Journal articles on the topic 'Convection induced by differential heating'
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1
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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Kumar, Mahesh, G. Janardhana Reddy, N. Naresh Kumar, and O. Anwar Bég. "Computational study of unsteady couple stress magnetic nanofluid flow from a stretching sheet with Ohmic dissipation." Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanomaterials, Nanoengineering and Nanosystems 233, no. 2-4 (April 24, 2019): 49–63. http://dx.doi.org/10.1177/2397791419843730.
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To provide a deeper insight of the transport phenomena inherent to the manufacturing of magnetic nano-polymer materials, in the present work a mathematical model is developed for time-dependent hydromagnetic rheological nano-polymer boundary layer flow and heat transfer over a stretching sheet in the presence of a transverse static magnetic field. Joule heating (Ohmic dissipation) and viscous heating effects are included since these phenomena arise frequently in magnetic materials processing. Stokes’ couple stress model is deployed to simulate non-Newtonian microstructural characteristics. The Tiwari–Das nanoscale model is adopted which permits different nanoparticles to be simulated (in this article, both copper–water and aluminium oxide–water nanofluids are considered). Similarity transformations are utilized to convert the governing partial differential conservation equations into a system of coupled, non-linear ordinary differential equations with appropriate wall and free stream boundary conditions. The shooting technique is used to solve the reduced non-linear coupled ordinary differential boundary value problem via MATLAB symbolic software. Validation with published results from the literature is included for the special cases of non-dissipative and Newtonian nanofluid flows. Fluid velocity and temperature profiles for both copper and aluminium oxide (Al2O3) nanofluids are observed to be enhanced with greater non-Newtonian couple stress parameter and magnetic parameter, whereas the opposite trend is computed with greater values of unsteadiness parameter. The boundary layer flow is accelerated with increasing buoyancy parameter, elastic sheet stretching parameter and convection parameter. Temperatures are generally increased with greater couple stress rheological parameter and are consistently higher for the aluminium oxide nanoparticle case. Temperatures are also boosted with magnetic parameter and exhibit an overshoot near the wall when magnetic parameter exceeds unity (magnetic force exceeds viscous force). A decrease in temperatures is induced with increasing sheet stretching parameter. Increasing Eckert number elevates temperatures considerably. With greater nanoparticle volume fraction, both skin friction and Nusselt number are elevated, and copper nanoparticles achieve higher magnitudes than aluminium oxide.
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Kasim, Abdul Rahman Mohd, Nur Syamilah Arifin, Syazwani Mohd Zokri, and Mohd Zuki Salleh. "The Investigation of a Fluid-Solid Interaction Mathematical Model under Combined Convective Jeffrey Flow and Radiation Effect Embedded Newtonian Heating as the Thermal Boundary Condition over a Vertical Stretching Sheet." Defect and Diffusion Forum 399 (February 2020): 65–75. http://dx.doi.org/10.4028/www.scientific.net/ddf.399.65.
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The investigation on the interaction between solid and fluid under combined convective flow has been carried out mathematically. The Jeffrey fluid model is taken as the fluid phase and the model is being embedded with the dust particles (solid phase). This two-phase model is constructed by introducing the fluid-particles interaction forces in the momentum equations of the fluid and dust phases, respectively. The natural and forced convections together with the aligned magnetic field are considered on the fluid flow. Also, the Newtonian heating as thermal boundary condition is induced on the vertical stretching sheet. In order to reduce the complexity of the model, the governing equations are transformed from partial differential equation into ordinary differential equation via suitable similarity transformation. The solutions are obtained in terms of velocity and temperature profiles for the fluid and particles phases respectively whereby the Keller-box method is utilized to obtain the desired outcomes. The influences of several significant physical parameters are visualized graphically to clarify the flow and heat transfer characteristic for both phases. The investigation found that the fluid’s velocity is affected by the presence of the dust particles which led to decelerate the fluid transference. The present flow model is able to be compared with the single-phase fluid cases if the fluid-particle interaction parameter is ignored.
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Walelign, Tadesse, Eshetu Haile, Tesfaye Kebede, and Gurju Awgichew. "Heat and Mass Transfer in Stagnation Point Flow of Maxwell Nanofluid Towards a Vertical Stretching Sheet with Effect of Induced Magnetic Field." Mathematical Problems in Engineering 2021 (March 16, 2021): 1–15. http://dx.doi.org/10.1155/2021/6610099.
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This paper presents a mathematical model analysis of heat and mass transfer in a two-dimensional flow of electrically conducting, thermally radiative, and chemically reactive Maxwell nanofluid towards a vertical stretching and permeable sheet embedded in a porous medium. Boundary layer approximation and suitable transformations are used to reduce the governing differential equations convenient for computation. Eventually, the transformed nonlinear differential equations along with the corresponding boundary conditions are solved in the framework of optimal homotopy analysis method. The effects of induced magnetic field, buoyancy force, viscous dissipation, heat source, Joule heating, and convective boundary condition are analyzed in detail. The rates of heat, mass, and momentum transfer with respect to the relevant parameters are also examined in terms of the local Nusselt number, Sherwood number, and skin friction coefficients, respectively. Among the many results of the study, it is shown that the induced magnetic field, flow velocity, and temperature profiles are increasing functions of the Maxwell parameter. The results of the present study are also in a close agreement with previously published results under common assumptions.
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Shi, Xundan, and J. M. Khodadadi. "Laminar Natural Convection Heat Transfer in a Differentially Heated Square Cavity Due to a Thin Fin on the Hot Wall." Journal of Heat Transfer 125, no. 4 (July 17, 2003): 624–34. http://dx.doi.org/10.1115/1.1571847.
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A finite-volume-based computational study of steady laminar natural convection (using Boussinesq approximation) within a differentially heated square cavity due to the presence of a single thin fin is presented. Attachment of highly conductive thin fins with lengths equal to 20, 35 and 50 percent of the side, positioned at 7 locations on the hot left wall were examined for Ra=104,105,106, and 107 and Pr=0.707 (total of 84 cases). Placing a fin on the hot left wall generally alters the clockwise rotating vortex that is established due to buoyancy-induced convection. Two competing mechanisms that are responsible for flow and thermal modifications are identified. One is due to the blockage effect of the fin, whereas the other is due to extra heating of the fluid that is accommodated by the fin. The degree of flow modification due to blockage is enhanced by increasing the length of the fin. Under certain conditions, smaller vortices are formed between the fin and the top insulated wall. Viewing the minimum value of the stream function field as a measure of the strength of flow modification, it is shown that for high Rayleigh numbers the flow field is enhanced regardless of the fin’s length and position. This suggests that the extra heating mechanism outweighs the blockage effect for high Rayleigh numbers. By introducing a fin, the heat transfer capacity on the anchoring wall is always degraded, however heat transfer on the cold wall without the fin can be promoted for high Rayleigh numbers and with the fins placed closer to the insulated walls. A correlation among the mean Nu, Ra, fin’s length and its position is proposed.
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Tassaddiq, Asifa, Ibni Amin, Meshal Shutaywi, Zahir Shah, Farhad Ali, Saeed Islam, and Asad Ullah. "Thin Film Flow of Couple Stress Magneto-Hydrodynamics Nanofluid with Convective Heat over an Inclined Exponentially Rotating Stretched Surface." Coatings 10, no. 4 (April 1, 2020): 338. http://dx.doi.org/10.3390/coatings10040338.
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In this article a couple stress magneto-hydrodynamic (MHD) nanofluid thin film flow over an exponential stretching sheet with joule heating and viscous dissipation is considered. Similarity transformations were used to obtain a non-linear coupled system of ordinary differential equations (ODEs) from a system of constitutive partial differential equations (PDEs). The system of ordinary differential equations of couple stress magneto-hydrodynamic (MHD) nanofluid flow was solved using the well-known Homotopy Analysis Method (HAM). Nusselt and Sherwood numbers were demonstrated in dimensionless forms. At zero Prandtl number the velocity profile was analytically described. Furthermore, the impact of different parameters over different state variables are presented with the help of graphs. Dimensionless numbers like magnetic parameter M, Brownian motion parameter Nb, Prandtl number Pr, thermophoretic parameter Nt, Schmidt number Sc, and rotation parameter S were analyzed over the velocity, temperature, and concentration profiles. It was observed that the magnetic parameter M increases the axial, radial, drainage, and induced profiles. It was also apparent that Nu reduces with greater values of Pr. On increasing values of the Brownian motion parameter the concentration profile declines, while the thermophoresis parameter increases.
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Kalmova, M. A. "Dynamic inverse piezo-effect problem for a long piezoceramic thermoelastic cylinder." Herald of Dagestan State Technical University. Technical Sciences 47, no. 4 (January 21, 2021): 57–68. http://dx.doi.org/10.21822/2073-6185-2020-47-4-57-68.
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Objective. The objective of this work is to solve an unrelated dynamic problem of thermoelectroelasticity for a long hollow piezoceramic cylinder under the action of an electric load on its surfaces in the form of a potential difference.Methods. The mathematical formulation of the considered problem of thermoelectroelasticity includes a system of non-selfadjoint differential equations. At the first stage, the authors consider the associated inverse piezoelectric effect problem without taking into account the influence of the temperature field, and at the next stage, study the hyperbolic heat conduction problem (Lord–Shulman theory) for a given (defined) electroelastic field.Result. A new closed solution to the dynamic inverse piezoelectric effect problem for a long piezoceramic thermoelastic cylinder is constructed. The case of the action of a dynamic electric load in the form of a potential difference on its front surfaces is considered. The ambient temperature and the law of convection heat transfer (3-kind boundary condition) are set. The calculated relations obtained using the generalized method of finite integral transformations allow determining the stress-strain state and thermoelectric fields induced in a piezoceramic element under an arbitrary electrical external influence.Conclusion. The constructed solution allows determining the stress-strain state and electric field in a piezoceramic cylinder, as well as analyzing the effect of the induced temperature field on the electroelastic state of the system under consideration using the hyperbolic Lord–Shulman theory of thermal conductivity. Analysis of the numerical results allows concluding that there are insignificant energy losses associated with heating the electroelastic system. The developed calculation algorithm is used in the design of non-resonant and resonant piezoelectric measuring devices.
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Noranuar, Wan Nurain Nabilah, Ahmad Qushairi Mohamad, Yeou Jiann Lim, Sharidan Shafie, and Chuang Ching Dennis Ling. "Radiative Non-Coaxial Rotating Flow for Viscous Fluid over Accelerated Disk with MHD and Porosity Effects." Sains Malaysiana 51, no. 8 (August 31, 2021): 2669–80. http://dx.doi.org/10.17576/jsm-2022-5108-25.
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An analytical solution to analyze the effects of radiation, magnetic, and permeability in an accelerating non-coaxial rotation phenomenon is not yet reported in the previous studies. Therefore, a radiative mixed convection flow for non-coaxial rotating MHD viscous fluid in a porous medium past an accelerated disk is studied. The fluid motion in this problem is induced by two sources which are rotating and buoyancy force. The dimensional coupled differential equations subjected to initial and accelerated boundary conditions are transformed to the dimensionless equations by utilizing appropriate dimensionless variables. The Laplace transform technique is applied to generate the closed form analytical solution for this problem. The impacts of Prandtl number, Grashof number, radiation, magnetic, porosity, and accelerated parameters on the temperature and velocity fields are illustrated graphically. The velocity and temperature profiles satisfy both the initial and boundary conditions, and the present results are found in accordance to the published work. The velocity is improved with the assistance of acceleration, radiation and porosity, while the implementation of magnetic field causes the opposite effect. Increasing radiation leads to the growth of the thermal boundary layer as well as reducing the heat transmission rate. This result can significantly contribute to the designing of heating systems because the imposition of radiation able to sustain an environment for a specific temperature. The obtained analytical solution can be used to check the correctness of the solution obtained from the numerical and experimental studies.
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Yuan, Z., Y. K. Qian, J. Wu, and J. Qi. "The basic mechanism behind the hurricane-free warm tropical ocean." Atmospheric Chemistry and Physics Discussions 10, no. 1 (January 25, 2010): 1957–82. http://dx.doi.org/10.5194/acpd-10-1957-2010.
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Abstract. No hurricane is detected in the tropics off the Brazilian coast due to the lack of initial conditions (e.g., the weak vertical shear of horizontal wind) despite that high sea surface temperature is available. According to previous studies, the initial conditions (as the ingredients of hurricane's embryo) are related so that the thick warm-and-moist layer (due to the updraft vapour) below a cold-and-dry layer frames the convective instability which enhances diabatic processes accompanied by tropical cyclones with the weak vertical shear. So the basic question is how, starting with an internal-disturbance-free balance-situation, external forces create the rapidly-upward acceleration of moist air at the warm sea surface. The answer is revealed by the vertical-momentum equation which shows that boosted by the external-force-induced significant lower-layer equatorial westerly wind (LLEWW), the upward (unit-mass) acceleration could be as significant as the midlatitude Coriolis force. Besides creating cyclonic vortices through the upward acceleration and diabatic processes, the external-force-induced significant-LLEWW could directly create cyclonic wind shears along with easterly jets for the low-level cyclonic vorticity through reducing the peak value of zonally-homogeneous trade easterlies (centered at the Equator between the Northern and Southern Hemisphere subtropical high-belts). We emphasize external forces to avoid the ''chicken-and-egg'' problem accompanying nonlinear interactions of internal-forcing processes. The external-force-induced significant-LLEWW could result from the deflection of the cross-equatorial flow characterized by the seasonal shift coincident with that of locations of most embryos. This significant cross-equatorial flow is driven by the significant differential heating between the largest continent with the highest plateau and the largest ocean with the warm pool located to the east and on the equatorward side of the continent on the rotating Earth. Unfortunately, in the tropics off the Brazilian coast, the differential heating is weak between the relatively-small ocean and land mostly covered by tropical rainforest. No significant-LLEWW means no hurricane's embryo. A warm spawning ground without the embryo means no hurricane. Our investigation suggests that the external-force-induced significant-LLEWW embedded in the significant trade easterlies over the warm ocean be necessary and sufficient for making the embryo originate in an internal-disturbance-free balance-situation.
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Hong, Yulan, Guosheng Liu, and J. L. F. Li. "Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements." Journal of Climate 29, no. 21 (October 6, 2016): 7651–74. http://dx.doi.org/10.1175/jcli-d-15-0799.1.
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Abstract Although it is well established that cirrus warms Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m−2) induced by ice clouds trapping longwave radiation exceeds their cooling effect (~−16.7 ± 1.7 W m−2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m−2) globally on the earth–atmosphere system. The net warming is over 15 W m−2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m−2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year-round in the tropics. Ice cloud optical depth τ is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ≈ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.
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Mat Noor, Nur Azlina, Sharidan Shafie, Y. S. Hamed, and Mohd Ariff Admon. "Soret and Dufour effects on MHD squeezing flow of Jeffrey fluid in horizontal channel with thermal radiation." PLOS ONE 17, no. 5 (May 19, 2022): e0266494. http://dx.doi.org/10.1371/journal.pone.0266494.
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The fluid flow with chemical reaction is one of well-known research areas in the field of computational fluid dynamic. It is potentially useful in the modelling of flow on a nuclear reactor. Motivated by the implementation of the flow in the industrial application, the aim of this study is to explore the time-dependent squeeze flow of magnetohydrodynamic Jeffrey fluid over permeable medium in the influences of Soret and Dufour, heat source/sink and chemical reaction. The presence of joule heating, joule dissipation and radiative heat transfer are analyzed. The flow is induced due to compress of two surfaces. Conversion of partial differential equations (PDEs) into ordinary differential equations (ODEs) is accomplished by imposing similarity variables. Then, the governing equations are resolved using Keller-box approach. The present outcomes are compared with previously outcomes in the literature to validate the precision of present outcomes. Both outcomes are shown in close agreement. The tabular and graphical results demonstrate that wall shear stress and velocity profile accelerate with the surfaces moving towards one another. Moreover, the concentration, temperature and velocity profiles decreasing for the increment of Hartmann numbers and Jeffrey fluid parameters. The impacts of heat generation/absorption, joule dissipation and Dufour numbers enhance the heat transfer rate and temperature profile. In contrast, the temperature profile drops and the heat transfer rate boosts when thermal radiation increases. The concentration profile decelerates, and the mass transfer rate elevates with raise in Soret number. Also, the mass transfer rate rises for destructive chemical reaction and contrary result is noted for convective chemical reaction.
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Nguyen, Thi-Chinh, and Ching-Yuang Huang. "A Comparative Modeling Study of Supertyphoons Mangkhut and Yutu (2018) Past the Philippines with Ocean-Coupled HWRF." Atmosphere 12, no. 8 (August 17, 2021): 1055. http://dx.doi.org/10.3390/atmos12081055.
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The ocean-coupled Hurricane Weather Research and Forecasting (HWRF) system was used to investigate the evolution of Supertyphoons Mangkhut and Yutu (2018) over the Philippines Sea and near landfall in the northern Philippines. The simulation results indicate that Mangkhut at a deepening stage has a smaller track sensitivity to the use of different physics schemes but greater intensity sensitivity, which becomes reversed for Yutu at a weakening stage. When both upstream tracks are well simulated with some specific suite of physics schemes, sensitivity experiments indicate that both track deviations near the northern Philippines are only weakly modified by the air–sea interaction (ocean-coupled or uncoupled processes), the topographic effects of the Philippines terrain (retained or not), and the initial ocean temperature change along both typhoon tracks. The interactions between the internal typhoon vortex and the large-scale flow play an important role in the overall movement of both typhoons, which were explored for their structural and convective evolutions near the terrain. The wavenumber-one potential vorticity (PV) tendency budget of the typhoon vortex was analyzed to explain the induced typhoon translation from different physical processes. The west-northwestward translation for the stronger Mangkhut near the northern Philippines is primarily induced by both horizontal and vertical PV advection but with the latter further enhanced to dominate the northward deflection when closing in to the terrain. However, the northwestward translation and track deflection near landfall for the weaker Yutu are driven by the dominant horizontal PV advection. Differential diabatic heating is relatively less important for affecting the movement of both typhoons near landfall.
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Khan, Masood, Mahnoor Sarfraz, Sabba Mehmood, and Malik Zaka Ullah. "Irreversibility process analysis for SiO2-MoS2/water-based flow over a rotating and stretching cylinder." Journal of Applied Biomaterials & Functional Materials 20 (January 2022): 228080002211203. http://dx.doi.org/10.1177/22808000221120329.
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Entropy is the measure of the amount of energy in any physical system that is not accessible for the useful work, which causes a decrease in a system’s thermodynamic efficiency. The idea of entropy generation analysis plays a vital role in characterizing the evolution of thermal processes and minimizing the impending loss of available mechanical power in thermo-fluid systems from an analytical perspective. It has a wide range of applications in biological, information, and engineering systems, such as transportation, telecommunication, and rate processes. The analysis of the entropy generation of axisymmetric magnetohydrodynamic hybrid nanofluid [Formula: see text]/water flow induced by rotating and stretching cylinder in the presence of heat radiation, ohmic heating, and the magnetic field is focus of this study. Thermal energy transport of hybrid nanofluids is performed by applying the Maxwell model. Heat transport is carried out by using convective boundary condition. The dimensionless ordinary differential equations are acquired by similarity transformations. The numerical solution for these differential equations is obtained by the bvp4c program in MATLAB. A comparison between nanofluid and hybrid nanofluid is made for flow field, temperature, and entropy generation. Comparison of nanofluid flow with hybrid nanofluid flow exhibits a higher rate of heat transmission, while entropy generation exhibits the opposite behavior. It is observed that the flow and heat distribution increase as the solid volume fraction’s value grows. An increase in entropy is indicated by augmentation in the Brinkman number and temperature ratio parameter, but the Bejan number shows a declining trend. Furthermore, outcomes of the Nusselt number for hybrid nanofluid and nanofluid are calculated for various parameters. It is noticed that the Nusselt number is reduced for enlarging the magnetic field and Eckert number. The axial and azimuthal wall stress parameters are declined by augmenting the Reynolds number.
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Park, Young-Gyu, and J. A. Whitehead. "Rotating Convection Driven by Differential Bottom Heating*." Journal of Physical Oceanography 29, no. 6 (June 1999): 1208–20. http://dx.doi.org/10.1175/1520-0485(1999)029<1208:rcdbdb>2.0.co;2.
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Gladush, G. G., S. V. Drobyazko, V. V. Likhanskii, A. I. Loboiko, and Yu M. Senatorov. "Thermocapillary convection induced by laser surface heating." Quantum Electronics 28, no. 5 (May 31, 1998): 426–29. http://dx.doi.org/10.1070/qe1998v028n05abeh001241.
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Wang, C. Y., T. F. Morse, and J. W. Cipolla. "Laser-Induced Natural Convection and Thermophoresis." Journal of Heat Transfer 107, no. 1 (February 1, 1985): 161–67. http://dx.doi.org/10.1115/1.3247373.
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The influence of axial laser volumetric heating and forced convection on the motion of aerosol particles in a vertical tube has been studied using the Boussinesq approximation. For constant wall temperature, an asymptotic case provides simple temperature and velocity profiles that determine the convection and thermophoretic motion of small aerosol particles. Laser heating induces upward buoyant motion near the tube center, and when forced convection is downward, there may be an inflection in the velocity profile. For constant laser heating (a small absorption limit), a velocity profile may be found that will minimize the distance over which particles are deposited on the wall. Such an observation may have some bearing on the manufacture of preforms from which optical fibers are drawn.
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Kormanyos, Kenneth R. "Controlled differential forced convection heating for glass tempering processes." Journal of Non-Crystalline Solids 218 (September 1997): 235–41. http://dx.doi.org/10.1016/s0022-3093(97)00279-2.
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MULLARNEY, JULIA C., ROSS W. GRIFFITHS, and GRAHAM O. HUGHES. "Convection driven by differential heating at a horizontal boundary." Journal of Fluid Mechanics 516 (October 10, 2004): 181–209. http://dx.doi.org/10.1017/s0022112004000485.
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Hempel, Nele-Johanna, Matthias M. Knopp, Ragna Berthelsen, and Korbinian Löbmann. "Convection-Induced vs. Microwave Radiation-Induced in situ Drug Amorphization." Molecules 25, no. 5 (February 27, 2020): 1068. http://dx.doi.org/10.3390/molecules25051068.
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The aim of the study was to investigate the suitability of a convection oven to induce in situ amorphization. The study was conducted using microwave radiation-induced in situ amorphization as reference, as it has recently been shown to enable the preparation of a fully (100%) amorphous solid dispersion of celecoxib (CCX) in polyvinylpyrrolidone (PVP) after 10 min of continuous microwaving. For comparison, the experimental setup of the microwave-induced method was mimicked for the convection-induced method. Compacts containing crystalline CCX and PVP were prepared and either pre-conditioned at 75% relative humidity or kept dry to investigate the effect of sorbed water on the amorphization kinetics. Subsequently, the compacts were heated for 5, 10, 15, 20, or 30 min in the convection oven at 100 °C. The degree of amorphization of CCX in the compacts was subsequently quantified using transmission Raman spectroscopy. Using the convection oven, the maximum degree of amorphization achieved was 96.1% ± 2.1% (n = 3) for the conditioned compacts after 30 min of heating and 14.3% ± 1.4% (n = 3) for the dry compacts after 20 min of heating, respectively. Based on the results from the convection and the microwave oven, it was found that the sorbed water acts as a plasticizer in the conditioned compacts (i.e., increasing molecular mobility), which is advantageous for in situ amorphization in both methods. Since the underlying mechanism of heating between the convection oven and microwave oven differs, it was found that convection-induced in situ amorphization is inferior to microwave radiation-induced in situ amorphization in terms of amorphization kinetics with the present experimental setup.
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Ookouchi, Yasumasa, and Tohru Hada. "Chaotic Convection in a Simple System Modified by Differential Heating." Journal of the Physical Society of Japan 66, no. 2 (February 15, 1997): 369–78. http://dx.doi.org/10.1143/jpsj.66.369.
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Li, Bo-Wei, Min-Cheng Zhong, and Feng Ji. "Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection." Applied Sciences 10, no. 21 (November 3, 2020): 7795. http://dx.doi.org/10.3390/app10217795.
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Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation.
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Ichikawa, Hiroki, Kei Kurita, Yasuko Yamagishi, and Takatoshi Yanagisawa. "Cell pattern of thermal convection induced by internal heating." Physics of Fluids 18, no. 3 (March 2006): 038101. http://dx.doi.org/10.1063/1.2181047.
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Al-Aseeri, M., W. Guo, L. E. Johns, and R. Narayanan. "Can convection induced by heating delay a thermal explosion?" Physics of Fluids 20, no. 10 (October 2008): 104107. http://dx.doi.org/10.1063/1.2992559.
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Antohe, B. V., and J. L. Lage. "Amplitude effect on convection induced by time-periodic horizontal heating." International Journal of Heat and Mass Transfer 39, no. 6 (April 1996): 1121–33. http://dx.doi.org/10.1016/0017-9310(95)00207-3.
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Mao, Yadan, Chengwang Lei, and John C. Patterson. "Unsteady nearshore natural convection induced by constant isothermal surface heating." Journal of Fluid Mechanics 707 (July 20, 2012): 342–68. http://dx.doi.org/10.1017/jfm.2012.283.
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AbstractThe present investigation is concerned with natural convection in a wedge-shaped domain induced by constant isothermal heating at the water surface. Complementary to the study of daytime heating by solar radiation relevant to nearshore regions of lakes and reservoirs previously reported by the same authors, this study focuses on sensible heating imposed by the atmosphere when it is warmer than the water body. A semi-analytical approach coupled with scaling analysis and numerical simulation is adopted to resolve the problem. Two flow regimes are identified depending on the comparison between the Rayleigh number and the inverse of the square of the bottom slope. For the lower Rayleigh number regime, the entire flow domain eventually becomes isothermal and stationary. For the higher Rayleigh number regime, the flow domain is composed of two distinct subregions, a conductive subregion near the shore and a convective subregion offshore. Within the conductive subregion, the maximum local flow velocity occurs when the thermal boundary layer reaches the local bottom, and the subregion eventually becomes isothermal and stationary. In the offshore convective subregion, a steady state is reached with a distinct thermal boundary layer below the surface and a steady flow velocity. The dividing position between the two subregions and the major time and velocity scales governing the flow development in both subregions are proposed by the scaling analysis and validated by corresponding numerical simulation.
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Bekezhanova, Victoria B., and A. S. Ovcharova. "Convection regimes induced by local boundary heating in a liquid–gas system." Journal of Fluid Mechanics 873 (June 24, 2019): 441–58. http://dx.doi.org/10.1017/jfm.2019.433.
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In the framework of the complete formulation of the conjugate problem, the liquid–gas flow structure arising upon local heating using thermal sources is investigated numerically. The two-layer system is confined by solid impermeable walls. The Navier–Stokes equations in the Boussinesq approximation in the ‘streamfunction–vorticity’ variables are used to describe the media motion. The dynamic conditions at the interface are formulated in terms of the tangential and normal velocities, while the temperature conditions at the external boundaries of the system take into account the presence of local heaters. The influence of the number of heaters and heating modes on the dynamics and character of the appearing convective regimes is analysed. The steady and commutated heating modes for one and two heaters arranged at the lower boundary are investigated. The heating initiates convective and thermocapillary mechanisms causing the fluid motion. Transient regimes with the successive formation of two-vortex, quadruple-vortex and two-vortex flows are observed before the stabilization of the system in the uniform heating mode. A stable thermocapillary deflection appears at the interface above the heater. The commutated mode of heating entails oscillations of the interface with a change in the deflection form and the formation of travelling vortices in the fluids. The impact of particular mechanisms on the flow patterns is analysed. The paper presents typical distributions of the velocity and temperature fields in the system and the position of the interface for the considered cases.
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Blandino, Joseph R., and Earl A. Thornton. "Thermally Induced Vibration of an Internally Heated Beam." Journal of Vibration and Acoustics 123, no. 1 (July 1, 2000): 67–75. http://dx.doi.org/10.1115/1.1320446.
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Virtually all previous research on thermally induced vibrations has investigated vibrations caused by surface heating. This paper describes the first detailed study of a thermally induced vibration caused by internal heating. A mathematical model was developed to predict the thermal-structural behavior of an internally heated beam. The results from the model were verified using experimental data for an internally heated beam undergoing thermally induced vibrations. The model was shown to predict the steady-state temperatures accurately. The model predicted the steady-state displacements adequately, although it predicted the displacement histories with some error. The analysis showed that the natural frequency of the beam was more important than the heating rate in determining if vibrations will occur. Once initiated, the amplitude of the vibration increased until the amplitude was such that the heat removed by convection balanced the internal heating. The steady-state amplitude was not affected by the initial displacement of the beam. The convection heat transfer caused the vibrations and controlled the steady-state amplitude. This study showed that thermally induced vibrations of internally heated beams belong to the class of vibrations called self-sustaining oscillations.
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Devi, Santosh, and Mukesh Kumar Sharma. "MHD Boundary Layer Flow over a Cone Embedded in Porous Media with Joule Heating and Viscous Dissipation." Defect and Diffusion Forum 401 (May 2020): 131–39. http://dx.doi.org/10.4028/www.scientific.net/ddf.401.131.
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Aim of the paper is to study the Magnetohydrodynamic boundary layer flow over a cone under the effect of joule heating and viscous dissipation. The surface of the cone is cooled and heated by the flowing fluid having constant temperature along with variable heat transfer coefficient.The surface of the cone is subjected under the convective heat flux. The governing equation for MHD boundary layer flow are non-linear partial differential equations, are transformed into ordinary differential equations using similarity techniques. The reduced ordinary coupled equations are solved with Runge-Kutta’s fourth order method followed by shooting techniques. The effects on flow and heat convection of various physical parameters pertinent to the modeled problem are computed and analyzed and shown through graphs. Keywords: Mixed convection, cone, Boundary layer, Joule Heating, Convective boundary condition.
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Stewart, W. E., and J. L. Verhulst. "Experimental Free Convection From Piping in District Heating Utilidors." Journal of Energy Resources Technology 108, no. 2 (June 1, 1986): 173–78. http://dx.doi.org/10.1115/1.3231258.
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Experiments were performed to study the two-dimensional natural convection heat transfer from two heated isothermal horizontal cylinders to an isothermal-cooled rectangular enclosure. The experiments were designed to simulate the heat transfer encountered in underground heat distribution systems where steam and condensate lines are routed through underground or in-ground corridors (utilidors) from a central plant. The steam supply and condensate return lines were simulated with two copper cylinders. The fluid between the cylinders and enclosure was distilled water to simulate the Rayleigh number range encountered with air in actual utilidors. Results were obtained for the overall heat transfer coefficient between the two cylinders and the enclosure. The data was correlated over a Rayleigh number, RaL, range of 2.1 × 108 to 4.8 × 109 representative of the Rayleigh number, based upon a hypothetical gap width, in a typical utilidor exposed to extreme enclosure to piping temperature differential boundary conditions. The corresponding Nusselt numbers, NuL, ranged from 21 to 59 when both cylinders were heated for water as the intermediate fluid. Corresponding heat transfer coefficients calculated for the utilidor case with air as the intermediate fluid were found to be smaller compared to some other correlations for concentric cylinders.
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Di Piazza, Ivan, and Michele Ciofalo. "MHD free convection in a liquid-metal filled cubic enclosure. I. Differential heating." International Journal of Heat and Mass Transfer 45, no. 7 (March 2002): 1477–92. http://dx.doi.org/10.1016/s0017-9310(01)00252-6.
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Benmenzer, Soufyane, and Mohamed Si-Ameur. "NATURAL CONVECTION INDUCED BY VOLUMETRIC HEATING IN AN INCLINED POROUS CAVITY." Computational Thermal Sciences: An International Journal 9, no. 1 (2017): 77–92. http://dx.doi.org/10.1615/computthermalscien.2017018862.
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Kiran, Palle, and S. H. Manjula. "Internal Heat Modulation on Darcy Convection in a Porous Media Saturated by Nanofluid." Journal of Nanofluids 12, no. 3 (April 1, 2023): 666–75. http://dx.doi.org/10.1166/jon.2023.1959.
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In this paper we investigate the effect of internal heat modulation over a nanofluid saturated porous medium. We consider a small variation in time dependant heat source and vary sinusoidally with slow time. An energy equation will be altered by adding time dependant internal heat source. This internal heat source has its time dependent and independent parts. Time dependent part shows that the internal heat modulation over a porous media and defines controls on heat/mass transfer in the layer. We have performed a nonlinear stability analysis to investigate heat/mass transfer in the system. The nonlinear system of partial differential equations are transformed into nonlinear ordinary differential equations under similarity transforms up to the second term. This system has different system parameters and they have been investigated on heat and mass transfer graphically. The dual nature, stabilize or destabilize is due to the significant effect of internal heating modulation of the system. Further, the effect of internal heating is to destabilize the system, as a consequence heat/mass transfer enhances. It is found that internal heating modulation can be used effectively to regulate heat/mass transfer in the system.
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Adamou-Graham, P., and P. G. Daniels. "Plume flows in porous media driven by horizontal differential heating." Journal of Fluid Mechanics 696 (March 6, 2012): 263–84. http://dx.doi.org/10.1017/jfm.2012.34.
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AbstractIn this paper we describe flow through a porous medium in a two-dimensional rectangular cavity driven by differential heating of the impermeable lower surface. The upper surface is held at constant pressure and at a constant temperature equal to the minimum temperature of the lower surface, while the sidewalls are impermeable and thermally insulated. Numerical results for general values of the Darcy–Rayleigh number $R$ and the cavity aspect ratio $A$ are compared with theoretical predictions for the small Darcy–Rayleigh number limit $(R\ensuremath{\rightarrow} 0)$ where the temperature field is conduction-dominated, and with a boundary-layer theory for the large Darcy–Rayleigh number limit $(R\ensuremath{\rightarrow} \infty )$ where convection is significant. In the latter case a horizontal boundary layer near the lower surface conveys fluid to the hot end of the cavity where it rises to the upper surface in a narrow plume. Predictions are made of the vertical heat transfer through the cavity.
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Li, Zhenning, Song Yang, Xiaoming Hu, Wenjie Dong, and Bian He. "Charge in Long-Lasting El Niño Events by Convection-Induced Wind Anomalies over the Western Pacific in Boreal Spring." Journal of Climate 31, no. 10 (April 12, 2018): 3755–63. http://dx.doi.org/10.1175/jcli-d-17-0558.1.
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Abstract In this study, El Niño events are classified as long El Niño (LE) events and short El Niño (SE) events based on their durations, and the characteristics of the early stages of these events are investigated. Results indicate that LE events tend to start earlier compared to SE events, initiating in boreal spring and peaking in winter. Their early occurrence is attributed to the western equatorial Pacific (WEP) sea surface wind anomalies that benefit the eastward propagation of warm water by forcing the downwelling Kelvin waves. It is also found that the wind anomalies are potentially induced by the convection anomalies over the WEP in spring. Experiments with a fully coupled climate model forced by convection heating anomalies over the WEP show that El Niño events become stronger and longer after introducing anomalous convection heating. The convection anomalies induce an extensive anomalous westerly belt over the WEP, which charges El Niño by eastward-propagating Kelvin waves. Moreover, induced by the anomalously northward-shifted ITCZ heating and the suppressed heating over the Maritime Continent, the equatorially asymmetric westerly belt reduces the meridional shear of mean easterly wind in the lower latitudes, which maintains an anomalous equatorward Sverdrup transport and in turn prolongs the persistence of El Niño events. A case study of the 2015/16 super El Niño and a regression study by using a rainfall index in critical regions support the above results.
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Vadasz, P. "Three-Dimensional Free Convection in a Long Rotating Porous Box: Analytical Solution." Journal of Heat Transfer 115, no. 3 (August 1, 1993): 639–44. http://dx.doi.org/10.1115/1.2910734.
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A three-dimensional analytical solution to the steady-state free convection problem in a long rotating porous box is presented for large values of the porous media Ekman number. 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 two small parameters representing the reciprocal Ekman number in porous media and the aspect ratio of the domain. The results are focused towards the Coriolis effect on the flow. Secondary circulation was obtained in a plane orthogonal to the leading free convection plane. The results show that the Coriolis effect on free convection is controlled by a combined dimensionless group representing the ratio of the centrifugal Rayleigh number to the porous media Ekman number.
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Ghalambaz, Mohammad, S. A. M. Mehryan, Muneer A. Ismael, Ali Chamkha, and D. Wen. "Fluid–structure interaction of free convection in a square cavity divided by a flexible membrane and subjected to sinusoidal temperature heating." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 6 (June 6, 2019): 2883–911. http://dx.doi.org/10.1108/hff-12-2018-0826.
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Purpose The purpose of the present paper is to model a cavity, which is equally divided vertically by a thin, flexible membrane. The membranes are inevitable components of many engineering devices such as distillation systems and fuel cells. In the present study, a cavity which is equally divided vertically by a thin, flexible membrane is model using the fluid–structure interaction (FSI) associated with a moving grid approach. Design/methodology/approach The cavity is differentially heated by a sinusoidal time-varying temperature on the left vertical wall, while the right vertical wall is cooled isothermally. There is no thermal diffusion from the upper and lower boundaries. The finite-element Galerkin technique with the aid of an arbitrary Lagrangian–Eulerian procedure is followed in the numerical procedure. The governing equations are transformed into non-dimensional forms to generalize the solution. Findings The effects of four pertinent parameters are investigated, i.e., Rayleigh number (104 = Ra = 107), elasticity modulus (5 × 1012 = ET = 1016), Prandtl number (0.7 = Pr = 200) and temperature oscillation frequency (2p = f = 240p). The outcomes show that the temperature frequency does not induce a notable effect on the mean values of the Nusselt number and the deformation of the flexible membrane. The convective heat transfer and the stretching of the thin, flexible membrane become higher with a fluid of a higher Prandtl number or with a partition of a lower elasticity modulus. Originality/value The authors believe that the modeling of natural convection and heat transfer in a cavity with the deformable membrane and oscillating wall heating is a new subject and the results have not been published elsewhere.
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Han, Ji-Young, and Jong-Jin Baik. "A Theoretical and Numerical Study of Urban Heat Island–Induced Circulation and Convection." Journal of the Atmospheric Sciences 65, no. 6 (June 1, 2008): 1859–77. http://dx.doi.org/10.1175/2007jas2326.1.
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Abstract Urban heat island–induced circulation and convection in three dimensions are investigated theoretically and numerically in the context of the response of a stably stratified uniform flow to specified low-level heating that represents an urban heat island. In a linear, theoretical part of the investigation, an analytic solution for the perturbation vertical velocity in a three-dimensional, time-dependent, hydrostatic, nonrotating, inviscid, Boussinesq airflow system is obtained. The solution reveals a typical internal gravity wave field, including low-level upward motion downwind of the heating center. Precipitation enhancement observed downwind of urban areas may be partly due to this downwind upward motion. The comparison of two- and three-dimensional flow fields indicates that the dispersion of gravity wave energy into an additional dimension results in a faster approach to a quasi-steady state and a weaker quasi-steady flow well above the concentrated heating region in three dimensions. In a nonlinear, numerical modeling part of the investigation, extensive dry and moist simulations using a nonhydrostatic, compressible model with advanced physical parameterizations [Advanced Regional Prediction System (ARPS)] are performed. While the maximum perturbation vertical velocity in the linear internal gravity wave field exists in the downwind region close to the heating center, the maximum updraft in three-dimensional dry simulations propagates downwind and then becomes quasi stationary. In three-dimensional moist simulations, it is demonstrated that the downwind upward motion induced by an urban heat island can initiate moist convection and result in downwind precipitation. The cloud induced by the downwind upward motion grows rapidly to become deep convective clouds. Heavy rainfalls are localized in a region not far from the heating center by a convective precipitating system that is nearly stationary. The differences in results between two and three dimensions are explained by the presence of (moist) convergence in an additional dimension. The numerical simulation results indicate that the intensity and horizontal structure of the urban heat island affect those of circulation and convection and hence the distribution of surface precipitation.
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Tasaka, Yuji, and Yasushi Takeda. "Effects of heat source distribution on natural convection induced by internal heating." International Journal of Heat and Mass Transfer 48, no. 6 (March 2005): 1164–74. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2004.09.044.
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Khaoula, Ben Abdelmlek, and Ben Nejma Fayçal. "Improved Energy Efficiency of Mixed Convection Heating Process in Eccentric Annulus." Advances in Mechanical Engineering 13, no. 8 (August 2021): 168781402110391. http://dx.doi.org/10.1177/16878140211039150.
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This paper deals with a numerical study of mixed convection heat transfer in horizontal eccentric annulus. The inner cylinder is supposed hot and rotating, however the outer one is kept cold and motionless. The numerical problem was solved using COMSOL Multiphysics® which is based on finite element method. The resolution of the partial differential equations was conducted through an implicit scheme with the use of the damped Newton’s method. The present numerical analysis concerns the effect of eccentricity, rotation speed and Rayleigh number on the flow patterns, heat transfer rate, and energy efficiency of the process. It was found that the heat transfer rate increases with the increase of Rayleigh number. In addition, the heat transfer rate drops with the increase of rotation speed. Finally, we have demonstrated that maximum energy efficiency is achieved not only with higher Rayleigh number but also it is maximum with small eccentricity.
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Yang, Qiu, and Andrew J. Majda. "Upscale Impact of Mesoscale Disturbances of Tropical Convection on Convectively Coupled Kelvin Waves." Journal of the Atmospheric Sciences 75, no. 1 (January 2018): 85–111. http://dx.doi.org/10.1175/jas-d-17-0178.1.
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Tropical convection associated with convectively coupled Kelvin waves (CCKWs) is typically organized by an eastward-moving synoptic-scale convective envelope with numerous embedded westward-moving mesoscale disturbances. Such a multiscale structure of tropical convection is a challenge for present-day cloud-resolving simulations and its representation in global climate models. It is of central importance to assess the upscale impact of mesoscale disturbances on CCKWs as mesoscale disturbances propagate at various tilt angles and speeds. Besides, it is still poorly understood whether the front-to-rear-tilted vertical structure of CCKWs can be induced by the upscale impact of mesoscale disturbances in the presence of upright mean heating. Here, a simple multiscale model is used to capture this multiscale structure, where mesoscale fluctuations are directly driven by mesoscale heating and synoptic-scale circulation is forced by mean heating and eddy transfer of momentum and temperature. The results show that the upscale impact of mesoscale disturbances that propagate at tilt angles of 110°–250° induces negative lower-tropospheric potential temperature anomalies in the leading edge, providing favorable conditions for shallow convection in a moist environment, while the remaining tilt-angle cases have opposite effects. Even in the presence of upright mean heating, the front-to-rear-tilted synoptic-scale circulation can still be induced by eddy terms at tilt angles of 120°–240°. In the case with fast-propagating mesoscale heating, positive potential temperature anomalies are induced in the lower troposphere, suppressing convection in a moist environment. This simple model also reproduces convective momentum transport and CCKWs in agreement with results from a recent cloud-resolving simulation.
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Chandran, P., N. C. Sacheti, B. S. Bhadauria, and A. K. Singh. "Natural Convection in a Hydrodynamically and Thermally Anisotropic Non-Rectangular Porous Cavity: Effect of Internal Heat Generation/Absorption." International Journal of Applied Mechanics and Engineering 23, no. 3 (August 1, 2018): 595–609. http://dx.doi.org/10.2478/ijame-2018-0032.
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Abstract Laminar natural convection in a trapezoidal porous vertical cavity has been investigated in this work. It is assumed that the porous enclosure is filled up with a permeable material subject to hydrodynamic and thermal anisotropy, the flow being governed by the Darcy law as applicable to a non-isotropic medium. It is further assumed that (i) there is heating at the left vertical wall and cooling at the right wall of the enclosure and (ii) the flow domain is subject to the presence of heat source or heat sink. The partial differential equations governing the resulting free convection have been solved numerically in the non-dimensional forms. There arises a number of parameters relating to buoyancy, internal heating, cavity aspect ratio and inclination of the upper surface to the horizontal. The influence of these parameters has been illustrated and analyzed through contours of streamlines and isotherms. We have also discussed the role of internal heating as well as anisotropy on the heat transfer characteristics.