Laminar Free Convection From a Sphere

1964 ◽  
Vol 86 (4) ◽  
pp. 537-541 ◽  
Author(s):  
T. Chiang ◽  
A. Ossin ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Surface Heat Flux ◽  
Numerical Solutions ◽  
Local Heat Transfer ◽  
Thermal Conditions ◽  
Local Heat ◽  
Surface Heat ◽  
Sphere Surface ◽  
Free Convective Flow ◽  
Boundary Layer Equations

The present paper is concerned with the solution to the problem of external free-convective flow from a sphere with various prescribed thermal conditions on the surface. Exact numerical solutions and heat-transfer results of the boundary-layer equations were obtained for the case of uniform surface temperature and the case of uniform surface heat flux, both at a Prandtl number of 0.70. Temperature and velocity profiles at various angular positions along the sphere surface and local heat-transfer results are presented. A comparison between the exact solution and the approximate solution from the integral method is also presented.

A New Experimental Technique for Measuring Surface Heat Transfer Coefficients Using Uncalibrated Liquid Crystals

1999 ◽  
Author(s):  
Wayne N. O. Turnbull ◽  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Technique ◽  
Surface Heat Flux ◽  
Local Heat ◽  
Surface Heat ◽  
Phase Delay ◽  
Transfer Coefficients ◽  
Periodic Surface ◽  
Heat Transfer Coefficients

Abstract A new experimental technique has been developed that permits the determination of local surface heat transfer coefficients on surfaces without requirement for calibration of the temperature-sensing device. The technique uses the phase delay that develops between the surface temperature response and an imposed periodic surface heat flux. This phase delay is dependent upon the thermophysical properties of the model, the heat flux driving frequency and the local heat transfer coefficient. It is not a function of magnitude of the local heat flux. Since only phase differences are being measured there is no requirement to calibrate the temperature sensor, in this instance a thermochromic liquid crystal. Application of a periodic surface heat flux to a flat plate resulted in a surface colour response that was a function of time. This response was captured using a standard colour CCD camera and the phase delay angles were determined using Fourier analysis. Only the 8 bit G component of the captured RGB signal was required, there being no need to determine a Hue value. From these experimentally obtained phase delay angles it was possible to determine heat transfer coefficients that compared well with those predicted using a standard correlation.

Radiant Interchange Between Circular Disks Having Arbitrarily Different Temperatures

1961 ◽  
Vol 83 (4) ◽  
pp. 494-502 ◽  
Author(s):  
E. M. Sparrow ◽  
J. L. Gregg
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Local Heat Transfer ◽  
Disk Surface ◽  
Radiant Heat ◽  
Local Heat ◽  
Radiant Heat Transfer ◽  
Disk Radius ◽  
Integral Equation Formulation ◽  
Different Temperatures

The problem of radiant heat transfer between parallel disks has been analyzed by generalizing the standard gray-body enclosure theory. In particular, the assumption that the radiant flux leaving a surface and the local heat flux are uniformly distributed over the surface has been lifted by an integral equation formulation. It has been shown that the general problem of disks at arbitrarily different temperatures can be conveniently broken down into two subproblems, each of which can be solved independently of the temperature level. Numerical solutions of the governing integral equations have been carried out for spacing ratios h/R (h = spacing, R = disk radius) ranging from 5.0 to 0.05 and for emissivities ranging from 0.1 to 0.9. Local heat-transfer results have been presented which, depending on spacing and emissivity, display marked variations over the disk surface. Over-all heat-transfer results have been calculated and compared with the predictions of the standard simplified enclosure theory. These predictions of the simplified theory were found to be unexpectedly good, especially in view of the large surface variations of the local heat transfer.

Effect of Uneven Wall Temperature on Local Heat Transfer in a Rotating Square Channel With Smooth Walls and Radial Outward Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 850-858 ◽  
Author(s):  
J.-C. Han ◽  
Y. M. Zhang
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Surface Heat Transfer ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Rotation Numbers

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating square channel with smooth walls and radial outward flow was investigated for Reynolds numbers from 2500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Three cases of thermal boundary conditions were studied: (A) four walls uniform temperature, (B) four walls uniform heat flux, and (C) leading and trailing walls hot and two side walls cold. The results show that the heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to rotation. For case A of four walls uniform temperature, the leading surface heat transfer coefficient decreases and then increases with increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. The decreased (or increased) heat transfer coefficients on the leading (or trailing) surface are due to the cross-stream and centrifugal buoyancy-induced flows from rotations. However, the trailing surface heat transfer coefficients, as well as those for the side walls, for case B are higher than for case A and the leading surface heat transfer coefficients for cases B and C are significantly higher than for case A. The results suggest that the local uneven wall temperature creates the local buoyancy forces, which change the effect of the rotation. Therefore, the local heat transfer coefficients on the leading, trailing, and side surfaces are altered by the uneven wall temperature.

An Experimental Investigation of the Heat Transfer to a Turbine Vane at Simulated Engine Conditions

1979 ◽  
Author(s):  
R. E. York ◽  
L. D. Hylton ◽  
R. G. Fox ◽  
J. C. Simonich
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Thermal Conditions ◽  
Local Heat ◽  
Data Sets ◽  
Transfer Data ◽  
Free Stream Turbulence ◽  
Turbine Vane ◽  
Turbulence Data ◽  
Few Data

Full application of 2D boundary layer calculations for heat transfer predictions during turbine vane design still awaits verification against relevant data. Although there are a few data sets in the literature, there is a definite need for basic vane heat transfer data under conditions that fully simulate the aerodynamic and thermal conditions of a modern turbine. Accordingly, an experiment was performed to obtain the local heat transfer distribution on a typical engine vane in an aerothermodynamic cascade facility. Heat transfer data were obtained for a range of Mach and Reynolds numbers. The cascade was closely coupled behind the facility burner so that the test included the effects of high free-stream turbulence. Turbulence data were obtained by LDV and are included.

Steady Free Convection to a Flat Plate With Uniform Surface Heat Flux and Nonuniform Acceleration

1964 ◽  
Vol 86 (4) ◽  
pp. 562-563 ◽  
Author(s):  
Robert Lemlich ◽  
Joseph Vardi
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Integral Method ◽  
Boundary Layer Thickness ◽  
Local Heat Transfer ◽  
Classical Case ◽  
Local Heat ◽  
Turbulent Boundary Layers ◽  
Surface Heat

Solutions for laminar and turbulent boundary layers are arrived at by means of the integral method. These show that the nonuniformity in acceleration results in distributions (along the plate) for the local heat transfer coefficient and boundary layer thickness which differ from the classical case of uniform acceleration. For the laminar boundary layer under nonuniform acceleration, these distributions yield results for uniform surface heat flux which are identical with those for uniform surface temperature. However, for the turbulent boundary layer, this identity does not apply.

The Free Convection of Heat from a Vertical Plate to Several Non-Newtonian “Pseudoplastic” Fluids

1972 ◽  
Vol 94 (1) ◽  
pp. 64-72 ◽  
Author(s):  
J. D. Dale ◽  
A. F. Emery
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Power Law ◽  
Vertical Plate ◽  
Numerical Solutions ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Minor Importance ◽  
Large Tank ◽  
Pseudoplastic Fluids

The local heat transfer, temperature, and velocity profiles were measured and numerically predicted for the free convection of heat from a vertical constant flux plate to several concentrations of carboxymethylcellulose (CMC) and carboxypolymethylene (Carbopol) powders in water. The fluids were found to have the thermal properties of water and in the shear stress range of interest to follow the power law of Ostwald–de Waele with flow indices varying from 0.395 to 1.0 and with fluid consistencies of 30 to 2300 times that of water. The tests were conducted using either of two plates (12 and 24 in. high) immersed in such a large tank (3000 lb of fluid) that the viscometric properties of the fluid remained unchanged, even for the long test periods used. All fluids, including those with yield stresses and those which suffered free surface effects, were found to transfer heat which could be correlated by the generalized Newtonian correlation Nux=C(Grx*Prx*n)13n+2 which suggests that the precise velocity characteristics of the fluid are of minor importance in determining the heat transfer performance of the system. The numerical solutions, based upon the boundary layer assumptions and the power-law model, were in excellent agreement with the experimental measurements.

Determination of Surface Heat Flux in Quenching

1999 ◽  
Author(s):  
M. K. Alam ◽  
H. Pasic ◽  
K. Anagurthi ◽  
R. Zhong
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Analytical Solution ◽  
Surface Heat Flux ◽  
Measurement Errors ◽  
Numerical Solutions ◽  
Heat Conduction Problem ◽  
Initial Guess ◽  
Surface Heat

Abstract Quench probes have been used to collect temperature data in controlled quenching experiments; the data is then used to deduce the heat transfer coefficients in the quenching medium. The process of determination of the heat transfer coefficient at the surface is the inverse heat conduction problem, which is extremely sensitive to measurement errors. This paper reports on an experimental and theoretical study of quenching carried out to determine the surface heat flux history during a quenching process by an inverse algorithm based on an analytical solution. The algorithm is applied to experimental data from a quenching experiment. The surface heat flux is then calculated, and the theoretical curve obtained from the analytical solution is compared with experimental results. The inverse calculation appears to produce fast, stable, but approximate results. These results can be used as the initial guess to improve the efficiency of iterative numerical solutions which are sensitive to the initial guess.

Turbulence and Heat Transfer Measurements in an Inclined Large Scale Film Cooling Array: Part II—Temperature and Heat Transfer Measurements

2011 ◽  
Author(s):  
Douglas R. Thurman ◽  
Lamyaa A. El-Gabry ◽  
Philip E. Poinsatte ◽  
James D. Heidmann
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Large Scale ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Surface Heat Transfer ◽  
Film Cooling Holes

The second of a two-part paper, this study focuses on the temperature field and surface heat transfer measurements on a large-scale models of an inclined row of film cooling holes. Detailed surface and flow field measurements were taken and presented in Part I. The model consists of three holes of 1.9-cm diameter that are spaced 3 hole diameters apart and inclined 30° from the surface. Additionally, another model with an anti-vortex adaptation to the film cooling holes is also tested. The coolant stream is metered and cooled to 20°C below the mainstream temperature. A thermocouple is used to obtain the flow temperatures along the jet centerline and at various streamwise locations. Steady state liquid crystal thermography is used to obtain surface heat transfer coefficients. Results are obtained for blowing ratios of up to 2 in order to capture off-design conditions in which the jet is lifted. Film cooling effectiveness values of 0.4 and 0.15 were found along the centerline for blowing ratios of 1 and 2 respectively. In addition, an anti-vortex design was tested and found to have improved film effectiveness. This paper presents the detailed temperature contours showing the extent of mixing between the coolant and freestream and the local heat transfer results.

Flow and heat transfer of the axisymmetric stagnation flow passing through irregular wafer

2008 ◽  
Vol 222 (7) ◽  
pp. 1237-1245
Author(s):  
C-C Wang ◽  
H-P Hu ◽  
Z-Y Lee
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Spline Approximation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Wafer Surface ◽  
Surface Geometry ◽  
Local Flow ◽  
Boundary Layer Equations ◽  
Heat Transfer Efficiency

A theoretical model for the two-dimensional, incompressible, and steady-state laminar forced convective flow over the irregular wafer is examined. Starting from the full Navier—Stokes equations and converting this into the boundary layer equations by the simple coordinate transformation. The resulting parabolic equations are solved using the cubic spline approximation. The numerical result shows that the local flow and local heat transfer characters of a wafer surface are greatly affected by the tiny concaves and convexes on the surface and have a frequency similar to that of surface geometry. The effect becomes obvious with the increase of radius, whereas the mean heat transfer efficiency remains slightly less than that of flat wafer.

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