Feasibility Study and Optimal Design of an Experimental Bench for Identification of Liquid Thermal Diffusivity

Expertise of innovative materials by nondestructive techniques is a key goal in process engineering development. In this context, if identification of thermal diffusivity of liquid is a crucial requirement to develop a reliable mathematical model of knowledge, it is essential to propose a complete and valid methodology. Based on the analysis of thermal wave propagation (generated by a periodic excitation), an experimentation is developed in order to avoid the implementation of a pyroelectric sensor required in usual photopyroelectric techniques. The proposed approach is investigated in a trilayer system. Theoretical aspects of the identification of thermal parameters in the frequency domain are presented. A feasibility study is discussed in order to justify this approach for liquids. A sensitivity analysis is implemented in a particular case to provide an optimal experimental bench. Finally, experimental results for several liquids are presented and discussed

Numerical design of experiment for sensitivity analysis - application to skin burn injury prediction

Temperature evolution and skin burn process resulting from a laser radiation exposure are investigated in this paper. Transient temperature in skin is numerically estimated using a 1-D multilayered model based on Penne\u27s equation. The degree of burn injury is numerically evaluated by using an Arrhenius-type function. Unfortunately, most of the mathematical model parameters are not well defined in literature. Thus, a sensitivity analysis has been performed in order to evaluate the effect of each parameters inaccuracy on temperature estimation and on burn injuries prediction (according to several authors\u27 characterization). Investigated parameters uncertainties that crucially invalidate the thermal model are as follows: epidermis and dermis volumetric heat, extinction coefficient, and skin thickness of the affected area. Considering the damage prediction, the activation energy is a key parameter for the validation of an efficient predictive tool

On the use of periodic photothermal methods for materials diagnosis

This work aims the analysis of valuation methods devoted to materials diagnosis in order to provide an efficient estimation in practical operational conditions and environment (by the observation of a thermal tracer representative of a damage). The followed methodology consists in implementing observation techniques based on a periodic photo-thermal excitation so that the observation of the heated structure response allows to identify characteristic parameters of the studied materials. In most cases, simplistic hypotheses required for analytical model validation are not satisfied. Thus, analysis in the frequency domain requires the computing of a specific finite elements method

Quasi-online method for the identification of heat flux densities and trajectories of two mobile heating sources

This paper deals with a complex inverse ill-posed problem related to the identification of numerous unknown parameters of a system described by partial differential equations. A quasi-online identification method of heat flux densities and trajectories of two mobile heating sources is proposed. This approach is based on a modification of the conjugate gradient method with automatically adaptive sliding window size in order to ensure online identification. A set of fixed sensors is located on the domain in order to measure temperature evolution. Observations are disturbed according to a realistic Gaussian noise. The effectiveness of the proposed method will be illustrated considering numerical results of several simulatio

Defect localization based on modulated photothermal local approach

A new method dedicated to macroscopic-like defect localization in composite materials is presented in this paper. The proposed method is based on non intrusive measurements of the sample temperature resulting from a local periodic low energy heating. In such an approach, the low temperature increases of the investigated material avoid damages which can occur with usual flash techniques. Since thermal waves propagation is modified due to the heterogeneity induced by the defect, analysis of both modulus and phase lag spatial distributions provides relevant knowledge. Up to now, macroscopic-like defect detection based on local periodic heating has not been widely investigated. Thus, differences between the global approach and the local approach have to be pointed out in order to verify the local method’s attractiveness. A mathematical model based on complex temperature is developed and provides a relevant predictive tool. In several configurations interest of local periodic heating is highlighted. For example, while several defects are included in the sample, the method capability to distinguish one from each other is shown considering a scanning approach. In order to validate these results, an experimental device has been developed. Several non destructive inspections are performed and defect detection is achieved using an infra-red camera providing observations of the sample surface.

A teaching experimental system for defect localisation based on frequency analysis in a thermal context

The aim of this paper is to present a newly developed pedagogical demonstrator. It is intended for students which study automated systems and computer engineering). This experimental device can be used as a support to illustrate the course on the identification of systems and more precisely to underline the interest of frequency analysis. It can be obviously implemented as part of a Master\u27s course allowing to deepen concepts specific to signal processing, filtering or even identification and diagnosis. It is mainly concerned with the teaching of information technology and information systems