Heat Transfer Enhancement and Vortex Flow Structure Over a Heated Cylinder Oscillating in the Crossflow Direction

1999 ◽  
Vol 121 (4) ◽  
pp. 789-795 ◽  
Author(s):  
C. Gau ◽  
J. M. Wu ◽  
C. Y. Liang
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Flow Structure ◽  
Oscillation Amplitude ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Dominant Mode ◽  
Enhancement Of Heat Transfer ◽  
Heated Cylinder

Experiments are preformed to study the flow structure and heat transfer over a heated oscillating cylinder. Both flow visualization using a smoke wire and local heat transfer measurements around the cylinder were made. The excitation frequencies of the cylinder are selected at Fe/Fn = 0, 0.5, 1, 1.5, 2, 2.5, and 3. These include excitations at harmonic, subharmonic, superharmonic, and nonharmonic frequencies. Synchronization of vortex shedding with the cylinder excitation occurs not only at Fe/Fn = 1 but also at Fe/Fn = 3, which can greatly enhance the heat transfer. The simultaneous enhancement of heat transfer at the stagnation point, its downstream region, and the wake region of the flow suggests that different modes of instabilities occurring in the shear layer of the near wake are actually initiated and amplified far upstream in the stagnation point, which were suppressed in the accelerated flow region and re-amplified in the decelerated flow region. As long as the dominant mode of the instability is amplified by the excitation of cylinder, enhancement of heat transfer can be obtained. During the experiments, the Reynolds numbers vary from 1600 to 4800, the ratios of oscillation amplitude to diameter of the cylinder from 0.064 to 0.016.

Heat Transfer From a Cylinder in Crossflow With Transpiration Cooling

1963 ◽  
Vol 85 (2) ◽  
pp. 173-177 ◽  
Author(s):  
B. V. Johnson ◽  
J. P. Hartnett
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Heat Transfer Performance ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Stagnation Flow ◽  
Experimental Values ◽  
Good Agreement

Local heat-transfer measurements are reported for a transpiration-cooled cylinder in crossflow. The stagnation point measurements are found to be in good agreement with results from plane stagnation flow theory. In the laminar region beyond the stagnation point, the equivalent wedge method is found to predict heat-transfer performance within 10 percent of the experimental values. In the separated flow region the experimental results demonstrate that the transpiration process is still very effective in reducing the heat transfer.

Synchronization of Vortex Shedding and Heat Transfer Enhancement Over a Heated Cylinder Oscillating With Small Amplitude in Streamwise Direction

2000 ◽  
Vol 123 (6) ◽  
pp. 1139-1148 ◽  
Author(s):  
C. Gau ◽  
S. X. Wu ◽  
H. S. Su
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Small Amplitude ◽  
Oscillation Amplitude ◽  
Vortex Formation ◽  
Excitation Frequency ◽  
Local Heat Transfer ◽  
Dominant Mode ◽  
Streamwise Direction ◽  
Heated Cylinder

Experiments are performed to study the flow structure and heat transfer over a heated cylinder oscillating radially with small amplitude in streamwise direction. Both flow visualization using a smoke wire in the upstream and the local heat transfer measurements based on wall temperatures around the cylinder were made. The excitation frequencies of the cylinder are selected at Fe/Fn=0, 0.5, 1, 1.5, 2, 2.5, and 3. The oscillation amplitude selected is less than a threshold value of A/D=0.06 where synchronization of vortex shedding with the cylinder excitation was not expected. However, experiments indicate that synchronization still occurs which stimulates a great interest to study its enhancement in the heat transfer. Synchronization occurred at Fe/Fn=2 is antisymmetric vortex formation while synchronization at Fe/Fn=2.5 and 3 is symmetric type. The forward motion (advancing into the cross flow) of the cylinder during one cycle of oscillation has an effect to suppress the instability and the vortex formation. This leads to the occurrence of a smaller and symmetric vortex formation and a less enhancement of heat transfer than the case of antisymmetric type Fe/Fn=2. For excitations at lower frequencies Fe/Fn⩽1.5, all the vortex formations occurred are mostly antisymmetric. The dominant mode of the instability in the shear layer is actually the natural shedding frequency Fn of the vortex. A closer excitation frequency to 2Fn causes a greater enhancement in the heat transfer. During the experiments, the Reynolds numbers varies from 1600 to 3200, the dimensionless amplitude A/D from 0.048 to 0.016.

Local and Average Heat Transfer Characteristics for a Disk Situated Perpendicular to a Uniform Flow

1985 ◽  
Vol 107 (2) ◽  
pp. 321-326 ◽  
Author(s):  
E. M. Sparrow ◽  
G. T. Geiger
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Radial Distance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Average Heat ◽  
Radial Profiles

Wind tunnel experiments were performed to determine both the average heat transfer coefficient and the radial distribution of the local heat transfer coefficient for a circular disk facing a uniform oncoming flow. The experiments covered the range of Reynolds numbers Re from 5000 to 50,000 and were performed using the naphthalene sublimation technique. To complement the experiments, an analysis incorporating both potential flow theory and boundary layer theory was used to predict the stagnation point heat transfer. The measured average Nusselt numbers definitively resolved a deep disparity between information from the literature and yielded the correlation Nu = 1.05 Pr0.36 Re1/2. The radial distributions of the local heat transfer coefficient were found to be congruent when they were normalized by Re1/2. Furthermore, the radial profiles showed that the local coefficient takes on its minimum value at the stagnation point and increases with increasing radial distance from the center of the disk. At the outer edge of the disk, the coefficient is more than twice as large as that at the stagnation point. The theoretical predictions of the stagnation point heat transfer exceeded the experimental values by about 6 percent. This overprediction is similar to that which occurs for cylinders and spheres in crossflow.

Numerical Investigation of Heat Transfer Enhancement on a Small Scale Vortex Generator

2009 ◽  
Author(s):  
Jiansheng Wang ◽  
Zhiqin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Small Scale ◽  
Transfer Enhancement

The heat transfer characteristic and flow structure of fluid in the rectangular channel with different height vortex generators in small scale are investigated with numerical simulation. Meantime, the properties of heat transfer and flow of fluid in the rectangular channel are compared with the channel which located small scale vortex generator. The variation law of local heat transfer and flow structure in channel is obtained. The mechanism of heat transfer enhancement of small scale vortex generators is discussed in detail. It is found that the influence of vortex generator on heat transfer is not in proportion to the size of vortex generator. What is more, turbulent flow structure near the wall, which influences the temperature distribution near the wall, induces the variety of local heat transfer. The fluid movement towards to the wall causes the heat transfer enhanced. On the contrary, the fluid movement away from the wall decreases the local heat transfer.

Annular Liquid Film Flow Under Local Heating in Microchannel

2005 ◽  
Author(s):  
Elizaveta Ya. Gatapova ◽  
Vladimir V. Kuznetsov ◽  
Oleg A. Kabov ◽  
Jean-Claude Legros
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Biot Number ◽  
Gas Flow ◽  
Film Flow ◽  
Local Heating ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Liquid Film Flow

In our previous investigations the formation of liquid bump of locally heated laminar liquid film with co-current gas flow was obtained [1,2]. The evaporation of liquid was left out of account. Heat transfer to the gas phase was approximately specified by a constant Biot number [2,3]. The aim of this work is an investigation of the evaporation effect, the hydrodynamics and the heat transfer of liquid film flow in a channel 0.2–1 mm height. The 2-D model of locally heated liquid film moving under gravity and the action of co-current gas flow with low viscosity in a channel are considered. The channel can be inclined at an angle with respect to horizon. It is supposed that the height of the channel is much less than its width. Surface tension is assumed to depend on temperature. The velocity profiles for gas and liquid regions are found from problem of joint motion of isothermal non-deformable liquid film and gas flow. Using the findings the joint solution of heat transfer and diffusion problem with corresponding boundary condition is calculated. Having the temperature field in the whole of liquid and gas flow region we find a local heat transfer coefficient on the gas-liquid interface and Biot number as a function of flow parameters and spatial variables.

Heat Transfer Enhancement Caused by Sliding Bubbles

2003 ◽  
Vol 125 (3) ◽  
pp. 503-509 ◽  
Author(s):  
Baris B. Bayazit ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Thin Foil ◽  
Local Heat ◽  
Superheated Liquid ◽  
Enhancement Of Heat Transfer ◽  
Inclined Plates ◽  
Inclined Surface

Measurements that illustrate the enhancement of heat transfer caused by a bubble sliding under an inclined surface are reported. The data were obtained on an electrically heated thin-foil surface that was exposed on its lower side to FC-87 and displayed the output of a liquid crystal coating on the upper (dry) side. A sequence of digital images was obtained from two cameras: one that recorded the response of the liquid crystal and one that recorded images of the bubble as it moved along the heated surface. With this information, the thermal imprint of the bubble was correlated to its motion and position. A bubble generator that produced FC-87 bubbles of repeatable and controllable size was also developed for this study. The results show that both the microlayer under a sliding bubble and the wake behind the bubble contribute substantially to the local heat transfer rate from the surface. The dynamic behavior of the bubbles corresponded well with studies of the motion of adiabatic bubbles under inclined plates, even though the bubbles in the present study grew rapidly because of heat transfer from the wall and the surrounding superheated liquid. Three regimes of bubble motion were observed: spherical, ellipsoidal and bubble-cap. The regimes depend upon bubble size and velocity. A model of the heat transfer within the microlayer was used to infer the microlayer thickness. Preliminary results indicate a microlayer thickness of 40–50 μm for bubbles in FC-87 and a plate inclination of 12 deg.

Local Heat-Transfer Measurements during Forced-Convection Boiling in a Helically Coiled Tube

1969 ◽  
Vol 184 (3) ◽  
pp. 52-58 ◽  
Author(s):  
K. J. Bell ◽  
A. Owhadi
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Flow Structure ◽  
High Pressures ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Two Phase ◽  
Radial Acceleration ◽  
Local Coefficients ◽  
Small Density

Forced-convection boiling heat transfer to water at atmospheric pressure was studied in two helically coiled tubes. Temperature measurements were made at four positions round the tube at each of nine stations along the tube, permitting calculation of the local heat-transfer coefficient at each point. The local coefficients are correlated by the Lockhart-Martinelli parameters for two-phase flow, using the Seban-McLaughlin correlation for liquid phase heat transfer in coiled tubes. The curves for each of the four peripheral positions, compared to that previously obtained for the peripheral mean coefficient, are consistent with a flow structure having a vapour core with a strong secondary flow serving to distribute the liquid over the entire surface of the tube. The correlation and its interpretation in terms of flow structure may fail at high pressures as a result of the much smaller change in the radial acceleration in systems with small density difference between liquid and vapour.

Natural Convection in Vertically Vented Enclosures

1991 ◽  
Vol 113 (4) ◽  
pp. 912-918 ◽  
Author(s):  
D. M. Sefcik ◽  
B. W. Webb ◽  
H. S. Heaton
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Visualization ◽  
Flow Structure ◽  
Control Volume ◽  
Local Maximum ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall

Steady, laminar natural convection in vertically vented two-dimensional enclosures has been investigated both experimentally and analytically. A vertically vented enclosure is one in which the buoyancy-driven flow and heat transfer are restricted by vents in the top and bottom bounding walls of the enclosure. The local heat transfer along the heated wall was determined using Mach-Zehnder interferometry, and the flow structure was determined using a smoke generation flow visualization technique. Analytically, the governing conservation equations were solved numerically using a control volume-based finite difference technique. The results reveal strongly nonuniform local heat transfer along the isothermal wall as a result of the blockage at the inlet. A local maximum and minimum occur in the lower half of the enclosure. The flow visualization and analytical predictions for the flow field reveal that these heat transfer extrema are attributed to separated flow effects near the inlet gap with the associated primary inlet flow impingement and bifurcation at the heated wall. The analysis predicts well the flow structure and local and average heat transfer data. The results show asymptotic behavior to the classical vertical parallel plate result in the limit as the vent gap approaches the enclosure width.

scholarly journals Steady interaction of a turbulent plane jet with a rectangular heated cavity

2016 ◽  
Vol 20 (5) ◽  
pp. 1485-1498
Author(s):  
Farida Iachachene ◽  
Amina Mataoui ◽  
Yacine Halouane
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core

Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5<Lh?10). The Nusselt number increased and attained its maximum value at the stagnation points and then decreased. The flow structure is found in good agreement with the available experimental data. The maximum local heat transfer between the cavity walls and the flow occurs at the potential core end. The ratio between the stagnation point Nusselt numbers of the cavity bottom (NuB0) to the maximum Nusselt number on the lateral cavity wall (NuLmax) decreased with the Reynolds number for all considered impinging distances. For a given lateral confinement, the stagnation Nusselt number of the asymmetrical interaction Lh?10 is almost equal to that of the symmetrical interaction Lh=10.

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