Details of Grant 

EPSRC Reference:	EP/C541456/1
Title:	Experimental and Theoretical Investigation of Fluid Flow in Screw Compressors
Principal Investigator:	Stosic, Professor N
Other Investigators:	Kovacevic, Professor A Nouri, Professor JM Arcoumanis, Professor C
Researcher Co-Investigators:
Project Partners:	Lotus Cars Ltd Syltone Ltd Trane (UK) Ltd
Department:	Sch of Engineering and Mathematical Sci
Organisation:	City, University of London
Scheme:	Standard Research (Pre-FEC)
Starts:	01 August 2005	Ends:	31 July 2008	Value (£):	226,795
EPSRC Research Topic Classifications:	Fluid Dynamics
EPSRC Industrial Sector Classifications:	Energy
Related Grants:
Panel History:
Summary on Grant Application Form
One of the most common types of machine used to compress gases is known as a twin screw compressor. This comprises a pair of meshing rotors with helical grooves machined in them contained in a casing, which fits closely round them. The rotors and casing are separated only by very small clearances. The rotors are driven by an external motor and mesh like gears in such a manner that as they rotate the space formed between them and the casing is reduced progressively. Thus any gas trapped in this space is compressed. The geometry of such machines is complex and the flow of the gas being compressed within them is difficult to analyse because it occurs in three stages. Firstly, gas enters between the lobes through an inlet port at one end of the casing during the start of rotation. As rotation continues, the space between the rotors no longer lines up with the inlet port and the gas is trapped and thus compressed. Finally, after further rotation, the opposite ends of the rotors pass a second port at the other end of the casing, through which the gas is discharged. The whole process is repeated between successive pairs of lobes to create a continuous but slightly pulsating flow of gas from low to high pressure. Because of the complex geometry of the machine and the intermittent nature of the flow process, up till recently it has been impossible to calculate exactly how the flow occurs within the machine, especially since oil is often injected with the gas to cool it as it is compressed and lubricate the rotors as they revolve. Recent analytical work has been carried out to analyse the flow in these machines by a procedure known as computational fluid mechanics (CFD). This, effectively divides the space within the compressor into a large number of small cells in each of which the gas properties are considered to be uniform but marginally different to those in the cells adjacent to them. This proposal is to attempt to validate and correct this model, if necessary, by obtaining measurements of flow within such a machine. Two complementary methods are proposed to obtain these measurements. One of these is known as Laser Doppler Velicometry (LDV) and the other as Particle Image Velocimetry (PIV). These, which essentially visualise and quantify the flow, will be complemented by measurements of the internal pressure and temperature during the compression process. To carry this out, a twin screw compressor will be installed in an existing test rig, suitably modified, and measurements of the fluid velocity distribution taken at various planes across the compressor, together with the associated pressure and temperature and power consumption. The pressure, temperature and flow field measurements will then be compared with calculations using the in-house CFD code, developed for this purpose, and a more simple one-dimensional flow analysis, which, also, has already been developed by the investigators. The results will be used to validate the computational models. In addition, in order to explore possible advantages of oil-flooded compressors versus machines operating without oil injection, experiments and calculations will be combined to allow determination of the oil distribution within the compressor and identify the optimum position for the oil injection nozzle in the next generation of twin screw compressors.
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Organisation Website:	http://www.city.ac.uk