PURPOSE OF THERMAL INSULATIONVarious thermal insulation systems taking advantage of different typesof thermal insulation materials on both an organic (such as expanded plastics,wood, wool, cork, straw, technical hemp) and inorganic (such as foamedglass, glass, and mineral fibers) basis are being designed and tested, and newmethods for analyzing the properties of both insulation materials andinsulation systems are being devised. The particular products differ in theirshape, flammability, composition, and structure, which in relation to designers’requirements define the possibilities of their application in engineeringPractice.

The required thickness of insulation for any specific application dependson the characteristics of insulating material as well as the purpose of theequipment. If a process is critical, the most important single considerationmay be reliability. If conservation of heat or power is the deciding factor, thesavings per year as compared to the installed cost is the most importantfactor.In contrast, when insulation is to be used for a temporary function such asholding the heat in while a lining is being heat cured, then the lowestPossible installed cost would be decisive. Thus, because of conflictingRequirements, there can be no multipurpose insulation. Nor is there a“Perfect” insulation for each set of requirements.

A low thermal conductivity is desirable to achieve a maximum resistanceTo heat transfer. Therefore, for any given heat loss, a material of low thermalConductivity will be thinner than an alternative material of high conductivity.This is of particular advantage for process pipes because thinner layersOf insulation reduce the surface area emitting heat and also reduce the outerSurface that requires protection. The main purpose of insulation is to limitThe transfer of energy between the inside and outside of a system.A thermal insulator is a poor conductor of heat and has a low thermalConductivity. Insulation is used in buildings and in manufacturing processesTo prevent heat loss or heat gain. Although its primary purpose is an economicOne, it also provides more accurate control of process temperaturesAnd protection of personnel. It prevents condensation on cold surfaces andThe resulting corrosion. Such materials are porous, containing large numberOf dormant air cells.

Thermal insulation may be applied for one or a combination of theFollowing purposes:• Saving energy by reducing the rate of heat transfer• Maintenance of process temperature• Prevention of freezing, condensation, vaporization, or formation ofUndesirable compounds such as hydrates• Protection of personnel from injury through contact with equipment• Prevention of condensation on surface of equipment conveying fluids atLow temperature• Avoidance of increase in equipment temperature from outside fire• To conserve refrigeration• Offers better process control by maintaining process temperature• Prevention of corrosion by keeping the exposed surface of a refrigeratedSystem above the dew point• Absorption of vibration.

DESIGN CONSIDERATIONS1)Location • Whether indoors, outdoors but protected, outdoors exposed to weather,Enclosed in ducts or trenches below ground level, underground and/orUnderwater

• Difficult or unusual site conditions that will influence the selection orApplication of insulating materials, or both

• Type of material to be insulated, with details of special or unusualMaterials.

2)Dimesnions Of Services• Surface dimensions of flat or large curved areas• External diameters of pipes

• Lengths of each size of pipe

3)Temperature conditions• Normal working temperature for each portion of the plant to beInsulated• Maximum temperature for each hot surface, if higher than the normalWorking temperature• Ambient temperature: where a specified temperature is required on theOuter surface of the insulation.

• Normally, the theoretical heat loss will be based on the manufacturer’sDeclared value of thermal conductivity and, unless otherwise stated, itWill refer to conditions of ambient still air at 20_C.

• Any requirement to prevent condensation on the warm face of anInsulated pipe or vessel containing cold media.

4)Preparation Of Surfaces:Requirements for the preparation of surfaces, including special requirements,E.g., for the removal of works-applied protective paint or lacquer,Or for the application at the site of paint or other protective coating toThe surface to be insulated, should be clearly stated.

5)Type Of Insulation Required6)Type Of Finish RequiredThe finish required could include, for example, hard-setting composition orSelf-setting cement, weatherproofing compound, or sheet metal.

7)Special Service RequirementsThis could include, for example, resistance to compression, resistance to fire,And resistance to abnormal vibration. If there is any special hazard fromContact with chemicals or oils in the plant, attention should be drawn to this.

8)Basis on Which the Thickness of InsulationIs Determined• Specified temperature on outer surface of insulation• Specified heat loss per unit dimension, linear or superficial

9) Information to Be Supplied by the Manufacturersof InsulationThe manufacturer’s declared value of thermal conductivity appropriateTo the temperature of use, plus the corresponding bulk density. TheManufacturer’s declared value should include any necessary commercialTolerances.

Factors for ConsiderationThe main controlling factors that shall be considered at an early design stageAre outlined in the following. Attention should be paid to details at theDesign stage to ensure the effectiveness of the complete system.

1. Temperature2. Mechanical stability3. Resistance to degradation4. Thermal effectiveness5. Type and dimensions of the plant to be insulated6. Compatibility of the components of the system7. Total weight of the system8. Potential hazard to health9. Corrosion hazard10. Fire hazard11. Space for insulating system

Design Criteria

1)Economic ThicknessWhere the sole object of applying insulation to a portion of plant is toAchieve the minimum total cost during a specific period, the appropriateThickness is known as the economic thickness. To some extent the relevantCalculations are unsatisfactory as they relate only to money values rather thanTo the conservation of energy and they require assumptions that are mainlyArbitrary. The principle is to find at what thickness further expenditure on insulationWould not be justified by the additional financial savings on heat to beAnticipated during the period (the “evaluation period”).An increase in the amount of insulation applied will raise the initialInstalled cost, but it will reduce the rate of heat loss through the insulation,

Thus reducing the total cost during the evaluation period.

2)Applications for Which Economic ThicknessesAre Not Appropriate

1. To maintain fluid inside a plant system within specific temperature limits,2. To ensure that a fluid in a pipe has specified physical properties at the point of delivery3. To avoid danger to personnel4. To limit the temperature of portions of hot plant in order to avoid damage from excessive

temperature5. To prevent condensation of moisture on the external surface of the insulation of “cold”

plant, and to maintain the internal temperature of a system above a specified minimum in order to avoid corrosive attack

6. To improve ambient comfort conditions.

3)Thermal EfficiencyThe term has had some popular use for a long time for expressing the effectiveness of some particular piece of insulation in preventing heat loss from some particular surface in givenDesign conditions.

T hermal Efficiency=QWithout insulation−Qwithinsulation

Qwithout insulation×100

4) Effect of Air Spaces It should be noted that an air space is much less effective for thermal insulationPurpose than a space of similar dimensions filled with one of theConvectional insulating materials. This fact is of particular significance atElevated temperatures.The provision of air spaces for thermal insulation purposes is not recommended.But air spaces may be incorporated between insulation andFinish for economic or drainage requirements.

5) Specified Conditions at the Point of DeliveryWhen it is necessary that a fluid emerges from a pipeline or duct system

Under specified physical conditions, the selection of insulating material andThe thickness applied require special consideration that shall take into accountThe rate of mass flow and certain physical properties of the fluid to beConveyed through the system; economic considerations may well become ofSecondary importance.

6) Provision for Differential Thermal Movement• Hot surfaces Due to the difference in expansion coefficients of metals and insulatingMaterials it is necessary to make allowance for the differential movementsBetween the hot surface, the insulant, and the finish. As a guide it isRecommended that such allowances or expansion joints be inserted

• Sliding and bellows expansion joints The insulation shall not interfere with the operation of the expansionJoints. For this reason, the bellows or joint are usually fitted with a metalCage, fastened at one end only, on which the insulation can be secured.

• Cold surfacesInsulating materials for use at subambient temperatures may haveCoefficients of thermal movement that not only vary with differentMaterials, but also differ appreciably from the corresponding movementsOf the pipe or item of equipment to which they are fitted. In some casesThe insulating material will be sufficiently compressible to accommodateThis differential movement but, with long straight lengths at extremeTemperatures or with non-compressible insulation, contraction jointsWill be required.These may take the form of a 10 mm gap in the insulation that isPacked with a flexible insulation.

7) Provision for Preventing Settlement and CrackingOn vertical surfaces provision shall be made for insulation supports to takeThe dead weight of the insulation. These shall project halfway through theInsulation thickness or in the case of multilayer work to a line halfwayThrough the thickness of the outer layer.These supports may take the form of flat bars, angles, or studs as

Appropriate. Preferably, provision should be made for tying back anyReinforcement for the finishing cement.

8) Fire HazardsNot all the thermal insulating materials in common use are nonflammable.Some of them, often used for refrigeration systems, are entirely of organicComposition and thus may constitute a fire hazard, or they may emit smokeAnd toxic fumes. Designers of thermal insulation systems shall thereforeConsider the process conditions and the plant arrangement before decidingWhether or not the proposed thermal insulating material might contribute toThe spread of fire, however initiated, and they shall vary their choice ofMaterial accordingly.

9) Protection Against Surface CondensationCondensation takes place on piping and equipment held at temperaturesBelow the dew point of the ambient air. Although the application of theInsulation can prevent condensation at the surface, it will not necessarilyPrevent the moisture being drawn through the insulation itself, andFrequently the dew point will be reached at some distance inside the layer ofInsulation. It is therefore imperative that a vapor barrier be applied on the warm sideOn the insulation layer. If an insulating material is applied to a cold surface inHumid conditions without a vapor barrier, the insulation can becomeSaturated, its heat-insulating properties impaired, and also, probably, itsMechanical strength. If the cold surface is at a temperature lower than theFreezing point, the moisture will freeze and tend to rupture and break awayThe insulation.The object of the vapor barrier is to prevent ingress of moisture. It mayBe desirable that the thickness of insulation be chosen so that the outsideSurface temperature of the insulation remains above the dew point.

HEAT TRANSFER THROUGH INSULATIONThe heat transfer equations that relate the heat flowThrough the insulation to the insulation thickness and to the thermal conductivityOf insulation materials for flat and cylindrical insulation are presented.The symbols and units are as follows:

Q = heat flow in w/mT1 = temperature of hot surface in _cT2 =temperature of cold surface in _cL = thickness of insulation in meterƛ=conductivity in w/mk• Equation for heat transfer for one thickness of flat insulation:

Q=T1−T 2

Lƛ

Common Thermal Insulation Materials

1. Fiberglass

Does not absorb water.

Fiberglass is the most common insulation used in modern times. Because of how it is made, by effectively weaving fine strands of glass into an insulation material, fiberglass is able to minimize heat transfer. The main downside of fiberglass is the danger of handling it. Since fiberglass is made out of finely woven silicon, glass powder and tiny shards of glass are formed. These can cause damage to the eyes, lungs, and even skin if the proper safety equipment isn’t worn. Nevertheless, when the proper safety equipment is used, fiberglass installation can be performed without incident.Fiberglass is an excellent non-flammable insulation material, with R-values ranging from R-2.9 to R-3.8 per inch. If you are seeking a cheap insulation this is definitely the way to go, though installing it requires safety precautions. Be sure to use eye protection, masks, and gloves when handling this product.

Mineral Wool.

2. Mineral WoolDoes not melt or support combustion.

Mineral wool actually refers to several different types of insulation. First, it may refer to glass wool which is fiberglass manufactured from recycled glass. Second, it may refer to rock wool which is a type of insulation made from basalt. Finally, it may refer to slag wool which is produced from the slag from steel mills. The majority of mineral wool in the United States is actually slag wool.Mineral wool can be purchased in batts or as a loose material. Most mineral wool does not have additives to make it fire resistant, making it poor for use in situation where extreme heat is present. However, it is not combustable. When used in conjunction with other, more fire resistant forms of insulation, mineral wool can definitely be an effective way of insulating large areas. Mineral wool has an R-value ranging from R-2.8 to R-3.5.

Cellulose Insulation Material.

3. Cellulose Contains the highest amount of recycled content.Cellulose insulation is perhaps one of the most eco-friendly forms of insulation. Cellulose is made from recycled cardboard, paper, and other similar materials and comes in loose form. Cellulose has an R-value between R-3.1 and R-3.7. Some recent studies on cellulose have shown that it might be an excellent product for use in minimizing fire damage. Because of the compactness of the material, cellulose contains next to no oxygen within it. Without oxygen within the material, this helps to minimize the amount of damage that a fire can cause.So not only is cellulose perhaps one of the most eco-friendly forms of insulation, but it is also one of the most fire resistant forms of insulation. However, there are certain downsides to this material as well, such as the allergies that some people may have to newspaper dust. Also, finding individuals skilled in using this type of insulation is relatively hard compared to, say, fiberglass. Still, cellulose is a cheap and effective means of insulating.

Polyurethane Insulation.

4. Polyurethane FoamMakes a great sound insulator.While not the most abundant of insulations, polyurethane foams are an excellent form of insulation. Nowadays, polyurethane foams use non-chlorofluorocarbon (CFC) gas for use as a blowing agent. This helps to decrease the amount of damage to the ozone layer. They are relatively light, weighing approximately two pounds per cubic foot (2 lb/ft^3). They have an R-value of approximately R-6.3 per inch of thickness. There are also low density foams that can be sprayed into areas that have no insulation. These types of polyurethane insulation tend to have approximately R-3.6 rating per inch of thickness. Another advantage of this type of insulation is that it is fire resistant.

Polystyrene (Styrofoam).

5. PolystyreneDifficult to use around imperfections, can become costly.Polystyrene is a waterproof thermoplastic foam which is an excellent sound and temperature insulation material. It comes in two types, expanded (EPS) and extruded (XEPS) also known as Styrofoam. The two types differ in performance ratings and cost. The more costly XEPS has a R-value of R-5.5 while EPS is R-4. Polystyrene insulation has a uniquely smooth surface which no other type of insulation possesses.

Typically the foam is created or cut into blocks, ideal for wall insulation. The foam is flammable and needs to be coated in a fireproofing chemical called Hexabromocyclododecane (HBCD). HBCD has been brought under fire recently for health and environmental risks associated with its use.

Other Common Insulation MaterialsAlthough the items listed above are the most common insulation materials, they are not the only ones used. Recently, materials like aerogel (used by NASA for the construction of heat resistant tiles, capable of withstanding heat up to approximately 2000 degrees Fahrenheit with little or no heat transfer), have become affordable and available.  One in particular is Pyrogel XT . Pyrogel is one of the most efficient industrial insulations in the world. Its required thicknesses are 50% – 80% less than other insulation materials. Although a little more expensive than some of the other insulation materials, Pyrogel is being used more and more for specific applications.

Asbestos.

Other insulation materials not mentioned are natural fibers such as hemp, sheep’s wool, cotton, and straw. Polyisocyanurate, similar to polyurethane, is a closed cell thermoset plastic with a high R-value making it a popular choice as an insulator as well. Some health hazardous materials that were used in the past as insulation and are now outlawed, unavailable, or uncommonly used are vermiculite, perlite, and urea-formaldehyde. These materials have reputations for containing formaldehyde or asbestos, which has essentially removed them from the list of commonly used insulation materials. .

There are many forms of insulation available, each with their own set of properties. Only by researching each kind thoroughly can you discover which will be the right kind for your particular needs. As a quick overview:

Aerogel is more expensive, but definitely the best type of insulation.

Fiberglass is cheap, but requires careful handling.

Mineral wool is effective, but not fire resistant.

Cellulose is fire resistant, eco-friendly, and effective, but hard to apply.

Polyurethane is an all around good insulation product, though not particularly eco-friendly.

Polystyrene is a diverse insulation material, but its safety is debated.

AerogelWith energy costs continually on the rise and taking its toll on the world population and the environment, the need for energy conservation has never been greater. It is estimated that 40% of our energy is used controlling the temperature in buildings. Of this, over 30% escapes from the building primarily through the conventionally insulated walls metal or wood studs in a process termed Thermal Bridging.

NASA has been developing Aerogel insulation technology for several years, using it on the space shuttle, space suits, and for many other advanced insulation requirements, including the last Mars mission. This technology has the potential to revolutionize energy conservation. As recently reported on the "Science Channel," Aerogel will be the breakthrough in building energy conserving buildings.

Review of Benefits:

-- Very significant saving in energy costs-- 100% recyclable-- Contains no ozone depleting substances-- Uses >30% recycled content-- Composite material consisting of over 95% air-- Hydrophobic, unaffected by moisture, mold or water-- Easily applied via stick-on-back-- "Class A" fire rated-- Economical-- Virtually no weight means low cost (& low emissions) shipping-- Adds acoustical isolation-- Not affected by age as it does not react with moisture of the atmosphere

Multi layer Insulation