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Gotowa bibliografia na temat „Transitional channel flow”

Autor: Grafiati

Data publikacji: 6 września 2023

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Artykuły w czasopismach na temat "Transitional channel flow"

Hager, Willi H. "Transitional Flow in Channel Junctions". Journal of Hydraulic Engineering 115, nr 2 (luty 1989): 243–59. http://dx.doi.org/10.1061/(asce)0733-9429(1989)115:2(243).

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Kumar, Sampath G. "Transitional flow in channel junctions". Journal of Hydraulic Research 31, nr 5 (wrzesień 1993): 601–4. http://dx.doi.org/10.1080/00221689309498773.

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ELSNAB, J., J. KLEWICKI, D. MAYNES i T. AMEEL. "Mean dynamics of transitional channel flow". Journal of Fluid Mechanics 678 (3.05.2011): 451–81. http://dx.doi.org/10.1017/jfm.2011.120.

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The redistribution of mean momentum and vorticity, along with the mechanisms underlying these redistribution processes, is explored for post-laminar flow in fully developed, pressure driven, channel flow. These flows, generically referred to as transitional, include an instability stage and a nonlinear development stage. The central focus is on the nonlinear development stage. The present analyses use existing direct numerical simulation data sets, as well as recently reported high-resolution molecular tagging velocimetry measurements. Primary considerations stem from the emergence of the effects of turbulent inertia as represented by the Reynolds stress gradient in the mean differential statement of dynamics. The results describe the flow evolution following the formation of a non-zero Reynolds stress peak that is known to first arise near the critical layer of the most unstable disturbance. The positive and negative peaks in the Reynolds stress gradient profile are observed to undergo a relative movement toward both the wall and centreline for subsequent increases in Reynolds number. The Reynolds stress profiles are shown to almost immediately exhibit the same sequence of curvatures that exists in the fully turbulent regime. In the transitional regime, the outer inflection point in this profile physically indicates a localized zone within which the mean dynamics are dominated by inertia. These observations connect to recent theoretical findings for the fully turbulent regime, e.g. as described by Fife, Klewicki & Wei (J. Discrete Continuous Dyn. Syst., vol. 24, 2009, p. 781) and Klewicki, Fife & Wei (J. Fluid Mech., vol. 638, 2009, p. 73). In accord with momentum equation analyses at higher Reynolds number, the present observations provide evidence that a logarithmic mean velocity profile is most rapidly approximated on a sub-domain located between the zero in the Reynolds stress gradient (maximum in the Reynolds stress) and the outer region location of the maximal Reynolds stress gradient (inflection point in the Reynolds stress profile). Overall, the present findings provide evidence that the dynamical processes during the post-laminar regime and those operative in the high Reynolds number regime are connected and describable within a single theoretical framework.

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Manneville, Paul, i Masaki Shimizu. "Transitional Channel Flow: A Minimal Stochastic Model". Entropy 22, nr 12 (29.11.2020): 1348. http://dx.doi.org/10.3390/e22121348.

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In line with Pomeau’s conjecture about the relevance of directed percolation (DP) to turbulence onset/decay in wall-bounded flows, we propose a minimal stochastic model dedicated to the interpretation of the spatially intermittent regimes observed in channel flow before its return to laminar flow. Numerical simulations show that a regime with bands obliquely drifting in two stream-wise symmetrical directions bifurcates into an asymmetrical regime, before ultimately decaying to laminar flow. The model is expressed in terms of a probabilistic cellular automaton of evolving von Neumann neighborhoods with probabilities educed from a close examination of simulation results. It implements band propagation and the two main local processes: longitudinal splitting involving bands with the same orientation, and transversal splitting giving birth to a daughter band with an orientation opposite to that of its mother. The ultimate decay stage observed to display one-dimensional DP properties in a two-dimensional geometry is interpreted as resulting from the irrelevance of lateral spreading in the single-orientation regime. The model also reproduces the bifurcation restoring the symmetry upon variation of the probability attached to transversal splitting, which opens the way to a study of the critical properties of that bifurcation, in analogy with thermodynamic phase transitions.

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Sahan, R. A., H. Gunes i A. Liakopoulos. "A modeling approach to transitional channel flow". Computers & Fluids 27, nr 1 (styczeń 1998): 121–36. http://dx.doi.org/10.1016/s0045-7930(97)00016-9.

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Piomelli, Ugo, i Thomas A. Zang. "Large-eddy simulation of transitional channel flow". Computer Physics Communications 65, nr 1-3 (kwiecień 1991): 224–30. http://dx.doi.org/10.1016/0010-4655(91)90175-k.

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Kashyap, Pavan, Yohann Duguet i Olivier Dauchot. "Flow Statistics in the Transitional Regime of Plane Channel Flow". Entropy 22, nr 9 (8.09.2020): 1001. http://dx.doi.org/10.3390/e22091001.

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The transitional regime of plane channel flow is investigated above the transitional point below which turbulence is not sustained, using direct numerical simulation in large domains. Statistics of laminar-turbulent spatio-temporal intermittency are reported. The geometry of the pattern is first characterized, including statistics for the angles of the laminar-turbulent stripes observed in this regime, with a comparison to experiments. High-order statistics of the local and instantaneous bulk velocity, wall shear stress and turbulent kinetic energy are then provided. The distributions of the two former quantities have non-trivial shapes, characterized by a large kurtosis and/or skewness. Interestingly, we observe a strong linear correlation between their kurtosis and their skewness squared, which is usually reported at much higher Reynolds number in the fully turbulent regime.

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Zagarola, Mark V., Alexander J. Smits i George E. Karniadakis. "Heat transfer enhancement in a transitional channel flow". Journal of Wind Engineering and Industrial Aerodynamics 49, nr 1-3 (grudzień 1993): 257–67. http://dx.doi.org/10.1016/0167-6105(93)90021-f.

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He, S., i M. Seddighi. "Turbulence in transient channel flow". Journal of Fluid Mechanics 715 (9.01.2013): 60–102. http://dx.doi.org/10.1017/jfm.2012.498.

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AbstractDirect numerical simulations (DNS) are performed of a transient channel flow following a rapid increase of flow rate from an initially turbulent flow. It is shown that a low-Reynolds-number turbulent flow can undergo a process of transition that resembles the laminar–turbulent transition. In response to the rapid increase of flow rate, the flow does not progressively evolve from the initial turbulent structure to a new one, but undergoes a process involving three distinct phases (pre-transition, transition and fully turbulent) that are equivalent to the three regions of the boundary layer bypass transition, namely, the buffeted laminar flow, the intermittent flow and the fully turbulent flow regions. This transient channel flow represents an alternative bypass transition scenario to the free-stream-turbulence (FST) induced transition, whereby the initial flow serving as the disturbance is a low-Reynolds-number turbulent wall shear flow with pre-existing streaky structures. The flow nevertheless undergoes a ‘receptivity’ process during which the initial structures are modulated by a time-developing boundary layer, forming streaks of apparently specific favourable spacing (of about double the new boundary layer thickness) which are elongated streamwise during the pre-transitional period. The structures are stable and the flow is laminar-like initially; but later in the transitional phase, localized turbulent spots are generated which grow spatially, merge with each other and eventually occupy the entire wall surfaces when the flow becomes fully turbulent. It appears that the presence of the initial turbulent structures does not promote early transition when compared with boundary layer transition of similar FST intensity. New turbulent structures first appear at high wavenumbers extending into a lower-wavenumber spectrum later as turbulent spots grow and join together. In line with the transient energy growth theory, the maximum turbulent kinetic energy in the pre-transitional phase grows linearly but only in terms of ${u}^{\ensuremath{\prime} } $, whilst ${v}^{\ensuremath{\prime} } $ and ${w}^{\ensuremath{\prime} } $ remain essentially unchanged. The energy production and dissipation rates are very low at this stage despite the high level of ${u}^{\ensuremath{\prime} } $. The pressure–strain term remains unchanged at that time, but increases rapidly later during transition along with the generation of turbulent spots, hence providing an unambiguous measure for the onset of transition.

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Wirtz, R. A., i Weiming Chen. "Laminar-Transitional Convection From Repeated Ribs in a Channel". Journal of Electronic Packaging 114, nr 1 (1.03.1992): 29–34. http://dx.doi.org/10.1115/1.2905438.

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Velocimetry, heat transfer, and pressure drop experiments are reported for laminar/transitional air flow in a channel containing rectangular transverse ribs located along one channel wall. The geometry is intended to represent an array of low profile electronic packages. At fixed pumping power per unit channel volume, the heat transfer rate per unit volume is independent of rib-to-rib spacing and increases with decreasing wall-to-wall spacing. The fully developed, rib-average heat transfer coefficient is found to be linearly related to the maximum streamwise rms turbulence measured above the rib-tops. Linear correlations, in terms of a descriptor of the rms streamwise turbulence, are shown to unify heat transfer/pressure drop data for channels containing either two-or three-dimensional protrusions.

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Rozprawy doktorskie na temat "Transitional channel flow"

Vanyaza, Sydwell Luvo. "Non-newtonian open-channel flow : effect of shape on laminar and transitional flow". Thesis, Cape Technikon, 2004. http://hdl.handle.net/20.500.11838/874.

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Thesis (MTech (Chemical Engineering))--Cape Technikon, 2004
When designing the open channels to transport the homogenous non-Newtonian slurries, the effect of channel shape is one of the parameters that should be checked and very little research has been conducted to address this matter. Open channels are commonly applied in the mining industry where mine tailings have to be transported to the disposal dams at high concentrations to save water consumption. This thesis addresses the effect of the cross-sectional shape of the channel with emphasis on laminar and transitional flow of non-Newtonian fluids. The literature review on the flow of Newtonian and non-Newtonian fluids has been presented. The most relevant one to this topic is the work done by Straub et al (1958) for Newtonian fluids and the analytical work presented by Kozicki and Tiu (1967) for non-Newtonian fluids. Authors like Coussot (1994) and Haldenwang (2003) referred to their work but did not comprehensively verified it experimentally. Three flume shapes were designed to investigate this problem namely, rectangular, semi circular, and trapezoidal flume shape. The test rig consisted of a 10 m long by 300mm wide tilting flume that can be partitioned into two sections to form a 150 mm wide channel. All three flume shapes were tested in both the 150 mm and 300 mm wide flumes. This flume is linked to the in-line tube viscometer with three tube diameters namely, 13 mm; 28 mm; and 80 mm. The experimental investigation covered a wide range of flow rates (0.1-45l/s), and flume slopes (1-5 degrees). The fluids tested were kaolin suspension (5.4 - 9% v/v), CMC solution (1 - 4% m/m), and bentonite suspension (4.6 and 6.2% mlm). The models found in the literature were evaluated with the large database compiled from the test results to predict the laminar and transitional flow of these fluids with the aim of checking the effect of the cross-sectional shape of these channels selected in these flow regimes. For all the flume shapes and non-Newtonian fluids selected in this thesis it was found that in predicting the laminar flow, the effect of shape is adequately accounted for by the use of hydraulic radius. In predicting the transitional flow, it was found that the effect of shape does not have to be included.

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Hagan, J. "Nonlinear instabilities and transition to turbulence in magnetohydrodynamic channel flow". Thesis, Coventry University, 2013. http://curve.coventry.ac.uk/open/items/cc5976b0-419c-4944-a2ff-3af446a03d05/1.

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The present study is concerned with the stability of a flow of viscous conducting liquid driven by a pressure gradient between two parallel walls in the presence of a transverse magnetic field, which is investigated using a Chebyshev collocation method. This magnetohydrodynamic counterpart of the classic plane Poiseuille flow is generally known as Hartmann flow. Although the magnetic field has a strong stabilizing effect, the turbulence is known to set in this flow similarly to its hydrodynamic counterpart well below the threshold predicted by the linear stability theory. Such a nonlinear transition to turbulence is thought to be mediated by unstable equilibrium flow states which may exist in addition to the base flow. Firstly, the weakly nonlinear stability analysis carried out in this study shows that Hartmann flow is subcritically unstable to small finite-amplitude disturbances regardless of the magnetic field strength. Secondly, two-dimensional nonlinear travelling wave states are found to exist in Hartmann flow at substantially subcritical Reynolds numbers starting from Ren = 2939 without the magnetic field and from Ren ∼ 6.50 × 103Ha in a sufficiently strong magnetic field defined by the Hartmann number Ha. Although the latter value is by a factor of seven lower than the linear stability threshold Rel ∼ 4.83×104Ha and by almost a factor of two lower than the value predicted by the mean-field (monoharmonic) approximation, it is still more than an order of magnitude higher than the experimentally observed value for the onset of turbulence in this flow. Three-dimensional disturbances are expected to bifurcate from these two-dimensional travelling waves or infinity and to extend to significantly lower Reynolds numbers. The by-product of this study are two developments of numerical techniques for linear and weakly nonlinear stability analysis. Firstly, a simple technique for avoiding spurious eigenvalues is developed for the solution of the Orr-Sommerfeld equation. Secondly, an efficient numerical method for evaluating Landau coefficients which describe small amplitude states in the vicinity of the linear stability threshold is introduced. The method differs from the standard approach by applying the solvability condition to the discretised rather than the continuous problem.

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Kabwe, Christine Mahemba Wa. "Transitional flow of non-newtonian fluids in open channels of different shapes". Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/924.

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Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology
Open channels are widely used in the mining industries where homogeneous non-Newtonian slurries have to be transported around plants (Sanders et al., 2002). As water becomes scarcer and more costly due to legislative limitations, higher concentrations of slurries have to be transported. Very little work had been done to predict the laminar-turbulent transition flow of non-Newtonian fluids in open-channels. The effect of open channel on flow of non-Newtonian fluids in the transition region is not well understood. A systematic study on the effect of open channel shape on transitional flow for different non-Newtonian fluids has as far as can be ascertained not been conducted to date. This work investigated the effect of the channel cross-sectional shape on transitional flow of non-Newtonian fluids. There are a number of analytical and empirical methods available for the prediction of transitional flow in open channels. However, there are no conclusive guidelines in the literature that would predict the transitional flow for different shapes. A large experimental database for non-Newtonian flow produced by the Flow Process Research Centre at the Cape Peninsula University of Technology in rectangular, trapezoidal, semi-circular and triangular channels at slopes varying from 1° to 5° was used to achieve the objective. The test fluids consisted of bentonite and kaolin clay suspensions, and solutions of carboxymethyl cellulose (CMC) of various concentrations. The shear stress - shear rate behaviour of each test fluid was measured using in-line tube viscometry. To evaluate predictive models of transitional flow in various channel shapes, a comparison of critical actual velocities with models velocities was conducted for power law, Bingham plastic and yield-shear thinning fluids. After comparison of various models in different flume shapes, Haldenwang‟s critical Reynolds number for rectangular channels was deemed to be the best predictive model. To improve Haldenwang‟s critical Reynolds number, new correlations based on Haldenwang‟s (2003) method were developed for each shape studied and their corresponding critical velocities were compared. By combining all the transition data for the four shapes a new correlation “combined model” was developed for onset of transition and onset of full turbulence which can adequately accommodate the four different channel shapes for all fluids tested.

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Klinkenberg, Joy. "Stability analysis of channel flow laden with small particles". Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42271.

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This thesis deals with the stability of particle laden flows. Both modal and non-modal linear analyses have been performed on two-way coupled particleladen flows, where particles are considered spherical, solid and either heavy or light. When heavy particles are considered, only Stokes drag is used as interaction term. Light particles cannot be modeled with Stokes drag alone, therefore added mass and fluid acceleration are used as additional interaction forces. The modal analysis investigates the asymptotic behavior of disturbances on a base flow, in this thesis a pressure-driven plane channel flow. A critical Reynolds number is found for particle laden flows: heavy particles increase the critical Reynolds number compared to a clean fluid, when particles are not too small or too large. Neutrally buoyant particles, on the other hand, have no influence on the critical Reynolds number. Non-modal analysis investigates the transient growth of disturbances, before the subsequent exponential behavior takes over. We investigate the kinetic energy growth of a disturbance, which can grow two to three orders of magnitude for clean fluid channel flows. This transient growth is usually the phenomenon that causes transition to turbulence: the energy can grow such that secondary instabilities and turbulence occurs. The total kinetic energy of a flow increases when particles are added to the flow as a function of the particle mass fraction. But instead of only investigating the total energy growth, the non-modal analysis is expanded such that we can differentiate between fluid and particle energy growth. When only the fluid is considered in a particle-laden flow, the transient growth is equal to the transient growth of a clean fluid. Besides thes Stokes drag, added mass and fluid acceleration, this thesis also discusses the influence of the Basset history term. This term is often neglected in stability analyses due to its arguably weak effect, but also due to difficulties in implementation. To implement the term correctly, the history of the particle has to be known. To overcome this and obtain a tractable problem, the square root in the history term is approximated by an exponential. It is found that the history force as a small effect on the transient growth. Finally, Direct numerical simulations are performed for flows with heavy particles to investigate the influence of particles on secondary instabilities. The threshold energy for two routes to turbulence is considered to investigate whether the threshold energy changes when particles are included. We show that particles influence secondary instabilities and particles may delay transition.
QC 20111013

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Patrick, Wilfred Vinod. "Computations of Flow Structures and Heat Transfer in a Dimpled Channel at Low to Moderate Reynolds Number". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33415.

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Time-accurate calculations are used to investigate the three-dimensional flow structure and understand its influence on the heat transfer in a channel with concave indentations on one wall. A dimple depth to channel height ratio of 0.4 and dimple depth to imprint diameter ratio of 0.2 is used in the calculations. The Reynolds number (based on channel height) varies from Re = 25 in the laminar regime to Re = 2000 in the early turbulent regime. Fully developed flow and heat transfer conditions were assumed and a constant heat flux boundary condition was applied to the walls of the channel. In the laminar regime, the flow and heat transfer characteristics are dominated by the recirculation zones in the dimple with resulting augmentation ratios below unity. Flow transition is found to occur between Re = 1020 and 1130 after which both heat transfer and friction augmentation increase to values of 3.22 and 2.75, respectively, at Re = 2000. The presence of large scale vortical structures ejected from the dimple cavity dominate all aspects of the flow and heat transfer, not only on the dimpled surface but also on the smooth wall. In all cases the thermal efficiency using dimples was found to be significantly larger than other heat transfer augmentation techniques currently employed.
Master of Science

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Vujisić, Ljubomir B. (Ljubomir Branislav). "Heat transfer at transition to turbulence in channel flows with eddy promoters". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36499.

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Coumes, Thomas M. "Effects of 1 Hz imposed bulk flow unsteadiness on laminar/turbulent transition in a straight channel". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27012.

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Greco, Francis J. "Effects of 2 Hz imposed bulk flow unsteadiness on laminar/turbulent transition in a straight channel". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27013.

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Högberg, Markus. "Optimal Control of Boundary Layer Transition". Doctoral thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3245.

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Osman, Sohaib Mustafa Mohammed. "Experimental investigation into convective heat transfer in the transition flow regime by using nanofluids in a rectangular channel". Thesis, University of Pretoria, 2019. http://hdl.handle.net/2263/77873.

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The growing demand for energy worldwide requires attention to the design and operating of heat exchangers and thermal devices to utilise and save thermal energy. There is a need to find new heat transport fluids with better heat transfer properties to increase convective heat transfer, and nanofluids are good alternatives to conventional heat transport fluids. Although extensive research has been done on the properties of nanofluids in recent decades, there is still a lack of research on convection heat transfer involving nanofluids, particularly in the transitional flow regime. This study focused on the application of nanofluids in heat exchangers as heat transport fluids by investigating forced convective heat transfer of alumina-water and titanium dioxide-water nanofluids prepared by using the one-step method. The particle size used was 46 nm and 42 nm for the aluminium oxide and the titanium dioxide respectively. Uniform heat flux boundary conditions were used by uniformly heating the rectangular channel electrically. Nanofluids with volume concentrations of 0.3, 0.5 and 1% were used for the alumina-water nanofluids, and volume concentrations of 0.3, 0.5, 0.7 and 1% were used for the titanium dioxide-water nanofluids. The viscosity of the nanofluids under investigation was determined experimentally, while the thermal conductivity and other properties were predicted by using suitable correlations from the literature. A Reynolds number range of 200 to 7 000 was covered, and the investigated flow rates included the laminar and turbulent flow regimes, as well as the transition regime from laminar to turbulent flow. Temperatures and pressure drops were measured to evaluate heat transfer coefficients, Nusselt numbers and pressure drop coefficients. Heat transfer and hydrodynamic characteristics in the transition flow regime were carefully studied and compared with those in the transition regime when flowing pure water in the same test section. The study also investigated another approach of enhancing heat transfer in heat exchangers by increasing the heat transfer area of the heat exchanger itself, and this was done by filling the rectangular test section with porous media to increase the heat transfer surface area and thus enhance heat transfer. Hence in this study, the effect of using porous media was also studied by filling the rectangular test section with high-porosity nickel foam. The permeability of the used nickel foam was determined by conducting pressure drop measurements through the nickel foam in the test section, and heat transfer and pressure drop parameters were measured and compared with those in the empty test section. The results showed that all the nanofluids used enhanced heat transfer, particularly in the transition flow regime. The 1.0% volume concentration alumina nanofluid showed maximum enhancement of the heat transfer coefficient, with values of 54% and 11% in the turbulent regime. The maximum enhancement of the heat transfer coefficient was 29.3% in the transition regime for the 1.0% volume concentration titanium dioxide-water nanofluid. The thermal performance factor in the transition flow regime was observed to be better than that in the turbulent and laminar flow regimes for all the nanofluids. The results of the nickel foam test section showed that the values of the friction coefficient were 24.5 times higher than the values of the empty test section, and the Nusselt number was observed to be three times higher when using nickel foam than without foam in the test section. No transition regime was observed for the foam-filled test section on either the heat transfer results or the pressure drop results; however, transition from laminar to turbulent was found for the test section without foam. The results of the thermal factor of the foam-filled test section showed a thermal performance factor higher than unity through the entire Reynolds number range of 2 000 to 6 500, with better thermal performance factor at lower Reynolds number.
Thesis (PhD (Mechanics))--University of Pretoria, 2019.
Mechanical and Aeronautical Engineering
PhD (Mechanics)
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Książki na temat "Transitional channel flow"

Piomelli, Ugo. Large-eddy simulation of transitional channel flow. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1990.

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A, Zang Thomas, i Langley Research Center, red. Large-eddy simulation of transitional channel flow. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1990.

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A, Zang Thomas, i Langley Research Center, red. Large-eddy simulation of transitional channel flow. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1990.

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Gilbert, Norbert. Numerische Simulation der Transition von der laminaren in die turbulente Kanalstromung. Koln: DFVLR, 1988.

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Morkovin, Mark Vladimir. Recent insights into instability and transition to turbulence in open-flow systems. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1988.

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Krist, Steven E. Numerical simulation of channel flow transition: Resolution requirements and structure of the hairpin vortex. [Washington, D.C.]: National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1987.

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A, Zang Thomas, i United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch., red. Numerical simulation of channel flow transition: Resolution requirements and structure of the hairpin vortex. [Washington, D.C.]: National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1987.

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Greco, Francis J. Effects of 2 Hz imposed bulk flow unsteadiness on laminar/turbulent transition in a straight channel. Monterey, Calif: Naval Postgraduate School, 1989.

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Coumes, Thomas M. Effects of 1 Hz imposed bulk flow unsteadiness on laminar/turbulent transition in a straight channel. Monterey, Calif: Naval Postgraduate School, 1989.

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Yousuff, Hussaini M., i Institute for Computer Applications in Science and Engineering., red. Non-linear evolution of a second mode wave in supersonic boundary layers. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1989.

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Części książek na temat "Transitional channel flow"

Dinavahi, Surya Prasad G., i Thomas A. Zang. "Reynolds Stress Budget in a Transitional Channel Flow". W Instability, Transition, and Turbulence, 327–36. New York, NY: Springer New York, 1992. http://dx.doi.org/10.1007/978-1-4612-2956-8_32.

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Sandham, N. D. "A Model Equation for Transitional and Turbulent Plane Channel Flow". W Turbulent Shear Flows 8, 67–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-77674-8_6.

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Tsukahara, Takahiro, Yasuo Kawaguchi, Hiroshi Kawamura, Nils Tillmark i P. Henrik Alfredsson. "Turbulence stripe in transitional channel flow with/without system rotation". W Seventh IUTAM Symposium on Laminar-Turbulent Transition, 421–26. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-3723-7_68.

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Fiebig, M., W. Hahne i D. Weber. "Heat Transfer and Drag Augmentation of Multiple Rows of Winglet Vortex Generators in Transitional Channel Flow: A Comparison of Numerical and Experimental Methods". W Notes on Numerical Fluid Mechanics (NNFM), 88–94. Wiesbaden: Vieweg+Teubner Verlag, 1996. http://dx.doi.org/10.1007/978-3-322-89838-8_12.

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Finlay, W. H. "Wavy Vortices in Rotating Channel Flow". W Laminar-Turbulent Transition, 559–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84103-3_51.

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Bridges, Thomas J., i Alison J. Cooper. "Modulated Rolls in Rotating Channel Flow". W Transition, Turbulence and Combustion, 165–79. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1032-7_15.

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Goldshtik, M. A., A. M. Lifshits i V. N. Shtern. "Threshold Regimes in the Plane Channel Flow". W Laminar-Turbulent Transition, 191–98. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-82462-3_23.

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Müller, Ulrich, i Leo Bühler. "Flow transition and stability". W Magnetofluiddynamics in Channels and Containers, 107–31. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/978-3-662-04405-6_10.

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Cabal, A., J. Szumbarski i J. M. Floryan. "Stability of Poiseuille Flow in a Corrugated Channel". W Laminar-Turbulent Transition, 345–50. Berlin, Heidelberg: Springer Berlin Heidelberg, 2000. http://dx.doi.org/10.1007/978-3-662-03997-7_51.

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Gilbert, N., i L. Kleiser. "Subcritical Transition to Turbulence in Channel Flow". W Direct and Large Eddy Simulation of Turbulence, 1–18. Wiesbaden: Vieweg+Teubner Verlag, 1986. http://dx.doi.org/10.1007/978-3-663-00197-3_1.

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Streszczenia konferencji na temat "Transitional channel flow"

Guzma´n, Amador M., Tania A. Aracena, Felipe A. Urzua i Rodrigo A. Escobar. "Flow Bifurcations and Transition Scenarios in Confined Flows: Channel Geometry and Operational Parameter Dependency". W ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14292.

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We have performed numerical simulations of confined flows in both symmetric and asymmetric wavy channels to investigate the flow bifurcations and transition scenarios dependency on geometrical and operational parameters. Laminar and time-dependent transitional flow regimes are obtained by direct numerical simulations of the mass and momentum equations using a computational program based on the spectral element method. Computational meshes for periodic computational domains are used to determine the transitional flow behavior for increasing Reynolds numbers and changing geometrical parameters. For the asymmetric wavy channel, the transition scenarios are highly dependent on the aspect ratio of the channel geometrical parameters. Depending on a specific geometric aspect ratio—one of the control parameters, the following scenarios develop: a) a first transition scenario with one flow bifurcation to a relatively low Reynolds numbers, Rec; b) a second scenario, with also one flow bifurcation, to a relatively high Reynolds numbers, Rec*; and, c) a third flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively, similar to the Ruelle-Takens-Newhouse scenario. In this third scenario, fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from laminar to transitional flow regimes. For the symmetric wavy channel and a high aspect ratio of r=0.375, a transition scenario with one flow bifurcation develops to a critical Reynolds numbers Rec** leading to a periodic flow. Further increases in the Reynolds number leads to successive periodic flows where the fundamental frequency ω1, increases continuously, in a scenario of frequency-doubling.

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Hewawaduge, Dhanushki, i Armin Zare. "The effect of base flow uncertainty on transitional channel flows". W 2022 American Control Conference (ACC). IEEE, 2022. http://dx.doi.org/10.23919/acc53348.2022.9867704.

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Jayeola, Mathew, Sichao Tan, Shouxu Qiao, Ayodeji Ala i Fulgence Dione. "Characteristic Behavior of Flow Field in Blocked Fuel Assembly Flow Channel under Steady Flow Condition". W 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-91739.

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Abstract Past histories of fuel assembly blockage incidents had made investigation of flow channel blockage in rod bundle a compelling field of thermal-hydraulic safety. This study experimentally investigate flow field structural characteristics in a 5 × 5 rod bundle under two sub-channel blockages with geometries; 2 × 5 and 2 × 3, in a non-mixing spacer grid. The blockage effects on velocity distribution and turbulence characteristics is examined under laminar, transitional and turbulent flow regimes across a range of Reynolds number between 1108 ∼ 8103. Under laminar flow, result of spatiotemporal analysis for flow downstream of the blocked spacer grid-SP2, showed formation of a large symmetric vortex pair shedding in wake formed at both edges of the blockage. For transitional and turbulent flow, the vortex gradually dissipate especially towards the flow channel’s wall due to interference of friction effect. Damping effect of blockage on upward velocity flow and pressure in the vortex dominated region creates a backflow zones accompanied by flow reversal. Analysis of turbulence characteristics examined for 2 × 5 blockage across adjacent bundle gaps and sub-channels showed immense variations with Reynolds number and channel wall impact. The study aimed to provide relevant reference basis to compare and analyze similar scenario under unsteady flow condition.

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Kockmann, Norbert, Craig Holvey i Dominique M. Roberge. "Transitional Flow and Related Transport Phenomena in Complex Microchannels". W ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2009. http://dx.doi.org/10.1115/icnmm2009-82139.

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In microchannels with typical dimensions from 10 μm to few hundreds μm, the flow is dominated by viscous forces, leading often to laminar flow conditions. At the entrance or in bends and curves, where the flow is accelerated or changes its direction, inertial forces generate transverse flow velocities. Due to continuity, compensating transverse velocity components generate vortex pairs, such as Dean flow in circular bends. The flow is still laminar, steady, and shows no statistically distributed fluctuations typical for turbulent flow. This deviation from straight laminar conditions, often in larger channels (100 μm to few mm) or for higher flow rates, is called transitional flow. That embraces the first occurrence of pulsating vortices, period doubling of vortex pairs, flow bifurcation, and regularly fluctuating wake flow or vortex shedding. With increased flow velocity, this process leads to chaotic flow phenomena being first evidence of turbulence. This paper describes the transitional flow characteristics in single channel elements such as bends and T-junction as well as around fins and posts in channels. These elements are used to augment the transport characteristics in microchannels for enhanced heat and mass transfer and for performing chemical reactions in microreactors. The profound understanding of the flow characteristics is fundamental for the understanding of transport phenomena. Additionally, this knowledge can be used to design successful microstructured devices for various applications by knowing how to generate and control vortices in microchannels. Concepts from chaotic advection are presented here to describe vortex flow and related transport characteristics. Though recent advances has shed new light on transport phenomena in complex channel structures, many issues are still unknown and huge potential is hidden in optimized channel devices.

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Guzman, Amador M., Fernando A. Donoso i Alfonso Ortega. "Transition Scenarios Due to Flow Bifurcations in Asymmetric Wavy Channel Flows With Different Spatial Periodicity on the Sinusoidal Walls". W ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-66216.

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Numerical investigations of transition scenarios due to flow bifurcations from laminar to time-dependent transitional flows in asymmetric wavy channels with different spatial periodicity on the sinusoidal wall are performed by direct numerical simulations of the mass and momentum conservation equations using a spectral element method computational program. Three aspect ratios r = a/(2L) are considered in this study: 0.125, 0.25, y 0.375. Computational meshes for both extended and periodic computational domains are used to determine first, the existence of spatial periodicity and second, the transitional flow behavior for increasing Reynolds numbers. Numerical results shows that the transition scenarios are highly dependent on the aspect ratio, r. The following scenarios develop: a) a first transition scenario with one flow bifurcation to a relatively low Reynolds numbers, Rec; b) a second scenario, with also one flow bifurcation, to a relatively high Reynolds numbers, Rec*; and, c) a third flow transition scenario with two Hopf bifurcations B1 and B2, occurring at critical Reynolds numbers Rec1 y Rec2, respectively. In this third scenario, fundamental frequencies ω1 and ω2, and sub and super harmonic combinations of the fundamental frequencies develop as the Reynolds number increases from a laminar to higher transitional flow regime. This transition scenario from a laminar flow to high transitional flow regimes is very similar to the Ruelle-Takens-Newhouse (RTN) found in another confined flow channels such as symmetric wavy, grooved and communicating channels.

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Guzman, Amador M., Maximiliano P. Beiza i Paul F. Fischer. "Transition Scenario of Periodic and Quasiperiodic Flow Bifurcations in Symmetric Communicating Channels". W ASME/JSME 2007 5th Joint Fluids Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/fedsm2007-37359.

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The flow transition scenario in symmetric communicating channels has been investigated using direct numerical simulations of the mass and momentum conservation equations in the Reynolds numbers range of Re = [170–227]. The governing equations are solved for laminar and time-dependent transitional flow regimes by the spectral element method, using a periodic computational domain, for a periodic length of nL and an aspect ratio of r = aˆ / (2Lˆ) = 0.0405, where aˆ = 2a is the height of block within the channel, n an integer and Lˆ = L + 1 is the periodic length. Periodic computational domains with n = 1 and 2 are used in this investigation to determine the periodic length effect on the flow pattern characteristics. Numerical investigations with different domain meshes are carried out for determining the appropriate discretization for capturing transitional time-dependent flows. The numerical results show a transition scenario with two-flow Hopf bifurcations which develop as the pressure gradient is increased from a laminar to a time-dependent flow regime. The first Hopf bifurcation occurs to a critical Reynolds number of Rec1 and leads to a time-dependent periodic flow characterized by a fundamental frequency ω1. Further increases in the pressure gradient lead to successive quasi periodic flows after a second Hopf bifurcation B2 occurring to a critical Reynolds number Rec2 < Rec1, with two fundamental frequencies ω1 and ω2, and linear combinations of both frequencies—where the fundamental frequency ω1 increases continuously—and ω2 > ω1. This transition scenario is somewhat different from the Ruelle-Takens-Newhouse transition scenario obtained for symmetric wavy channels; in symmetric wavy channels, periodic and quasi periodic flow regimes develop as the Reynolds number increases. The friction factor for the symmetric communicating channel in the transitional regime is higher than the friction factor for the Poiseuille plane channel. The qualitative and quantitative behavior is compared to other channel geometries that also develop other transition scenarios.

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Hong, Chungpyo, Toru Yamada, Yutaka Asako, Mohammad Faghri, Koichi Suzuki i Ichiro Ueno. "Experimental Investigations of Laminar, Transitional to Turbulent Gas Flow in a Micro-Channel". W ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40254.

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This paper presents experimental results on flow characteristics of laminar, transitional to turbulent gas flows through micro-channels. The experiments were performed for three micro-channels. The micro-channels were etched into silicon wafers, capped with glass, and their hydraulic diameter are 69.48, 99.36 and 147.76 μm. The pressure was measured at seven locations along the channel length to determine local values of Mach number and friction factor for a wide range of flow regime from laminar to turbulent flow. Flow characteristics in transitional flow regime to turbulence were obtained. The result shows that f·Re is a function of Mach number and higher than incompressible value due to the compressibility effect. The values of f·Re were compared with f·Re correlations in available literature.

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Kaneko, Shizuma, Takahiro Tsukahara i Yasuo Kawaguchi. "DNS Study of Transitional Channel Flow Accompanied by Turbulent-Stripe Structures". W ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-31122.

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A regular pattern of turbulent and quasi-laminar fluid motion is known to appear in plane Poiseuille flow near the lowest Reynolds number for which turbulence can be sustained. We focused on this transitional structure called the turbulent stripe and investigated its energy transport process, using a direct numerical simulation. We obtained the budget for Reynolds stresses including v′w′ and w′u′. The spatial outline of the energy transport with respect to the turbulent stripe is proposed. The turbulent energy is produced in both the turbulent region and the quasi-laminar region, and the energy transfer between these two regions is found to be small.

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Ilak, Milos, i Clarence Rowley. "Feedback Control of Transitional Channel Flow using Balanced Proper Orthogonal Decomposition". W 5th AIAA Theoretical Fluid Mechanics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2008. http://dx.doi.org/10.2514/6.2008-4230.

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Hashimoto, S., A. Hasobe, T. Tsukahara, Y. Kawaguchi i H. Kawamura. "An experimental study on turbulent-stripe structure in transitional channel flow". W Turbulence, Heat and Mass Transfer 6. Proceedings of the Sixth International Symposium On Turbulence, Heat and Mass Transfer. Connecticut: Begellhouse, 2009. http://dx.doi.org/10.1615/ichmt.2009.turbulheatmasstransf.2370.

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Raporty organizacyjne na temat "Transitional channel flow"

Moin, Parviz, i Thomas Bewley. Optimal and Robust Control Transition and Turbulence in Plane Channel Flow. Fort Belvoir, VA: Defense Technical Information Center, grudzień 1996. http://dx.doi.org/10.21236/ada329660.

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Cai, Y., M. W. Wambsganss i J. A. Jendrzejczyk. Application of chaos theory in identification of two-phase flow patterns and transitions in a small, horizontal, rectangular channel. Office of Scientific and Technical Information (OSTI), luty 1996. http://dx.doi.org/10.2172/207657.

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Wilkowski, G. M., D. Rudland, P. Mincer, B. Metrovich i D. Rider. ASME-PVP05 Brittle-to-Ductile Fracture Initiation Transition Temperature for Old Linepipe w Surface-Crack. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), styczeń 2005. http://dx.doi.org/10.55274/r0011772.

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Much work has been done to assess constraint effects on the crack-driving force for specimens and cracks in pipes. The material's transition temperature where the fracture process changes from ductile tearing to cleavage fracture at crack initiation is affected by the constraint conditions but is a material property that cannot be determined analytically. This paper presents a methodology to account for constraint effects to predict the lowest temperature where ductile fracture initiation occurs and relates that temperature back to Charpy impact data for X60 and lower grades, particularly for older vintage linepipe materials. The method involves a series of transition temperature shifts to account for thickness effects, strain-rate effects, and constraint effects to give a master curve of transition temperatures from Charpy data to through-wall-cracked or surface-cracked pipes (with various a/t values) under quasi-static loading. These transition temperature shifts were based on hundreds of pipe tests and thousands of specimen tests over several decades of work by numerous investigators. This method is being validated by examining 1927 and 1948 vintage linepipe steels. In addition, data have been developed on the 1927 vintage pipe material to assess the effect of the bluntness of a corrosion flaw on the lowest temperature where ductile fracture will still initiate under quasi-static loading. An additional transition temperature shift occurs as a function of the bluntness of the flaw.

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McKinnon, Mark, Craig Weinschenk i Daniel Madrzykowski. Modeling Gas Burner Fires in Ranch and Colonial Style Structures. UL Firefighter Safety Research Institute, czerwiec 2020. http://dx.doi.org/10.54206/102376/mwje4818.

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The test scenarios ranged from fires in the structures with no exterior ventilation to room fires with flow paths that connected the fires with remote intake and exhaust vents. In the ranch, two replicate fires were conducted for each room of origin and each ventilation condition. Rooms of fire origin included the living room, bedroom, and kitchen. In the colonial, the focus was on varying the flow paths to examine the change in fire behavior and the resulting damage. No replicates were conducted in the colonial. After each fire scene was documented, the interior finish and furnishings were replaced in affected areas of the structure. Instrumentation was installed to measure gas temperature, gas pressure, and gas movement within the structures. In addition, oxygen sensors were installed to determine when a sufficient level of oxygen was available for flaming combustion. Standard video and firefighting IR cameras were also installed inside of the structures to capture information about the fire dynamics of the experiments. Video cameras were also positioned outside of the structures to monitor the flow of smoke, flames, and air at the exterior vents. Each of the fires were started from a small flaming source. The fires were allowed to develop until they self-extinguished due to a lack of oxygen or until the fire had transitioned through flashover. The times that fires burned post-flashover varied based on the damage occurring within the structure. The goal was have patterns remaining on the ceiling, walls, and floors post-test. In total, thirteen experiments were conducted in the ranch structure and eight experiments were conducted in the colonial structure. All experiments were conducted at UL's Large Fire Laboratory in Northbrook, IL. Increasing the ventilation available to the fire, in both the ranch and the colonial, resulted in additional burn time, additional fire growth, and a larger area of fire damage within the structures. These changes are consistent with fire dynamics based assessments and were repeatable. Fire patterns within the room of origin led to the area of origin when the ventilation of the structure was considered. Fire patterns generated pre-flashover, persisted post-flashover if the ventilation points were remote from the area of origin.

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Russo, Margherita, Fabrizio Alboni, Jorge Carreto Sanginés, Manlio De Domenico, Giuseppe Mangioni, Simone Righi i Annamaria Simonazzi. The Changing Shape of the World Automobile Industry: A Multilayer Network Analysis of International Trade in Components and Parts. Institute for New Economic Thinking Working Paper Series, styczeń 2022. http://dx.doi.org/10.36687/inetwp173.

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In 2018, after 25 years of the North America Trade Agreement (NAFTA), the United States requested new rules which, among other requirements, increased the regional con-tent in the production of automotive components and parts traded between the three part-ner countries, United States, Canada and Mexico. Signed by all three countries, the new trade agreement, USMCA, is to go into force in 2022. Nonetheless, after the 2020 Presi-dential election, the new treaty's future is under discussion, and its impact on the automo-tive industry is not entirely defined. Another significant shift in this industry – the acceler-ated rise of electric vehicles – also occurred in 2020: while the COVID-19 pandemic largely halted most plants in the automotive value chain all over the world, at the reopen-ing, the tide is now running against internal combustion engine vehicles, at least in the an-nouncements and in some large investments planned in Europe, Asia and the US. The definition of the pre-pandemic situation is a very helpful starting point for the analysis of the possible repercussions of the technological and geo-political transition, which has been accelerated by the epidemic, on geographical clusters and sectorial special-isations of the main regions and countries. This paper analyses the trade networks emerg-ing in the past 25 years in a new analytical framework. In the economic literature on inter-national trade, the study of the automotive global value chains has been addressed by us-ing network analysis, focusing on the centrality of geographical regions and countries while largely overlooking the contribution of countries' bilateral trading in components and parts as structuring forces of the subnetwork of countries and their specific position in the overall trade network. The paper focuses on such subnetworks as meso-level structures emerging in trade network over the last 25 years. Using the Infomap multilayer clustering algorithm, we are able to identify clusters of countries and their specific trades in the automotive internation-al trade network and to highlight the relative importance of each cluster, the interconnec-tions between them, and the contribution of countries and of components and parts in the clusters. We draw the data from the UN Comtrade database of directed export and import flows of 30 automotive components and parts among 42 countries (accounting for 98% of world trade flows of those items). The paper highlights the changes that occurred over 25 years in the geography of the trade relations, with particular with regard to denser and more hierarchical network gener-ated by Germany’s trade relations within EU countries and by the US preferential trade agreements with Canada and Mexico, and the upsurge of China. With a similar overall va-riety of traded components and parts within the main clusters (dominated respectively by Germany, US and Japan-China), the Infomap multilayer analysis singles out which com-ponents and parts determined the relative positions of countries in the various clusters and the changes over time in the relative positions of countries and their specialisations in mul-tilateral trades. Connections between clusters increase over time, while the relative im-portance of the main clusters and of some individual countries change significantly. The focus on US and Mexico and on Germany and Central Eastern European countries (Czech Republic, Hungary, Poland, Slovakia) will drive the comparative analysis.

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Olsson, Olle. Industrial decarbonization done right: identifying success factors for well-functioning permitting processes. Stockholm Environment Institute, listopad 2021. http://dx.doi.org/10.51414/sei2021.034.

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1 Introduction 1.1 The urgency of industrial decarbonization The last few years have seen several of the world’s largest carbon dioxide-emitting countries and leading heavy industry companies committing to mid-century net-zero targets (Buckley 2021; Denyer and Kashiwagi 2020; McCurry 2020; Myers 2020). Consequently, the discussion on economy-wide transition to net-zero is accelerating, with focus shifting from “if” to “when” and “how”, even for heavy industry sectors like steel, cement and chemicals. This makes it increasingly urgent to analyse not just whether it is technologically feasible to decarbonize heavy industry, but also investigate issues more directly related to practical implementation. This includes site-specific planning, infrastructure availability, and consultation with local authorities and other stakeholders. Many of the latter considerations are formalized as part of the permitting processes that are an essential vehicle to ensure that industrial interests are balanced against interests of society at large. However, doing this balancing act can turn out to be very complicated and associated with uncertainties as to their outcome, as well as being demanding in resources and time. At the same time, to ensure broad buy-in and support from society, the investments needed must be implemented in a way that takes a broad spectrum of sustainability concerns into account, not just climate change mitigation. A key question is if and how permitting processes can run more smoothly and efficiently while still ensuring inclusive consultations, fair procedures and adherence to legal certainty. This policy brief discusses this question from the starting point of Swedish conditions, but many of the points raised will be relevant for a broader international discussion on taking industrial decarbonization to implementation. 1.2 Industrial transition and permitting processes in Sweden Decarbonization of the industrial sector in Sweden essentially entails a relatively small number of investment projects in the cement, steel, petrochemical and refinery sectors, where the vast majority of carbon emissions are concentrated (Karltorp et al. 2019; Nykvist et al. 2020). However, while few in number, the size of these investments means that their implementation will by necessity become relevant to many other parts of society. In connection with the increasing focus on how to implement industrial decarbonization in Sweden, discussions about permitting processes have been brought higher up on the agenda. While there has been an active discussion on permitting processes in Sweden for quite some time, it has primarily been focused on aspects related to mining and wind power (Larsen et al. 2017; Raitio et al. 2020). The last few years have, however, focused increasingly on industrial projects, in particular related to a proposed – though eventually cancelled – expansion of an oil refinery in the southwestern part of the country (Blad 2020). In terms of political discussions, both the governmental initiative Fossil-free Sweden (2020) and the Swedish Climate Policy Council (2020) emphasize that permitting processes need to become faster in order for Sweden’s industrial transition to be implemented in line with the time plan set by the 2017 Swedish Climate Act. Business representatives and organizations are also voicing concerns about the slow speed of permitting (Balanskommissionen 2019; Jacke 2018). At the same time, criticism has been raised that much of the environmental damage done in Sweden comes from activities conducted within limits set by environmental permits, which could be a flaw in the system (Malmaeus and Lindblom 2019). Finally, recent public inquiries have also discussed permitting processes.

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Kirchhoff, Helmut, i Ziv Reich. Protection of the photosynthetic apparatus during desiccation in resurrection plants. United States Department of Agriculture, luty 2014. http://dx.doi.org/10.32747/2014.7699861.bard.

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In this project, we studied the photosynthetic apparatus during dehydration and rehydration of the homoiochlorophyllous resurrection plant Craterostigmapumilum (retains most of the photosynthetic components during desiccation). Resurrection plants have the remarkable capability to withstand desiccation, being able to revive after prolonged severe water deficit in a few days upon rehydration. Homoiochlorophyllous resurrection plants are very efficient in protecting the photosynthetic machinery against damage by reactive oxygen production under drought. The main purpose of this BARD project was to unravel these largely unknown protection strategies for C. pumilum. In detail, the specific objectives were: (1) To determine the distribution and local organization of photosynthetic protein complexes and formation of inverted hexagonal phases within the thylakoid membranes at different dehydration/rehydration states. (2) To determine the 3D structure and characterize the geometry, topology, and mechanics of the thylakoid network at the different states. (3) Generation of molecular models for thylakoids at the different states and study the implications for diffusion within the thylakoid lumen. (4) Characterization of inter-system electron transport, quantum efficiencies, photosystem antenna sizes and distribution, NPQ, and photoinhibition at different hydration states. (5) Measuring the partition of photosynthetic reducing equivalents between the Calvin cycle, photorespiration, and the water-water cycle. At the beginning of the project, we decided to use C. pumilum instead of C. wilmsii because the former species was available from our collaborator Dr. Farrant. In addition to the original two dehydration states (40 relative water content=RWC and 5% RWC), we characterized a third state (15-20%) because some interesting changes occurs at this RWC. Furthermore, it was not possible to detect D1 protein levels by Western blot analysis because antibodies against other higher plants failed to detect D1 in C. pumilum. We developed growth conditions that allow reproducible generation of different dehydration and rehydration states for C. pumilum. Furthermore, advanced spectroscopy and microscopy for C. pumilum were established to obtain a detailed picture of structural and functional changes of the photosynthetic apparatus in different hydrated states. Main findings of our study are: 1. Anthocyan accumulation during desiccation alleviates the light pressure within the leaves (Fig. 1). 2. During desiccation, stomatal closure leads to drastic reductions in CO2 fixation and photorespiration. We could not identify alternative electron sinks as a solution to reduce ROS production. 3. On the supramolecular level, semicrystalline protein arrays were identified in thylakoid membranes in the desiccated state (see Fig. 3). On the electron transport level, a specific series of shut downs occur (summarized in Fig. 2). The main events include: Early shutdown of the ATPase activity, cessation of electron transport between cyt. bf complex and PSI (can reduce ROS formation at PSI); at higher dehydration levels uncoupling of LHCII from PSII and cessation of electron flow from PSII accompanied by crystal formation. The later could severe as a swift PSII reservoir during rehydration. The specific order of events in the course of dehydration and rehydration discovered in this project is indicative for regulated structural transitions specifically realized in resurrection plants. This detailed knowledge can serve as an interesting starting point for rationale genetic engineering of drought-tolerant crops.

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Financial Stability Report - Second Semester of 2021. Banco de la República, wrzesień 2022. http://dx.doi.org/10.32468/rept-estab-fin.sem2.eng-2021.

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Banco de la República’s main objective is to preserve the purchasing power of the currency in coordination with the general economic policy that is intended to stabilize output and employment at long-term sustainable levels. Properly meeting the goal assigned to the Bank by the 1991 Constitution critically depends on preserving financial stability. This is understood to be a general condition in which the financial system assesses and manages the financial risks in a way that facilitates the economy’s performance and efficient allocation of resources while, at the same time, it is able to, on its own, absorb, dissipate, and mitigate the shocks that may arise as a result of adverse events. This Financial Stability Report meets the goal of giving Banco de la República’s diagnosis of the financial system’s and its debtors’ recent performance as well as of the main risks and vulnerabilities that could affect the stability of the Colombian economy. In this way, participants in financial markets and the public are being informed, and public debate on trends and risks affecting the system is being encouraged. The results presented here also serve the monetary authority as a basis for making decisions that will enhance financial stability in the general context of its objectives. In recent months, several positive aspects of the financial system have preserved a remarkable degree of continuity and stability: the liquidity and capital adequacy of financial institutions have remained well above the regulatory minimums at both the individual and consolidated levels, the coverage of past-due loans by loan-loss provisions remains high, and the financial markets for public and private debt and stocks have continued to function normally. At the same time, a surge in all the types of loan portfolios, a sharp downturn in the non-performing loan portfolio, and a rise in the profitability of credit institutions can be seen for the first time since the beginning of the pandemic. In line with the general recovery of the economy, the main vulnerability to the stability of the Colombian financial system identified in the previous edition—uncertainty about changes in the non-performing loans portfolio—has receded and remains on a downward trend. In this edition, the main source of vulnerability identified for financial stability in the short term is the system’s exposure to sudden changes in international financial conditions; the results presented in this Report indicate that the system is sufficiently resilient to such scenarios. In compliance with its constitutional objectives and in coordination with the financial system’s security network, Banco de la República will continue to closely monitor the outlook for financial stability at this juncture and will make the decisions necessary to ensure the proper functioning of the economy, facilitate the flow of sufficient credit and liquidity resources, and further the smooth functioning of the payment system. Leonardo Villar Gomez Governor Box 1 -Decomposition of the Net Interest Margin in Colombia and Chile Wilmar Cabrera Daniela Rodríguez-Novoa Box 2 - Spatial Analysis of New Home Prices in Bogota, Medellín, and Cali Using a Geostatistical Approach María Fernanda Meneses Camilo Eduardo Sánchez Box 3 - Interest Rate Model for the SYSMO Stress Test Exercise Wilmar Cabrera Diego Cuesta Santiago Gamba Camilo Gómez Box 4 - The Transition from LIBOR and other International Benchmark Rates Daniela X. Gualtero Briceño Javier E. Pirateque Niño

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