Performance Analysis and Modeling of Thermally Sprayed Resistive Heaters

Many processes and systems require hot surfaces. These are usually heated using electrical elements located in their vicinity. However, this solution is subject to intrinsic limitations associated with heating element geometry and physical location. Thermally spraying electrical elements directly on surfaces can overcome these limitations by tailoring the geometry of the heating element to the application. Moreover, the element heat transfer is maximized by minimizing the distance between the heater and the surface to be heated. This article is aimed at modeling and characterizing resistive heaters sprayed on metallic substrates. Heaters were fabricated by using a plasma-sprayed alumina dielectric insulator and a wire flame-sprayed iron-based alloy resistive element. Samples were energized and kept at a constant temperature of 425 °C for up to 4 months. SEM cross-sectional observations revealed the formation of cracks at very specific locations in the alumina layer after thermal use. Finite-element modeling shows that these cracks originate from high local thermal stresses and can be predicted according to the considered geometry. The simulation model was refined using experimental parameters obtained by several techniques such as emissivity and time-dependent temperature profile (infra-red camera), resistivity (four-probe technique), thermal diffusivity (laser flash method), and mechanical properties (micro and nanoindentation). The influence of the alumina thickness and the substrate material on crack formation was evaluated.     

Performance analyses of VHTR plants with direct and indirect closed Brayton cycles and different working fluids

This paper investigated the performance of Very High Temperature Reactor (VHTR) power plants with helium working fluid and direct and indirect Closed Brayton Cycles (CBCs), and with binary mixture working fluids of He–Xe and He–N₂ (molecular weight of 15 g/mole) and indirect CBCs. Also investigated are the effects of using low- and high-pressure compressors with intercooling, versus a single compressor, using bleed cooling the reactor pressure vessel in direct CBC helium plants, and varying the reactor exit temperature from 700 °C to 950 °C on the plant thermal efficiency, cycle pressure ratio and the size of and number of stages in the turbine and compressor. Analyses are performed for a shaft rotation speed of 3000 rpm, reactor thermal power of 600 MW and a temperature pinch of 50 °C in the intermediate heat exchanger (IHX) for the indirect CBCs.     

Structural, photoluminescent and electrical properties of CdTe films with different compositions fabricated by CMBD

CdTe films with different compositions (Cd-rich, Te-rich and stoichiometric) were fabricated by a novel and low cost chemical molecular beam deposition method (CMBD) in atmospheric pressure hydrogen flow. Cd and Te granules were used as precursors. The films were deposited on ceramic (SiO₂:Al₂O₃) substrates at 580 °C and 600 °C. The growth rate was varied in the range of 9-30 Å/s. The composition (Cd/Te) of the samples was changed by controlling the molecular beam intensity (MBI) ratio. Three samples fabricated at MBI ratios Cd/Te = 0.5, 1.0 and 1.16 were investigated by XRD, AFM, EDX, SEM, photoluminescence (PL) and Hall methods.     

Bibliography on Mathematical Models of Drying and Dryers

Mathematical modelling of drying processes as well as dryers has become an active and challenging area of research internationally. Despite the volume of literature published and continuing to appear on this subject, much remains to be accomplished in view of the intrinsic complexities associated with coupled heat, mass and momentum transfer with or without phase change occurring in porous media which are often deformable as well. Characterization of the solid media is still a major obstacle to modelling of drying. Since industrial drying is increasingly carried out using several modes of heat transfer (e.g. convection coupled wih conduction or microwave or infrared heating modelling of drying or dryers will remain an important research area in the years to come.

We hope that this bibliography will serve as a useful tool for both the novice as well as the experienced researcher in the subject area in locating appropriate literature for a critical evaluation.     

In vitro comparison of hepatic metabolism of 9cis-11 trans and 10trans-12cis isomers of CLA in the rat

Hepatic metabolism of the two main isomers of CLA (9cis-11 trans, 10trans-12cisC_18∶2) was compared to that of oleic acid (representative of the main plasma FA) in 16 rats by using the in vitro method of incubated liver slices. Liver tissue samples were incubated at 37°C for 17h under an atmosphere of 95% O₂/5%CO₂ in a medium supplemented with 0.75 mM of FA mixture (representative of circulating nonesterified FA) and with 55 μM [1-¹⁴C]9cis-11 trans C_18∶2, [1-¹⁴C]10trans-12cis C_18∶2, or [1-¹⁴C]oleate. The uptake of CLA by hepatocytes was similar for both isomers (9%) and was three times higher (P<0.01) than for oleate (2.6%). The rate of CLA isomer oxidation was two times higher (49 and 40% of incorporated amounts of 9cis-11 trans and 10trans-12 cis, respectively) than that of oleate (P<0.01). Total oxidation of oleate and CLA isomers into [¹⁴CO₂] was low (2 to 7% of total oxidized FA) compared to the partial oxidation (93 to 98%) leading to the production of [¹⁴C] acid-soluble products. CLA isoemrs escaping from catabolism were both highly desaturated (26.7 and 26.8%) into conjugated 18∶3. Oleate and CLA isomers were mainly esterified into neutral lipids (30%). They were slowly secreted as parts of VLDL particles (<0.4% of FA incorporated into cells), the extent of secretion of oleate and of 10trans-12 cis being 2.2-fold higher than that of 9cis-11 trans (P<0.02). In conclusion, this study clearly showed that both CLA isomers were highly catabolized by hepatocytes, reducing their availability for peripheral tissues. Moreover, more than 25% of CLA escaping from catabolism was converted into conjugated 18∶3, the biological properties of which remain to be elucidated.     

Mixing of a self-assembled supramolecular polymer and a covalent polymer in organic solutions

We report on a neutron scattering study of the molecular structure of a self-assembled supramolecular polymer composed of a bicopper complex within a solution of a covalent polymer (atactic polystyrene/trans-decalin). The study is achieved by putting two binary phases in contact and allowing for diffusion of both components in either phase. It is shown that the one-dimensional bicopper filaments are compatible to a high extent with the atactic polymer. These results are discussed in the light of a recently devised encapsulation process of the bicopper filaments within the fibrils of a physical network of isotactic polystyrene.     

Metal transfer to plants grown on a dredged sediment: use of radioactive isotope 203Hg and titanium

Improperly disposed of dredged sediments contaminated with metals may induce long-term leaching and an increase of metal concentrations in ground waters and vegetal cover plants. The objective of the study was to quantify the sediment-to-plant transfer of Cu, Pb, Hg and Zn with a particular focus on the pathway of Hg and to determine whether the establishment of vegetal cover modifies the metal availability. A pot experiment with rape (Brassica napus), cabbage (Brassica oleraccea) and red fescue (Festuca rubra) was set up using a sediment first spiked with the radioisotope 203Hg. Zinc concentrations (197-543 mg kg(-1) DM) in leaves were higher than Cu concentration (197-543 mg kg(-1) DM), Pb concentration (2.3-2.6 mg kg(-1) DM) and Hg concentration (0.9-1.7 mg kg(-1) DM). Leaves-to-sediment ratios decreased as follows: Zn > Cu > Hg > Pb. According to Ti measurements, metal contamination by dry deposition was less than 1%. Mercury concentration in plant leaves was higher than European and French thresholds. Foliar absorption of volatile Hg was a major pathway for Hg contamination with a root absorption of Hg higher in rape than in cabbage and red fescue. Growth of each species increased Cu solubility. Zinc solubility was increased only in the presence of rape. The highest increase of Cu solubility was observed for red fescue whereas this species largely decreased Zn solubility. Dissolved organic carbon (DOC) measurements suggested that Cu solubilisation could result from organic matter or release of natural plant exudates. Dissolved inorganic carbon (DIC) measures suggested that the high Zn solubility in the presence of rape could originate from a generation of acidity in rape rhizosphere and a subsequent dissolution of calcium carbonates. Consequently, emission of volatile Hg from contaminated dredged sediments and also the potential increase of metal solubility by a vegetal cover of grass when used in phytostabilisation must be taken into account by decision makers.