Multiple states and heat transfer in two-dimensional tilted convection with large aspect ratios

2018 ◽  
Vol 3 (11) ◽  
Author(s):  
Qi Wang ◽  
Zhen-Hua Wan ◽  
Rui Yan ◽  
De-Jun Sun
Keyword(s):  
Heat Transfer ◽  
Two Dimensional ◽  
Aspect Ratios

Modelling the influence of wall roughness on heat transfer in thermal convection

2011 ◽  
Vol 686 ◽  
pp. 568-582 ◽  
Author(s):  
Olga Shishkina ◽  
Claus Wagner
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Thermal Convection ◽  
Navier Stokes ◽  
Wall Roughness ◽  
Two Dimensional ◽  
Boundary Layer Equations ◽  
Aspect Ratios ◽  
Blasius Boundary Layer ◽  
Rayleigh Numbers

AbstractThe objective of this study is to approximate heat transport in thermal convection enhanced by the roughness of heated/cooled horizontal plates. The roughness is introduced by a set of rectangular heated/cooled obstacles located at the corresponding plates. An analytical model to estimate the Nusselt number deviations caused by the wall roughness is developed. It is based on the two-dimensional Prandtl–Blasius boundary layer equations and therefore is valid for moderate Rayleigh numbers and regular wall roughness, for which the height of the obstacles and the distances between them are significantly larger than the thickness of the thermal boundary layers. To validate this model, the transport of heat and momentum in rectangular convection cells is studied in two-dimensional Navier–Stokes simulations, for different aspect ratios of the obstacles. It is found that the model predicts the heat transport with errors ${\leq }6\hspace{0.167em} \% $ for all investigated cases.

Flow Instabilities and Heat Transfer in Buoyancy Driven Flows of Inelastic Non-Newtonian Fluids in Inclined Rectangular Cavities

2010 ◽  
Author(s):  
Dennis Siginer ◽  
Lyes Khezzar
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Heat Transfer Rate ◽  
Power Law ◽  
Transfer Rate ◽  
Newtonian Fluids ◽  
Two Dimensional ◽  
Aspect Ratios ◽  
Flow Configurations ◽  
Rayleigh Numbers

Steady two-dimensional natural convection in rectangular two dimensional cavities filled with non-Newtonian power law-Boussinesq fluids is numerically investigated. The conservation equations of mass, momentum and energy are solved using the finite volume method for varying inclination angles between 0° and 90° and two cavity height based Rayleigh numbers, Ra = 104 and 105, a Prandtl number of Pr = 102 and two cavity aspect ratios of 1, 4. For the vertical inclination of 90°, computations were performed for two Rayleigh numbers Ra = 104 and 105 and three Prandtl numbers of Pr = 102, 103 and 104. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. A comprehensive comparison between the Newtonian and the non-Newtonian cases is presented based on the dependence of the average Nusselt number Nu on the angle of inclination together with the Rayleigh number, Prandtl number, power law index n and aspect ratio dependent flow configurations which undergo several exchange of stability as the angle of inclination O̸ is gradually increased from the horizontal resulting in a rather sudden drop in the heat transfer rate triggered by the last loss of stability and transition to a single cell configuration. Despite significant differences in the heat transfer rate and flow configurations both Newtonian and non-Newtonian fluids of the power law type exhibit qualitatively similar behavior.

scholarly journals Numerical study of flow and heat transfer in differentially heated enclosures

2014 ◽  
Vol 18 (2) ◽  
pp. 451-463 ◽  
Author(s):  
Byong-Hoon Chang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Two Dimensional ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Heated Air ◽  
Side Walls ◽  
Laminar Natural Convection

Two-dimensional laminar natural convection is studied numerically for differentially heated air-filled rectangular enclosures with adiabatic side walls and aspect ratios of 1, 2, 4 and 8. The inclination angle of the enclosure was varied from 0? to 180?, and the effect of inclination on flow field and heat transfer was investigated over the range 103 ? Ra ? 106. Correlations of average Nusselt number based on the present results are presented for horizontal and vertical cases. Large discrepancies were found among published results.

The effect of aspect ratios of rib on the heat transfer and laminar water/TiO 2 nanofluid flow in a two-dimensional rectangular microchannel

2017 ◽  
Vol 236 ◽  
pp. 254-265 ◽  
Author(s):  
Qumars Gravndyan ◽  
Omid Ali Akbari ◽  
Davood Toghraie ◽  
Ali Marzban ◽  
Ramin Mashayekhi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Two Dimensional ◽  
Nanofluid Flow ◽  
Rectangular Microchannel ◽  
Aspect Ratios

Numerical Study of Natural Convective Heat Transfer in a Two-Dimensional Cavity With Centrally Located Partition Utilizing Nanofluids

2009 ◽  
Vol 1 (3) ◽  
Author(s):  
S. H. Anilkumar ◽  
Biju T. Kuzhiveli
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Finite Difference Schemes ◽  
Valuable Insight ◽  
Computational Domain ◽  
Two Dimensional ◽  
Volume Fractions ◽  
Aspect Ratios ◽  
Wide Range

A two-dimensional single-phase natural convective heat transfer in a cavity with centrally located thin partition utilizing nanofluids has been numerically analyzed. The nanofluid used, which is composed of aluminum nanoparticles in suspension of Benzene, was provided at various solid volume fractions. The study is carried out numerically for a range of Rayleigh numbers, solid volume fractions, partition heights, and aspect ratios. Regions with the same velocity and temperature distributions are identified as a symmetry of sections. One-half of such a rectangular region is chosen as the computational domain, taking into account the symmetry about the thin partition. The governing equations are modeled by a stream function-vorticity formulation and are solved numerically by finite-difference schemes. Comparison with previously published numerical and experimental results showed excellent agreement. It is demonstrated that the partition height has a strong effect on both the heat transfer rate and the flow pattern. Results are presented in the form of streamlines and isotherm plots. The variation in the local Nusselt number along the thin partition provides valuable insight into the physical processes. A new correlation is proposed for the heat transfer studies in a wide range of thermal and geometric parameters.

scholarly journals Aspect ratio effects in Rayleigh–Bénard convection of Herschel–Bulkley fluids

2017 ◽  
Vol 34 (5) ◽  
pp. 1658-1676 ◽  
Author(s):  
Mohammad Saeid Aghighi ◽  
Amine Ammar
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Rayleigh Number ◽  
Two Dimensional ◽  
Content Type ◽  
Bingham Number ◽  
Aspect Ratios ◽  
Power Law Index ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

Purpose The purpose of this paper is to analyze two-dimensional steady-state Rayleigh–Bénard convection within rectangular enclosures in different aspect ratios filled with yield stress fluids obeying the Herschel–Bulkley model. Design/methodology/approach In this study, a numerical method based on the finite element has been developed for analyzing two-dimensional natural convection of a Herschel–Bulkley fluid. The effects of Bingham number Bn and power law index n on heat and momentum transport have been investigated for a nominal Rayleigh number range (5 × 103 < Ra < 105), three different aspect ratios (ratio of enclosure length:height AR = 1, 2, 3) and a single representative value of nominal Prandtl number (Pr = 10). Findings Results show that the mean Nusselt number Nu¯ increases with increasing Rayleigh number due to strengthening of convective transport. However, with the same nominal value of Ra, the values of Nu¯ for shear thinning fluids n < 1 are greater than shear thickening fluids n > 1. The values of Nu¯ decrease with Bingham number and for large values of Bn, Nu¯ rapidly approaches unity, which indicates that heat transfer takes place principally by thermal conduction. The effects of aspect ratios have also been investigated and results show that Nu¯ increases with increasing AR due to stronger convection effects. Originality/value This paper presents a numerical study of Rayleigh–Bérnard flows involving Herschel–Bulkley fluids for a wide range of Rayleigh numbers, Bingham numbers and power law index based on finite element method. The effects of aspect ratio on flow and heat transfer of Herschel–Bulkley fluids are also studied.

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