Search Results (13)

In order to achieve high-quality repair of complex curved parts, a remanufacturing process method utilizing laser cladding and reverse engineering technology is proposed to be implemented by robots. This study focuses on the oscillating helical surface of a screw pump rotor. A single-pass laser cladding test is conducted using Response Surface Methodology (RSM) to construct a predictive model and identify optimal process parameters. The model’s accuracy is validated through analysis of variance (ANOVA) and index verification, while the optimal lap rate is determined through multi-pass laser cladding testing. Using reverse engineering technology, the generation of laser cladding paths for complex surfaces is explored, and the trajectory planning for the laser cladding robot is carried out. Simulations and experiments of robotic laser cladding on complex surfaces are performed, with the optimal process parameters guiding both the experiment and simulation. The optimum single-pass cladding layer, with a lap rate of 25.6%, is achieved when the laser power is 2217 W, the powder feed rate is 2.86 r/min, and the scanning speed is 400 mm/min. The study successfully plans the path for laser cladding on complex curved parts, verifying its feasibility and effectiveness, verifying that there is good metallurgical bonding between the cladding layer and the substrate, and helping to select the appropriate process parameters that are consistent with the requirements of a particular application, thus providing valuable guidance for the remanufacture of failed metal parts. Full article

To address wear failure in screw pump stator and rotor friction pairs, this study constructed a numerical model of a rhombus-like micro-dimple texture on friction pair surfaces based on the scale structure of rhombus rattlesnakes. The model was based on the fluid dynamic pressure lubrication mechanism. The CFD method was used to calculate the bearing capacity, friction coefficient, flow field pressure distribution, and flow trace distribution of an oil film carrying surface. The effects of the area rate, depth, shape, and angle of the rhombus-like dimple texture and the actual well fluid viscosity of shale oil on the surface lubrication performance of screw pump stator and rotor friction pairs were analyzed. The results demonstrated that increasing the texture area rate and the angle of the long sides and decreasing the texture angle resulted in a decrease in the oil film surface friction coefficient and an increase in the average pressure and net bearing capacity as well as the hydrodynamic lubrication performance. The average pressure increased and then decreased as the texture depth increased, while the friction coefficient of the oil film surface initially decreased and then increased. At a texture depth of 20 μm, the friction coefficient reached its lowest value while the average pressure and net bearing capacity of the oil film reached their highest value, which resulted in optimal hydrodynamic lubrication performance. When the texture depth became greater than 20 μm, vortices were gradually formed within the texture, which decreased the hydrodynamic lubrication performance. When the area rate of the rhombus-like dimple texture, depth, angle between long sides, and angle were, respectively, equal to 27%, 20 μm, 74°, and 0°, the net bearing capacity of the oil film was maximized, the friction coefficient was minimized, and the hydrodynamic lubrication performance and anti-wear effect reached their highest values. The increase in the viscosity of the actual well fluid could enhance the dynamic pressure lubrication performance and improve the bearing capacity. Full article

This paper develops a composite weaving structure, combining hexagonal micro-bumps and hexagonal grooves, in the design of the rubber surface of the screw pump. This allows us to solve the problem of high torque and fast wear of the rubber stator during the operation of screw pump lifting oil recovery, based on the bionic hexagonal surface structure, traditional surface damping principle, and fluid dynamic pressure lubrication theory. Finite element analysis is first conducted to quantitatively analyze the impacts of the parallel side distance, groove width, and groove depth on the surface flow field and wall pressure field of the composite hexagonal structure. Based on the simulation law, the rubber surface laser structure is then designed and prepared by nanosecond laser processing. Afterward, tribological experiments are conducted under the condition of long-term immersion in the actual extraction fluid of shale oil wells. This aims at simulating the actual downhole oil production conditions and quantitatively studying the impact of the size of the composite hexagonal structure on the lubrication characteristics of the friction part of the stationary rotor, as well as the effect of abrasion reduction. The results show that, within the simulation range, the smaller the parallel side distance, the higher the load-carrying capacity. In addition, the hexagonal weave with a parallel side distance of 3 mm has a higher wall load carrying capacity than that with distances of 4 mm and 5 mm. When the groove width is equal to 0.4 mm, the oil film load carrying capacity is higher than that in the case of 0.2 mm. When the groove depth increases, the oil film pressure first increases and then stabilizes or decreases after reaching 0.3 mm. In the hexagonal weave, the friction ratio of the rotor is equal to 0.4 mm. In the tribological experiment of hexagonal weave, the smaller the parallel side distance, the smaller the friction coefficient, and the 0.5 mm weave has the highest performance. Full article

Rotor structure has a great influence on the gas backflow in a screw vacuum pump. The characteristics of the gas main flow along the spiral groove of the screw rotor and the gas reverse flow along the tooth-shaped, tooth side, radial, and circumferential clearances are investigated. A new mathematical model of the pumping flow and backflow involved in a flow balance model is proposed to investigate the actions of the shearing force and pressure difference force. The calculated backflow is verified by comparing the experimental measured results. The relationships of the structural parameters of the screw rotor are established. The effects of the rotor parameters, such as pitch, diameter, and compression ratio, on backflow are revealed. The results show that the rotor diameter and compression ratio remain constant and that the influence of pitch on the backflow is slightly weak, with backflow variations of less than 3%, whereas the pitch, rotor length, and compression ratio are constant and the rotor addendum diameter is directly proportional to the backflow. The addendum diameter of rotor #4 is the largest, and its backflow is about 1.5 times larger than that of rotor #1. When the rotor radial sizes and the pitch of the suction end are constant, the compression ratio is inversely proportional to the backflow in the low-pressure region and proportional to the backflow in the high-pressure regions. Therefore, for a vacuum pump operating in low-pressure areas, the use of the compression ratio of 2.2 or higher is favorable for the reduction in backflow. Full article

A theoretical model for the micro-texture on the inner wall of the stator rubber in screw pumps was developed. The finite element analysis method was employed. The pressure and streamline distributions for warhead-type, concentric circle-type, and multilayer rectangular-type textured surfaces were calculated. The effects of textured morphology, groove depth, groove width, and other parameters on the lubrication field were systematically investigated and analyzed. A nanosecond laser was employed to process the textured rubber surface of the stator in the screw pump. Subsequently, a micro-texture friction performance test was conducted on the rubber surface of the stator in actual complex well fluids from shale oil wells. Given the results of the simulation analysis and experimental tests, the lubrication characteristics of textured rubber surfaces with varying texture morphologies, rotational speeds, and mating loads were revealed. Furthermore, it indicated that the irregular symmetric warhead-type micro-texture exhibited excellent dynamic pressure lubrication performance compared with concentric circle-type and multilayer rectangular-type textures. The irregular symmetry enhanced the dynamic pressure lubrication effect, enhanced the additional net load-bearing capacity of the oil film surface, and reduced friction. As the groove depth increased, the volume and number of vortices within the groove also increased. The fluid kinetic energy was transformed into vortex energy, leading to a reduction in wall stress on the surface of the oil film, thereby affecting its bearing capacity. Initially, the maximum pressure on the wall surface of the oil film increased and then decreased. The optimal dynamic pressure lubrication effect was achieved with a warhead-type texture size of 3 mm, a groove width of 0.2 mm, and a groove depth of 0.1 mm. Well-designed texture morphology and depth parameters significantly enhanced the oil film-bearing capacity of the stator rubber surface, improving the dynamic pressure lubrication effect, and consequently extending the service life of the stator–rotor interface in the screw pump. Full article

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity. Full article

By researching the influence of micro-groove texture on the surface tribological properties of the stator and rotor pair of oil production hydraulic motors, this paper aims to reduce the frictional resistance moment of the spiral pair of hydraulic motors, and further solve the problem of the difficult restart of the pump of a certain type of hydraulic-driven screw pump. According to the spiral pair of screw motors, a metal-rubber flat plate reciprocating friction model is established, and rectangular micro-grooves with different texture angles and depths are machined on the surface of the metal specimen. A combination of finite element simulation and tribological tests is used to carry out a study on the influence of different texture parameters on the friction performance of the hydraulic motor spiral pair. The results showed that at a certain texture angle, the friction coefficient of each specimen basically increases with the texture depth. When the texture depth is constant, the friction coefficient increases first and then decreases with the increase of the texture angle. The texture angle is the main factor affecting the friction coefficient. Under the same test conditions, the friction coefficient of the textured specimen can be reduced by 20.2% compared with the untextured specimen. In the metal-rubber contact pair of the stator and rotor of the hydraulic motor, the friction reduction mechanism of the texture mainly transport the lubricating medium through the micro-grooves to improve the lubricating conditions. Samples with a reasonable design of texture parameters can effectively reduce the friction coefficient of the friction pair without reducing the service life of the hydraulic motor, which is conducive to the smooth restart of the oil production system of the hydraulically driven screw pump. Full article

Screw machines, mainly including single-screw type and twin-screw type, have gone through significant development and improvement during the past decade. This paper reviews the relevant studies available in the open literature for acquiring insight into and to establish the state of the art of the research and application status of screw machines. The related research on different aspects, which would affect the performance and reliability of screw machines includes rotor profile and geometric characteristics, thermodynamic modelling, vibration and noise, lubrication and wear, control of capacity and built-in volume ratio, and liquid injection technology. In the aspect of thermodynamic modelling, the available methods, i.e., empirical or semi-empirical model, lump model, and 3D CFD model, adopted for the performance prediction and optimal design of screw machines are summarized. Then, the review covers the application status of screw machines in the fields of air compression and expansion, refrigeration and heat pump, organic Rankine cycle (ORC), and other popular applications, with an emphasis on the reported performance and progress in technologies of screw machines. Finally, conclusions and perspectives for future research in the area of screw machines are presented. The review provides readers with a good understanding of the research focus and progress in the field of screw machines. Full article

The labyrinth screw pump is a new type of low-flow rotor pump with a simple structure and good sealing performance. It is suitable for the transport of high-viscosity, high-gas-content, and particle-containing media. In this study, a rectangular labyrinth screw pump was used as the research object. The effect of the medium viscosity on the performance of the labyrinth pump was studied through numerical simulations, and the correctness of the simulation method was verified using existing test data. The efficiency and head of the labyrinth screw pump were selected as the optimization objectives, and the pump structural parameters were selected as the optimization parameters. A structural optimization model of the labyrinth screw pump based on response surface theory was established. The structural parameters of the labyrinth pump were reasonably simplified through size correlations, and then parameter sensitivity analysis was performed to determine the important structural parameters that needed to be optimized. The OSFD (optimized space-filling design) was used to combine the optimized parameters and generate the sample space. The response surface theory was combined with a neural network prediction model and a multi-objective genetic algorithm to perform optimization calculations. The results showed that there was an interactive influence between the structural parameters of the stator and rotor of the labyrinth screw pump. Compared with the original model, the optimized model pump had an efficiency increase of 13.55% and a lift increase of 19.53% when conveying a medium with a viscosity of 133 cp. Full article

Progressive cavity pumps are used in industry for the circulation of high viscosity fluids, such as crude oil and petroleum products, sewage sludge, oils, salt water, and wastewater. Also known as single screw pumps, these pumps are composed of a single rotor which has the shape of a rounded screw, which moves inside a rubber stator. The stator has an double helical internal surface which, together with the helical surface of the rotor, creates a cavity that moves along the rotor. The movement effect of the cavity inside the stator is the movement of the fluid with a constant flow and high pressure. In this paper, an algorithm for profiling the rollers for generating the helical surface of the pump rotor with progressive cavities is proposed. These rollers are constituted as tools for the plastic deformation of the blank (in case the pump rotor is obtained by volumetric deformation) or for its superficial hardening. Full article

The market for dry vacuum pumps is expected to increase in the coming years. Improving the efficiency of these machines requires comprehensive understanding of the flow dynamics within the working chambers. For this purpose, Computational Fluid Dynamics (CFD) is used as it offers better insight of the working process of a screw machine. In this study, a twin-screw vacuum pump with a large helix angle was analysed. This is a challenging case for CFD due to the limitations of grid generation in the transverse plane on the mesh quality. Two types of transverse meshes were generated using the software SCORG^TM: casing to rotor non-conformal mesh and casing to rotor conformal mesh. The quality of the mesh in terms of aspect ratio and orthogonality were compared. The casing to rotor conformal mesh was used with ANSYS Fluent in order to obtain performance characteristics of the vacuum pump with the moderate helix angle of 62° such as the mass flow rate, rotor torque, and indicated power. The performance prediction results were satisfactory but the grid quality was relatively low with orthogonality reaching 40° and aspect ratio over 250 in some cases. As the helix angle increases the quality of mesh decreases. This paper presents the new development of a grid generation algorithm which uses the normal rack to map the fluid domain in the normal plane instead of the transverse plane. This new mesh generation method is expected to better align the computational grid with the main and leakage flows in order to significantly improve grid quality and reduce the numerical diffusion in case of screw machines with large helix angles. Full article

A detailed study of the fluid flow and thermodynamic processes in positive displacement machines requires 3D CFD modeling in order to capture their real geometry, including leakage gaps. However, limitations in the conventional computational grids, used in commercial software packages, exclude their use for classical twin screw machines. The screw compressor rotor grid generator (SCORG) is a customized grid generation tool developed to overcome these limitations. This paper shows how it can be further extended to include non-conventional rotor designs, such as those with variable lead or profile variation and even internally geared machines with conical rotors. Other arrangements possible with this improvement include multiple gate rotors to increase volumetric displacement or dual lead, high wrap angle rotors for very high-pressure differences and vacuum applications. A case study of a water-injected twin screw compressor is included to demonstrate its use for both detailed flow analysis and design. Full article

Although Lead-cooled Fast Reactor (LFR) is not a new concept, it continues to be an example of innovation in the nuclear field. Recently, there has been strong interest in liquid lead (Pb) or liquid lead–bismuth eutectic (LBE) both critical and subcritical systems in a relevant number of Countries, including studies performed in the frame of GENERATION-IV initiative. In this paper, the theoretical and computational findings for three different designs of Primary Circulation Pump (PCP) evolving liquid lead (namely the jet pump, the Archimedean pump and the blade pump) are presented with reference to the ALFRED (Advanced Lead Fast Reactor European Demonstrator) design. The pumps are first analyzed from the theoretical point of view and then modeled with a 3D CFD code. Required design performance of the pumps are approximatively around an effective head of 2 bar with a mass flow rate of 5000 kg/s. Taking into account the geometrical constraints of the reactor and the fluid dynamics characteristics of the molten lead, the maximum design velocity for molten lead fluid flow of 2 m/s may be exceeded giving rise to unacceptable erosion phenomena of the blade or rotating component of the primary pumping system. For this reason a deep investigation of non-conventional axial pumps has been performed. The results presented shows that the design of the jet pump looks like beyond the current technological feasibility while, once the mechanical challenges of the Archimedean (screw) pump and the fluid-dynamic issues of the blade pump will be addressed, both could represent viable solutions as PCP for ALFRED. Particularly, the blade pump shows the best performance in terms of pressure head generated in normal operation conditions as well as pressure drop in locked rotor conditions. Further optimizations (mainly for what the geometrical configuration is concerned) are still necessary. Full article