Multi-Layer Insulation (MLI)

Irreplaceable thermal insulation designed to be used mainly for systems operating in the temperature range from -150 to even -269 degrees Celsius. It ensures the highest increase in the efficiency of cryogenic equipment and minimizes the loss of any stored cryogen due to evaporation. The insulation allows both a significant reduction of the external dimensions and total weight of any installation, that must be insulated. The MLI is recommended primarily for stationary and transporting tanks for liquefied gases, cryostats, cryogenic process lines, superconductivity based systems and space industries.

INSULATIONS TYPES

In our offer there are 4 MLI compositions.
ZLK / ZL: Aluminum foil + Fiberglass spacer
ELK / EL: Aluminum Foil + Chemical fiber spacer
EDLK / EDL - Aluminized polyester + Chemical fiber spacer
ZDLK / ZDL: Aluminized polyester + Fiberglass spacer

Designed for temperatures up to -269 ° C

Thickness of single layer:
Aluminum foil 0,0065mm
Spacer 0,07mm

Single layer weight:
Aluminum foil 18,0 g/m2
Spacer 14,0±2,0 g/m2

Characteristic:

  • Non-flammable, flame retardant, dedicated for flammable substances such as oxygen and LNG.
  • Good pomping out conditions
  • It does not contain organic compounds or carbon, which allows it to be used in special research facilities
Multi-layer-insulation-ZLK_ZL

Designed for temperatures: -170°C to -269°C

Thickness of single layer:
Aluminium foil 0,0065mm
Spacer 0,06mm

Single layer weight:
Aluminum foil 18,0 g/m2
Spacer 10,0±2,0 g/m2

    Characteristic:
  • the elastic spacer is used for multiple insulation assembly
  • dimensional stability - the spacer retains its dimensions even when assembled several times
  • high purity - aluminum foil is cleaned of oily layer formed during rolling
Multi-layer-insulation-ELK_EL

Temperature range: -170°C to -269°C

Thickness of single layer:
Double sided aluminized polyester 0,012mm
Spacer 0,06mm

Single layer weight:
Aluminum foil 18,0 g/m2
Spacer 10,0±2,0 g/m2

    Characteristic:
  • Highly flexible and tensile insulation, dedicated to the insulation of complex systems and moving and shaping elements
  • the material used allows for multiple mounting
  • exceptional ease of handling and assembly
  • high purity - no oiling during the production process
Multi-layer-insulation-EDLK_EDL

Temperature range: up to -269°C

Thickness of single layer:
Double-sided aluminized polyester 0,012mm
Spacer 0,07mm

Single layer weight:
Aluminum foil 18,0 g/m2
Spacer 14,0±2,0 g/m2

    Characteristic:
  • the material used allows for multiple mounting
  • high purity - no oiling during the production process
Multi-layer-insulation-ZDLK_ZDL

MLI – What is it?

MLI (Multi-layer insulation) is a type of thermal insulation reducing the radiation heat inleaks from the environment to the cold system. MLI consists of radiation shield layers in the form of aluminum foil or aluminized material. These shields are separated by fibre material spacer. These layers are separated by spacers made of fibrous material in order to separate the radiation screens and to limit the heat transfer by conduction.

The thickness of a single radiation shield layer is approximately 10 μm, while the spacers, depending on the material used are approximately 50-70 μm thick

Why MLI?

MLI is the most effective thermal insulation method. Under laboratory conditions it achieves the thermal conductivity up to 0,03 mW/mK[1]. Thus, multi-layer insulation is currently the most commonly used cryogenic insulation for both research and industrial purposes.

For a tank containing LNG (P=1 bar abs,T=111 K)the heat flux from the environment is about 0.3-0.4 W/m2 for 40 layers of MLI and a vacuum of 10-3 Pa.

The diagramss below show the results of research carried out by the Cracow University of Technology. It compares MLI and perlite insulation at three different pressure levels. It can be observed that MLI achieves the best insulation parameters for all three pressure values.

advantages multi-layer-insulationadvantages multi-layer-insulationadvantages multi-layer-insulation

The advantages of MLI

The thickness of the compared insulations is also worth noting. MLI described in the diagram is only 16 mm thick for 40 layers of insulation. For comparison, the perlite insulation is 100 mm thick. This means that with six times lower thickness, MLI insulation achieves much better insulation properties than perlite.

Larger volume and weight of the perlite insulation is also associated with heavier construction of entire system, resulting in higher production and transportation costs. MLI provides low heat gains and so low losses of cryogenic liquid or cooling power generated at very low temperatures. Thanks to this MLI is called the most economical type of insulation for cryogenic applications.

Zastosowanie superizolacji MLI - NOPZ

Application of the MLI

MLI is used in systems where large temperature difference exist (cryogenics) and also in such installations, where radiation heat transfer takes place (space industry).

 

MLI is the most effective insulation method for[2]:

  • stationary and transport liquefied gases tanks (LNG, LN2, LH2, LO2)
  • cryostats
  • cryogenic pipelines
  • superconducting devices
  • cryo-chambers
  • space equipment

Regardless of the application, specialist knowledge of insulation installation method is required. The number of layers and MLI packing density have a major impact on effectiveness of the insulation.

How to use MLI?

Multi-layer insulation should be used under technical vacuum conditions. For the best possible insulation performance, the insulation should be installed on the inner vessel of the vacuum coat to keep it in contact with a low temperature source.

Frako-Term is able to provide MLI not only in the form of a roll, but also as ready-to-install insulation blankets. MLI blanket is a form of insulation with a geometry fitting the insulated surface. Such form of MLI ensures easier installation and guarantees a durable, effective and aesthetic result.

MLI should be stored in a dry environment, otherwise the spacer may absorb the ambient moisture. Damp insulation loses its properties and can be irreversibly damaged. For the same reason it is essential to wear rubber gloves when handling MLI. Fingerprints left by a bare hand negatively affect the insulating properties of the material. Before applying MLI, the installation should be properly prepared. It must be checked for cleanliness and leak-tightness, and the MLI application process should take place in clean conditions. Frako-Term is able to provide all the necessary information on this matter, as well as conduct training in MLI installation and preparation of the insulated system (e.g. a storage tank) for this process.

BIBLIOGRAPHY:

[1] Lisowski Edward,Lisowski Filip,Influence of vacuum level on insulation thermal performance for LNG cryogenic road tankers, Cracow University of Technology

[2] https://pl.wikipedia.org/wiki/MLI

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