A Nonstationary Method and Experimental Equipment for Measuring the Thermal Conductivity of Heat Insulators

The study aims to test an advanced technique but insufficiently valued in the world in the process of experimental manufacture of borosilicate glass foam. It is about the unconventional technique of heating solids by using the microwave radiation converted into heat. The experimental equipment on which the tests were performed was a 0.8-kW microwave oven commonly used in the household with constructive adaptations to be operational at high temperature. The adopted manufacturing recipe was composed of borosilicate glass waste with the addition of calcium carbonate, boric acid and water in different weight proportions. The material was sintered at 829-834 ºC by predominantly direct microwave heating and the optimal foamed product had characteristics similar to those manufactured by conventional techniques (apparent density of 0.33 g/cm3, thermal conductivity of 0.070 W/m•K, compressive strength of 3.1 MPa and a homogeneous microstructure with pore size between 0.7-1.0 mm). The energy efficiency of the unconventional manufacturing process was remarkable, the specific energy consumption being only 0.92 kWh/kg.

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Evaluation of Physical Characteristics and Sorption of Cement Mortars with Recycled Ceramic Aggregate

Materials ◽

10.3390/ma14247852 ◽

2021 ◽

Vol 14 (24) ◽

pp. 7852

Author(s):

Agata Stolarska ◽

Teresa Rucińska

Keyword(s):

Thermal Conductivity ◽

Compressive Strength ◽

Flexural Strength ◽

Thermal Conductivity Coefficient ◽

Sorption Isotherms ◽

Sorption Kinetics ◽

Fine Aggregate ◽

Air Content ◽

Nonstationary Method ◽

Moisture Conditions

The subjects of this study were mortars with varying amounts of recycled ceramic aggregate (RCA). As part of the fine aggregate, the RCA volume share is 10%, 20%, 30%, 50% and 100%. First, fresh mixture parameters were evaluated, such as consistency and air content measurement by pressure method. Next, specimens were molded for compressive strength and flexural strength tests after 7, 28 and 56 days of curing. The thermo-humidity parameters of the composites, i.e., coefficient of capillary action and thermal conductivity coefficient were also investigated using nonstationary method. Sorption kinetics of the mortars at different moisture conditions at 20 °C were also evaluated. Sorption tests were carried out using two methods: TM and DVS. The sorption isotherms were plotted on the basis of equilibrium moisture content for the materials tested. The isotherms obtained by the two methods were evaluated. The results allowed us to draw conclusions on the physical and mechanical parameters of the composites with different amounts of RCA and to evaluate the ability to absorb moisture from the environment by these types of materials. A clear decrease in the compressive strength after 28 days of curing compared to the reference mortar was recorded after using 30% to 100% of RCA (approx. 26% to approx. 39%). Changes in flexural strength were significantly smaller, reaching no more than approx. 7.5%. It was shown that the amount of RCA translates into the ability to sorb moisture, which may affect the application of this type of composites. The amount of RCA translates also into the thermal conductivity coefficient, which decreased with increasing amount of RCA.

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A NONSTATIONARY METHOD FOR DETERMINING THERMAL CONDUCTIVITY OF SOIL IN SITU

Soil Science ◽

10.1097/00010694-195202000-00001 ◽

1952 ◽

Vol 73 (2) ◽

pp. 83-90 ◽

Cited By ~ 137

Author(s):

D. A. DE VRIES

Keyword(s):

Thermal Conductivity ◽

Nonstationary Method

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Comparison of the Thermal Properties of Geopolymer and Modified Gypsum

Polymers ◽

10.3390/polym13081220 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1220

Author(s):

Karol Prałat ◽

Justyna Ciemnicka ◽

Artur Koper ◽

Katarzyna Ewa Buczkowska ◽

Piotr Łoś

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Thermal Diffusivity ◽

Heat Conductivity ◽

Reference Sample ◽

Simultaneous Increase ◽

Heat Conductivity Coefficient ◽

Nonstationary Method ◽

Experimental Values ◽

Physical Quantities

The paper presents the results of research concerning the influence of micromaterials on the heat conductivity coefficient λ, specifically heat Cp and thermal diffusivity a of modified gypsum and geopolymer. Microspheres, hydroxyethyl methylcellulose (HEMC) polymer, and aerogel were used as the gypsum’s modifying materials. The study also investigated an alkali potassium-activated methakaolin-based geopolymer with the addition of aluminium dust. During the measurements of thermal parameters, the nonstationary method was chosen, and an Isomet device—which recorded the required physical quantities—was used. When compared to the reference sample, a decrease in the thermal conductivity and diffusivity of the hardened gypsum— and a simultaneous increase in specific heat—was observed with the addition of micromaterials. The geopolymer sample was characterized by the lowest value of thermal conductivity, equal to 0.1141 W/(m·K). It was over 62% lower than the reference sample containing only gypsum. The experimental values of the thermal conductivity of the gypsum samples with the addition of HEMC, aerogel and microspheres were, respectively, over 23%, 6%, and 8% lower than those of the unmodified gypsum samples. The lowest values of thermal conductivity were observed in the case of the gypsum samples modified with polymer; this resulted from the fact that the polymer caused the greatest change in the structure of the gypsum’s composite, which were expressed by the lowest density and highest porosity.

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