Temperature measurement in flames is a challenging problem. Recently, hyperspectral imaging has demonstrated to be able to provide accurate temperature maps in a standard flame. However, hyperspectral imagers are expensive instruments, and the data analysis is laborious. Thus, a more simple approach to temperature imaging would be advisable. Since important and systematic differences exist in the low-resolution spectra of flames as a function of their temperature and chemical composition, it is in principle possible to retrieve these parameters by means of multispectral imaging. In this work, a standard flame, whose temperature and CO2 concentration are known, is studied with an infrared camera in the MIR band (3 to 5 μm), provided with a six interference filter wheel. High- resolution emission spectra are calculated, using the HITEMP2010 database, as a function of flame temperature (T) and CO2 column density (QCO2 , measured in ppm·m), and integrated over the spectral transmittance profile of the selected interference filters. Measured radiances in each channel are compared to these simulated values and the absolute error is minimized at each pixel to retrieve values of T and Q, obtaining temperature and column density maps for the flame. Results are compared to the known values of the standard flame. First estimations of errors are found to be ΔT< 100 K and ΔQCO2 < 400 ppm·m for flames with T∼2200 K and QCO2 ∼3500 ppm·m. The possibility of reducing the number of filters and their effect on accuracy is studied.
In the last decades, composite materials, particularly thermosetting carbon fiber reinforced polymers, have become the main structural material for the aerospace industry. Recently, interest has grown in thermoplastic composites, since they are chemically more stable, faster to process, fatigue-resistant and recyclable. Nevertheless, when submitted to high temperatures these materials may degrade in ways not presently well known. Therefore, the study of the thermo-mechanical properties of thermoplastic composites when exposed to fire or high-temperature events is of primary interest. In particular, a good knowledge of its behavior could improve physical modeling to the point of reducing the number of prescribed fire tests by virtualizing some of them. The first step is to measure the thermal parameters of real samples in a practical way. We have established a methodology that extends the classical flash method to obtain the effective thermal parameters (diffusivity, specific heat, heat conductivity, and Biot number) of thermoplastic composite materials by a non-contact method based on IR imaging. Values obtained have been used to simulate thermal behavior with a FEM-based solver, from room temperature up to 900°C, with an agreement with experimental data better than 1% in temperature (K) for temperatures below ∼ 260°C and better than 3% up to ∼ 850°C.
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