381 research outputs found
Application Of Ultrasonic Technology To Improve The Reliability Of Magnetic-Drive Centrifugal Pumps
Get PDFLectureIt is widely acknowledged that sealless magnetic drive pumps give total containment of the pumped process liquid, which in an industry where there are ever tightening environmental constraints on plant operation and increasing health and safety requirements, offers a real advantage of reliability and safety to users. However, as with any piece of process machinery, magnetic drive pumps are designed to operate within specific parameters and operation outside of these parameters can lead to reduced levels of reliability. Whilst traditional instrumentation (measurement of temperature or power) will assist in improving the reliability of the machine, these instruments are not monitoring the primary cause of the issue; instead they are monitoring the effect that the fault condition has on another part of the machine. By constantly monitoring the condition of the pumped liquid present in the internal flow regime of a magnetic-drive pump, it is possible to rapidly identify potential issues and react to them accordingly. Ultrasonic technology has been utilised to rapidly and accurately detect the presence of vapour in the liquid stream. The technology provides a precise and sensitive response to even the smallest change in phase, therefore improving the overall reliability of the machine. This paper presents an overview of the ultrasonic technology that has been utilised to monitor the condition of magnetic-drive centrifugal pumps, including highlights of extensive testing that has been carried out and some real world examples involving the application of this technology on volatile light hydrocarbon processes
An improved solid state terminal analog speech synthesizer.
Get PDFMassachusetts Institute of Technology. Dept. of Electrical Engineering. Thesis. 1965. M.S.Bibliography: leaves [79-82].M.S
Quantifying gross vs. net agricultural land use change in Great Britain using the Integrated Administration and Control System
Get PDFLand use change has impacts upon many natural processes, and is one of the key measures of anthropogenic disturbance on ecosystems. Agricultural land covers 70% of Great Britain's (GB) land surface and annually undergoes disturbance and change through farming practices such as crop rotation, ploughing and the planting and subsequent logging of forestry. It is important to quantify how much of GB's agricultural land undergoes such changes and what those changes are at an annual temporal resolution. Integrated Administration and Control System (IACS) data give annual snapshots of agricultural land use at the field level, allowing for high resolution spatiotemporal land use change studies at the national scale. Crucially, not only do the data allow for simple net change studies (total area change of a land use, in a specific areal unit) but also for gross change calculations (summation of all changes to and from a land use), meaning that both gains and losses to and from each land use category can be defined. In this study we analysed IACS data for GB from 2005 to 2013, and quantified gross change for over 90% of the agricultural area in GB for the first time. It was found that gross change totalled 63,500 km2 in GB compared to 20,600 km2 of net change, i.e. the real year-on-year change is, on average, three times larger than net change. This detailed information on nature of land use change allows for increased accuracy in modelling the impact of land use change on ecosystem processes and is directly applicable across EU member states, where collection of such survey data is a requirement. The modelled carbon flux associated with gross land use change was at times >100 Gg C y−1 larger than that based on net land use change for some land use transitions
Innovations in the Art of Microneurosurgery for Reaching Deep-Seated Cerebral Lesions
Get PDFDeep-seated cerebral lesions have fascinated and frustrated countless surgical innovators since the dawn of the microneurosurgical era. To determine the optimal approach, the microneurosurgeon must take into account the characteristics and location of the pathological lesion as well as the operator’s range of technical expertise. Increasingly, microneurosurgeons must select between multiple operative corridors that can access to the surgical target. Innovative trajectories have emerged for many indications that provide more flexible operative angles and superior exposure but result in longer working distances and more technically demanding maneuvers. In this article, we highlight 4 innovative surgical corridors and compare their strengths and weaknesses against those of more conventional approaches. Our goal is to use these examples to illustrate the following principles of microneurosurgical innovation: (1) discover more efficient and flexible exposures with superior working angles; (2) ensure maximal early protection of critical neurovascular structures; and (3) effectively handle target pathology with minimal disruption of normal tissues
Laminar drag reduction in surfactant-contaminated superhydrophobic channels
Full text linkWhile superhydrophobic surfaces (SHSs) show promise for drag reduction
applications, their performance can be compromised by traces of surfactant,
which generate Marangoni stresses that increase drag. This question is
addressed for soluble surfactant in a three-dimensional laminar channel flow,
with periodic SHSs on both walls. We assume that diffusion is sufficiently
strong for cross-channel concentration gradients to be small. Exploiting a
long-wave theory that accounts for a rapid transverse Marangoni-driven flow, we
derive a one-dimensional model for surfactant evolution, which allows us to
predict the drag reduction across the parameter space. The system exhibits
multiple regimes, involving competition between Marangoni effects, bulk and
interfacial diffusion, advection and shear dispersion. We map out asymptotic
regions in the high-dimensional parameter space, deriving approximations of the
drag reduction in each region and comparing them to numerical simulations. Our
atlas of maps provides a comprehensive analytical guide for designing
surfactant-contaminated channels with SHSs, to maximise the drag reduction in
applications
Unsteady evolution of slip and drag in surfactant-contaminated superhydrophobic channels
Full text linkRecognising that surfactants may impede the drag reduction resulting from
superhydrophobic surfaces (SHSs), and that surfactant concentrations can
fluctuate in space and time, we examine the unsteady transport of soluble
surfactant in a laminar pressure-driven channel flow bounded between two SHSs.
The SHSs are periodic in the streamwise and spanwise directions. We assume that
the channel length is much longer than the streamwise period, the streamwise
period is much longer than the channel height and spanwise period, and bulk
diffusion is sufficiently strong for cross-channel concentration gradients to
be small. By combining long-wave and homogenisation theories, we derive an
unsteady advection-diffusion equation for surfactant flux transport over the
length of the channel, which is coupled to a quasi-steady advection-diffusion
equation for surfactant transport over individual plastrons. As diffusion over
the length of the channel is typically small, the leading-order surfactant flux
is governed by a nonlinear advection equation that we solve using the method of
characteristics. We predict the propagation speed of a bolus of surfactant and
describe its nonlinear evolution via interaction with the SHS. The propagation
speed can fall significantly below the average streamwise velocity as the
surfactant adsorbs and rigidifies the plastrons. Smaller concentrations of
surfactant are therefore advected faster than larger ones, so that
wave-steepening effects can lead to shock formation in the surfactant-flux
distribution. These findings reveal the spatio-temporal evolution of the slip
velocity and enable prediction of the dynamic drag reduction and effective slip
length in microchannel applications
A model for slip and drag in turbulent flows over superhydrophobic surfaces with surfactant
Get PDFInternational audienceSuperhydrophobic surfaces (SHSs) can reduce the friction drag in turbulent flows. In the laminar regime, it has been shown that trace amounts of surfactant can negate this drag reduction, at times rendering these surfaces no better than solid walls (Peaudecerf et al., Proc. Natl. Acad. Sci. USA 114(28), 7254-9, 2017). However, surfactant effects on the drag-reducing properties of SHSs have not yet been studied under turbulent flow conditions, where predicting the effects of surfactant in direct numerical simulations remains expensive by today’s standards. We present a model for turbulent flow inclusive of surfactant, in either a channel or boundary-layer configuration, over long but finite-length streamwise ridges that are periodic in the spanwise direction, with period and gas fraction . We adopt a technique based on a shifted log law to acquire an expression for the drag reduction. The average streamwise and spanwise slip lengths are derived by introducing a local laminar model within the viscous sublayer, whereby the effect of surfactant is modelled by modifying the average streamwise and spanwise slip lengths. Our model agrees with available laboratory experimental data from the literature when conditions are clean (surfactant-free), or when there are low surfactant levels. However, we find an appreciable drag increase for larger background surfactant concentrations that are characteristic of turbulent flows over SHSs for marine applications
The effect of workplace mobility on air pollution exposure inequality - a case study in the Central Belt of Scotland
Get PDFA large number of epidemiological studies have identified air pollution as a major risk to human health. Exposures to the pollutants PM2.5, NO2 and O3 cause cardiovascular and respiratory diseases, cancer and premature mortality. Whilst previous studies have reported demographic inequalities in exposure, with the most deprived and susceptible often being disproportionately exposed to the highest pollutant concentrations, the vast majority of these studies have quantified exposure based only on individuals' place of residence. Here we use anonymised personal data from UK Census 2011, and hourly modelled air pollution concentrations at 0.8 km × 1.4 km spatial resolution in the Central Belt of Scotland, to investigate how inclusion of time spent at place of work or study affects demographic inequalities in exposure. We split the population by sex, ethnic group, age and socio-economic status. Exposure gradients are observed across all demographic characteristics. Air pollution exposures of males are more affected by workplace exposures than females. The White ethnic group has the lowest exposures to NO2 and PM2.5, and highest to O3. Exposures to NO2 and PM2.5 tend to peak between the ages of 21 and 30, but those aged 31–50 tend to be most impacted by the inclusion of time spent at workplace in the exposure assessment. People in the two least deprived deciles consistently have the lowest residential-only and combined residential-workplace exposure to NO2 and PM2.5, but experience the highest increase in exposure when including workplace. Overall, including workplace exposure results in relatively small change in median exposure but attenuates some of the exposure inequalities associated with ethnicity and socioeconomic status observed in exposure assessments based only on place of residence
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