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Статті в журналах з теми "Convection induced by differential heating"
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Vadasz, P. "Natural Convection in Porous Media Induced by the Centrifugal Body Force: The Solution for Small Aspect Ratio." Journal of Energy Resources Technology 114, no. 3 (September 1, 1992): 250–54. http://dx.doi.org/10.1115/1.2905949.
Повний текст джерелаАнотація:
The analytical solution to the natural convection problem in a rotating rectangular porous domain is presented for a small aspect ratio of the domain. The convection results from differential heating of the horizontal walls leading to temperature gradients orthogonal to the centrifugal body force. The solution to the nonlinear set of partial differential equations was obtained through an asymptotic expansion of the dependent variables in terms of a small parameter representing the aspect ratio of the domain. The convection regime is apparent in the results, although it has a weak effect on the mean heat flux.
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Grandpeix, Jean-Yves, and Jean-Philippe Lafore. "A Density Current Parameterization Coupled with Emanuel’s Convection Scheme. Part I: The Models." Journal of the Atmospheric Sciences 67, no. 4 (April 1, 2010): 881–97. http://dx.doi.org/10.1175/2009jas3044.1.
Повний текст джерелаАнотація:
Abstract The aim of the present series of papers is to develop a density current parameterization for global circulation models. This first paper is devoted to the presentation of this new wake parameterization coupled with Emanuel’s convective scheme. The model represents a population of identical circular cold pools (the wakes) with vertical frontiers. The wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts. The budget equations for mass, energy, and water yield evolution equations for the prognostic variables (the vertical profiles of the temperature and humidity differences between the wakes and their exterior). They also provide additional terms for the equations of the mean variables. The driving terms of the wake equations are the differential heating and drying due to convective drafts. The action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precipitating downdrafts to the wake region and the effect of the saturated drafts to their exterior. Conversely, the action of the wakes on convection is implemented by introducing two new variables representing the convergence at the leading edge of the wakes. The available lifting energy (ALE) determines the triggers of deep convection: convection occurs when ALE exceeds the convective inhibition. The available lifting power (ALP) determines the intensity of convection; it is equal to the power input into the system by the collapse of the wakes. The ALE/ALP closure, together with the splitting of the convective heating and drying, implements the full coupling between wake and convection. The coupled wake–convection scheme thus created makes it possible to represent the moist convective processes more realistically, to prepare the coupling of convection with boundary layer and orographic processes, and to consider simulating the propagation of convective systems.
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Sun, Jianhua, and Fuqing Zhang. "Impacts of Mountain–Plains Solenoid on Diurnal Variations of Rainfalls along the Mei-Yu Front over the East China Plains." Monthly Weather Review 140, no. 2 (February 2012): 379–97. http://dx.doi.org/10.1175/mwr-d-11-00041.1.
Повний текст джерелаАнотація:
Convection-permitting numerical experiments using the Weather Research and Forecasting (WRF) model are performed to examine the impact of a thermally driven mountain–plains solenoid (MPS) on the diurnal variations of precipitation and mesoscale convective vortices along the mei-yu front over the east China plains during 1–10 July 2007. The focus of the analyses is a 10-day simulation that used the 10-day average of the global analysis at 0000 UTC as the initial condition and the 10-day averages every 6 h as lateral boundary conditions (with diurnal variations only). Despite differences in the rainfall intensity and location, this idealized experiment successfully simulated the observed diurnal variation and eastward propagation of rainfall and mesoscale convective vortices along the mei-yu front. It was found that the upward branch of the MPS, along with the attendant nocturnal low-level jet, is primarily responsible for the midnight-to-early-morning rainfall enhancement along the mei-yu front. The MPS is induced by differential heating between the high mountain ranges in central China and the low-lying plains in east China. Diabatic heating from moist convection initiated and/or enhanced by the solenoid circulation subsequently leads to the formation of a mesoscale convective vortex that further organizes and amplifies moist convection while propagating eastward along the mei-yu front. The downward branch of the MPS, on the other hand, leads to the suppression of precipitation over the plains during the daytime. The impacts of this regional MPS on the rainfall diurnal variations are further attested to by another idealized WRF simulation that uses fixed lateral boundary conditions.
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Lau, K. M., H. T. Wu, Y. C. Sud, and G. K. Walker. "Effects of Cloud Microphysics on Tropical Atmospheric Hydrologic Processes and Intraseasonal Variability." Journal of Climate 18, no. 22 (November 15, 2005): 4731–51. http://dx.doi.org/10.1175/jcli3561.1.
Повний текст джерелаАнотація:
Abstract The sensitivity of tropical atmospheric hydrologic processes to cloud microphysics is investigated using the NASA Goddard Earth Observing System (GEOS) general circulation model (GCM). Results show that a faster autoconversion rate leads to (a) enhanced deep convection in the climatological convective zones anchored to tropical land regions; (b) more warm rain, but less cloud over oceanic regions; and (c) an increased convective-to-stratiform rain ratio over the entire Tropics. Fewer clouds enhance longwave cooling and reduce shortwave heating in the upper troposphere, while more warm rain produces more condensation heating in the lower troposphere. This vertical differential heating destabilizes the tropical atmosphere, producing a positive feedback resulting in more rain and an enhanced atmospheric water cycle over the Tropics. The feedback is maintained via secondary circulations between convective tower and anvil regions (cold rain), and adjacent middle-to-low cloud (warm rain) regions. The lower cell is capped by horizontal divergence and maximum cloud detrainment near the freezing–melting (0°C) level, with rising motion (relative to the vertical mean) in the warm rain region connected to sinking motion in the cold rain region. The upper cell is found above the 0°C level, with induced subsidence in the warm rain and dry regions, coupled to forced ascent in the deep convection region. It is that warm rain plays an important role in regulating the time scales of convective cycles, and in altering the tropical large-scale circulation through radiative–dynamic interactions. Reduced cloud–radiation feedback due to a faster autoconversion rate results in intermittent but more energetic eastward propagating Madden–Julian oscillations (MJOs). Conversely, a slower autoconversion rate, with increased cloud radiation produces MJOs with more realistic westward-propagating transients embedded in eastward-propagating supercloud clusters. The implications of the present results on climate change and water cycle dynamics research are discussed.
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Parish, Thomas R., Richard D. Clark, and Todd D. Sikora. "Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet." Monthly Weather Review 148, no. 11 (November 2020): 4641–56. http://dx.doi.org/10.1175/mwr-d-19-0394.1.
Повний текст джерелаАнотація:
AbstractThe Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.
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Wu, Wei, Zhiping Wen, Renguang Wu, and Tongmei Wang. "Air–Sea Interaction over the Subtropical North Pacific during the ENSO Transition Phase." Journal of Climate 24, no. 22 (November 15, 2011): 5772–85. http://dx.doi.org/10.1175/2011jcli3820.1.
Повний текст джерелаАнотація:
Abstract In the present study, monthly mean objectively analyzed air–sea fluxes (OAFlux) and NCEP–Department of Energy (DOE) reanalysis datasets are employed to investigate air–sea interaction over the subtropical North Pacific during the El Niño–Southern Oscillation (ENSO) transition phase. A coupled low-frequency mode is identified, for which surface net heat flux and atmospheric circulation changes are strongly coupled during the ENSO transition phase. This mode features anomalous cooling (warming) and low-level anomalous cyclonic (anticyclonic) circulation over the subtropical North Pacific. When this mode is prominent, the atmospheric circulation anomalies lead to SST cooling (warming) through surface heat flux anomalies associated with increases (decreases) in the sea–air temperature and humidity differences induced by anomalous cold (warm) advection. In turn, positive heat flux anomalies induce more surface heating, and the SST cooling (warming) causes less (more) deep convective heating. The anomalous surface heating and deep convective heating contribute significantly to anomalous circulation through the thermal adaptation mechanism (adaptation of atmospheric circulation to vertical differential heating). This positive feedback favors the maintenance of these anomalous winds over the subtropical North Pacific.
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Kapoor, S., and P. Bera. "Effect of Periodicity of Non-Uniform Sinusoidal Side Heating on Natural Convection in an Anisotropic Porous-Enclosure." Applied Mechanics and Materials 110-116 (October 2011): 1613–18. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.1613.
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A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.
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Khan, Wasim Ullah, Muhammad Awais, Nabeela Parveen, Aamir Ali, Saeed Ehsan Awan, Muhammad Yousaf Malik, and Yigang He. "Analytical Assessment of (Al2O3–Ag/H2O) Hybrid Nanofluid Influenced by Induced Magnetic Field for Second Law Analysis with Mixed Convection, Viscous Dissipation and Heat Generation." Coatings 11, no. 5 (April 23, 2021): 498. http://dx.doi.org/10.3390/coatings11050498.
Повний текст джерелаАнотація:
The current study is an attempt to analytically characterize the second law analysis and mixed convective rheology of the (Al2O3–Ag/H2O) hybrid nanofluid flow influenced by magnetic induction effects towards a stretching sheet. Viscous dissipation and internal heat generation effects are encountered in the analysis as well. The mathematical model of partial differential equations is fabricated by employing boundary-layer approximation. The transformed system of nonlinear ordinary differential equations is solved using the homotopy analysis method. The entropy generation number is formulated in terms of fluid friction, heat transfer and Joule heating. The effects of dimensionless parameters on flow variables and entropy generation number are examined using graphs and tables. Further, the convergence of HAM solutions is examined in terms of defined physical quantities up to 20th iterations, and confirmed. It is observed that large λ1 upgrades velocity, entropy generation and heat transfer rate, and drops the temperature. High values of δ enlarge velocity and temperature while reducing heat transport and entropy generation number. Viscous dissipation strongly influences an increase in flow and heat transfer rate caused by a no-slip condition on the sheet.
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Trier, Stanley B., and Robert D. Sharman. "Convection-Permitting Simulations of the Environment Supporting Widespread Turbulence within the Upper-Level Outflow of a Mesoscale Convective System." Monthly Weather Review 137, no. 6 (June 1, 2009): 1972–90. http://dx.doi.org/10.1175/2008mwr2770.1.
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Abstract Widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern Kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system (MCS) on 17 June 2005. A noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection (i.e., large reflectivity) regions of the MCS. Herein, the MCS life cycle and the turbulence environment in its upper-level outflow are studied using Rapid Update Cycle (RUC) analyses and cloud-permitting simulations with the Weather Research and Forecast Model (WRF). It is demonstrated that strong vertical shear beneath the MCS outflow jet is critical to providing an environment that could support dynamic (e.g., shearing type) instabilities conducive to turbulence. Comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the local Richardson number (Ri) to ∼0.25 at the northern edge of the anvil were almost entirely a consequence of the MCS-induced westerly outflow jet. The large vertical shear is found to decrease Ri both directly, and by contributing to reductions in static stability near the northern anvil edge through differential advection of (equivalent) potential temperature gradients, which are in turn influenced by adiabatic cooling associated with the mesoscale updraft located upstream within the anvil. On the south side of the MCS, the vertical shear associated with easterly outflow was significantly offset by environmental westerly shear, which resulted in larger Ri and less widespread model turbulent kinetic energy (TKE) than at the northern anvil edge.
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Wawira, Njue Caroline, Mathew Kinyanjui, and Kang’ethe Giterere. "Hydromagnetic Non-Newtonian Fluid Flow in a Convergent Conduit." Journal of Applied Mathematics 2022 (December 17, 2022): 1–13. http://dx.doi.org/10.1155/2022/8131528.
Повний текст джерелаАнотація:
In the present study, a hydromagnetic non-Newtonian (dilatant) fluid flow in a convergent conduit, in the presence of a variable transverse magnetic field, has been investigated. The governing nonlinear partial differential equations are reduced to system of ordinary differential equations. These equations are solved numerically by the collocation method and implemented in MATLAB. The study determines the flow profiles and the impact of the flow parameters on the flow variables. Joule heating, variable viscosity, viscous dissipation, skin friction, the rate of heat transfer, and the induced magnetic field are taken into account. The obtained results are presented graphically and the impact of varying flow parameters on the skin friction coefficient and the Nusselt number is presented in tabular form. These results indicate that an increase in the Reynolds number, Eckert’s number, and the Joule heating parameter increases the fluid’s velocity, while an increase in the Hartmann number and the unsteadiness parameter decreases the convective heat transfer and the fluid’s velocity. Further, the skin friction coefficient decreases with increase in the Reynolds number, the Hartmann number, and the Joule heating parameter. Therefore, a less viscous fluid is appropriate to facilitate the fluid’s motion, but the presence of high magnetic field reduces the fluid’s motion.
Дисертації з теми "Convection induced by differential heating"
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Park, Young-Gyu. "Rotating convection driven by differential bottom heating and its application." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/55050.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.Includes bibliographical references (leaves 133-137).
by Young-Gyu Park.
Ph.D.
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Orlacchio, Rosa. "Millimeter waves for biomedical electromagnetics : study of changes induced at the cellular level by pulsed electromagnetically-induced heating." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S077.
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La partie inférieure de la bande de les ondes millimétriques (OMM, c'est-à-dire 20–100 GHz) constitue une alternative attrayante pour le traitement thermique non invasif du mélanome. Le chauffage pulsé induit électromagnétiquement peut entraîner des dommages plus importants dans les cellules par rapport au chauffage continu traditionnel. Dans ce travail, nous étudions les modifications induites au niveau cellulaire dans les cellules de mélanome à la suite d'une exposition au chauffage induit par en onde continue (CW) et ou en régime modulé (PWM) avec avec la même élévation de température moyenne, à 58.4 GHz. Premièrement, l’impact de la convection thermique sur la dynamique de la température dans des modèles représentant des conditions d’exposition in vitro typiques lors du chauffage par CW et PWM est étudié expérimentalement. Deuxièmement, la réponse au choc thermique, médiée par la phosphorylation d'une protéine de choc thermique (HSP27) et l'activation de Caspase-3, indicateur de l'apoptose cellulaire, est quantifiée pour surveiller la réponse biologique en utilisant une approche expérimentale basée sur la microscopie à fluorescence. Deux durées d'impulsion (1.5 s et 6 s) sont considérées. Nos résultats démontrent que les impulsions thermiques sont capables d'induire une réponse cellulaire plus forte dans les cellules de mélanome à la fois en termes de choc thermique et de mortalité cellulaire par rapport à celle induite en CW. Plus la durée de l'impulsion est courte, plus la réponse cellulaire est grandeThe lower part of the millimeter wave (MMW) band (i.e., 20–100 GHz) is an attractive alternative for non-invasive thermal treatment of melanoma. Besides, pulsed electromagneticallyinduced heating can lead to stronger damage in cells compared to traditional continuous heating. In in-vitro experiments, continuous-wave (CW) or pulsed-wave (PW) amplitude-modulated MMW can be efficiently used to locally heat cell monolayers with a typical thickness ranging between 3 μm and 10 μm. In this work we investigate the modifications induced at the cellular level in melanoma cells following exposure to CW and PW MMW-induced heating with the same average temperature rise, at 58.4 GHz. First, the impact of thermal convection on temperature dynamics in models representing typical in vitro exposure conditions during CW and PW-induced heating is experimentally investigated. Second, the heat shock response, mediated by phosphorylation of a small heat shock protein (HSP27) and activation of Caspase-3, indicator of cellular apoptosis, are quantified to monitor the biological response using an experimental approach based on fluorescence microscopy. Two pulse durations (1.5 s and 6 s) are considered. Our results demonstrate that thermal pulses are able to induce a stronger cellular response in melanoma cells both in terms of heat shock and cellular mortality compared to the one induced by CW. The shorter the pulse duration, the greater the cellular response
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Przydrozna, Aleksandra Anna. "Filling flows induced by a convector in a room." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277224.
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Over the last two centuries, there has been a continual evolution of how occupied rooms are heated, with inventors competing to design new heating devices. In particular, there is a wide range of convector types, which vary in shape, size, design, material, operating medium and application. With approximately 190 million convectors installed in the UK alone, the question arises regarding the dependencies on the efficiency of heat distribution through convector-induced filling flows. A standard approach to evaluate convector performance is based on the convector strength only, the implication being the stronger the convector the better the performance. This work has gone beyond the limits of a stereotypical assessment in pursuit of answers regarding the physics of convector-induced filling and a new objective method to evaluate the efficiency of this transient process. The ultimate goal has been to provide a deep understanding of filling and stratification induced by a convector, in order to heat rooms rapidly and effectively. An experimental facility has been designed that approximates dynamic similarity between the experimental set-up and a real-life room with a convector. In the experiments, a rectangular sectioned water tank represents a room and a saline source rectangular sectioned panel with sintered side walls provides a convector representation. Experiments have been performed in water with a saline solution to ensure high Rayleigh numbers. Diagnostic techniques involve a combination of a shadowgraph method, a dye-attenuation method, direct salinity measurements and a new application of Particle Image Velocimetry (PIV). Interesting insight into convector-induced buoyancy-driven flows has been gained. As a result, new guidelines aimed at heating rooms more rapidly and effectively have been proposed. The key outcome that can be immediately applied is that, for a given convector strength, heat distribution with height can be improved by adjusting the convector position. For instance, faster filling leading to more uniform heat distribution occurs in rooms with convectors detached from side walls, due to large-scale mixing flows in the early period of filling. Also shorter convectors relative to the room height, positioned close to the floor level, promote faster and more uniform filling. An attempt to describe the transient filling has been made and to do so statistical methods, application specific, have been developed. As a result, the empirical equations describing both the filling rates in different stages of filling and the development of stratification have been derived, which rank the governing parameters, based on their importance, as either dominant or subordinate. Two dominant parameters governing filling flows are the non-dimensional accumulation parameter B and the Rayleigh number ΔRa, which are related to the convector strength. The impact of these two parameters is constant throughout the process. The parameters accounting for the system geometry and filling time (T) are subordinate parameters. Their impact, visible in the early period, decreases as filling continues.
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Chan, Wai Sum. "Spatial and temporal features of hydrodynamics and biogeochemistry in Myponga Reservoir, South Australia." Thesis, 2011. http://hdl.handle.net/2440/76100.
Повний текст джерелаАнотація:
Understanding hydrodynamic and biogeochemical processes in lakes is fundamentally important to the management of phytoplankton population and the improvement of water quality. Physical processes such as wind-driven surface mixing, thermal stratification and differential heating and cooling can affect the distribution of water, phytoplankton and sediments and the availability of nutrients and light. These lake processes, which are highly variable in space and time, affect phytoplankton dynamics in the field. This study aims to determine the spatial and temporal variability of phytoplankton and processes that either contribute to or override the variability in the artificially mixed Myponga Reservoir, South Australia. A sediment survey showed that sediments underlying deep water were richer in organic matter, carbon, nitrogen and phosphorus than the sediments underlying shallow water. This may lead to different nutrient release rates between the shallow and deep areas. Both sediment resuspension and anoxic sediment nutrient release were important internal sources of nutrient to support phytoplankton growth in summer when external nutrient supplies were limited by low rainfall in the catchment. An analysis of historical water temperature data revealed the development of micro-stratification at the sediment-water interface in summer, especially during a heatwave (air temperature > 40ºC for several consecutive days). Prolonged micro-stratification could potentially induce anoxic layers at the sediment surface, resulting in the release of nutrients. A risk assessment was conducted to predict the release of phosphorus from anoxic sediments and to evaluate the potential impact of cyanobacterial population (Anabaena circinalis) and the release of secondary metabolites (e.g. saxitoxin and geosmin). Spatial variability of surface mixed layer depths exists between the side-arm and main basin. A simple light model based on the relationships of surface mixed layer depth, daily light dose and phytoplankton growth rate, was developed to estimate the potential variation of phytoplankton population in the two different light habitats (the main basin and side-arm). The model showed that phytoplankton abundance in the main basin was lower than in the side-arm. However, differential heating drove a large basin-scale convection, which circulated the water between the side-arm and main basin within hours. This circulation overrode the time scale of days for the light-dependent growth effect between the two sites and hence there was no observable change in phytoplankton community structure. Although no spatial variability of phytoplankton was observed at community level, significant variations of phytoplankton cellular content and stoichiometry were detected. Higher carbon cellular content in the side-arm than in the main basin was probably due to a greater exposure to light (shallower surface mixed layer in the side-arm) for photosynthesis. In the situation where nutrients were scare, higher phosphorus cellular content was found in the side-arm than in the main basin; this was possibly due to a greater exposure to resuspended nutrients from the lake bottom (shallower water in the side-arm). There was also a strong seasonal pattern in phytoplankton cellular content and stoichiometry between summer and early winter of 2009. The carbon content of phytoplankton increased over time, while the phosphorus content decreased. After the first heavy rain event (70 mm over a four-day period) in early May, carbon cellular content decreased, while phosphorus cellular content increased. These changes in phytoplankton contents were most likely related to the bio-availability of phosphorus in water. This study reviews many complex, interactive processes driving the variability of lake physics and chemistry. The variability can yield rapid biological responses at physiological and cellular levels (e.g. Fv:Fm and cellular content), but does not necessarily appear at community levels (e.g. phytoplankton biomass, diversity). Often, conventional monitoring in lakes and reservoirs overlooks the subtle variability of phytoplankton dynamics. The relative scaling among physical, chemical and biological processes, therefore, is important to adequately describe the spatial and temporal variability in lakes and reservoirs.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2011
Книги з теми "Convection induced by differential heating"
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C, Sorensen D., and Institute for Computer Applications in Science and Engineering., eds. An asymptotic induced numerical method for the convection-diffusion-reaction equation. Hampton, VA: Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, 1988.
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Center, Lewis Research, ed. Final technical report for NASA grant NAG3-1501 entitled oscillatory/chaotic thermocapillatary flow induced by radiant heating: Submitted January, 1998 for the period 6-1-93 to 11-30-96. Cleveland, Ohio: NASA Lewis Research Center, 1998.
Знайти повний текст джерелаЧастини книг з теми "Convection induced by differential heating"
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Reames, Donald V. "Introducing the Sun and SEPs." In Solar Energetic Particles, 1–18. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66402-2_1.
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AbstractThe structure of the Sun, with its energy generation and heating, creates convection and differential rotation of the outer solar plasma. This convection and rotation of the ionized plasma generates the solar magnetic field. This field and its variation spawn all of the solar activity: solar active regions, flares, jets, and coronal mass ejections (CMEs). Solar activity provides the origin and environment for both the impulsive and gradual solar energetic particle (SEP) events. This chapter introduces the background environment and basic properties of SEP events, time durations, abundances, and solar cycle variations.
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Kapoor, S. "Computational Study of Double Diffusive MHD Buoyancy Induced Free Convection in Porous Media with Chemical Reaction and Internal Heating." In Advanced Applications of Computational Mathematics, 135–50. New York: River Publishers, 2022. http://dx.doi.org/10.1201/9781003336983-9.
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Epstein, Irving R., and John A. Pojman. "Stirring and Mixing Effects." In An Introduction to Nonlinear Chemical Dynamics. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195096705.003.0021.
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In almost everything that we have discussed so far, we have assumed, explicitly or implicitly, either that the systems we are looking at are perfectly mixed or that they are not mixed at all. In the former case, concentrations are the same everywhere in the system, so that ordinary differential equations for the evolution of the concentrations in time provide an appropriate description for the system. There are no spatial variables; in terms of geometry, the system is effectively zero-dimensional. At the other extreme, we have unstirred systems. Here, concentrations can vary throughout the system, position is a key independent variable, and diffusion plays an essential role, leading to the development of waves and patterns. Geometrically, the system is three-dimensional, though for mathematical convenience, or because one length is very different from the other two, we may be able to approximate it as one- or two-dimensional. In reality, we hardly ever find either extreme—that of perfect mixing or that of pure, unmixed diffusion. In the laboratory, where experiments in beakers or CSTRs are typically stirred at hundreds of revolutions per minute, we shall see that there is overwhelming evidence that, even if efforts are made to improve the mixing efficiency, significant concentration gradients arise and persist. Increasing the stirring rate helps somewhat, but beyond about 2000 rpm, cavitation (the formation of stirring-induced bubbles in the solution) begins to set in. Even close to this limit, mixing is not perfect. In unstirred aqueous systems, as we have seen in Chapter 9, it is difficult to avoid convective mixing. Preventing small amounts of mechanically induced mixing requires considerable effort in isolating the system from external vibrations, even those caused by the occasional truck making a delivery to the laboratory stockroom. It is possible to suppress the effects of convection and mechanical motion in highly viscous media, such as the gels used in the experiments on Turing patterns as discussed in the previous chapter. There, we can finally study a pure reaction-diffusion system. Systems in nature—the oceans, the atmosphere, a living cell—are important examples in which chemical reactions with nonlinear kinetics occur under conditions of imperfect mixing.
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Chuan, Goh Kim. "The Climate of Southeast Asia." In The Physical Geography of Southeast Asia. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780199248025.003.0015.
Повний текст джерелаАнотація:
Southeast Asia lies between the continental influence of the rest of Asia to the north and the more oceanic influence of the Indian and Pacific Oceans to the south and the east respectively. While its overall net energy balance is very much determined by its latitudinal position, which is approximately between 20°N and 10°S, the locational factors referred to above largely give the regional climate its distinctive character. Within the broad latitudinal extent defined above, the Southeast Asian region has often been conveniently separated into two sub-areas: continental and insular Southeast Asia. In some ways these sub-regions represent a valid delineation into the more seasonal climatic region influenced by the monsoon system of winds and the uniformly humid equatorial climate. The former comprises Myanmar, Thailand, Lao PDR, Cambodia, and Viet Nam, while the latter includes Malaysia, Singapore, Indonesia, and the Philippines. The continental Southeast Asia experiences greater seasonality, more extremes in both temperature and rainfall, and more pronounced dry spells; whereas the insular parts, termed the ‘maritime continent’ (Ramage 1968), with a much greater expanse of sea than land (the sea area of Indonesia, for example, is four times its land area), have more equable climate. The northern and southern continental interactions in winter and summer and the differential heating due to the asymmetric character of the two sub-regions give rise to the monsoon development (Hastenrath 1991), which, to a large extent, influences the rainfall characteristics of the region as a whole. In a sense, more than temperature variations, this monsoonal influence gives the Southeast Asian climate its distinctive character. Figure 5.2 shows the two monsoon wind systems that affect Southeast Asia. In addition to these annual reversals of the monsoon winds, the seasonal migration of the Intertropical Convergence Zone (ITCZ)—closest to the Equator during the northern hemispheric winter and farthest north during summer—is a significant factor in influencing the monthly weather regime of the region. Being a belt of low-pressure trough coinciding with the band of highest surface temperature, the ITCZ attracts the moist easterlies from both hemispheres towards its trough resulting in uplift of air, intense convection, and precipitation. This whole process provides a mechanism for the transfer of latent heat from the low to the higher latitudes (Houze et al. 1981; Hastenrath 1991).
Тези доповідей конференцій з теми "Convection induced by differential heating"
1
Lei, Zhiheng, and Bakhtier Farouk. "Convection and Transport in a Differentially Heated Enclosure Filled With Supercritical Carbon Dioxide: Short- and Long-Time Solutions." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68390.
Повний текст джерелаАнотація:
Supercritical fluids are characterized by high densities, high thermal conductivities (compared to gases) and low viscosities, but low thermal diffusivities (compared to liquids). Due to the high compressibility, thermally induced acoustic waves are generated when supercritical fluids are heated/cooled along any bounding surface. In this study, we obtain both short- and long-time solutions for convective flows in a supercritical carbon dioxide filled enclosure. The NIST database 12 [1] is used to obtain the property relations for supercritical carbon dioxide. The generation and propagation of themoacoustic waves produced immediately after rapid heating of a wall are investigated by solving the fully compressible Navier-Stokes equations with an accurate equation of state, via a high-order explicit numerical scheme. For longer time solutions, when the acoustic waves damp out, an implicit solution algorithm is used to simulate the heat transfer in the above enclosure filled with supercritical carbon dioxide for longer periods time. This novel scheme allows us to investigate convective flows in an enclosure filled with supercritical fluid in a comprehensive manner.
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Reich, Alton J., Choon Tham, and Stan Smith. "Computational Modeling of Laser Induced Heating." In ASME/JSME 2004 Pressure Vessels and Piping Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/pvp2004-3091.
Повний текст джерелаАнотація:
Lasers are increasingly being used as a heat source in industrial applications due to their ability to deliver energy at a distance. In order to properly design systems that involve laser heating, accurate information about heat up rates is required. In complex systems, the rate of heating is a function of the laser parameters; such as spot size, beam intensity and beam profile; surface treatments and their characteristic coupling coefficient; and fluid convection adjacent to the surface being heated. This paper will describe recent efforts to simulate the heating of an enclosed container using a laser. The model complexity required to achieve good results, relative to test data, will be discussed.
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Ziskind, G., V. Dubovsky, and R. Letan. "Radiation and Induced Convection in Ventilated Enclosures." In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/htd-24305.
Повний текст джерелаАнотація:
Abstract The paper presents a thorough numerical investigation of the effects of radiation and induced convection inside an enclosure. The objective is to assess the interaction of these two mechanisms in real size buildings with heating elements inside. As a first step, a small size model is studied. The investigation is performed for closed and partially open enclosures. Temperature distributions and flow fields inside the enclosure are obtained for different values of the heat-transfer parameters, like emissivity of the hot element and the walls, and the thermal resistance of the walls. It is shown that radiation can considerably affect the air flow inside the enclosure. Real-size structures, where turbulent flow prevails, are compared to the model. Three-dimensional simulations are performed. The influence of grid refinement on the results is discussed. The results obtained for a uniform grid are compared to those for a non-uniform one, having higher density at the boundaries. Special attention is paid to the radiation modeling, where the influence of angular discretization is important.
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Kazeminejad, H. "Laminar Free Convection in a Vertical Channel With Asymmetrical Heating." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72014.
Повний текст джерелаАнотація:
A numerical investigation of laminar free convective heat transfer in a vertical channel with asymmetrical heating has been presented. Uniform wall temperatures are prescribed as thermal boundary conditions. The governing differential equations were solved by a finite volume method. The SIMPLER algorithm for pressure velocity coupling was adopted. A new iterative scheme based on mass balance at inlet and outlet has been used. By solving the flow as an elliptic problem, the effect of vertical diffusion of thermal energy, which was neglected in previous numerical studies, was taken into consideration. Variation of the mean velocity and average Nusselt number for Rayleigh number range of 10 to 103, channel aspect ratio range of 10 to 103 and Prandtl numbers of 0.72 and 5 are determined. For uniform wall temperature the average Nusselt number based on wall to ambient temperature difference and heat flux at different points are compared to the experimental results. The results revealed that the average Nusselt number from the thermally active surface in an asymmetric channel to be higher than from a comparable surface in a symmetric configuration, for fixed channel aspect ratio, at low values of Rayleigh number. There was no appreciable change in Nusselt number when Prandtl number was changed from 0.72 to 5. The minimum axial pressure for free convective flow of air is the highest for the symmetric heating condition.
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Kolchanova, E. A., and N. V. Kolchanov. "THE EFFECT OF THIN AIR INTERLAYER ON CONVECTION INDUCED BY INTERNAL HEATING IN LAYERED POROUS MEDIUM." In ХХI International Conference on the Methods of Aerophysical Research (ICMAR 2022). Novosibirsk: Федеральное государственное бюджетное учреждение «Сибирское отделение Российской академии наук», 2022. http://dx.doi.org/10.53954/9785604788967_94.
Повний текст джерела
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Glitzky, A., K. Gartner, J. Fuhrmann, T. Koprucki, A. Fischer, B. Lussem, K. Leo, and R. Scholz. "Electro-thermal modeling of organic semiconductors describing negative differential resistance induced by self-heating." In 2013 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD). IEEE, 2013. http://dx.doi.org/10.1109/nusod.2013.6633132.
Повний текст джерела
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Bahga, S. S., A. Bhattacharya, and Roop L. Mahajan. "Numerical Modeling of Buoyancy Induced Convection in Finned Heat Sinks in Presence of Unheated and Heated Shrouds." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-80895.
Повний текст джерелаАнотація:
This paper investigates the effects of the presence of unheated and heated shrouds on the thermal performance of longitudinal finned heat sinks. A comprehensive numerical study was conducted to determine the impact of the shroud clearance from the tip of the fins and shroud heating. The first part of the study deals with the effects of an unheated shroud on finned heat sinks of different fin height, fin pitch and length in an attempt to cover a wide range of geometry. The numerical results reveal an optimum clearance for maximum heat transfer. For all heat sinks studied the unheated shroud improved the performance by as much as 15% until the shroud was very close when the performance decreased by as much as 10%. In the second part of the paper, the effects of heating of the shroud were considered. In these numerical runs, an isothermal boundary condition was imposed on the shroud. For the heating levels considered, it was found that heating of the shrouds can increase or lower the thermal performance of the heat sink depending on the heat sink geometry and shroud clearance. Finally, the numerical results also revealed a systematic dependence of the normalized Nusselt number on the Rayleigh number for a given heat sink geometry.
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Zhou, Leping, Yunfang Zhang, Lijun Yang, Xiaoze Du, Minami Yoda, and G. P. Peterson. "Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire." In ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/mnhmt2012-75067.
Повний текст джерелаАнотація:
The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.
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Torres-Hurtado, S. A., E. Flores-Flores, G. Beltran-Perez, Steven L. Neale, J. C. Ramirez-San-Juan, and R. Ramos-García. "Trapping and manipulation of microparticles using Rayleigh convection generated by laser-induced heating of an absorbing thin film." In SPIE NanoScience + Engineering, edited by Kishan Dholakia and Gabriel C. Spalding. SPIE, 2014. http://dx.doi.org/10.1117/12.2061266.
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Khan, Naushad Hasin, and M. A. Hassan. "Free Convection in Viscoplastic Fluid due to Partial Bi-Heating From Bottom." In ASME 2016 Heat Transfer Summer Conference collocated with the ASME 2016 Fluids Engineering Division Summer Meeting and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/ht2016-1065.
Повний текст джерелаАнотація:
The numerical investigation of laminar natural convection of viscoplastic fluid in a two dimensional square enclosure has been reported in this work. The enclosed fluid is subjected to partial bi-heating from the bottom wall and symmetrical cooling from the sides under steady condition. Yield stress fluid has been heated through two heaters symmetrically placed on the either side of the centre of the bottom wall of the square enclosure. The viscoplastic fluid is the one which requires a minimum critical stress called yield stress to flow otherwise behave as a solid, have been modeled with Herschel–Bulkley model. Such fluids have significant technological relevance due to its wide application ranging from cosmetics products, food processing industries, pharmaceuticals to natural occurring like flow of debris and lava. The solution of governing partial differential equations has been approached using finite volume based formulation. Non uniform set of grid has been used. The effects of yield stress, heat flux, and power law index on the flow and thermal characteristics of the free convection of Herschel-Bulkley fluids have been studied for a particular value of Prandtl number. The flow and thermal fields have been investigated for the following ranges of conditions: Rayleigh number varies between 103 and 106 whereas power law index ranges from 0 to 1. The heat transfer characteristic has been depicted with the help of isotherms and the flow field has been illustrated by streamlines. The onset of convection is substantially delayed due to presence of yield stress of the fluid. This results in enhanced critical Rayleigh number for onset of convection. With increase in the Yield number in turn yield stress, results in the weakening of heat transfer through convection and at a particular relatively higher value of Yield number the heat transfer is solely taken place by conduction mode. Due to the symmetry in both heating and boundary conditions, the obtained isotherms and streamlines of the right half are symmetrical to the left half of the square enclosure. The conductive mode of heat transfer becomes dominated by increasing yield stress and reducing Ra and vice versa. The simultaneous presence of yielded and unyielded region presents an interesting pattern in the convection zone. Furthermore, it can be seen that rise in heat flux, in turn Ra, promotes the buoyancy driven circulation of viscoplastic fluid i.e. enhances natural convective heat transfer. In addition, the effect of power law index has been investigated. Power law index has little effect on thermal distribution and flow field.