Vacuum insulated structures
An article includes walls defining an insulating space therebetween and a vent forming an exit for gas molecules during evacuation of the space. A distance separating the walls is variable in a portion adjacent the vent such that gas molecules are directed towards the vent imparting a greater probability of molecule egress than ingress such that deeper vacuum is developed without requiring getter material. The variable-distance portion may be formed by converging walls. Alternatively, a portion of one of the walls may be formed such that a normal line at any location within that portion is directed substantially towards a vent opening in the other wall.
1. A method of insulating an article having first and second walls spaced at a distance from each other to define an insulating space therebetween, the method comprising:
providing a vent in communication with the insulating space;
providing an exit pathway for gas molecules to exit from the insulating space through the vent by varying the distance between the first and second walls in a portion of the insulating space proximate to the vent such that gas molecules are guided towards the vent when a vacuum is applied to the vent;
placing the article in a vacuum chamber to apply a vacuum to the vent, wherein the vacuum applied to the vent is sufficiently low that molecule-to-molecule interactions within the insulating space no longer dominate;
generating a vacuum within the insulating space that is deeper than the vacuum applied to the vent as a result of the exit pathway increasing the probability of gas molecule egress from the insulating space as compared with the probability of gas molecule ingress into the insulating space; and
sealing the vent to maintain the deeper vacuum within the insulating space.
2. The method according to claim 1 , wherein the exit pathway is defined by converging portions of the first and second walls.
3. The method according to claim 2 , wherein the first and second walls are respectively provided by inner and outer tubes and wherein the outer tube includes an angled portion that converges towards the inner tube.
4. The method according to claim 3 , further comprising:
providing a layer of spacer material between the inner and outer tubes that limits direct contact between the tubes while permitting flexing of the tubes.
5. The method according to claim 1 , wherein the first and second walls are respectively inner and outer walls, the vent is located in the outer wall, and the exit pathway includes a concavely curved surface formed on the inner wall such that a line normal to the concavely curved surface at any location within the exit pathway is directed substantially towards the vent.
6. The method according to claim 1 , wherein sealing the vent includes of:
placing a brazing material adjacent the vent; and
heating the brazing material such that the brazing material melts and flows by capillary action into an evacuation path defined by the vent to block the evacuation path.
7. A method of insulating an article having first and second walls spaced at a distance from each other to define an insulating space therebetween, the method comprising:
providing a vent in communication with the insulating space;
providing an exit pathway for gas molecules to exit from the insulating space through the vent by varying the distance between the first and second walls in a portion of the insulating space proximate to the vent such that gas molecules are guided towards the vent when a vacuum is applied to the vent;
applying a vacuum to the vent;
generating a vacuum within the insulating space tat is deeper than the vacuum applied to the vent as a result of the exit pathway increasing the probability of gas molecule egress from the insulating space as compared with the probability of gas molecule ingress into the insulating space; and
sealing the vent to maintain the deeper vacuum within the insulating space.