Recommended Thickness of Insulation

Recommended Thickness of Insulation Indoor insulation thickness appears in Table II-2I, and outdoor thickness appears in Table 11-22. These selections were based upon calcium silicate insulation with a suitable aluminum jacket. However, the variation in thickness for fiberglass, cellular glass, and rockwool is minimal. Fiberglass is available for maximum temperatures of 260, 343, and 454°C ( 500, 650, and 850°F). Rock wool, cellular glass, and calcium sihcate are used up to 649°C (I200°F). 

Much mention has been made of this Standard with regard to insulation. It contains definitions, physical characteristics and recommended thicknesses of insulation for a wide range of industrial applications, including ... 

It should be apparent that insulation does not eliminate heat transfer it merely reduces it. The thicker the insulation, the lower the rate of heat transfer but also the higher the cost of insulation. Therefore, there should be an optimum thickness of Insulation that corresponds to a minimum combined cost of insulation and heat lost. The determination of the optimum thickness of insulation is illustrated in Fig. 7-38. Notice that the cost of insulation increases roughly linearly with thickness while the cost of heat loss decreases exponentially. The total cost, which i.s the sum of the insulation cost and the lost heat cost, decreases fir.st, reaches a minimum, and then increases. The thickness corresponding to the minimum total co.st is the optimum thickness of insulation, and this is the recommended thickness of insulation to be installed. 

As an alternative option, the insulation should meet the recommendations of BS 5422 1977. This Standard tabulates thicknesses of insulation too numerous to mention here, according to whether (1) the pipes carry central heating or domestic hot water, (2) the system is heated by gas and oil or solid fuel, (3) the water temperature is 75°C, 100°C or 150°C and (4) the thermal conductivity of the insulant is 0.04, 0.55 or 0.70 W/mK at the appropriate mean temperature. 

BS 5422 (which also gives insulation thickness for protection against freezing) recommend thickness of 32 mm and 38 mm, respectively, for pipes of 48 mm outside diameter or less. It must be emphasized that these thicknesses only give protection for a relatively short time period (i.e. overnight). It is not possible by means of insulation alone to protect permanently static water. 

Before insulation is installed, carbon steel surfaces between 32°F and 200°F (0°C and 93°C) should be prepared and painted in accordance with manufacturer s recommendations. A vapor barrier should be provided over the outer layer of the insulation. Minimum thickness of insulation for fireproofing should be 2 in (5 cm). Moisture contamination to the insulation should be avoided to prevent damage to the insulation as a result of steam pressure caused by a fire. 

For efficient current distribution, steel-reinforced concrete walls should be provided at the wall entrance of pipes and at least 1 m around them and up to the soil surface with at least 2 mm thick electrically insulating layers of plastic or bitumen. This is also recommended if the pipelines are laid in soil parallel to steel-reinforced concrete foundations and the closest spacing is smaller than twice the pipe diameter or smaller than 0.5 m [2]. 

For the uncertainty determination of the geometric surface area, the calculations of combined uncertainty were performed on the basis of the experimental measurements and the analysis of a full set of parameters (up to 10) each of them may contribute to the combined uncertainty of the total geometric area of the surface of the test plate according to the recommendation [7], Experimentally we estimated only seven parameters contributing to uncertainty geometric surface area, length, width, thickness, complete-ness/evenness of insulation, surface roughness and its anisotropy [5],... 

Five Caril grades of expandable PPE/PS beads (diameter 0.3 to 0.5 mm) offer HDT up to 120°C, thus are suitable for the production of microwaveble and steam-cleanable packaging with the wall thickness > 1 mm. The recommended density of molded product is p = 60 kg/m. Other foamable, flame retardant PPE/PS blends, with good acoustic and thermal insulation properties, have been produced in suspension polymerization of a PPE solution in styrene and pentane. Resulting beads had diameter d = 0.5 to 1.0 mm and could... 

BS 4618 recommends preconditioning of the test specimens at not more than 1% relative humidity (RH) for the study of effect of temperature. ASTM D257 covers resistivity measurements for insulating materials. Electrode sizes are not stipulated (round, square and rectangular types are permitted). The gap between guard ring and center electrode is made approximately equal to twice the specimen thickness. The test voltage is usually 500 V applied for 60 s, as in the British test. 

Recommended maximum insulation thickness in combination with thickness of hard refractory is given in reference 51. Saving of heat does not necessarily mean saving money because the fixed charges on the cost of insulation may exceed the cost... 

The furnaee insulation ean be furnace brick or slabs of insulation (e.g. FMTs Ceramaform) of selected thickness, which can be cut to shape with a wood saw and interlocked using lap joints to prevent loss of heat from the furnace interior (Figure 10.11). At the time of fitting, due allowance must be made for the shrinkage factor, which in this case is about 4%. Carbon powder insulation can be used, but is not recommended. 

Pipe insulation [8]. A pipe 15 [m] long and 3 [in.] in diameter carries steam, and the process engineer recommends insulating the pipe to reduce heat loss and, thus, reduce steam condensation. The cost of steam condensation is 1 [MU/kg ]. The insulation has a cost of 0.012 [MU/cm ] and a thermal conductivity k) of 0.04 [W/m K]. Neglecting the thickness of the pipe, determine the thickness of the insulation material that delivers the lowest annual cost. Because the cost of insulation is a fixed cost (once), it should be multiplied by 0.16 to be expressed as an annual cost. Therefore, the total cost to be minimized is... 

Since wind barriers are located at the cold side of the thermal insulation (in cold climates) they should combine a sufficient air and water tightness with a high vapour permeance. Materials which combine these properties and are often recommended as wind barriers are the spunbonded plastic films (also called house-wraps). These films are composed of rolled synthetic filaments (typically polypropylene or polyethylene fibres) that are welded together to form a continuous porous fabric. Measuring procedures and results of vapour transfer properties of spunbonded plastic films are reported in detail by Janssens and Hens [36]. The diffusion thicknesses of the films are a few centimetres and of the same order of magnitude as an air boundary layer. 

Making LSR moulds requires expert know-how. It is recommended that only mould designers and makers who already have experience in this technique are used. In view of the high mould temperatures you need insulating platens with a thickness of 10 mm for the mould. 

The maximum recommended film thickness is 25 p.m. At greater thicknesses, volatiles from the curing reaction, mainly water and some formaldehyde and phenol, can cause defects. These coatings have excellent electrical insulation properties, ie, up to 20 V/p.m, because of low moisture absorption and low conductance. The coatings are hard with low flexibiUty, depending on curing conditions and film thickness. 

More liquid ammonia should be added from time to time to maintain approximately the same level. Liquid ammonia can be handled in ordinary apparatus, and it is not necessary to use a Dewar flask or to cool the reaction flask in a Dry Ice bath, as a thick frost forms on the outside and partially insulates the contents. In making very volatile alkylacetylenes, such as ethyl-acetylene and propylacetylene, it is advisable to cool the apparatus in a Dry Ice bath, to minimize loss by entrainment, and to use a Dry Ice condenser. With the higher alkylacetylenes the use of a Dry Ice condenser, as recommended by llenne and... 

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