Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

1972 ◽  
Vol 94 (1) ◽  
pp. 7-14 ◽  
Author(s):  
L. B. Newman ◽  
E. M. Sparrow ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensor ◽  
Forward Region ◽  
Number Range ◽  
Free Stream Turbulence

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

scholarly journals Non-stationary convective heat transfer in an air synthetic impinging jet. Experiment and numerical simulation

2021 ◽  
Vol 2119 (1) ◽  
pp. 012024
Author(s):  
V.V. Lemanov ◽  
M.A. Pakhomov ◽  
V.I. Terekhov ◽  
Z. Travnicek
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Reynolds Stress Model ◽  
Heat Flux Sensor ◽  
Flux Sensor

Abstract An unsteady local heat transfer in an air synthetic non-steady-state jet impingement onto a flat plate with a variation of the Reynolds number, nozzle-to-plate distance and pulses frequency is experimentally and numerically studied. Measurements of the averaged and pulsating heat transfer at the stagnation point are conducted using a heat flux sensor. The axisymmetric URANS method and the Reynolds stress model are used for numerical simulations. For local values of heat transfer, zones with the maximum instantaneous value of heat flux and heat transfer coefficient are identified. The heat transfer increases at relatively low nozzle-to-plate distances (H/d ≤ 4). The heat transfer decreases at high distance from the orifice and target surface. An increase in the Reynolds number causes reduction of heat transfer.

The Influence of Free Stream Turbulence on the Local Heat Transfer From Cylinders

1960 ◽  
Vol 82 (2) ◽  
pp. 101-107 ◽  
Author(s):  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Intensity ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients

Local heat-transfer coefficients and recovery factors are presented for three different cylinders in a two-dimensional subsonic air flow, with emphasis on the effect of screen-produced turbulence on these quantities. The increase in turbulent intensity so realized produced larger local heat-transfer coefficients, in a way dependent upon the location on the cylinders, through a direct increase in the heat transfer to the laminar boundary layer, through an earlier transition to turbulence, or through an alteration in the character of the separated flow. Alternatively, recovery factors were affected less, being invariant with respect to the turbulent intensity for attached boundary layer flow, but demonstrating large changes in those separated flow regions for which increased free stream turbulence produced substantial changes in the nature of the separated flow.

Effect of Laminarization and Retransition on Heat Transfer for Low Reynolds Number Flow Through a Converging to Constant Area Duct

1982 ◽  
Vol 104 (2) ◽  
pp. 363-371 ◽  
Author(s):  
H. Tanaka ◽  
H. Kawamura ◽  
A. Tateno ◽  
S. Hatamiya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Parallel Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Parallel Plates ◽  
Number Range ◽  
Reynolds Number Flow ◽  
Turbulent Air Flow

A fully developed turbulent air flow between two parallel plates with the spacing of 15 mm was accelerated through a linearly converging passage of 200 mm in length, from which it flowed into a parallel-plate channel again. A foil heater was fastened on one wall surface over the entire channel, and local heat-transfer coefficient distribution was measured over the channel Reynolds number range of 5000 to 14,000 and also the slope of the accelerating section between 2/200 mm/mm and 10/200 mm/mm. (The acceleration parameter K ranged between 1.4 × 10−6 and 2 × 10−5.) The Nusselt number at the outlet of the accelerating section was considerably lower than in the initial fully turbulent state, suggesting laminarization of the flow. The measured Nusselt number continued to decrease in the first part of the downstream parallel-plate section to a minimum and then began to increase sharply, suggesting reversion to turbulent flow. Heat transfer along the parallel-converging-parallel plate system was reproduced fairly satisfactorily by applying a k-kL model of turbulence.

Heat Transfer Measurements on a Turbine Airfoil With Pressure Side Separation

2009 ◽  
Author(s):  
Helge Ladisch ◽  
Achmed Schulz ◽  
Hans-Jo¨rg Bauer
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Separation Bubble ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Local Heat ◽  
Free Stream Turbulence ◽  
Pressure Surface ◽  
Low Pressure Turbine

Heat transfer measurements on a highly loaded low-pressure turbine airfoil with a separation bubble on the pressure surface are presented. The experiments were conducted in a linear cascade at various free-stream turbulence intensities (Tu1 = 1.6% to 10%) and Reynolds numbers of the inflow. The effect of both quantities on heat transfer, separation and laminar-turbulent transition is quantified. Particle-Image-Velocimetry has been performed to study the characteristics of the separation bubble. The results reveal a considerable influence of the boundary layer separation on the local heat transfer. The size of the separation region is strongly influenced by free-stream turbulence level and Reynolds number.

Experimental Measurement of the Effect of Heat Flux on Local Heat Transfer Coefficient and Friction Coefficient in an Annulus

1965 ◽  
Vol 7 (3) ◽  
pp. 300-305 ◽  
Author(s):  
B. S. Larkin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Friction Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Number Range ◽  
Temperature Method

This paper describes a closed-circuit apparatus for the measurement of local heat transfer coefficients from the inner surface and overall friction coefficients for air flowing through an annulus (radius ratio 1.7). Results were obtained for Reynolds numbers from 35 000 to 170 000 for temperature ratios Ti/Tb up to 1.74. A novel type of heater bar was used in order to avoid some of the disadvantages of the more usual designs. The results were very consistent. It was found that the effect of heat flux on the heat transfer coefficient could be eliminated either by the film temperature method using a film temperature coefficient of 0.25 or by including a temperature ratio term ( TiTb)-0.2 in the Nu-Re relationship. Over most of the Reynolds number range the overall friction coefficient did not vary with heat flux.

Rod Bundle Heat Transfer: Steady-State Steam Cooling Experiments

2006 ◽  
Author(s):  
J. P. Spring ◽  
D. M. McLaughlin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Steam Cooling

Through the joint efforts of the Pennsylvania State University and the United States Nuclear Regulatory Commission, an experimental rod bundle heat transfer (RBHT) facility was designed and built. The rod bundle consists of a 7×7 square pitch array with spacer grids and geometry similar to that found in a modern pressurized water reactor. From this facility, a series of steady-state steam cooling experiments were performed. The bundle inlet Reynolds number was varied from 1 400 to 30 000 over a pressure range from 1.36 to 4 bars (20 to 60 psia). The bundle inlet steam temperature was controlled to be at saturation for the specified pressure and the fluid exit temperature exceeded 550 °C in the highest power tests. One important quantity of interest is the local convective heat transfer coefficient defined in terms of the local bulk mean temperature of the flow, local wall temperature, and heat flux. Steam temperatures were measured at the center of selected subchannels along the length of the bundle by traversing miniaturized thermocouples. Using an analogy between momentum and energy transport, a method was developed for relating the local subchannel centerline temperature measurement to the local bulk mean temperature. Wall temperatures were measured using internal thermocouples strategically placed along the length of each rod and the local wall heat flux was obtained from an inverse conduction program. The local heat transfer coefficient was calculated from the data at each rod thermocouple location. The local heat transfer coefficients calculated for locations where the flow was fully developed were compared against several published correlations. The Weisman and El-Genk correlations were found to agree best with the RBHT steam cooling data, especially over the range of turbulent Reynolds numbers. The effect of spacer grids on the heat transfer enhancement was also determined from instrumentation placed downstream of the spacer grid locations. The local heat transfer was found to be greatest at locations immediately downstream of the grid, and as the flow moved further downstream from the grid it became more developed, thus causing the heat transfer to diminish. The amount of heat transfer enhancement was found to depend not only on the spacer grid design, but also on the local Reynolds number. It was seen that decreasing Reynolds number leads to greater heat transfer enhancement.

Experimental Study of Surface-Mounted Obstacle Effects on Heat Transfer Enhancement by Using Transient Liquid Crystal Thermograph

2002 ◽  
Vol 124 (4) ◽  
pp. 762-769 ◽  
Author(s):  
W. M. Yan ◽  
R. C. Hsieh ◽  
C. Y. Soong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Crystal ◽  
Heat Transfer Enhancement ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Tandem Array ◽  
Vortical Flow ◽  
Transfer Enhancement

Effects of surface-mounted obstacles on the local heat transfer enhancement of a base plate are investigated by using transient liquid crystal thermograph technique. To explore the geometry effects of short obstacles, the height less than one hydraulic diameter (d), three cross-sectional shapes of obstacles, i.e., circular, square and diamond, with variations in number of obstacles, obstacle spacing, and free-stream Reynolds number are considered. The maximum number of the obstacles in tandem array is 3 and the spacing between obstacles is 1d, 2d, or 4d. The free-stream Reynolds number ranges from 2100 to 4200. The experimental results reveal that the local heat transfer enhancement in front of leading circular and square obstacles are better than the diamond one, while the influenced area by the obstacle of the diamond shape is most remarkable. The present results disclose that an intermediate height (0.5d) of the protruding elements is more beneficial to the heat transfer enhancement in wake of the obstacle. With the sweepback leading edge of the top surface, the diamond and circular obstacles produce vortical flow across the obstacles and thus enhance heat transfer downstream in wake. Increasing Reynolds number leads to an enhancement in heat transfer performance. The number of and the spacing between the obstacles in tandem array are also influential factors to the flow structure and heat transfer enhancement on the basic plate.

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