Fluid flow and heat transfer characteristics of natural convection in square cavities due to discrete source–sink pairs

Lattice Boltzmann method (LBM) was applied to predict fluid flow and heat transfer characteristics of natural convection in a two-dimensional square cavity driven by two discrete source-sink pairs on one vertical sidewall. The size of sources and sinks was L/4. The arrangement of the sources and sinks were alternately located. Simulations were conducted at Rayleigh number 103 to 105. The characteristics were represented by streamlines and isotherms. It was found that the solution is comparatively acceptable with other previous study applying conventional approach.

Laminar natural convection in a square cavity with 3D random roughness elements considering the compressibility of the fluid

Laminar natural convection in a two-dimensional square cavity filled with a pure air (Pr = 0.71) is studied numerically in the present article with nonuniform side-wall temperature. The heated vertical wall is assumed to have spatial sinusoidal temperature variations about a constant mean value, which is higher than the cold side-wall temperature, while the top and the bottom walls are adiabatic. A finite-volume method is used to solve numerically the nondimensional governing equations in the vorticity–stream function formulation. The effects of the amplitude and the wave number of the heated side-wall temperature variation on the natural convection in the cavity are investigated. It is found that the average Nusselt number varies based on the hot-wall temperature. It increases with an increase in the amplitude, while the maximum average Nusselt number occurs at the wave number of k = 0.7 for Rayleigh number range 103 ≤ Ra ≤ 106. It is found that the values of maximum fluid circulation occur at a similar wave number, which produces maximum heat transfer for small values of Ra, while it occurs at higher values of wave number at high Ra.

Comment on: “Fluid flow and heat transfer characteristics of natural convection in square cavities due to discrete source-sink pairs” [International Journal of Heat and Mass Transfer 51 (2008) 5949–5957]

Numerical simulations of the effect of an isotropic heat field on the entropy generation due to natural convection in a square cavity

The laminar natural convection in an air-filled square cavity with a partition on the heated vertical wall was experimentally investigated. Temperature measurements and flow visualizations were performed for cases with heated and cooled vertical walls (corresponding to a global Grashof number Gr H of approximately 1.4 × 108) and non dimensional top wall temperatures θ T of 0.57 (insulated) to 2.3. Experiments were performed with an aluminum partition with non dimensional height H P /H of 0.0625 and 0.125 attached to the heated vertical wall at y/H = 0.65 and 0.95. The blockage effect and/or the thermal effect of the partition resulted in changes to the temperature and flow fields but were mainly limited to the vicinity of the partition. For the cases with the heated top wall, the change in the height of the partition at y/H = 0.95 resulted in changes to the ambient temperature outside the boundary layer due to the reduction of the size of the recirculating flow in the corner region. The changes in the partition height and the top wall temperature affected the blockage effect of the partition, resulting in the local Nusselt number near the corner region to be affected. The local Nusselt number over most of the heated vertical wall of the partitioned cavity (y/H < 0.7) was correlated to the local Rayleigh number in the form Nu = C · Ra n .

Natural convection in a square cavity containing two heat-generating cylinders with different geometries

Numerical simulation of entropy generation due to natural convection heat transfer using Kernel Derivative-Free (KDF) Incompressible Smoothed Particle Hydrodynamics (ISPH) model

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Mohd Irwan Mohd Azmi, Nor Azwadi Che Sidik, Fudhail Abd. Munir, Suhaimi Misha, Nazri Md Daud, Nadlene Razali, Idris Mat Sahat; Free convection in square cavity driven by discrete three source–sink pairs on one sidewall. AIP Conference Proceedings 29 June 2012; 1440 (1): 242–246. https://doi.org/10.1063/1.4704223 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Wavy microchannels have been shown to possess improved heat transfer capabilities because of greater fluid mixing and boundary layer thinning. In this study, fluid flow and heat transfer characteristics of circular wavy microchannels with tangentially branched secondary channels, were numerically investigated. Its heat transfer and fluid flow characteristics were compared with other specific wavy microchannel geometries. Three-dimensional numerical studies were carried out in the Reynolds number range of 100–300 with uniform heat flux wall boundary condition, using Ansys Fluent commercial software. Validation of the model was done with experimental data from literature. Circular wavy microchannels, owing to constant curvature, lead to nearly constant Dean vortices strength. The tangential branched secondary channels helped in further effective fluid mixing and in reinitializing the boundary layer. These phenomena had significant effect on its heat transfer and fluid flow behavior. Circular wavy microchannels with tangentially branched secondary channels, having secondary channel width to primary channel width ratio (ω) equal to 0.25, showed higher overall performance than other designs considered in the present study. Velocity vectors, velocity and temperature contours are presented to explain the fluid flow and heat transfer characteristics. It is observed that circular wavy microchannels with tangentially branched secondary channel design (ω = 0.25) gives 39.36% higher Nusselt number with 21% increased pressure drop as compared to sinusoidal wavy microchannel design. The overall performance factor of circular wavy microchannel with tangentially branched secondary channel design (ω = 0.25) is higher in the Reynolds number range of 100–250 than all other designs considered in this study.

To investigate how the nonuniform fluid density distribution caused by large temperature variations affects the development of unsteady natural convection, we perform a series of direct numerical simulations of two-dimensional compressible natural convection in an air-filled square cavity. The cavity has a hot wall on the left and a cold wall on the right, and two horizontal walls are adiabatic. The simulations are done using a kinetic approach based on a modeled Boltzmann equation, from which the fully compressible Navier–Stokes–Fourier equations are recovered. No Boussinesq approximation or low Mach number approximation is made. An extra source term is introduced to adjust the fluid Prandtl number. Simulations are performed for a range of Rayleigh numbers (107−109) with a fixed dimensionless temperature difference of ε=0.6 to determine the critical Rayleigh number and study the development of unsteady flow. To illustrate the instability mechanism, instantaneous fluctuation field, time trace of temperature, and velocity at selected monitoring points, the spectrum and other statistics are presented and discussed. As expected, significant differences are observed between the instability of compressible natural convection and the Boussinesq-type natural convection. With a large temperature difference, the transition to unsteady flow is asymmetric for the flows near the hot wall and cold wall. For the Rayleigh number range we studied, the cold wall region is dominated by low-frequency impact instability of the boundary thermal jet at the bottom corner. For the hot wall region, besides the upper corner impact instability, a boundary layer instability featuring high-frequency oscillations is observed.

Numerical simulation of two-dimensional piston effect and natural convection in a square cavity heated from one side

Transient natural convection in a square cavity filled with a porous medium is studied numerically. The cavity is assumed heated from one vertical wall and cooled at the top, while the other walls are kept adiabatic. The governing equations are solved numerically by a finite difference method. The effects of Rayleigh number on the initial transient state up to the steady state are investigated for Rayleigh number ranging from 10 to 2 × 102. The evolutions of flow patterns and temperature distributions were presented for Rayleigh numbers, Ra = 102 and 103. It is observed that the time taken to reach the steady state is longer for low Rayleigh number and shorter for high Rayleigh number.

Heat transfer and fluid flow characteristics in microchannels heat exchanger using nanofluids: A review

Fluid flow and heat transfer around circular cylinder – flat and curved plates combinations