Document Type

Theses, Masters

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Available under a Creative Commons Attribution Non-Commercial Share Alike 4.0 International Licence

Abstract

The primary aim of this project is to obtain a fundamental understanding of the fluid dynamics and thermodynamics of the primary and secondary flows in a Ranque-Hilsch Vortex Tube (RHVT). These flows are highly complex and are three dimensional, compressible and viscous in nature. To obtain an understanding of these, a state of the art Computational Fluid Dynamics (CFD) software package is applied for flow prediction with advanced turbulence models, and is employed to predict the primary and secondary flows in a RHVT. The models that are used include : the k-e model, the SST model by Menter, and the Reynolds Stress Model. The results from the turbulence modes are analysed and compared to establish how accurate they are at computing this type of flow field. In this CFD study of the RHVT, the flow fields and temperature outputs are investigated. This study begins with the appropriate selection of experimental results from a range of authors for similar vortex tubes. These results are collated and a three dimensional model of a similar experimental RHVT is drawn, upon which an unstructured tetrahedral mesh is developed using the CAD and meshing facilities of the CFD package respectively. This model is developed in such a way that components of the RHVT could be easily adjusted in size in order to carry out small scale parametric studies of the vortex tube. The analysis moves on to the correct stipulation of suitable and accurate boundary conditions. Once a set of appropriate and realistic boundary conditions is established, the flow fields within the RHVT are captured. Initially the k –e turbulence model is utilised to perform a mesh element density convergence study with the cold static and total temperature outputs of the RHVT as the measured criteria. Once mesh independent results are established, additional turbulence models such as the SST model by Menter and the Reynolds Stress model are run on this mesh to ascertain the performance of each turbulence model. When the optimum turbulence model is ascertained and investigation was carried out into the source of heat migration in the RHVT. This began by varying the tube geometry, i.e. the cold outlet diameter, and analysing its influence on the presence of secondary flow and therefore the influence of secondary flow on the heat transfer within the RHVT. An additional analysis of the work due to friction within the vortex tube is also performed in order to verify the presence of such work within the RHVT. Finally a recommendation is made within the conclusion of this thesis as to a method of how to take the study of work due to friction within the vortex tube forward for further analysis.

DOI

https://doi.org/10.21427/D7ZG8R

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