Deformation analysis of the main components in a single Screw compressor

The single screw compressor is used in many fields such as air compression, chemical industry and refrigeration. During operation, different gas pressures and temperatures applied on the components can cause different degrees of deformation, which leads to a difference between the thermally induced clearance and the designed clearance. However, limited research about clearance design is reported. In this paper, a temperature measurement instrument and a convective heat transfer model were described and used to establish the temperature of a single screw air compressor’s casing, screw rotor and star wheel. 3-D models of these three main components were built. The gas force deformation, thermal-structure deformation and thermal-force coupling deformation were carried out by using a finite element simulation method. Results show that the clearance between the bottom of the groove and the top of star wheel is reduced by 0.066mm, the clearance between the side of groove and the star wheel is reduced by 0.015mm, and the clearance between the cylinder and the rotor is reduced by 0.01mm. It is suggested that these deformations should be taken into account during the design of these clearances

Effective Flow And Force Areas Of Discharge Valve In A Rotary Compressor

In this paper, two fluid–structure interaction (FSI) models of the discharge valve are presented to study the effect of partly covering the discharge port by the cylinder and the roller on the effective flow and force areas. One is the full FSI model and another is the simplified FSI model in which the discharge port is not covered and the cylinder shape is simplified to be cylindrical. The pressure in the compression chamber, the displacement of the valve reed, the volumetric flow rate through the valve and the gas force acting on the valve reed head are obtained by the two FSI model. The results comparison between the two FSI models shows the effective flow and force area in the full FSI model are much different from those in the simplified FSI model. The factors which affect the covering area of the discharge port must be taken into consideration in the calculations of these two areas

Pressure Loss Analysis of the Perforated Tube Attenuator

Gas pulsation produces excessive noise in the piping system of the reciprocating compressor and even causes damage in the piping and the machine. Therefore, it is very important for reasonable analysis and proper control of pressure pulsation. The perforated tube attenuator is widely applied in the compressor because of its favourable performance of acoustic attenuation. For the attenuator design, pressure loss and transmission loss are the two equally significant parameters characterizing its performance. Even if an attenuator can greatly reduce the compressor pressure pulsation, but cause large pressure loss, it will not be used yet. So it’s necessary to pursue the attenuator with low pressure loss as well as low pressure pulsation. The traditional method of calculating pressure loss of the attenuator is according to empirical formulas, which only fit for simple structures. But for the perforated tube attenuator, the flow is complex, and the empirical formulas are not available to calculate the pressure loss. Presently, CFD method is used to calculate pressure loss of the attenuator with complex structure. Most perforated attenuators could consist of hundreds of small holes distributed on the pipe, so three-dimensional flow models ensure the accurate solution. This paper predicts pressure loss of the perforated tube attenuator with various geometry parameters using CFD. A three-dimensional CFD model of the attenuator was established under the following assumptions: (1) The physical parameters of the solid and fluid domain of the attenuator are constant; (2) The flow is steady turbulent flow; (3) The influence of the gravity is ignored; (4) The inlet velocity of the attenuator is homogeneous without impulse effect. The standard - model is used in this paper. The flow through the attenuator follows the law of conservation of mass, law of conservation of momentum and the law of conservation of energy. The solution of the model was implemented with the FVM method of the commercial CFD code fluent. According to the CFD model, the following three aspects were analyzed: (1) The influence of the hole diameter on the pressure loss (2) The influence of porosities on the pressure loss (3) The influence of the inlet velocity on the pressure loss Based on analysis of the above three aspects, an attenuator with low pressure loss as well as low pressure pulsation was designed

Experimental Studies of The Multi-cylinders Compound Profile Meshing Pair

In order to improve the wear resistance of the meshing pair in Single Screw Compressor, our team developed the multi-cylinders compound profile which could be used in the meshing pair instead of the traditional profile. In this paper, the reliability and utility of the new profile was verified by an experiment. In this experiment, a designed multi-cylinders compound profile meshing pair was applied in an oil-flooded single screw air compressor as the experimental prototype, then the prototype ran 2000 hours continuously in the experimental platform. and the displacement was detected with changing discharge pressure and rotating speed. It is shown that the prototype has a steady displacement, and the energy efficiency grade is very close to the best grade. The displacement is slightly reduced with the discharge pressure arising, but the reduction is far less than the original single line profile meshing pair machine. These prove that the new pair has good sealing performance. A comparative observation on the star wheel profile is conducted at the end of test, and the results demonstrate that the nodular cast iron star wheel new designed has high wear resistant property and good hydrodynamic lubrication characteristic. Thus, the nodular cast iron can be used to make star wheel to reduce the cost of the single screw instead of the expensive PEEK material

Flexible-body Dynamics Simulation of Crankshaft Torsional Vibration System

Abstract:The crankshaft accidents due to vibration become severe with increasing number of rows of reciprocating compressors.The crankshaft vibration needs to be studied thoroughly to promote development of the reciprocating compressor.Early calculations of crankshaft torsional vibration was mainly with discretization method, the crankshaft is discretized into a series of lumped inertia and lumped stiffness,then calculate the swing angle of crankshaft in the gas force and inertia force,but because of the simplified calculation,which has low precision.The currently calculation method of crankshaft torsional vibration is simplified into an equivalent system model,the model is composed of a lumped mass disc,massless elastic shaft and a damping.In calculation the torsional natural frequency and forced vibration usually adopt the Holzer method and transfer matrix method,due to this method only calculation the crankshaft torsional direction, so it can only obtained the crankshaft natural frequency and vibration characteristics in the direction.To make the crankshaft torsional vibration calculation more accurately,we proposed a new calculation model based on the flexible multibody dynamics theory.The process of the model establishment and solving by ADAMS was introduced.The torsional vibration of a crankshaft, which often suffers from the crankpin fracture,was calculated before and after the structure change.Results show that before the structure change,the crankshaft natural frequency was closed to the excitation frequency,so that the tortional vibration amplitude of the crankshaft is very large.The stress of piston pins in the first and second row increase so rapidly along the directionof the cylinder center line that the impact factor ofthe crank pin bearing reache the upper limit,thus the oil film of it is damaged.After the structure change,the natural frequency of crankshaft is away from the excitation frequency,the vibration amplitude of the crankshaft torsional vibration decrease substantially,and the crankpin fracture does not happen anymore.This is a successful validation of the proposed calculation method

Research on Injected Effect and Heat-transfer Characteristics of Narrow-Slit Injection Orifice Used for the Screw Compressor

A narrow-slit injection orifice which is used for the screw compressor injection is described in this paper. Different from the traditional injection orifice, the orifice is slit shaped but not circular. Liquid which is injected by the narrow-slit injection orifice appears as a curtain shape so that the heat transfer area is increased. The cooling effect is enhanced and then the efficiency of the compressor is improved. The injected velocity of the orifice is simulated through the CFD software, and then the experiments are carried out. The study verified the accuracy of the simulation results. It will provide a theoretical foundation for the design of the narrow-slit injection orifice used for the screw compressor

Stress Analysis Of Key Components And Vibration Property Research Of The Meshing Pair In Single Screw Compressors

The single screw compressor(SSC) is widely applied to air compression, refrigeration, petrochemical industry, waste heat recovery, etc. Among SSCs, the respective strength and stiffness of the casing, screw rotor and gaterotor, where relative motions occur, play a key role on the machine running and clearance fit. Dynamic properties of the meshing pair directly affect the SSC’s vibration, as well as gaterotor’s wear-out failure. In this thesis, the strength, stiffness and dynamic characteristics of the meshing pair under different operation conditions or with components made of different materials were analyzed. Analytical method and FEM were combined to calculate and analyze the issues above. Main contents and conclusions are as follows: Stress and deformation analysis of key components were implemented by ANSYS Workbench. The results show that both the maximum stress of the casing and the deformation of the gaterotor are basically linear to the discharge pressure. The first six natural frequencies and the corresponding vibration modes of the screw rotor and gaterotor were obtained to analyze and predict their respective vibration properties. It turned out that natural properties of the screw rotor change little on account of rotation speed and damping. Neither the screw rotor nor the gaterotor would resonate. Some exploratory work about the coupling interaction between gaterotor and its support was done. It is concluded that the gaterotor would suffer the support’s collision excitations consequently

Analysis on Lubricant Film Force for Two Types of Meshing Pair Profile in Single Screw Compressor

Single screw compressors are widely used in various industrial fields, however the performance usually drops obviously after thousands of hours of operation due to the wear between the star-wheel and the gate rotor. A lot of meshing pair profiles and manufacturing methods are proposed to solve this problem. Thus, good oil lubrication conditions are conducive to improve the wear resistance of the meshing pair so as to increase the compressor‘s operation life. In this paper, the geometric models of the clearances for both profiles, a kind of multi-column profile and single-column profile for oil flooded compressors are carried out, and a mathematical lubrication model is used to analyses the oil lubrication. Results show that the torques caused by the oil film force on both sides of the star-wheel tooth are unbalanced. The total torques of the analyzed multi-column profile is smaller than that of the single column profile, which indicates a better lubrication condition. The analysis can also be used to optimize the profile design of the meshing pair of single screw compressors.