Experimental study of critical heat flux in open two-phase thermosyphon

Critical heat flux in an open two-phase thermosyphon has been measured employing water, R113 and R22 for a wide range ofL/D=4.8 to 960 and density ratio ofρ _L /ρ _G =6.17 to 1602. The CHF data measured, are found to be in fairly good agreement with those calculated from a criterion that the CHF takes place when reaches a maximum liquid falling rate in counter-current annular flow of liquid and vapor. Normal operation of the thermosyphon cannot be obtained at any liquid of water, R113 and R22 for a small tube diameter of less than 2 mm.     

Multivariate control charts based on NAS and mid‐infrared spectroscopy for quality control of B5 blends of methyl soybean biodiesel in diesel

In this work, mid‐infrared spectroscopy and multivariate control charts based on net analyte signal were applied for quality control of B5 blends of biodiesel/diesel (5% biodiesel/95% diesel). Control charts were constructed using instrumental signal decomposition, generating three charts: the net analyte signal chart for monitoring the analyte of interest (methyl soybean biodiesel); the interference chart, which corresponds to the contribution of all other compounds in the diesel sample (diesel); and the residual chart, which corresponds to non‐systematic variations. Statistical limits were established for each developed chart, using samples inside quality specifications (normal operation conditions). To validate multivariate control charts, new samples were analyzed. The new samples represented samples in‐control and samples out‐of‐control in relation to the content of biodiesel, adulterated biodiesel with severe vegetable oils and adulterated diesel with residual automotive lubricant oil, kerosene, and gasoline. The results obtained show an excellent distinction between the samples inside and out of the quality specifications, with 91% and 100% correctly classified, respectively, which demonstrates that the methodology developed is a viable alternative for quality monitoring of this type of fuel. Copyright © 2015 John Wiley & Sons, Ltd.     

Heat transfer during transient cooling of high temperature surface with an impinging jet

 An experimental study of transient boiling heat transfer during a cooling of a hot cylindrical block with an impinging water jet has been made at atmospheric pressure. The experimental data were taken for the following conditions: a degree of subcooling of ΔT _sub = 20–80 K, a jet velocity of u _j  = 5–15 m/s, a nozzle diameter of d _j  = 2 mm and three materials of copper, brass and carbon steel. The block was initially and uniformly heated to about 250 °C and the transient temperatures in the block were measured at eight locations in r-direction at two different depths from the surface during the cooling of hot block. The surface heat flux distribution with time was evaluated using a numerical analysis of 2-D heat conduction. Behavior of the wetting front, which is extending the nucleate boiling region outward, is observed with a high-speed video camera. A position of wetting region is measured and it is correlated well with a power function of time. The changes in estimated heat flux and temperature were compared with the position of wetting region to clarify the effects of subcooling, jet velocity and thermal properties of block on the transient cooling. Received on 17 March 2000     

Water molecule adsorption properties on the BiVO4 (100) surface

The water absorption properties at the surface of BiVO4 are attracting a great deal of attention because the system is a promising candidate as a photocatalyst operating in the visible light range. This has motivated the present investigation via first principles molecular dynamics, which has revealed that a H2O molecule is adsorbed molecularly, instead of dissociatively, at the fivefold Bi site with an adsorption energy of approximately 0.58 eV/molecule. The band gap of the system shrinks slightly (by approximately 0.2 eV) upon water adsorption and it is likely that oxygen atoms belonging to the adsorbed water molecules to the Bi sites are oxidized, as inferred by the small Bi-Owater equilibrium distance (approximately 2.6-2.8 A) very close to the Bi-O bond in the bulk crystal. In the case of water adsorption at a Bi site, the distance between Hwater and V, which is a reduction site, is larger than in the case of adsorption at a V site, indicating that the proton reduction processes may be suppressed.     

Steric Effect of Carboxylate Ligands on Pd‐Catalyzed Intramolecular C(sp2)–H and C(sp3)–H Arylation Reactions

A bulky carboxylic acid bearing three cyclohexylmethyl substituents at the α‐position, namely, tri(cyclohexylmethyl)acetic acid, is demonstrated to act as an efficient ligand source in Pd‐catalyzed intramolecular C(sp²)?H and C(sp³)?H arylation reactions. The reactions proceed smoothly under mild reaction conditions, even at room temperature due to the steric bulk of the carboxylate ligands, which accelerates the rate‐determining C?H bond activation step in the catalytic cycle.     

Critical heat flux in pool boiling on a vertical heater

Critical heat flux during pool boiling on a vertical heater of wire or plate has been measured employing water and R113. The experiment was made for a wire of 0.5 to 2 mm in diameter and for a plate of 5, 7 and 30 mm in width and from 20 to 300 mm in height. The pressure was 1 and 2 bar for water and 1, 2, 3 and 4 bar for R113. The experiment shows that for the case of both wire and plate of 5, 7 mm, a large coalesced bubble entirely surrounds the vertical heater and rises surrounding it, while for the case of w = 30 mm, a large bubble cannot surround and rises along its surface. The characteristic of CHF can be divided into two regimes depending on the flow condition when CHF takes place. Correlations are proposed for the CHF of the wire and the plate of w = 5, and 7 mm, yielding good accuracy. The CHF for the plate of w = 30 mm has a similar tendency to that in one side headed surface and can be predicted reasonably by existing correlation for one side heated surface.     

Mechanical Properties and Intermolecular Interactions in Molecular Composites Composed of Wholly Aromatic Polyamide and Poly-(Amide-Imide)

Poly(p-phenylene-3,4′-oxydiphenylene terephthalamide) (PPOT) and poly(4,4′-oxydiphenylene-4-carbonamidephthalimide-N-yl) (PAI) are compatible. Molecular composites were prepared by solution blending and subsequently solvent casting. The glass transition temperature of the composite increased with increasing fraction of PPOT. Intermolecular interactions between the two components increase due to formation of hydrogen bonds between the amide linkages of the component polymers. The elastic modulus of the composite was always higher than the modulus predicted on the basis of the additivity. Similar deviations from additivity were observed for the bulk density. These desirable results arise from an increase of the packing density of molecules due to the additional hydrogen bonding also shown by the infrared spectra.     

Extra virgin (EV) and ordinary (ON) olive oils: distinction and detection of adulteration (EV with ON) as determined by direct infusion electrospray ionization mass spectrometry and chemometric approaches

Extra virgin (EV), the finest and most expensive among all the olive oil grades, is often adulterated by the cheapest and lowest quality ordinary (ON) olive oil. A new methodology is described herein that provides a simple, rapid, and accurate way not only to detect such type of adulteration, but also to distinguish between these olive oil grades (EV and ON). This approach is based on the application of direct infusion electrospray ionization mass spectrometry in the positive ion mode, ESI(+)‐MS, followed by the treatment of the MS data via exploratory statistical approaches, PCA (principal component analysis) and HCA (hierarchical clustering analysis). Ten distinct brands of each EV and ON olive oil, acquired at local stores, were analyzed by ESI(+)‐MS and the results from HCA and PCA clearly indicated the formation of two distinct groups related to these two categories. For the adulteration study, one brand of each olive oil grade (EV and ON) was selected. The counterfeit samples (a total of 20) were then prepared by adding assorted proportions, from 1 to 20% w/w, with increments of 1% w/w, of the ON to the EV olive oil. The PCA and HCA methodologies, applied to the ESI(+)‐MS data from the counterfeit (20) and authentic (10) EV samples, were able to readily detect adulteration, even at levels as low as 1% w/w. Copyright © 2010 John Wiley & Sons, Ltd.     

Replica-exchange extensions of simulated tempering method

In this paper we consider combinations of two well-known generalized-ensemble algorithms, namely, simulated tempering and replica-exchange method. We discuss two examples of such combinations. One is the replica-exchange simulated tempering and the other is the simulated tempering replica-exchange method. In the former method, a short replica-exchange simulation is first performed and the simulated tempering weight factor is obtained by the multiple-histogram reweighting techniques. This process of simulated tempering weight factor determination is faster and simpler than that in the usual iterative process. A long simulated tempering production run is then performed with this weight factor. The latter method is a further extension of the former in which a simulated tempering replica-exchange simulation is performed with a small number of replicas. These algorithms are particularly useful for studying frustrated systems with rough energy landscape. We give the formulations of these two methods in detail and demonstrate their effectiveness taking the example of the system of a 17-residue helical peptide.     

Dissociation of water molecule at three-fold oxygen coordinated V site on the InVO4 (0 0 1) surface

Water molecule adsorption properties at the surface of InVO₄ have been investigated using an ab initio molecular dynamics approach. It was found that the water molecules were adsorbed dissociatively to the three-fold oxygen coordinated V sites on the (0 0 1) surface. The dissociative adsorption energy was estimated to be 0.8-0.9 eV per molecule. The equilibrium distance between V and O of the hydroxyl -OH was almost the same as the V-O distance of tetrahedra VO₄ in the InVO₄ bulk crystal (1.7-1.8 Å).