Desenvolvimento de equipamento para medição da condutividade térmica por meio da técnica fluxométrica

Abstract

Thermal conductivity is a property that indicates the ability of a given material to transfer heat. It is an important parameter in materials that make up the envelope of buildings, mainly because they influence thermal comfort and the habitability of users and also the energy consumption of the building. Designers usually use values established in technical standards to assess the insulation capacity of building envelopes. This is mainly due to the high cost of the equipment that measure the thermal conductivity available commercially, which are usually manufactured outside Brazil. Thus, the objective of this research was the development of a thermal conductivity meter, using electronic components, sensors and transducers at a more affordable cost, with a microprocessor based on the Arduino platform. The working principle defined for the project was based on the fluxmetric method, with two heat flux transducers and a sample, in a so-called symmetrical configuration. It is an applied research project that uses bibliographic and patent research for the development of an innovative prototype. Through experimental analysis, the prototype was tested based on tests with samples of materials whose properties are known in the literature, but which were also tested using a heat flow meter at the Brazilian Center for Energy Efficiency (CB3E), as well the use of the ISOMET 2114 thermal conductivity meter, for direct comparisons with the prototype. With the plaster sample obtained from the CB3E, the prototype was properly calibrated, but points of attention were pointed out regarding the thickness of the Expanded Polystyrene (EPS) sample from the CB3E. For the CB3E plaster sample, a combined uncertainty of 3.59% was reached, which results in an expanded uncertainty of ±7.18% for a confidence interval of 95%, values that leave the prototype consistent with the range of ±3% to ±10% for the heat flow meter principle, according to the literature. This was followed by a comparison with other samples with their properties defined by the ISOMET, comparisons with values obtained in the literature and in manufacturers' catalogues. Good perspectives were observed in relation to the catalog values for the EVA, EPS, mineralized wood fiber aggregated with cement (WWCB), gypsum and cement board samples, with 90.66% of the variance of the dependent variable. However, when the prototype and ISOMET readings were compared, the “R²” correlation was just 43.57%, indicating that the comparison between both metering principles should be performed with caution. Finally, it is concluded that the prototype has a potential to be a patentable product as a Utility Model due to the use of Peltier modules on the hot and cold plates and because its microprocessing being based on an Arduino platform. However, it was seen that it is still necessary to carry out more studies with the use of samples, certified by a primary method, in this case by the Guarded Hot Plate, a condition that was not satisfied due to lack of evidence of a laboratory that had this equipment operating at the research period.