transient conditions, start/stop mode, screw compressors
Oil injected screw compressors used for air applications and refrigeration are usually installed in simple packages which often do not include oil pump for supply of oil to the bearings and the working chamber. The period of an unlubricated operation depends on the size of the oil system and the length of the discharge piping. When the back pressure reaches the chamber pressure, a normal mode of lubrication will start. Due to the lack of lubrication, rotors will be in direct contact with insufficient or no oil film between them, while the pressure in the compression chamber will increase causing the temperature to rise. The leakage flow will be higher than normal which will increase the overall temperature in the compression chamber. It is expected that some surface damage may occur on the rotors. In a case of a frequent start-stop mode, such operation may cause quick wear and rapid decrease in thecompressor performance. This paper is expected to address such issues and to define a scope of work required to understand the oil flooded compressor process in a transient operation mode. This will allow prediction of wear in such compressors and will give some insight to the required modifications to prevent these issues and increase the compressor reliability.