An investigation of the fluid dynamics and heat transfer of high pressure flows in integrated gas delivery systems

Abstract

Fast filling of high-pressure gas storage cylinders causes heating that can damage the cylinder. This thesis presents the development of computational models that predict the thermal response during the fast filling of high-pressure gas storage cylinders with hydrogen or natural gas. The new computational models are validated and then used to assess a range of approaches for achieving rapid filling, without overheating the cylinder. A two-dimensional axisymmetric computational fluid dynamic (CFD) simulation of the fast refuelling of a hydrogen cylinder was performed and successfully validated by comparing the mass-averaged gas temperature throughout the fill to the published experimental results. Heat transfer models for fast-filling of cylinders with a range of length-to-diameter ratios (L/D) were developed with the heat transfer coefficient models calibrated using the CFD simulation data. A single-zone model was implemented for cylinders having a L/D less than 3.3 and a two-zone model for cylinders with a higher L/D. Both models model have shown a reasonable accuracy and robustness in simulating the fastfilling of hydrogen cylinders having different material properties and also for different fill times, while significantly lowering the computational time. The singlezone model was included as part of a series of elements that were used to model a hydrogen/CNG fast-filling station. Two case studies were performed that involved the fast-filling of a hydrogen vehicle (Toyota Mirai) and a natural gas vehicle (Honda Civic GX). The simulations showed that the filling of the hydrogen vehicle can be performed within one minute over a range of ambient temperatures and the use of phase change materials as part of the structure of the cylinder reduces the pre-cooling requirement. A study of the effects of inlet pressure profiles showed that, in the case of the Honda Civic GX, a fill time of approximately 19 seconds can be achieved, while gaining an increase of approximately 6 % in the final mass of gas by applying a step pressure profile at the exit of the dispenser.

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ORCID for Edward Richardson: orcid.org/0000-0002-7631-0377

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