obtained for the methylation products. The chemical shift and coupling interaction establish that aryl ethers are a very important constituent of the alkylated coal. The carbon n.m.r. spectra of the coal alkylated with ¹³C-enriched alkyl iodides are intense. The resonances of the C-alkylation products appear in a single broad band with a maximum intensity in spectral regions compatible with the formation of the reductive alkylation products of certain polynuclear aromatic hydrocarbons or the base-catalysed alkylation of certain benzylic carbon atoms. The resonances of the N -alkylation products appear in two distinct bands. These resonances are tentatively assigned to amines produced as a result of reductive alkylation of heterocyclic compounds. The resonances of the 0-alkylation products appear in three distinct bands which can be assigned to alkyl aryl ethers, alkyl aryl ethers with substituents at the adjacent positions, and to alkyl carboxylates. The ratio of ethers to carboxylates in the soluble alkylation products was determined to be 7.8 for butylation and 8.0 for methylation. The Chromatographic fractions contain different amounts of C-, N-, and 0-alkylation products. This finding suggests that the coal structure is not highly uniform.     

The effect of surface embrittlement on the mechanical behavior of rubber-modified polymers

An experimental study was conducted to better understand the mechanism of surface embrittlement in rubber-modified thermoplastics. Brittle polymer films were laminated onto acryionitnie-Duraaiene-styrene terpolymer and high-impact polystyrene to simulate either embrittlement due to environmental degradation or brittle paint systems. The effect of varying coating thickness and molecular weight was studied in tensile and impact testing. Results of this study suggest that the multiple crazing mechanism normally associated with the energy-absorbing capability of rubber-toughened polymers is severely restricted due to the formation of multiple surface cracks resulting from coating failure. This is particularly true when the coating thickness reaches a critical value at which a single surface crack is able to propagate across the coating/substrate interface in an unstable manner.     

Competition and school achievement among Anglo-American and Mexican-American children.

Tested the hypothesis that the less competitive orientation of Mexican-American children is related to their lower school achievement. 230 Anglo-American and Mexican-American children attending kindergarten, Grades 1–2, 4, and 6 of a semirural low-income school were administered individual measures of competition, individualism, field independence, and school achievement (California Achievement Tests, Cooperative Primary Tests, and the Comprehensive Tests of Basic Skills). Results indicate significant effects of culture, sex, and age, but competition and individualism were not significantly correlated with each other and were not consistently related to field independence and school achievement. Results support the general conclusion that the less competitive social orientation of Mexican-American children as measured by experimental games is not necessarily a disadvantage with regard to school achievement. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absorption and distribution studies on chlorinated oleic acid and extracts of chlorinated lipid and protein fractions of flour in rats

Fourty-five reconstructions of the profunda femoris artery were performed in 41 patients during the period from 1972 to 1974. 78% were operated upon for pain at rest or distal gangrene. Three patients died postoperatively and in 5 cases the reconstruction failed to save the limb. In 1 additional case the operation probably lowered the amputation level to below knee. There was only 1 late occlusion. In the present material profundaplasty alone or combined with iliac reconstruction could relieve rest pain and save limbs when no other possibilities except amputation existed. However, when significant obstruction of the profounda femoris artery is demonsrated by angiography, profundaplasty should probably be perferred to femoro-popliteal reconstruction in most cases since it represents a minor operation with encouraging long-term results. Lateral angiograms of the deep femoral artery should supplement conventional angiography or lower limb atherosclerosis.     

CHARACTERIZATION OF PETROLEUM RESIDUA THROUGH REDUCTIVE CHEMISTRY

ABSTRACT

Distillation residua from petroleum, containing 26 — 32% aromatic carbon (f_a), are reduced by K⁰ in tetrahydrofuran to form anions which are then alkylated by alkyl iodides. Consumption of potassium in 24 hours at room temperature is in the range 4 to 5 mmol K per gram resid, of which 19—23% goes to the formation of “K₂S” from the removal of sulfur from the resid. The anions of the resid are characterized by alkylation of the resid with ¹³C enriched methyl iodide followed by examination by heteronuclear correlated two—dimensional nuclear magnetic resonance of ¹H and ¹³C spins. Analysis of proton and carbon shifts of individual methyls demonstrates that attachment of methyls to carbon atoms of the resid is the principal chemistry of the reductive methylation.