Topic of Discussion: Thermal insulation
Thermal insulation definition
When two objects are in thermal contact with each other or under the influence of radiation, the process of depletion of heat transfer among the entities is known as thermal insulation. It is quite the opposite of what thermal conductivity can be defined as. Essentially, an object with very low thermal conductivity can be regarded as a well-insulated material.
Thermal insulator
While thermal insulation is the process of depletion of heat transfer, thermal insulators are materials that employ the insulation process. It prevents heat energy from being transferred from one object to another. This can be viewed in detail from a thermodynamics perspective while comprehending heat energy principles and more.
Heat Insulation
It is a form of energy that depends upon another factor called temperature. The transfer of energy in the form of heat from one body to another result in a temperature difference. Heat usually flows from a hotter to a colder body. It plays a significant role in the principles of thermodynamics. If a body is cold, it means that heat is removed and not coldness added, which brings about a fun fact about this form of energy.
Heat can be transferred by three different means.
- Conduction
- Convention
- Radiation
Conduction is the energy transfer process between two objects where the medium of exchange is through direct contact. At the same time, convection is the transfer of energy through the motion of matter, using air as a medium. Radiation is the transfer process that happens without any medium but with the aid of electromagnetic waves.
The three equations concerning the three forms of heat transfer are as follows,
Conduction: Q = [k · A · (Thot – Tcold)]/d
Convection: Q = hc · A · (Ts – Tf)
Radiation: P = e · σ · A · (Tr4 – Tc4) (Using Stefan-Boltzmann law)
Examples of the modes of transfer that can be found in our everyday life under conduction can be as simple as accelerated vibrating molecules in the hand when in contact with a hot coffee mug. This means that the hand has heated up where the transfer of energy took place through direct contact.
A typical example of convection would be refrigeration, where the food items kept in the fridge would essentially get cold through convection of air and other coolants.
Radiation is the mode of transfer through a void, such as the heat from the sun that reaches the earth.
Why thermal insulation? Its purposes and requirements
The objective of thermal insulation is to moderate the temperature in something as small as an individual house to as complex as a nuclear reactor. Thermal insulation is to fortify the constructional elements against damage caused by moisture or thermal impact on the component. The wear on the object or the part can be decreased during winter with thermal insulation, which serves the purpose of energy conservation. At the same time, during the summer, overheating is significantly depleted.
Advantages of thermal insulation
Thermal insulation creates an optimum environment that keeps the surroundings warm in the winter and chill during the summer, enabling a comfortable living and operating. Due to the demand for a comfortable lifestyle environment, thermal insulation greatly enhances energy conservation and maintenance costs. It also helps prevent the deposition of moisture on the interior walls of a room or a container that can be caused due to the effect of temperature and humidity.
Thermal insulation materials
- Fiberglass
- Polyurethane foam
- Cellulose
- Polystyrene
- Mineral wool
Thermal insulation Fiberglass:
it is the most common and frequently used for thermal insulation method in modern-day houses. It is derived from finely woven silicon, recycled glass fragments, and sand particles containing glass powder.
Fiberglass or glass wool is generally used as an acoustic insulation material, an indoor material applied under pitched roofs or wooden floors. Since fiberglass loses their value insulation when in contact with damp or moisture, they are mostly seen inside homes and not outside.
Insulation values of the material are given by,
- Density = 25 kg/m³
- Heat storage capacity = 800 J/kgK
- Fire class => A2, S1, d0 (extinguish by self and low flame ability)
- λ= 0.032 to 0.040 W/mL-K
- Diffusion resistance: 1
Cellulose:
This type of thermal insulation method is considered one of the most eco-friendly processes in the modern-day. Cellulose comprises 70-80% recycled denim, paper or cardboard in the form of loose foam heavily treated (15% volume) with (NH₄)₂SO₄, boric acid or borax. It is considered the best form of thermal insulation against fire resistance solutions that are essentially used to moderate heat loss and gain noise transmission.
Properties of cellulose,
- Thermal conductivity = 40 mW/m·K
- R value = R-2.6 to R-3.8 per 100mm
- Density = 57 kg/m3
Mineral wool:
The glass wool or mineral wool is used widely for its functional properties, easy purchase, and simple handling. Mineral wool comprises spun yarn manufactured from melted or recycled glass or stone (rock wool). Rock wool is made from basalt, where the threads are combined in a unique way for a wooly structure to be formed for insulation. Hereafter the wool is compressed into mineral batts or boards that can be purchased off the market for insulation purposes.
Mineral wool is generally used to Insulate cavity walls, exterior walls, partition walls, and stored floors. They are also extensively applied in industrial applications like machines, air conditioners, etc.
Properties:
- λ= 0.03 W/mK to 0.04 W/mK
- Density= 30-200 kg/m³
- R= 0.035 W/mK
Image credit: Achim Hering, Rockwool 4lbs per ft3 fibrex5, CC BY 3.0
Polystyrene:
This is also commonly known as styrofoam, is a waterproof thermoplastic foam that insulates temperature and sound very effectively. They come in two types: EPS (expanded) and XEPS(extruded), differing in cost and performance. They possess a very smooth surface of insulation not found in any other types, usually created into cut blocks, making it very ideal for insulation. The foam is sometimes flammable and requires a coating of Hexabromocyclododecane (HBCD), a fireproofing chemical.
Its significant advantages are that it possesses magnificent cushioning properties, lightweight in nature, low thermal conductivity, and absorbs very little moisture, mostly 98% air and 100% recyclable.
Properties:
- R= 4-5.5
- Density= 0.05 g/cm3
- λ= 0.033 W/(m·K)
- Refractive index= 1.6
Image credit:Phyrexian, Polistirolo, CC BY-SA 3.0
Polyurethane foam:
It is the most abundant and exceptional form of thermal insulation utilizing non-chlorofluorocarbon (CFC) as a blowing agent to decrease the ozone layer’s damage. They are low-density foams that consist of low conductivity gas in their shells that can be sprayed onto the insulated areas.
They are lightweight in relativity and weigh almost 2lb/ft3. They are also fire-resistant and used on surfaces like brick blocks, concrete, etc., by direct fixation. It is also used in the case of unfinished masonry by cutting the foam into the desired shape and size. The foam is then covered with constructive adhesive, pressing it against the masonry surface and seal the joints between the sheets with the expanding foam.
Properties:
- λ= 0.022 W/mK to 0.028 W/mK
- Density= 30 kg/m3 to 100 kg/m3
- R= 6.3/ inch of thickness
Types of thermal Insulation
Blanket: Batt and Roll Insulation
The most well-known and broadly accessible sort of insulation is Blanket insulation, which comes in Batts or Rolls. It comprises flexible fiber, fiberglass’s. Batts and Rolls are also finished from mineral-wool, plastic, and natural fiber, such as cotton and sheep’s wool. The Blanket insulation is most likely to be used in unfinished walls, floors, and ceilings and these insulation could easily be fitted in-between studs, joists, and beams. This insulation type is highly used since it is suited for standard stud and joist spacing that is comparatively free from different obstruction. This type is also relatively expensive in comparison to the others.
Concrete Block thermal Insulation
Concrete block insulation is incorporated in several ways, like adding foam bead or air into the concrete mixture to get the desired R-values. Concrete Block insulation is widely used for unfinished walls, including foundation walls, and is also used prominently for construction and renovation. Installation requires specialized skills like stacking, insulating concrete blocks without using mortar, and surface bonding. The cores are insulated to achieve R’s desired values, which helps us moderate temperatures as well.
Insulating Concrete foam
The material used in the making of this is foam boards or foam blocks. This type of insulation is highly used to complete unfinished walls, as well as foundation walls for new construction. They are incorporated as a part of the building assembly also. This category of insulation is highly in use for construction. Since they are built into the home’s walls, it increases the thermal resistance.
Rigid fibrous or fiber insulation
Fiberglass and mineral wool are used to assimilate fiber insulation. Rigid fibrous insulation is highly used in regions that withstand high temperatures and often used for ducts in unconditioned spaces. Fiber insulation is established by HVAC contractors, usually manufactures the insulation and install them onto vents. These are mainly utilized for the reason of its ability to withstand high temp.
Structural insulated panels (SIPs)
This is primarily foam-board or liquid-foam insulation core and straw-core insulation. They are incorporated in unfinished walls, ceilings, floors, and the initial construction of roofs. They are implemented by construction workers who fit SIPs together to form walls and roofs. The perks of using this type of insulation provide consistent and higher insulation compared to traditional insulation. SIPs take a limited amount of time to implement.
Thermal insulation in the nuclear sector
The generic idea of a nuclear power plant is that it is utilized to generate electricity with nuclear fission.
Nuclear reactor cores serve a particular purpose in energy-releasing enormous amounts of heat and work output. The containment of the nuclear reactor in an container is a large space incorporating the nuclear steam supply system (NSSS).
The NSSS has a reactor, valves, pipe, pumps, and other various components and equipment. The NSSS produces a very substantial net positive heat load. Insulation on hot pipe and equipment inside the reactor has one objective: to control containment cooling loads. Containment cooling is performed to remove that heat linked directly to a water body (river, lakes, etc.) or vapor compression cooling such as air conditioning. The nuclear plants’ technical specifications will be alarmed if heat source release heat more than the cooling rate in standard.
Thermal properties of insulation
There are particular primary considerations to be chosen during the selection process of insulation. These properties vary with the material selected, ranging from wool to nuclear reactor thermal insulation. The difference in the insulation types’ thermal properties makes a difference in the amount of efficiency, performance, and sustainability.
The various properties to be considered are:
Emissivity (E):
A material written as ε is defined as the ratio of energy radiated by the material to the energy emitted by a black body at a similar temperature. In layman’s terms, it is useful in emitting energy as thermal radiation such as infrared energy.
Thermal conductance (C):
It can be termed by the unit temperature difference between two bodies that infer the time rate of a steady-state heat flow through a unit area of the given material.
Temperature limits:
upper and lower levels of temperature should be satisfied by the materials chosen for insulation.
Thermal resistance (R-Value): the temperature difference between two surfaces induces a unit heat flow rate through the objects’ unit area (K.m2/W).
Thermal transmittance (U):
through an assembly, heat flow’s overall conductance is coined as thermal transmittance.
Thermal conductivity (k-value):
Where, L= thickness of the material, (m)
T= temperature, (K)
q = heat flow rate, (W/m2)
To learn more about thermodynamics click here!
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