Transport budgets in turbulent lifted flames of methane autoigniting in a vitiated co-flow

Autoignition of hydrocarbon fuels is an outstanding research problem of significant practical relevance in engines and gas turbine applications. This paper presents a numerical study of the autoignition of methane, the simplest in the hydrocarbon family. The model burner used here produces a simple, yet representative lifted jet flame issuing in a vitiated surrounding. The calculations employ a composition probability density function (PDF) approach coupled to the commercial CFD package, FLUENT. The in situ adaptive tabulation (ISAT) method is used to implement detailed chemical kinetics. An analysis of species concentrations and transport budgets of convection, turbulent diffusion, and chemical reaction terms is performed with respect to selected species at the base of the lifted turbulent flames. This analysis provides a clearer understanding of the mechanism and the dominant species that control autoignition. Calculations are also performed for test cases that clearly distinguish autoignition from premixed flame propagation, as these are the two most plausible mechanisms for flame stabilization for the turbulent lifted flames under investigation. It is revealed that a radical pool of precursors containing minor species such as CH₃, CH₂O, C₂H₂, C₂H₄, C₂H₆, HO₂, and H₂O₂ builds up prior to autoignition. The transport budgets show a clear convective-reactive balance when autoignition occurs. This is in contrast to the reactive-diffusive balance that occurs in the reaction zone of premixed flames. The buildup of a pool of radical species and the convective-reactive balance of their transport budgets are deemed to be good indicators of the occurrence of autoignition.     

System for deep venous thrombosis detection using objective compression measures

A system for objective vessel compression assessment for deep venous thrombosis characterization using ultrasound image data and a sensorized ultrasound probe is presented. Two new objective measures calculated from applied force and transverse vessel area are also presented and used to describe vessel compressibility. A modified star-Kalman algorithm is used for feature detection in acquired ultrasound images, and objective measures of vessel compressibility are calculated from the detected features and acquired force and location data from the sensorized probe. A three-dimensional shape model of the examined vessel that includes compressibility measures mapped as colors to its surface is presented on the user interface, as well as a virtual representation of the image plane. The compressibility measures were validated using expert segmentation of healthy and diseased vessels and compared using paired t-tests, which showed a significant difference between healthy and diseased cases for both measures. 100% sensitivity and specificity were obtained for both measures. The system was implemented in real-time (16 Hz) and evaluated using a tissue phantom and on healthy human subjects. Sensitivity was 100% and 60%, while specificity was 97% for both measures when implemented. The initial results for the system and its components are promising.     

Removal of trace quantities of nickel from solution

Chitosan, which is produced from the natural polymer chitin, is a much more efficient scavenger of nickel ion than other natural ion exchange materials tested. An industrial waste containing about 7 ppm Ni²⁺ and 10,000 ppm Na⁺ was reduced to less than 0.1 ppm Ni²⁺ by contact in a packed column of chitosan. Capacity of the chitosan substrate under these conditions was a little more than 1 meq/g. The substrate can be regenerated by contact with buffered NH₄Cl at pH 10. The high sodium content of the nickel waste did not prevent sorption of Ni²⁺, but it apparently produced an interference with atomic absorption spectrophotometer analyses, giving a spurious reading of 0.8 ppm Ni²⁺ when the major nickel line at 232 nm was used for analysis.     

Dynamic cylindrical cavity expansion in an incompressible elastoplastic medium

Summary Self-similar dynamic expansion of a pressurized circular cylindrical cavity, embedded in an infinite elastoplastic incompressible medium, is here investigated with the large strain J₂ flow theory. Assuming steady-state conditions, thus bypassing the initial loading history, it is shown that plane-strain fields are sustained with no diverging logarithmic stress appearing in the remote elastic field. Yet, even in the absence of remotely applied stress, the appearance of small stresses at infinity is unavoidable. The present solution is exact but limited to relatively low cavity expansion velocities. A closed form expression is given for the cavitation pressure with elastic/perfectly-plastic response. A fairly general result is derived for the cavitation pressure in hardening media with a definite yield point and in linear-hardening solids as a special case. Contact is made with earlier results of quasi-static cavity expansion along with a comparison to the self-similar dynamic expansion of a spherical cavity in an incompressible Mises solid. Upper and lower bounds for penetration depth tests are suggested by using the present cylindrical cavitation model and the incompressible spherical cavitation model.     

Limiting Use of Potential Energy Storage Compared to Batteries for a Lebanese Hybrid Wind/PV System

In l,ebanon, hybrid wind/PV systems are used to provide electricity when the public electricity is cut off This paper treats the storage problems of electrical energy generated by the used renewable sources. A theoretical study on two types of electrical energy storage systems is given. These systems are the electrochemical energy storage devices （batteries） and the potential （or hydraulic） energy storage system. In order to find the limiting case of use between these two energy storage systems, economical study and comparison between them are discussed and analyzed.     

The effects of osmium tetroxide post‐fixation and drying steps on leafy liverwort ultrastructure study by scanning electron microscopy

Leafy liverwort is one of the most abundant and diverse plants in Indonesia. Their high variation and beneficial secondary metabolites contained in the oil bodies have attracted researchers' attention. The ultrastructural analysis of leafy liverworts is important as a means of species identification and also for further exploration of their oil bodies. However, the optimization of the preparation steps for observing leafy liverworts by SEM is necessary to avoid sample destruction. Fixation and drying play important roles in maintaining a sample's structure as close to its natural state as possible. Thus, in this study, we evaluated the effect of 4% Osmium tetroxide (OsO₄) and drying on leafy liverworts ultrastructure. Microlejeunea, Acrolejeunea, and Frullania were fixed with 2.5% glutaraldehyde. Some samples were then post‐fixed with 4% OsO₄, while the rest were directly dehydrated with an ethanol series and then subjected to different drying methods, i.e. air drying, freeze drying, and drying with hexamethyldisilazane (HMDS). According to the data obtained, post‐fixation with 4% OsO₄ could better maintain the integrity of the samples and enhance the contrast of leafy liverwort SEM images. In addition, samples dried with HMDS showed more detailed structures compared to those that were air dried. Different ultrastructure were found among the different leafy liverworts observed by SEM. Our data suggested the advantages of SEM in providing ultrastructure information on leafy liverworts as well as the optimum conditions to observe them with less deformation. OsO₄ post‐fixation could enhance the contrast of leafy liverwort SEM images and maintain the structure of the samples. Drying with HMDS provided a convenient way for rapid SEM preparation with less structural distortion.     

Turbulent piloted dilute spray flames: Flow fields and droplet dynamics

This paper presents a comprehensive mapping of the flow and droplet fields in turbulent non-reacting as well as reacting dilute spray jets of acetone and ethanol fuels. The burner is well-designed such that the boundary conditions are characterized with sufficient details and the stability limits of the flames are known. The flow is intentionally simple so that attention is shifted to the study of flow–droplet interactions with and without heat release. Velocity, turbulence and droplet size data are measured using a conventional LDV/PDA system and measurements are reported at a number of axial locations in the flow. Sequences of conditions are investigated to resolve the effects of increasing the droplet loading (at a fixed carrier flow rate, where the carrier is air) and the effects of increasing the carrier velocity (at a fixed liquid flow rate).It is shown that the decay in the mean axial excess velocity on the centerline of acetone and ethanol flames is significantly slower than in non-reacting spray jets. The centerline rms velocity fluctuations in non-reacting jets peak around x/D = 10 while in the acetone and ethanol flames the peak occurs further downstream at around 80% of the length of the flame. In both reacting and non-reacting jets, large droplets exit the nozzle with negative slip velocities and a changeover occurs further downstream where the slip velocity of large droplets becomes positive. Radial dispersion of droplets decreases with increasing Stokes number while the axial rms fluctuations may remain high due to “memory” effects as well as to droplet shedding from the inner wall of the fuel pipe hence leading to high anisotropy. The extensive data base, noting similarities and differences between the non-reacting and reacting jets, will facilitate model development and validation for dilute sprays.     

Piezoelectric energy harvester utilizing mandibular deformation to power implantable biosystems: A feasibility study

Journal of Mechanical Science and Technology - This study explores the feasibility of energy harvesting from the deformation of a piezoelectric material attached on the human mandible to power an...