Conjugate heat transfer in Rayleigh-Benard convection in a square enclosure.
Ontology highlight
ABSTRACT:
SUBMITTER: Saleh H
PROVIDER: S-EPMC4058157 | biostudies-other | 2014
REPOSITORIES: biostudies-other
Similar Datasets
Project description:Experimental study on free convection heat transfer was carried out inside shallow square enclosures filled with water. Two enclosures were used with size L × L × H (m3), where L and H are the side length and the inside thickness of the enclosure, respectively. Two different aspect ratios, ? = L/H, 7.143 and 12.0 were used. Constant heat flux boundary condition was applied at the bottom surface and stream of ambient air was applied at the top surface. Different values of constant heat fluxes were used as boundary conditions. For each aspect ratio of the enclosure, average Nusselt numbers were developed and correlated with the modified Rayleigh number. The results show that the heat transfer coefficient increases with the modified Rayleigh number with observed overlapping region between the two aspect ratios. A general overall correlation was developed using the aspect ratio as a parameter. The results also show that at the overlapping zone, the Nusselt number decreases as the aspect ratio increases for the fixed modified Rayleigh number.
| S-EPMC6209140 | biostudies-literature
Project description:The aim of the present numerical study is to analyze the conjugate natural convection heat transfer in a differentially heated square enclosure containing a conductive polygon object. The left wall is heated and the right wall is cooled, while the horizontal walls are kept adiabatic. The COMSOL Multiphysics software is applied to solve the dimensionless governing equations. The governing parameters considered are the polygon type, 3 ≤ N ≤ ∞, the horizontal position, 0.25 ≤ X 0 ≤ 0.75, the polygon size, 0 ≤ A ≤ π/16, the thermal conductivity ratio, 0.1 ≤ K r ≤ 10.0, and the Rayleigh number, 10(3) ≤ Ra ≤ 10(6). The critical size of the solid polygon was found exists at low conductivities. The heat transfer rate increases with the increase of the size of the solid polygon, until it reaches its maximum value. Here, the size of the solid polygon is reaches its critical value. Further, beyond this critical size of the solid polygon, will decrease the heat transfer rate.
| S-EPMC4060576 | biostudies-other
Project description:Turbulent Rayleigh-Bénard convection displays a large-scale order in the form of rolls and cells on lengths larger than the layer height once the fluctuations of temperature and velocity are removed. These turbulent superstructures are reminiscent of the patterns close to the onset of convection. Here we report numerical simulations of turbulent convection in fluids at different Prandtl number ranging from 0.005 to 70 and for Rayleigh numbers up to 107. We identify characteristic scales and times that separate the fast, small-scale turbulent fluctuations from the gradually changing large-scale superstructures. The characteristic scales of the large-scale patterns, which change with Prandtl and Rayleigh number, are also correlated with the boundary layer dynamics, and in particular the clustering of thermal plumes at the top and bottom plates. Our analysis suggests a scale separation and thus the existence of a simplified description of the turbulent superstructures in geo- and astrophysical settings.
| S-EPMC5974373 | biostudies-literature
Project description:Direct numerical simulations are employed to reveal three distinctly different flow regions in rotating spherical Rayleigh-Bénard convection. In the high-latitude region I vertical (parallel to the axis of rotation) convective columns are generated between the hot inner and the cold outer sphere. The mid-latitude region II is dominated by vertically aligned convective columns formed between the Northern and Southern hemispheres of the outer sphere. The diffusion-free scaling, which indicates bulk-dominated convection, originates from this mid-latitude region. In the equator region III , the vortices are affected by the outer spherical boundary and are much shorter than in region II .
| S-EPMC9285093 | biostudies-literature
Project description:We identify unique features of a highly-absorbing negatively photochromic molecular switch, donor acceptor Stenhouse adduct (DASA), that enable its use for self-regulating light-activated control of fluid flow. Leveraging features of DASA's chemical properties and solvent-dependent reaction kinetics, we demonstrate its use for photo-controlled Rayleigh-Bénard convection to generate dynamic, self-regulating flows with unparalleled fluid velocities (~mm s-1) simply by illuminating the fluid with visible light. The exceptional absorbance of DASAs in solution, uniquely controllable reaction kinetics and resulting spatially-confined photothermal flows demonstrate the ways in which photoswitches present exciting opportunities for their use in optofluidics applications requiring tunable flow behavior.
| S-EPMC7248117 | biostudies-literature
Project description:Combined sonication with dual-frequency ultrasound has been investigated to enhance heat transfer in forced convection. The test section used for this study consists of a channel with, on one hand, heating blocks normal to the water flow, equipped with thermocouples, and, on the other hand, two ultrasonic emitters. One is facing the heating blocks, thus the ultrasonic field is perpendicular, and the second ultrasonic field is collinear to the water flow. Two types of ultrasonic waves were used: low-frequency ultrasound (25 kHz) to generate mainly acoustic cavitation and high-frequency ultrasound (2 MHz) well-known to induce Eckart's acoustic streaming. A thermal approach was conducted to investigate heat transfer enhancement in the presence of ultrasound. This approach was completed with PIV measurements to assess the hydrodynamic behavior modifications under ultrasound. Sonochemiluminescence experiments were performed to account for the presence and the location of acoustic cavitation within the water flow. The results have shown a synergetic effect using combined low-and-high-frequency sonication. Enhancement of heat transfer is related to greater induced turbulence within the water flow by comparison with single-frequency sonication. However, the ultrasonically-induced turbulence is not homogeneously distributed within the water flow and the synergy effect on heat transfer enhancement depends mainly on the generation of turbulence along the heating wall. For the optimal configuration of dual-frequency sonication used in this work, a local heat transfer enhancement factor up to 366% was observed and Turbulent Kinetic Energy was enhanced by up to 84% when compared to silent regime.
| S-EPMC7786629 | biostudies-literature
Project description:Two differently-produced open-cell aluminum foams were compared to a commercially available finned heat sink. Further, an aluminum plate and block were tested as a reference. All heat sinks have the same base plate dimensions of four by six inches. The first foam was made by investment casting of a polyurethane preform and has a porosity of 0.946 and a pore density of 10 pores per linear inch. The second foam is manufactured by casting over a solvable core and has a porosity of 0.85 and a pore density of 2.5 pores per linear inch. The effects of orientation and radiative heat transfer are experimentally investigated. The heat sinks are tested in a vertical and horizontal orientation. The effect of radiative heat transfer is investigated by comparing a painted/anodized heat sink with an untreated one. The heat flux through the heat sink for a certain temperature difference between the environment and the heat sink's base plate is used as the performance indicator. For temperature differences larger than 30 °C, the finned heat sink outperforms the in-house-made aluminum foam heat sink on average by 17%. Furthermore, the in-house-made aluminum foam dissipates on average 12% less heat than the other aluminum foam for a temperature difference larger than 40 °C. By painting/anodizing the heat sinks, the heat transfer rate increased on average by 10% to 50%. Finally, the thermal performance of the horizontal in-house-made aluminum foam heat sink is up to 18% larger than the one of the vertical aluminum foam heat sink.
| S-EPMC5455404 | biostudies-other
Project description:This article investigates heat transfer enhancement in free convection flow of Maxwell nanofluids with carbon nanotubes (CNTs) over a vertically static plate with constant wall temperature. Two kinds of CNTs i.e. single walls carbon nanotubes (SWCNTs) and multiple walls carbon nanotubes (MWCNTs) are suspended in four different types of base liquids (Kerosene oil, Engine oil, water and ethylene glycol). Kerosene oil-based nanofluids are given a special consideration due to their higher thermal conductivities, unique properties and applications. The problem is modelled in terms of PDE's with initial and boundary conditions. Some relevant non-dimensional variables are inserted in order to transmute the governing problem into dimensionless form. The resulting problem is solved via Laplace transform technique and exact solutions for velocity, shear stress and temperature are acquired. These solutions are significantly controlled by the variations of parameters including the relaxation time, Prandtl number, Grashof number and nanoparticles volume fraction. Velocity and temperature increases with elevation in Grashof number while Shear stress minimizes with increasing Maxwell parameter. A comparison between SWCNTs and MWCNTs in each case is made. Moreover, a graph showing the comparison amongst four different types of nanofluids for both CNTs is also plotted.
| S-EPMC5446429 | biostudies-literature
Project description:This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.
| S-EPMC5353556 | biostudies-literature
Project description:The current work reports the thermophysical and flow measurements of novel thermal solvents based on deep eutectic solvents (DESs) and alumina-based nanoparticle-dispersed deep eutectic solvents (NDDESs) for its use as a potential solar energy storage medium. The DESs were synthesized using a hydrogen bond donor (i.e., oleic acid) and a hydrogen bond acceptor (i.e., dl-menthol) by using the COSMO-SAC-predicted equimolar ratio at a temperature of 350.15 K. Thereafter, NDDESs or nanofluids were formed by dispersing different volume fractions (0.001, 0.005, 0.0075, and 0.01) of Al2O3 nanoparticles in the DESs. The optimum volume fraction (0.005) of Al2O3 nanoparticles was selected through their thermophysical properties (density, viscosity, thermal conductivity, and specific heat capacity) and its agglomeration or stability behavior. As expected, NDDESs with a 0.005 volume fraction gave a higher enhancement in thermal conductivity, viscosity, heat capacity, and density as compared to DESs. To evaluate the heat transfer coefficient, forced convection experiments were conducted in a circular test section for both DESs and NDDESs under laminar conditions (Re = 124, 186, and 250). The enhancement of the local heat transfer coefficient was found to be higher when compared to their thermophysical properties. This was due to the nanoparticle migration resulting in a non-uniform distribution of both thermal conductivity and viscosity fields, which was inherently found to reduce the thermal boundary layer thickness. In the final section, the heat transfer coefficient and the Nusselt number were also validated with COMSOL Multiphysics simulations.
| S-EPMC6644315 | biostudies-literature