Thermocouple thermal inertia effects on impingement heat transfer experiments using the transient liquid crystal technique

2012 ◽  
Vol 23 (11) ◽  
pp. 115303 ◽  
Author(s):  
Alexandros Terzis ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand ◽  
Peter Ott
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Thermal Inertia ◽  
Inertia Effects ◽  
Impingement Heat Transfer ◽  
Transient Liquid Crystal Technique

scholarly journals The Transient Liquid Crystal Technique: Influence of Surface Curvature and Finite Wall Thickness

2004 ◽  
Author(s):  
G. Wagner ◽  
M. Kotulla ◽  
P. Ott ◽  
B. Weigand ◽  
J. von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Flat Plate ◽  
Hollow Cylinder ◽  
Wall Thickness ◽  
Reduction Method ◽  
Radius Of Curvature ◽  
Test Model ◽  
Curvature Effects ◽  
Transient Liquid Crystal Technique

The transient liquid crystal technique is nowadays widely used for measuring the heat transfer characteristics in gas turbine applications. Usually, the assumption is made that the wall of the test model can be treated as a flat and semi-infinite solid. This assumption is correct as long as the penetration depth of the heat compared to the thickness of the wall and to the radius of curvature is small. However, those two assumptions are not always respected for measurements near the leading edge of a blade. This paper presents a rigorous treatment of the curvature and finite wall thickness effects. The unsteady heat transfer for a hollow cylinder has been investigated analytically and a data reduction method taking into account curvature and finite wall thickness effects has been developed. Experimental tests made on hollow cylinder models have been evaluated using the new reduction method as well as the traditional semi-infinite flat plate approach and a third method that approximately accounts for curvature effects. It has been found that curvature and finite thickness of the wall have in some cases a significant influence on the obtained heat transfer coefficient. The parameters influencing the accuracy of the semi-infinite flat plate model and the approximate curvature correction are determined and the domains of validity are represented.

Heat Transfer Study of a Novel Low-Crossflow Design for Jet Impingement

2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna ◽  
Mario Abreu ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Impingement Heat Transfer ◽  
Hole Arrays ◽  
Transient Liquid Crystal Technique ◽  
Rate Requirement ◽  
Transfer Study

Impingement heat transfer is significantly affected by initial cross-flow or by the presence of cross-flow from upstream spent jets. In this study, a zero cross-flow design is presented. The zero-crossflow design creates spacing between hole arrays to allow for spent flow to be directed away from impinging jets. Three configurations with different impingement holes placements are studied and compared with pure impingement with spent crossflow cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. The zero-cross flow design clearly shows minimal degradation of impingement heat transfer due to crossflow compared to conventional design with lower mass flow rate requirement and lesser number of overall impingement holes due to the reduced cross-flow effect on the impingement region.

Hole Staggering Effect on the Cooling Performance of Narrow Impingement Channels Using the Transient Liquid Crystal Technique

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Alexandros Terzis ◽  
Guillaume Wagner ◽  
Jens von Wolfersdorf ◽  
Peter Ott ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
Transfer Coefficients ◽  
Noticeable Effect ◽  
Cooling Performance ◽  
Heat Transfer Coefficients ◽  
Cooling Hole ◽  
Turbine Airfoils ◽  
Transient Liquid Crystal Technique

This study examines experimentally the cooling performance of narrow impingement channels as could be cast-in in modern turbine airfoils. Full surface heat transfer coefficients are evaluated for the target plate and the sidewalls of the channels using the transient liquid crystal technique. Several narrow impingement channel geometries, consisting of a single row of five cooling holes, have been investigated composing a test matrix of nine different models. The experimental data are analyzed by means of various post-processing procedures aiming to clarify and quantify the effect of cooling hole offset position from the channel centerline on the local and average heat transfer coefficients and over a range of Reynolds numbers (11,100–86,000). The results indicated a noticeable effect of the jet pattern on the distribution of convection coefficients as well as similarities with conventional multi-jet impingement cooling systems.

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