Executive Summary : | Transfer of cryogenic fluids (Cryogens) such as liquid nitrogen, oxygen, helium etc. from the storage dewar to the various end applications is a daily occurrence in laboratories / industries. Both flexible and rigid transfer lines are used to transfer these cryogens. The latent heat of vaporization and the boiling point of these cryogens are very low. Vacuum insulated (with or without superinsulation) transfer lines are most suitable to minimize the heat transfer and evaporation of the cryogens during the transfer process. Flexible transfer lines are more convenient in view of the maneuverability of the lines especially under space constraints. Hence, cryogenic transfer lines are specially designed to minimize the heat transfer from the ambient to the cryogenic fluid flowing through it. These transfer lines are generally consists of: (a) inner and outer lines (pipes/corrugated bellows) with interspace vacuum, (b) port for evacuation of the interspace, (c) safeties to vent the high pressure gas in case of a sudden loss of vacuum in the interspace, (d) suitable low thermal conductivity spacers in the interspace to support the inner line within the outer lines, (e) special getters to maintain high vacuum in the interspace for long duration operations and (f) suitable end connections as per the end applications. In large / commercial operations the evaporation of the cryogen is high and demands for proper design of transfer lines. Superinsulated transfer lines (with interspace vacuum pressure in the range of 10E-4 mbar and Multi-Layer Insulation (MLI)) are most suitable for efficient transfer of cryogens. The diameter and thickness of the inner and outer lines should be minimum to have less thermal mass to minimize the heat transfer to the flowing cryogen and fast cool-down of the transfer line. To our knowledge not enough data is available on the design and the heat transfer analysis of both for flexible and rigid cryogenic transfer lines in open literatures. In view of the above, the project proposal deals with the following. 1) Design and development of both flexible and rigid transfer lines of various diameters (from 6 to 32 mm ID) and of different lengths (from 1 to 5 m long) with various types of insulations. 2) Analytical, CFD and experimental investigations on the heat load and the pressure drop for the designed and developed transfer lines. 3) Detailed experimental studies on cool-down, heat loads and pressure drops of the developed flexible and rigid transfer lines for LN2 / LHe flow. 4) Development of an analytical model on the design, heat load and pressure drop estimations for flexible and rigid transfer lines based on the studies. This development will provide sufficient design data and technical knowhow both for flexible and rigid transfer lines for cryogenic fluids and will enable the users to develop their own transfer line(s) depending on the end applications. |