Planar imaging thermometry in gaseous flows using upconversion excitation of thermographic phosphors

Temperature measurement in gaseous flows is of significant practical importance for determining convection coefficients for heat transfer calculations, validating computation fluid dynamic simulations, and understanding the fundamentals of turbulent mixing and transport in flows. Here, we report on a new diagnostic technique for measuring temperature in gaseous flows which relies upon upconversion luminescence from inorganic phosphors. The phosphor used for the study consists of erbium (Er3+) and ytterbium (Yb3+) ions doped into a yttrium oxysulfide host material. The theoretical background behind the upconversion diagnostic is presented and spectral emission data taken using upconversion excitation are used to design a temperature diagnostic which is quite sensitive for temperatures ranging from approximately 300–600 K. Demonstration temperature measurements were performed in an air jet heated to temperatures ranging from 295–523 K. Single-shot images of temperature were obtained with a temperature precision of approximately ±5 K (1 standard deviation basis). This is the first known application of upconversion excitation to imaging temperatures in gaseous flows.