Blast media fragmenter

1. A subsonic blast media fragmenter comprising

a. a body defining an internal flow path, said internal flow path comprising:

i. an inlet;

ii. a converging section disposed downstream of said inlet; and

iii. an outlet disposed downstream of said converging section;

said internal flow path configured to maintain a fluid flow with entrained cryogenic blast media particles at subsonic speed from said inlet to said outlet; and

b. at least one fragmenting element disposed intermediate said converging section and said outlet,

said internal flow path having a first length between said inlet and said at least one fragmenting element sufficient for the entrained particles' speed to increase to the fluid flow's velocity prior to reaching said at least one fragmenting element.

2. The subsonic blast media fragmenter of claim 1 , comprising a constant cross-section area section disposed intermediate said converging section and said at least one fragmenting element, said constant cross-section area section's length being sufficient for the entrained particles' speed to increase to the fluid flow's velocity prior to reaching said at least one fragmenting element.

3. The subsonic blast media fragmenter of claim 2 , comprising an expansion section disposed intermediate said constant cross-section area section and said at least one fragmenting element.

4. The subsonic blast media fragmenter of claim 3 , wherein immediately downstream of said at least one fragmenting element said internal flow path has a larger cross-sectional area than immediately upstream of said at least one fragmenting element.

5. The subsonic blast media fragmenter of claim 1 , comprising an expansion section disposed intermediate said converging section and said at least one fragmenting element.

6. The subsonic blast media fragmenter of claim 5 , wherein immediately downstream of said at least one fragmenting element said internal flow path has a larger cross-sectional area than immediately upstream of said at least one fragmenting element.

7. A method of changing a size of blast media particles entrained in a subsonic fluid flow, each of said blast media particles having a respective initial size, the method comprising:

a. converging said subsonic fluid flow from a first speed to a second speed, said second speed being subsonic and greater than said first speed;

b. propelling a plurality of said blast media particles through one or more openings defined by a fragmenting element; and

c. changing at least one of the propelled plurality of blast media particles from its respective initial size to a second smaller size by said propelling of said at least one of the plurality of said blast media particles through said one or more openings.

8. The method of claim 7 , comprising maintaining said subsonic fluid flow at said second speed for a first length prior to propelling said plurality of said blast media particles through said one or more openings.

9. The method of claim 7 , comprising, after said subsonic fluid flow has attained said second speed, not converging said subsonic fluid flow for a first length prior to propelling said plurality of said blast media particles through one or more openings.

10. The method of claim 9 , wherein not converging said subsonic fluid flow for a first length comprises flowing said subsonic fluid flow through an internal passage way, said internal passageway having a constant cross-sectional area along said first length.

11. The method of claim 7 , comprising expanding the subsonic fluid flow immediately prior to propelling said plurality of said blast media particles through one or more openings.

12. The method of claim 7 , comprising expanding the subsonic fluid flow immediately after propelling said plurality of said blast media particles through one or more openings.

13. The method of claim 7 , comprising converging the subsonic fluid flow after propelling said plurality of said blast media particles through one or more openings.

14. A subsonic blast media fragmenter comprising

a. an internal flow path, said internal flow path comprising:

i. an inlet;

ii. a converging section disposed downstream of said inlet; and

iii. an outlet disposed downstream of said converging section;

said internal flow path configured to maintain a fluid flow with entrained cryogenic blast media particles at subsonic speed from said inlet to said outlet and

b. at least one fragmenting element disposed intermediate said converging section and said outlet,

said internal flow path having a first length between said inlet and said at least one fragmenting element sufficient for the entrained particles' speed to increase to the fluid flow's velocity prior to reaching said at least one fragmenting element.

15. The subsonic blast media fragmenter of claim 14 , wherein said converging section is disposed immediately downstream of said inlet.

16. The subsonic blast media fragmenter of claim 14 , wherein said internal flow path is defined by a body of unitary construction.

17. A subsonic flow path configured to convey a subsonic fluid flow with entrained cryogenic blast media particles at subsonic speed throughout said flow path's length, the cryogenic blast media particles having respective sizes, the subsonic flow path comprising:

a. a converging section configured to transition the subsonic fluid flow from a first speed to a second speed, said second speed being subsonic and higher than said first speed; and

b. at least one fragmenting element disposed downstream of said converging section, said at least one fragmenting element configured to reduce the respective sizes of the cryogenic blast media particles as they flow past the fragmenting element

said subsonic flow path having a first length upstream of said at least one fragmenting element which is sufficient for the entrained cryogenic blast media particles' speed to increase to the fluid flow's velocity prior to reaching said at least one fragmenting element.

18. The subsonic flow path of claim 17 , comprising a constant cross-section area section disposed intermediate said converging section and said at least one fragmenting element.

19. The subsonic flow path of claim 17 , wherein the subsonic flow path comprises a larger cross-sectional area immediately downstream of the at least one fragmenting element than immediately upstream of said at least one fragmenting element.