what is the composition of MLI Blanket
Its made of alternating layers of reflective material and a non-thermally conductive layer to act as a spacer, generally about 60 layers per inch of thickness.
The reflective layer can be aluminum foil or aluminized mylar either one or double sided.
The non-thermally conductive layer can be a wide variety of materials but is most commonly a material called "bridal veil". Not sure exactly what it is.
I want to purchase an MLI blanket . how to get it i.e. how to place the order
Is it found in a ready to use form .i mean Is it found in a 60 layer composed with spacer layer or they are composed latter as required
You can't purchase a premade blanket, but you can buy the materials. Before you do that, you need to know how to use them and how to design the container they will be incorporated into. MLI is usually used in the vacuum space of cryogenic vessels and sometimes on spacecraft, but knowing how to design and manufacture the equipment the MLI will be wrapped around is crucial to getting low heat transfer. What is the blanket for? Do you want some help in the design, because without knowing how to do that, MLI is useless.
much thanks for ur valuable comments
actually i am working on thermal control of satellite so i want to use MLI blanket for insulating the structure from the environment
I am supposing an orbit height of about 700 km
and a near polar orbit for my study.so please if u could help me choose the correct MLI composition and designing details
I'm assuming you're doing this for a school project or something similar. All the companies that design and manufacture satellites have their own ways of making thermal blankets that take into consideration such things as cleanliness, durability, thermal performance, and other things. They will likely use materials specifically designed and manufactured for the space environment. Also, the use of MLI on spacecraft is a bit different from its use in cryogenic vessels. For example, in a cryogenic vessel, you need supports for the inner vessel that minimize heat transfer via thermal conductivity. You also need "getters" for removing small amounts of air, hydrogen, water and other vapors that outgas after assembly. In comparison, spacecraft don't have an external shell and vacuum space because they use the vacuum of space itself. They also don't need getters since any outgassing will simply escape to space, though they still need to be extremely clean to minimize outgassing. A similarity is they will both use alternating layers of highly reflective material and a spacer material.
In industry, the thermal analysis uses an "apparent thermal conductivity" as opposed to a radiation heat transfer analysis. If you look at a major supplier of MLI for industry, you'll find charts relating to apparent thermal conductivity such as this one here:
(Click on "Grade property sheet")
This web page has three different products:
There's another reference for apparent thermal conductivity here:
So you could use the apparent thermal conductivity, or you could calculate a thermal resistance assuming you could find the thermal conductivity and emissivity of the individual layers and just apply the fundamental principals.
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We used to make them from aluminised mylar - available from any cryogenics/vacuum company. And 'bridal veil' which is nylon 'lace' netting exactly the stuff used for bridal veils, which we used to buy from a department store.
You just lay down a layer of mylar, then a square of veil cut to about 1cm smaller all round, then a layer of mylar and so on until you have the required thickness / insulation.
We then sealed the edges by tacking every cm with a clean soldering iron. Since we were using them in a cryostat we wanted the air inside the sandwich to escape quickly.You can also buy aluminised tape from the same people to seal the edges.
Main difficulty building this in the Cambridge swamp was keeping it dry enough, water is a bugger in vacuum.
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