Validation of the transient liquid crystal thermography technique for heat transfer measurements on a rotating cooling passage

The transient liquid crystal thermography can be a suitable tool to study heat\u2010transfer performances on internal cooling schemes of gas turbine blades. One of the hot topics related to this methodology is about the level of reliability of the heat\u2010transfer assessments in rotating tests where the fluid experiences time\u2010dependent rotating effects. The present study contribution aims to experimentally validate by cross\u2010comparison of the outcomes obtained by employing the transient technique with those from the steady\u2010state liquid crystal thermography in which the rotational effects occur as time\u2010stable by definition. Heat\u2010transfer measurements have been conducted on a rib\u2010roughened square cross\u2010section channel, with an inlet Reynolds number equal to 20,000 and rotation number up to 0.2. Special attention has been paid to the definition of the more reliable calibration strategy for liquid crystals that are employed in the transient thermography and to the proper estimation of the heat losses in the post\u2010processing of the steady\u2010state experimental data. The results show great accordance between the indications provided by the two techniques both in static and rotating conditions, demonstrating the possibility to exploit the advantages of the transient liquid crystal thermography for the investigation of heat transfer into rotating cooling channels

Balancing ion parameters and fluorocarbon chemical reactants for SiO2 pattern transfer control using fluorocarbon-based atomic layer etching

In manufacturing, etch profiles play a significant role in device patterning. Here, the authors present a study of the evolution of etch profiles of nanopatterned silicon oxide using a chromium hard mask and a CHF3/Ar atomic layer etching in a conventional inductively coupled plasma tool. The authors show the effect of substrate electrode temperature, chamber pressure, and electrode forward power on the etch profile evolution of nanopatterned silicon oxide. Chamber pressure has an especially significant role, with lower pressure leading to lower etch rates and higher pattern fidelity. The authors also find that at higher electrode forward power, the physical component of etching increases and more anisotropic etching is achieved. By carefully tuning the process parameters, the authors are able to find the best conditions to achieve aspect-ratio independent etching and high fidelity patterning, with an average sidewall angle of 87° ± 1.5° and undercut values as low as 3.7 ± 0.5% for five trench sizes ranging from 150 to 30 nm. Furthermore, they provide some guidelines to understand the impact of plasma parameters on plasma ion distribution and thus on the atomic layer etching process

Ecological Relevance of Hemolymph Total Protein Concentration in Seven Unrelated Crustacean Species from Different Habitats Measured Predictively by a Density-Salinity Refractometer

In recent years, blood metabolites have been investigated as a tool for monitoring physiological condition in wild or cultured crustaceans exposed to different environmental conditions. Blood protein levels fluctuate with changes in environmental and physiological conditions and play fundamental roles in the physiology of crustaceans from O2 transport to reproduction up to stress responses. Proteins are major contributors to hemolymph density, and the present study correlates the easy and low cost measure of hemolymph density by a density-salinity refractometer with the total protein concentration, measured with a colorimetric method. Moreover, the study evaluates the accuracy of the relationship and provides a conversion factor from hemolymph density to protein in seven species of crustaceans, representative of taxa far apart in the phylogenetic tree and characterized by different life habits. Measuring serum-protein concentration by using a refractometer can provide a non-destructive field method to assess crustacean populations/species protein-related modifications of physiological state without need of costly laboratory facilities and procedures

Effects of different cross-sections of Body Centered Cubic cells on pressure drop and heat transfer of additively manufactured heat sinks

In many industrial applications, heat loads management requires the design and production of compact heat exchangers which are expected to handle high thermal loads with acceptable pressure losses, while assuring good mechanical performances. These challenging targets can be achieved by filling the cavities where the cool/hot fluid circulates with lattice structures promoting the heat exchange between the fluid and the cavity boundaries. Such lattice structures can be only produced through Additive Manufacturing due to their high geometric complexity. Recent experimental investigations proved the effectiveness of some kinds of lattice structures having a circular cross section. Here the aerothermal behaviour of Body-Centred Cubic (BCC) lattice stagger arrays in a rectangular channel was experimentally investigated by considerably extending the previous studies to higher Reynolds numbers (up to 30′000) and to new types of lattice structures. Specifically, three new BCC structures having a cam-like, drop-like and elliptical cross section were explored in this work and compared against those having circular cross section. All the samples were manufactured by means of Laser Powder Bed Fusion and made from AlSi10Mg. At first, the heat exchangers were comprehensively characterized by means of optical non-destructive methods. Successively they were tested in a dedicated rig by imposing constant heat flux boundary conditions. The characteristics of the transitional or fully turbulent approaching flow to the test section are also reported thanks to dedicated flow field measurements performed by Particle Image Velocimetry. According to the obtained results, the BCC structure with the circular cross section of larger diameter is the most effective in terms of heat transfer, although it is largely penalized by the pressure losses. Similar heat transfer performances were achieved by the tapered cross section of elliptical shape with the advantage of a considerably lower friction factor. Pressure losses resulted almost identical for all the tapered cross sections but lower than those of the circular one having an equal frontal dimension. When considering the thermal performance factor the circular shape becomes unfavourable for Re>20′000, while the elliptical cross section is the best choice to efficiently promote heat transfer up to Re=30′000

Sub-Pixel Response Measurement of Near-Infrared Sensors

Wide-field survey instruments are used to efficiently observe large regions of the sky. To achieve the necessary field of view, and to provide a higher signal-to-noise ratio for faint sources, many modern instruments are undersampled. However, precision photometry with undersampled imagers requires a detailed understanding of the sensitivity variations on a scale much smaller than a pixel. To address this, a near-infrared spot projection system has been developed to precisely characterize near-infrared focal plane arrays and to study the effect of sub-pixel non uniformity on precision photometry. Measurements of large format near-infrared detectors demonstrate the power of this system for understanding sub-pixel response.Comment: 9 pages, 13 figures, submitted to PAS

Study of the microstructure of the grade 91 steel after more than 100.000h of creep exposure at 600°C

International audienceThis paper presents results on the evolution of microstructure (both matrix and precipitates) of an ASME Grade 91 steel that has been creep tested for 113,431 h at 600 °C under a load of 80 MPa. The microstructure was investigated using transmission electron microscopy (TEM) and revealed chromium rich M23C6 carbides, MX-type precipitates, Laves phases and modified Z-phases. Only a small amount of modified Z-phase was found. In order to quantify coarsening of precipitates and growth of new phases during creep, the size distributions of the identified precipitates were determined by analysis of TEM images. In addition to this, the size distribution of Laves phases was determined by image analysis of scanning electron micrographs. Substructure modifications and creep damage were investigated on cross sections of the creep specimen using Electron Backscatter Diffraction and Scanning Electron Microscopy

Microglia in prion diseases: Angels or demons?

Prion diseases are rare transmissible neurodegenerative disorders caused by the accumulation of a misfolded isoform (PrPSc) of the cellular prion protein (PrPC) in the central nervous system (CNS). Neuropathological hallmarks of prion diseases are neuronal loss, astrogliosis, and enhanced microglial proliferation and activation. As immune cells of the CNS, microglia participate both in the maintenance of the normal brain physiology and in driving the neuroinflammatory response to acute or chronic (e.g., neurodegenerative disorders) insults. Microglia involvement in prion diseases, however, is far from being clearly understood. During this review, we summarize and discuss controversial findings, both in patient and animal models, suggesting a neuroprotective role of microglia in prion disease pathogenesis and progression, or\u2014conversely\u2014a microglia-mediated exacerbation of neurotoxicity in later stages of disease. We also will consider the active participation of PrPC in microglial functions, by discussing previous reports, but also by presenting unpublished results that support a role for PrPC in cytokine secretion by activated primary microglia