Implementing an Exchange from Nitrogen to Helium in a Large Hyperbaric Chamber
Abstract
A 954 cubic foot (27 cubic meter) hyperbaric chamber at a pressure of 4 atmospheres absolute was purged of a nitrogen/oxygen gas mixture (92.5%/7.5%) by flushing with 100% helium. The helium entered the top of the chamber, and the N2/O2 exited at the bottom so that the lighter gas layered above the heavier gas. Turbulence was kept to a minimum by turning off the life support system, limiting movement of inside divers, and by utilizing overboard dump masks for the breathing gas. Use of the layering technique allowed the chamber to be completely purged of N2/O2 in 55 minutes, using 8,143 cu ft (230 cu meters) of helium. If the layering technique had worked perfectly at the flow rate used (148 cu ft/min (4.19 cu meters/min.)), it would have taken 26 minutes and 3,816 cu ft (108 cu meters) of gas to rid the chamber of nitrogen. On the other hand, if the incoming gas mixed completely and instantaneously with the chamber gas, it would have taken 117 minutes and 17,316 cu ft (511 cu meters) of gas to bring the chamber nitrogen concentration below 1%. Thus, by avoiding unnecessary turbulence and thereby taking advantage of the layering phenomenon, the best estimate in saving of time and gas is approximately one hour and 9,000 cu ft (255 cu meters) of helium. In experiments where the environmental gas must be changed from a dense gas to a lighter gas and time and/or gas saving is important, the layering phenomenon may be used advantageously by limiting the degree of mixing.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 21, 1977
- Accession Number
- ADA049273
Entities
People
- D. D. Wray
- James E. Jordan
- Kenneth R. Bondi
Organizations
- Naval Submarine Medical Research Laboratory