High-precision flow temperature imaging using ZnO thermographic phosphor tracer particles

Area of Science:

• Fluid dynamics
• Materials science
• Optical diagnostics

Background:

• Thermographic particle image velocimetry (PIV) is a key technique for flow measurement.
• Accurate temperature measurement in turbulent flows is crucial for understanding heat transfer and fluid behavior.
• Existing thermographic phosphors have limitations in temperature sensitivity and precision.

Purpose of the Study:

• To characterize zinc oxide (ZnO) particles as tracers for temperature measurements in turbulent flows.
• To compare the temperature precision of ZnO with a standard thermographic phosphor (BAM:Eu(2+)).
• To investigate and correct for factors affecting ZnO luminescence intensity ratios.

Main Methods:

• Utilized a two-color, ratio-based thermographic technique.
• Employed ZnO particles as temperature-sensitive tracers in a turbulent air jet (Re = 2000).
• Investigated the influence of laser fluence and excitation irradiance on ZnO luminescence.
• Developed a correction method for laser-dependent effects.

Main Results:

• ZnO demonstrated a threefold increase in temperature precision at room temperature compared to BAM:Eu(2+).
• Identified and quantified the dependence of ZnO luminescence intensity ratio on laser fluence and irradiance.
• Successfully corrected for laser-dependent effects, achieving temperature images with 4 K precision at 363 K.
• Observed increasing sensitivity of ZnO across the 300-500 K range, with a potential precision of 3 K at 500 K.

Conclusions:

• ZnO particles are a highly sensitive tracer for temperature measurements in turbulent flows via thermographic PIV.
• The developed correction method enhances the reliability of ZnO-based thermography.
• ZnO extends the capabilities of thermographic PIV for studying flows with subtle temperature variations.