Thermo-Fluids Research Centre (TFRC)


Download link for and information about the Screw Compressor Optimal Rotor Profiling and Thermodynamics (SCORPATH) software from the Centre for Compressor Technology.

About the SCORPATH software

The Centre for Compressor Technology at City, University of London is entirely involved in design of superior rotor profiles and appropriate screw compressors and this is fully confirmed literally throughout the World. The dry and oil-flooded air compressors as well as refrigeration compressors in various configurations 2/3, 3/5, 4/5, 4/6, 5/6and 6/7 are created and calculated by use of our design software ‘SCORPATH’, which is based on a comprehensive mathematical model of the screw compressor eometry and working process and it is regularly checked by comparison with measured data obtained either on our experimental stands or by our numerous customers. Moreover, the families of our compressors were thoroughly tested by our customers who have published their results. We do not have a single reason to suspect that our further compressor designs would confirm our predictions in full.

The centre has worked for or with companies in Australia, China, England, Finland, France, Germany, India, Iran, Italy, Korea, Russia, Spain, Turkey and the U.S.A and in former Yugoslavia.

'N' rotor profiles for screw compressors, based on a patented rack  generation procedure, offer greater flow area, less leakage, smaller internal friction and greater lobe strength than any other known rotor profile. More specifically, we can design the rotor profiles within the envelope of your existing compressors, i.e. to retain your previous compressor design and retrofit the rotors only, or to design a new compressor(s) around the 'N' rotors. In both cases a substantial improvement of up to 6.5 % increase in capacity and 2- 2.5 % decrease in specific power will be achieved in comparison with any other rotors of the same size and compressor speed and inlet and outlet pressures.

Starting with these, or any other rotor profile types, the Centre can perform accurate performance predictions followed by complete detail design of compressors for any application.

Using 'SCORPATH' software for design of screw compressors,  developed in the Centre, full performance estimates can be carried  out on new designs of these and any other types of positive displacement machine. Product evaluation can thereby be completed before proceeding to manufacture and testing.

SCORPATH (Screw Compressor Optimal Rotor Profiling And THermodynamics) is a design tool package which calculates and presents screw compressors and their processes and systems. Its packed version is entirely placed into only one, 'SCORPATH' directory and consists of 445 files arranged in 5 subdirectories, of which 19 are executive, EXE files and 48 are FORTRAN source files, 77 script files and 37 graphics support files. The package is accompanied with the full FORTRAN compiler and a complete package of graphical presentation software. In the working version, the package consist of minimum 522 files. Additional files are mainly output data files. The package has two masks for a convenient user access, one is in DOS, another in Windows 9x, 2000, NT or XP environment driven either by the keyboard or mouse. A skilled and experienced user will use handy script files which are supplied to run SCORPATH efficiently when he inevitably founds the windows environment is, as usually, too complicated and insufficiently efficient as any other system dedicated to low-level computer users.

The software obtains accurate performance predictions followed by complete detail design of compressors for any application. Full performance estimates can be carried out on all types of screw machines. Product evaluation can thereby be completed before proceeding to manufacture and testing.

There exist several bundles and modules of SCORPATH at various levels. The most comprehensive is a full source version delivered together with compilers and output/graphical support to enable users to develop and upgrade the program according to their own needs and requirements. The simplest are single modular units which are the useful for a specialized user interested in specific tasks like screw compressor geometry calculation, thermodynamics of dry or oil flooded compressors, refrigeration package, tool profiling, compressor optimization, leakage minimization. Between these, one can find the optimal package which will respond to individual needs.  Main features of SCORPATH are:

Geometry Generation

General procedure for screw compressor geometry calculation  based on a given screw compressor profile. An example is given for a public domain profile. Sealing lines, blow-hole area and screw compressor volume are calculated here. Rotor flow areas, sealing lines and blow-hole area are also calculated here. A clearance distribution provides efficient and reliable rotor operation. Tool is  calculated and the unique tool-rotor procedure enables the customer to check the tool profile against any manufacturing errors. For a given built-in volume both, suction and discharge ports are calculated and transferred to a CAD system by the convenient interface.

If licensed with the 'N' profile rotors, the customer is entitled to the rotor generation procedure which is based on a unique rack profiling method.

This profile generation part of the package relies on the accurate graphical presentation which can downscale lengths to the tiny fraction of micrometers, like the applied software is. Any attempt to do plot the rotors in a commercial data-base software, like for example, Excel will fail because these software packages are absolute inferior in such graphical presentation.

More information.

Screenshot from the SCORPATH software

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Compressor cycle process, p-V diagram, mass flow, work and power, specific power and efficiencies Real fluid property routines: IIR, Lee-Kesler, NIST. Loads, force and torque calculations Compressor design optimization.

Since the screw compressor process is subjected to relatively high leakages and it is accompanied by oil flooding, standard preintegrated thermodynamic relations can not be applied to provide any accurate and reliable calculation. Only a system of  differential transport equations of continuity, momentum and energy solved simultaneously can give a satisfactory result. This was incorporated into SCORPATH from the beginning, however this has been noticed only recently causing all mayor screw compressor companies to switch their calculation to a differential calculation of the screw compressor process.

The system of differential equations, closed by a set of algebraic equations of state and thermodynamic properties, is solved by Runge-Kutta method of fourth order. This practically excludes any other programming language to be used except a high level translator, such FORTRAN, c and Pascal are. The first one, the most common in engineering practice is used here and all source codes are written in it.

Therefore any attempt to solve the differential equations of  thermodynamic process in a low-level data base system such as Excel is, will fail. Furthermore, any simplification of the differential approach to an algebraic one will lead to the practice recently abandoned in the screw compressor community and deteriorate the achieved level of accuracy.

However, it is possible and it is very welcome, to write the input and output files in some data-base form if it is found more convenient for the user than the ASCII form currently applied in SCORPATH. The package is so flexible that this can be conveniently done.

More information.

Screenshot from the SCORPATH software

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The following list of varieties of SCORPATH is referred here for your additional information.

SCORPATH can be delivered in the following bundles:

1. Full Source licence, SCORPATH complete (SGHTOR) (binary and source of the complete code)

2. Full Binary licence (GTHOR), the same functionality  as 1, but without the source code. This licence can be split into various independent modules for a separate purchase:
2.1 SCORPATH - G, Screw Compressor Geometry
2.2 SCORPATH - THOR, Thermodynamics, oil injection, refrigerants, compressor optimization
2.3 SCORPATH  - T, Tool Geometry

3. Demo and/or evaluation licence - free

4. One year maintenance/support - free
2 additional years maintenance/support upon request
4 additional years maintenance/support upon request

Each package is supplied either on CD Rom or distributed by e-mail. It is accompanied by appropriate user manual. Each package is supplied with adequate graphic subprograms which enable graphical presentations of the results.Binary versions are in DOS/Windows 3.1/95/98/2000/NT or available in Unix upon request. Source is given in Fortran-77. A full compiler and script makefiles are provided with the source licence. Maintenance and update is limited to the original source only.

All licences are perpetual and each purchase includes one year software maintenance and support which may be extended to 3 or 5 years which include yearly software updates. The software is licenced for a specific workstation, number of  copies is not limited within the purchaser company, however, the maintenance/support and software updates are limited to one per purchase. A training for your engineers in the rotor profile and compressor design will be provided through one week free of charge at City, University of London.

Although SCORPATH is undoubtedly a comprehensive software which considerably helps in the screw compressor design, it still needs a reasonable human input and can not in any circumstance replace a good compressor designer.

If you by some event once purchase a licence for 'N' rotors with us a full licence of the software package 'SCORPATH' will be provided free of charge as an integral parameter of the profile design which will enable you to modify your profiles.

I hope that this additional information keeps you better informed about our work in screw compressors and SCORPATH,  If you have any additional specific questions related to the profile and compressor you would like to be designed for your use, please let us know and we will be happy to answer them.