An efficient prediction model of effective thermal conductivity for metal powder bed in additive manufacturing

The particle accumulation structure is commonly found in diverse engineering fields, including additive manufacturing powder, powder metallurgy, advanced reactor, grain storage and catalyst bed. The relative thermal conductivity of such structure is an important parameter to study the heat transfer behavior of the accumulation. In the study, the key factors affecting on the thermal conductivity of the powder is analyzed. Based on the results, the expression for calculating the thermal conductivity of the sphere metal powder is successfully reduced to only one parameter d50 and an efficient calculation model is proposed which can applicate both in room and high temperature. Meanwhile, the corresponding error is less than 20.9% in room temperature and 50% in high temperature.

Analysis of Impact of Moisture Content on Rock Thermal Conductivity Coefficient Using TCS Method

The coefficient of thermal conductivity scanner (TCS) was used to test granodiorite, sandstone and rhyolite samples, focuses on the changing rule of the thermal conductivity coefficient of rock under different moisture content. The coefficient of thermal conductivity of the rock increases with water content, and follow a linear relationship. The relative thermal conductivity of three kinds of rock sample is: granodiorite higher than sandstone and higher than rhyolite. The higher the structure density at the same time, the smaller the porosity, the stronger the cementation, the higher the strength, the greater the thermal conductivity of rock mass. This conclusion can be used with geothermal energy development, and has certain reference value.

A Thermal Barrier With Adaptive Heat Transfer Characteristics

A thermal barrier with adaptive heat transfer characteristics for applications in zero gravity environments is considered. The barrier consists of a mixture of fluid with a small volume fraction of arbitrarily oriented, randomly distributed particles of ellipsoidal shape. Heat flux control is obtained by changing the orientation of the particles. Heat flow may be increased up to several hundred times by rotating the particles from being parallel to the walls to being transverse to the walls and by increasing their aspect ratio, volume fraction, and relative thermal conductivity. An increase in the size of the particles results in the appearance of wall effects, which may substantially reduce heat flow as compared to the case of an infinite medium. Very large temperature variation is found to occur near the walls where an apparent “slip” of temperature occurs for barriers whose thickness is large compared to the particle size.