Dissertations / Theses on the topic 'Duct wall'
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1
Slabaugh, Carson. "HEAT TRANSFER AUGMENTATION IN A NARROW RECTANGULAR DUCT WITH DIMPLES APPLIED TO A SINGLE WALL." Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2172.
Abstract:
Establishing a clean and renewable energy supply is the preeminent engineering challenge of our time. Turbines, in some form, are responsible for more than 98 percent of all electricity generated in the United State and 100 percent of commercial and military air transport. The operation of these engines is clearly responsible for significant consumption of hydrocarbon fuels and, in turn, emission of green house gases into the atmosphere. With such wide-scale implementation, it is understood that even the smallest increase in the operating efficiency of these machines can lead to enormous improvements over the current energy situation. These effects can extend from a reduction in the emission of greenhouse gases to lessening the nation s dependence of foreign energy sources to lower energy prices for the consumer. The prominent means of increasing engine efficiency is by raising the  Turbine Inlet Temperature  the temperature of the mainstream flow after combustion, entering the first stage of the turbine section. The challenge is presented when these temperatures are forced beyond the allowable limits of the materials inside the machine. In order to protect these components, active cooling and protection methods are employed. The focus of this work is the development of more efficient means of cooling  hot turbine components. In doing so, the goal is to maximize the amount of heat removed by the coolant while minimizing the coolant mass flow rate: by removing a greater amount of heat with a lower coolant mass flow rate, more compressed air is left in the mainstream gas flow for combustion and power generation. This study is an investigation of the heat transfer augmentation through the fully-developed portion of a narrow rectangular duct (AR=2) characterized by the application of dimples to the bottom wall of the channel. Experimental testing and numerical modeling is performed for full support and validation of presented findings. The geometries are studied at channel Reynolds numbers of 20000, 30000, and 40000. The purpose is to understand the contribution of dimple geometries in the formation of flow structures that improve the advection of heat away from the channel walls. Experimental data reported includes the local and Nusselt number augmentation of the channel walls and the overall friction augmentation throughout the length of the duct. Computational results validate local Nusselt number results from experiments, in addition to providing further insight to local flow physics causing the observed surface phenomena. By contributing to a clearer understanding of the effects produced by these geometries, the development of more effective channel-cooling designs can be achieved.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering MSME
2
Krishnan, Vaidyanathan. "The nature of Turbulence in a Narrow Apex Angle Isosceles Triangular Duct." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3811.
Abstract:
An experimental investigation was performed to ascertain the nature of turbulence in a narrow apex angle isosceles triangular duct. The study involved the design and construction of a low noise, low turbulence wind tunnel that had an isosceles triangular test section with an apex angle of 11.5[degrees]. Experiments involved the measurement of velocity fluctuations using hot wire anemometry and wall pressure fluctuations using a condenser microphone. Measurement of the velocity fluctuations reconfirms the coexistence of laminar and turbulent regions at a given cross section for a range of Reynolds numbers. The laminar region is concentrated closer to the apex while the turbulent region is found closer to the base. The point of transition is a function of the Reynolds number and moves closer to the apex as the flow rate is increased. Moreover, it was found in this investigation that traditional scaling of the turbulent statistical quantities do not hold good in this geometry. Although velocity fluctuations showed distinctive flow regimes, no such distinction could be seen in the dynamic wall pressure data. The nature of the dynamic wall pressure was uniform throughout the entire cross section suggesting that wall pressure fluctuations, unlike the velocity fluctuations, are able to travel from the base to the apex, without being damped. This implies that the relationship between the velocity and the pressure fluctuations applicable in the other systems does not hold well in a narrow apex angle isosceles triangular duct. Further, the typical scaling relationships applied to wall pressure spectra of other geometries doesn't apply in this scenario and the ratio of the RMS pressure fluctuation to the mean shear is much higher compared to a flat plate or pipe flow situation.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering PhD
3
He, Long. "A Study of Immersed Boundary Method in a Ribbed Duct for the Internal Cooling of Turbine Blades." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78069.
Abstract:
In this dissertation, Immersed Boundary Method (IBM) is evaluated in ribbed duct geometries to show the potential of simulating complex geometry with a simple structured grid. IBM is first investigated in well-accepted benchmark cases: channel flow and pipe flow with circular cross-section. IBM captures all the flow features with very good accuracy in these two cases. Then a two side ribbed duct geometry is test using IBM at Reynolds number of 20,000 under fully developed assumption. The IBM results agrees well with body conforming grid predictions. A one side ribbed duct geometry is also tested at a bulk Reynolds number of 1.5⨉10⁴. Three cases have been examined for this geometry: a stationary case; a case of positive rotation at a rotation number (Ro=ΩDₕ/U) of 0.3 (destabilizing); and a case of negative rotation at Ro= -0.3 (stabilizing). Time averaged mean, turbulent quantities are presented, together with heat transfer. The overall good agreement between IBM, BCG and experimental results suggests that IBM is a promising method to apply to complex blade geometries. Due to the disadvantage of IBM that it requires large amount of cells to resolve the boundary near the immersed surface, wall modeled LES (WMLES) is evaluated in the final part of this thesis. WMLES is used for simulating turbulent flow in a developing staggered ribbed U-bend duct. Three cases have been tested at a bulk Reynolds number of 10⁵: a stationary case; a positive rotation case at a rotation number Ro=0.2; and a negative rotation case at Ro=-0.2. Coriolis force effects are included in the calculation to evaluate the wall model under the influence of these effects which are known to affect shear layer turbulence production on the leading and trailing sides of the duct. Wall model LES prediction shows good agreement with experimental data.Master of Science
4
Kandindi, Muteba. "Heat transfer and pressure drop investigation for prescribed heat fluxes on both the inner and outer wall of the annular duct." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61299.
Abstract:
Heat exchangers are used in industrial processes to recover heat between two
processes fluids and are widely used. Although the equations for heat transfer and
pressure drop characteristics in a double pipe heat exchangers are available, there is
still need to completely understand how these characteristics interact which
geometrical factors like annular diameter ratio or some thermal boundaries conditions
which have not yet drawn more attention from the research community.
The purpose of this study was to experimentally measure the heat transfer and
pressure drop characteristics of a concentric annular duct of ratio 0.593 for different
heat fluxes simultaneously on the inner and outer tube in the turbulent flow regime
and to describe or discuss the impact or interaction of heat flux ratios on the flow and
heat transfer behaviour.
An experimental set]up was designed to achieve this goal. It consisted of an overall
facility and a removable test section. The test section allowed for the measurement of
the temperature along the length of the test section, the pressure drop, the heat flux
inputs and the flow rate. These quantities were used to determine the heat transfer
coefficients and friction factors of the!system.
The concentric duct was an annulus formed of a single (15.88]mm]outer diameter and
14.46]mm]inner diameter) copper tube inserted inside a 0.91mm] thick] copper tube of
26.76 mm of inner diameter. The overall length of the annular duct was 4.84 m. To
transfer heat, a heating element made of constantan wire was wrapped around each
heat transfer area.
Heat transfer and pressure drop data were obtained on heating the inner and the outer
wall separately with four different heat flux densities and eight heat flux ratio were
used for the case of simultaneously heating both walls. Reynolds numbers for
unilateral heating range from 5800 to 12 000 while bilateral heating were focus around
two Reynolds numbers, 6 500 and 9 500.
Satisfactory results were found between the measurements of this experiment and
currently available literature for the case of unilateral heating. An estimate of the
accuracy of the experimental setup showed the maximum relative error was about 5 %
in the determination of the Nusselt number and 1.8 % for the friction factor.
Diabatic friction factors have been presented using adiabatic friction factors with a
correction term which considered the effect of temperature difference between the
fluid and walls. Heat flux density ratio showed to have an impact on the heat transfer
characteristics. The Nusselt number on the inner wall could be enhanced by 19% with
increasing the heat flux ratio up to 2.3 times.Dissertation (MSc)--University of Pretoria, 2016.
Mechanical and Aeronautical Engineering
MSc
Unrestricted
5
Myers, Jeremy. "Computational Fluid Dynamics in a Terminal Alveolated Bronchiole Duct with Expanding Walls: Proof-of-Concept in OpenFOAM." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/5011.
Abstract:
Mathematical Biology has found recent success applying Computational Fluid Dynamics (CFD) to model airflow in the human lung. Detailed modeling of flow patterns in the alveoli, where the oxygen-carbon dioxide gas exchange occurs, has provided data that is useful in treating illnesses and designing drug-delivery systems. Unfortunately, many CFD software packages have high licensing fees that are out of reach for independent researchers. This thesis uses three open-source software packages, Gmsh, OpenFOAM, and ParaView, to design a mesh, create a simulation, and visualize the results of an idealized terminal alveolar sac model. This model successfully demonstrates that OpenFOAM can be used to model airflow in the acinar region of the lung under biologically relevant conditions.
6
Jamois, Alexis. "Modélisation et réalisation d'absorbants acoustiques par impression 3D : étude en incidence normale et application au traitement d'un conduit." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0010.
Abstract:
Au cours des dernières années, il est devenu possible de réaliser des absorbants acoustiques dont la géométrie était difficile à produire auparavant, grâce au perfectionnement des techniques d’impression 3D. La facilité d’utilisation et les prix abordables de ces techniques permettent d’imaginer la conception de dispositifs absorbants sur mesure pour répondre à une demande spécifique très rapidement. Cela nécessite d’une part de pouvoir imprimer précisément les géométries conçues et d’autre part de pouvoir prédire la performance acoustique des matériaux imprimés dans la configuration souhaitée. Les objectifs de cette thèse sont d’étudier l’effet de la variabilité des dimensions d’échantillons produits par impression 3D sur la performance acoustique et d’examiner différentes méthodes pour prédire la performance acoustique allant d’approches microscopiques complètes mais coûteuses, à des approches macroscopiques rapides mais simplifiées. La stéréolithographie a été choisie pour imprimer les échantillons à la suite d’une revue des moyens d’impression évalués dans la littérature. Les géométries étudiées consistent en un empilement de volumes (sphériques ou cubiques), reliés dans les trois directions de l’espace par des canaux à l’image de cristaux cubiques. Une variante à double réseau permet également d’ouvrir quelques pistes en vue d’une optimisation des performances acoustiques. Pour étudier l’effet de la variabilité, un grand nombre d’échantillons a été fabriqué avec différents jeux de paramètres d’impression et les dimensions caractéristiques des échantillons produits ont été mesurées. Un choix judicieux des paramètres permet de réduire la dispersion. La pertinence d’une approche fluide équivalent est montrée : elle permet de reproduire fidèlement et à coût réduit les résultats d’une approche directe résolvant les équations de Navier-Stokes linéarisées dans les pores des échantillons. Dans cette approche, les paramètres JCAPL des fonctions du fluide équivalent sont identifiés à partir d’un volume élémentaire représentatif de l’échantillon. Les échantillons sont d’abord étudiés en incidence normale. Le caractère très résonnant des matériaux rend le coefficient d’absorption très sensible à tout écart entre les dimensions cibles et les dimensions effectivement réalisées. Il en est ainsi pour les dimensions intérieures (diamètre des sphères ou des canaux) et pour le diamètre propre de l’échantillon. La nature rigide des échantillons produits par impression 3D rend très délicate leur adaptation stricte au diamètre du tube de Kundt. Les résultats de la mesure et les prédictions sont cependant globalement en bon accord et confirment dans ce cas classiquement traité dans la littérature, la validité du modèle de fluide équivalent. Des échantillons ont été ensuite réalisés spécifiquement pour être testés en paroi de conduit, par mesure de la perte par transmission. Les résultats expérimentaux confirment là aussi la pertinence de l’utilisation de l’approche fluide équivalent pour prédire les performances de ce type de matériau dans des conditions moins classiquesConventional rigid porous materials such as wools or foams do not provide effective absorption at low frequencies in complex industrial environments. For these applications, the structures developed are generally quarter-wave resonators or Helmholtz resonators. In recent years, 3D printing techniques have made it possible to produce resonator geometries that were previously difficult to produce. The ease of use and affordability of these techniques means that it is now possible to create tailor-made absorbing devices to meet specific requirements very quickly. This long-term objective requires, on the one hand, validation of the reliability of the dimensions obtained during the production of absorbent structures and, on the other hand, the ability to effectively model a variety of geometries in different contexts. In this thesis, stereolithography was chosen to print the samples based on literature results. Studies have concluded that it is more accurate for acoustic devices than other techniques. The geometry chosen for this study consists in a stack of volumes (spherical or cubic), connected in the three directions of space by channels in the image of cubic crystals. A large number of samples were manufactured varying the production parameters in order to measure the variability of the characteristic dimensions of the samples. Among the various modelling approaches presented, the numerical tests carried out led to the choice of equivalent fluid modelling based on the identification of JCAPL parameters. They are identified in a representative volume homogenised throughout the sample. This homogenisation of behaviour is suited to the geometries studied because of their periodic nature. The reaction of the geometries we are considering makes impedance modelling impossible. The samples are first studied at normal incidence, in order to link the variability of realisation to the measured acoustic behaviour. The measurement results and the predictions are in good agreement. Some samples were made specifically for duct wall measurement, in order to validate the use of the equivalent fluid approach. These tests were also used to confirm the conclusions drawn for normal incidence. The variability of the geometry has a real impact on the acoustic behaviour, but the main problem with rigid 3D printed samples is their adaptation to the measurement benches
7
AIT, ALDJET BOUHADEF KHEDIDJA. "Evaporation d'eau entre plaques parallèles humides sous l'effet d'un écoulement d'air en convection forcée : application à l'évaluation des transferts couplés de chaleur et de masse." Poitiers, 1988. http://www.theses.fr/1988POIT2009.
Abstract:
Le modele theorique est vase sur la resolution des equations couplees de transport-diffusion de masse et de chaleur, au sein du fluide en ecoulement, pour un regime de couches limites laminaires bidimensionnelles stationnaires. Le couplage des deux problemes thermique et massique est realise par l'intermediaire des conditions parietales. Des correlations sont etablies entre le coefficient de transfert de masse et les parametres adimensionnels caracterisant le probleme. Des performances d'evaporation, suivant les debits d'air et les conditions d'entree imposees, en decoulent. Des resultats experimentaux detailles, sur l'exploration des champs de vitesses, temperatures, et humidites locales, sont ensuite presentes pour les deux cas de regime: laminaire et turbulent. Les coefficients d'echange massique, local et global sont egalement evalues
8
Eames, Ian. "Displacement of material by a solid body moving away from a wall." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362975.
9
Walgode, Vitor. "Analysis and design of rectangular ducts with thin walls." Thesis, The University of Sydney, 1992. https://hdl.handle.net/2123/26742.
Abstract:
The objective of this research project, is to investigate if the current design practice of rectangular ducts with thin walls is adequate and if it can be improved. In order to achieve this goal, the following steps were taken:
1. Investigation of the available background research relevant to this topic.
2. Development of a finite element analysis model representative of the duct behaviour
for the cases in which the most suitable theories have a preponderant experimental
basis, taking in consideration the limitations of the available software (MSC/fAL 2).
3. Evaluation of the possibility of design improvement based on the previous work.
10
Sebastian, Robin. "Numerical simulation of acoustic propagation in a turbulent channel flow with an acoustic liner." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2297/document.
Abstract:
Les matériaux absorbants acoustiques, qui sont d’un intérêt stratégique en aéronautique pour la diminution passive du bruit des réacteurs d’avion, conduisent à une physique complexe où l’écoulement turbulent, des ondes acoustiques, et l’absorbant interagissent. Cette thèse porte sur la simulation de cette interaction dans le problème modèle d’un écoulement de canal turbulent avec des parois impédantes, par le biais de simulations numériques aux grandes échelles implicites, dans un contexte de calcul haute performance.Une étude est d’abord faite des grandes échelles dans un canal turbulent avec des parois rigides, en s’intéressant plus particulièrement à l’effet d’une faible compressibilité (Mach <3) sur les caractéristiques de ces échelles.Un canal turbulent avec une paroi de type impédance est ensuite simulé, avec une condition habituelle de périodicité dans le sens de l’écoulement. On observe que pour des faibles valeurs de la résistance et des fréquences de résonance basses, l’écoulement est instable, ce qui engendre une onde le long de l’absorbant, qui modifie la turbulence et augmente la trainée.Enfin, on se tourne vers une simulation de canal spatial en levant la condition de périodicité dans la direction de l’écoulement, ce qui permet d’introduire une onde acoustique en entrée de domaine. L’atténuation de l’onde dans l’écoulement turbulent est étudiée avec des parois rigides, puis un absorbant acoustique est introduit. Dans cette configuration plus réaliste, il est confirmé que l’écoulement peut devenir instable au bord amont de l’absorbant, ce qui empêche l’atténuation de l’onde acoustique incidenteAcoustic liners are a key technology in aeronautics for the passive reduction of the noise generated by aircraft engines. They are employed in a complex flow scenario in which the acoustic waves, the turbulent flow, and the acoustic liner are interacting.During this thesis, in a context of high performance computing, a compressible Navier-Stokes solver has been developed to perform implicit large eddy simulations of a model problem of this interaction: a turbulent plane channel flow with one wall modeled as an impedance condition.As a preliminary step the wall-turbulence in rigid channel flows and associated large-scale motions are investigated. A straightforward algorithm to detect these flow features is developed and the effect of compressibility on the flow structures and their contribution to the drag are studied. Then, the interaction between the acoustic liner and turbulent flow is investigated assuming periodicity in the streamwise direction. It is shown that low resistance and low resonance frequency tend to trigger flow instability, which modifies the conventional wall-turbulence and also results in drag increase.Finally, the simulation of a spatial channel flow was addressed. In this case no periodicity is assumed and an acoustic wave can be injected at the inlet of the domain. The effect of turbulence on sound attenuation is studied without liner, before a liner is introduced on a part of the channel bottom wall. In this more realistic case, it is confirmed that low resistance acoustic liners trigger an instability at the leading edge of the liner, resulting in drag increase and excess noise generation
11
Gottmann, Matthias 1964. "Local wall shear stress and interface behavior of adiabatic air-water flows in rectangular ducts." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282445.
Abstract:
An experiment was designed and built to study vertical annular air-water flows in a channel with a rectangular cross section with no heat transfer. Flush-wire electrical conductivity probes were theoretically analyzed to demonstrate their potential to accurately measure liquid film thickness in the experiment with high temporal and spatial resolution. Flush-wire probes were then successfully implemented and film thickness measurements obtained. From theoretical analysis, the suitability of micromachined hot film and floating element wall shear stress sensors for measurements of wall shear stress in the annular flow was investigated. A microfabricated hot film wall shear stress sensor was subsequently packaged and installed in the experiment, where it provided wall shear stress measurements with high temporal and spatial resolution. After the implementation of these new measurement techniques, a large suite of test cases was run and data for film thickness and wall shear stress acquired. A statistical analysis of the film thickness data indicates the existence of two distinct wave regimes, ripple waves and disturbance waves, within the annular flow regime. Spectral decomposition of film thickness and wall shear stress data demonstrates the existence of dominant frequencies in the wave spectrum and an exponential decay of wave amplitudes at high frequencies indicative of a force balance between capillary and momentum forces. Wave velocities were determined from cross correlations which again provided evidence of different types of waves each with different wave velocities and spatial extensions. A semi-analytical model for wave velocities as a function of superficial Reynolds numbers was validated and improved. The improved model gives an accurate prediction for wave velocities and is based on physical arguments representing the appropriate length scales in annular flow. The experimental results and data analysis provide a new perspective of annular two-phase flows in a channel with a rectangular cross section.
12
Sebastian, Robin. "Numerical simulation of acoustic propagation in a turbulent channel flow with an acoustic liner." Electronic Thesis or Diss., Poitiers, 2018. http://www.theses.fr/2018POIT2297.
Abstract:
Les matériaux absorbants acoustiques, qui sont d’un intérêt stratégique en aéronautique pour la diminution passive du bruit des réacteurs d’avion, conduisent à une physique complexe où l’écoulement turbulent, des ondes acoustiques, et l’absorbant interagissent. Cette thèse porte sur la simulation de cette interaction dans le problème modèle d’un écoulement de canal turbulent avec des parois impédantes, par le biais de simulations numériques aux grandes échelles implicites, dans un contexte de calcul haute performance.Une étude est d’abord faite des grandes échelles dans un canal turbulent avec des parois rigides, en s’intéressant plus particulièrement à l’effet d’une faible compressibilité (Mach <3) sur les caractéristiques de ces échelles.Un canal turbulent avec une paroi de type impédance est ensuite simulé, avec une condition habituelle de périodicité dans le sens de l’écoulement. On observe que pour des faibles valeurs de la résistance et des fréquences de résonance basses, l’écoulement est instable, ce qui engendre une onde le long de l’absorbant, qui modifie la turbulence et augmente la trainée.Enfin, on se tourne vers une simulation de canal spatial en levant la condition de périodicité dans la direction de l’écoulement, ce qui permet d’introduire une onde acoustique en entrée de domaine. L’atténuation de l’onde dans l’écoulement turbulent est étudiée avec des parois rigides, puis un absorbant acoustique est introduit. Dans cette configuration plus réaliste, il est confirmé que l’écoulement peut devenir instable au bord amont de l’absorbant, ce qui empêche l’atténuation de l’onde acoustique incidenteAcoustic liners are a key technology in aeronautics for the passive reduction of the noise generated by aircraft engines. They are employed in a complex flow scenario in which the acoustic waves, the turbulent flow, and the acoustic liner are interacting.During this thesis, in a context of high performance computing, a compressible Navier-Stokes solver has been developed to perform implicit large eddy simulations of a model problem of this interaction: a turbulent plane channel flow with one wall modeled as an impedance condition.As a preliminary step the wall-turbulence in rigid channel flows and associated large-scale motions are investigated. A straightforward algorithm to detect these flow features is developed and the effect of compressibility on the flow structures and their contribution to the drag are studied. Then, the interaction between the acoustic liner and turbulent flow is investigated assuming periodicity in the streamwise direction. It is shown that low resistance and low resonance frequency tend to trigger flow instability, which modifies the conventional wall-turbulence and also results in drag increase.Finally, the simulation of a spatial channel flow was addressed. In this case no periodicity is assumed and an acoustic wave can be injected at the inlet of the domain. The effect of turbulence on sound attenuation is studied without liner, before a liner is introduced on a part of the channel bottom wall. In this more realistic case, it is confirmed that low resistance acoustic liners trigger an instability at the leading edge of the liner, resulting in drag increase and excess noise generation
13
Hussmo, Daniel. "Dammhantering vid väggsågning." Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Produktutveckling, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-35033.
Abstract:
Vid väggsågning i betong uppkommer det mycket damm. Detta damm tas till viss del upp av det vatten som appliceras för att kyla klingan under sågning, vilket leder till en så kallad slurry. Slurryn samt dammet behöver efter avklarad sågning tas upp vilket resulterar i extra arbetsmoment för brukaren av sågen. Det största problemet här är dock det damm som inandas vilket kan leda till sjukdomar såsom silikos. Dessa sjukdomar kommer i framtiden antagligen leda till nya lagkrav kring hur dammet behöver tas hand om innan brukaren kan andas in det. Syftet med studien har därmed varit att utreda hur damm och slurry kan tas upp vid väggsågning. Problemet med väggsågning gentemot andra former av bearbetning i betong har varit svårigheten att täta av gentemot ytan som bearbetning sker i. I fallen med borrning är det tillexempel möjligt att sluta av området och skapa undertryck som då suger upp damm och slurry. För att ge en grund till konceptframtagning utfördes en observation av väggsågning för att skapa förståelse för hur dammet och slurryn beter sig under sågning. Vidare utfördes även en fallstudie för att samla data gällande hur problemet löses idag samt samla punkter från industrin gällande vilka egenskaper lösningen bör ha för att anses som attraktiv i håltagningsindustrin. Utifrån den insamlade empirin genererades koncept med hjälp av brainstorming samt morfologi. Dessa utvärderades sedan med Husqvarna samt med hjälp av Pughs matris där kriterierna för sållningen togs utifrån fallstudiens resultat. Resultatet här blev en pådragsenhet som fäster i klingskyddets befintliga geometrier och tar upp damm och slurry vid den punkt i klingskyddet där den största delen av damm och slurry koncentreras vid sågning. Efter sållningen togs en prototyp fram för att kunna verifiera att damm och slurry kunde tas upp samt för att mäta dess effektivitet. Resultatet av prototyptestet var att konceptet kunde ta upp cirka 23% av slurryn samt markant reducera det synliga dammet. Konceptet kunde därmed anses uppfylla studiens syfte, speciellt gällande dammet då dess skadliga effekter på så sätt kan reduceras.Wall sawing in concrete generates a lot of dust. The dust is partly collected by the water that is applied as a coolant for the blade, which leads to a mixture called ”slurry”. The slurry as well as the dust needs to be removed after the sawing has been completed, which adds extra steps to the process for the user of the saw. The biggest issue here is the dust that is inhaled by the user, which can lead to diseases such as silicosis . This will probably lead to new regulations regarding how dust is managed, which has been the background of this thesis. The purpose of this study is therefore to evaluate how dust and slurry can be collected during wall sawing. The problem in wall sawing compared to other forms of processing of concrete is the difficulty in creating a seal towards the surface where the processing is being executed. It is for instance easier to create a sealed space around the are of processing during drilling where you can create a vacuum to collect the dust and slurry. An observation was conducted in order to give a basis for how the dust and slurry is acting during sawing. A case study was also executed to gather data regarding how the problem is solved today in the industry as well as to provide intel regarding important attributes that concepts must have in order to be considered attractive to the industry. Concepts were generated with the collected data as a base through brainstorming and morphology. The concepts were evaluated together with Husqvarna as well as with pugh’s matrix, where the set of criterias had been collected from the case study. The result was a slide on unit that locks to existing geometries and collects dust and slurry at the point where the biggest concentration is achieved during sawing. After the evaluation, a prototype was constructed in order to verify that dust and slurry could be collected and to measure the efficiency of the concept. The result of the test was that the prototype could collect approximately 23% of the slurry as well as significantly reduce the amount of visible dust. The concept could thereby fulfil the purpose of the study, especially regarding the decreasion of dust since the harmful effects of inhalation could be reduced.
14
Candanedo, Ibarra José A. "Time-mean wall static pressure distributions and module friction factors for spatially periodic fully developed flows in interrupted-plate rectangular ducts." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80002.
Abstract:
An experimental study of spatially periodic fully developed flows of air in straight rectangular ducts with interrupted-plate inserts is presented. These flows have features similar to those produced in plate-fin passages of compact heat exchanger cores. The formulation of mathematical models and numerical solution methods for the prediction of these flows continues to be a challenging and largely unattained goal. The main goal of this work is to contribute experimental results suitable for testing and refining such models and solution methods. Airflows in nine different interrupted-plate rectangular ducts were considered. Reynolds numbers considered (based on Kays and London's definition of hydraulic diameter and the maximum average streamwise velocity) ranged from about 2,000 to 65,000. Time-mean static pressure distributions along the axial centreline of the top wall of the ducts, and module friction factor versus Reynolds number data, all in the spatially periodic fully developed region, were obtained.
15
Gorin, S. Steven. "Control of the effects of wind, sand, and dust by the citadel walls, in Chan Chan, Peru." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53698.
Abstract:
Chan Chan, the prehistoric capital of the Chimu culture (ca. A.D. 900 to 1450), is located in the Moche Valley close to the Pacific Ocean on the North Coast of Peru. Its sandy desert environment is dominated by the dry onshore turbulent and gusty winds from the south. The nucleus of this large urban community built of adobe is visually and spatially dominated by 10 monumental rectilinear high walled citadels that were thought to be the domain of the rulers. The form and function of these immense citadels has been an enigma for scholars since their discovery by the Spanish ca. 1535. Previous efforts to explain the citadels and the walls have emphasized the social, political, and economic needs of the culture. The use of the citadels to control the effects of the wind, sand, and dust in the valley had not been previously considered.
Through the use of theoretical constructions and wind tunnel experiments, it is established that the form of the classic variant of the citadel was developed from a longtime interaction between the man—built environment and the natural environment. The Chimu had designed a courtyard system that reduced stress and discomfort from wind, sand, and dust by means of architectural features that included: the rectilinear citadel plan with the long axis parallel to the prevailing winds; the contiguous courtyards with the long axis in common; the high exterior walls; the high interior transverse walls; and the triangular cross section of the walls. It is demonstrated that these features kept out the blowing sand, reduced the wind speeds at pedestrian level, and kept dust, entrained in the airstream by the anthropogenic activity outside the walls, from entering the enclosures. It is also demonstrated that there is a correlation between the degree of protection afforded in a sector of the citadel and the social, political, and economic activities that took place in that sector.PH. D.
16
Chovet, Rogelio. "Caractérisation expérimentale et numérique du comportement rhéologique d'un fluide complexe : application à une mousse en écoulement dans un canal horizontal droit avec et sans singularités." Thesis, Valenciennes, 2015. http://www.theses.fr/2015VALE0021/document.
Abstract:
Ce travail porte sur l’étude expérimentale et numérique de l’écoulement des mousses humides dans un canal horizontal droit de section carrée avec ou sans singularités. Il est consacré tout particulièrement à déterminer les paramètres pertinents de l’écoulement dont la chute de pression longitudinale, les champs de vitesse de l’écoulement de mousse en proche parois, les épaisseurs de films liquides minces et épais en paroi et l’évolution de la contrainte pariétale pour une mousse humide dont la fraction gazeuse varie de 55 à 85% et la vitesse débitante de la mousse est 2, 4 puis 6 cm/s. Une fois ces paramètres déterminés en conduite horizontale droite, nous avons ensuite effectué des mesures sur différentes géométries représentant un élargissement brusque, une chicane verticale et écoulement de mousse autour d’un cylindre, dont le but est d’étudier la réorganisation de l’écoulement en vue de déterminer le comportement rhéologique des mousses en écoulement à l’aval et à l’amont des singularités. Finalement, une étude de simulation numérique (CFD) en utilisant les lois de comportement de type Bingham, pour fluides non newtoniens, a été effectuée afin de tester sa capacité de représenter des écoulements type mousse humide dans une conduite horizontale avec ou sans singularités. Nous avons vérifié tout d’abord l’évolution longitudinale de la pression statique qui est linéaire à l’amont comme à l’aval loin des zones influencées par les singularités. La chute de pression singulière reste à peu près constante pour une vitesse débitante donnée de la mousse. À partir de la technique de Vélocimétrie par Image de Particule (PIV), nous avons déterminé les composantes de vitesse au voisinage immédiat des singularités. Ces mesures nous ont permis de mettre en évidence l’existence de différents régimes d’écoulement, et de déterminer la réorganisation et le comportement rhéologique de l’écoulement de mousse autour des géométries étudiées. L’analyse des mesures d’épaisseur de films liquides, obtenues par la méthode conductimétrique, indique que la paroi reste mouillée par un film liquide suffisamment épais pour qu’on puisse appliquer la méthode électrochimique. Les signaux polarographiques obtenus avec la mousse présentent alors de fortes fluctuations. La comparaison de celles-ci avec les contraintes pariétales déduites à partir des mesures de la chute de pression montre bien une bonne concordance. L’étude numérique (CFD), effectuée pour une fraction volumique de gaz égale à 70% et qui s’écoule avec une vitesse débitante de 2 cm/s, montre que le modèle rhéologique de Bingham pourrait être bien adapté à ce genre de mousse humide évoluant en écoulement en blocThis work is an experimental and numerical study of aqueous foam flow inside a horizontal square duct, with and without flow disruption devices (fdd). It is especially devoted to determine the pertinent parameters of the flow: longitudinal pressure losses, velocity fields of foam flow near the walls, liquid film thickness (thick and thin), and the wall shear stress evolution, for an aqueous foam with a void fraction range between 55 and 85%, for a mean foam flow velocity of 2, 4 and 6 cm/s. Once they were determined, inside the horizontal channel, we carried out measurements over different geometries: half-sudden expansion, vertical fence and foam flow around a cylinder. The goal was to study the foam flow reorganization to well understand the rheological behavior of aqueous foam flow in the vicinities of different fdd. Finally, a numerical simulation (CFD), using the Bingham behavior model of non-Newtonian fluid, was undertaken to test its capacity to represent the aqueous foam flow inside the horizontal duct with flow disruption devices. First of all, we verified the static longitudinal pressure evolution, which varies linearly upstream and downstream far from the fdd. The singular pressure loss remains constant for a given mean foam velocity and a foam quality (void fraction). From the Particle Imaging Velocimetry (PIV) technique (2D), we determined the two velocity components in the immediate vicinities of the disruption devices. They allowed us to put into evidence the different foam flow regimes and to observe the foam flow reorganization and rheological behavior through the studied fdd. The slip-layer thickness analysis, obtained using the conductimetry method, shows that the wall presents a liquid film thick enough to apply an electrochemical technique (polarography). Thus, the polarographic signals, obtained for the foam flow, present important fluctuations. They were compared to the wall shear stress deducted from the measurement of pressure losses, showing a good similarity between them. The numerical study (CFD), carried out for aqueous foam flow with a void fraction of 70% and a mean foam flow velocity of 2 cm/s, shows that the Bingham rheological model can be adapted to this kind of aqueous foam flow which is flowing like a block
17
Weckmann, Armin. "Material migration in tokamaks: Studies of deposition processes and characterisation of dust particles." Licentiate thesis, KTH, Fusionsplasmafysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-178026.
Abstract:
Thermonuclear fusion may become an attractive future power source. The most promising of all fusion machine concepts is the tokamak. Despite decades of active research, still huge tasks remain before a fusion power plant can go online. One of these important tasks deals with the interaction between the fusion plasma and the reactor wall. This work focuses on how eroded wall materials of different origin and mass are transported in a tokamak device. Element transport can be examined by injection of certain species of unique and predetermined origin, so called tracers. Tracer experiments were conducted at the TEXTOR tokamak before its final shutdown. This offered an unique opportunity for studies of the wall and other internal components: For the first time it was possible to completely dismantle such a machine and analyse every single part of reactor wall, obtaining a detailed pattern of material migration. Main focus of this work is on the high-Z metals tungsten and molybdenum, which were introduced by WF6 and MoF6 injection into the TEXTOR tokamak in several material migration experiments. It is shown that Mo and W migrate in a similar way around the tokamak and that Mo can be used as tracer for W transport. It is further shown how other materials - medium-Z (Ni), low-Z (N-15 and F), fuel species (D) - migrate and get deposited. Finally, the outcome of dust sampling studies is discussed. It is shown that dust appearance and composition depends on origin, formation conditions and that it can originate even from remote systems like the NBI system. Furthermore, metal splashes and droplets have been found, some of them clearly indicating boiling processes.QC 20151203
18
Dutt, Anne J. [Verfasser], and Hans-Werner [Akademischer Betreuer] Wahl. "Subjective Aging Experiences and Negative Affectivity: Examination of Fundamental Associations and of Underlying Pathways / Anne Josephine Dutt ; Betreuer: Hans-Werner Wahl." Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177385473/34.
19
Saad, Tony. "Theoretical Models for Wall Injected Duct Flows." 2010. http://trace.tennessee.edu/utk_graddiss/748.
Abstract:
This dissertation is concerned with the mathematical modeling of the flow in a porous cylinder with a focus on applications to solid rocket motors. After discussing the historical development and major contributions to the understanding of wall injected flows, we present an inviscid rotational model for solid and hybrid rockets with arbitrary headwall injection. Then, we address the problem of pressure integration and find that for a given divergence free velocity field, unless the vorticity transport equation is identically satisfied, one cannot find an analytic expression for the pressure by direct integration of the Navier-Stokes equations. This is followed by the application of a variational procedure to seek novel solutions with varying levels of kinetic energies. These are found to cover a wide spectrum of admissible motions ranging from purely irrotational to highly rotational fields. Subsequently, a second law analysis as well as an extension of Kelvin's energy theorem to open boundaries are presented to verify and corroborate the variational model. Finally, the focus is shifted to address the problem of laminar viscous flow in a porous cylinder with regressing walls. This is tackled using two different analytical techniques, namely, perturbation and decomposition. Comparisons with numerical Runge--Kutta solutions are also provided for a variety of wall Reynolds numbers and wall regression speeds.
20
Hwa, Chang Shu, and 張淑華. "Study on the Wall Vibration Produced by the Acoustic Propagation through a Duct." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/32417943484507369127.
Abstract:
碩士國立臺灣大學
造船及海洋工程學研究所
89
This study is mainly intended to the determination on the wall vibration of duct, which is produced by the acoustic wave propagation through it. Therefore, the sound pressure in a steel duct is measured first. And then regarding the result as the required excited force to the other ducts else. Furthermore, some thin-shell ducts with materials iron, aluminum and plastics are selected to be the elastic ducts for this study. In the mean time, the resulting vibration for each elastic duct is calculated when excited by the same acoustic field as that obtained from the case for steel duct. From the viewpoint of energy conservation, the energy loss of an actual duct while in vibration due to its internal damping must equal the difference of acoustic power output at entrance from that at exit. Two acoustic power outputs can be measured by sound intensity method. The result as obtained clearly shows the predicted vibrations of elastic ducts are quite agreeable with that of measurement. Thereafter, the empirical formula developed from energy loss viewpoint can be used in some acceptable accuracy to predict the vibration of duct when acoustic waves propagate through it at low frequency. Upon the assumption as above, the law of energy conservation tells that the acoustic energy difference of the acoustic power of source from that at the exit of duct must equal the damping power efflux produced by the duct vibration. Therefore in mathematical expression, if we let the damping force of duct wall be equal to , the related damping power efflux will be , where U is the velocity amplitude, and . So forth the conservation of acoustic energy shows: where are, respectively, the acoustic intensities at source and exit. r, L are the radius and length of duct respectively. Since for single frequency sound, the amplitude A of wall vibration can be obtained as:
21
Chen, Tsung-Chih, and 陳宗志. "Active Control on the Acoustic Fields in Duct Using the Wall-Vibration Induced Acoustic Sources." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/78329946878278244270.
Abstract:
碩士國立臺灣大學
工程科學及海洋工程學研究所
97
There are two techniques in noise control,which are passive and active noise control.This thesis is to provide another approach to active noise control(ANC).It is to use a piezoelectric transducer(PZT) to excite the duct wall.The wall-vibration induced feedback sound wave can combine with primary noise to reduce the downstream sound pressure.Accordingly,only a duct and a piezoelectric tr- ansducer are wanted in this approach.Thus the cost and the space required for the apparatus to be wanted are saved much more. In experiment,we use a FIR digital filter as the main structure of the control system and meanwhile take a single-frequency or a dual-frequency signal as the reference input directly produced by a function generator.Weighting coefficients of the digital filter are adjusted by using LMS algorithm in order to achieve the best performance.Besides,the sound radiation by vibrating an infinite cylindrical shell will be analyzed. The result of this study shows great attenuation of downstream sound pressure level by about 40 dB will be obtained at some frequencies.Similar situation occurs for dual frequencies at which greater radiation from duct wall exists,the attenuation of downstream sound pressure levels by about 15~35dB is obtained.The actuality as discussed can demonstrate it is feasible to use wall-vibration induced source to adaptively active control on the sound transmissi- on in a circular duct.
22
You, Chuan-bei, and 游川倍. "Experimental Study on the Performance of Sudden Expansion Silencer with Inner Baffle-Wall and Connnecting Duct." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/88445846136011392701.
Abstract:
碩士國立中興大學
機械工程學系
86
This study investigates the performance of sudden expansion silencer with internal baffle-wall and connecting duct in relation to some design parameters. Such parameters are the length and the asymmetry of input and output ducts, the length and height of the connecting duct as well as the porosity ratio. The inflow frequency ranges from 10Hz to 120Hz. The evaluation is based on the magnitude of pressure variation within and sound level measurement downstream of the silencer . Frequency responses of both pressure variation and the sound level are coincident for frequency lower than 100Hz. However, deviation arises for frequency higher than 100Hz because of the presence of small scale eddy in the exhaust jet. Large porosity ratio can eliminates the noise level at low frequency range. Noise reduction is significant while the internal baffle-wall is inserted. Besides, the longer the connecting duct, the more reduction of the sound level. The height of the connecting duct determines the passage of energy at lower frequency. Thus, small height of the connecting duct can reduce effectively the sound level at low frequency range, and vice versa. Furthermore, longer inlet duct can increase the sound level at frequency higher than 100Hz. On the other hand, the longer outlet duct will decrease the resonant frequency of the flow tone inside the silencer. In the limiting case of no tail duct, the resonant frequency locates beyond 120Hz and the sound level is high within 00z In gnraly, h betperormne o nis reutio ca e atane ifthe veticl bfle-al i intlle isie teasymeti siener Beies, smaller eghtofth conctig uc an uitblelngt o te ilt ad utet ducts cn hlp olocteth reoantfreuncyofth flwton inie tesilencer Hihporsiy ati an lsob faoabl torduc te oun eve atlow frquecyrage.Keyword: suden xpnson iencr、aflewal Bconctig duc、orsit ati
23
Chen, Jiann Liang, and 陳建良. "Experimental Study of Convective Heat Transfer in a Radially Rotating Square Duct with Uniform Wall Heat Flux and Inward Flow." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/80870383751185376599.
24
Rodrigues, Sylvie Vaz. "Calibração de sondas do tipo Irwin em condições de gradiente de pressão nulo." Master's thesis, 2016. http://hdl.handle.net/10316/38832.
Abstract:
Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.O principal objetivo deste trabalho é a calibração de sondas do tipo Irwin (1980) quando utilizadas em condições de gradiente pressão nulo. De modo a atingir este objetivo, foram realizados ensaios laboratoriais utilizando uma conduta de secção transversal rectangular, com cinco metros de comprimento, acoplada a um ventilador radial, onde foram colocadas sondas de pressão estática e as sondas de tensão parietal. Esta conduta tem como particularidade um tecto móvel que permite configurar diversas relações largura- altura (L:H). Testaram-se diversos caudais de ar, variando a área de obstrução do ventilador. Registou-se a distribuição de pressão ao longo da conduta de modo a identificar a zona de escoamento desenvolvido, local onde são colocadas as sondas para calibração. Com base na queda de pressão, pode-se então determinar o fator de atrito e correspondente tensão parietal. De modo a poder relacionar o escoamento no interior de uma conduta rectangular com o escoamento no interior de condutas circular, foi utilizado um parâmetro característico chamado de diâmetro hidráulico, por forma a comparar os resultados de conduta rectangular com valores de condutas circulares. Utilizando como referência os valores de pressão, medidos nas tomadas de pressão estática, fez-se o cálculo da tensão parietal, e foram então calibradas as sondas para medição de tensão parietal relacionando a diferença de pressão, em cada sonda, com os valores de tensão parietal calculados. Os maiores desvios, em relação à tensão parietal medida, foram observados para os caudais mais baixos.
The main objective of this work is to calibrate type Irwin probes (1980) when used in zero gradient conditions. In order to achieve this objective laboratory tests were carried out using a rectangular cross section duct with five meters long, coupled to a radial fan, where were placed static pressure probes and wall shear stress probes. This duct has the particularity of a mobile roof that allows to configure various relations length-height (L: H). Several airflows rates were tested, by varying the fan blockage area. The pressure distribution along the duct was measured to identify the area of developed flow, where the probes are placed for calibration. Based on the pressure drop, were determined the corresponding friction factor and wall shear stress. In order to relate the flow within a rectangular duct with the flow inside circular ducts, a parameter called hydraulic diameter was used in order to compare the results of rectangular duct with circular ducts values. Using as reference pressure values measured in static pressure taps, the wall shear stress was calculated, and then were calibrated probes for wall shear stress measurement relating the pressure difference in each probe, to the wall shear stress values calculated. The largest deviation in relation to the measured wall shear stress has been observed to lower flowrates.
25
Whitelonis, Nicholas John 1984. "Investigation of high-frequency propagation channels through pipes and ducts for building interior reconnaissance." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5651.
Abstract:
Recently, there is strong interest in the through-wall sensing capabilities of radar for use in law enforcement, search and rescue, and urban military operations. Due to the high attenuation of walls, through-wall radar typically operates in the low GHz frequency region, where resolution is limited. It is worthwhile to explore other means of propagating radar waves into and back out of a building’s interior for sensing applications. One possibility is through duct-like structures that are commonly found in a building, such as metal pipes used for plumbing or air conditioning ducts. The objective of this dissertation is to investigate techniques to acquire radar images of targets through a pipe.
First, using the pipe as an electromagnetic propagation channel is studied. A modal approach previously developed for computing the radar cross-section of a circular duct is modified to compute the transmission through a pipe. This modal approach for transmission is validated against measured data. It is also shown that a pipe is a high-pass propagation channel. The modal analysis is then extended to two-way, through-pipe propagation for backscattering analysis. The backscattering from a target is observed through a pipe in simulation and measurement.
Next, methods to form two-dimensional radar images from backscattering data collected through a pipe are explored. Four different methods previously developed for free-space imaging are applied to the problem of imaging through a pipe: beamforming, matched filter processing, MUSIC, and compressed sensing. In all four methods it is necessary to take into account the propagation through the pipe in order to properly generate a focused radar image. Each method is demonstrated using simulation and validated against measurement data. The beamforming and matched filter methods are found to suffer from poor cross-range resolution. To improve resolution, the MUSIC algorithm is applied and shown to give superior resolution at the expense of more complicated data collection. The final method, compressed sensing, is shown to achieve good cross-range resolution with simpler data collection. A comparison of the tradeoffs between the four methods is summarized and discussed.
Two additional extensions are studied. First, a method for computing the transmission through an arbitrary pipe network using the generalized scattering matrix approach is proposed and implemented. Second, a new method for computing joint time-frequency distributions based on compressed sensing is applied to analyze the backscattering phenomenology from a pipe.text
26
Chiang, Yu Wei, and 蔣有為. "Experimental Study on Heat Transfer in Square Ducts with One- Porous-Wall Suction." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/06960831289873566200.
27
Cheng, Yaw Chung, and 鄭耀宗. "Theoretical and Experimental Study on Laminar Flow and Heat Transfer in One-Porous-Wall Ducts." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/24505119407195943575.
28
黃成瑋. "Numerical Calculations of Heat Transfer and Friction Characteristic in Rectangular Ducts with Slit and Solid Ribs Mounted on One Wall." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/33386057453239936113.
Abstract:
碩士國立成功大學
機械工程學系
88
This study presents the numerical calculation on turbulent heat transfer, fluid flow and friction characteristics comparison in rectangular ducts with slit ribs, solid ribs mounted on one wall and smooth duct. The turbulent governing equations are solved by a Control-Volume-based finite-difference method with power-law scheme and the well know k-εturbulence model and its associate wall function to describe the turbulent structure. The velocity and pressure terms of momentum equations are solved by SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) method. An orthogonal, non-uniform, staggered grids are used for the establishment of mesh grids. The parameters studied include the entrance flow Reynolds number (Re=8000、15000、33000、58000) and rib void fraction (b=0.211、0.307、0.489); whereas the rib height-to-duct hydraulic diameter is fixed at 0.167 (H/De=0.167) and the working medium is air. The flow field numerical calculations indicate that the flow patterns around the slit rib and solid rib are different due to the different transport phenomena and it also influences the heat transfer. At the same Reynolds number, the recirculation phenomena that existed behind the solid rib disappears in the corresponding region of the slit rib. Relative to solid rib duct, the slit rib has a lower friction factor owing to less duct blockage. As to the heat transfer effect, both the solid rib and slit rib walls enhanced the heat transfer as compared with the smooth duct, because both the solid rib or slit rib are the mechanisms of heat transfer augmentation. With greater turbulence-mixing effect, the slit-ribbed geometry provides better heat transfer than solid-ribbed geometry. In addition, the slit rib has a more significant fin effect than the solid rib due to its larger heat transfer surface area.
29
Sun, Yi-Shin, and 孫臆勛. "A Study on Stains on External Building Wall Due to Dust and Rainfall─Effects of Surface Roughness and Angle Factors." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/50716473072749017917.
Abstract:
碩士國立成功大學
建築學系碩博士班
90
The issue of building material’s durability has been taken seriously in recent years. The most noticeable among all kinds of deteriorations is the external building walls being soiled by its surrounding environmental factors, but it is always ignored. However, there is no standard test method available for accessing the dust pollution on external walls in Taiwan. The stain-resistance of wall materials can neither be quantitatively determined nor further analyzed. Thus several Japanese researches and standards were reviewed in this study in order to suggest an experimental method to observe the staining. It is expected to understand more about how the external wall materials are stained by dust and rainfall. The adhesion of dust to wall materials can be influenced by dozens of factors. The dirty surface flow and the cleansing ability of the rainfall can be influenced by many factors as well, including rainfall intensity and the contours of the external walls. Several important factors were selected for experiment according to an investigation and some literature. They are “angles” and “surface roughness” of the external wall panels. The result of the experiment tells that the way it stains differs with the angles and surface properties of the panels. The stains are more severe on flatter panels or rougher materials. The different degree of soiling can be attributed to the adhesion of dry dust, the cleansing ability of the rainfall, and the surface flow which brings dust or takes it off.