دانلود رایگان مقاله سنجش هدایت حرارتی و ارزش ظرفیت گرمایی مواد ناهمگن با دستگاه جریان گرمامتر

Abstract

The aim of this study was to observe the suitability of the heat flow meter apparatus for thermal conductivity and specific heat capacity tests of concrete, as well as to determine specific heat capacity values for 14 different plasters. In total, two concrete types, five floor screed plasters, two fixing plasters, six wall screed plasters, and one specialized plaster that had small EPS spheres added into it were tested. The main novelty value of this research is studying how well heat flow meter apparatus can determine specific heat capacities of inhomogeneous materials. Also, how precisely thermal conductivity could be measured from small concrete specimens of interest. The results measured with the most suitable methods were in line with published values, which indicate that the apparatus was suitable for both tests.

4. Conclusions and discussion

In this research, both thermal conductivity and specific heat capacity tests on concrete were made as well as specific heat capacity tests on different plasters. In order to obtain reliable results, it is important to use the correct and the most suitable measurement method in the thermal conductivity tests, as can be noted by comparing different methods in Figs. 1 and 2. In these figures three out of four methods give results that are close to each other but the fourth one gives results of a correct magnitude. Please note that the variation in results in Figs. 1 and 2 is caused by inhomogeneous material and specimens. The apparatus is designed for testing of relatively small specimens which in case of inhomogeneous materials might cause problems if the specimens have any imperfections since these imperfections may become more obvious. Significance of inhomogeneous of the specimens is accentuated by that the maximum size of aggregate of concrete here was 16 mm and specimen thickness bare 10 mm or 20 mm which means that specimens that happened to have larger particles differ significantly from those that happened to have none. However, one of the goals of this study was to examine how well the apparatus could test inhomogeneous materials and therefore this variation in specimens was not considered to be a too crucial deficiency but rather an important observation point. When doing actual thermal conductivity tests with a heat flow meter apparatus the method should be chosen accurately. This study with the recommendation of the apparatus manufacturer shows that the best way to measure the thermal conductivity of tested specimens is to use both the rubber sheets and thermocouples because it is the best way to eliminate errors caused by air caps and poor contact between the specimen's surfaces and the apparatus's plates especially with small specimens with large maximum particle size. It is recommended to test at least ten specimens when testing thermal conductivity of inhomogeneous materials and to consider the test method every time when measuring new material.