Pseudoriemannian metrics on spaces of bilinear structures

The space of all non degenerate bilinear structures on a manifold $M$ carries a one parameter family of pseudo Riemannian metrics. We determine the geodesic equation, covariant derivative, curvature, and we solve the geodesic equation explicitly. Each space of pseudo Riemannian metrics with fixed signature is a geodesically closed submanifold. The space of non degenerate 2-forms is also a geodesically closed submanifold. Then we show that, if we fix a distribution on $M$, the space of all Riemannia metrics splits as the product of three spaces which are everywhere mutually orthogonal, for the usual metric. We investigate this situation in detail

Study for the feasibility of fluidized bed membrane reactors: membrane supports reutilization and hydrodynamics at high temperature

Membrane reactors can bring various potential advantages in terms of efficiency and economics for H2 production compared to the benchmark technology based on the Fired Tubular Reforming plant. However, for further implementation at industrial scale still some different aspects should be studied and investigated more in depth, especially those with an important impact on the economics of the process. Membrane costs are still high and can represent up to 15% of the total capital costs in a large scale production plant. A main responsible of these high costs is the high price of the support material (Hastelloy-X). To enhance the success of membrane reactors for hydrogen production, the present work focuses on the study of the reutilization of metallic supported Pd-Ag membrane for high temperature applications, especially by focusing on the reutilization of the support material. In this work, a metallic supported Pd-Ag membrane has been reutilized and tested after continuous operation under high temperatures for more than 1200 h. According to N2 permeance tests done during the characterization of the support for the original membrane and the repaired one, the metallic support might have suffered some sintering during long-term test. Furthermore, part of the ceramic layer of the fresh support membrane remained after the embrittlement, and thus this layer might have become thicker. The repaired membrane has been tested for more than 700 h and lower hydrogen perm-selectivities than in the original membrane are obtained, as well as an expected decrease in permeance. The membrane has also been tested under the influence of different parameters for water gas shift reaction conditions. It has been demonstrated that there is no interaction of the Pd-Ag layer with the Ni/CaAl2O4, thus resulting in a constant permeance in the fluidized bed membrane reactor. However, a catalytic effect of the support material (Inconel) has been observed due to the high CO conversions, besides the effect of the catalyst used. Furthermore, to better understand the behaviour of membrane reactors, especially the fluidized bed membrane reactor concept, better closure equations are needed to describe the fluid-dynamic behaviour of this concept at reacting conditions. In this work, it is aimed to extend a recently fundamental research carried out by Mustafa Taşdemir [1] for fluidized beds at room temperature, who developed a correlation to predict solids movement inside fluidized beds as function of bubble properties using novel optical LED-PIV/DIA techniques. This implies to apply this findings to the recently developed technique to study the hydrodynamic characteristics of fluidized beds at high temperatures, ePIV/DIA. To do so, LED-PIV/DIA and ePIV/DIA techniques are compared at room temperature, resulting in an overestimation of the bubble diameter and an underestimation of the solids hold-up when using the endoscopic technique. It might be related to the larger interrogation area used to treat ePIV/DIA recordings, besides the fact that the endoscope reduces the intensity of the laser hampering the detection of the smallest bubbles and averaging the larger ones. Furthermore, it is located in a corner resulting in a weak illumination at the top and bottom right corners and thus, an underestimation of the solids hold-up is found. The deviations observed between both techniques result in a difficult fitting of theoretical and experimental results at high temperature, hindering the extension of the novel correlation

Characterization of wake properties in freely bubbling fluidized beds using Particle Image Velocimetry

The performance of fluidized beds in many physical or chemical operations is predominantly determined by the hydrodynamics and mass transfer characteristics. However, a proper description of a fluidized bed using phenomenological models requires correlations based on many different assumptions for the bubble and emulsion phases, where most of these assumptions have not been validated thoroughly at different operating conditions. One of the most typical assumptions is the fact that the wake of a bubble rises with exactly the same velocity as the bubble and occupies a specific and constant fraction in the bed, commonly around 15% of the bubble volume (1). The wake fraction has been studied using optical techniques and the geometry of the single bubbles injected has been analysed at different experimental conditions (2). However, these results are mainly based on geometric observations, and are not based on specific properties of fluidized beds. In this study, two new methods for the characterization of wake properties in fluidized beds are developed and studied based on the dynamics of the solids phase. Particle Image Velocimetry (PIV) allows to determine the solids phase velocity profiles in detail, which is used for the investigation of the wake properties. PIV combined with Digital Image Analysis (DIA) can provide the average solids mass fluxes throughout the fluidized bed, along with the bubble properties. When relating all positive solids fluxes to the solids carried along by the bubbles in their wakes, the average wake fraction can be obtained directly, as presented in the Figure 1. This method provides information on average results and therefore accounts for all bubbles observed during the experimental evaluation. Please click Additional Files below to see the full abstract

Measurement of solids circulation rates with optical techniques in circulating beds and comparison to pressure drop methods

The number of applications employing circulating fluidized beds has increased considerably over the last years following the important development of chemical looping technologies for power generation (combustion) or fuel conversion (reforming) with inherent CO2 capture. The performance of these reactors is strongly determined by the amount of solids transferred from one reactor to the other, commonly referred to as the Solids Circulation Rate (SCR). The solids inventory, particle characteristics and gas velocities strongly influence the SCR. The determination of the SCR has been carried out using invasive and non-invasive measurement techniques. The direct measurement through solids collection in the loop seal is the most applied technique, but this technique requires opening of the loop seals and thus may be expensive, whereas other methods suffer from large inaccuracies. There is yet no optimal technique available that combines good accuracy with reasonable costs, as recently also discussed by Alghamdi et al. (1). In this work, a pseudo 2D internally circulating fluidized bed (Figure 1) has been built to explore the potential of optical techniques like Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA) for non-invasive, whole-field measurements. Moreover, the setup allows for the measurement of the pressure drop (fluctuations) along the riser and the collection of particles circulating from one reactor to the other, so that the three different measurement techniques can be compared. Please click Additional Files below to see the full abstract

Comparison of five different RNA sources to examine the lactating bovine mammary gland transcriptome using RNA-Sequencing.

The objective of this study was to examine five different sources of RNA, namely mammary gland tissue (MGT), milk somatic cells (SC), laser microdissected mammary epithelial cells (LCMEC), milk fat globules (MFG) and antibody-captured milk mammary epithelial cells (mMEC) to analyze the bovine mammary gland transcriptome using RNA-Sequencing. Our results provide a comparison between different sampling methods (invasive and non-invasive) to define the transcriptome of mammary gland tissue and milk cells. This information will be of value to investigators in choosing the most appropriate sampling method for different research applications to study specific physiological states during lactation. One of the simplest procedures to study the transcriptome associated with milk appears to be the isolation of total RNA directly from SC or MFG released into milk during lactation. Our results indicate that the SC and MFG transcriptome are representative of MGT and LCMEC and can be used as effective and alternative samples to study mammary gland expression without the need to perform a tissue biopsy

Pd-Based Membranes for High Temperature Applications: Current Status

It is an editorialNot availabl

Mass transfer in fluidized bed reactors using a novel non-invasive, whole field and high temporal resolution infra-red technique

Mass transfer rates between bubble and emulsion phases in fluidized beds, together with solids motion, determine the performance of fluidized bed reactors. Mass transfer has widely been studied in the literature using many different experimental techniques, such as colored gases, X-Ray or MRI. They show, however, important disadvantages like high costs or the use of unsafe gases. Moreover, they often lack the required spatial and temporal resolution and many assumptions have to be taken in order to determine mass transfer coefficients, e.g. the concentration is measured in a single point and this concentration is subsequently assumed to be representative for the entire bubble. In a recent work by Dang et al. (1) a novel technique has been developed for non-invasive, whole-field concentration measurements in the dilute regions of a fluidized bed with a high temporal resolution. The technique is based on the measurement of the decrease in the IR intensity at a specific wavelength inside the bubbles due to the absorption by a tracer gas using a high-speed IR camera. Because of the required IR accessibility, the application is limited to pseudo 2D columns and the walls of the column should be made of a material with a high transmittance for IR radiation. This novel technique has shown very promising results, but it is limited to small reactors due to the use of expensive materials (viz. sapphire) causing the results to be influenced by wall effects. In this work, this technique has been further developed in order to allow scaling-up of the system through the use of less expensive materials. The developed system is based on selective IR absorption by propane as tracer gas in a mixture with N2 in a pseudo-2D quartz column (see Figure 1). The decrease in the IR intensity is measured and calibrated, so that the instantaneous propane concentration profiles inside the bubbles are determined. By solving the component mass balances for the bubble phase, the mass transfer coefficients are calculated. Please click Additional Files below to see the full abstract

Attrition-resistant membranes for fluidized-bed membrane reactors: Double-skin membranes

Pd-Ag supported membranes have been prepared by coating a ceramic interdiffusion barrier onto a Hastelloy X (0.2 µm media grade) porous support followed by deposition of the hydrogen selective Pd-Ag (4–5 µm) layer by electroless plating. To one of the membranes an additional porous Al2O3-YSZ layer (protective layer with 50 wt% of YSZ) was deposited by dip-coating followed by calcination at 550 °C on top of the Pd-Ag layer, and this membrane is referred to as a double-skin membrane. Both membranes were integrated at the same time in a single reactor in order to assess and compare the performance of both membranes under identical conditions. The membranes have first been tested in an empty reactor with pure gases (H2 and N2) and afterwards in the presence of a catalyst (rhodium onto promoted alumina) fluidized in the bubbling regime. The membranes immersed in the bubbling bed were tested at 400 °C and 500 °C for 115 and 500 h, respectively. The effect of the protective layer on the permeation properties and stability of the membranes were studied. The double-skinned membraned showed a H2 permeance of 1.55·10−6 mol m−2 s−1 Pa−1 at 500 °C and 4 bar of pressure difference with an ideal perm-selectivity virtually infinite before incorporation of particles. This selectivity did not decay during the long term test under fluidization with catalyst particles.The presented work is funded within FERRET project as part of European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n. 621181. Note: “The present publication reflects only the authors' views and the Union is not liable for any use that may be made of the information contained therein”