190 research outputs found
Space air-conditioning of mechanically-ventilated rooms : computation of flow and heat transfer
No full textComputational studies of two- and three-dimensional, turbulent
recirculating flows within mechanically-ventilated enclosures are
reported. Two principal cases are examined: (i) two-dimensional
offset jets: and (ii) three-dimensional flow induced in rooms by
supply jets emanating from low or high side-wall registers. The
calculations were undertaken using iterative finite-domain proceedures
which solve the conservation equations for mass, momentum and
enthalpy, together with additional transport equations for the
turbulent kinetic energy and its dissipation rate . The effect of
buoyancy waS. explicitly accounted for when modelling these equations,
in order that they could be employed to simulate buoyant flow in
ventilated rooms. Computations of the mean velocity, temperature and
convective heat transfer distribution are reported, and compared with
experimental data where available.
A modified version of the two-dimensional elliptic code of Pun
and Spalding (1977) was employed to simulate the offset jet case.
These involve the discharge of a turbulent jet parallel to a flat
surface and eventually attaching to it. The investigations covered a
wide range of offset ratio (3.5-32.4). and the computed flow
properties are compared with measurements from several sources. These
comparisons show good agreement downstream of the reattachment point,
while some discrepancies are evident upstream from this location. The
differences therefore occur mainly in the recirculating flow region,
and are believed to arise from shortcoming in the starting profiles,
the turbulance model and the treatment of the near-wall flow.
A three-dimensional elliptic finite-domain code was developed to
simulate the complex, jet-induced flow within rectangular enclosures.
The code was verified using both laminar and turbulent flow test cases
on simpler geometries. Comparisons with the measurements and
predictions reported by previous researchers were employed for this
purpose. Subsequentlyr the ventilated room simulations were
undertaken using three different ventilation arrangements with thermal
conditions corresponding to isothermall non-buoyant (constant
property) and buoyancy"affected flows. The computations were again
compared with experimental and numerical predictions of previous
researchers. This comparison displayed generally good agreement with
these sources.
A study of the flow and convective heat exchange within a
warm-air heated rom, for which buoyancy effects are significant# is
also reported in a bound paper (Alamdari, Hammonda nd Mohammad, 1986)
for three different heat loads. Its aim to assess the balance between
accuracy and economy provided by the present higher-level method
compared with the intermediate-level convection model of Alamdari and
Hammond (1982) when used to supply building thermal simulation
programs with accurate convection heat transfer data. The computed
results of both models were compared, and indicate that the
intermediate-level is a valuable alternative source that can satisfy
the needs of building thermal modellers. It provides resonable
accuracy at a very modest cost in computing terms
EU network carriers, low cost carriers and consumer behaviour: A Delphi study of future trends
No full textThis paper uses a Delphi panel of 26 air transport experts to forecast the
structure of air transport in the EU in 2015 in respect of network carriers, low
cost airlines and passenger behaviour. Secondary research was used to construct
a number of scenarios about the future structure and strategy of EU network and
low cost airlines and also traveller behaviour. Consensus of opinions was sought
amongst the panel in a two-round process. The consensus opinion of the Delphi
experts was that; network carrier consolidation will reduce EU players to less
than five, there will be only two or three large low cost carriers, Business
Class products will disappear on short hauls. and leisure travellers will take
an increasing number of multiple short-duration holidays
Regional development in airlines and travel agents relationship.
No full textOn average, 17% of airline operating cost are attributed to distribution costs which are associated with commissions to travel agents, ticketing, credit card fees, CRS fees and promotion. In recent years, airlines in North America and in Europe have been questioning the role of travel agents in the distribution chain and renegotiating commission fee structures. As a result, some large agents have introduced a management fee philosophy where the clients, especially corporations, pay a fee to the travel agent in return for predetermined services. Such services include providing up-to-the minute reports on travel patterns of employees, effectiveness of travel policies, advice on complicated itineraries, etc. Such changes in airline and travel agent relationships initially started in the US and were followed by the European carriers. However, Asian carriers have been slow in following their US and European counterparts. This raises a number of questions: What are the barriers, if any for Asian carriers, to follow their counter parts in Europe and US? Would airlines in the three regions be able to bypass travel agents and sell directly to their customers? Would the customers prefer to go direct to airlines? Would there be a variation in the airlines, and agents, relationship in each region? This paper addresses these questions by analysing the distribution strategies of major carriers in the US, Europe and Asia. It also discusses the changing relationship between airlines and travel agents, and the trend towards direct selling by airlines in each region
Experimental heat/mass transfer studies of turbulent wall-bounded jets associated with mechanicallly ventilated enclosures
No full textThe development and use of a'n experimental test rig
is reported which is capable of modelling two- and
three-dimensional wall-bounded air jets. This test rig
was primarily produced in order to facilitate the
experimental verification of computer codes for
calculating convective heat transfer within mechanically-
ventilated enclosures. Special attention was therefore
given in the design of the rig to heat transfer
measurements within such enclosures.
The analogy between heat and mass transfer and the
application of the naphthalene sublimation technique are
explained. Also use of phase change paints in heat
transfer measurements in general, and wall-jets in
particular, is discussed and experimentally demonstrated.
The boundary conditions for the application of each of the
above two methods are then specified. The mass transfer
method may be used for the case of a heated plate and a
jet at ambient temperature while the phase change paint
method is applicable to a heated jet.
Heat/mass transfer studies are carried out for two
different geometries. First beneath a plane wall-jet-
obstructed by a normal flat-plate (Alamdari, Hammond and
Montazerin (1986 bound paper)), where the data are
compared with the computations of the 'intermediate-level'
convection model of Alamdari and Hammond (1982) and the
high-level 'elliptic' finite domain flow model of Pun and
Spalding (1977). The comparison has been a clear
demonstration of the capabilities of the computer codes
and has shown that although their results over flat
surfaces are in good agreement with the test data, their
predictions for jets flowing round corners need further
research. Secondly the flow and heat transfer
characteristics of a three-dimensional jet parallel to a
flat plate has been studied. In this case the flow field
and mass transfer are modelled and an equation is finally
derived which estimates the average heat transfer over a
plate parallel to a bluff-jet for a variety of off-set
heights, Reynolds numbers and nozzle aspect ratios and can
readily be used by design engineers handling such flows
Convective heat transfer within mechanically-ventilated building spaces
No full textA hierarchy of interacting and interdependent approaches have
been developed for calculating internal surface convective heat
transfer coefficients within mechanically-ventilated rooms. A
'high-level' computer code is developed for non-bucyant and
buoyant flow based on the "elliptic' code of Pun and Spalding
(1977), in which 'upwind' finite-difference approximations to the
governing partial-differential equations for continuity, momentum
and thermal energy are formulated in terms of 'primitive'
pressure-velocity variables. Closure of these time-averaged,
elliptic equations is obtained via transport equations for both
the turbulence kinetic energy and its dissipation rate. The
high-level code solves the difference equations for a
predetermined size, staggered grid in an iterative 'line-by-line'
manner using a guess-and-correct procedure.
An 'intermediate-level' computer code (the ROOM-CHT program)
has also been developed for the above purpose, which employs
'informed" estimates of the flow and thermal field based on the
known mean flow properties of wall-jets. The corresponding heat
transfer distribution across the room surface is calculated using
wall-jet profile analysis or improved data correlations for
bucyancy-driven convection as appropriate.
Caqputations are presented for a room into which air is
injected through a low or high side wall register. The supply of
air governed by both cyclic and modulating control was examined.
The intermediate-level code is advocated as being the most
appropriate for meeting the requirements of dynamic building
thermal models. This code was verified by comparison with the
high-level code and with experimental measurements. The oomputed
heat transfer coefficients from the intermediate-level code were
found to be in good agreement with that of the high-level code.
Both indicate significantly higher values than those which would
be obtained from established design guides. These high values
suggest errors in building thermal models based on guide data,
including substantial under-estimation of preheat times
Exploratory dielectric study involving ultra-low content of Si-C-Al in epoxy
No full textBall milling was used to prepare a mixture of Silicon, Graphite and Aluminum, in equal proportion. X-ray analysis (XRD) confirmed that SiC was not produced in the present milling conditions. Aluminum was identified as being partially oxidized. The powder microstructure was found to be rather micrometric in size. Epoxy samples were casted using the Si-C-Al powder as an additive. Neat epoxy and a composite containing 0.1 wt% of the filler were prepared. A series of dielectric tests were performed in order to compare the behavior of neat and composite epoxy. Dielectric responses at 20°C were found to be very similar, whether the excitation field was low or high. However, erosion experiments have allowed to discriminate the performance of the samples, with a definite worsened resistance to discharges from the composite sample
Validation of Vectra 3D Imaging Systems: A Review
No full textAim: Three-dimensional facial imaging systems are a useful tool that is gradually replacing two-dimensional imaging and traditional anthropometry with calipers. In this varied and growing landscape of new devices, Canfield (Canfield Scientific, Parsippany, NJ, USA) has proposed a series of static and portable 3D imaging systems. The aim of this systematic review was to evaluate the current literature regarding the validation of Canfield’s Vectra imaging systems. Materials and Methods: A search strategy was developed on electronic databases including PubMed, Web of Science and Scopus by using specific keywords. After the study selection phase, a total of 10 articles were included in the present review. Results: A total of 10 articles were finally included in the present review. For six articles, we conducted a validation of the Vectra static devices, focusing especially on the Vectra M5, Vectra M3 and Vectra XT. For four articles, we validated the Vectra H1 portable system. Conclusions: All of the reviewed articles concluded that Canfield’s Vectra 3D imaging systems are capable of capturing accurate and reproducible stereophotogrammetric images. Minor errors were reported, particularly in the acquisition of the perioral region, but all the evaluated devices are considered to be valid and accurate tools for clinicians
The identification and analysis of the critical success factors of strategic airline alliances
No full textSince the beginning of the decade, the structure of the industry has been changing
rapidly as airlines from various parts of the world have been forming alliances. These
alliances transcend the traditional types of co-operation which have always existed in
the industry and constitute a strategy designed to give the partners a competitive edge.
However, many of these alliances are failing. This can be attributed to a poor
understanding of the managerial and operational characteristics of airline alliances.
This research attempts to correct this deficiency by identifying and analysing the
factors which are important to airline alliance success.
In order to set the background of the research, the various ways in which firms have
traditionally been linked are reviewed. The evolution of co-operation in the airline
industry in the US, Europe and Asia is traced and the forces which have driven airlines
to adopt the alliance strategy are identified. The various collaborative strategies of
airlines are described.
The definition of alliance success is critical to this research. Various definitions are
explored and the ones considered most appropriate for this study are taken as alliance
stability and alliance operational performance. The issues to be considered in ensuring
airline alliance stability are qualitatively analysed. Among the most important ones are
a pragmatic and careful approach in the formation process of the alliance, an
understanding of the relationship between the partners with particular importance given
to commitment and the generation of trust, and recognition of the evolutionary process
of alliances as the priorities of the partners change over time.
The operational objectives of airline alliances are identified and classified as either
market-related or production-related. Market-related objectives include economies of
scope and density, and market power. Alliance performance is mathematically
modelled using linear and logit regression techniques. The results of the analyses point
to the following: network size and network complementarity, network integration,connection quality, the type of flight (on-line, code-shared or interline) and alliance
frequency of service as important alliance success factors. The reaction of competitors
is also found to determine the benefits of airline collaboration.
On the production side, the objective of allying is to decrease unit costs and increase
efficiency by combining certain operational areas. A case study of Austrian Airlines is
performed to identify the cost and productivity areas which have benefited from
alliance formation. Graphical analysis shows that benefits were reaped mostly in the
areas of labour productivity and aircraft utilisation. This implies that these are the areas
which should be targeted when making use of the alliance strategy. Unit costs were not
found to be greatly affected by alliance formation
Performance evaluation of mixed metal oxide anodes for zinc electrowinning
No full textL'adoption d'anodes revêtues d'oxyde métallique mixte (MMO) dans les cuves d'extraction électrolytique de zinc permettrait réduire la consommation énergétique et résoudre les problèmes opérationnels liés à la corrosion des anodes de plomb. Néanmoins, c'est préoccupant que tels anodes MMO disponibles commercialement pourraient être avariés prématurément dans les électrolytes de zinc habituels, en raison d'être sujets à une déposition intense de MnO₂. Dans un tel contexte, ce projet a étudié la relation que la concentration de Mn²⁺ dans l'électrolyte de zinc affecte les caractéristiques des dépôts de MnO₂ et, par conséquent, l'intégrité de trois types d'anodes MMO à base de IrO₂. A cet effet, une évaluation exploratoire a été réalisée pour suivre les potentiels anodiques et les taux de formation de MnO₂ à moyen terme, en fonction de la concentration de Mn²⁺. Ensuite, la microscopie électronique à balayage (MEB) et la spectroscopie à rayons X à dispersion d'énergie (EDS) ont été utilisées pour caractériser les anodes après des tests de polarisation galvanostatique de 72 heures à différents concentrations de Mn²⁺. Les résultats ont suggéré que les dépôts de MnO₂ développent des morphologies différentes et induisent des différents processus de détérioration des anodes, en fonction de la concentration de Mn²⁺ et du type d'anode. En particulier, les anodes de type «D» ont été recouverts de films de MnO₂ qui s'écaillaient facilement à partir d'une épaisseur critique, produisant ainsi des contraintes induites. D'après des images par MEB, tels morceaux de MnO₂ détachés ont emporté des fragments du revêtement MMO adhérés en dessous. D'ailleurs, des agglomérats de cristallites allongées de MnO₂ se sont formés sur les anodes «E» et «F», ce qui a déclenché des ruptures dans leur revêtements MMO. À partir des résultats obtenus et de certains critères pour la détermination des niveaux de tolérance à Mn²⁺ de chaque type d'anode, une analyse financière a été proposée pour cribler le type d'anode le plus approprié pour la production de zinc, en fonction de son potentiel et également de la stratégie de contrôle de manganèse nécessaire à son fonctionnement adéquat.The adoption of Mixed Metal Oxide (MMO)-coated anodes in zinc electrowinning cellhouses would provide energy savings and resolve operational issues related to lead corrosion by-products. But a major concern is that commercially available MMO anodes could deteriorate prematurely in typical zinc electrolytes, due to intense MnO₂ deposition. In this context, the present study investigated the relationship that Mn²⁺ concentration in zinc electrolytes affects the characteristics of MnO₂ deposits and, consequently, the integrity of three types of IrO₂-bearing MMO anodes. For this purpose, firstly, an exploratory anode performance assessment was conducted to monitor the anode potentials and the MnO₂ formation rates in the medium term, as a function of Mn²⁺ concentration. Then, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the anode samples after 72-hour galvanostatic polarization tests at different Mn²⁺ concentrations. The results have suggested that MnO₂ deposits developed different morphologies and induced different anode deterioration processes, depending on the Mn²⁺ concentration and the anode type. In particular, anodes type "D" were covered by MnO₂ films that would easily chip off after reaching a critical thickness, thus producing induced stresses. According to SEM images, these MnO₂ pieces detached take out MMO coating fragments adhered to them. Meanwhile, MnO₂ clusters of elongated crystallites developed over anodes "E" and "F", and they were found to induce ruptures throughout the MMO coatings. Considering these results and specific criteria to define the Mn²⁺ tolerance levels of these anodes, a financial analysis was proposed for screening the most suitable anode type for industrial use, based on both the anodic potential demonstrated and the manganese control strategy required for its satisfactory operation
Leadership and organisation as a function of the different prevailing professional cultures
No full textThe following research project develops leadership and organisational structures that are in
accordance with the requirements created by different professional backgrounds.
In order to do, that the theoretical construct Professional Culture is introduced. This construct
unites the whole set of values, convictions and behavioural patterns that evolve within a
common professional background.
Further, Professional Culture is put into relation to its peer constructs of National and
Organisational Culture.
In a subsequent step, the different Professional Cultures and their characteristics are identified
and appropriate leadership and organisational structures are proposed. This is undertaken with
the help of an extensive empirical study and a broad literature review leading to the inclusion
of a significant theoretical base into the study. In particular the so-called GLOBE-Study
proved to be beneficial.
The methodology used is based on both a quantitative and a qualitative approach in order to
gain the maximum amount and quality of data possible. This methodology was employed in
both a significant pilot study and the main study. The surveyed sample itself is composed of
196 respondents for the pilot study and 507 respondents from various organisations and
countries for the main study which gives the study a sound empirical base.
In total, twelve different Professional Cultures are isolated and characterised. These
Professional Cultures include a vast variety of different occupations, stretching from Blue
Collar Workers to Executive Management.
An example for the differences in requirements encountered is the appropriate leadership style
for blue collar workers and the one for executive management. Whereas the fon-ner explicitly
favour a more steering and guiding leadership style, the latter prefer and need fteedom and
inspiration by their leaders.
Finally, a cross-evaluation is undertaken in order to validate the insights gained in the course
of the research project.
In summary, the following study gives a comprehensive overview of a number of different
Professional Cultures and their characteristics
,
including their corresponding leadership and
organisational structures
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