Revisiting the Dewar Design for Liquid Oxygen Storage in Fuel Cell Energy Systems

Dewars are used to store liquid oxygen (LOX) in a fuel cell-driven Air Independent Propulsion (AIP) system for subsea vehicles. The dewar should have good storability to reduce snorkeling frequency. It is a double-walled vessel in which the two vessels are held together with a support system. The annular space contains the insulation. Heat flows from the ambient into the LOX through the insulation and support systems. Many types of dewar are available commercially; however, there exist no design guidelines in the open literature. Heat inleak is one of the primary concerns in the dewar design. For the first time, a comprehensive study is presented in this paper to highlight the relative importance of the support system and the insulation in dictating the heat inleak into the dewar. We determined the effects of heat inleak on the dewar design. The study revealed that the heat inleak through the support is considerably larger than that through the insulation. The results clearly emphasize the importance of the support system design in improving the storability of the LOX dewars in a fuel cell system.