Weifeng Wu

A Multicolumn Envelope Meshing Pair for Single Screw Compressors

This paper introduces a new meshing pair profile envelope by multicolumn in single screw compressors. The screw groove flank of the new meshing pair is a multisegment surface, and the star-wheel tooth flank consisted of multicylindrical surfaces. When the compressor is operating, the position of the contact line on the tooth flank with the screw groove flank uniformly moves in one revolution, which is rather different from the stationary contact position of existing meshing pair profiles. The new meshing pair will result in the improved wear-resistance and longer operation life, lower gas leakage, and higher efficiency of the compressor.

Simulation of the surface profile of the groove bottom enveloped by milling cutters in single screw compressors

In machining of a single screw compressor, the milling technique of screw rotor grooves with cylindrical milling cutters has far higher machining efficiency than turning. But, the screw groove bottom surface produced by the flat end of milling cutters will fail to mesh with the flat tooth tip hermetically, and thus give rise to compressed gas leakage. This paper carries out a mathematic simulation of the screw groove bottom surface profiles. The research brings screw groove bottom profiles machined by different cylindrical milling cutters to light, and provides some references for designing the column envelope meshing pairs in single screw compressors.

Geometric Design Investigation of Single Screw Compressor Rotor Grooves Produced by Cylindrical Milling

Cylindrical milling of a screw rotor groove in a single screw compressor has higher machining efficiency than turning. However, the screw groove bottom produced by the flat end of the milling cutter fails to mesh hermetically with the flat tooth tip due to the oversized clearance between them. The clearance forms two leakage paths leading to a compressed gas leakage. The shape of the path is roughly the same as that of two parallel oblate divergent nozzles in an inverse orientation. A mathematical simulation is presented for the surface profile of the screw groove bottom for a single screw compressor generated using several cylindrical milling cutters. The results contribute to improving the design of the meshing pairs in the single screw compressor.

Numerical investigation on the expansion of supercritical carbon dioxide jet

Supercritical carbon dioxide (SC-CO2) fluid is characterized by low rock breaking threshold pressure and high rock breaking rate. Meanwhile, SC-CO2 fluid has relatively low viscosity near to gas and high density near to liquid. So, it has great advantages in drilling and rock breaking over water. In this paper, numerical study of SC-CO2 flowing through a nozzle is presented. The purpose of this simulation is to ascertain why the SC-CO2 jet flow has better ability in drilling and rock breaking than the water jet flow. The simulation model was controlled by the RANS equations together with the continuity equation as well as the energy equation. The realizable k-epsilon turbulence model was adopted to govern the turbulent characteristics. Pressure boundary conditions were applied to the inlet and outlet boundary. The properties of carbon dioxide and water were described by UDF. It is found that: (1) under the same boundary conditions, the decay of dimensionless central axial velocity and dynamic pressure of water is quicker than that of the SC-CO2, and the core length of SC-CO2 jet is about 4.5 times of the nozzle diameter, which is 1 times longer than that of the water; (2) With the increase of inlet pressure or the decrease of outlet pressure, the dimensionless central axial velocity and dynamic pressure attenuation of water keeps the same, while the decay of central axial velocity of SC-CO2 turns gentle; (3) the change of central axial temperature of SC-CO2 is more complex than that of the water.

Geometrical Design and Investigation of a New Profile of the Three Screw Pump

This paper presents a new edge blunting method of the three screw pump rotor with an elliptic arc and equations of the rotor profile after edge blunting. Through comparisons of different geometrical parameters of the pump, i.e., flow area, contact line length per lobe, blow hole area, etc., the new profile is proved to be better than the existing profiles of the three screw pump. The new streamlined profile, with a significantly smaller blow hole area, is of reference significance for the optimization design and further improvement of three screw pump.

Design of the Curved Flank for the Star-Wheel Tooth in Single Screw Compressors

The wear of star-wheel teeth is an important problem in single screw compressors. In order to prolong the service life of star wheels, a new curved flank of the tooth is proposed. Section profile of the tooth flank is a curve, which could be elliptical, hyperbolic, involute, or new defined. The screw groove flank is the envelope surface corresponding to the surface of the tooth flank. During the tooth meshing with the groove, the contact line moves in the tooth flank area.

Numerical investigation on the impact of the converging angle of the suction chamber on annular jet pumps

The internal flow of an annular jet pump is an annular wall jet developed in a limited space, which is affected by its structure, shape, area ratio and flow rate ratio. In this paper, numerical simulation of an annular jet pump with area ratio A=1.75 was conducted based on realizable k-e turbulence model. And the impact of the converging angle of the suction chamber to the pump performance and the expansion of annular jet is investigated. According to the simulated results, the following conclusion is obtained. With the converging angle of the suction chamber (α) being 20°, the pump performance turns out to be the best. And with the increasing α, the maximal axial velocity and the squeezing effect to the annular jet are larger, while the mixing level of the two flows drops. In addition, the half-width of the annular jet, in the suction chamber, is proportional to tan(α/2) which is the tangent of the half angle of the suction chamber.

Research of laminar liquid flow in asymmetric narrow channels

Purpose – The purpose of this paper is to find a solution of laminar liquid flow in asymmetric narrow channels. In many cases, an intuitive solution is much more useful and necessary for engineering applications, although numerical solutions can be obtained.Design/methodology/approach – The Navier‐Stokes equations of laminar liquid flow in asymmetric narrow channels are simplified based on geometric characteristics of narrow channels, physical characteristics of liquid and boundary conditions. The simplified Navier‐Stokes equations are solved theoretically. Verification of the obtained results is carried out based on comparing with the Jeffery‐Hamel flow, which is an exact solution of liquid flow in convergent or divergent channels proposed by Jeffery.Findings – This paper proposed an intuitive solution of laminar liquid flow in asymmetric narrow channels. Obtained results show that the solution can provide a fairly precise flowrate, when a ratio between the width of the channel and the curvature of the b...

Numerical analysis of bubble dynamics in the diffuser of a jet pump under variable ambient pressure

Recent studies have shown that the collapse of cavitation bubbles in a jet pump can generate an extremely high pressure with many potential applications. The dynamics of the bubble is governed by the Rayleigh-Plesset equation. With the bubble dynamics equation and the heat and mass transfer model solved with the Runge-Kutta fourth order adaptive step size method, the oscillations of the bubble in the diffuser of the jet pump are assessed under varied conditions. To obtain the pressure variation along the diffuser, the Bernoulli equation and the pressure measured in experiment are coupled. The results of simulation show that a transient motion of the bubbles can be obtained in the diffuser quantitatively, to obtain the pressure and temperature shock in the bubble. Moreover, increasing the outlet pressure coefficient would result in a more intense bubble collapsing process, which can be used in the subsequent studies of the cavitation applications. The predictions are compared with experiments with good agreement.

Hydrodynamic lubricating characteristics of water flooded single screw compressors based on two types of meshing pair profile

Reliability of the traditional single screw compressor (SSC) is poor since its discharge capacity decreases sharply. This is because that the lubrication between the screw and the gate-rotor meshing pair is poor, which leads to a rapid abrasion of the meshing pair. In this paper, a simulation model is established to analyze the lubrication problem of the meshing pair in the SSC. Based on the traditional single straight line enveloped meshing pair profile and the new proposed multi-columns-enveloped meshing pair profile, the hydrodynamic lubricating characteristics of the water-flooded single screw compressor are investigated. Results show that the water film can keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the optimized multi-columns-enveloped meshing pair, but the water film cannot keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the single straight line enveloped meshing pair. A prototype of the water flooded SSC with the optimized multi-columns-enveloped meshing pair was developed and has passed a 2000-h endurance test without discharge capacity reduction.