Insulation - Thermal

4 THERMAL INSULATIVE AND FIRE RESISTANCE PROPERTIES OF SOREL CEMENT 

The ASTM-tested (American Society for Testing and Materials) foamed MOC cement is used as thermal insulation in the cavity of house walls 

Thermal insulation is the second largest application of cellular polymers, and the largest application for the rigid materials, because of their thermal conductivity, ease of application, cost, moisture absorption, and water vapor transmission (or permeance). 

The thermal conductivities of various commercial insulating materials are given in Table 10.7. Plastic foams containing a captive blowing agent have much lower thermal conductivities than other insulating materials. 

Thermal Insulation, properly applied, assures effective operation of process equipment and conserves valuable heat. There is always a wide variety of insulating materials for a given situation and careful consideration must be given to each type so that an intelligent decision may be made. Thermal insulation should be the simplest, most generally accepted, cost-effective method of saving energy immediately available to a plant owner. 

Energy loss due to the lack of insulation and improperly installed or maintained insulation may easily be visualized by monitoring steam usage before and after a rainstorm. During a recent 15 minute sudden rainstorm at a typical chemical plant, the steam load increased from 638,000 Ib/hr to 677,000 Ib/hr within a 15 minute period. After the rain stops, the steam load does not immediately decrease because all water that enters the insulation must be vaporized and driven out. We can easily justify the insulation of all flanges, valves, manways, etc. 

Bare flanges, valves, manways, etc., and deteriorated insulation may be visually detected by an inspection of the system. However a much more subtle source of energy loss, one that is much harder to detect, are those lines and equipment that appear to be adequately insulated, but with a less than appropriate thickness of insulation. 

Energy conservation is the most common use for thermal insulation. In most cases, it is not too difficult to recognize when and where to use insulation. Insulation is commonly used to accomplish the following  

The amount of insulation that should be used when insulating for energy conservation must be based on economic factors. Many factors affect the cost of energy  

The material must not be used in the presence of air above 200° C. These products are particularly useful for vacuum furnace insulation [70] and can be used in vacuum or in the presence of an inert gas up to 2750°C. 

Carbon felts can be used as an insulation material, made from scrap material which is relatively cheap, where further carbonization continues in use. Under these conditions, the possibility of shrinkage and outgassing products has to be accommodated. Superior, but expensive, carbon and graphite felts can be made by carbonizing long small diameter organic filaments, which are very stable and have low shrinkage. 

In aircraft, fire protection can be offered to the cabin by using a layer of insulating batting between the aircraft skin and the cabin interior panels. The fuselage insulation is placed in bags to resist moisture penetration and the bags are fitted between the outer skin and interior trim panels. 

Dow Chemical Co. developed a high-performance product based on PAN carbon fiber type materials using non-conducting carbonaceous curly fibers. The technology produced permanently bulked carbonaceous fibers with 65-85% carbon and bulked carbon fibers with over 85% carbon, which could be used as the basis for lightweight (3.2-16 kgm ) fire retardant insulation and for fire blocking panels. 

Source Reprinted from Calcarb Ltd. technical literature and Matthews FL, Rawlings RD, Composite Materials, CRC Press, 152, 2002. 

Hollow nylon filaments that contain ceramics, to store heat, have been developed in Japan by Unitika. The company has been producing Microart 

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One may now consider how changes can be made in a system across an adiabatic wall. The first law of thermodynamics can now be stated as another generalization of experimental observation, but in an unfamiliar form the M/ork required to transform an adiabatic (thermally insulated) system, from a completely specified initial state to a completely specifiedfinal state is independent of the source of the work (mechanical, electrical, etc.) and independent of the nature of the adiabatic path. This is exactly what Joule observed the same amount of work, mechanical or electrical, was always required to bring an adiabatically enclosed volume of water from one temperature 0 to another 02. 

Thermal Insulation. In addition to their low thermal conductivity, as discussed in the section above, siUca aerogels can be prepared to be highly transparent in the visible spectmm region. Thus, they are promising materials as superinsulating window-spacer. To take further advantage of its... 

Polyurethane. SmaU quantities of polyurethane film are produced as a tough mbber-like film. Polyurethane is more commonly used to produce foamed sheet, both flexible and rigid. The flexible foam is used as cushioning in furniture and bedding the rigid foam is widely used for architectural insulation because of its outstanding thermal insulation efficiency (see Urethane POLYMERS). 

MoistureResista.nce, Plastic foams are advantageous compared to other thermal insulations in several appHcations where they are exposed to moisture pickup, particularly when subjected to a combination of thermal and moisture gradients. In some cases the foams are exposed to freeze—thaw cycles as well. The behavior of plastic foams has been studied under laboratory conditions simulating these use conditions as well as under the actual use conditions. 

Other. Because a foam consists of many small, trapped gas bubbles, it can be very effective as a thermal insulator. Usually soHd foams are used for insulation purposes, but there are some instances where Hquid foams also find uses for insulation (see Eoamed plastics Insulation, thermal). Eor example, it is possible to apply and remove the insulation simply by forming or coUapsing the foam, providing additional control of the insulation process. Another novel use that is being explored is the potential of absorbing much of the pressure produced by an explosion. The energy in the shock wave is first partially absorbed by breaking the bubbles into very small droplets, and then further absorbed as the droplets are evaporated (53). 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

Energy Use and Conservation. A variety of materials are needed for high performance thermal insulation, particularly as components of nuclear reactors. Replacements for asbestos fibers are needed for components such as reactor core flooring, plumbing, and packaging. The fibers must be very resistant to high temperatures with outstanding dimensional stabiHty and resistance to compression. 

With a batch process, such as hot isostatic compaction (HIP), heat exchange as used in a continuous reactor is not possible, and it is common practice to provide a furnace within the pressure vessel which is thermally insulated to ensure that the temperature of the vessel does not rise above 300°C. Most HIP operations involve gas pressures in the range 70—200 MPa (10—29,000 psi) and temperatures of 1250—2000°C, occasionally 2250°C (74). The pressure vessel may have a bore diameter from 27 to 1524 mm (75) and is nearly always provided with threaded closures sealed with O-rings made of elastomer provided the temperature is low enough. 

Eig. 1. Thermal conductivity components vs density for a typical thermal insulation material at 300 K A, total conductivity B, air conduction C, radiation ... 

Although thermal performance is a principal property of thermal insulation (13—15), suitabiHty for temperature and environmental conditions compressive, flexure, shear, and tensile strengths resistance to moisture absorption dimensional stabiHty shock and vibration resistance chemical, environmental, and erosion resistance space limitations fire resistance health effects availabiHty and ease of appHcation and economics are also considerations. 

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... 

Table 1. Typical Properties of Cellular Plastic Materials Used as Thermal Insulation...

Flame Resistance. Traditionally, small-scale laboratory flammabiUty tests have been used to initially characterize foams (38). However, these do not reflect the performance of such materials in bulk form. Fire characteristics of thermal insulations for building appHcations are generally reported in the form of quaHtative or semiquantitative results from ASTM E84 or similar tunnel tests (39). Similar larger scale tests are used for aircraft and marine appHcations. 

Thermal Insulation Systems—A Survey, NASA Report SP-5027, NASA, Washington, D.C., 1967. 

An Assessment of Thermal Insulation Materials and Systemsfor Building Applications, DOE Report, BNE-S0862 UC-9Sd, U.S. Dept, of Energy, Washington, D.C., 1978 R. P. Tye and D. L. McElroy, eds., ASTM STP 718, Thermal Insulation Peformance, American Society for Testing and Materials, Philadelphia, Pa., 1980, pp. 9—26. 

F. Sherwood-Rowland, Chlorofluorocarbons and Depletion of Stratospheric O ne, Improved Thermal Insulation—Problems and Perspectives, D. A. Brandreth, ed., Technomic Puhlishing Co., Inc., Lancaster, Pa., 1991, pp. 5—25. 

W. Tobiasson, A. Greatorex, and D. VanPelt, "Wetting of Styrene and Urethane Roof Insulations ia the Laboratory and on a Protected Roof Membrane," F. J. PoweU and S. L. Matthew, eds., ia Thermal Insulation Materials and Systems STP922, ASTM, Philadelphia, Pa., 1987. 

The main use of lead metaborate is in glazes on pottery, porcelain, and chinaware, as weU as in enamels for cast iron. Other appHcations include as radiation-shielding plastics, as a gelatinous thermal insulator containing asbestos fibers for neutron shielding, and as an additive to improve the properties of semiconducting materials used in thermistors (137). 

Some inorganic nonaqueous solvents can be used in systems operable at near room temperature, eg, thionyl chloride others, however, require special handling, eg, Hquid ammonia, which must be used below its boiling point of —33° C in a thermally insulated container and in an inert atmosphere. 

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