Heat transfer in foams consists of conduction through solid and gaseous phases, convection within the cells as well as radiation through the whole medium. Radiation thermal conduction affects the overall thermal conductivity by 40% in a high porosity. Therefore, the investigation of that term seems to be necessary. Radiation thermal conduction depends on the extinction coefficient which its determination is experimentally complex. In this study, this coefficient is theoretically estimated using Glicksman model for polyolefin foams and is verified in comparison with the experimental data. Extinction coefficient which plays an effective role in the radiation thermal conduction depends on the morphological properties including foam and solid densities, cell and strut diameters. The results demonstrate that the radiation thermal conduction decreases by reducing cell size and increasing foam density and strut diameter. An L25 orthogonal array of Taguchi approach is used for optimization of radiation thermal conduction respect to foam density, cell and strut diameters as variable parameters. The analysis of variance results illuminate that foam density and cell diameter with 58 and 32% contribution are the most effective parameters on the radiation thermal conduction, respectively. At optimum conditions according to the prediction tool of Taguchi approach, the radiation thermal conduction significantly decreases to 1.0908 mW/mK.

Zirconia based thermal barrier coatings (TBCs) are extensively used in gas turbines engines to protect and provide thermal insulation for hot-section metal components. Consequently, the key parameter of these coatings is low thermal conductivity. The present paper deals with evaluation of effect of the microstructure and stabilizer type on zirconia based TBCs thermal insulation capability. For this scope, three type of coatings including conventional yttria stabilized zirconia (YSZ), conventional ceria and yttria stabilized zirconia (CYSZ) and nanostructured yttria stabilized zirconia have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738 substrates. Microstructural evaluation and phase analysis were performed using field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) respectively. Results revealed that with employing of ceria stabilizer and fabrication of nano-structure in coating, the thermal insulation capability of zirconia based TBCs were enhanced.

Alumina (Al2O3) nanoparticles were used as the additive for modifying a novolac phenolic resin using the solution mixing method. Different weight percentages of nano alumina 3 and 8 w% were loaded into the resin, called 3ARC and 8ARC nanocomposites, respectively. These nanocomposites were investigated by field emission scanning electron microscopy (FE-SEM), X-ray fluorescence spectroscopy (XRF), energy-dispersive X-ray spectroscopy (EDS), and oxyacetylene flame test (OFT). The FE-SEM images exhibited that at low concentrations (3ARC), the nano alumina particles were dispersed uniformly on the surface of novolac resin, however, at high concentrations, the dispersion was repressed by aggregation in the nanocomposites. OFT proved that with increasing alumina content in the nanocomposite, the back temperature of the sample decreases and thus improves the thermal insulation properties.

This paper explores the incorporation of aramid fibers, recognized for their high mechanical flexibility and low thermal conductivity (TC), to serve as reinforcing agents within the highly porous aerogel matrix in order to overcome their fragility and weak mechanical structure that impose limitations on their practical utility especially in piping insulation. The thermal properties are determined using a micromechanical modeling approach that considers parameters such as temperature, fiber volume fraction, thermal conductivity, and porosity of the silica aerogel. For specific conditions, including an Aramid fiber radius of 6 microns, a silica aerogel thermal conductivity of 0.017 W.m-1.K-1, and a porosity of 95%, the resulting AFRA composite exhibits an Effective Thermal Conductivity (ETC) of 0.0234 W.m-1.K-1. Notably, this value is lower than the thermal conductivity of air at ambient temperature. The findings are further validated through experimental and analytical techniques. A response surface methodology (RSM) based on Box-Behnken design (BBD) is employed. This approach leads to the development of a quadratic equation intricately relating the key parameters to the ETC of the AFRA. The aim is optimization, identifying target optimal values for these parameters to further enhance the performance of AFRA composites.

The loss of energy, especially in industrial and residential buildings is one of the main reasons of increased energy consumption. Improving the thermal insulation properties of materials is a fundamental method for reducing the energy losses. Polymeric foams are introduced as materials with excellent thermal insulation properties for this purpose. In the present study, a deep theoretical investigation is performed on the overall thermal conductivity of low-density polyethylene (LDPE) foams. The thermal conductivity by radiation is predicted using two different methods. The most appropriate model is selected through comparing results with experimental data. The results show that the theoretical model has an appropriate agreement with the experimental results. The effects of foam characteristics including foam density, cell size, and cell wall thickness on the overall thermal conductivity are investigated. The results indicate that by decreasing the cell size and increasing the cell wall thickness, the overall thermal conductivity is decreased significantly. Also, there is an optimum foam density in order to achieve the smallest thermal conductivity. The lowest overall thermal conductivity achieved in the studied range is 30 mW/ mK at a foam density of 37. 5 kg. m-3, cell size of 100 μ m, and cell wall thickness of 6 μ m.

In order to reduce the energy consumption in buildings and reduction of thermal losses, it is necessary to use thermal insulation in .building envelopes. Thickness of thermal insulation and its position in the building envelope are important, because they vary in different climates.In this study the above-mentioned parameters are investigated for three different cities in Iran.Including: Tehran with moderate climate, Tabrii with cold climate and Ahvaz with hot climate. The Opaque software was used for calculating annual thermal building loads.Based on the obtained results, in Tehran city, insertion of 5 to 7.5 cm insulation as two slice in wall envelope have greatest reduction in yearly thermal loads. Also, in Tabriz city insertion of 5 to 7.5 cm insulation as a whole (1 piece) in internal layer of wall have greatest reduction in yearly thermal loads, in Ahvaz city insertion of 5 to 7.5 cm insulation as a whole (1 piece) in external layer of wall have greatest reduction in yearly thermal loads.