Scroll Vacuum Pump Research Articles

Noise analysis of dry scroll vacuum pump based on experiment and CFD

The scroll vacuum pump is a dry vacuum pump with a wide range of applications. The radiated noise of a multi-stage scroll vacuum pump under different suction pressures is tested. The discharge velocity field is measured by the PIV technique. When the suction pressure changes from 101 kPa to 5 Pa, the average sound pressure level of the scroll pump decreases from 80.37 dB to 58.13 dB, which is reduced by 22.24 dB. The maximum and minimum sound power levels are 97 dB and 74.76 dB, respectively. The spectrum characteristics and the distribution law of radiated noise are analyzed. The measured noises at the rear of all operating conditions are the smallest, followed by the positions above the front part, and the next is the directly above position. Aeroacoustics is the main noise source in the scroll pump. Based on the CFD method, the simulation calculation is carried out at different suction pressures and the maximum simulation error is −5.7%. The location and formation mechanism of the aeroacoustics source are analyzed. In different working processes, the main excitation sources of aeroacoustics are different. The results are helpful to the noise source identification and aeroacoustics improvement of the scroll vacuum pump.

Study the Effect of Operating Temperature on Performance in Dry Scroll Vacuum Pump

The dry scroll vacuum pump is a kind of variable capacity dry vacuum pump that is applied in chemical, pharmaceutical, semiconductor, and scientific instruments. Analyzing the thermodynamic characteristics of the scroll vacuum pump and studying the impact of operating temperature on its consistent performance are necessary for the design and application of the cooling system of the scroll vacuum pump. Based on the dynamics mesh method, the computational fluid dynamics (CFD) simulation model of a multi-stage dry scroll vacuum pump is established in this study. Under the suction pressure of 1000 Pa, the simulation calculation is carried out at different operating temperatures of fixed scrolls (25 °C, 45 °C, and 65 °C). The results show that the pumping speed, the gas compression power, and the energy efficiency ratio are significantly affected by different temperatures. The operating temperature of the pump has been reduced from 65 °C to 25 °C, the pumping speed is increased by approximately 5.97%, the gas compression power is increased by approximately 4.32%, and the energy efficiency ratio is increased by approximately 1.745%. This research provides a transient simulation method using dynamic mesh technology for the study of the dry scroll vacuum pump, and the results can provide a theoretical basis for the design and application of the cooling system of the dry scroll vacuum pump.

Non‐contact vacuum pumps

SummaryAn overview of the main methods for mathematical modeling of the working process of non‐contact vacuum pumps is given. The specifics and the main stages of mathematical model development for screw, scroll, claw and Roots vacuum pumps are considered. The results of mathematical modeling of pump characteristics are presented and compared with experimental data. The mathematical modeling technique presented here can be recommended for analyzing the influence of pump geometry and operating conditions on the pump characteristics of non‐contact oil‐free vacuum pumps.

Modelling of working processes of non-contact oil free vacuum pumps by computational fluid dynamics (CFD) methods

Numerical mathematical models of non-contact oil free scroll, Roots and screw vacuum pumps are developed. Modelling was carried out with the help of software CFD ANSYS-CFX and program TwinMesh for dynamic meshing. Pumping characteristics of non-contact pumps in viscous flow with the help of SST-turbulence model were calculated for varying rotors profiles, clearances, and rotating speeds. Comparison with experimental data verified adequacy of developed CFD models.

Повышение эффективности рабочего процесса безмаслянного спирального вакуумного насоса

Improving the quality of manufactured products involves reducing any contaminants introduced into the vacuum chamber from the pumping means. Scroll vacuum pumps, which are constantly developing, are the most promising for oil-free pumping. Relying on the mathematical model developed, we examined the influence of the main parameters of the scroll on the scroll pump performance, in particular, the influence of the radius of the base circle on the pumping speed and the power consumption of the scroll pump at fixed and variable radii of the pump housing bore. Maintaining the overall dimensions of the pump with an increase in the radius of the base circle proves to lead to an exponential increase in the limiting residual pressure and a decrease in energy efficiency due to a decrease in the number of scroll wraps and, as a consequence, an increase in backflows. For the pump under consideration, when the base circle radius is more than 3.5 mm, the limiting residual pressure exceeds 10 Pa, and the vacuum scroll pump can no longer be a full-fledged oil-free alternative to oil-sealed vacuum pumps. With an increase in the radius of the base circle, while maintaining the number of scroll wraps, the radius of curvature of the outer wraps will increase; this results in the backflow decrease, leading to a decrease, albeit insignificant, in the limiting residual pressure. The energy efficiency of the scroll pump decreases with decreasing pump inlet pressure. The above dependencies make it possible to choose the optimal geometry of the scrolls, based on the specific conditions for which the vacuum scroll pump is designed

Исследование процесса откачки конденсируемых паров безмасляными спиральными вакуумными насосами

When operating a vacuum pump, it is often necessary to pump out liquid vapors or vapor-gas media that can condense in its working cavities. To prevent condensation in displacement pumps including scroll pumps, gas ballast device is used. The maximum tolerable water vapor pressure at the inlet and maximum pump capacity by water vapor are the main parameters of a pump with gas ballast device. The highest water vapor pressure at the inlet and the maximum capacity of the oil-free scroll vacuum pump by water vapor were determined experimentally. For this purpose pumping speed, gas flow through the gas ballast device, and gas temperature at the scroll vacuum pump outlet were measured on a specially designed stand. A method for calculating the partial pressure of water vapor in scroll vacuum pumps using a mathematical model of pumping process is proposed. Experimental and calculated results are in good agreement.

Study of oil free scroll vacuum pump characteristics

SummaryTo verify the mathematical model of a scroll vacuum pump working process, an experimental unit for obtaining indicator diagrams was developed. The pump was modified to install gauges to measure quick‐varying pressures in the working chambers of the pump at different operating modes. The dependence of pressure on the rotation angle of the drive shaft at different inlet pressures is obtained. Comparison of experimental and calculated data shows convergence within 15 %.

Construction and simulation of novel asymmetrical scroll wraps for scroll vacuum pumps

The existing asynchronous suction scroll vacuum pump with only one suction port has higher area utilization ratio than that of the existing synchronous suction scroll vacuum pump with two suction ports, but its built-in volume ratios of two groups of working chambers are not equal, which leads to the gas mixing at different pressures at the end of the compression process, and creates irreversible losses. In order to solve this problem, an asymmetrical twin-circular arc modified method was proposed in this study; and then a new type of asymmetrical twin-circular arc modified wrap (ACMW) with only one suction port, whose built-in volume ratios of two groups of working chambers are equal, was constructed. In addition, influences of its geometric parameters on the working performance of the scroll vacuum pump were studied, and 3D numerical simulations of its working process were conducted and compared. The study results demonstrate that wrap of the proposed orbiting scroll becomes thicker while wrap of the proposed fixed scroll is gradually thinner, as offset distance δ increases. The novel ACMW will play an important role in improving the working performance of the scroll vacuum pumps.

Анализ энергетических характеристик безмасляного спирального вакуумного насоса

This paper presents an analysis of the indicator power of an oil-free scroll vacuum pump based on the indicator diagrams obtained through high-speed pressure sensors. These values are compared with the results of calculations using a mathematical model of the pump working process. It is shown that the divergence of the calculated results and experimental values does not exceed 4%, which confirms the adequacy of the developed mathematical model. The total power of the scroll pump exceeds the indicator power by more than 2 times due to the friction losses between the face seals and disks of the reciprocal scroll elements, friction losses in the stuffing box seals and rolling bearings, as well as due to the coefficient of efficiency of the motor. The influence of the radial clearance between the scroll elements on the power consumption is considered. It is shown that at low pressures nearing the ultimate pressure, the power increases with the increased clearance, while at inlet pressures exceeding 40 kPa it decreases. The performed analysis can be used for selecting the optimal geometrical parameters of the scroll elements and increasing power efficiency of the pump depending on specific operating conditions.

All-Metal Scroll Vacuum Pumps for Tritium Processing Systems

Over the past decade, Air Squared has been actively developing and improving the highly anticipated 15 m3/h tritium vacuum pump to replace the obsolete industry standard Normetex scroll pump. The all-metal pump features a metal bellows that hermetically seals all tritium gas from any material other than metal. Air Squared has listened to the tritium market’s needs and is currently developing the latest addition to the Air Squared tritium vacuum pump line: the 150 m3/h liquid cooled all-metal (LCAM) scroll vacuum pump. Through numerous hours of testing, Air Squared has demonstrated the advantages of LCAM scroll vacuum pumps. The effect that thermal expansion has on highly toleranced all-metal pumps has been observed and characterized to predict pump performance as well as provide safe operational temperature limits. Performance characteristics of the 15 m3/h pump have been analyzed with different process gases to understand the effects of pumping light gases. Vacuum pumping speed curves have been generated at various interstage pressures to understand the advantages that roughing pump systems have when used in series with all-metal scroll vacuum pumps. This paper presents Air Squared’s 15 m3/h designs and highlights the performance characteristics. The effects that pump temperature, process gas, and fore-vacuum have on all-metal scroll vacuum pumps are explained with empirical data collected over a decade of research. With the knowledge and data collected, Air Squared has a pathway for a new industry standard 15 m3/h and 150 m3/h positive displacement scroll pump for tritium service to support international nuclear fusion and tritium research.

Development of scroll vacuum pump characteristics by thermal deformations compensation

Influence of thermal deformations of scroll vacuum pumps working elements on clearances in working mechanism is considered. Analysis of influence of a clearance value on indicator diagrams and pumping speed was carried out. It is shown that alteration of a clearance due to thermal deformations decreases pumping speed at low pressures. The design of scroll elements compensating clearances alteration in pump operation and improving pumping characteristics is presented.

Indicator diagrams of oil free scroll vacuum pumps

SummaryExperimental test unit for obtaining indicator diagrams of a scroll vacuum pump was developed. Indicator diagrams for different pump inlet pressures and different rotation speeds of the drive shaft were obtained. The obtained results are analyzed.

Математическая модель рабочего процесса безмасляного спирального вакуумного насоса

Математическая модель рабочего процесса безмасляного спирального вакуумного насоса

Scroll Geometry of Scroll Vacuum Pump

SummaryThe influence of the end part of the scroll on the pumping characteristics and indicated power of the oil free scroll vacuum pump is considered.With the help of developed mathematical model of the scroll pump dependence of pumping speed on the inlet pressure at different curvature radii of the scroll end part and compression duration is obtained. The influence of compression duration on the ultimate pressure and delivery rate is examined. Dependence of the indicated power on the inlet pressure at different number of scroll wraps and compression duration is calculated.

Mathematical model of working process of oil free scroll vacuum pump

SummaryA mathematical model of oil free scroll machine working in vacuum conditions is considered. Differential equations and main assumptions in the model are presented. Four types of control volumes are specified. The model takes into consideration heat exchange between the pump working elements, change of clearances due to thermal deformations, and mobility of the scroll element wall in calculation of leakage. The comparison of the calculated values of the pumping speed with experimental values obtained at different rotation speed of the driveshaft is carried out.

Influence of compression time on scroll vacuum pump power characteristics

Influence of compression time on scroll vacuum pump power characteristics

Mobile refrigeration system for precool and warm up of superconducting magnets

Conservation of helium has become more important in recent years due to global shortages in supply. Magnetic resonance imaging (MRI) superconducting magnets use approximately 20% of the world’s helium reserves in liquid form to cool down and maintain operating temperatures at 4 K. This paper describes a mobile cryogenic refrigeration system, which has been developed by Sumitomo (SHI) Cryogenics of America, Inc. to conserve helium by shipping MRI magnets warm and cooling them down or servicing them on site at a medical facility.The system can cool a typical magnet from room temperature to below 40K in less than a week. The system consists of four single stage Displex®-type Gifford-McMahon (GM) expanders in a cryostat with heat exchangers integrated on the cold ends that cool the helium gas, which is circulated in a closed-loop system through the magnet by a cryogenic fan. The system is configured with heaters on the heat exchangers to effectively warm up a magnet. The system includes a scroll vacuum pump, which is used to evacuate the helium circuit with or without the magnet and turbo pump to evacuate the cryostat. Vacuum-jacketed transfer lines connect the cryostat to the magnet. The system is designed with its own controller for continuous operation of precool, warm up and evacuation processes with automatic and manual controls. The cryostat, pumps and gas controls are mounted on a dewar cart. One compressor and the system controller are mounted on a compressor and control cart, and the other three compressors are mounted on separate carts.

CFD simulation of a dry scroll vacuum pump with clearances, solid heating and thermal deformation

Although dry scroll vacuum pumps (DSPV) are essential devices in many different industrial processes, the CFD simulation of such pumps is not widely used and often restricted to simplified cases due to its complexity: The working principle with a fixed and an orbiting scroll leads to working chambers that are changing in time and are connected through moving small radial and axial clearances in the range of 10 to 100 μm. Due to the low densities and low mass flow rates in vacuum pumps, it is important to include heat transfer towards and inside the solid components. Solid heating is very slow compared to the scroll revolution speed and the gas behaviour, thus a special workflow is necessary to reach the working conditions in reasonable simulation times. The resulting solid temperature is then used to compute the thermal deformation, which usually results in gap size changes that influence leakage flows. In this paper, setup steps and results for the simulation of a DSVP are shown and compared to theoretical and experimental results. The time-varying working chambers are meshed with TwinMesh, a hexahedral meshing programme for positive displacement machines. The CFD simulation with ANSYS CFX accounts for gas flow with compressibility and turbulence effects, conjugate heat transfer between gas and solids, and leakage flows through the clearances. Time-resolved results for torques, chamber pressure, mass flow, and heat flow between gas and solids are shown, as well as time- and space-resolved results for pressure, velocity, and temperature for different operating conditions of the DSVP.

Потери во входном и выходном трактах безмасляного спирального вакуумного насоса

Потери во входном и выходном трактах безмасляного спирального вакуумного насоса

CFD-based analysis of gas flow in dry scroll vacuum pump

Based on dynamics mesh method, Computational Fluid Dynamics (CFD) simulation model of two-stage dry scroll vacuum pump was established. Simulation calculation was carried out under the condition of suction pressure at 10000Pa, 1000Pa and 100Pa,respectively. When suction pressure was 10000Pa, the numerical calculation results were basically in accordance with the experimental pumping speed. When suction pressure decreased to 1000Pa, the simulation error decreased −5.7%. When suction pressure was below 1000Pa, due to the gas regime, the calculational results deviated from the experimental results dramatically. Three-scroll profile was applied to the scroll chamberⅠ connected with the suction port, which improved the pumping speed and compression ratio as well as reducing the fluctuation of suction speed significantly. Gas expanded initially in the chamber and was then compressed by external compression. Gas compression mainly occurred in scroll chamber Ⅱ connected with the exhaust port. Gas was compressed by changing the compression chamber. The variation of the pressure in compression chamber was greatly affected by gas leakage.