Cavitation effects on textured compression rings in mixed lubrication

Thin lubricant films and cavitation to ring–bore contact have a directly correlation between wear and emissions output of internal combustion engines. Thus, there is a need to develop innovate engineering solutions such as surface texturing. In particular, micro textures are manufactured in order to keep more lubricant in weakly lubricated contact. An isothermal mixed‐hydrodynamic analysis was developed for textured compression rings, which utilised the effects of two‐phase flow using Navier–Stokes equations, vapour transport and asperity interaction. Realistic boundary conditions are used from a real motorbike engine. This paper employs a computational model including multiphase flow of the ring–bore conjunction in order to predict the effects of surface texturing of the barrel face ring around the dead centres. The model is validated using numerical and experimental results from the literature. Additionally, flow simulations have been performed, on how micro‐dimples shape and depth on the ring liner affect on the total friction and minimum lubricant film. Copyright © 2016 John Wiley & Sons, Ltd.     

Teaching simple water quality models

Based on the experience of the authors and the literature, a learning procedure is presented that provides the required knowledge on water quality mathematical modeling in a educational, critical and practical manner; it consists of three steps: (1) brief presentation of the basic modeling theory that is applied using a simple problem, which can be selected from a series of general water quality problems contained in this work, (2) construction of a simple computer program in EXCEL to solve, simulate and examine this problem interactively, and (3) brief presentation of the basic Computational Fluid Dynamics theory and its application in a real life problem; the present study focuses on the first two steps. The proposed procedure also includes 25 questions and answers on scientific, educational and practical matters aiming at making the presentation interactive and interesting. It is currently being applied in two courses at the National Technical University of Athens and the Technical University of Munich; it can be easily modified to be used as a teaching–learning tool in a specific standard or e-learning course.     

Microbiological aspects and shelf life of processed seafood products

BACKGROUND: Fresh fish and seafoods are very perishable products mainly owing to microbial activity of specific spoilage micro‐organisms. Application of hurdle technology leads to a variety of processed products with extended shelf life. In this study, sensory evaluation and microbiological analysis were carried out on 17 processed seafood products stored at 4 °C to determine their shelf life and the predominant spoilage micro‐organisms. RESULTS: Shelf life determined by sensory analysis varied from 66 to 180 days depending on the product. The cause of spoilage for most of the products was the development of off‐flavours/off‐odours, while two products were rejected owing to oil discolouration. Pseudomonads were in most cases below detection limit. H₂S‐producing bacteria, Brochothrix thermosphacta and Enterobacteriaceae were below detection limit throughout the experiment. The predominant spoilage micro‐organisms were lactic acid bacteria and yeasts. Hygiene indicators such as Staphylococcus spp. and total coliforms were also below detection limit in all samples. CONCLUSION: Primarily the initial pH and secondarily the NaCl content determined shelf life duration. Under the applied conditions, lactic acid bacteria and yeasts predominated. The contribution of chemical oxidation and/or autolysis to spoilage and shelf life might be important for most of the products. © 2012 Society of Chemical Industry     

The effect of Nafion sulfonate surface concentration on cationic polyacrylamide adsorption

Perfluorosulfonate ionomer membranes (PFSIs) were cast from Nafion^® propanol-water solutions of varying equivalent weights (950, 1100, and 1200 Da) and all annealed at 100 °C under vacuum. Sulfonate group surface concentration on the various membranes and its effect on the adsorption of a cationic polyacrylamide were investigated utilizing X-ray photoelectron spectroscopy (XPS). The cationic polyacrylamide is employed in the microelectronics industry for electroless printed circuit fabrication and may be used to pattern electrodes directly onto the PFSI surfaces for fuel cell miniaturization. Sulfonate surface concentration was found to be well correlated to the sulfonate bulk concentration obtained from the known equivalent weights of the Nafion^® solutions. Adsorbed cationic polyacrylamide surface coverage was found to be independent of the immersion time in the adsorbate solution. A wide variation in adsorbate coverage (from 0 to 60% of the surface) occurred over a comparatively small variation in the sulfonate repeat unit surface concentration (from 0 to 20% of the total Nafion^® repeat units). Adsorbate coverage goes through a maximum as the sulfonate concentration increases and is consistent with a random, enthalpy-driven adsorption process. Greater sulfonate concentration and lower associated adsorbate coverage was detected on cast membranes than previously found with commercially prepared membranes.     

Electroluminescence from a volatile europium complex

Three new strongly chelating heterocyclic ligands containing pyridine, imidazole and triazine rings have been used to make ternary complexes of Europium(III) ions together with trifluoroacetylacetonate. The complex containing 5,6-diphenyl-3-(2-pyridyl)-1,2,3-triazine produced efficient electroluminescence in an Organic Light Emitting Diode in the presence of Poly(9-vinylcarbazole) and 8-Hydroxyquinoline aluminum salt, used as hole and electron transporters, respectively. The external quantum efficiency of this device was 0.16%.     

Segmented and shielded structures for reduction of thermal expansion-induced tilt errors

The design and prototype tests of a segmented and shielded instrumentation structure, based on tube modules connected by canoe ball type kinematic couplings, are presented with application to a high-precision microscope for biological science experiments. The segmented tube design is shown to be significantly less sensitive to deformation from uneven thermal disturbances than a single tube structure. The gaps between the tube segments relieve thermal strains and restrict axial heat conduction, and the large-radius kinematic couplings provide high thermal resistance interconnects without significantly degrading structural stiffness. Simulation results, based on two- and three-dimensional models of heat conduction, are verified with experimental measurements of prototype structures and are used to predict the dependence of the tilt error on the geometry, boundary conditions, and material properties of the tubular segments. Adding layers of low-cost foam insulation and thin metal shielding to the walls of the structure further improves performance. Kinematic couplings could allow the structure to be disassembled and reassembled without re-calibration, and thus, pre-calibrated tube modules with different components could be easily and quickly interchanged between experiments.