Enhanced vacuum-insulated articles with controlled microporous insulation
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. An insulated article, comprising:
a first wall bounding an interior volume;
a second wall spaced at a distance from the first wall to define an insulating space therebetween, the insulating space having a pressure of from about 10 −4 to about 10 −7 Torr;
a vent communicating with the insulating space to provide an exit pathway for gas molecules from the space,
the vent being sealable for maintaining a vacuum within the insulating space following evacuation of gas molecules through the vent,
the distance between the first and second walls being variable in a portion of the insulating space adjacent the vent such that gas molecules within the insulating space are directed towards the vent by the variable-distance portion of the first and second walls during the evacuation of the insulating space,
the directing of the gas molecules by the variable-distance portion of the first and second walls imparting to the gas molecules a greater probability of egress from the insulating space than ingress; and
an amount of an insulating material disposed within the insulating space between the first wall and the second wall,
the insulating material comprising particles, fibers, or both, the particles, fibers, or both defining a cross-sectional dimension in the range of from about 5 nm to about 25 nm.
2. The insulated article according to claim 1 , wherein one of the walls includes a portion that converges toward the other wall adjacent the vent, and wherein the distance between the walls is at a minimum adjacent the location at which the vent communicates with the insulating space.
3. The insulated article according to claim 2 , wherein the converging wall portion of the one of the walls is located adjacent an end of the associated wall.
4. The insulated article according to claim 1 , wherein the first wall is characterized as a tube, wherein the second wall is characterized as a tube, and wherein one of the first tube and the second tube is outer to the other and wherein the wall including the converging portion is provided by the outer of the tubes.
5. The insulated article according to claim 1 , further comprising a coating disposed on a surface of the one of the walls, the coating formed by a material having an emissivity that is less than that of the wall on which it is disposed.
6. The insulated article according to claim 1 , wherein the insulating material defines a plurality of pores therein, the majority of which pores have a size of about 70 nm or smaller.
7. The insulated article according to claim 1 , wherein the amount of an insulating material has a thermal conductivity of from about 0.002 to about 0.01 W/m*K.
8. The insulated article according to claim 1 , wherein the amount of an insulating material comprises alumina, silica, or both.
9. The insulated article according to claim 1 , wherein the amount of an insulating material comprises from about 70 to about 90% void space, by volume.
10. An insulated article comprising:
a first tube bounding an interior volume;
a second tube spaced at a distance from the first wall to define an insulating space therebetween, the insulating space having a pressure of from about 10 −4 to about 10 −7 Torr;
a vent communicating with the insulating space to provide an exit pathway for gas molecules from the space,
the vent being sealable for maintaining a vacuum within the insulating space following evacuation of gas molecules through the vent,
the distance between the first and second tubes being variable in a portion of the insulating space adjacent the vent such that gas molecules within the insulating space are directed towards the vent by the variable-distance portion of the first and second tubes during the evacuation of the insulating space,
the directing of the gas molecules by the variable-distance portion of the first and second walls imparting to the gas molecules a greater probability of egress from the insulating space than ingress,
the article further comprising an amount of an insulating material disposed in the insulating space between the first and second tubes,
the insulating material comprising particles, fibers, or both, the particles, fibers, or both defining a cross-sectional dimension in the range of from about 5 nm to about 25 nm.
11. The insulated article according to claim 10 , wherein the amount of an insulating material comprises a porous material.
12. The insulated article according to claim 10 , wherein the amount of an insulating material has a thermal conductivity of from about 0.002 to about 0.1 W/m*K.
13. The insulated article according to claim 10 , wherein the amount of an insulating material comprises alumina, silica, or both.
14. The insulated article according to claim 10 , wherein the amount of an insulating material comprises from about 70 to about 90% void space, by volume.
15. The insulated article according to claim 10 , wherein the insulating material defines a plurality of pores therein, the majority of which pores have a size of about 70 nm or smaller.