| Abstract | We introduce a measurement concept using seeded thermographic phosphor particles, which achieves high spatial resolution and rejection of surface induced signals, and is thereby applicable to resolve two-dimensional temperature distribution in sub-millimeter thermal boundary layers. Unlike previous implementations of ratiometric phosphor thermometry in fluid flows, which is based on the division of two spectrally or temporally separated images of the luminescence from groups of seeded particles, here we treat the individual phosphor particles as independent temperature detectors positioned at the discrete particle locations. 2D rotated Gaussian functions are fitted to each particle image as to integrate particle signals in the two frames for ratio-based thermometry and to position the particles with sub-pixel resolution (< 10 μm). In addition, the fitting method allows to separate the luminescence signal of the imaged particles from interfering signals with a low spatial frequency, for example from surface reflection or re-scattering of luminescence light. After assessing the spatial resolution, and the robustness of the temperature measurements against high levels of re-scattered signals, near-wall measurements are demonstrated. The ability to finely resolve the temperature distribution within a 500 μm thin thermal boundary layer is validated against the laminar Prandtl–Blasius equation. As the thermometry counterpart and complement to Particle Tracking Velocimetry, this technique allows to probe the fine details of heat transfer in boundary layers. |
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