by Gordon Reid, sdirector – cryogenic products, RIX, greid@rixindustries.com

RIX Industries (CSA CSM) announced in August that it had supplied mission-critical cryocooler technology for shipboard pilot and medical applications onboard the USS Gerald R. Ford (CVN-78). The company and its engineering team applied their experience in providing the US Navy with military grade compressors and nitrogen generators for decades to design and manufacture a state-of-the-art liquid and gaseous oxygen generating plant that is now used onboard the ship.

The USS Gerald R. Ford (CVN-78), one of many newly designed nuclear-powered aircraft carriers, is the first of its kind to enter the fleet and is replacing the decommissioned USS Enterprise (CVN-65) after 51 years of service. As is the case with any new aircraft carrier design, the Navy set goals for the USS Gerald R. Ford (CVN-78) to reduce ownership cost, decrease operational manpower and virtually eliminate maintenance.

Early on in the development of the ship, the Navy, in conjunction with Huntington Ingalls and Northrop Grumman, recognized that traditional liquid oxygen (LOX) generating technology used on existing carriers provided the team with a unique opportunity to meet the Navy’s goals with an improved design.

Aircraft carriers use highly concentrated gaseous and liquid oxygen for pilot and medical applications. Many legacy production plants utilize fractional distillation column technology to produce oxygen and turbo Brayton cryogenic plants for liquefaction. These systems consume large amounts of energy and valuable ship space, require frequent maintenance during startup and operation and typically take twenty or more hours from startup to reach stability and purity.

The solution
The design of the RIX oxygen generating plant includes a compact, packaged Stirling cryocooler for liquefaction, a significant upgrade from previously used technologies. This “thermo-acoustic” cooler uses high amplitude sound waves to pump heat from one location to another. The acoustic power is produced by high efficiency, linear reciprocating motors with clearance sealed pistons. These pistons do not require the lubrication or routine maintenance needed with high speed rotating compressors and expanders. Instead, the acoustic power is fed to cryogenic coldheads that have no valves or moving components whatsoever.

RIX’s improved design has other benefits. The cyrocooler produces liquid oxygen 20 minutes after startup, providing both quick availability and energy savings. These benefits are impervious to ship movement, providing an uninterrupted supply of liquid oxygen. In addition, the size and weight of the RIX cryocooler is approximately 50% that of its predecessor.

Rigorous testing
All Navy-approved shipboard equipment must pass a series of rigorous tests that prove the equipment is suitable for extreme use in mission-critical scenarios. Testing criteria of this nature includes extensive shock, noise and vibration tests, as well as power quality testing to ensure signals generated by the equipment do not interfere with other critical, shipboard systems. During one particular Naval shock test, MIL-S-901D, the complete RIX system was subjected to multiple shock episodes, with the highest test imparting an impressive 80-Gs of acceleration directly on the cryocooler. Although it was not required to operate after this test, the RIX system not only survived with very little damage, it was able to reach cryogenic temperatures in 10 minutes and LOX liquefaction temperatures in 20 minutes. The RIX system also passed extreme Builder’s and Acceptance trials performed at sea with the US Navy. Late in 2019, RIX’s liquid and gaseous oxygen production system passed all testing requirements with the US Navy.

Historically, highly trained and skilled personnel were required for startup and operation of the legacy liquid oxygen production plants used on Navy aircraft carriers and hospital ships. The RIX Industries design provides a fully autonomous system that starts at the push of a button and produces liquid oxygen in 20 minutes.
The RIX liquid and gaseous oxygen production system also uses maintenance-free cryogenic cooling technology and provides an intuitive user interface that communicates with other shipboard machinery systems. Its rugged, reliable design and extraordinary results during testing prove that it will perform during mission-critical scenarios and in harsh environments. The features of the RIX LOX production system provide the US Navy with technology that will benefit current and future ship programs.