Heat Transfer in Separated, Reattached, and Redevelopment Regions Behind a Double Step at Entrance to a Flat Duct

1967 ◽  
Vol 89 (2) ◽  
pp. 163-167 ◽  
Author(s):  
E. G. Filetti ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Duct Flow ◽  
Double Step ◽  
Maximum Heat ◽  
Transfer Rates ◽  
Maximum Heat Transfer ◽  
Flow Cross

Experimental data are presented for local heat transfer rates near the entrance to a flat duct in which there is an abrupt symmetrical enlargement in flow cross section. Two enlargement area ratios are considered, and Reynolds numbers, based on duct hydraulic diameter, varied from 70,000 to 205,000. It is found that such a flow is characterized by a long stall on one side and a short stall on the other. Maximum heat transfer occurs in both cases at the point of reattachment, followed by a decay toward the values for fully developed duct flow. Empirical equations are given for the Nusselt number at the reattachment point, correlated as functions of duct Reynolds number and enlargement ratio.

Effect of Periodicity of Non-Uniform Sinusoidal Side Heating on Natural Convection in an Anisotropic Porous-Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 1613-1618 ◽  
Author(s):  
S. Kapoor ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Stream Function ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Porous Enclosure

A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.

Heat Transfer to Turbulent Swirling Flow Through a Sudden Axisymmetric Expansion

1987 ◽  
Vol 109 (3) ◽  
pp. 613-620 ◽  
Author(s):  
P. A. Dellenback ◽  
D. E. Metzger ◽  
G. P. Neitzel
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Bulk Fluid ◽  
Maximum Heat ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Maximum Heat Transfer

Experimental data are presented for local heat transfer rates in the tube downstream of an abrupt 2:1 expansion. Water, with a nominal inlet Prandtl number of 6, was used as the working fluid. In the upstream tube, the Reynolds number was varied from 30,000 to 100,000 and the swirl number was varied from zero to 1.2. A uniform wall heat flux boundary condition was employed, which resulted in wall-to-bulk fluid temperatures ranging from 14° C to 50°C. Plots of local Nusselt numbers show a sharply peaked behavior at the point of maximum heat transfer, with increasing swirl greatly exaggerating the peaking. As swirl incressed from zero to its maximum value, the location of peak Nusselt numbers was observed to shift from 8.0 to 1.5 step heights downstream of the expansion. This upstream movement of the maximum Nusselt number was accompanied by an increase in its magnitude from 3 to 9.5 times larger than fully developed tube flow values. For all cases, the location of maximum heat transfer occurred upstream of the flow reattachment point.

Heat Transfer Measurements on a Cooled Flat Plate Simulating Actual Size Turbine Hardware

1999 ◽  
Author(s):  
J. Lepicovsky ◽  
T. J. Bencic
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mach Number ◽  
Flat Plate ◽  
Boundary Layers ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Rates ◽  
Cooling Passage

Application of thin-film thermocouples and temperature sensitive paint to surface temperature and heat transfer rate measurement on a flat plate with internal cooling is described in this paper. The test arrangement was designed to model flow and heat transfer conditions in terms of gas (external) and coolant (internal) Reynolds numbers that are typical for cooled turbine components. The test article is geometrically simple; however, from the heat transfer point of view it represents a fairly complex case. For both flows, internal and external, the hydrodynamic boundary layers start well ahead of the thermal boundary layers. The thermally active surface is preceded by an adiabatic starting length. Also, the heat transfer occurs under nonisothermal wall conditions and nonuniform heat flux conditions. The heat transfer experiments were carried out for a range of Mach number and Reynolds number on the gas side from 0.17 to 0.53 and from 135 000 to 580 000, respectively. On the coolant side, the corresponding ranges were from 0.3 to 0.52 for the flow Mach number, and from 20 000 to 65 000 for the Reynolds number. Measured bulk heat transfer rates demonstrated expected trends as functions of external (gas) and internal (coolant) Reynolds numbers. Local heat transfer rates measured along the mid-span line behaved as expected in relation to the internal (coolant) Reynolds number. However, they seem to be insensitive to changes in the external (gas) Reynolds number — at least for the particular test arrangement. Local heat transfer rates, however, strongly depend on the location with respect to the width of the cooling passage. These results were not expected; they may be caused by three dimensional nature of heat convection and conduction in this test arrangement.

Heat Transfer in an Impingement Cooling System for Turbine Airfoils With a Sparse Distribution of Holes

2008 ◽  
Author(s):  
Jose Javier Alvarez ◽  
Pedro de la Calzada ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Duct Flow ◽  
Transfer Coefficients ◽  
Surface Distribution ◽  
Heat Transfer Coefficients ◽  
Turbine Airfoils

An experimental investigation of an engine representative Inter-Turbine Duct (ITD) vane with a very sparse distribution of impingement holes along the aerofoil surfaces was conducted using a transient liquid crystal technique. The low jet Reynolds numbers tested drove long crystal phase change times, which required special care when taking measured temperatures for processing the data to obtain accurate local heat transfer coefficients (HTC). Three jet Reynolds numbers (Re) around the design case were measured so that its local influence could be found. HTC results in terms of surface distribution and surface averaged values are presented and compared with some available literature correlations. Finally, an assessment is made of the extension of the local areas of influence where either impingement or duct flow prevails. The correlations which should be used in each of these influence areas are also identified and used to bound experimental results wihtin those limits.

Experimental Modeling of Convection Downstream from an Electronic Package Row

1989 ◽  
Vol 111 (3) ◽  
pp. 207-212 ◽  
Author(s):  
R. A. Wirtz ◽  
W. McAuliffe
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Channel Height ◽  
Transfer Rates ◽  
Recirculating Flow ◽  
Flow Reynolds Number ◽  
The Heat Transfer Coefficient

Experiments on convective heat transfer in the wake of a row of closely spaced pin-mount packages are reported. Flow visualization and interferometric heat transfer measurements are made in an induced draft wind tunnel where the package row is modeled with a two-dimensional transverse rib attached to one channel wall. The transverse rib has an aspect ratio of 5.25:1.0, and the channel height-to-rib height ratio is 4.0:1.0. Results are reported for coolant Reynolds numbers ranging from 1000 to 4000. Flow visualization shows the wake region to be similar to flow past a simple back step. Recirculating flow is found to extend from nine to three rib heights downstream from the rib, depending on the magnitude of the flow Reynolds number. Local heat transfer within this region is reduced relative to what would occur in the absence of the transverse rib, with average values of the heat transfer coefficient bracketed between laminar and turbulent correlations for simple back steps. Heat transfer rates further downstream, after reattachment of the flow, are in excess of those expected for flow with no transverse rib.

AN EXPERIMENTAL AND NUMERICAL STUDY OF HEAT TRANSFER IN A SIMULATED COLLECTOR FOR A SOLAR DRYER

1993 ◽  
Vol 17 (2) ◽  
pp. 145-160
Author(s):  
P.H. Oosthuizen ◽  
A. Sheriff
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Lower Surface ◽  
Local Heat ◽  
Electrical Heating ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Transfer Rates ◽  
Thermocouple Probe

Indirect passive solar crop dryers have the potential to considerably reduce the losses that presently occur during drying of some crops in many parts of the “developing” world. The performance so far achieved with such dryers has, however, not proved to be very satisfactory. If this performance is to be improved it is necessary to have an accurate computer model of such dryers to assist in their design. An important element is any dryer model is an accurate equation for the convective heat transfer in the collector. To assist in the development of such an equation, an experimental and numerical study of the collector heat transfer has been undertaken. In the experimental study, the collector was simulated by a 1m long by 1m wide channel with a gap of 4 cm between the upper and lower surfaces. The lower surface of the channel consisted of an aluminium plate with an electrical heating element, simulating the solar heating, bonded to its lower surface. Air was blown through this channel at a measured rate and the temperature profiles at various points along the channel were measured using a shielded thermocouple probe. Local heat transfer rates were then determined from these measured temperature profiles. In the numerical study, the parabolic forms of the governing equations were solved by a forward-marching finite difference procedure.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

1987 ◽  
Vol 109 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J. W. Baughn ◽  
H. Iacovides ◽  
D. C. Jackson ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Pipe Bend ◽  
Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

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