Calibrating for viewing angle effect during heat transfer measurements on a curved surface

Liquid crystal thermography (LCT) has been widely used for the determinatio n of surface heat transfer distribution. However, this technique is sensiti ve to illumination and viewing angle and therefore limited to surfaces with only slight curvature. A liquid crystal calibration technique using true-c olour image processing system has now been developed to alleviate the effec t of viewing angle on oblique/curved surfaces. Application of the calibrati on and transient liquid crystal thermographic techniques and uncertainty an alysis to a heated air slot jet impinging on a semi-cylindrical convex surf ace has been demonstrated. It is shown that the local heat transfer coeffic ient may be overestimated by up to 39.1% at a viewing angle of 69 degrees f rom the normal under test conditions. However, the overall uncertainty in h eat transfer coefficient can be significantly reduced from the maximum valu e of 36.3% to within 11.1%;, by using the implemented viewing calibration t echnique. (C) 2001 Elsevier Science Ltd. All rights reserved.