Takahiro Ohmura

Measurements of Thermal Properties of Gaskets for the Design of Bolted Flange Joints Under Thermal Conduction Conditions

In this study, the thermal properties of the gaskets, which were used for designing the bolted flange joints, such as effective thermal conductivity, specific heat, linear thermal expansion coefficient and so on were measured. Especially, the effective thermal conductivities were measured by using the heat flow method. The relationship between the gasket structure and the thickness was shown by using an equivalent thermal resistance, and an empirical equation of effective thermal conductivity, which was related to the bulk density and absolute temperature, was proposed by deriving the heat conduction in solid, radiation and gas. Also, in the measurement of the linear thermal expansion coefficients of the gaskets, the measured values were shown to change substantially below 150 °C, and to depend on the heating rate and the load applied on the gasket sample.Copyright

Effect of mechanical processing on thermal and mechanical properties of fibrous fumed alumina compacts

ABSTRACT In the present study, the fibrous fumed alumina compact with low thermal conductivity is prepared with a mechanical processing technique. The thermal conductivity of the compact remains low up to a temperature of 350°C. For the fibrous compact, the mechanical processing parameters play important role on controlling the thermal insulation capability. The thermal conductivity of compact increases from 0.036 to 0.042 W/m∙K by increasing the rotating speed of rotor. On the other hand, the value remains low by increasing processing time. The strength is decreased due to the increase of processing time. Thus, a lower rotating speed and a shorter processing time could result in a compact with favorable thermal insulation and strength. The results can be related to the surface structure of the coated alumina fibers and granulated structure within the compacts.

Effect of hydrophobic nano-silica on the thermal insulation of fibrous silica compacts

Abstract The particle’s surface property plays an important role on controlling the thermal insulation performance of fibrous silica compacts. In the present study, the effect of addition of hydrophobic silica on the thermal conductivity of the fibrous silica compacts is investigated. The measurement was conducted using laser flash method and differential scanning calorimeter (DSC) method. The thermal conductivity of fibrous silica compacts is only 0.042 W/m K. The addition of 5% hydrophobic silica further reduces the thermal conductivity of fibrous silica compacts to 0.033 W/m K. The thermal conductivity reaches a constant value with higher hydrophobic silica content. The flexural strength decreases with the increase of hydrophobic silica content. A compromise between the thermal insulation and strength is needed. The performance of fibrous silica compacts shows strong dependence on the surface structure of glass fibers.

Estimation Method for Attenuation Coefficient of Thermal Radiation in Thermal Insulators by Using Thermal Conductivity

A new method of estimating the attenuation coefficients of thermal radiation in thermal insulators was proposed. This is a means of deriving the attenuation coefficient using thermal conductivity of thermal insulators. It has already been proposed that the effective thermal conductivity of thermal radiation in thermal insulators is proportional to T3/ρ, determined using the absolute temperature T and the bulk density ρ. On the other hand, the effective thermal conductivity of thermal radiation in porous media with a high porosity is generally proportional to T3/β, determined using the absorption coefficient β with respect to the thickness of the object. From the above relation, the estimation equation for the attenuation coefficient β/ρ was derived. By using this equation, the attenuation coefficient of porous media, as thermal insulators having an uneven bulk density, must be derived as the representative value of the specimen. Furthermore, the attenuation coefficients of three kinds of thermal insulators were also estimated.