Finite volume analysis and optimisation of a high pressure homogeniser
Clarke, Andrew P. (2009) Finite volume analysis and optimisation of a high pressure homogeniser. Master of Engineering thesis, Dublin City University.
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The homogeniser is a machine that is mostly used to change the appearance and rheological properties of a fluid by means of a high pressure radial gap. It can be implemented to kill off harmful bacteria and organisms as well as reduce the size of individual components or particles to increase the shelf live of many products. The homogeniser can be used to release useful organic materials from within cells or microbes. The homogeniser can be found in small scale production and large scale production. The small scale production homogeniser allows smaller gap sizes but is restricted to lower flow rates in relation to the larger scale homogeniser.
The primary aim of this thesis is to determine optimum geometries for the small-scale high-pressure homogeniser in the disruption of anaerobic microbes from waste water sludge to release organic material to produce methane with maize crop. It is believed that breaking apart microbial walls of microbes in the sludge can release organic material that can further increase methane production and also reduce digester volume. In this case, the waste water sludge with microbes was implemented with a mixture of dry maize silage to produce methane by means of anaerobic conditions. The homogeniser is used to break up tough microbes in secondary waste water sludge to reduce digester volume and anaerobic methane production waiting times.
Geometries of the homogeniser and prototypes were generated using Gambit 2.3. Pressure, velocity and flow fields were estimated and analysed using Fluent 6.3. The model was estimated by means of a stationary microbe model. Shear forces on microbes were analysed for various positions along the streamline of flow and compared. The homogeniser setup with the highest peak shear forces was used as an optimum homogeniser setup. The initial homogeniser model was replicated from the original experimental homogeniser in the lab. Model simulations were validated from empirical formulae from other works. The optimised design made use of a 27.8˚ inlet chamfer with the valve gap chamfer diverging at 2.5˚ each side (valve seat and valve head) downstream of the valve beginning. The finalised optimised design is presented using Pro-Engineer in Appendix C.
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