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Title: A computational and experimental investigation into the performance of industrial refrigeration helical oil separators
Author: Brown, Lewis
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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An oil separator is a key component in an industrial refrigeration system as it prevents the compressor discharge oil creating a liquid film on the internal walls of the heat exchangers which leads to a reduction in efficiency of the system and increased operating costs. The Henry Technologies helical oil separator operates in refrigeration systems globally yet there is currently no available data on the performance of the unit. In this investigation the performance of the helical separator has been captured for a range of operating conditions using a custom built test facility. An assessment has also been made to determine the ability of current state-of-the-art computational models to predict the performance of the separator. The computational modelling approach used in this study was the Euler-Lagrange, which requires the solution of the continuous gas phase prior to the injection of the dispersed liquid phase. A Perspex replica of the helical separator being investigated was used to carry out LDA velocity component measurements and produce laser sheeting images which could be used to validate the single phase computational model. The unsteady nature of the swirling flow field in the separator, as a result of the PVC, required the implementation of the advanced LES turbulence model with high order discretization schemes. Separation efficiency and pressure drop measurements have also been obtained for various gas and liquid flow rates at 0 BarG and 3 BarG working pressures which clearly demonstrate that as the gas flowrate and operating pressure decreases the separation efficiency also decreases. The flow regime at the inlet to the separator consists of a heavily stratified liquid film with an annular dispersed droplet mist. Since the DPM model only models the trajectories of droplets; experimental data was obtained which characterised the performance of the separator subject to a droplet only mist with the liquid film being extracted and quantified just upstream of the inlet. The Malvern Spraytec laser diffraction apparatus was employed to determine the droplet size and distribution entering and leaving the separator allowing a grade-efficiency curve to be produced for the unit. Using the size, distribution, liquid flowrate and separation efficiency of the separator for the droplet mist only condition the DPM model was used to simulate the droplet trajectories with the validated single phase gas flow model. The droplet breakup and liquid film models were explored to determine the optimum modelling criteria which could predict the droplet separation efficiency obtained through the experimental testing. Using the information obtained through the experimental testing, computational simulations and the theory presented within the literature for droplet separation, design improvements have been suggested for the Henry Technologies separator. These include increasing the discharge flowrate through the no mesh separator, assessing a unit with a tangential inlet and compressed helix, designing a wire mesh attachment for the separator inlet and a swirl generator to be located in the centre tube. All design improvements resulted in increased separation efficiency but were coupled with an increase in pressure drop.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available