The radiative heat transfer coefficient at high temperatures is determined using a combination of experimental measurement and computational modeling. In the experimental part, cement mortar specimen is heated in a laboratory furnace to 600°C and the temperature field inside is recorded using built-in K-type thermocouples connected to a data logger. The measured temperatures are then used as input parameters in the three dimensional computational modeling whose objective is to find the best correlation between the measured and calculated data via four free parameters, namely the thermal conductivity of the specimen, effective thermal conductivity of thermal insulation, and heat transfer coefficients at normal and high temperatures. The optimization procedure which is performed using the genetic algorithms provides the value of the high-temperature radiative heat transfer coefficient of 3.64 W/(m2K).
A method for lightweight-gypsum material design using waste stone dust as the foaming agent is described. The main objective is to reach several physical properties which are inversely related in a certain way. Therefore, a linear optimization method is applied to handle this task systematically. The optimization process is based on sequential measurement of physical properties. The results are subsequently point-awarded according to a complex point criterion and new composition is proposed. After 17 trials the final mixture is obtained, having the bulk density equal to (586 ± 19) kg/m3 and compressive strength (1.10 ± 0.07) MPa. According to a detailed comparative analysis with reference gypsum, the newly developed material can be used as excellent thermally insulating interior plaster with the thermal conductivity of (0.082 ± 0.005) W/(m·K). In addition, its practical application can bring substantial economic and environmental benefits as the material contains 25 % of waste stone dust.