7,389,173 research outputs found
Free-convection condensation on single horizontal pin-fin tubes
No full textPhDNew experimental data are reported for free-convection condensation of ethylene
glycol and R-113 on three-dimensional pin-fin tubes. Effects of pin geometry and tube
thermal conductivity (for copper, brass and bronze giving a mean range of 400, 120 and
80 W/m K over the range of temperature of interest) were investigated. All tests were
performed at near atmospheric pressure with downward flowing vapour at low velocity.
Heat-transfer enhancement was found to be approximately twice the corresponding
active surface area of the tubes, i.e. the surface area of the parts of the tube and pin
surface not covered by condensate retained by surface tension. For ethylene glycol, the
best performing pin-fin tube gave a heat-transfer enhancement of 5.8, about 24 %
higher than the ‘equivalent’ two-dimensional integral-fin tube (i.e. with the same finroot
diameter, longitudinal fin spacing and thickness and fin height). For R-113, the
best enhancement was 5.9, about 10 % higher than the equivalent integral-fin tube.
For both fluids tested, vapour-side, heat-transfer enhancement was found to increase
with decreasing circumferential pin spacing and increasing pin height. Circumferential
pin thickness had little effect on heat-transfer enhancement. Effects of tube thermal
conductivity were found to be more significant for ethylene glycol than R-113.
Retention angle measurements were made under static conditions (without
condensation) and were found to be larger than for equivalent integral-fin tubes. An
expression for condensate retention angle on pin-fin tubes was proposed and found to
agree with the measured retention angles to ±15%.
A semi-empirical model for condensation heat transfer on horizontal pin-fin tubes has
been developed which accounts for the combined effect of gravity and surface tension.
The model predicts the majority of available data to ±20 %
Dutch space; interview with Arnaud de Jong, CEO
No full textDutch Space, the largest space company in the Netherlands and part of Airbus Defence and Space, appointed a new CEO last year. The Leonardo Times sat down with the CEO Arnaud de Jong for an interview. We discuss his career, developments in Dutch Space, his take on competition in the commercial space domain and his future outlook on European and International space markets.Aerospace Engineerin
The Influence of Specimen Misalignment on Wear in Conforming Pin on Disk Tests
Get PDFA pin-on-disk test apparatus was modified to decrease the degree of misalignment
between the pin end and the disk counterface. This was achieved by separate
alignment of both pin and disk. Disk alignment was allowed by incorporating a
kinematic three-ball arrangement into the disk under-face. A self-aligning pin
alignment system was introduced which did not require the perpendicularity of
the pin to be measured. The unmodified system had an alignment within that
permitted by the ASTM G99-95a standard. However, the modified, and improved,
alignment system produced significant changes in recorded wear behaviour in
comparison with the unmodified system. The standard deviation of the wear data
was considerably reduced and the correlation of the wear data with applied load
significantly improved. The modified alignment also reduced the absolute value
of wear recorded. This effect was observed for both wear volume assessed from
mass change and wear volume assessed from pin height change. The reduced
constraint of a misaligned pin in comparison with that of a well-aligned pin may
account for the difference in these results
An optimization study of a multiple-row pin-vented brake disc to promote brake cooling using computational fluid dynamics
Get PDFBrake disc cooling is an important area of research for high-performance brake disc manufacturers, users as well as academia. In high-demand braking applications, vented discs are increasingly being used as these are considered to have high heat-dissipating characteristics. The cooling efficiency of ventilated brakes depend on three key characteristics: the mass flowrate through the disc, i.e. the pumping efficiency of the rotor, the average heat transfer coefficient on the surface of the disc, and the wetted area of the rotor. Recent research has shown that the pin-vented discs have high heat transfer rates because of an increase in turbulence which results in a higher heat transfer coefficient. The pin-vented discs also have a higher resistance to thermal deformation owing to the more even distribution of material, resulting in lower thermal stress build-up within the rotor. The pin-vented discs in general have multiple rows of pins. In this paper an optimal configuration of various rows has been found for the maximum heat transfer rate. It has also been found that the ratio of wetted area of the disc to the frontal area of pins defines the heat transfer rate from the disc uniquely and can be used as a design parameter for the optimal design of a brake dis
PIN generation using EEG : a stability study
Get PDFIn a previous study, it has been shown that brain activity, i.e.
electroencephalogram (EEG) signals, can be used to generate personal
identification number (PIN). The method was based on brain–computer
interface (BCI) technology using a P300-based BCI approach and showed that
a single-channel EEG was sufficient to generate PIN without any error for
three subjects. The advantage of this method is obviously its better fraud
resistance compared to conventional methods of PIN generation such as
entering the numbers using a keypad. Here, we investigate the stability of these
EEG signals when used with a neural network classifier, i.e. to investigate the
changes in the performance of the method over time. Our results, based on
recording conducted over a period of three months, indicate that a single
channel is no longer sufficient and a multiple electrode configuration is
necessary to maintain acceptable performances. Alternatively, a recording
session to retrain the neural network classifier can be conducted on shorter
intervals, though practically this might not be viable
PESI - a taxonomic backbone for Europe
Get PDFThis is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
The attached file is the published version of the article.NHM Repositor
Democracy, globalization and ethnic violence
Get PDF<p>Bezemer, Dirk, and Jong-A-Pin, Richard Democracy, globalization and ethnic violence</p><p>Do democratization and globalization processes combine to increase the incidence of violence in developing and emerging economies? The present paper examines this hypothesis by a study of internal violence in Sub-Sahara Africa with its recent democratization wave, the globalization process and the presence of advantaged ethnic minorities. Specifically, we examine if democratization and globalization lead to ethnic violence in the presence of 'market-dominant' minorities. We explore the theoretical underpinning of this scenario and empirically assess its implications employing panel fixed effects regressions over the period 1984-2003. We find support in a Sub-Saharan African sample but no evidence for a worldwide effect. Journal of Comparative Economics 41 (1) (2013) 108-125. University of Groningen, The Netherlands. (C) 2012 Association for Comparative Economic Studies Published by Elsevier Inc. All rights reserved.</p>
GaN-based PIN alpha particle detectors
No full textGaN-based PIN alpha particle detectors are studied in this article. The electrical properties of detectors have been investigated, such as current-voltage (I-V) and capacitance-voltage (C-V). The reverse current of all detectors is in nA range applied at 30 V. which is suitable for detector operation. The charge collection efficiency (CCE) is measured to be approximately 80% but the energy resolution is calculated to be about 40% mostly because the intrinsic layer is not sufficiently thick enough. (C) 2011 Elsevier B.V. All rights reserved.Instruments & InstrumentationNuclear Science & TechnologyPhysics, Particles & FieldsSpectroscopySCI(E)EI2ARTICLE110-1366
A cohesive zone model for predicting delamination suppression in z-pin reinforced laminates
No full textThis paper presents a cohesive zone model based finite element analysis of
delamination resistance of z-pin reinforced double cantilever beam (DCB). The
main difference between this and existing cohesive zone models is that each z-
pin bridging force is governed by a traction-separation law derived from a meso-
mechanical model of the pin pullout process, which is independent of the
fracture toughness of unreinforced laminate. Therefore, two different traction-
separation laws are used: one representing the toughness of unreinforced
laminate and the other the enhanced delamination toughness owing to the pin
bridging action. This approach can account for the large scale bridging effect
and avoid using concentrated pin forces, thus removing the mesh dependency and
permitting more accurate analysis solution. Computations were performed using a
simplified unit strip model. Predicted delamination growth and load vs.
displacement relation are in excellent agreement with the prediction by a
complete model, and both models are in good agreement with test measured load
vs. displacement relation. For a pinned DCB specimen, the unit strip model can
reduce the computing time by 85%
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