City Research Online

Abstract

A twin screw expander’s working chamber can be modelled in detail using 3D CFD and for a given operating condition the rotor configuration can be improved to achieve optimum internal expansion and maximize power recovery. In literature, it has been reported that use of an accurate fluid property definition such as NIST REFPROP database is essential to reproduce accurate pressure and temperature changes in the expansion chamber. However, when applied in the framework of a transient, 3D CFD computation, such databases have shown to increase the computational time by more than 50%. A numerically efficient alternative is to use a cubic equation of state. In this paper, some of the cubic equation of state definitions available in the ANSYS CFX flow solver for dry real gas properties have been evaluated in the application of an R245fa twin screw expander. The expander has a 4-5 lobe combination, ‘N’ rotor profile and a built-in volumetric expansion ratio of 4.5. Expander performance has been evaluated at 544 kPa filling pressure at 94.26℃ using SCORG generated rotor grids for expander chamber, port grids for high pressure and low pressure ports. CFD results have been reported in terms of the internal pressure and temperature variation, mass flow rate, and indicated power output. Under the same operating condition, the CFD computational model is evaluated using NIST REFPROP database and the deviation in results are compared.

Publication Type:	Conference or Workshop Item (Paper)
Additional Information:	Copyright, the authors, 2021.
Publisher Keywords:	Twin Screw Expander; CFD; SCORG; Real Gas Cubic Equation of State; R245fa; NIST-REFPROP
Subjects:	Q Science > QC Physics T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering

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