vacuum flask

you need two bottles, one within the other with an insulation gap that you fill with cabosil that is sealed and has zero moisture. That will be inferior to a vacuum bottle (dewar style), but better than zero insulation.

Charts for various materials can be found if yu cannot use cabosil(the best0, you can use foams of various types as long as they tolerate the hot water temperature.

You can calculate this by reference to cabosil specs and the glass bottle wall thickness.

Dear Aurizon: thanks a lot for your advice:OK two bottles,cabosil or foams are to expensive for my project,what would happen with regular fine sand? how big should be the gap?

Is it possible to have a vacuum gap in two plastic bottles?

please reply,i know you are an expert.

my best wishes for you.

Joab

Hello, The two bottle method is good, also if you line the outside of the inner bottle with foil and the inside of the outer bottle with foil and a sealed air space. Also limit the contact of the inside bottle with the outside. To keep direct path as small as possible will help with the heat loss. The foil will act a radiant reflector keeping the heat in.

metalSmith's

Dear Sir: thanks for your advice,how can i foil the inner and outer face of a bottle?

would it be OK vacuum metallizing?

please reply.

my best regards: joab

Before doing this, make sure the 2 liter bottle you're using does not contain BPA; the hot water will leach BPA perhaps 10-20 times faster than cold water. Look for the recycling code 7 on the bottom; this also includes some non-recyclable plastics that do not release BPA, but it's better to be safe than sorry.

What would plastisol do for you? Plain ol' styrofoam or fiberglass would do as good or better job.

If you use thermoset plastics, and maybe reinforce the gap between the inner container and the outer shell with an insulating material, like a large-cell honeycomb thermoset plastic with holes in the neutral plane so that a vacuum can be created between the two shells prior to sealing, then you would virtually have a non-glass and non-metal thermos bottle.

The thermos bottle depends on the vacuum to eliminate two paths and on the mirrored surface to eliminate one path. The direct conduction through the end plug and the joint between the two flasks can be minimized.

One is the convective path, and the other is the kinetic molecular path.

The convective path can be eliminated easily enough. The elimination of the kinetic transfer path needs a good vacuum. Two plastic bottle might outgas too much for a very good thermos.

Commercial dewars use superinsulation. In a 1 inch space they may have 100-200 layers of both side aluminized mylar and they also add 2-3% cabosil as they roll up he mylar to stop the mylar from touching. They then heat it and draw as good a vacuum as possible and seal it. The mylar and cabosil are better than mirrored glass alone.

They also use it for arctic buildings.

You can get 1.2L vacuum flasks very cheaply. Why not use 2 of them and save yourself the time and trouble of making an inferior substitute?