Abstract
Growing demands for energy are motivating researchers to conduct in-depth analysis of positive displacement machines such as oil-injected screw compressors which are frequently used in industrial applications like refrigeration, oil and gas and air compression. The performance of these machines is strongly dependent on the oil injection. Optimisation of oil has a great energy saving potential by both increasing efficiency and reducing other impacts on the environment. Therefore, a three-dimensional, transient computational fluid dynamics study of oil injection in a twin-screw compressor is conducted in this research. This study explores pseudo single-fluid multiphase (SFM) models of VOF (Volume of Fluid) and a mixture for their capability to predict the performance of the oil-injected twin screw compressor and compare this with the experimental values. SCORGTM (Screw Compressor Rotor Grid Generator) is used to generate numerical grids for unstructured solver Fluent with the special interface developed to facilitate user defined nodal displacement (UDND). The performance predictions with both VOF and mixture models provide accurate values for power consumption and flow rates with low deviation between computational fluid dynamics (CFD) and the experiment at 6000 RPM and 7.0 bar discharge pressure. In addition, the study reflects on differences in predicting oil distribution with VOF, mixture and Eulerian-Eulerian two-fluid models. Overall, this study provides an insight into multiphase flow-modelling techniques available for oil-injected twin-screw compressors comprehensively accounting for the details of oil distribution in the compression chamber and integral compressor performance.
Highlights
Twin-screw compressors have been widely used in compression processes due to their advantages such as compact structure, stable operation and high efficiency
This study provides an insight into multiphase flow-modelling techniques available for oil-injected twin-screw compressors comprehensively accounting for the details of oil distribution in the compression chamber and integral compressor performance
Another solver used for a case study of oil-injected twin-screw compressors is Pumplinx which has only one multiphase flow model available VOF [18]
Summary
Twin-screw compressors have been widely used in compression processes due to their advantages such as compact structure, stable operation and high efficiency. A parametric study on oil injection variants conducted by Stosic et al [6] concluded that oil mass flow and oil port position had more significant effect on integral performance. Kovacevic [10,11,12] made a breakthrough in CFD modelling of screw machines by developing a methodology to produce block-structured grids for deforming domains and this was further developed to form single domain-type mesh This had resulted in better solution accuracy for single phase flow of air in oil free compressor [13,14]. In Fluent, the interface between two phases is reconstructed for every time step based on calculated volume fraction distributions Another solver used for a case study of oil-injected twin-screw compressors is Pumplinx which has only one multiphase flow model available VOF [18]. How is the oil distributed within the compression chamber for various multiphase flow models and what is its effect on integral performance?
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