PIV Study on the Dimple Mid-Plane of a Narrow Rectangular Channel With Dimples Applied to One Wall

2011 ◽  
Author(s):  
Lucky V. Tran ◽  
Michelle I. Valentino ◽  
Abhishek Saha ◽  
Carson D. Slabaugh ◽  
Mark Ricklick ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Particle Image ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Local Flow ◽  
Flow Disturbances ◽  
Image Velocimetry ◽  
Channel Aspect Ratio ◽  
Effective Channel

This paper presents an investigation of the fluid flow in the fully developed portion of a rectangular channel (Aspect Ratio of 2) with dimples applied to one wall at channel Reynolds numbers of 20,000, 30,000, and 40,000. The dimples are applied in a staggered-row, racetrack configuration. Results for three different dimple geometries are presented: a large dimple, small dimple, and double dimple. Heat transfer and aerodynamic results from preceding works are presented in Nusselt number and friction factor augmentation plots as determined experimentally. Using particle image velocimetry, the region near the dimple feature is studied in detail in the location of the entrainment and ejection of vortical packets into and out of the dimple; the downstream wake region behind each dimple is also studied to examine the effects of the local flow phenomenon that result in improved heat transfer in the areas of the channel wall not occupied by a feature. The focus of the paper is to examine the secondary flows in these dimpled channels in order to support the previously presented heat transfer trends. The flow visualization is also intended to improve the understanding of the flow disturbances in a dimpled channel; a better understanding of these effects would lead the development of more effective channel cooling designs.

A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Three Dimple Geometries

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Michelle I. Valentino ◽  
Lucky V. Tran ◽  
Mark Ricklick ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Heat Transfer Augmentation ◽  
Flow Disturbances ◽  
Side Walls

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for waste heat recovery. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 28,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to isolate the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the nonfeatured portion of the channel wall resulting from the secondary flows created by the features. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with the highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested. Heat transfer within the dimple was shown to be less than that of the surrounding flat regions at low Reynolds numbers. Results for each dimple geometry show that dimples are capable of promoting heat transfer over the entire bottom wall surface as well as the side walls; thus the effects are not confined to within the dimple cavity.

scholarly journals Secondary flows and heat transfer in shallow flow around a cylinder: LES, PIV

2019 ◽  
Vol 196 ◽  
pp. 00028 ◽  
Author(s):  
Egor Palkin ◽  
Maxim Shestakov ◽  
Rustam Mullyadzhanov
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Plane Channel ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Secondary Motion ◽  
Horseshoe Vortices

We report on Large-eddy simulations (LES) of flow around a short cylinder mounted in a narrow plane channel in a range of Reynolds numbers 1000, 2000, 3750 based on the bulk velocity of the flow and diameter of the cylinder supplemented with Particle image velocimetry (PIV) measurements for the highest considered Re. First two cases appear to be steady, however, for Re=3750 the flow becomes unsteady with the wake dominated by periodic vortex shedding. In front of the cylinder typical horseshoe vortices are identified intensifying the skin friction and heat transfer on the wall, while in the near wake we observe a quasiperiodic low-frequency secondary motion in the form of a pair of counterrotating eddies developing in the transverse direction. The Karman vortex street remains the dominant pattern, but further downstream from the cylinder the transport across the channel is associated with the secondary streamwise vortices, as also previously observed in slot jets. We observe their impact on heat transfer and skin friction on the wall of the channel.

Effect of Rib Spacing on Heat Transfer in a Two Pass Rectangular Channel (AR = 2:1) at High Rotation Numbers

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Jiang Lei ◽  
Je-Chin Han ◽  
Michael Huh
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Orientation Angle ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Flow Angle ◽  
Rotation Numbers ◽  
Channel Aspect Ratio

In this paper, the effect of rib spacing on heat transfer in a rotating two-passage channel (aspect ratio, AR = 2:1) at orientation angle of 135 deg was studied. Parallel ribs were applied’ on leading and trailing walls of the rotating channel at the flow angle of 45 deg. The rib-height-to-hydraulic diameter ratio (e/Dh) was 0.098. The rib-pitch-to-rib-height (P/e) ratios studied were 5, 7.5, and 10. For each rib spacing, tests were taken at five Reynolds numbers from 10,000 to 40,000, and for each Reynolds number, experiments were conducted at four rotational speeds up to 400 rpm. Results show that the heat transfer enhancement increases with decreasing P/e from 10 to 5 under nonrotation conditions. However, the effect of rotation on the heat transfer enhancement remains about the same for varying P/e from 10 to 5. Correlations of Nusselt number ratio (Nu/Nus) to rotation number (Ro) or local buoyancy parameter (Box) are existent on all surfaces (leading, trailing, inner and outer walls, and tip cap region) in the two-passage 2:1 aspect ratio channel.

Aerothermal Investigation of a Two-Pass Rotating Cooling Channel by Means of Particle Image Velocimetry and Liquid Crystal Thermography

2018 ◽  
Author(s):  
Dimitra Tsakmakidou ◽  
Ignacio Mayo ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Particle Image Velocimetry ◽  
Liquid Crystal ◽  
Particle Image ◽  
Flow Stability ◽  
Secondary Flows ◽  
Mean Flow ◽  
Liquid Crystal Thermography ◽  
Dean Vortices ◽  
Image Velocimetry

Heat transfer and aerodynamic measurements are conducted by means of Liquid Crystal Thermography and Particle Image Velocimetry in a two-pass rotating ribbed channel. The channel presents a square cross section, a sharp U-bend connecting the inlet and outlet passes and square ribs placed on two opposite walls, normal to the mean flow. In the heat transfer experimental campaign, the Reynolds (Re) and rotation (Ro) numbers are respectively ranging between 15,000–55,000 and 0–0.26 to investigate their influence upstream and downstream of the bend region. The aerodynamic measurements are taken in the symmetry plane of the channel at Re = 15,000 and Ro = 0 and 0.26, to complement the heat transfer data in the same regions. The results show how the Coriolis forces affect the flow stability and the secondary flow pattern. In the first pass, the behavior with varying Reynolds and rotation numbers is very similar to the one observed in a similar single-pass channel in terms of flow stability, velocity distribution and heat transfer performance. The measurements indicate an increase of the turbulent kinetic energy and the heat transfer downstream of the bend due to the large separation bubble, the high streamline curvature and the Dean vortices. Both the heat transfer and velocity distributions suggest that the interaction of the Dean vortices and Coriolis-induced secondary flows downstream of the bend is also highly dependent on the rotational regime.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

Experimental Study of Jet Flow Impingement Within a Rod Bundle Using PIV Technique

2008 ◽  
Author(s):  
Noushin Amini ◽  
Yassin A. Hassan
Keyword(s):  
Particle Image ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Reynolds Stresses ◽  
Particle Image Velocimetry Technique ◽  
Time Resolved ◽  
Rod Bundle ◽  
Piv Technique ◽  
Image Velocimetry

In this investigation Particle Image Velocimetry technique was implemented to a matched refractive index facility which was placed in a rectangular channel of L:1016 mm×W:76.2 mm×H:76.2 mm. Water was pumped into either one or both of the inlet jets which were entering the channel’s top wall with several different Reynolds numbers. The instantaneous and time-resolved velocity fields were successfully obtained from which several flow characteristics such as vorticity, turbulence instabilities and Reynolds stresses can be calculated.

A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Two Dimple Geometries

2011 ◽  
Author(s):  
Michelle I. Valentino ◽  
Lucky V. Tran ◽  
Mark Ricklick ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Heat Exchangers ◽  
Channel Wall ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
High Effectiveness ◽  
Heat Transfer Augmentation ◽  
Flow Disturbances

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for regeneration. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 27,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to minimize (to a negligible level) the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the non-featured portion of the channel wall. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 375-385 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Flow Behavior ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Local Flow ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]

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