IR Thermography for Non-Destructive Monitoring of Moisture in Cultural Heritage

One of the main sources of damage to historical buildings is the presence of humidity. It is fundamental to develop a diagnosis protocol to identify the presence of water, evaluate the damage in a building (the whole structure, part of it or individual materials), assess its vulnerability and, finally, carry out a restoration plan. IR thermography is a sustainable method to guarantee structure analysis and preservation. Here, an application is presented, permitting us to identify the wet and dry areas and transition zone related to evaporation on the surface of the investigated materials. Thanks to temperature maps, it is possible to observe saturated regions, qualitatively at first and then quantitatively, processing the images by plotting reference lines/points and correlating surface temperatures with moisture

Laser Flash technique: A critical analysis of testing parameters and models for fitting experimental data

Laser Flash is considered the standard technique for measuring the thermal diffusivity of solids. To avoid any permanent damage of the sample when a LF measurement is carried out on brittle materials, characterized by very low values of thermal diffusivity, thermal effusivity, and toughness, as the case of freestanding APS TBC samples, the energy density deposited onto the sample surface should be minimized. The damaging effect of the energy deposited on the surface of free standing TBC samples during LF measurements has been experimentally investigated. The damage has been evaluated experimentally and analyzed by suitable heat conduction modeling and some suggestions are provided [1]. ZrO2 is semitransparent to near IR radiation. This is the typical wavelenght range of the laser heating source of the laser flash equipment. Moreover, the characterization of TBCs at high temperatures is particularly interesting as the typical working temperature of gas-turbine is \u3e1000 °C [2]. At these temperatures the radiative heat transfer through the TBC becomes more and more relevant. The effect of blackening surfaces by a thin layer of graphite is considered [3]. Experiments are carried out at ambient temperature by means of a thermographic camera, at higher temperature in vacuum until 1200 °C and in argon atmosphere until 1000 °C. Data are analysed taking into account the heat exchange with the environment [4]. Successively, the possibility of radiative exchange between the two blackened sides of the sample [5] is taken into account. Finally, the possibility of simultaneous heating of the two sides of the sample, due to the semitransparency of the material is considered. This last model explains the anomalous immediate heating of the side facing the detector as shown in Fig. 1 Laser Flash is a very reliable technique for measuring thermal diffusivity of single layer samples but, especially for coatings, measuring their thermal diffusivity directly on a component they are deposited onto is a need. To satisfy this request in-reflection configuration photothermal techniques have been developed and successfully applied [6] . Furthermore, when the thickness of the substrate is not too thick, also the LF technique can be used on two-layer samples as some algorithms for estimating thermal diffusivity of a single material in a two layer sample have been developed since many years [7,8]. In particular all these models require to know the density, the specific heat and the thermal conductivity of the second layer. The effects of the uncertainty in the evaluation/estimation of the thermophysical parameters of the second layer will be discussed theoretically and compared with some experiments designed to highlight the most critical issues in this type of measurement. Please click Additional Files below to see the full abstract

Detection of insulation flaws and thermal bridges in insulated truck box panels

This paper focuses on the detection of defects and thermal bridges in insulated truck box panels, utilising infrared thermography. Unlike the traditional way in which passive thermography is applied, this research uses both heating and cooling methods in active thermography configurations. Lamp heating is used as the hot external stimulation, while a compressed air jet is applied as the cold external stimulation. A thermal camera captures the whole process. In addition, numerical simulations under COMSOL® platform are also conducted. Experimental and simulation results for two situations are compared and discussed

Periodic thermal behavior of walls: an experimental approach

The need for testing methods that could verify the performance of building components is continuously increasing, as it is mandatory to reduce the overall energy need of the buildings. This work provides a method that determines the dynamic behavior of walls. The time-shift due to the thermal and physical properties of the component is measured using infrared thermography. A case study on a typical wall sample is proposed, validating the technique

Thermophysical, microstructural characterization and non-destructive control of TBCs by photothermal and thermographic techniques: some lessons learned

Since several years, photothermal and thermographic techniques have been used to perform the thermo-physical characterisation of TBCs and the non-destructive assessment of TBC integrity. Furthermore, in the last decade some attempts to use these techniques for carrying out a non-destructive microstructural characterization have been done, as well. In this talk the description of a thermographic technique able to simultaneously measure the through-the-thickness and the in-plane thermal diffusivity of free standing TBCs samples and thus giving evidence of the typical microstructural anisotropy of APS TBCs will be provided [1]. Furthermore, some effects of the laser radiation used in a laser flash experiment on the TBC thermal diffusivity and a new model for fitting the experimental data will be presented [2,3]. The main results of an activity focused to identify potentialities and limitations of using Laser flash experiments on multilayered samples for estimating thermal diffusivity of TBCs samples will be provided. A theoretical and experimental analysis of the real capabilities of infrared techniques to estimate the porosity content and the microstructure of porous ceramic materials such as thermal barrier coatings (TBCs) by studying thermal diffusivity variations when pores are filled with air or vacuum will be provided [4,5]. Please click Additional Files below to see the full abstract

Numerical Model and Experimental Analysis of the Thermal Behavior of Electric Radiant Heating Panels

Electric radiant heating panels are frequently selected during the design phase of residential and industrial heating systems, especially for retrofit of existing buildings, as an alternative to other common heating systems, such as radiators or air conditioners. The possibility of saving living and working space and the ease of installation are the main advantages of electric radiant solutions. This paper investigates the thermal performance of a typical electric radiant panel. A climatic room was equipped with temperature sensors and heat flow meters to perform a steady state experimental analysis. For the dynamic behavior, a mathematical model was created and compared to a thermographic measurement procedure. The results showed for the steady state an efficiency of energy transformation close to one, while in a transient thermal regime the time constant to reach the steady state condition was slightly faster than the typical ones of hydronic systems

Indoor monitoring of Scrovegni Chapel Crypt

The indoor microclimate of the Scrovegni Chapel in Padova (Italy) was analysed first in the ‘80s. The early study operates in the best way for what concerns the choice of measurement devices and their positioning. Starting from 1995 a Scientific-technical Board coordinates the various initiatives commissioned for the surveys of a conservation of the Scrovegni building structures and for the preservation of frescos. However only during the last ten years, the activities of the Board have been addressed also on the study of the hypogeal environments under the Chapel and in the external environment around it in order to prevent possible damage due to the presence of water which frequently submerges the floor and part of the vertical structures of the crypt (perimeter walls and brick partitions). The investigations have been therefore extended to the crypt. The present work reports the preliminary results of the cyclical survey campaign launched last year and still ongoing: passive thermographic techniques (non-invasive and non-destructive) have been used for the identification and the investigation of the relationship between the boundary seasonal thermohygrometric conditions and the rainfall variations and other exogenous phenomena related to the complex water system of the area on which the Scrovegni Chapel stands

Monitoring Moisture Diffusion after Contact Sponge Application

The contact sponge method is applied on a piece of clay brick. According to the standard, the sponge is moistened with water, applied on the surface of the material by means of a cup, and weighted before and after the application. It allows us to determine the amount of water absorbed by the porous material by unit area and unit time. After the application, the moistened area begins to evaporate and cool down. The IR camera is used to monitor the temperature variation of the imprint of the sponge. Meanwhile, moisture diffuses on the material as well. The IR camera is used to monitor the in-plane diffusion of moisture by following the imprint of the sponge that enlarges with time. A suitable model is used to evaluate the shape of the imprint that varies with time

Statement of Peer Review

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