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An efficient way of convection heat transfer measurement on a curved surface

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Accurate determination of convective heat transfer coefficients on complex surfaces with high spatial resolution is essential in the design and analysis of thermal systems. This study focuses on the implementation of a recently developed true color image-processing technique for the quantitative interpretation of liquid crystal images obtained from a curved surface. The interpretation includes the use of a linear hue versus temperature relation as an accurate temperature measuring tool, a color image analysis system and a transient heat transfer model for the conversion of time accurate temperature information into heat transfer coefficient maps. A square to rectangular transition duct is used as a heat transfer model representative of a curved geometry. The transient heat transfer experiments are performed with ambient temperature air in the transition duct model which is preheated by a custom designed electric heater. The measurements are performed on the curved bottom surface of the transition duct. Two dimensional surface distributions of heat transfer coefficient on the curved surface are presented with high spatial resolution. The hue-capturing technique provides extremely fine details of heat transfer coefficient when compared to other conventional discrete sensor methods. The technique is a highly automated heat transfer measurement method which reduces lengthy data reduction processes and significantly improves spatial resolution.

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c :

Specific heat


Charge coupled device

h :

Convective heat transfer coefficienth=q/(T w−T)(W/m2K)


Normalized hue, saturation and intensity

k :

Thermal conductivity


National Television System Committee

q :

Heat flux,q=−k∂T/∂y(W/m2)


Normalized red, green and blue


Chiral nematic liquid crystal starting to respond at about 35°C with an approximate bandwidth of 1°C

T :

Static temperature

t :


y :

Normal distance from the wall surface


Thermal diffusivity of air, α=k/(ρCp)


Nondimensional time, β=h√t/√ϱck


Normalized temperature θ=(T−T i)/(T −Ti)



i :

Initial condition

p :

At constant pressure

w :

Wall condition


Free stream value


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Correspondence to Kui-Soon Kim.

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Kim, K. An efficient way of convection heat transfer measurement on a curved surface. KSME Journal 7, 349–363 (1993).

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Key Words

  • Convection
  • Curved Surface
  • Liquid Crystal