Operation and performance of screw machines with high built-in volume ratio

A performance calculation of a screw compressor with increased built-in volume ratio was performed in this paper to establish how increased built-in volume ratio influences its efficiency. It is known that screw compressors have limited built-in ratio which is determined by their standard discharge port size and position. However, if the discharge port is reduced beyond its cusp position, the screw machine built-in volume is increased. In such a case, influence of the oil volume in the air-oil mixture of oil-flooded compressors increases the machine built-in volume further. The performance improvement achieved if the built-in volume ratio is doubled in comparison with the standard port during the machine operation at high pressure ratio of more than 20, is up to 26% for the specific power and adiabatic efficiency. This confirms superiority of the reduced size high pressure port for compressors which operate at high pressure ratio

Experimental investigation on water injected twin screw compressor for fuel cell humidification

A water injection in Twin Screw compressors was examined in order to develop effective humidification and cooling schemes for fuel cell stacks as well as cooling for compressors. The temperature and the relative humidity of the air at suction and exhaust of the compressor were monitored under constant pressure and water injection rate and at variable compressor’s operating speeds. The experimental results showed that the relative humidity of the outlet air was increased by the water injection. The injection tends to have more effect on humidity at low operating speeds/ mass flow rates. Further humidification can be achieved at higher speeds as higher evaporation rate becomes available. It was also found that the rate of power produced by the fuel cell stack was higher than the rate used to run the compressor for the same amount of air supplied. The efficiency of the Balance-Of-Plant (BOP) was therefore higher when more air is delivered to the stack. However, this increase in the air supply needs additional subsystems for further humidification/ cooling of the BOP system

The influence of port shape on gas pulsations in a screw compressor discharge chamber

Gas pulsations in suction and discharge chambers are a significant source of noise in screw compressors. This paper shows how such effects in the discharge chamber are influenced both by the compressor operating conditions and its geometric characteristics. An area function is identified for the discharge port as an important parameter influencing the gas pulsations and it is shown how their amplitude can be reduced by optimization of the port shape

Some aspects of laboratory testing and computer modelling of two-stage compressors with inter and after-cooling

Laboratory testing and computer simulation of a two-stage reciprocating air compressor with inter and after-cooling was undertaken with the purpose of studying the physical processes occurring in the compressor and obtaining information useful for design purposes. The testing includes measurements of instantaneous temperature and pressure in suction and delivery chambers and interconnecting pipes in both cylinders, instantaneous torque and average quantities, during the steady and transient state operation. Results are presented and the problems are discussed. The suitability of the micro-thennocouple for measurement of instantaneous temperatures, its dynamic behaviour and strength limitations, as well as mounting and calibration problems are considered. The measurement of pulsating pressure by means of piezoelectric and capacitive transducers in combined use are presented with specific reference to the effect of transducer location. Results are reported of the computer modelling of the thermodynamic processes including the unsteady gas flow in the piping system with friction and heat transfer effects, and comparison made with experimental data. Some practical implications are discussed of the testing and computer modelling upon desig

Development and Design of Energy Efficient Oil-Flooded Screw Compressors

It is estimated that about 17% of the world's generated power is used for compression. Thus all, even minor improvement of the efficiency of compressors will substantially reduce CO2 emission. This paper presents development of family of energy efficient oil-flooded screw compressors for Kirloskar Pneumatic Company Ltd. The developmental techniques adopted to improve efficiency such as introduction of superior 'N' rotor profile, rotor clearance management, performance calculation using 3D CCM (Computational Continuum Mechanics), direct parametric interface to CAD (Computer Aided Design), which contains bearing selection for complete 3D solid modelling. Also, contemporary prototyping and experimental investigation is supported by the fully computerised data acquisition and processing. The cumulative improvement of all these elements of the design process resulted in a very efficient machine which guarantees the competitive position of Kirloskar Pneumatic Company Limited in the screw compressor market

Some aspects of laboratory testing and computer modelling of two-stage compressors with inter and after-cooling

Laboratory testing and computer simulation of a two-stage reciprocating air compressor with inter and after-cooling was undertaken with the purpose of studying the physical processes occurring in the compressor and obtaining information useful for design purposes. The testing includes measurements of instantaneous temperature and pressure in suction and delivery chambers and interconnecting pipes in both cylinders, instantaneous torque and average quantities, during the steady and transient state operation. Results are presented and the problems are discussed. The suitability of the micro-thennocouple for measurement of instantaneous temperatures, its dynamic behaviour and strength limitations, as well as mounting and calibration problems are considered. The measurement of pulsating pressure by means of piezoelectric and capacitive transducers in combined use are presented with specific reference to the effect of transducer location. Results are reported of the computer modelling of the thermodynamic processes including the unsteady gas flow in the piping system with friction and heat transfer effects, and comparison made with experimental data. Some practical implications are discussed of the testing and computer modelling upon desig

CFD Analysis of Oil Flooded Twin Screw Compressors

Modelling of screw compressors using Computational Fluid Dynamics (CFD) offers better insight into the working chamber of twin screw machines when compared with chamber models. As shown by authors in earlier publications, CFD models predict performance of dry gas and refrigeration compressors fairly accurately. However numerical flow models used for modelling of oil flooded twin screw compressors are still at the development stage. This is mainly due to the lack of understanding of the flow complexity and the techniques used for solving coupled equations that represent interactions between the gas and the oil in such machines. This paper presents the modelling approach used for calculation of the performance of an oil flooded screw compressor. It requires a structured numerical mesh which can represent all moving parts of the compressor in a single numerical domain. Such mesh is generated by SCORGTM using novel boundary distribution technique called casing-to-rotor conformal boundary mapping. A test oil injected twin screw compressor with rotor configuration 4/5 and 127 mm main rotor diameter was measured in the compressor rig of the Centre for Compressor Technology at City University London. Measurements of the chamber pressure history and integral parameters of the compressor such as mass flow rate of gas and oil, indicated power and temperatures are used for the comparison with CFD results. The analysis showed a close match in the prediction of the mass flow rates of gas. The indicated power obtained by CFD predictions matched well with the measured shaft power. The model provided an exceptional visualization of the interaction of gas and oil inside the compression chamber. The mixing of the phases, distribution of oil, heat transfer between gas and oil and also effects on sealing due to high oil concentration in leakage gaps were well captured