Quantitative IR Thermography Research Articles

A comparison between thermographic and flow-meter methods for the evaluation of thermal transmittance of different wall constructions

One of the key parameters that “meter” the energy performance of the whole structure of buildings is the thermal transmittance.This parameter can be evaluated with a theoretical approach, regulated by standard ISO 6946, once the stratigraphy of the envelope and the properties of the constituent materials are known, or by using a heat flow meter (HFM), following the recommendations provided in standard ISO 9869.Recently, the use of quantitative IR Thermography (IRT) has been proposed by several researchers; this method allows to determine the overall transmittance of an envelope in a short time (especially in comparison with HFM method). However, the theoretical or experimental transmittance, measured on real buildings having walls composed by different materials, can be rather distant from those calculated or measured with different procedures.For this reason, for a correct certification of the thermal performance of a building envelope, it is necessary the availability of experimental procedures for a direct and reliable evaluation of the thermal transmittance, suitable for different walls.Research has found that, especially in historical constructions, faults in the building envelope and the age of the materials can greatly affect the HFM measurements.The aim of this work is to analyze in situ the thermal performance of three different walls which have been selected according to: different materials, different age, and different construction. On each envelope, a comparison between U-values, measured by HFM and IRT, and computed according the standard procedure, has been effected.

Validation of quantitative IR thermography for estimating the U-value by a hot box apparatus

Energy saving plays a key role in the reduction of energy consumption and carbon emission, and therefore it is essential for reaching the goal of the 20-20-2020 policy.In particular, buildings are responsible of about 30% of the total amount of Europe energy consumption; the increase of their energy efficiency with the reduction of the thermal transmittance of the envelope is a point of strength with the actions and strategies of the policy makers.Currently, the study of energy performance of buildings is based on international standards, in particular the Italian one allows to calculate the U-value according the ISO 6946 or by in-situ measurements, using a heat flow meter (HFM), following recommendations provided in ISO 9869.In the last few years, a new technique, based on Infrared Thermography (IRT) (also referred to as Infrared Thermovision Technique - ITT), has been proposed for in situ determination of the thermal transmittance of opaque building elements. Some case studies have been reported.This method has already been applied on existing buildings, providing reliable results, but also revealing some weaknesses.In order to overcome such weak points and to assess a systematic procedure for the application of IRT, a validation of the method has been performed in a monitored environment.Infrared camera, the heat flow meter sensors and a nearby meteorological station have been used for thermal transmittance measurement. Comparison between the U-values measured in a hot box with IRT as well as values calculated following international standards and HFM results has been effected. Results give a good description of the advantages, as well as of the open problems, of IR Thermography for estimating the U-value.Further studies will help to refine the technique, and to identify the best operative conditions.

In situ examination of structural cracks at historic masonry structures by quantitative infrared thermography and ultrasonic testing

The key concern of the study was the in situ assessment of cracks in historic masonry structures by quantitative IR thermography (QIRT). To better understand the potentials and/or limits of QIRT for that purpose, the non-destructive in situ survey composed of QIRT and ultrasonic testing was conducted on a sixteenth century monument, suffering from structural cracks that had occurred in recent years. Its aim was to discover the thermal behaviour and ultrasonic characteristics of cracks in relation to depth and moisture content. The superficial and deep cracks were found to have different thermal responses to exposed conditions which made them easily distinguishable by QIRT analyses. The results of thermal monitoring during the exposure of heating conditions were promising in giving hints of methods for the depth assessment of deep cracks in masonry. The in situ ultrasonic data taken in indirect transmission mode provided knowledge on the depth of cracks that enhanced the accuracy of the non-destructive in situ survey.

Thermal analysis of an historical Turkish bath by quantitative IR thermography

The study is focused on the use quantitative IR thermography (QIRT) for the examination of thermal performance of an historical Turkish bath (hamam). A simple heat transfer model was applied to achieve reference surface temperatures during the IRT surveys. The reference temperatures calculated and the real surface temperatures measured have been compared each other to better understand the thermal performance of historical structure in a non destructive way. Another issue was the failures evaluation in relation to the recent restoring interventions. The study was supported by microclimatic monitoring of indoor and outdoor conditions. The thermophysical properties of the historic materials were determined by laboratory analysis and the data were used for the heat loss calculations

Determination of critical moisture content in porous materials by IR thermography

This study is focused on the improvement on the porous material characterisation, measuring the transition stage between the saturated and dry phases, which has been defined in literature as the critical moisture content (Θc). This study develops a procedure based on Quantitative IR Thermography (QIRT) determining the effective Θc, as a physical property for the porous material. The Θc for San Marco bricks were examined in laboratory by QIRT and the standard gravimetric method (SGM). It was seen that QIRT can be used to determine the Θc and was also found to be more practical and sensitive than the SGM. The results obtained in the laboratory were promising to give the hints of methods for quantitative moisture content measurements and in-situ QIRT investigations.

Study of acoustic disturbances effect on laminar separation bubble by IR thermography

This work concerns the study of sound effect on laminar separation bubble phenomenon which happens on the upper surface of aerodynamic bodies having small thickness and operating at low Reynolds number. The laminar bubble increases the aerodynamic drag of the wing: so the boundary layer control becomes important, in order to avoid the separation problem. In addition to control methods such as turbulators or boundary layer blowing/suction systems it would be possible in accordance with linear stability theory to induce the formation and amplification of the Tollmien–Schlichting waves introducing a sound wave having a particular frequency as a disturbance in the freestream. In this study a thin airfoil is tested at a Reynolds number of 60,000. The airfoil is installed inside a low speed wind tunnel test chamber; at the inlet of the wind tunnel is positioned a sub woofer sound source connected to an amplifier and a signal generator. In this way it was possible to generate a pure tone in the freestream. The experiments were conducted using a quantitative IR thermography method in order to get the positions of the laminar bubble characteristic points (separation, transition and reattachment point) with and without the acoustic disturbance. The frequency range between 200 and 800 Hz with step of 100 Hz was inspected. The airfoil angle of attack was varied between 2° and 8°; inside this interval the laminar bubble was visible by thermography.

Surface and subsurface analysis of limiter and divertor plates by photoacoustic and photothermal techniques

The product kρc is the relevant thermophysical parameter for the heating up of material walls in contact with plasma and, apart form the emissivity, it is also the decisive thermal parameter for the quantitative IR thermography; here k, ρ, and c are the thermal conductivity, density and specific heat capacity, respectively, of the wall material. The Photoacoustic Calorimetry (PAC) provides the diagnostic means to measure this quantity kρc directly. First results of PAC measurements with graphite limiter plates exposed in ASDEX to about 600 discharges are presented and compared to the unused graphite material. Further prospects of the nondestructive photoacoustic techniques in plasma-surf ace interaction problems are discussed, in relation to coatings/claddings and redeposition layers.

Influence of a meal on skin temperatures estimated from quantitative IR-thermography.

In young men at 25 degrees C, quantitative IR-thermography showed that fasting values of skin temperatures over suspected areas of brown adipose tissue (BAT) were higher than where no BAT is thought to occur. However, at 30 min and again at 60-90 min after a meal of 2.5 MJ, the magnitude of the increase in skin temperature was similar in areas with or without suspected BAT. In conclusion, either thermography was unable to detect the activation of BAT, or the meal did not stimulate heat production in the sites of suspected BAT.

Effect of atmospheric attenuation on temperature measurements made using IR scanning systems

The atmosphere attenuates IR radiation in certain frequency bands even at distances as short as 1 m. Within the 3-5-microm range used by many IR thermographic systems, H20 and CO2 absorb a finite fraction of the source radiation. To achieve reliable quantitative IR thermography, it is necessary to correct the received signal for this attenuation. This paper develops a simple model and presents numerical calculations of the attenuation expected at a few meters distance for one typical thermographic imaging system. (The extension to other equipment could easily be done by substituting different numerical data for the detector response.) The attenuation factors due to CO2 and H20 are 6 and 8%, respectively, at a 10-m range. A wide variety of target temperature and ambient humidity conditions were examined; representative curves selected from this output are presented. Because of the importance of precise IR measurements for industrial applications, the effect of varying CO2 concentrations was also studied.