Insulation materials, thermal facings

The walls of a furnace are built of a 150 mm thickness of a refractory of thermal conductivity 1.5 W/m K. The surface temperatures of the inner and outer faces of the refractory are 1400 K and 540 K respectively. If a layer of insulating material 25 mm thick of... 

Answer by Author The thermal conductivity data were obtained with one face of the insulation material in contact with liquid nitrogen at -320 F, and the other face heated electrically to a higher temperature. Depending on the electric power input and the material tested, the temperature differences between hot and cold faces varied from 13 to 463 F. The temperature differences for the various materials can be obtained from the data of Figs. 1 and 2 utilizing the arithmetic-mean temperatures which are plotted, and the cold-face temperature of -320 F. 

Thermal Insulation. Foamed plastics (qv) are used as thermal insulation for aU types of constmction because of their low heat- and moisture-transmission values. Polystyrene is used either as foamed board or expandable beads. The foam may be faced with a stmctural surfacing material, eg, a kraft liner-board, to form a panel for insulating mobile homes. These foams can dupHcate the appearance of wood and be used as trim. Foams can also be used as backing, for example, on aluminum siding, to provide heat and sound insulation. Foamed beads can be incorporated in concrete to reduce its density and provide some thermal insulation. 

Cmtinuous Laminated Board. Laminated board with incombustible facing materials (glass fiber, ceramic, alumina-paper), or kraft paper is also widely used as a thermal-insulating building material. For example, laminated board is used for roof, ceiling, wall, and floor applications and for refrigeration storehouses. For producing continuous... 

This specification applies to faced or unfaced, rigid cellular phenolic thermal insulation in either board or tubular form. Materials covered are used as roof insulation, sheathing or rigid board for non-load bearing, building material applications, and pipe insulation between -40° and 125°C (-40° and 257°F). 

Expanded polystyrene foam (EPS) has different applications, because of its physical form (beads) and properties (higher permeability to water and less effective adhesion to facing materials than polyurethane). The expansion gases, pentane and steam, escape fairly rapidly from the foam, so the thermal conductivity of the foam filled with air is about twice that of the best polyurethane foam—a 50 mm thick slab of foam has a U-value of 0.5-0.6 Wm K . EPS mouldings can be used as shutters (formwork) for pouring concrete in a composite wall. The two EPS layers are connected at intervals to fix the thickness of the concrete. Extruded polystyrene foam (XPS) is used in plank form for insulation imder the concrete floor of houses, and in roofing panels. 

Thermal conductivity (k) n. The basic measure of steady heat-transfer rate within solid materials (and still fluids) by atomic or molecular contact and vibration. It derives from Fourier s law of heat conduction and may be thought of as the rate of heat flow between two opposite faces of a unit cube whose other faces are perfectly insulated when the temperature at the warmer face is 1 K above that of the cooler face. The SI dimensions corresponding to this concept are (J/S)/(m K/m), which reduces to W/m K. Some conversions from other units to SI are given in the Appendix. For plastics and other materials, k increases with rising temperature. Tide DR (ed) (2004) CRC Handbook of chemistry and physics. CRC Press, Boca Raton, EL. Ready RG (1996) Thermodynamics. Pleum Publishing Company, New York. Seanor DA (1982) Electrical conduction in polymers. Academic Press, New York. 

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