Evaluation of viewing-angle effect on determination of local heat transfer coefficients on a curved surface using transient and heated-coating liquid-crystal methods

2001 ◽  
Vol 31 (4) ◽  
pp. 447-456 ◽  
Author(s):  
T. L. Chan
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Curved Surface ◽  
Viewing Angle ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Angle Effect

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

1989 ◽  
Vol 111 (4) ◽  
pp. 877-881 ◽  
Author(s):  
J. W. Baughn ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
N. Saniei
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux, while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

Improved Accuracy in Jet Impingement Heat Transfer Experiments Considering the Layer Thicknesses of a Triple Thermochromic Liquid Crystal Coating

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Alexandros Terzis ◽  
Stavros Bontitsopoulos ◽  
Peter Ott ◽  
Jens von Wolfersdorf ◽  
Anestis I. Kalfas
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Thickness Gauge ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Paint Thickness

This paper examines the applicability of a triple layer of thermochromic liquid crystals (TLCs) for the determination of local heat transfer coefficients using the transient liquid crystal (LC) technique. The experiments were carried out in a narrow impingement channel, typically used for turbine blade cooling applications. Three types of narrow bandwidth LCs (1 °C range) of 35 °C, 38 °C, and 41 °C were individually painted on the target plate of the cooling cavity and the overall paint thickness was accurately determined with an integral coating thickness gauge. The 1D transient heat conduction equation is then implicitly solved for each individual TLC layer on its realistic depth on the painted surface. Local heat transfer coefficients are therefore calculated three times for the same location in the flow improving the measurement accuracy, especially at regions where the LC detection times are too short (stagnation points) or too long (wall-jet regions). The results indicate that if multiple LC layers are used and the paint thickness is not considered, the heat transfer coefficients can be significantly underestimated.

Sign in / Sign up

Export Citation Format

Share Document