Simultaneous velocity and diffusivity mapping in the case of 3-D transient heat diffusion: heat pulse thermography and IR image sequence analysis

Abstract

A non uniform heat pulse is used as a non intrusive marker on opaque liquids or highly deformable solid media, in order to estimate both the full velocity and thermal diffusivity fields from thermal image processing. The difficult issue of identifying both the local transport and diffusion properties is addressed by adopting two different inverse approaches. First, a new specific version of the Total Least Squares (TLS) method is implemented, yielding both sensitivity analysis and confidence estimation, with no prior knowledge of the measurement noise variance. A second strategy is proposed from an iterative Digital Image Correlation (DIC) approach, yielding an hybrid DIC/TLS method. Both methods are first validated on simulated data,and calibrated with homogenous materials under uniform displacement. Two different grids are used in order to analyze the effect of the spatial period of the heat pulse on the retrieved parameters. Then, the effective velocity and thermal diffusivity fields are retrieved from an experimental bench in the case of a moving Thermisorel® sample. The Fine grid is found to yield better estimation results than the coarse grid. Thermal diffusivity mapping obtained with the TLS method is more trusted.

Keywords:

• Flash method
• Infrared camera
• Thermal diffusivity
• Velocity distribution
• Inverse methods
• Parameter estimation
• Total Least Squares
• Digital Image Correlation