Mathematical modelling and computer simulation are now employed extensively for the analysis and design optimisation of screw compressors and by their use, new screw rotor profiles have been developed to improve machine performance. Descriptions of this are given is given in publications available on the City Compressor Centre web site, which contain details of various approaches to one dimensional flow analysis of screw compressors and how this is used to estimate performance.

The software developed and used by the authors for the conceptual as well as the preliminary design of screw machines is called SCORPATH – Screw Compressor Rotor Profiling and Thermodynamics. It calculates and optimises compressor performance for a specified duty. To start the procedure of rotor profiling, the profile point coordinates in the transverse plane of one rotor, and their first derivatives, must be known. The full rotor and compressor parameters, in the form of rotor throughput, rotor displacement, size of leakage flow area, as well as suction and discharge port coordinates are calculated from the rotor transverse plane coordinates and rotor length and lead. They are later used as input parameters for the calculation of the thermodynamic and fluid flow processes within the screw compressor as well as for further design tasks, such as the generation of detailed drawings.

The algorithm of the thermodynamic and flow processes used is based on a mathematical model comprising a set of equations which describe the physics of all the processes within the screw compressor. Press here for full details.

Depending on their field of application and whether they operate in the dry or oil-flooded mode, the requirements for optimum design of screw compressor rotors and other elements differ for each application and working fluid being compressed. Multivariable optimisation therefore should be employed as an important element in the design procedure, while optimisation targets must be set according to the design requirement. Thus, if high efficiency is required, the specific power or adiabatic and volumetric efficiencies will be targets.  However, if the compressor capacity is to be maximized to keep the cost to a minimum, then compressor flow will be the optimisation target.  A box constrained simplex method was used here to find the local minima.