LOCAL HEAT TRANSFER MEASUREMENTS ON ARRAYS OF PIN FINS IN A RECTANGULAR DUCT

1990 ◽  
Author(s):  
James W. Baughn ◽  
Nader Saniei
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Duct ◽  
Pin Fins

Enhanced Heat Transfer in a Flat Rectangular Duct With Streamwise-Periodic Disturbances at One Principal Wall

1983 ◽  
Vol 105 (4) ◽  
pp. 851-861 ◽  
Author(s):  
E. M. Sparrow ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Local Maxima ◽  
Periodic Disturbances ◽  
Pressure Distributions ◽  
Friction Factors

Experiments were performed in a flat rectangular duct to determine the heat transfer and pressure drop response to periodic, rod-type disturbance elements situated adjacent to one principal wall and oriented transverse to the flow direction. In a portion of the experiments, heat transfer occurred only at the rodded wall, while in the remainder, heat was transferred at both principal walls of the duct. Highly detailed axial distributions of the local heat transfer coefficient were obtained. These distributions revealed the rapid establishment of a periodic (i.e., cyclic) fully developed regime as well as recurring local maxima and minima. Cycle-average, fully developed heat transfer coefficients were evaluated and were found to be much larger than those for a smooth-walled duct. Linear pressure distributions were measured between periodically positioned stations in the fully developed region, and the corresponding friction factors were several times greater than the smooth-duct values. The heat transfer and friction data were very well correlated using parameters that take account of the effective surface roughness associated with the disturbance rods.

Comparison of Pressure Drop and Endwall Heat Transfer Measurements to Flow Visualization Testing of Solid and Porous Pin Fin Arrays

2009 ◽  
Author(s):  
Jared M. Pent ◽  
Jay S. Kapat ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Visualization ◽  
Local Heat Transfer ◽  
Ccd Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Porous Aluminum ◽  
Pin Fins ◽  
A Charge

This paper examines the local and averaged endwall heat transfer effects of a staggered array of porous aluminum pin fins with a channel blockage ratio (blocked channel area divided by open channel area) of 50%. Two sets of pins were used with pore densities of 0 (solid) and 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates using each set of pins. Local heat transfer coefficients on the endwall were measured using Thermochromatic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. The heat transfer and pressure data was then compared to flow visualization tests that were run using a fog generator. Results are presented for the two sets of pins with Reynolds numbers between 25000 and 130000. Local HTC (heat transfer coefficient) profiles as well as spanwise and streamwise averaged HTC plots are displayed for both pin arrays. The thermal performance was calculated for each pin set and Reynolds number. All experiments were carried out in a channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72.

Flow Boiling Heat Transfer on Micro Pin Fins Entrenched in a Microchannel

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Axial Distance ◽  
Mass Fluxes ◽  
Pin Fins

Flow boiling of 1-methoxyheptafluoropropane (HFE 7000) in 222 μm hydraulic diameter channels containing a single row of 24 inline 100 μm pin fins was studied for mass fluxes from 350 kg/m2 s to 827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2. Flow visualization revealed the existence of isolated bubbles, bubbles interacting, multiple flow, and annular flow. The observed flow patterns were mapped as a function of the boiling number and the normalized axial distance. The local heat transfer coefficient during subcooled boiling was measured and found to be considerably higher than the corresponding single-phase flow. Furthermore, a thermal performance evaluation comparison with a plain microchannel revealed that the presence of pin fins considerably enhanced the heat transfer coefficient.

Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Hybrid Technique ◽  
Pin Fins ◽  
Cooling Passage ◽  
Rib Roughened

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened channel combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = [1/4]E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e., C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross ribs, namely the broken rib and full rib are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin-fins. 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 experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all pin elements. The presence of ribs enhances local heat transfer coefficient on the endwall substantially by approximately 20% to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperform cases with broken ribs or full ribs.

Heat Transfer Enhancement in Tip-Turn Region of Two-Pass Channel With a 180-Degree Turn

2011 ◽  
Author(s):  
Pavin Ganmol ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Sharp Turn ◽  
Pin Fins ◽  
Series Of Experiments ◽  
Turn Region

The design geometry and transport phenomena associated with the tip internal cooling can be very complex and has been little studied. Internal cooling channel near a tip region typically inherits a sharp, 180-degree, turn and little or no enhancement installation exists. To explore potential design for enhancement cooling, a series of experiments are performed to investigate the heat transfer enhancement by placing different pin-fins configurations in the tip-turn region of a two-pass channel with a 180-degree sharp turn. Transient liquid crystal technique is applied to acquire detailed local heat transfer data both on the channel surface and pin elements, for Reynolds number between 13,000 and 28,000. Present results suggest that the pin-fins can enhance heat transfer up to 2.3 fold in the tip-turn region and up to 1.3 fold for the entire channel. The presence of the pin-fins also changes the flow pattern in the post turn region which is resulting in more evenly distributed heat transfer downstream of the turn.

Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel

2011 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Hybrid Technique ◽  
Pin Fins ◽  
Cooling Passage ◽  
Rib Roughened

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened walls combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross-ribs, namely the broken ribs and full ribs are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin fins. 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 experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. The presence of ribs has enhanced the local heat transfer coefficient on the endwall substantially by about 20% up to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperforms cases with broken ribs and full ribs.

Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays

2020 ◽  
Author(s):  
Marcel Otto ◽  
Gaurav Gupta ◽  
Patrick Tran ◽  
Shinjan Ghosh ◽  
Jayanta Kapat
Keyword(s):  
Heat Transfer ◽  
Maximum Velocity ◽  
Local Heat Transfer ◽  
Horseshoe Vortex ◽  
Local Heat ◽  
Channel Length ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Vortical Structures ◽  
Pin Fins

Abstract Arrays of staggered pin fins are a typical geometry found in the trailing edge region of modern airfoils. If coolant is supplied by bleeding from the mid-section of the airfoil instead of provided through the root, the channel length is not long enough to reach a fully developed flow which is commonly found from the fifth row downstream. This present study focuses on the developing section (four rows) of a staggered array with a height to diameter ratio of 2 and a spanwise and streamwise spacing of 2.5 respectively. Measurements are conducted at two Reynolds numbers of 10,000 and 30,000 based on the maximum velocity and pin diameter. Stereoscopic PIV is used to describe the flow field and turbulence characteristics in the wake of the first and third row pin. It is found that the dominating vortical structures depend highly on the Reynolds number. A transient thermochromic liquid crystal technique is used to obtain local heat transfer coefficients on the endwall which are then discussed in the context with the vortical structures. The structure of the horseshoe vortex and the transient wake shedding behave differently in the first and second row. The interaction of both vortex systems affects directly the endwall heat transfer. The results are supplemented by a thorough discussion of TLC and PIV uncertainty.

Maldistributed Inlet Flow Effects on Turbulent Heat Transfer and Pressure Drop in a Flat Rectangular Duct

1983 ◽  
Vol 105 (3) ◽  
pp. 527-535 ◽  
Author(s):  
E. M. Sparrow ◽  
N. Cur
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Inlet Flow ◽  
Heat Transfer Coefficients ◽  
Flow Maldistribution

The effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were studied experimentally. Local heat transfer coefficients were measured on the principal walls of the duct for two blockages and for Reynolds numbers spanning the range between 6000 and 30,000. Measurements were also made of the pressure distribution along the duct, and the fluid flow pattern was visualized by the oil-lampblack technique. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. These nonuniformities persisted to far downstream locations, especially in the presence of severe inlet flow maldistributions. Spanwise-average heat transfer coefficients, evaluated from the local data, were found to be enhanced in the downstream portion of the duct due to the flow maldistribution. However, at more upstream locations, where the entering flow reattached to the duct wall following its separation at the sharp-edged inlet, the average coefficients were reduced by the presence of the maldistribution.

Developing Heat Transfer and Friction in a Ribbed Rectangular Duct With Flow Separation at Inlet

1992 ◽  
Vol 114 (3) ◽  
pp. 565-573 ◽  
Author(s):  
Tong-Miin Liou ◽  
Jenn-Jiang Hwang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulent Flows ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Equal Mass ◽  
Rectangular Duct ◽  
Entry Length ◽  
A Value ◽  
Semi Empirical

The local heat transfer and pressure drop characteristics of developing turbulent flows in a rectangular duct with an abrupt-contraction entrance and repeated square-rib pairs on the two opposite walls have been investigated experimentally. Both entrance-region and periodic-fully-developed-region results were obtained. Laser holographic interferometry was employed in the local and average heat transfer measurements. The Reynolds number was varied from 5.0 × 103 to 5.0 × 104; the rib pitch-to-height ratios were 10, 15, and 20; and the rib height-to-duct height ratio was kept at a value of 0.13. The results allowed the entry length to be determined and the regions susceptible to hot spots to be located. Semi-empirical heat transfer and friction correlations for the periodic fully developed region were developed. Moreover, performance comparisons between the ribbed and smooth ducts were made under two types of constraint, namely equal mass flow rate and equal pumping power. Finally, the effect of thermal entry length on the length mean Nusselt number was also investigated. The results showed that the length mean Nusselt number ratio was a function of only the duct length and independent of PR and Re, and could be further correlated by an equation of the form Num/Nup = 1 + 1.844/(X/De).

Heat Transfer Experiments and Flow Visualization for Arrays of Short Pin Fins

1982 ◽  
Author(s):  
D. E. Metzger ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Large Scale ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Additional Information ◽  
Pin Fins ◽  
Scale Test ◽  
Turbine Airfoils

Results from several sets of experiments are presented to illustrate the character of streamwise heat transfer development in large aspect ratio ducts filled with uniform staggered arrays of circular pins. The short (height-to-diameter ratio 1.0) pins span the full height of the duct and are packed in moderately dense arrays (pitch-to-diameter ratios 1.32 to 2.5) typical of internal cooling applications in gas turbine airfoils. Heat transfer experiments have been performed on two separate test sections utilizing (i) highly conducting, fin effectiveness unity pins, and (ii) low conductivity, fin effectiveness near zero pins. In both cases the streamwise development of heat transfer, averaged across the duct width, is resolved to a single pin row spacing. Additional information on the flowfield and local heat transfer is provided from a large scale test rig where kerosene-lamp black flow visualization and small heat flux gages were utilized.

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