Design and Development of Cryogenic Transfer Lines and Studies on Flow Phenomena

Abstract

Cryogenics refers to the field of science and engineering below 123 K (-150 ºC). Also it deals with the production, utilization and maintenance of the same. Below 123 K, the so called “Permanent gases” such as Argon, Oxygen, Nitrogen, Hydrogen and Helium can be liquefied. Because of their low boiling point and latent heat of vaporization, special storage and transfer systems are needed for storing these cryogens for end applications. Hence, it is necessary to use insulated cryogenic transfer lines to minimize the evaporation losses and enable maximum fluid collection during the transfer of the cryogens. Flexible transfer lines are manoeuvrable, easy to handle and can take care of differences in the heights between the storage and receiver tanks when compared to rigid transfer lines. On the other hand, the design and fabrication of flexible Cryogenic Transfer Lines (FCTLs) are more cumbersome than those of rigid cryogenic transfer lines. To the best of our knowledge, the procedure available to design and develop a FCTL is scanty in the open literature. The work presented in the thesis perhaps tries to fill the gap by detailing the theoretical background for the development of the super-insulated vacuum jacketed FCTLs. The minimum diameter and thickness of the inner line/tube for a particular flow rate and pressure have been estimated theoretically. Total heat load by different modes of heat transfer and pressure drops both for single and two phase flows through the transfer line also have been estimated theoretically. Based on the theoretical studies, a quick disassemble type flexible transfer line of 20.5 mm ID, 62.0 mm OD and ~ 3 m long has been designed and fabricated, so that many experiments could be performed on the same transfer line with varied experimental conditions. Studies on cool-down, heat transfer and pressure drop have been carried out towards optimizing the various critical parameters such as numbers of Multi-Layer Insulations (MLI) and spacer distances. The studies show that 20 layers of MLI is optimum for better performance of the developed FCTL, whereas the spacer distance of 8 inches (203.2 mm) is optimum in the interspace for minimum heat transfer to the FCTL. Studies also have been carried out for measuring the void fraction and flow pattern in the developed flexible transfer line with liquid nitrogen (LN2) flow. Simple and cost-effective capacitance and diode based sensors have been developed and integrated in-line to the developed transfer line for measuring the void fraction and the flow pattern respectively. Both CFD and experimental studies have been performed to estimate the void fraction of the two phase flow on the developed transfer line and matches well with each other. Wavy flow pattern has been observed both by CFD and experimental studies with the diode sensor. Based on the studies and the expertise gained in the development of 3 m long flexible transfer line, a 5 m long flexible transfer line of 34.8 mm ID and 102.0 mm OD with Bayonet end connections has been developed for the specific application of national importance for liquid helium (LHe) transfer. Studies have been performed towards the performance evaluation of the above transfer line. It is presumed that the work presented in the thesis will serve for a better understanding of the design and fabrication of flexible transfer lines for cryogenic fluids and the flow phenomena therein.