Thermal Insulation Materials

Common Types of Insulation Materials

Thermal insulation materials are specifically designed to reduce the heat flow by limiting heat conduction, convection and radiation. During development and quality control, the extent to which thermal insulation materials fulfill their performance expectations is continuously scrutinized. NETZSCH offers a broad range of instruments for the characterization of thermal conductivity and other properties of insulating materials.

Thermal insulation materials are specifically designed to reduce the heat flow by limiting heat conduction, convection, radiation or all three while performing one or more of the following function:

  • Conserving energy by reducing heat loss or gain
  • Controlling surface temperatures for personnel protection and comfort
  • Facilitating vapor flow and water condensation of a process
  • Increasing operating efficiency of heating/ventilating/cooling, plumbing, steam, process and power systems found in commercial andindustrial installations
  • Assisting mechanical systems in meeting standard criteria in food and cosmetic plants

 

There are three general material types into which thermal insulation materials can be categorized.

Fibrous Insulations

Fibrous insulations are composed of small diameter fibers which finely divide the air space. The fibers may be perpendicular or parallel to the surface being insulated, and they may or may not be bonded together. Silica, glass, rock wool, slag wool and alumina silica fibers are used. The most widely used insulations of this type are glass fiber and mineral wool.

Cellular Insulations

Cellular insulations contain small individual cells separated from each other. The cellular material may be glass or foamed plastic such as polystyrene (closed cell), polyurethane, polyisocyanurate, polyolefin, or elastomer.

Granular Insulations

Granular insulations have small nodules which contain voids or hollows. These are not considered true cellular materials since gas can be transferred between the individual spaces. This type may be produced as a loose or pourable material, or combined with a binder and fibers to make a rigid insulation. Examples of these insulations are calcium silicate, expanded vermiculite, perlite, cellulose, diatomaceous earth and expanded polystyrene.


Recommended literature:

Recommended literature:

Detailed Insight Into the World of Thermal Analysis

Detailed Insight Into the World of Thermal Analysis

To analyze insulations with respect to their heat transfer behavior, a heat flow meter (HFM) or guarded hot plate (GHP) is normally used. These standardized measurement methods directly yield the thermal conductivity of insulation materials or the thermal resistance of multi-layer systems.

The thermal conductivity of refractory materials is determined on large samples with hot wire systems (TCT).

Using other thermoanalytical measurement techniques, the thermal stability or composition of insulating materials can be investigated. The curing behavior of organic binders used in insulation materials can also be characterized by means of DEA (Dielectric Analysis).

Main Modes of Heat Transfer

Heat transfer is the transition of thermal energy, or simply heat, from a hotter object to a cooler object. There are three main modes of heat transfer:

Convection

Convection is usually the dominant form of heat transfer in liquids and gases. Convection comprises the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid/gas together with heat transfer by conduction.

Radiation

Radiation is the only form of heat transfer that can occur in the absence of any form of medium (i.e., in a vacuum). Thermal radiation is based on the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface.

Conduction

Conduction is the most significant means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms. The free movement of electrons also contributes to conductive heat transfer. To quantify the ease with which a particular medium conducts, the thermal conductivity, also known as the conduction coefficient,λ, has been employed. The thermal conductivity λ is defined as the quantity of heat, Q, transmitted in time (t) through a thickness (x), in a direction normal to a surface of area (A), due to a temperature difference (∆T).A quantitative expression relating the rate of heat transfer, the temperature gradient and the nature of the conducting medium is attributed to Fourier (1822; Fourier’s Law, 1-dim.).

During development and quality control, the extent to which thermal insulation materials fulfill their performance expectations is continuously scrutinized. Some of the questions which arise include:

  • How is a particular insulation material performing? 
  • How can I insulate cryo tanks in the best possible way? 
  • What is the optimum insulation for furnaces operating under different temperature, gas or pressure conditions? 
  • What is the heating/cooling load of a building? 
  • How does this change with the weather, and how can I improve it?
  • How can I improve the heat transfer from an electronic component? 
  • How do I design a heat exchanger system to achieve the required efficiency, and what are the best materials to use?

To answer questions like these, material properties such as thermal diffusivity and thermal conductivity must be known. To analyze insulations with respect to their heat transfer behavior, a heat flow meter (HFM) or guarded hot plate (GHP) is usually used. For highly conductive ceramics, metals or diamond composites, the Laser Flash method (LFA) is often employed. The thermal conductivity of refractory materials is determined on large samples with hot wire systems.

In addition, further thermophysical properties such as specific heat (cp) can be analyzed with high-temperature differential scanning calorimeters (DSC), while density and length changes can be investigated with dilatometers.

Some Application Examples

Some Application Examples

DEA Measurement of Rock Mineral Wool

For the DEA measurement, a mineral wool infiltrated with the uncured resin was analyzed. Presented is the logarithm of the ion viscosity and loss factor of the polyester resin on the wool versus temperature. During heating, the ion viscosity decreases above approx. 70°C and the loss factor increases in the same temperature range. This is due to the softening of the dried resin. Above 153°C, the ion viscosity increases up to approx. 237°C. This indicates a decrease in the ion mobility and therefore represents the curing process of the resin. The curing process is finished at this temperature. (measurement with DEA 288 Epsilon)

Curing process of mineral wool infiltrated with an uncured resinCuring process of mineral wool infiltrated with an uncured resin

Temperature-Modulated DSC Measurement of a Mineral Fiber Insulation

Temperature-modulated DSC (TM-DSC) is a tool generally employed for low-temperature applications on polymers. The STA 449 F1 Jupiter® and DSC 404F1 Pegasus® are the first instruments capable of doing temperature modulation at high temperatures. Presented here are measurement results for mineral fiber insulation. In the total DSC curve, relaxation, oxidation and glass transition are overlapped. The glass transition can only be analyzed accurately in the reversing part of the DSC curve.

Temperature-Modulated DSC measurement of a mineral fiber insulationTemperature-Modulated DSC measurement of a mineral fiber insulation

Thermal Conductivity of Aerogel

As part of a Round Robin Test, a nanoporous aerogel board was measured with various NETZSCH heat flow meters as well as with the NETZSCH guarded hot plate system (absolute measurement technique). The results obtained by the three different instruments are in good agreement in the overlapping temperature range.

Thermal Conductivity of AerogelThermal Conductivity of Aerogel