Storage tank for cryogenic liquids

A method of filling a cryogenic storage space with a cryogenic fluid while preventing an ullage space at an initial pressure from being filled with said cryogenic fluid, said method comprising:

• a. delivering said cryogenic fluid to said cryogenic storage space through a fill conduit defining a narrow passage and a broad passage, said broad passage disposed downstream from said narrow passage,
• b. allowing fluid communication between said narrow passage and said ullage space through an ullage conduit, said ullage conduit defining an ullage exit into said fill conduit at said narrow passage,
• c. selecting a flow rate for said cryogenic fluid through said fill conduit such that a narrow passage pressure is established at said ullage exit that is lower than said initial pressure while said cryogen space is being filled with said cryogenic fluid,
• d. stopping flow through said fill conduit when said cryogen space is substantially liquid full.

A cryogenic tank assembly for holding a cryogenic fluid comprising:

• a. a vessel defining a cryogen space,
• b. a ullage vessel defining a ullage space,
• c. a fill conduit for directing said cryogenic fluid into said cryogen space, said fill conduit comprising
• i. an inlet for receiving said cryogenic fluid from outside said cryogenic tank assembly,
• ii. an exit within said cryogen space for delivering said cryogenic fluid to said cryogen space during a course of filling of said cryogenic space,
• iii. a broad passage defining a broad cross-sectional area, and,
• iv. a narrow passage defining a narrow cross-sectional area that is smaller than said broad cross-sectional area, wherein said broad passage is downstream from said narrow passage,
• v. an ullage opening defining an ullage cross-sectional area that is smaller than said narrow cross-sectional area, said ullage opening defining a ullage passage between said narrow passage and said ullage space,
• wherein said cryogenic fluid is restricted from said ullage space during said course of filling.