Submission
ANALYSIS OF REAL GAS EQUATION OF STATE FOR 3D CFD MODELLING OF TWIN SCREW EXPANDERS
DOI: 10.18462/iir.compr.2021.0434
Session: Rotary, scroll, screw compressors 1
Accept state: Submission accepted
Authors
| Name | Organization | |
|---|---|---|
| Sham Rane, PhD | City, University of London | |
| Ahmed Kovačević, PhD | City, University of London | |
| Matthew Read, PhD | City, University of London | |
| Nikola Stošić, PhD | City, University of London |
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. Special attention is required in the design of the high-pressure port to minimize filling pressure loss. In literature, it has been reported that use of an accurate fluid property definition such as NIST – REFPROP or CoolPROP database is essential to reproduce accurate pressure and enthalpy 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 2.0. Expander performance has been evaluated at 5.57 bar filling pressure at 82℃ using SCORG generated rotor grids for expander chamber, port grids for high pressure and low pressure ports. Observed differences in the CFD results have been reported in terms of the internal expansion pressure and temperature variation, mass flow rate, and indicated power output. Local variation of enthalpy in the main and gate rotor chambers has been compared. Under the same operating condition, the CFD computational model is evaluated using NIST-REFPROP database and the deviation in results with cubic equation of state are compared.
Keywords
Twin Screw Expander
CFD
SCORG
Real Gas Cubic Equation of State
R245fa
NIST-REFPROP