Experimental approach to suppress two-phase flow in cryogenic liquid transfer process with the inverted U-bend pipe

LNG (Liquefied Natural Gas) offloading process from LNG cargo to storage tank includes substantial vertical upward fluid transportation. During this LNG transportation process, local boiling may occur at elevated position of the transport pipe due to the decrease of hydrostatic pressure and obstruct liquid flow, concluding long transport time or insufficient transport to a tank. Small scale LN2 (Liquid Nitrogen) transfer system has been fabricated to simulate this LNG transportation process and flow characteristics. Subcooled LN2 is transferred to 5 m upward, 1 m horizontally, and 5 m downward through vacuum insulated stainless steel pipe. Glass pipes are installed at the middle part of transportation pipes to visualize the two-phase flow pattern during fluid transfer. Cryogenic valve is installed at the outlet of transfer pipe to regulate the system pressure inside the transfer tube. Pressurization by manipulating the cryogenic valve at the outlet, has effectively suppressed two-phase flow, which results in transportation advantages, such as low pressure drop and smooth flow. This paper presents the detailed experimental data of the whole procedure of the tested LN2 transfer system.

► Cavitation occurred during the transport of the cryogenic liquid transfer.
► Two phase flow suppression is verified with pressurization of the system.
► Flow visualization is performed with two phase nitrogen flow.
► Pressurization and subcooling degree are important factors for suppression two-phase flow.