1,720,968 research outputs found
Aircraft crown compartment thermal management: the influence of internal heat dissipating elements
No full textThe content of this thesis describes the interaction of internal heat dissipating
elements with their heated enclosure with the applied case of a crown compartment
in a single aisle commercial aircraft. The crown compartment is defined as
the confined area between the passenger cabin and the upper external fuselage.
Aircraft compartments are subject to a wide variety of boundary conditions during
operation which leads to the setting up of highly complex internal thermal
environments. These compartments require strict thermal management to ensure
safe and reliable operation of the installed systems.
The work conducted firstly examines the fundamental fluid flow and natural
convection heat transfer inside a differentially heated square cavity with a centrally
located heated horizontal cylinder. There is a distinct lack of information
available in literature which focuses on the change in heat transfer experienced by
the cylinder due to the interaction with the enclosure. An increase in the cylinder
heat transfer is observed due to this interaction. Experimental thermocouple and
PIV measurements confirmed the presence of a transition process whereby the
flow transitions from being dominated by the temperature difference across the
cavity to that dominated by the temperature difference due to the cylinder for
the range 2 ×104 < Racyl < 8 ×104.
A similar investigation was then conducted for the crown compartment. A
study of the unpopulated case, i.e. no internal heat dissipating elements, for the
range 323.15K Tfus 378.15K revealed a stratified high temperature region
in the upper area and a low temperature forced flow region in the bottom of the
compartment due to the cabin ventilation system entering the crown.
With the inclusion of representative heat dissipating elements, namely the
SEPDC avionic system and Route G electrical conduit, the populated compartment
flow and thermal fields become dominated by the SEPDC, and no transition
process, as found for the square cavity, was observed. Design of Experiments and
regression analysis techniques, combined with numerical and experimental testing,
resulted in the generation of thermal models capable of predicting the heat
transfer of the surfaces of the elements with the average differences between the
predictions and experiments ranging from 7.24 - 26.38%. The optimal placement
of the elements, from a thermal management point of view, were found to be
when they are positioned as close to the crown floor as possible where they come
in contact with the forced convective cooling flow from the inlet, and when they
are positioned towards the centreline of the compartment where the hot buoyant
air does not become trapped between the elements and the fuselage insulation.
The methodology employed allows aircraft thermal engineers to optimise equipment
placement in all compartments during the design phase of an aircraft. The
determined models can be included in the global aircraft numerical models to improve
accuracy and reduce model size and computation time. This in turn reduces
the need for expensive physical testing and redesign, which inevitably results in
delays to aircraft development time
Aircraft crown compartment thermal management: the influence of internal heat dissipating elements
No full textThe content of this thesis describes the interaction of internal heat dissipating
elements with their heated enclosure with the applied case of a crown compartment
in a single aisle commercial aircraft. The crown compartment is defined as
the confined area between the passenger cabin and the upper external fuselage.
Aircraft compartments are subject to a wide variety of boundary conditions during
operation which leads to the setting up of highly complex internal thermal
environments. These compartments require strict thermal management to ensure
safe and reliable operation of the installed systems.
The work conducted firstly examines the fundamental fluid flow and natural
convection heat transfer inside a differentially heated square cavity with a centrally
located heated horizontal cylinder. There is a distinct lack of information
available in literature which focuses on the change in heat transfer experienced by
the cylinder due to the interaction with the enclosure. An increase in the cylinder
heat transfer is observed due to this interaction. Experimental thermocouple and
PIV measurements confirmed the presence of a transition process whereby the
flow transitions from being dominated by the temperature difference across the
cavity to that dominated by the temperature difference due to the cylinder for
the range 2 ×104 < Racyl < 8 ×104.
A similar investigation was then conducted for the crown compartment. A
study of the unpopulated case, i.e. no internal heat dissipating elements, for the
range 323.15K Tfus 378.15K revealed a stratified high temperature region
in the upper area and a low temperature forced flow region in the bottom of the
compartment due to the cabin ventilation system entering the crown.
With the inclusion of representative heat dissipating elements, namely the
SEPDC avionic system and Route G electrical conduit, the populated compartment
flow and thermal fields become dominated by the SEPDC, and no transition
process, as found for the square cavity, was observed. Design of Experiments and
regression analysis techniques, combined with numerical and experimental testing,
resulted in the generation of thermal models capable of predicting the heat
transfer of the surfaces of the elements with the average differences between the
predictions and experiments ranging from 7.24 - 26.38%. The optimal placement
of the elements, from a thermal management point of view, were found to be
when they are positioned as close to the crown floor as possible where they come
in contact with the forced convective cooling flow from the inlet, and when they
are positioned towards the centreline of the compartment where the hot buoyant
air does not become trapped between the elements and the fuselage insulation.
The methodology employed allows aircraft thermal engineers to optimise equipment
placement in all compartments during the design phase of an aircraft. The
determined models can be included in the global aircraft numerical models to improve
accuracy and reduce model size and computation time. This in turn reduces
the need for expensive physical testing and redesign, which inevitably results in
delays to aircraft development time
Thermodynamic analysis of a heat engine: experiments with the Stirling cycle
No full textThis paper presents a practical thermodynamic analysis of a desktop Stirling engine to demonstrate some of the fundamental principles involving the conversion of heat to work as part of an introductory undergraduate course. Experimental measurements of temperature, pressure and volume using an Arduino microcontroller allows for the construction of P-ν and T-s process diagrams from thermodynamic relationships. By comparing the quantitative data from actual and ideal cycles, the Stirling engine represents an effective teaching tool for reinforcing core content with students.</p
The effect of wind on the optimal design and performance of a modular air-cooled condenser for a concentrated solar power plant
No full textAir-cooled condensers overcome one of the main issues facing the construction of concentrated solar power plants by replacing water with air as the medium for cooling of the steam turbine waste heat. The recent development of modular air-cooled condensers as an improvement on conventional designs means that the effect of wind on their performance needs to be quantified. This study examines these effects by numerically modelling the condenser at the system level and using the results to build a mathematical model to predict the optimal condenser configuration. These types of mathematical models can be easily used by a power plant designer to quickly predict what the performance of the power plant will be based on the condenser geometry using data from numerical models of appropriate size and boundary conditions. The designer can then make a trade-off between the plant performance and initial capital costs in commissioning the power plant.
It has been found that when trying to optimise the performance, the historical wind condition distributions for a specific location should be used as significantly different condenser designs and orientations are required at different locations due to these distributions of local wind conditions.ACCEPTEDpeer-reviewe
Experimental and numerical analysis of thermally dissipating equipment in an aircraft confined compartment
No full textAircraft confined compartments are subject to a wide range of boundary conditions during operation which leads to the setting up of complex internal thermal environments. These compartments require strict thermal management to ensure safe and reliable operation of installed systems. This work investigates the thermal and fluid flow fields in one such compartment the crown area in a fuselage of a commercial aircraft which contains thermally dissipating equipment. Experimental heat transfer and Ply measurements are compared to 3D numerical simulations and are shown to be in very good agreement. There was found to be significant thermal stratification present due to the ventilation not penetrating into the bulk of the fluid. Convective heat transfer coefficients on the surfaces of the dissipating equipment varied as a function of their location, with the highest values occurring when they are placed close to the ventilation inlet. An enthalpic correction was applied to 2D simulations leading to significantly reduced solution times, and results which give a good approximation of the 3D model results.This type of detailed study of aircraft confined compartments is necessary to improve understanding of the flow regimes present in these areas, and leads to optimal positioning of installed systems in terms of thermal management, as well improving global thermal aircraft model predictions.ACCEPTEDpeer-reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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