What is Thermal Insulation? Definition, Meaning, Materials, Examples


In this article, we will learn what is thermal insulation, its definition, meaning, materials, examples, properties, etc.

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What is Thermal Insulation? Definition, Meaning

Thermal Insulation Basics & Meaning

From childhood, we all know there 2 types of material. Conductors and insulators. The conductor is one that conducts heat and electricity while the insulator being one that doesn’t conduct heat electricity.

Insulation is the focus of this article. We see insulation everywhere. From handles of the pan to coating around electric wires. From rubber gloves to rubber shoes of the technician. But that’s not it.

  • The insulating material has a wide range of applications.
  • From building houses to space tech, from automobiles to refrigerators it is used.
  • Insulation is stressed today in the context of smart buildings.
  • The insulating material can be natural or man-made and they are used as per design specification.
  • So now we know it is not just the ability of a material to conduct heat is important but the ability of a material to not conduct heat is also important.

Before knowing about thermal insulation is becomes very important to know how heat transfer takes place.

Thermal Insulation Definition

Heat transfer will happen as long as there is sufficient temperature between two different bodies. Thermal insulation comes between such bodies, and it reduces contact between them or reduces the range of radiation they go through.

Thermal insulation does two things,

  • it firstly reduces the rate of thermal conduction between two bodies and
  • secondly it absorbs less amount of heat also it tries to reflect heat as much as possible.

Thermal insulation is defined as,

“Thermal insulation is nothing but a process by which we can reduce the amount of heat transfers.”  

How Does Thermal Insulation Work?

Heat gets transferred from higher temperature to lower temperature. Higher is the temperature difference faster is heat transfer rate. There are three basic mathods by which heat mainly gets transferred, these are,

what thermal insulation definition conduction convection radiation
What thermal insulation definition conduction convection radiation
  • conduction,
  • convection, and
  • radiation.

Let’s see the basics of these processes.

Conduction

It is the process in which energy gets passed from molecule to molecule. Heat gets transfer when material molecules/atoms are in contact with each other. They get heated one by one like a domino effect.

The only condition being there must be a temperature difference between them. Thermal conductivity is the rate at which heat gets transferred from that material. Heat transfer will be dependent on the thermal conductivity of that material and temperature difference.

Q = -K ΔT

Where,

  • Q = local heat flux density
  • k = conductivity of material
  • ΔT = temperature difference

Convection

It is the process in which substance heat gets transferred when material/ molecule which is getting heated is moving and gets heated along with movement. It is dependent on temperature difference and contact area.

Q = h A  ΔT

Where,

  • Q = heat transfer rate
  • H = convection heat transfer coefficient
  • A = exposed surface area
  • ΔT = temperature difference

Radiation

In this type of mode of heat transfer, heat gets transmitted in the form of electromagnetic waves like infrared radiation. Hot body emanates these waves.

Such energy gets transmitted from the transparent body. Shiny and white surfaces reflect more light while black bodies absorb more light. Radiant heat is how the earth receives its solar insolation.

Q = σ A (T14-T24)

Where,

  • Q = heat transfer rate
  •  σ = Stefan-Boltzmann constant = 5.67 x 10-8 j/s.m2.k4
  • A = exposed surface area
  • T1 = absolute temperature in kelvin
  • T2 = surface temperature

To understand all modes of heat transfer let’s take this example. Water is boiling over coking gas in utensils. The heat from cooking gas gets transmitted to utensils by radiation. This utensil gets heated by this radiant heat. The heating of utensils takes place by conduction.

Conduction causes utensils to heat up. This heat is then transmitted to water. Water that gets hot turns lighter, and it starts to move at the top while colder water moves down. This way convection current sets in and water gets heated by convection.

As particles/atoms of water are continuously moving hence this is a convection mode of heat transfer while in case of utensils, molecules get heated as their adjacent atom gets heated. This is why that mode is called conduction where atoms are stationary.

Thermal Insulation Terms

Some important concepts are important to understand thermal insulation,

  • Heat energy

One kilocalorie (1000 calories or 1 kcal) is defined as the amount of heat and energy which is needed to raise the temperature of one kg of water by increasing one degree Celsius (°C). Its SI standard is Joule (J). One kcal equals 4.18 kJ.

  • Thermal conductivity

It measures the capacity of material that conducts heat through its mass. Different types of materials have different specific thermal conductivity values. These are used effectively for their insulating and conducting purposes.

It is defined as the amount of heat/energy (in kcal, Btu, or J) conducted in unit time from the unit area having a unit thickness of material which is having a unit temperature difference. Its SI unit is watt/m /°C

  • Thermal conductivity coefficient

It is an amount of heat (in kcal) conducted by an area of one m2 of material within one hour which is having a thickness of 1 m, whose temperature decrease is 1 °C through the body in steady conditions of heat flow. SI unit is W/m2 /k

  • Heat transfer coefficient

It is denoted by U indicates. It is an overall coefficient of heat transmission in case of any section or composite of a material. The SI unit for U is kcal/hr. /m2/°C.

  • Thermal resistivity

It is a reciprocal of thermal conductivity.

  • Thermal resistance

It is denoted by R-value which can be used as resistance that any particular material offers to the way of heat flow. Material with good insulating properties has a high R-value. The R-value is directly proportional to the insulation material’s thickness. 

Thermal Insulation Materials & Examples

Nowadays there are many cheap and common insulation materials that can be bought from the market. All of these insulation materials have their pro and cons. It becomes very important to know what your needs are and selecting material as per demand.

There are various factors such as price, environment-friendly material, long life, R-value, flammability, sound insulation, and water moisture absorption capacity and impact on its life.

What are thermal insulation examples?

  • Fibreglass
  • Mineral Wool
  • Cellulose
  • Polyurethane Foam
  • Aerogel

Let’s see the basic details of the most common thermal insulation materials.

Fibreglass Thermal Insulation Material

Nowadays one of the most common insulating materials is fiberglass. This is because of its structure, as it has efficiently woven fine strands of glass that are embedded in it as insulation material. Due to such composition, this fiberglass can really minimize heat transfer.

Properties

  • This material is non-flammable.
  •  Its R-values lies in range of R-2.9 to R-3.8 per inch.
  • Best material in case cost consideration.  

Limitations

  • Topmost issue associated with fiberglass is risk of handling it. As it consists of fiberglass made of finely woven silicon, tiny shards of glass and glass powder, such composition make it highly susceptible to cause damages to the lungs, eye, and skin. Therefore, it becomes very important to use conventional safety equipment. Always make sure you use eye protection, gloves, and masks whilst doing installation.

Mineral Wool Thermal Insulation Material

Actually, mineral wool in itself has types based on its composition.

  • First, one is a type of insulation material that is produced from basalt which is known as rock wool.
  • The second one being fiberglass which is manufactured from glass which is recycled known as glass wool.
  • The third one is a type that is obtained from a slag (a type of waste) of steel mills called slag wool.

Properties

  • It can be obtained loosely or in form of batts.
  • It is not inflammable.
  • Effective material to insulate large areas.
  • Its R-value is ranges between R-2.8 to R-3.5.

 Limitation

  • There are no additives inside it, so it gives poor result at extreme temperature situation.

Cellulose Thermal Insulation Material

It is one of the most environmentally friendly materials. It is generally produced from recycled paper, cardboard. It is obtained in loose form.

Properties

  • R-value ranges between R-3.1 and R-3.7.
  • It has excellent properties when it faces fire.
  • It is very compact in nature, so it holds very less oxygen in it. Which reduces chances of big fire hazard.
  • It is low cost and effective material.

Limitations  

  • One of the biggest issues is dust allergy which is faced by many people.
  • Skilled labour is needed for installation.

Polyurethane Foam Thermal Insulation Material

Earlier this materials production came into question due to its impact on the environment. But now it is produced in such a way that it uses non-chlorofluorocarbon (CFC) gases which are used as a blowing agent.

This way it reduces harmful effects to the ozone layer.

Properties

  • Its R-value lies around R-6.3 per inch.
  • They are very light in weight, weight half kg per cubic feet.
  • They have fire resistant properties.

Limitations

  • Skilled labour needed for installation.
  • If CFC are used in its production, then it affects health of ozone layer.

Polystyrene Thermal Insulation Material

It is a waterproof thermoplastic material that has excellent thermal insulation properties. It has two types mainly expanded (EPS) and extruded (XEPS) which is also known as Styrofoam. These 2 materials have different costs and different properties.

Properties

  • The expensive one XEPS type which has R-value of R-5.5 but of EPS it is R-4.
  • Excellent thermal and sound insulation properties.
  • Lastly, they provide very smooth surface.
  • It is obtained in form of blocks and hence it is excellent wall proofing material,

Limitations

  • It is inflammable and therefore it has to be coated with anti-inflammable material such as Hexabromocyclododecane (HBCD).

Aerogel Thermal Insulation Material

Aerogel is a synthetic and porous material that is ultra-light in nature. As it is derived from a gel and from that liquid component of the gel has been replaced by gas.

The product obtained is a solid having very low density and low thermal conductivity. It is also known as frozen smoke and solid air, or blue smoke because of its translucent nature. Also, the way it scatters light in the material.

Properties

  • Very good conductive, convective, and radiative insulator.

Limitations

  • It is very costly compared to others.

Other Common Insulating Materials

Nowadays materials such as aerogel too have become affordable and available. NASA had earlier used this same material for the construction of heat-resistant tiles and was able to face and withstand heat up to roughly 2000 degrees Fahrenheit.

One new entry onto this particular item is Pyrogel XT. It is really one of the best efficient technical insulations in the world. A fascinating fact about it is it requires thickness about 50% – 80% less compared to the other insulation materials.

It is expensive when compared with other insulation materials, but it is used only for specific applications.

Other insulation materials which are also used are natural fibers like,

  • hemp,
  • cotton,
  • sheep’s wool, and
  • straw.

Health concerns have raised doubts over many materials and hence they have been removed from use. Some hazardous materials due to health reasons are now banned.

Some of these names were perlite, vermiculite, and urea-formaldehyde. Materials that contain formaldehyde or asbestos have been permanently removed from the list of regularly used insulation materials.

Summarise all Materials We Discussed,

  • Aerogel is expensive but definitely the most suitable type of insulation.
  • Fiberglass is economical but needs careful material handling and installation.
  • Mineral wool is easy to use but it is not fire-resistant.
  • Cellulose has fire-resistant properties, and it is very effective, and eco-friendly but installation of it becomes hard.
  • Polyurethane is also good insulation material but not environment friendly.
  • Polystyrene has different types, and it is diverse insulation material but its safety is argued.

Applications of Thermal Insulation

  • Natural insulation in animal and birds

Animal fur traps gases around them. We can see this polar bear or sheep. As gases when entrapped have poor thermal conductivity.

  • Buildings

Electricity bills keep mounting day by day to maintain ambient temperature. It is important to design smart buildings with insulating material to reduce cooling load as well as to keep them warm on cooler days. Energy consumption needs can be reduced.

Also, houses build in colder regions use insulation to preserve heat. This is done by building hollow walls and inside such walls, there is an insulating material.

  • Mechanical processes and systems

Commercial and industrial layouts need to maintain specific process variables. For this material is needed. Steam power plants to nuclear power plants everywhere we can see their use.

  • Refrigeration

Refrigeration lines have to be insulated from the atmosphere to increase cop.

  • Space crafts and installations

Solar insolation has an impact on the working of the equipment. So, satellites too have been provided coverings. In case of rocket launchers and spacecraft, a very high thermal resistive material is used as when it enters earth orbit it faces extremely high heat. Columbia spacecraft accident happened due to failure in this heat-insulating shield.

  • Automobiles and aeroplanes

Internal combustion engine produces a lot of heat, and it can’t reach the cabin. So various packings are given. In case of an airplane, it has to be light as well as good in insulation but it also needs to have good strength.

  • Server rooms

The specific temperature has to be maintained so as to keep the server room cool. To avoid increasing heat load such rooms are provided with packing.

  • Cold storage

To reduce heat load walls are insulated from the outside environment.

  • Air conditioning

Big halls are insulated with such material to reduce heat load.

Calculations in Thermal Insulation

Q = U ΔT

Where,

  • Q = local flux density
  •  ΔT = temperature difference
  •  U = Overall heat transfer coefficient which is obtained by newton law cooling

For bare wall

U =1/[1/H1 + L1/K1 + 1H2]

Where,

  • U = Overall heat transfer coefficient which is obtained by newton law cooling
  • k = conductivity of the material
  • h = convective heat transfer coefficient

For composite wall

U = 1/[1/H1 + L1/K1 + L2/K2 + 1H2]

Where,

  • U = Overall heat transfer coefficient which is obtained by newton law cooling
  • k = conductivity of the material
  • h = convective heat transfer coefficient

Conclusion

Hence, we have learned the basics of thermal insulation, definition, meanig, materials, examples, properties, etc.

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