Approach To The Numeric Geometry Analysis of Positive Displacement Compressors, Its Application To A Single Screw Compressor Simulation And Verification By Experiment
Thermodynamic models to simulate positive displacement compressors are well known for a few decades already and can describe the compressor performance quite well. One of the most complex part of the simulation process however is the positive displacement compressor geometry simulation. In the current context, under geometry simulation, values of working compressor volumes, as well as cross-sections of port openings, at different shaft (rotor) angles are considered. In the current paper, as an example, the Greene formula approach was applied to a geometry simulation of a single screw compressor. Working chamber geometry was defined by “cutting “ it with the gate rotor blade; flute volume was computed using Greene formula; suction and discharge ports were intersected with this volume so that port opening contours were defined and their respective cross sectional areas were calculated. The results of this geometry simulation were applied for a thermodynamic model of a single screw compressor. Experimental investigation of a single screw working process using pressure transducers has been conducted. Geometry simulation data was applied to calculate compression work from experimental pressure traces. Pressure-volume diagrams obtained experimentally were compared to the simulated ones. Also, indicator work obtained from simulation and experiment, was compared to the power input to the shaft, and demonstrated good correlation.
Performance study on a single-screw compressor for a portable natural gas liquefaction process
Portable natural gas liquefaction devices are widely used to exploit unconventional natural gas resources and one of key components is a compressor. In this paper, a new natural gas liquefaction process is simulated and optimized and a single-screw compressor with 200 mm diameter is designed to be applied in this process. To verify the performance of the single-screw compressor, an experimental system was set up and performance parameters were studied, including volumetric efficiency, specific power rate, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil. The influence of the lubricating oil on the volumetric efficiency was also observed. Furthermore, the impact of actual compressor performance on the liquefaction process was also analyzed. The results indicate that the performance of the compressor changes greatly when it operates deviating from its design condition. The maximum volumetric efficiency, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil are 0.91, 0.64, 0.56 and 0.22, respectively. The minimum specific power rate is 6.5 kW·(m3·min−1)−1. In addition, the lubricating oil has a good effect of sealing so that the volumetric efficiency can be improved by 10.5%. Considering the actual performance of the single-screw compressor, specific power consumption of the process increases by 43.3%.
Computer Modelinq of an Oil Flooded Single Screw Air Compressor
A computer model of a single screw oil-flooded low pressure air compressor was developed which predicts the internal conditions based on certain empirical values. A characteristic thread technique is used for steady state operation. A polytropic process is used and the model will iterate for the polytropic coefficient to best correlate internal predictions with empirical values. The geometric variables and relationships used to describe the general cylindrical mainrotor-planar gaterotor single screw mechanism are developed. The control volumes and their corresponding governing thermodynamic relationships are defined. The equations used to model the leakage for the various paths are described. The results of the model are compared to the empirical data and the validity of the assumptions used to reduce the general equations is discussed.