A Numerical Study of the Effect of Blind Opening on Laminar-to-Turbulent Transition in the Flow Over a Simple Recessed Window-Plane Blind System

2010 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Turbulent Flow ◽  
Numerical Study ◽  
Plane Surface ◽  
Radiant Heat ◽  
Approximate Model ◽  
Radiant Heat Transfer ◽  
Buoyancy Forces ◽  
Open Plane

Most numerical studies of convective heat transfer between a window-blind system and a room are based on the assumption that the flow remains laminar. However, in the case of larger windows it is to be expected that transition to turbulent flow will occur in the system. The aim of the present study was to numerically determine when transition to turbulent flow occurs in a recessed window system and the effect of a simple partially open plane blind on when transition occurs. An approximate model of a recessed window that is covered by a partially open plane blind has been considered. The inner surface of the window is modeled as a plane vertical isothermal surface and the blind as a thin plane surface that offers no resistance to heat transfer. The fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being dealt with using the Boussinesq approach. Radiant heat transfer effects have been neglected. The k-epsilon turbulence model with the full effects of the buoyancy forces being accounted for has been used in obtaining the solution. The governing equations have been solved using the commercial finite-volume based cfd code FLUENT. The solution has as parameters: (1) the Rayleigh number, (2) the Prandtl number, (3) the dimensionless ‘window’ recess depth, (4) the dimensionless blind opening, and (5) whether the ‘window’ surface is at a higher or lower temperature than the room air. Because of the application being considered results have only been obtained for Pr = 0.7 and for the case where the ‘window’ surface is at a higher temperature than the room air. The effect of transition on the mean Nusselt number variation with Rayleigh number with various blind openings for various dimensionless window recess depths has in particular been studied.

A Numerical Study on the Slab Heating Characteristics in a Reheating Furnace With the Formation and Growth of Scale on the Slab Surface

2009 ◽  
Author(s):  
Dong Eun Lee ◽  
Jung Hyun Jang ◽  
Man Young Kim
Keyword(s):  
Heat Transfer ◽  
Present Model ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Radiant Heat ◽  
Transfer Model ◽  
Radiant Heat Transfer ◽  
Reheating Furnace ◽  
Combustion Gases ◽  
Scale Layer

In this work, the development of a mathematical heat transfer model for a walking-beam type reheating furnace is described and preliminary model predictions are presented. The model can predict the heat flux distribution within the furnace and the temperature distribution in the slab throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings, including the radiant heat transfer among the slabs, the skids, the hot combustion gases and the furnace wall as well as the gas convection heat transfer in the furnace. In addition, present model is designed to be able to predict the formation and growth of the scale layer on the slab in order to investigate its effect on the slab heating. A comparison is made between the predictions of the present model and the data from an in situ measurement in the furnace, and a reasonable agreement is found. The results of the present simulation show that the effect of the scale layer on the slab heating is considerable.

A Numerical Study of Three-Dimensional Convective Heat Transfer From a Window Covered by a Simple Partially-Open Plane Blind

2008 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Murat Basarir ◽  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Three Dimensional ◽  
Side Surface ◽  
Governing Equations ◽  
Three Dimensional Flow ◽  
Buoyancy Forces ◽  
Fluid Properties ◽  
Higher Temperature ◽  
Open Plane

Heat transfer from the room-side surface of a window covered by a plane blind to the surrounding room has been considered. The window is at a higher temperature than the air in the room. There is an open gap between the blind system and the window at the top of the window and the effect of the size of this gap on the window-to-air heat transfer rate has been numerically examined. Three-dimensional flow has been considered. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the window. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. The effects of the other dimensionless parameters on the window Nusselt number have been numerically determined.

A Numerical Study of Laminar and Turbulent Natural Convective Heat Transfer From an Isothermal Vertical Plate With a Wavy Surface

2010 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Turbulent Flow ◽  
Convective Heat Transfer ◽  
Transfer Rate ◽  
Surface Waviness ◽  
Dimensionless Amplitude ◽  
Buoyancy Forces ◽  
Rayleigh Numbers

Natural convective heat transfer from a wide isothermal plate which has a wavy surface, i.e., has a surface which periodically rises and falls, has been numerically studied. The main purpose of the study was to examine the effect of the surface waviness on the conditions under which transition from laminar to turbulent flow occurred and to study the effect of the surface waviness on the heat transfer rate. The surface waves, which have a saw-tooth cross-sectional shape, are normal to the direction of flow over the surface and have a relatively small amplitude. The range of Rayleigh numbers considered in the present study extends from values that for a non-wavy plate would be associated with laminar flow to values that would be associated with fully turbulent flow. The flow has been assumed to be steady and fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Boussinesq type approximation. A standard k-epsilon turbulence model with full account being taken of the effects of the buoyancy forces has been used in obtaining the solution. The solution has been obtained using the commercial CFD solver FLUENT. The solution has the following parameters: the Rayleigh number based on the plate height, the Prandtl number, the dimensionless amplitude of the surface waviness, and the dimensionless pitch of the surface waviness. Results have been obtained for a Prandtl number of 0.7 and for a single dimensionless pitch value for Rayleigh numbers between approximately 106 and 1012. The effects of Rayleigh number and dimensionless amplitude on the mean heat transfer rate have been studied. It is convenient in presenting the results to introduce two mean heat transfer rates, one based on the total surface area and the other based on the projected frontal area of the surface.

scholarly journals 3D Buoyancy Induced Heat Transfer in Triangular Solar Collector Having a Corrugated Bottom Wall

2018 ◽  
Vol 8 (2) ◽  
pp. 2651-2655 ◽  
Author(s):  
W. Aich
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Solar Collector ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Bottom Wall ◽  
Velocity Magnitude ◽  
Buoyancy Forces ◽  
Volume Method ◽  
Particles Trajectories

A numerical study of the natural convection heat transfer and fluid flow in 3D triangular solar collector having a corrugated bottom wall has been carried out using finite volume method. The aim of the study is to investigate how buoyancy forces influence airflow and temperature patterns inside the collector heated from below and cooled on its inclined walls while vertical ones are assumed to be perfect thermal insulators. Rayleigh number is the main parameter which changes from 103 to 105 and Prandtl number is fixed at Pr=0.71. Results are reported in terms of particles trajectories, iso-surfaces of temperature, velocity magnitude and mean Nusselt number. It has been found that the flow structure is sensitive to the value of Rayleigh number and that heat transfer is enhanced with increasing of this parameter.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

Radiant Heat Transfer From Isothermal Dispersions With Isotropic Scattering

1967 ◽  
Vol 89 (4) ◽  
pp. 300-308 ◽  
Author(s):  
R. H. Edwards ◽  
R. P. Bobco
Keyword(s):  
Heat Transfer ◽  
Approximate Solutions ◽  
Radiant Heat ◽  
Second Order ◽  
Isotropic Scattering ◽  
Radiant Heat Transfer ◽  
Approximate Methods ◽  
First Order ◽  
Order Solution ◽  
Radiant Transfer

Two approximate methods are presented for making radiant heat-transfer computations from gray, isothermal dispersions which absorb, emit, and scatter isotropically. The integrodifferential equation of radiant transfer is solved using moment techniques to obtain a first-order solution. A second-order solution is found by iteration. The approximate solutions are compared to exact solutions found in the literature of astrophysics for the case of a plane-parallel geometry. The exact and approximate solutions are both expressed in terms of directional and hemispherical emissivities at a boundary. The comparison for a slab, which is neither optically thin nor thick (τ = 1), indicates that the second-order solution is accurate to within 10 percent for both directional and hemispherical properties. These results suggest that relatively simple techniques may be used to make design computations for more complex geometries and boundary conditions.

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