Fabrics thermal insulation

A low (<0.4 W / (m-K)) thermal conductivity polymer, fabricated iato alow density foam consisting of a multitude of tiny closed ceUs, provides good thermal performance. CeUular plastic thermal insulation can be used in the 4—350 K temperature range. CeUular plastic materials have been developed in... 

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

Thickness. Because two fabrics that have identical weight per unit area values may have widely varying bulks, the specification of thickness is essential for properly characterizing a fabric. Fabric thickness has been shown to be direcdy proportional to thermal insulation, or warmth (121). Fabric warmth is the result of the entrapment of air between fibers and yams. A thicker fabric in general allows an increased amount of entrapped air and thus is warmer. 

Thermal conductivity of a fabric is related to its air permeabiUty, or movement of air between the interstices of the yam and fabric. For fabrics of a given thickness, the one that has greater air permeabiUty allows greater heat dissipation by convection. Thus thermal insulation falls as air velocity rises. 

From the beginning of this century, the demand for asbestos fibers grew in a spectacular fashion for numerous applications, in particular for thermal insulation in steam engines and technologies (4). Moreover, the development of the Hatschek machine in 1900 for the continuous fabrication of sheets from an asbestos—cement composite opened an important field of industrial application for asbestos fibers. 

It is often a requirement for industrial fabrications that once complete they are dried. The reason for this are as diverse as the applications it is used for but typical applications for drying include electrieal transformers, gas and liquid pipelines, thermal insulation and cryogenic applications. Drying through the application of vacuum allied with energy input is often the only solution. Drying with vacuum is... 

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

The insulation properties of many fire-rated ASTs marketed today are typically provided by concrete i.e., tlie primary steel tank is surrounded by concrete. Due to the weight of concrete, this design is normally limited to small tanks. Another popular AST technology meeting all applicable code requirements for insulated tanks and fabricated to UL 2085 is a tank that utilizes a lightweight monolithic thermal insulation in between two walls of steel to minimize heat transfer from the outer tank to the inner tank and to make tank handling more palatable. 

Their reviews suggest that standard bench-scale tests for separate determination of flame resistance, thermal insulation/protection, and heat resistance may be undertaken on a single fabric or a composite form in a manner that reflects a real application or product requirement. 

In Sections 24.3 and 24.5 the flammability and fire resistance of individual fiber/fabric type are discussed. However, as also discussed before, the fire resistance of a fabric not only depends upon the nature of components and the FR treatments applied, but also on fabric area density, construction, air permeability, and moisture content. Nonwovens, for example, will have superior properties to woven or knitted structure, even if all other variables are kept the same.93 The air entrapped within the interstices of any fabric structure and between layers of fabrics within a garment assembly provides the real thermal insulation. For effective thermal and fire resistance in a fabric structure, these insulating air domains need to be maintained.22 In general, for protective clothing and fire-block materials, for best performance multilayered fabric structures are employed. The assembly structures can be engineered to maximize their performance. It is beyond the scope of this chapter to go into details of these composite structures hence the reader is referred to the literature on specified applications and products available. 

The greater tolerance for radiation damage in inorganic materials makes them attractive for fusion magnets, but their brittleness and the difficulty of fabrication techniques presents a serious limitation to their practical uses. Therefore, the application of organic materials has been considered for electrical insulators, thermal insulators and a part of structural supports in the magnets [4 9]. 

Perhaps the most innovative and interesting product with improved thermal insulation properties is fabric made of hollow fibers with a gas and solvent inside the fibers. A decrease in temperature converts the solvent into a solid phase, thus liberating a gas and increasing the thermal resistance of the fabric (ill). Although the solvents are exotic and the durability of such fabrics has not been assessed, further studies employing phase-change materials offer great potential. 

The Fibrous Minerals. The fibrous minerals contain very long silicate ions in the form of tetrahedra condensed into a chain, as shown in Figure 31-6. These crystals can be cleaved readily in directions parallel to the silicate chains, but not in the directions which cut the chains. Accordingly crystals of these minerals show the extraordinary property of being easily unravelled into fibers. The principal minerals of this sort, tremolite, C.a.jMg..Si 022(0H)2, and chrysotile, Mg6Si40u(0H)p/H20, are called asbestos. Deposits of these minerals are found, especially in South Africa, in layers several inches thick. These minerals are shredded into fibers, which are then spun or felted into asbestos yarn, fabric, and board for use for thermal insulation and as si heat-resistant structural material. 

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