Experimental Study on the Effect of Non-Uniform Inlet Velocity Profile on Internal Cooling in Rectangular Channels With Multi-Features

2015 ◽  
Author(s):  
S. Huang ◽  
Y. Y. Yan ◽  
J. D. Maltson
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Velocity Profile ◽  
Transfer Coefficient ◽  
Internal Cooling ◽  
Inlet Velocity ◽  
Pin Fin ◽  
Rectangular Channels ◽  
Pin Fin Array ◽  
Pin Fin Arrays

Experiments were conducted to investigate the overall thermal performance of rectangular channels with a non-uniform inlet velocity profile. Two test sections with multiple internal cooling features had been used. One test section was implemented with two circular staggered pin-fin arrays with different pin diameters. The other one was implemented with a combination of a staggered pin-fin array and a perforated blockage array. The average surface heat transfer coefficient of the pedestal and perforated blockage and the local distribution of heat transfer coefficient on endwall were measured by the lumped capacitance method and transient liquid crystal method, respectively. The pressure drop across each array was measured. The heat transfer coefficients were measured over the Reynolds number range from 9,000 to 17,000. The spanwise pitches of the upstream pin-fin arrays were 2.33 and 4.66 for the channel with the multiple pin-fin array and the channel with perforated blockage, respectively. The effect of a non-uniform velocity profile on local heat transfer pattern and row-resolved heat transfer coefficient has been investigated.

Heat Transfer of Pico Projector Using a Piezoelectric Fan With an Aluminum Blade

2017 ◽  
Author(s):  
Jin-Cherng Shyu ◽  
Shu-Kai Jheng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Pin Fin ◽  
Specific Frequency ◽  
Tip Velocity ◽  
Pin Fin Array ◽  
The Heat Transfer Coefficient

A 120 mm × 53 mm × 19 mm horizontally-oriented pico projector in which both a pin-fin array and a piezoelectric fan were installed was tested to measure the thermal resistance at various heating powers. The operating frequency of the 40 mm × 10 mm aluminum piezoelectric fan ranged from 242 Hz to 257 Hz. The heat transfer coefficient of the pin-fin array was also estimated based on a thermal resistance network of the pico projector. The results showed that the thermal resistance of the pico projector which had a piezoelectric fan vibrating at a specific frequency would not monotonically reduce as the heating power increased. The heat transfer coefficient of the 1.5-mm-wide pin-fin array was higher than that of the 2.0-mm-wide pin-fin array at a given fan tip velocity ranging from 0.26 m/s to 0.76 m/s. The highest heat transfer coefficient of the 1.5-mm-wide pin-fin array reached approximately 21 W/m2K, while the highest heat transfer coefficient of the 2.0-mm-wide pin-fin array was approximately 16 W/m2K. A correlation between Nusselt number of the pin-fin array and Reynolds number was also developed in this study in a form of Nu = 0.3526Re0.1774.

Heat Transfer and Pressure Drop for Short Pin-Fin Arrays With Pin-Endwall Fillet

1990 ◽  
Vol 112 (4) ◽  
pp. 926-932 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Circular Cylinders ◽  
Significant Finding ◽  
Array Configuration ◽  
Pin Fin ◽  
Pin Fin Arrays

The effects of array configuration and pin-endwall fillet on the heat transfer and pressure drop of short pin-fin arrays are investigated experimentally. The pin-fin element with endwall fillet, typical in actual turbine cooling applications, is modeled by a spool-like cylinder. The arrays studied include an in-line and a staggered array, each having seven rows of five pins. These arrays have the same geometric parameters, i.e., H/D = 1, S/D = X/D = 2.5, and the Reynolds number ranging from 5 × 103 to 3 × 104. One of the present results shows that the staggered array always has a higher array-averaged heat transfer coefficient than its in-line counterpart. However, the pressure drop for the staggered array is higher compared to the in-line configuration. These trends are unaffected by the existence of the pin-endwall fillet. Another significant finding is that an array with pin-endwall fillet generally produces lower heat transfer coefficient and higher pressure drop than that without endwall fillet. This leads to the conclusion that pin-endwall fillet is undesirable for heat transfer augmentation. In addition, nai¨ve use of the heat transfer results obtained with perfectly circular cylinders tends to overestimate the pin-fin cooling capability in the actual turbine. The effects of endwall fillet on the array heat transfer and pressure drop are much more pronounced for the staggered array than for the inline array; however, they diminish as the Reynolds number increases.

Heat Transfer Contributions of Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition Modeling

1999 ◽  
Vol 121 (2) ◽  
pp. 257-263 ◽  
Author(s):  
M. K. Chyu ◽  
Y. C. Hsing ◽  
T. I.-P. Shih ◽  
V. Natarajan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Thermal Boundary Conditions ◽  
The Individual ◽  
Pin Fin Arrays

Short pin-fin arrays are often used for cooling turbine airfoils, particularly near the trailing edge. An accurate heat transfer estimation from a pin-fin array should account for the total heat transfer over the entire wetted surface, which includes the pin surfaces and uncovered endwalls. One design question frequently raised is the actual magnitudes of heat transfer coefficients on both pins and endwalls. Results from earlier studies have led to different and often contradicting conclusions. This variation, in part, is caused by imperfect or unrealistic thermal boundary conditions prescribed in the individual test models. Either pins or endwalls, but generally not both, were heated in those previous studies. Using a mass transfer analogy based on the naphthalene sublimation technique, the present experiment is capable of revealing the individual heat transfer contributions from pins and endwalls with the entire wetted surface thermally active. The particular pin-fin geometry investigated, S/D = X/D = 2.5 and H/D = 1.0, is considered to be one of the optimal array arrangement for turbine airfoil cooling. Both inline and staggered arrays with the identical geometric parameters are studied for 5000 ≤ Re ≤ 25,000. The present results reveal that the general trends of the row-resolved heat transfer coefficients on either pins or endwalls are somewhat insensitive to the nature of thermal boundary conditions prescribed on the test surface. However, the actual magnitudes of heat transfer coefficients can be substantially different, due to variations in the flow bulk temperature. The present study also concludes that the pins have consistently 10 to 20 percent higher heat transfer coefficient than the endwalls. However, such a difference in heat transfer coefficient imposes very insignificant influence on the overall array-averaged heat transfer, since the wetted area of the uncovered endwalls is nearly four times greater than that of the pins.

scholarly journals Heat Transfer Contributions of Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition Modeling

1998 ◽  
Author(s):  
M. K. Chyu ◽  
Y. C. Hsing ◽  
T. I.-P. Shih ◽  
V. Natarajan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Thermal Boundary Conditions ◽  
The Individual ◽  
Pin Fin Arrays

Short pin-fin arrays are often used for cooling turbine airfoils, particularly near the trailing edge. An accurate heat transfer estimation from a pin-fin array should account for the total heat transfer over the entire wetted surface which includes the pin surfaces and uncovered end walls. One design question frequently raised is the actual magnitudes of heat transfer coefficients on both pins and endwalls. Results from earlier studies have led to different and often contradicting conclusions. This variation, in part, is caused by imperfect or unrealistic thermal boundary conditions prescribed in the individual test models. Either pins or endwalls, but generally not both, were heated in those previous studies. Using a mass transfer analogy based on the naphthalene sublimation technique, the present experiment is capable of revealing the individual heat transfer contributions from pins and endwalls with the entire wetted surface thermally active. The particular pin-fin geometry investigated, S/D = X/D = 2.5 and H/D = 1.0, is considered to be one of the optimal array arrangement for turbine airfoil cooling. Both inline and staggered arrays with the identical geometric parameters are studied for 5,000 ≤ Re ≤ 25,000. The present results reveal that the general trends of the row-resolved heat transfer coefficients on either pins or endwalls are somewhat insensitive to the nature of thermal boundary conditions prescribed on the test surface. However, the actual magnitudes of heat transfer coefficients can be substantially different, due to variations in the flow bulk temperature. The present study also concludes that the pins have consistently 10 to 20% higher heat transfer coefficient than the endwalls. However, such a difference in heat transfer coefficient imposes very insignificant influence on the overall array-averaged heat transfer, since the wetted area of the uncovered endwalls is nearly four times greater than that of the pins.

Heat Transfer Enhancement of Internal Cooling Passage With Triangular and Semi-Circular Shaped Pin-Fin Arrays

2012 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Pin Fin ◽  
Pin Fins ◽  
Cooling Passage ◽  
Internal Cooling Passage ◽  
Pin Fin Array ◽  
Pin Fin Arrays

A systematic experimental study has been conducted to explore the heat transfer behavior of triangular and semicircular shaped pin-fin arrays as compared to the circular shaped pin-fin array, that serve as a baseline case. The main advantage of using triangular and semi-circular shaped pin-fin arrays will results in reduced component weight and potentially increases in heat transfer performance. Three staggered arrays with different inter-pin spacing in both transverse and longitudinal are explored in order to determine the optimal configuration for these three dimensional element. Both semi-circular and circular shaped pin-fin arrays are based on typical inter-pin spacing of 2.5 times the pin diameter. The channel geometry (width, W = 76.2mm, height, E = 25.4mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. All pin-fin elements are fully bridged from one endwall to the opposite endwall. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The heat transfer measurement employs a hybrid liquid crystal imaging technique, which combined one-dimensional, transient conduction model and lumped heat-capacitance model. Triangular pin-fin arrays produce the highest heat transfer enhancement, while the semi-circular pin-fin array yields the lowest heat transfer enhancement. Sharp edges at each triangular pin-fin generated more wake and turbulence, resulting in more mixing, induces greater heat transfer enhancement by approximately 10%–20% as compared to the typical pin-fins of circular cross-section. More uniform heat transfer is also observed on the endwall and neighboring pin-fins in all triangular shaped pin-fin arrays. However, triangular pin-fin arrays give the highest pressure loss due to the largest induced form drag among all cases, while circular pin-fin array exhibits the lowest pressure loss.

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.

Heat Transfer in an Airfoil Trailing Edge Configuration With Shaped Pedestals Mounted Internal Cooling Channel and Pressure Side Cutback

2006 ◽  
Author(s):  
Shuping P. Chen ◽  
Peiwen W. Li ◽  
Minking K. Chyu ◽  
Frank J. Cunha ◽  
William Abdel-Messeh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Internal Cooling ◽  
Hybrid Technique ◽  
Pressure Side ◽  
Cooling Channel ◽  
Trailing Edge ◽  
The Heat Transfer Coefficient

Described in this paper is an experimental study of heat transfer over a trailing edge configuration preceded with an internal cooling channel of pedestal array. The pedestal array consists of both circular pedestals and oblong shaped blocks. Downstream to the pedestal array, the trailing edge features pressure side cutback partitioned by the oblong shaped blocks. The local heat transfer coefficient over the entire wetted surface in the internal cooling chamber has been determined by using a “hybrid” measurement technique based on transient liquid crystal imaging. The hybrid technique employs the transient conduction model in a semi-infinite solid for resolving the heat transfer coefficient on the endwall surface uncovered by the pedestals. The heat transfer coefficient over a pedestal can be resolved by the lumped capacitance method with an assumption of low Biot number. The overall heat transfer for both the pedestals and endwalls combined shows a significant enhancement compared to the case with thermally developed smooth channel. Near the downstream most section of the suction side, the land, due to pressure side cutback, is exposed to the stream mixed with hot gas and discharged coolant. Both the adiabatic effectiveness and heat transfer coefficient on the land section are characterized by using the transient liquid crystal technique.

scholarly journals Row Resolved Heat Transfer Variations in Pin-Fin Arrays Including Effects of Non-Uniform Arrays and Flow Convergence

1986 ◽  
Author(s):  
D. E. Metzger ◽  
W. B. Shepard ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Cross Sectional Area ◽  
Experimental Program ◽  
Internal Cooling ◽  
Sectional Area ◽  
Order Unity ◽  
Cross Sectional ◽  
Turbine Engine ◽  
Pin Fin ◽  
Pin Fin Arrays

Measured streamwise (longitudinal) heat transfer variations, spanwise (transverse) averaged and resolved to single row spacings, are presented for large aspect ratio ducts containing staggered arrays of circular pin fins which span the entire duct height. A number of different array geometries have been investigated in an experimental program, including uniformly spaced arrays in constant cross sectional area ducts with streamwise row spacings over the range 1.5 to 5.0 pin diameters. Such arrays, with pin length-to-diameter ratio of order unity, are often used to enhance heat transfer in internal cooling passages of gas turbine engine airfoils. The effects of various length interruptions in the pin pattern and of abrapt changes in pin diameter are presented for constant cross sectional area ducts. In addition, results are presented for the effect of duct convergence, a common situation in the cooled turbine airfoil application. A concise summary of all the observed behavior is given, useful for predicting the performance of arbitrarily spaced pin fin arrays that may be specified to produce a particular cooling distribution. Predictions are compared with two final test, configurations which combine aspects of all of the effects investigated in the experimental program.

Detailed Experimental Characterization of Heat Transfer Coefficient Over the Internal Cooling Passages of an Additive Manufactured Turbine Airfoil

2016 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Jae Y. Um ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Scale Model ◽  
Internal Cooling ◽  
Trailing Edge

This report describes the detailed experimental study to characterize the local heat transfer coefficient distribution over the internal cooling passages of a simplified generic airfoil. The airfoil is manufactured through additive manufacturing based on actual geometry and dimensions (1X scale model) of row one airfoil, applicable in large gas turbine system. At the mainbody section, the serpentine channel consists of three passages without any surface features or vortex generators. Both the leading edge and trailing edge sections are subjected to direct impingement. The trailing edge section is divided into three chambers, separated by two rows of blockages. This study employs the well-documented transient liquid crystal technique, where the local heat transfer coefficient on both pressure and suction sides is deduced. The experiments were performed at varying Reynolds number, ranging from approximately 31,000–63,000. The heat transfer distribution on the pressure side and suction side is largely comparable in the first and third pass, except for the second pass. Highest heat transfer occurs at the trailing edge region, which is ultimately dominated by impingement due to the presence of three rows of blockages. A cursory numerical calculation is performed using commercially available software, ANSYS CFX to obtain detailed flow field distribution within the airfoil, which explains the heat transfer behavior at each passage. The flow parameter results revealed that the pressure ratio is strongly proportional with increasing Reynolds number.

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