In 1910, physicist Marian von Smoluchowski had demonstrated that gas molecules near the walls of vessels lose their normal mobility and thus the temperature also fluctuates. Thus, more than 100 years ago, he was able to lay the foundation for supported vacuum insulation.
GVI® systems consist of a double-walled, vacuum-tight shell structure that is evacuated. But they still differ significantly from previous solutions: The insulation space is completely filled with a microporous, often even nanoporous filling material. The vacuum effect thus already occurs at a very low gas pressure.
In addition, the filler in these vacuum insulations has a more or less pronounced supporting function: the insulations can withstand enormous pressure, supporting elements become obsolete. This, as well as the low vacuum requirements, results in considerable cost advantages of GVI® systems compared to classic multi-layer systems.
GVI® technology uses the principle of the thermos flask – and makes it even better
VIPs are prefabricated, flat elements that can be used today, for example, to insulate cooling appliances or entire house fronts. The vacuum-tight envelope of these construction elements consists of multi-layer PE films with an aluminium coating. VIPs must be protected against damage due to the limit temperatures.
Experience has been gained with other cladding materials such as stainless steel, especially for very large components and extreme temperatures. The figure shows a cryogenic cabin assembled from individual surface elements for cryogenic cooling.
VICs are vacuum-insulated cabinets – more or less all-enclosing, double-walled containers. Almost any geometry can be created with such housings. VIC insulation properties are also significantly better compared to VIP insulation, since the numerous thermal bridges at the joints of the individual elements are eliminated. In addition, VICs are significantly more resistant to any form of mechanical stress.
The insulating characteristics of a ready-to-install GVI® system are determined by the filler material and the construction as well as the cladding materials used. Depending on the system, the cladding material always forms a connection somewhere from the warm to the cold side of the component. Due to increased solid-state heat conduction, these thermal bridges should be carefully planned and designed in order to minimize total heat loss.
Heat losses via the (undisturbed) vacuum-insulated surfaces depend on the filling material used. This results in a fundamental correlation between microporosity, residual gas pressure and solid content. The finer the porosity of the filler, the higher the permissible residual gas pressure. With coarsely porous materials, the cell walls are often thicker. With corresponding material properties (specific thermal conductivity), the overall thermal conductivity of the system is also higher.
Wrapping materials
We use metallic cladding materials for GVI® systems as standard. Due to their relatively low specific thermal conductivity, high strength and good weldability, austenitic stainless steels offer special advantages. Other materials such as the light metals aluminium or magnesium offer advantages, especially for extreme lightweight design applications.
Organic (lightweight) materials are also often used for lower temperature loads. Large-surface containers can be manufactured from glass-fibre reinforced plastics (GRP). Our experience has shown that such housings are sufficiently vacuum-tight if the matrix resin is properly selected.
Filler materials
These are usually mineral compounds with minimal solid-state thermal conductivity, very low emissions, sufficient supporting capacity and a fine porous structure. The pores must be open in order to ensure good evacuation.
Depending on the type of application, prefabricated moulded parts such as plates or pipe segments and free-flowing materials can be inserted into the double-walled insulating shell.
With the appropriate design, supported vacuum insulation exhibits very high compressive strength and rigidity. This effect can be influenced by the choice of cladding material thickness and the overall design. Compressive strength also depends on the properties of the core material.
A great deal of experience has been gained from insulation applications in the automotive sector involving exposure to strong vibration and jarring loads, which have to be borne primarily by the filler material. With the appropriate design, this is possible without any problems.
The fibre boards we use meet all requirements compared to the powders used in classic VIPs – especially when high forces have to be absorbed at the same time.
