Fibers thermal conductivity values

Polyurethane. Polyurethanes (pu) are predominantly thermosets. The preparation processes for polyurethane foams have several steps (see Urethane polymers) and many variations that lead to products of widely differing properties. Polyurethane foams can have quite low thermal conductivity values, among the lowest of all types of thermal insulation, and have replaced polystyrene and glass fiber as insulation in refrigeration. The sprayed-on foam can be appHed to walls, roofs, tanks, and pipes, and between walls or surfacing materials directly. The slabs can be used as insulation in the usual ways. 

The coefficient of linear thermal expansion, specific heat, thermal diffusivity, thermal conductivity for 1-D and 2-D SiC/RBSN at four temperatures in nitrogen measured parallel and perpendicular to the fibers are summarizedin Tables III and IV. In general, through-the thickness thermal conductivity value at room temperature for SiC/RBSN composites is low when compared with a value 7 W/m-k for the unreinforced RBSN or with a value of 30 W/m-k for the sintered silicon nitrides [13]. Both weak bonding between the SiC... 

Board material The FR-4 versus polyimide board material properties did not have a significant impact on trace temperature, which is determined primarily by the thermal conductivity of the dielectric laminate material construction. Table 16.2 lists measured thermal conductivity values for each of the test boards.The column labeled kz presents values through the thickness of the board and represents the resin thermal conductivity.The values in columns kx and ky are in-plane and the difference is attributed to the influence of the glass fiber. 

Typical thermal conductivity values (all in W/mK) are 0.2 to 0.3 for pol5Tners, 1 to 2 for carbon black, 10 to 20 for polyacrylonitrile (PAN) based carbon fiber, 100 to 800 (depends on the heat treatment temperature) for petrolaim pitch-based carbon fiber, 400 for copper, and 600 for graphite. Electrical resistivity (1/electrical conductivity) values (all in ohm-cm) for various materials are lO to 10 for polymers, 10" for electrically conductive carbon black, 10 for PAN-based carbon fiber, 10" for pitch based carbon fiber, 10 for graphite, and lO" for metals such as aluminum and copper. One proach to inqjroving the conductivity of a polymer is through the addition of conductive filler, such as carbon and metal [1, 2]. Typically for a bipolar plate, the desired thermal and electricM conductivity are 20 W/mK and 50 S/cm (0.02 ohm-cm). 

Since weight is frequently a factor in the applications of composite structures, values for eleetrical and thermal conductivity, and tensile strength and modulus are even more impressive when normalized by the mass of the fiber. 

The thermal conductivity of solids has a wide range of numerical values, depending upon whether the solid is a relatively good conductor of heat, such as metal, or a poor conductor, such as glass-fiber or calcium silicalc. The laUer serves as insulation. 

For certain products, skill is required to estimate a product s performance under steady-state heat-flow conditions, especially those made of RPs (Fig. 7-19). The method and repeatability of the processing technique can have a significant effect. In general, thermal conductivity is low for plastics and the plastic s structure does not alter its value significantly. To increase it the usual approach is to add metallic fillers, glass fibers, or electrically insulating fillers such as alumina. Foaming can be used to decrease thermal conductivity. 

These tests were performed on materials with the same characteristics but with different thicknesses thus, the intrinsic thermal conductivity could be resolved at different temperatures and compression pressures. Through these tests, the thermal conductivity of TGP-H carbon fiber papers was measured and achieved the same value as that reported by the manufacturer. In addition, it was observed that the thermal conductivity of the CFPs decreased from 1.80 + 0.27 W m i K i (af 26°C) to 1.24 + 0.19 W m-i K i (at 73°C). This result was suggested to be due to the presence of carbonized thermosetting resin on the CFPs. The thermal conductivity of fhe resin, which is a thermosetting polymer and acts as a binder, decreases with increasing temperature. For carbon cloth (without any resin), no significant changes in thermal conductivity were noted when the temperature was increased. 

Theoretical values of the effective thermal conductivity of polyester fabrics (6J (estimated by an expression developed for fibers placed in parallel with each other surrounded by a known amount of air and vice versa) agreed well with line heat source measurements of the thermal conductivity of fabrics varying in thickness, construction, and fiber content (7.). These results also indicate that the thermal conductivity of fabrics in directions parallel to the surface is greater than that perpendicular to the surface, especially for filament yarn the thermal conductivity of woven fabrics in directions parallel to the warp yarns, which were arranged more closely, was greater than in directions parallel to the filling yarns (7.) ... 

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