Abstract:The maximum sphere method and the minimum cross-section method are proposed to calculate the interlobe clearance between two mating screw rotors and to determine the shapes and sizes of all the leakage paths. These two methods are inspired by the red-lead and tooth-contact pattern and can be used to evaluate the interlobe leakage and to design the mating rotor profiles. The combined results of these two methods provide the basis for an exact evaluation of the fluid leakage, and this feature increases flexibili… Show more
“…The decrease of clearances can increase the mass flow rate and volumetric efficiency, on the contrary, the enlargement of clearances will bring larger leakage amount. 24,25 In order to investigate the effects of the different clearance size on the mass flow rate, the interlobe clearance and radial clearance are varied by 0.06 mm and investigates separately. The case indicated with 0.18 and 0.24 reflects the size of interlobe and radial clearance gaps, respectively.…”
Section: Validation Of Performance Calculation By Experimental Resultsmentioning
confidence: 99%
“…For the calculation of the pump performance, the interlobe clearance was set to 0.12 mm and the radial clearance is set to 0.24mm, which is in Figure 22 Author submitted manuscript clearance during the working process which was the reason to set the initial clearance to the theoretical assembly values. The decrease of clearances can increase the mass flow rate and volumetric efficiency, on the contrary, the enlargement of clearances will bring larger leakage amount [23], [24]. In order to investigate the effects of the different clearance size on the mass flow rate, the interlobe clearance and radial clearance are varied by 0.06mm and investigates separately, The case indicated with 0.18 and 0.24 reflects the size of interlobe and radial clearance gaps respectively.…”
Section: Effect Of the Clearance Size On Leakage Lossesmentioning
modelling of twin-screw pumps based on computational fluid dynamics. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, doi: 10.1177/0954406216670684 This is the accepted version of the paper.This version of the publication may differ from the final published version.
Permanent
AbstractIncreasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps, presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well validated CFD (computational fluid dynamics) models. The novel structured numerical mesh consisting of a single computational domain for moving screw pump rotors was developed to allow 3-D CFD simulation of such machine possible. Based on Finite Volume Method (FVM), the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The CFD model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimise such machines in terms of clearance selection, shape of the ports, piping system etc. In future this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.
“…The decrease of clearances can increase the mass flow rate and volumetric efficiency, on the contrary, the enlargement of clearances will bring larger leakage amount. 24,25 In order to investigate the effects of the different clearance size on the mass flow rate, the interlobe clearance and radial clearance are varied by 0.06 mm and investigates separately. The case indicated with 0.18 and 0.24 reflects the size of interlobe and radial clearance gaps, respectively.…”
Section: Validation Of Performance Calculation By Experimental Resultsmentioning
confidence: 99%
“…For the calculation of the pump performance, the interlobe clearance was set to 0.12 mm and the radial clearance is set to 0.24mm, which is in Figure 22 Author submitted manuscript clearance during the working process which was the reason to set the initial clearance to the theoretical assembly values. The decrease of clearances can increase the mass flow rate and volumetric efficiency, on the contrary, the enlargement of clearances will bring larger leakage amount [23], [24]. In order to investigate the effects of the different clearance size on the mass flow rate, the interlobe clearance and radial clearance are varied by 0.06mm and investigates separately, The case indicated with 0.18 and 0.24 reflects the size of interlobe and radial clearance gaps respectively.…”
Section: Effect Of the Clearance Size On Leakage Lossesmentioning
modelling of twin-screw pumps based on computational fluid dynamics. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, doi: 10.1177/0954406216670684 This is the accepted version of the paper.This version of the publication may differ from the final published version.
Permanent
AbstractIncreasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps, presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well validated CFD (computational fluid dynamics) models. The novel structured numerical mesh consisting of a single computational domain for moving screw pump rotors was developed to allow 3-D CFD simulation of such machine possible. Based on Finite Volume Method (FVM), the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The CFD model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimise such machines in terms of clearance selection, shape of the ports, piping system etc. In future this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.
“…Cusps on one rotor engage with the cycloid sections of another rotor to form a point-seal (point-meshing) between two rotor surfaces. Figure 1 shows the transverse rotor profile, the generated normal rack and the 3-D contact line for a pair of typical screw rotor, 9 named Type I rotor. Five sections are defined for this type of rotor profile, orderly consisting of one outer circular arc A-B, one epicycloid B-C, one epicycloid C-D, one inner circular arc D-E and one epicycloid E-A.…”
Section: Meshing Clearance Calculation Methods For Screw Rotor Pairs Wmentioning
confidence: 99%
“…The ICCD was found to give a good estimation of the clearance distribution for different profiles and for non-conjugating tooth profiles on two mating rotors. Later, Fong and Huang 9 improved the ICCD method using the maximum sphere method and the minimum cross-section method to evaluate the inter-lobe clearance between two mating screw rotors and determine the shapes and sizes of all of the leakage paths. Buckney et al.…”
In practical production, it is impossible even to measure the inter-lobe (meshing) clearance of a screw rotor pair. However, understanding of the clearance distribution is essential since it is a major leakage path which greatly affects the twin-screw pump performance. Previous publications did not disclose explicit detail on how to calculate the meshing clearance for screw rotor pairs with point-meshing features. Therefore, this study proposes a meshing clearance calculation method for screw rotor pairs with point-meshing features. The complex meshing clearance can be simply determined by calculating the shortest distance between two normal-rack profiles generated using point-enveloping principle. Clearance distributions are much more intelligible to be exhibited on a 3-D contact line and the rotor profile. Due to its immeasurability in practice, the adaptability and the solution accuracy of the proposed numerical method are verified by applications on different rotor profiles and comparisons with measured results from a 3-D CAD model. The meshing clearance in a variable-pitch screw rotor pair and the clearance adjustability are also illustrated through the proposed examples.
“…The characteristics of flow field in clearances play an important role in determining the performance (such as leakage rate, volumetric efficiency) of rotary screw machines. 42,43 When designing screw rotors, two types of clearances need to be considered, radial clearance and inter-lobe clearance (Figure 17). Figure 17.Radial clearance and inter-lobe clearance in screw pump.…”
Section: Mechanism Of Clearance Cavitation In Twin-screw Pumpsmentioning
This is the accepted version of the paper.This version of the publication may differ from the final published version.
Permanent repository link
AbstractIn order to investigate the flow characteristics and the formation process of cavitation in twinscrew pumps, three-dimensional CFD (Computational Fluid Dynamics) numerical analysis has been carried out. A conformal structured moving mesh generated by an in-house code SCORG was applied for the rotor domain. The VOF (Volume of Fluid) Method has been adopted for dealing with the liquid-gas two-phase flow, while the bubble dynamics was handled by a homogenous cavitation model. By changing the rotation speed and discharge pressure, the intensity, distribution area and variation of cavitation at different rotor angle were obtained. The effects of rotation speed and discharge pressure on cavitation characteristics have been analysed. Calculation results with cavitation model are compared with the results without cavitation and the experimentally obtained values. The influence of cavitation on the performance of a screw pump in terms of the mass flow rate, pressure distribution, rotor torque and the shaft power have been analysed and discussed. For analysis of cavitation in clearances, a 2-D numerical model which includes radial and inter-lobe clearances was used. The relationship between volumetric efficiency and cavitation intensity was developed by variation of boundary conditions.
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