An experimental method for evaluating the heat transfer coefficient of liquid-cooled short pin fins using infrared thermography

In film cooling situations, there is a need to determine both local adiabatic wall temperature and heat transfer coefficient to fully assess the local heat flux into the surface. Typical film cooling situations are termed three temperature problems where the complex interaction between the jets and mainstream dictates the surface temperature. The coolant temperature is much cooler than the mainstream resulting in a mixed temperature in the film region downstream of injection. An infrared thermography technique using a transient surface temperature acquisition is described which determines both the heat transfer coefficient and film effectiveness (nondimensional adiabatic wall temperature) from a single test. Hot mainstream and cooler air injected through discrete holes are imposed suddenly on an ambient temperature surface and the wall temperature response is captured using infrared thermography. The wall temperature and the known mainstream and coolant temperatures are used to determine the two unknowns (the heat transfer coefficient and film effectiveness) at every point on the test surface. The advantage of this technique over existing techniques is the ability to obtain the information using a single transient test. Transient liquid crystal techniques have been one of the standard techniques for determining h and η for turbine film cooling for several years. Liquid crystal techniques do not account for nonuniform initial model temperatures while the transient IR technique measures the entire initial model distribution. The transient liquid crystal technique is very sensitive to the angle of illumination and view while the IR technique is not. The IR technique is more robust in being able to take measurements over a wider temperature range which improves the accuracy of h and η. The IR requires less intensive calibration than liquid crystal techniques. Results are presented for film cooling downstream of a single hole on a turbine blade leading edge model.

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Heat Transfer in Trailing Edge Wedge-Shaped Pin-Fin Channels With Slot Ejection Under High Rotation Numbers

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-22832 ◽

2010 ◽

Cited By ~ 5

Author(s):

Akhilesh P. Rallabandi ◽

Yao-Hsien Liu ◽

Je-Chin Han

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Significant Enhancement ◽

Trailing Edge ◽

Pin Fin ◽

High Heat Transfer ◽

Smooth Channel ◽

Pin Fins ◽

The Heat Transfer Coefficient

The heat transfer characteristics of a rotating pin-fin roughened wedge shaped channel have been studied. The model incorporates ejection through slots machined on the narrower end of the wedge, simulating a rotor blade trailing edge. The copperplate regional average method is used to determine the heat transfer coefficient; pressure taps have been used to estimate the flow discharged through each slot. Tests have been conducted at high rotation (≈ 1 ) and buoyancy (≈ 2) numbers, in a pressurized rotating rig. Reynolds Numbers investigated range from 10,000 to 40,000 and rotational speeds range from 0–400rpm. Pin-fins studied are made of copper as well as non-conducting garolite. Results show high heat transfer coefficients in the proximity of the slot. A significant enhancement in heat transfer due to the pin-fins, compared with a smooth channel is observed. Even the non-conducting pin-fins, indicative of heat transfer on the end-wall show a significant enhancement in the heat transfer coefficient. Results also show a strong rotation effect, increasing significantly the heat transfer coefficient on the trailing surface — and reducing the heat transfer on the leading surface.

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Effect of Pin Tip Dual Clearance on Flow and Heat Transfer at Low Reynolds Numbers

Journal of Heat Transfer ◽

10.1115/1.4027184 ◽

2014 ◽

Vol 136 (7) ◽

Author(s):

Michael L. Seibert ◽

Neal E. Blackwell ◽

Danesh K. Tafti

Keyword(s):

Heat Transfer ◽

Mass Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Heat And Mass Transfer ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Microchannel Reactors ◽

Pin Fins ◽

The Heat Transfer Coefficient

This paper examines the augmentation of heat and mass transfer due to dual clearances on cylindrical pin fins, relative to a channel between parallel plates, in mini/microchannel reactors at low Reynolds numbers. In this work, diffusion limitations to heat and mass transfer in smooth-walled mini/microchannel reactors were minimized by the implementation of microcylinder pin fins with dual clearances that, (1) promote the production of instabilities in the wakes that enhance mixing and (2) reduce the viscosity dominated regions at pin-wall interfaces. A smooth catalyst coating is assumed on all exposed surfaces of the microchannel interior walls and pin fins. Due to the analogy of heat and mass transfer, augmentation of the Nusselt number is equivalent to the augmentation of the Sherwood number. Heat transfer augmentation is investigated in air (Pr = 0.705) at dual clearances ranging from 0 to 0.4 of the channel height and Reynolds numbers from 10 to 600. The pin fins and the clearance augmented the heat transfer coefficient by a factor of 4.0. The combination of the augmentation of the heat transfer coefficient and the increase in the surface area, by the clearances, results in an increase in the conductance over a plane channel, by a factor of 7.1. The results are extendable to overcoming laminar diffusion with laminar periodic wakes of fuel vapors such as methanol vapor in air where Scfuel ∼ Prair. For turbulent wakes impinging upon downstream pins, the results can be extended to fuel vapors with (Scfuel)turb ∼ (Prair)turb. A large eddy simulation (LES) approach was used in this study.

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Time-accurate CFD conjugate analysis of transient measurements of the heat-transfer coefficient in a channel with pin fins

Propulsion and Power Research ◽

10.1016/j.jppr.2013.01.003 ◽

2013 ◽

Vol 2 (1) ◽

pp. 10-19 ◽

Cited By ~ 7

Author(s):

Tom I-P. Shih ◽

Saiprashanth Gomatam Ramachandran ◽

Minking K. Chyu

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Pin Fins ◽

The Heat Transfer Coefficient ◽

Transient Measurements

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Evaporation of lignin-lean black liquor

TAPPI Journal ◽

10.32964/tj14.7.441 ◽

2015 ◽

Vol 14 (7) ◽

pp. 441-450

Author(s):

HENRIK WALLMO, ◽

ULF ANDERSSON ◽

MATHIAS GOURDON ◽

MARTIN WIMBY

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Black Liquor ◽

Salt Content ◽

Solubility Limit ◽

Lignin Removal ◽

Kraft Black Liquor ◽

Black Liquors ◽

The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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