Two-Dimensional Effects on Heat Transfer Rates From an Array of Straight Fins

1977 ◽  
Vol 99 (1) ◽  
pp. 129-132 ◽  
Author(s):  
N. V. Suryanarayana
Keyword(s):  
Heat Transfer ◽  
Two Dimensional ◽  
Transfer Rates ◽  
Dimensional Effects

The Effect of Entrance Configuration on Local Heat-transfer Coefficients in Subsonic Diffusers

1972 ◽  
Vol 94 (4) ◽  
pp. 355-359 ◽  
Author(s):  
E. O. Stoffel ◽  
J. R. Welty
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Transfer Equations ◽  
Subsonic Diffuser

The effects of square and reentrant entrances on flow regimes (no “appreciable” separation, large transitory stall, and fully developed two-dimensional stall) and local heat-transfer coefficients were determined with air flowing through a symmetrical, plane-wall, two-dimensional subsonic diffuser with one of the diverging walls heated and maintained isothermal. Flow and heat-transfer studies were made for the following ranges: 2θ = 0 to 45 deg, L/W = 6 to 18, and Rextut = 4 × 104 to 3 × 105. Results indicated that 2θ, L/W, and entrance configuration greatly affected the flow regime and heat transfer. Equations relating Um′ to Ut, Ur to Ut, and equations of the type Nu = C Pr0.6Rex0.8 are presented. For the configurations tested, heat-transfer rates were greater for reentrant than for square entrances.

scholarly journals Laser interferometry - Report #HT-01-2017

2021 ◽  
Author(s):  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Light Beam ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Laser Interferometry ◽  
Local Heat ◽  
Temperature Fields ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Transfer Rates

An introduction is given to the optical setup and principle of operation of classical and holographic interferometers that are used for convective he at transfer measurements. The equations for the evaluation of the temperature field are derived and methods of analysis are discussed for both two-dimensional and three-dimensional temperature fields. Emphasis is given to techniques for measuring local heat transfer rates. For two-dimensional fields, a method is presented for measuring the surface temperature gradient directly from a finite (wedge) fringe interferogram. This “direct gradient method” is shown to be most useful for the measurement of low convective heat transfer rates. For three-dimensional fields, the equations for calculating the beam-averaged local heat flux are presented. The measurement of the fluid temperature averaged along the light beam is shown to be approximate. However, an analysis is presented showing that for most cases the error associated with temperature variations in the light beam direction is small. Digital image analysis of interferograms to obtain fringe spacings is also discussed briefly.

Two-dimensional simulation of unsteady heat transfer from a circular cylinder in crossflow

2007 ◽  
Vol 570 ◽  
pp. 177-215 ◽  
Author(s):  
SALEM BOUHAIRIE ◽  
VINCENT H. CHU
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Length Scale ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Transfer Rates ◽  
Two Dimensional Model

The heat transfer from the surface of a circular cylinder into a crossflow has been computed using a two-dimensional model, for a range of Reynolds numbers from Re=200 to 15550. The boundary-layer separation, the local and overall heat-transfer rates, the eddy- and flare-detachment frequencies and the width of the flares were determined from the numerical simulations. In this range of Reynolds numbers, the heat-transfer process is unsteady and is characterized by a viscous length scale that is inversely proportional to the square root of the Reynolds number. To ensure uniform numerical accuracy for all Reynolds numbers, the dimensions of the computational mesh were selected in proportion to this viscous length scale. The small scales were resolved by at least three nodes within the boundary layers. The frequency of the heat flares increases, and the width of each flare decreases, with the Reynolds number, in proportion to the viscous time and length scales. Despite the presence of three-dimensional structures for the range of Reynolds numbers considered, the two-dimensional model captures the unsteady processes and produced results that were consistent with the available experimental data. It correctly simulated the overall, the front-stagnation and the back-to-total heat-transfer rates.

Negatively Buoyant Plume Flow in a Baffle

2008 ◽  
Author(s):  
S. K. S. Boetcher ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Two Dimensional ◽  
Buoyant Plume ◽  
Buoyant Flow ◽  
Transfer Rates ◽  
Offset Distance ◽  
Plume Flow ◽  
Negatively Buoyant ◽  
Surrounding Fluid

Transient two-dimensional negatively buoyant flow into a straight adiabatic baffle beneath an isothermal circular cylinder is numerically simulated. The surrounding fluid is considered infinite in extent and at constant temperature. Governing parameters are the baffle width and the offset of the entrance of the baffle beneath the center of the cylinder. Overall characteristics of the flow and entrainment of the surrounding fluid are found to be dependent on the baffle offset; however, the attachment length of the flow to the baffle wall is relatively insensitive to the offset. Heat transfer rates to the cylinder are calculated for various times for various baffle offsets. There is a weak dependence on baffle-offset distance with heat transfer rate.

Buoyant Flow and Heat Transfer in a Conducting Baffle

2008 ◽  
Author(s):  
S. K. S. Boetcher ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Quasi Steady State ◽  
Two Dimensional ◽  
Buoyant Flow ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Rayleigh Numbers ◽  
Negatively Buoyant ◽  
Surrounding Fluid

A numerical simulation of transient two-dimensional negatively buoyant flow into a straight baffle situated below an isothermal circular cylinder is performed. Both an adiabatic and a highly conducting baffle are considered over a range of Rayleigh numbers, 106 < RaD < 107. During the quasi-steady-state period, the surrounding fluid is effectively considered infinite in extent and at constant temperature. It is found that in general, the conducting baffle is at a disadvantage in maintaining a short attachment length which is needed to optimally slow the flow to prevent mixing. Qualitative flow fields are shown and heat transfer rates to the cylinder are calculated at the quasi-steady state.

Heat transfer at small Grashof numbers

1957 ◽  
Vol 238 (1214) ◽  
pp. 412-423 ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Ambient Temperature ◽  
Heat Conduction Equation ◽  
Body Shape ◽  
The Body ◽  
Conduction Equation ◽  
Two Dimensional ◽  
Transfer Rates ◽  
Theory And Experiment

Rough physical arguments suggest that the heat transfer from a body, immersed in a fluid, should be determined by the heat-conduction equation alone whenever the Grashof number, G , associated with the problem is small. However, heat-transfer rates predicted in this fashion are not always in accordance with the experimentally determined values. It is shown that, while convection is negligible in comparison with conduction near the body, it becomes as important at distances from the body of the order ( G ) -n , where n varies between 1/3 and ½ with the body shape. Whenever this distance is large in comparison with all the dimensions of the body the use of the conduction equation yields correct heat-transfer rates. If, however, this distance is small in comparison with the body length, the heat transfer may be calculated from the two-dimensional convection solution. An examination of the solutions in these two extreme cases reveals that the heat loss is the same as that by conduction to a certain surrounding surface maintained at ambient temperature. This interpretation enables certain qualitative deductions to be made for the case when the ratio of the lengths is neither large nor small. The agreement between theory and experiment is satisfactory.

The Measurement of Natural Convective Heat Transfer in Triangular Enclosures

1979 ◽  
Vol 101 (4) ◽  
pp. 648-654 ◽  
Author(s):  
R. D. Flack ◽  
T. T. Konopnicki ◽  
J. H. Rooke
Keyword(s):  
Heat Transfer ◽  
Two Dimensional ◽  
Transfer Rates ◽  
Transfer Data ◽  
Rectangular Enclosure ◽  
Wollaston Prism ◽  
Flow Interactions ◽  
Side Walls ◽  
Laminar Convection ◽  
Base Width

Heat transfer rates were experimentally measured for laminar convection air flows in two-dimensional triangular enclosures with two side walls which were heated and cooled and an adiabatic bottom. Both local and overall heat transfer data were obtained by the use of a Wollaston prism schlieren interferometer. The angle between the two isothermal side walls was varied between 60 and 120 deg, which resulted in a variation in aspect ratio (enclosure height/base width) between 0.29 and 0.87, while the Grashof number was varied between 2.9 × 106 and 9.0 × 106. Results are compared to previously obtained isothermal inclined flat plate data and rectangular enclosure data. Present results agree with rectangular enclosure results. One deviation from local rectangular enclosure data was found in the apex regions of the triangular enclosures, where complex thermal and flow interactions occurred due to proximity of the two side walls.

scholarly journals Laser interferometry - Report #HT-01-2017

2021 ◽  
Author(s):  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Light Beam ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Laser Interferometry ◽  
Local Heat ◽  
Temperature Fields ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Transfer Rates

An introduction is given to the optical setup and principle of operation of classical and holographic interferometers that are used for convective he at transfer measurements. The equations for the evaluation of the temperature field are derived and methods of analysis are discussed for both two-dimensional and three-dimensional temperature fields. Emphasis is given to techniques for measuring local heat transfer rates. For two-dimensional fields, a method is presented for measuring the surface temperature gradient directly from a finite (wedge) fringe interferogram. This “direct gradient method” is shown to be most useful for the measurement of low convective heat transfer rates. For three-dimensional fields, the equations for calculating the beam-averaged local heat flux are presented. The measurement of the fluid temperature averaged along the light beam is shown to be approximate. However, an analysis is presented showing that for most cases the error associated with temperature variations in the light beam direction is small. Digital image analysis of interferograms to obtain fringe spacings is also discussed briefly.

Two-Dimensional Effects on the Response of Packed Bed Regenerators

1989 ◽  
Vol 111 (2) ◽  
pp. 328-336 ◽  
Author(s):  
J. A. Khan ◽  
D. E. Beasley
Keyword(s):  
Heat Transfer ◽  
Void Fraction ◽  
Transient Response ◽  
Packed Bed ◽  
Wall Effect ◽  
Heat Transfer Fluid ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Dimensional Effects ◽  
Wide Range

Packed beds have a wide range of applications as heat transfer and energy storage devices. Employed as a regenerator, a packed bed is subject to the flow of a heat transfer fluid, which alternately stores and recovers energy from a packing of discrete particles. The flow direction reverses during the addition and removal of energy. The nature of a packing of discrete particles in a container is such that variations in the resistance to flow and in the void fraction occur across the cross section of the packing. Particularly, the region of the bed near the boundary of the container has a markedly reduced resistance to flow. In addition, the wall effect on the packing geometry changes the void fraction in the near-wall region. The purpose of the present study is to quantify the two-dimensional effects of nonuniform void fraction, velocity, and temperature distributions in a packed bed regenerator on the dynamic and steady periodic behavior. A two-dimensional numerical model of the transient response of a packed bed subject to the flow of a heat transfer fluid has been developed and verified through comparison with measured responses. The model includes the effects of nonuniform velocity and porosity in the bed, and the effects of axial and radial thermal dispersion. The results of the present computations are compared with one-dimensional transient periodic results to demonstrate the two-dimensional effects on the transient response of a packed bed regenerator to a step change in fluid temperature. The classical dimensionless parameters, such as reduced length and reduced time, are not sufficient to characterize the two-dimensional transient nature of a packed bed regenerator. This study identifies the range of bed-to-particle-diameter ratios over which the transient response is significantly influenced by the wall effect on void fraction and flow.

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