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Modelling the impact of water intrusion on heat transfer within vacuum jacketed piping

Marchant, Kieran (2017). Modelling the impact of water intrusion on heat transfer within vacuum jacketed piping. Bachelor of Engineering (4th Year Project) Thesis, Charles Darwin University.

Document type: Thesis
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Author Marchant, Kieran
Title Modelling the impact of water intrusion on heat transfer within vacuum jacketed piping
Institution Charles Darwin University
Publication Date 2017-06
Thesis Type Bachelor of Engineering (4th Year Project)
Supervisor Thennadil, Suresh
Diaz, Luis H.
0904 - Chemical Engineering
Abstract Currently, established cryogenic industries are faced with increasing heat transfer due to deteriorating insulation systems. Although various thermal insulation methods are utilised within the cryogenic industry, a common method is to employ a vacuum jacket. Vacuum Jacketed Piping (VJP) is characterised by a system of concentric pipes with an evacuated annular space, which aims to restrict the flow of atmospheric heat into the system. This ensures the internal liquid remains cold to maintain its form, rather than absorbing heat and evaporating to produce Boil Off Gas (BOG), which must be re-liquefied to be stored and sold.

With the establishment of vacuum conditions within the jacket, low pressures are maintained using seals. Due to the extreme pressure differentials between the evacuated space and the environment of around 800 million times less than atmospheric, each seal has an inherent leak, which enables atmospheric contaminants to enter the annular space. Because of this, these insulation systems are expensive and are utilised over long periods of time, which results in a build-up of contaminates, causing a reduction in insulation performance. One contaminant in particular, water, has a substantial impact on the thermal efficiency of VJP, due to the tendency to freeze around the internal pipe. For flexible vacuum jacketed pipes, the ice layer significantly hinders the structural integrity of the system to alleviate internal stresses. This demonstrates the importance of analysing the level of water intrusion into vacuum jacketed systems.

With tightening maintenance budgets in the current industry climate, the decision matrix to assess whether a process component should be maintained is dependent on its overall impact to the process. Without detailed heat transfer modelling of insulation performance, isolating specific impacts on BOG production using plant data is difficult and relatively inaccurate. This establishes the importance for a model to be developed to assist operating facilities in identifying the thermal performance of vacuum jacketed insulation.

The water content required to form ice layers of sufficient thicknesses was analysed and the overall impact of this layer on the total heat transfer was determined. Despite the model’s ability to explore the relationship between various heat transfer variables, the overall applicability to practical systems requires further data to ensure the results correspond to those calculated.
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Created: Wed, 05 Jul 2017, 09:01:53 CST by Jessie Ng