AUTONOMOUS CONTROL OF CRYOGENIC LIQUID REPLENISHMENT AND LIQUEFACTION SYSTEMS

摘要

Autonomous control of a cryogenic liquefaction and replenishment system was performed to demonstrate the feasibility of an autonomous liquid oxygen generation system for unmanned underwater vehicles (UUVs). The patented (U.S. Pat. No. 6,431,750) Cryo-Tracker (C-T) probe was an integral part of the control system and an enabling technology that provided feedback in the form of continuous monitoring of the liquid level. Liquid level feedback from the C-T probe was compared to two control limits that were preprogrammed in LabVIEW. The control limits constituted a control range for the liquid level. A signal from LabVIEW switched on the liquefaction system when feedback indicated the liquid level was below the control range and switched off the liquefaction system when liquid was replenished to the upper limit. The liquefaction and replenishment system was comprised of a compressor-driven pulse tube cryocooler, which was integrated with a heat exchanger to liquefy gaseous nitrogen and autonomously fill and maintain a predetermined level of liquid nitrogen in a laboratory-size insulated container. Continuous liquid level monitoring with the C-T probe enabled the level to be maintained constant within ±0.05 inches (±1.3 mm). The test results proved the feasibility of utilizing this control system for autonomous recharging of liquid oxygen systems for unmanned underwater vehicles as well as other applications that require autonomous liquefaction and replenishment of cryogenic liquids.