Optical convective heat transfer measurements using infrared thermography and frequency domain phosphor thermometry

A novel technique for spatially resolved heat transfer measurements is proposed. Utilizing its transmissive properties the temperature distributions at the upper and lower surface of an acrylic glass plate mounted on a heated copper surface are measured. Infrared thermography is employed to determine the external wall temperature. The temperature at the interface between acrylic glass and copper base plate is measured with a thermographic phosphor. The temperature dependent phosphorescence lifetime of the applied Cr3+:Al2O3 (ruby) powder is assessed using frequency-domain processing of high-speed camera recordings. The measured temperature boundary conditions are used to perform a finite element computation of the conductive heat flux that is imposed by an electric heater. The heat transfer coefficient distribution is corrected iteratively to compensate lateral conduction errors. The newly developed technique is validated by means of jet impingement heat transfer measurements and compared to numerical results and data available in the literature.