Measurement of Heat Transfer Coefficient Distributions and Flow Field in a Model of a Turbine Blade Cooling Passage With Tangential Injection

2006 ◽  
Author(s):  
John P. C. W. Ling ◽  
Peter T. Ireland ◽  
Neil W. Harvey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Cooling System ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Cooling Passage

In certain regions of turbine aerofoils, cooling system designers need to cool the blades with convection systems that provide high heat transfer coefficients. The present research has investigated a circular cooling passage with tangential injection suitable for a blade leading edge. The heat transfer coefficients are measured using the conventional transient heat transfer, liquid crystal technique. The results are compared to the data from steady state experiments performed by Hedlund et al. [1]. The cooling system performance is compared in detail to average data from earlier tangential injection experiments and to local heat transfer coefficient expected from a normal impingement system. The vortex flow field was also studied by numerical prediction and near-wall velocity measurements. The investigation of the flow structure has led to understanding of flow mechanisms responsible for the high heat transfer coefficient. The vortex flow field was also investigated using computational fluid dynamics and with hot wire anemometry. The latter near wall measurements were combined with the law of the wall and Colburn analogy to validate the flow and heat transfer measurements.

Detailed Heat Transfer Measurements in a Model of an Integrally Cast Cooling Passage

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Ioannis Ieronymidis ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Robert Kingston
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Contact ◽  
Casting Process ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Cooling Passage

Detailed measurements of the heat transfer coefficient (htc) distributions on the internal surfaces of a novel gas turbine blade cooling configuration were carried out using a transient liquid crystal technique. The cooling geometry, in which a series of racetrack passages are connected to a central plenum, provides high heat transfer coefficients in regions of the blade in good thermal contact with the outer blade surface. The Reynolds number changes along its length because of the ejection of fluid through a series of 19 transfer holes in a staggered arrangement, which are used to connect ceramic cores during the casting process. Heat transfer coefficient distributions on these holes surface are particularly important in the prediction of blade life, as are heat transfer coefficients within the hole. The results at passage inlet Reynolds numbers of 21,667, 45,596, and 69,959 are presented along with in-hole htc distributions at Rehole=5930, 12,479, 19,147; and suction ratios of 0.98, 1.31, 2.08, and 18.67, respectively. All values are engine representative. Characteristic regions of high heat transfer downstream of the transfer holes were observed with enhancement of up to 92% over the Dittus–Boelter level. Within the transfer holes, the average htc level was strongly affected by the cross-flow at the hole entrance. htc levels were low in these short (l/d=1.5) holes fed from regions of developed boundary layer.

Detailed Heat Transfer Measurements in a Model of an Integrally Cast Cooling Passage

2006 ◽  
Author(s):  
Ioannis Ieronymidis ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Robert Kingston
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Contact ◽  
Casting Process ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Cooling Passage

Detailed measurements of the heat transfer coefficient distributions on the internal surfaces of a novel gas turbine blade cooling configuration were carried out using a transient liquid crystal technique. The cooling geometry, in which a series of racetrack passages are connected to a central plenum, provides high heat transfer coefficients in regions of the blade in good thermal contact with the outer blade surface. The Reynolds number changes along its length because of the ejection of fluid through a series of 19 transfer holes in a staggered arrangement, which are used to connect ceramic cores during the casting process. Heat transfer coefficient distributions on this holes surface are particularly important in the prediction of blade life, as are heat transfer coefficients within the hole. Results at passage inlet Reynolds numbers of 21667, 45596 and 69959 are presented along with in-hole htc distributions at Rehole = 5930, 12479, 19147 and suction ratios of 0.98, 1.31, 2.08, 18.67. All values are engine representative. The results were compared to predictions made using the commercial CFD package Fluent. Characteristic regions of high heat transfer downstream of the transfer holes were observed with enhancement of up to 92% over the Dittus-Boelter level. Within the transfer holes, the average htc level was strongly affected by the crossflow at the hole entrance. Htc levels were low in these short (l/d = 1.5) holes fed from regions of developed boundary layer.

Heat Transfer Enhancement in Narrow Diverging Channels

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Justin Lamont ◽  
Sridharan Ramesh ◽  
Srinath V. Ekkad ◽  
Anil Tolpadi ◽  
Christopher Kaminski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Color Change ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All of the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to the pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals and a transient test was used to obtain the local heat transfer coefficients from the measured color change. An analysis of the results shows that the choice of designs is limited by the available pressure drop, even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and a reasonable pressure drop, whereas ribbed ducts provide significantly higher heat transfer coefficients and a higher overall pressure drop.

Heat Transfer Enhancement in Narrow Diverging Channels

2012 ◽  
Author(s):  
Justin Lamont ◽  
Sridharan Ramesh ◽  
Srinath V. Ekkad ◽  
Anil Tolpadi ◽  
Christopher Kaminski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Color Change ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals, and a transient test was used to obtain the local heat transfer coefficients from the measured color change. Analysis of results shows that choice of designs is limited by available pressure drop even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and reasonable pressure drop whereas ribbed ducts provide significantly higher heat transfer coefficients and higher overall pressure drop.

Jets in a Crossflow: Effects of Hole Spacing to Diameter Ratio on the Spatial Distribution of Heat Transfer

1991 ◽  
Author(s):  
V. Scherer ◽  
S. Wittig ◽  
K. Morad ◽  
N. Mikhael
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Diameter Ratio ◽  
Test Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Detailed measurements of local heat transfer coefficients are presented for air injection through a row of holes into a crossflow. Pitch-to-diameter ratios of 2,4, and 6 are realized and the momentum flux ratio is varied in the range from 0.25 to 4.0. The injection angle of the jets is fixed at 90°. The experimental technique developed uses an Infrared Camera to measure the temperature distribution on the constant heat flux test surface. This measurement technique allows detailed spatial resolution of the heat transfer and gives information about the three-dimensional mixing process of the jets with the mainstream. The experimental results indicate a large influence of the hole spacing to diameter ratio, (s/d), on the heat transfer coefficient. With s/d = 2.0, the spanwise heat transfer coefficients in the vicinity of the injection holes are noticed to be highly uniform. For momentum flux ratios, J, greater than 1, two regions of high heat transfer coefficient exist. The first region occurs in the vicinity of the injection holes. The second region observed some distance downstream is due to the reattachment of the jets to the surface.

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

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.

Experimental and Numerical Simulation of a Synthetic Jet for Cooling of Electronics

2011 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Mark North ◽  
Tianhong Cui
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Large Scale ◽  
Cooling System ◽  
Synthetic Jet ◽  
Computational Results ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
Heat Transfer Coefficients

Compared to traditional continuous jets, synthetic jets have specific advantages, such as lower power requirement, simpler structure, and the ability to produce an unsteady turbulent flow which is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a round synthetic jet flow on the tip region of a longitudinal fin surface used in an electronics cooling system. Unique to this study are the geometry of the cooled surface and the variations in geometry of the jet nozzle or nozzles. Also unique are measurements in actual-scale systems and in a scaled-up system, and computation. In the computation, the diaphragm movement of the synthetic jet is a moving wall and the flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-stagnation-line spacing, are recorded. The computational results show a good match with the experimental results. In the experiments, an actual-scale system is tested and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up is tested. The three approaches are used to determine heat transfer coefficients on the fin on and near the stagnation line. Focus is on the large scale test results and the computation. Application to the actual-size cases is discussed. The dynamically-similar mock-up matches the dimensionless Reynolds number, Stokes number, and Prandtl number of the actual setting with a scale factor of 44. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m2K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how cooling performance changes with orifice design.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

A Photographic Study of Flow Boiling Stability on a Plain Surface With Tapered Manifold

2015 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Flow Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Transfer ◽  
Plain Surface ◽  
High Heat Transfer Coefficient

Flow boiling in microchannels offers many advantages such as high heat transfer coefficient, higher surface area to volume ratio, low coolant inventory, uniform temperature control and compact design. The application of these flow boiling systems has been severely limited due to early critical heat flux (CHF) and flow instability. Recently, a number of studies have focused on variable flow cross-sectional area to augment the thermal performance of microchannels. In a previous work, the open microchannel with manifold (OMM) configuration was experimentally investigated to provide high heat transfer coefficient coupled with high CHF and low pressure drop. In the current work, high speed images of plain surface using tapered manifold are obtained to gain an insight into the nucleating bubble behavior. The mechanism of bubble nucleation, growth and departure are described through high speed images. Formation of dry spots for both tapered and uniform manifold geometry is also discussed.

Heat Transfer Characteristics of a Flow Passage With Long Pin Fins and Improving Heat Transfer Coefficient by Adding Turbulence Promoters on a Endwall

2001 ◽  
Author(s):  
K. Takeishi ◽  
T. Nakae ◽  
K. Watanabe ◽  
M. Hirayama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Heat ◽  
Atmospheric Conditions ◽  
Pin Fin ◽  
High Heat Transfer ◽  
Turbine Vanes ◽  
Pin Fins

Pin fins are normally used for cooling the trailing edge region of a turbine, where their aspect ratio (height H/diameter D) is characteristically low. In small turbine vanes and blades, however, pin fins may also be located in the middle region of the airfoil. In this case, the aspect ratio can be quite large, usually obtaining values greater than 4. Heat transfer tests, which are conducted under atmospheric conditions for the cooling design of turbine vanes and blades, may overestimate the heat transfer coefficient of the pin-finned flow channel for such long pin fins. The fin efficiency of a long pin fin is almost unity in a low heat transfer situation as it would be encountered under atmospheric conditions, but can be considerably lower under high heat transfer conditions and for pin fins made of low thermal conductivity material. A series of tests with corresponding heat transfer models has been conducted in order to clarify the heat transfer characteristics of the long pin-finned flow channel. It is assumed that heat transfer coefficients can be predicted by the linear combination of two heat transfer equations, which were separately developed for the pin fin surface and for tubes in crossflow. To confirm the suggested combined equations, experiments have been carried out, in which the aspect ratio and the thermal conductivity of the pin were the test parameters. To maintain a high heat transfer coefficient for a long pin fin under high-pressure conditions, the heat transfer was augmented by adding a turbulence promoter on the pin-finned endwall surface. A corresponding equation that describes this situation has been developed. The predicted and measured values showed good agreement. In this paper, a comprehensive study on the heat transfer of a long pin-fin array will be presented.

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