Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
UNCERTAINTIES ASSESSMENT ON THE INFRARED THERMOGRAPHY CALIBRATION TECHNIQUES
Submission Author:
Victor Eduardo Corte Baptistella , SP
Co-Authors:
Victor Eduardo Corte Baptistella, Gherhardt Ribatski
Presenter: Victor Eduardo Corte Baptistella
doi://10.26678/ABCM.COBEM2021.COB2021-1784
Abstract
Infrared thermography is a powerful technique to measure surface temperatures and evaluate heat transfer coefficients during dynamic thermal processes such as pool and flow boiling, jet impingement and drop evaporation. For that, the test section must allow optical access to the surface under study in the IR spectrum, this is obtained through the following methods: (i) using a metal foil or channel covered with a high emissivity paint on the outside surface; (ii) using a thin conducting film deposited on an IR transparent or semi-transparent substrate. The film heater is in direct contact with the fluid and the substrate is interposed between the heater and the camera. The first configuration has the advantage of being simple and allowing the use of a polynomial curve fit to map the IR signal into surface temperatures. However, the heat diffusion through the channel wall damps the temperature variations of the inner wall, limiting the observed time scales, and in the case of the foil, it is not representative of real surfaces due to its low heat capacity. The second configuration, although more complex, allows the evaluation of the inner surface temperature distribution without wall damping effects, however, its application needs either a negligible effect of the substrate to the signal reaching the camera sensor or a calibration procedure to compensate the substrate effects. This work aims at the comparison of data reduction and calibration techniques developed for temperature measurements in an ITO-sapphire heater using an IR camera. Although sapphire has a non-negligible IR absorption, it is commonly used, because of its mechanical properties in comparison to materials such as calcium fluoride, which are fragile but have no IR absorption. The errors provided by the polynomial curve fit and different calibration models are parametrically compared. These models separate the irradiated energy reaching the camera into heater, substrate, and ambient energy, by solving a radiation-conduction coupled system of equations and can be based on averaged optical properties and wavelength-dependent properties. In summary, this study evaluates to what extent a complex model is needed to derive the surface temperature based on IR measurements and to assess the sensitivity of the model results to uncertainties on optical and thermophysical properties of the substrate and to the boundary and initial conditions assumed to solve the equations comprising the model.
Keywords
Infrared thermography, Heat transfer, IR absorption, Boiling
