Heat transfer and flow field measurements of a pulsating round jet impinging on a flat heated surface

Integrally cast turbine airfoils with wall-integrated cooling cavities are greatly applicable in modern turbines providing enhanced heat exchange capabilities compared to conventional cooling passages. In such arrangements, narrow impingement channels can be formed where the generated crossflow is an important design parameter for the achievement of the desired cooling efficiency. In this study, a regulation of the generated crossflow for a narrow impingement channel consisting of a single row of five inline jets is obtained by varying the width of the channel in the streamwise direction. A divergent impingement channel is therefore investigated and compared to a uniform channel of the same open area ratio. Flow field and wall heat transfer experiments are carried out at engine representative Reynolds numbers using particle image velocimetry (PIV) and liquid crystal thermography (LCT). The PIV measurements are taken at planes normal to the target wall along the centerline for each individual jet, providing quantitative flow visualization of jet and crossflow interactions. The heat transfer distributions on the target plate of the channels are evaluated with transient techniques and a multilayer of liquid crystals (LCs). Effects of channel divergence are investigated combining both the heat transfer and flow field measurements. The applicability of existing heat transfer correlations for uniform jet arrays to divergent geometries is also discussed.

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Heat Transfer, Pressure Loss and Flow Field Measurements Downstream of Staggered Two-Row Circular and Elliptical Pin Fin Arrays

Journal of Heat Transfer ◽

10.1115/1.1860563 ◽

2005 ◽

Vol 127 (5) ◽

pp. 458-471 ◽

Cited By ~ 45

Author(s):

Oguz Uzol ◽

Cengiz Camci

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Pressure Loss ◽

Total Pressure ◽

Local Heat Transfer ◽

Field Measurements ◽

Local Heat ◽

Wake Flow ◽

Pin Fin ◽

Pin Fin Arrays

This paper presents the results of heat transfer, total pressure loss, and wake flow field measurements downstream of two-row staggered elliptical and circular pin fin arrays. Two different types of elliptical fins are tested, i.e., a Standard Elliptical Fin (SEF) and a fin that is based on NACA four digit symmetrical airfoil shapes (N fin). The results are compared to those of a corresponding circular pin fin array. The minor axis lengths for both types of elliptical fins are kept equal to the diameter of the circular fins. Experiments are performed using Liquid Crystal Thermography and total pressure probe wake surveys in a Reynolds number range of 18 000 and 86 000 as well as Particle Image Velocimetry (PIV) measurements at ReD=18 000. The pin fins had a height-to-diameter ratio of 1.5. The streamwise and the transverse spacings were equal to one circular fin diameter, i.e., S/D=X/D=2. For the circular fin array, average Nusselt numbers on the endwall within the wake are about 27% higher than those of SEF and N fin arrays. Different local heat transfer enhancement patterns are observed for elliptical and circular fins. In terms of total pressure loss, there is a substantial reduction in case of SEF and N fins. The loss levels for the circular fin are 46.5% and 59.5% higher on average than those of the SEF and N fins, respectively. An examination of the Reynolds analogy performance parameter show that the performance indices of the SEF and the N fins are 1.49 and 2.0 times higher on average than that of circular fins, respectively. The thermal performance indices show a collapse of the data, and the differences are much less evident. Nevertheless, N fins still show slightly higher thermal performance values. The wake flow field measurements show that the circular fin array creates a relatively large low momentum wake zone compared to the SEF and N fin arrays. The wake trajectories of the first row of fins in circular, SEF and N fin arrays are also different from each other. The turbulent kinetic energy levels within the wake of the circular fin array are higher than those for the SEF and the N fin arrays. The transverse variations in turbulence levels correlate well with the corresponding local heat transfer enhancement variations.

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

Volume 5: Heat Transfer, Parts A and B ◽

10.1115/gt2011-46491 ◽

2011 ◽

Cited By ~ 4

Author(s):

Lamyaa A. El-Gabry ◽

Douglas R. Thurman ◽

Philip E. Poinsatte ◽

James D. Heidmann

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Film Cooling ◽

Large Scale ◽

Field Measurements ◽

Scale Model ◽

Liquid Crystal Thermography ◽

Detailed Surface ◽

Cooling Hole ◽

Hotwire Anemometry

A large-scale model of an inclined row of film cooling holes is used to obtain detailed surface and flow field measurements that will enable future computational fluid dynamics code development and validation. The model consists of three holes of 1.9-cm diameter that are spaced 3 hole diameters apart and inclined 30° from the surface. The length to diameter ratio of the coolant holes is about 18. Measurements include film effectiveness using IR thermography and near wall thermocouples, heat transfer using liquid crystal thermography, flow field temperatures using a thermocouple, and velocity and turbulence quantities using hotwire anemometry. Results are obtained for blowing ratios of up to 2 in order to capture severe conditions in which the jet is lifted. This first part of the two-part paper presents the detailed velocity component and turbulence stresses along the centerline of the film-cooling hole and at various streamwise locations.

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Simultaneously combined liquid crystal surface heat transfer and PIV flow-field measurements

Experiments in Fluids ◽

10.1007/s003480000136 ◽

2001 ◽

Vol 30 (1) ◽

pp. 1-10 ◽

Cited By ~ 17

Author(s):

T. J. Praisner ◽

D. R. Sabatino ◽

C. R. Smith

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Flow Field ◽

Crystal Surface ◽

Field Measurements ◽

Surface Heat ◽

Surface Heat Transfer

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Experimental Flow Field and Heat Transfer Study of a Slot Jet Reattaching Onto a Flat Plate

10.1115/imece2001/htd-24104 ◽

2001 ◽

Author(s):

V. Narayanan ◽

J. Seyed-Yagoobi ◽

R. H. Page

Keyword(s):

Heat Transfer ◽

Flow Field ◽

Surface Pressure ◽

Local Heat Transfer ◽

Field Measurements ◽

Local Heat ◽

Surface Pressure Distribution ◽

Mean Pressure ◽

Transfer Study ◽

Impingement Surface

Abstract Detailed heat transfer, impingement surface pressure and flow field measurements on a submerged slot jet reattachment nozzle are presented. The nozzle is comprised of a rectangular region of aspect ratio 20:1, with circular ends. The jet exits the nozzle parallel to an adjacent flat impingement surface and reattaches onto it. Contours of local heat transfer exhibit three-dimensionality within the recirculation and reattachment regions with increase in nozzle-to-surface spacing. Mean and time averaged fluctuating surface pressure distribution at the center plane of the nozzle along the minor indicate that the location of peak fluctuating pressure occurs upstream of the peak mean pressure. Flow field measurements are presented for a nozzle-to-surface spacing of 3.85 exit hydraulic diameters from the surface, at a turbulent exit Reynolds number of 10 500. Surface pressure and flow field observations are used to explain heat transfer results in the recirculation and reattachment regions.

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Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-22864 ◽

2010 ◽

Author(s):

Rayhaan Farrelly ◽

Alan McGuinn ◽

Tim Persoons ◽

Darina Murray

Keyword(s):

Heat Transfer ◽

Flow Field ◽

High Speed ◽

Local Heat Transfer ◽

Field Measurements ◽

Local Heat ◽

Synthetic Jet ◽

Synthetic Jets ◽

Flow Measurements ◽

Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

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Surface Roughness and Its Effects on the Heat Transfer Mechanism in Spray Cooling

Journal of Heat Transfer ◽

10.1115/1.2911248 ◽

1992 ◽

Vol 114 (1) ◽

pp. 211-219 ◽

Cited By ~ 165

Author(s):

M. R. Pais ◽

L. C. Chow ◽

E. T. Mahefkey

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Flow Field ◽

Surface Texture ◽

Heated Surface ◽

Surface Profile ◽

Spray Cooling ◽

Heat Fluxes ◽

Maximum Heat ◽

Flow Rates

In the spray cooling of a heated surface, variations in the surface texture influence the flow field, altering the maximum liquid film thickness, the bubble diameter, vapor entrapment, bubble departure characteristics, and the ability to transfer heat. A new method for determining and designating the surface texture is proposed, and the effects of surface roughness on evaporation/nucleation in the spray cooling flow field studied. A one-dimensional Fourier analysis is applied to determine experimentally the surface profile of a surface polished with emery paper covering a spectrum of grit sizes between 0.3 to 22 μm. Heat transfer measurements for liquid flow rates between 1 to 5 l/h and air flow rates between 0.1 to 0.4 l/s are presented. Maximum heat fluxes of 1200 W/cm2 for the 0.3 μm surface at very low superheats were obtained.

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Thermal and Flow Field Characteristics in a Rectangular Duct With Broken V-Shaped Ribs

Heat Transfer: Volume 1 ◽

10.1115/ht2003-47105 ◽

2003 ◽

Author(s):

Lieke Wang ◽

Xiufang Gao ◽

Bengt Sunde´n

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Liquid Crystal ◽

Flow Field ◽

Transfer Coefficient ◽

Field Measurements ◽

High Heat ◽

Rectangular Duct ◽

Local Maxima ◽

High Heat Transfer

In the present study, the thermal and hydraulic characteristics of a rectangular duct with aspect ratio of 1/8 roughened by broken V-shaped ribs pointing upstream are investigated experimentally using Liquid Crystal Thermography (LCT) and Particle Image Velocimetry (PIV). The heat transfer distributions on the roughened wall were evaluated using liquid crystal images. It was found that the heat transfer coefficient had a spanwise variation on the ribbed wall, with high heat transfer coefficient at the upstream end of the rib and low value at the other end, similar to the continuous V-shaped ribs. However, the heat transfer distribution in the case of broken V-shaped ribs was observed more uniform, with local maxima due to the gap flow. In addition, the saw-tooth fashion of heat transfer distribution was also observed along the streamwise direction. The isothermal flow field measurements were obtained by PIV to catch the flow structures introduced by the ribs. The spanwise profile of the main flow velocity was found altered, and a complicated secondary flow was detected over the cross section. This flow phenomenon was caused by the ribs and the gaps between ribs.

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