Stationary Diffuser Research Articles

Study of nanofluid flow and heat transfer in a stationary cone-disk system

Rheometric, viscosimetric, bio-medical, and several other pharmaceutical machineries utilize the structural advantages provided by the geometry of a stationary conical diffuser. The problem of the Buongiorno nanofluid flow in the conical gap of a stationary cone-disk system for isothermal boundaries is studied. The governing system, comprising the incompressibility condition, Navier–Stokes equation, energy conservation equation, and conservation of Nanoparticle Volume Fraction (NVF) equation, is analyzed. The Lie-group theory has been used to derive a self-similar model. Solutions of the self-similar equations were computed numerically, and the expressions for the Nusselt number and Sherwood number are obtained. The parametric investigation reveals that the heat and mass transfer rate subside significantly when pre-swirl is introduced to the flow. Furthermore, the nanofluid slip mechanisms enhance the effective temperature of the system.

Effect of stationary diffuser size on performance and pressure field characteristics of an axial-flow pump in pump mode

Effect of stationary diffuser size on performance and pressure field characteristics of an axial-flow pump in pump mode

Noise reduction in high-resolution speckle displacement measurements through ensemble averaging

To measure surface displacement on micro samples, a non-invasive method with both a low displacement measurement uncertainty below 100 nm and high spatial resolution of around 20 µm is required. In digital image speckle correlation, both requirements can be fulfilled individually but not simultaneously. To lower the displacement measurement uncertainty without deteriorating the spatial resolution, an ensemble averaging technique over multiple uncorrelated speckle patterns is presented. To generate and reproduce different speckle patterns, two concepts for the respective modulation of laser light illumination are investigated: a low-cost concept with a rotating glass diffuser, as well as a faster concept using a digital micromirror device combined with a stationary diffuser with a maximum pattern rate of 17.9 kHz. Both setups lead to a measurement uncertainty reduction by one order of magnitude over a wide range of spatial resolutions. As a result, displacements in the micrometer range are measured with a measurement uncertainty of 40 nm and spatial resolution of 20 µm.

Numerical and experimental study on the pressure fluctuation, vibration, and noise of multistage pump with radial diffuser

Multistage pump can provide high-pressure liquid, which is widely used in various areas of national economy. In order to improve the stability and reduce the noise of multistage pump, the relationships among the pressure fluctuation, vibration, and noise were studied deeply by using computational fluid dynamics and experimental measurement. Based on the unsteady numerical calculation, the phase of the pressure fluctuation wave in the middle section of the impeller and the diffuser was obtained, and the unsteady velocity distribution was acquired in the rotor–stator interaction (RSI) region between the rotational impeller and the stationary diffuser. Moreover, the vibration and noise tests of a five-stage pump with radial diffuser were performed. The results show that the phase distribution of the pressure fluctuation wave in the impeller and diffuser can be divided into four regions: the impeller flow channel region, the impeller transition region, the diffuser transition region, and the diffuser flow channel region. In addition, the pressure fluctuation, vibration and noise of the multistage pump are strongly related to each other, that is, RSI induces strong unsteady flow and pressure fluctuation in the pump, which makes the pump produce serious vibration and cause the corresponding noise. The key to controlling the vibration and noise is to reduce the effect of RSI between the impeller and the diffuser.

Performance Enhancement of a Low-Pressure Ratio Centrifugal Compressor Stage with a Rotating Vaneless Diffuser by Impeller Disk Extended Shrouds

Numerical simulations have been carried out to examine the performance and flow parameters of forced rotating vaneless diffuser obtained by the extension of impeller disks of a low-pressure ratio shrouded type centrifugal compressor stage with diffuser diameter ratio 1.40. Four different levels of shroud extensions (i.e., impeller disks alone) forming the rotating vaneless diffusers are analyzed at four different flow coefficients. The extension of impeller disks alone by 40% of impeller exit diameter leads to a fully forced rotating vaneless diffuser thereby replacing the existing stationary vaneless diffuser. The comparative studies are performed using the same impeller with a stationary vaneless diffuser also having a diffuser diameter ratio of 1.40. Static pressure rise in ES40 is found to be higher than SVD by around 9.84% at design flow coefficient and also at above off-design flow rates. Energy coefficient is highest for ES40, followed by ES30 compared to SVD. For ES40, the static pressure recovery coefficient also is higher compared to SVD. The efficiency of ES40 is lesser by around 5.40% to 3.43% compared to SVD, at design as well as at above off-design flow coefficients. The stagnation pressure losses for ES40 drastically reduced compared to SVD. The comparison of stagnation pressure contours and absolute velocity contours near the hub and shroud walls of ES40 and SVD configurations shows that the rotating diffuser walls as in ES40 causes further addition of energy to the fluid. This adds up the kinetic energy level of the fluid which due to better diffusion, results in gain of static pressure rise. Moreover, there is a net increase in stagnation pressure distribution at the exit of diffuser due to rotating vaneless diffuser. Also, the presence of a fully rotating vaneless diffuser (ES40) smooth out the distorted entry flow profiles, thereby improving the performance of the centrifugal compressor stage.

Optimization of Centrifugal Pump Impeller Outlet Vane Angle by Using Modal Analysis

A centrifugal pump is one of the simplest pieces of equipment in any process plant. Liquid is forced into an impeller either by atmospheric pressure, or in case of a jet pump by artificial pressure. The vanes of impeller pass kinetic energy to the liquid, thereby causing the liquid to rotate. The liquid leaves the impeller at high velocity. The impeller is surrounded by a volute casing or in case of a turbine pump a stationary diffuser ring. The volute or stationary diffuser ring converts the kinetic energy into pressure energy. An impeller is a circular metallic disc with a built-in passage for the flow of fluid. As the performance of the pump depends on the type of impeller, it is important to select a suitable design and to maintain the impeller in good condition. It is important to recognize that the design of any machine involving aerodynamics, thermodynamics, fluid dynamics, stress analysis, vibration analysis, the selection of materials, and the requirements for manufacturing. Though impellers have been developed as highly efficient, design is still based on various empirical and semi empirical rules proposed by designers. Further the scope of work was extended towards performance evaluation of impeller by changing vane angle of impeller vanes. To optimize impeller vane angle, design and modeling of impeller for various vane angle. The modeling of the impeller will do by using solid modeling software, CATIA V5 R17. It is proposed to design a impeller for various vane angles, analyze its strength and deformation using FEM software like ANSYSE V12. Modal analysis is performed on impeller to find out first 5 natural frequencies

Numerical Study on the Effect of Free Rotating Vaneless Diffuser of Exit Diameter to Inlet Diameter Ratio 1.3 with Speed Ratio 0.50 on Centrifugal Compressor Performance

Innovative methods in the design of radial diffuser are necessary for reducing the energy losses associated with diffusion in order to design an efficient centrifugal compressor. Rotating vaneless diffusers is one such concept, in which a particular type, free rotating vaneless diffuser, the diffuser speed becomes a fraction of the rotating impeller speed and rotates independently. In this paper, an impeller with stationary vaneless diffuser alone of diffuser diameter ratio 1.40 and the same impeller with a freely rotating vaneless diffuser of diffuser diameter ratio 1.30 along with stationary vaneless diffuser at downstream for the remaining radius ratio are analyzed for flow diffusion and performance. Higher static pressure rise with reduced stagnation pressure losses and a marginally lesser efficiency by around 3.5% compared to SVD is achieved by the free rotating vaneless diffuser configuration (FRVD30SR0.5).

Suppression of tonal noise in a centrifugal fan using guide vanes

This paper presents the work aiming for tonal noise reduction in a centrifugal fan. In previous studies, it is well documented that tonal noise is the dominant noise source generated in centrifugal fans. Tonal noise is generated due to the aerodynamic interaction between the rotating impeller and stationary diffuser vanes. The generation of tonal noise is related to the pressure fluctuation at the leading edge of the stationary vane. The tonal noise is periodic in time which occurs at the blade passing frequency (BPF) and its harmonics. Much of previous studies, have shown that the stationary vane causes the tonal noise and generation of non-rotational turbulent noise. However, omitting stationary vanes will lead to the increase of non-rotational turbulent noise resulted from the high velocity of the flow leaving the impeller. Hence in order to reduce the tonal noise and the non-rotational noise, guide vanes were designed as part of this study to replace the diffuser vanes, which were originally used in the chosen centrifugal fan. The leading edge of the guide vane is tapered. This modification reduces the strength of pressure fluctuation resulting from the interaction between the impeller outflow and stationary vane. The sound pressure level at blade passing frequency (BPF) is reduced by 6.8dB, the 2nd BPF is reduced by 4.1dB and the 3rd BPF reduced by about 17.5dB. The overall reduction was 0.9dB. The centrifugal fan with tapered guide vanes radiates lower tonal noise compared to the existing diffuser vanes. These reductions are achieved without compromising the performance of the centrifugal fan. The behavior of the fluid flow was studied using computational fluid dynamics (CFD) tools and the acoustics characteristics were determined through experiments in an anechoic chamber.

Experimental and Numerical Investigation of the Unsteady Flow Field in a Vaned Diffuser of a High-Speed Centrifugal Compressor

Vaned diffusers in centrifugal compressor stages are used to achieve higher stage pressure ratios, higher stage efficiencies, and more compact designs. The interaction of the stationary diffuser with the impeller can lead to resonant vibration with potentially devastating effects. This paper presents unsteady diffuser vane surface pressure measurements using in-house developed, flush mounted, fast response piezoresistive pressure transducers. The unsteady pressures were recorded for nine operating conditions, covering a wide range of the compressor map. Experimental work was complemented by 3D unsteady computational fluid dynamics (CFD) simulations using ansys cfx V12.1 to detail the unsteady diffuser aerodynamics. Pressure fluctuations of up to 34.4% of the inlet pressure were found. High pressure variations are present all along the vane and are not restricted to the leading edge region. Frequency analysis of the measured vane surface pressures show that reduced impeller loading, and the corresponding reduction of tip leakage fluid changes the characteristics of the fluctuations from a main blade count to a total blade count. The unsteady pressure fluctuations in the diffuser originate from three distinct locations. The impact of the jet-wake flow leaving the impeller results in high variation close to the leading edge. It was observed that CFD results overpredicted the amplitude of the pressure fluctuation on average by 62%.

Enhancement of Flow Diffusion in a Centrifugal Compressor Stage with Backward Curved Impeller by Shroud Extension – A Numerical Study

Efficient, compact centrifugal compressor with higher pressure ratios along with adequate surge margins necessitates developing non-conventional diffuser designs. A method of reducing shear losses on the stationary vaneless diffuser sidewalls is by rotating the side walls of vaneless diffuser. Forced rotating vaneless diffuser, a type in which the diffuser is integral with impeller and rotates at same speed, is obtained by extending the impeller disks beyond the blades. In this paper, the conventional stationary vaneless diffuser is redesigned to act as a ‘forced’ rotating vaneless diffuser. The effect of shroud extension is analyzed for the backward curved centrifugal impeller with shrouds extended by 40% with impeller exit diameter on flow diffusion and compared to an impeller with stationary vaneless diffuser. A higher static pressure rise by around 10% along with reduced losses is achieved by shroud extension configuration, RVD-ES. This indicates that the rate of diffusion is higher in the extended shroud configuration.

Free Rotating Vaneless Diffuser of Diffuser Diameter Ratio 1.30 with Different Speed Ratios and its Effect on Centrifugal Compressor Performance Improvement

Free rotating vaneless diffuser is one of the novel methods in the design of radial diffuser for reducing the energy losses associated with diffusion. In the present study, the impeller with a stationary vaneless diffuser of diffuser diameter ratio 1.40 and impeller with a free rotating vaneless diffuser of diffuser diameter ratio 1.30 along with stationary vaneless diffuser at downstream for the remaining radius ratio, running at speed ratios 0.25 and 0.75 times the impeller rotational speed are analyzed. A higher static pressure rise with reduced losses is achieved by free rotating vaneless diffuser configuration, Free RVD30 SR0.75. The static pressure recovery coefficient increased by 23 to 80%, by rotating the diffuser independently over the entire flow range. Also, losses are lesser due to reduced shear between the through flow and independently rotating walls of the diffuser. The efficiency of both Free RVD30 SR0.25 and Free RVD30 SR0.75 are marginally lesser by 3.5 to 5.3% with SVD. This clearly reveals that the diffusion rate is higher in the free rotating vaneless diffuser configuration.

A Numerical Study of the Unsteady Interaction Effects on Diffuser Performance in a Centrifugal Compressor

Interaction between rotating impeller and stationary diffuser in a centrifugal compressor is of practical importance in evaluating system performance. The present study aims at investigating how the interaction influences the unsteady diffuser performance and understanding the physical phenomena in the centrifugal compressor. A computational fluid dynamics (CFD) method has been applied to predict the flow field in the compressor, which has a conventional vaned diffuser (VD) and a low solidity vaned diffuser (LSVD). The radial gaps between impeller and diffuser and different flow coefficients are varied. The results obtained show that the major parameter that influences the unsteady variation of diffuser performance is due to the circumferential variation of the flow angle at the diffuser vane leading edge. The physical phenomena behind the pressure recovery variation are identified as the unsteady vortex shedding and the associated energy losses. The vortex core region as well as the shedding of vortices from the diffuser vane are triggered by the variation in the diffuser vane loading, which in turn is influenced by the circumferential variation of the impeller wake region. There is little unsteady variation of flow angle in the span-wise direction. This indicates that the steady state performance characteristics are related to the span-wise variation of flow angle, while the unsteady characteristics are contributed by the circumferential variation of flow angle. At design conditions, dominant frequency components of pressure fluctuation are all periodic and at near stall, these are aperiodic.

Modification of Centrifugal Impeller and Effect of Impeller Extended Shrouds on Centrifugal Compressor Performance

Efficient, compact centrifugal compressors with higher pressure ratios along with adequate surge margins are required for the future. Achieving these necessitates development of newer non-conventional diffuser designs and rotating vaneless diffusers is one such concept. One method of reducing the shear losses on the stationary vaneless diffuser sidewalls, with probable improved efficiency and flow range of low-to-medium specific speed stages, is the use of a “rotating diffuser”. A particular type of rotating vaneless diffuser is forced rotating vaneless diffuser, in which the rotational speed equals that of the impeller and the rotating vaneless diffuser is integral with the centrifugal impeller which is created by extending the impeller disks beyond the blades. In the present paper, the effect of extended shroud by 10% with impeller exit diameter are analysed on flow diffusion and performance and compared with stationary vaneless diffuser. The higher static pressure rise with reduced losses and increased efficiency is achieved by shroud extension.

Computational Study on the Effect of Blade Cutback on the Performance of the Centrifugal Compressor

Minimizing the energy losses associated with diffusion and also increasing the stable operating ranges of the diffusion systems necessitates developing non-conventional diffuser designs. Rotating vaneless diffusers is one such concept, in which a particular type, forced rotating vaneless diffuser, the diffuser is integral with impeller and rotates at the same speed as the impeller, is obtained by blade cutback, which involves blade trimming but leaving the impeller disks as it is. In this paper, the shrouded impeller with blade cutback by 5% to its vane length by which it introduces a rotating vaneless diffuser in between and a conventional shrouded impeller, both with stationary vanless diffuser are analysed on flow diffusion and performance aspects. The matching peak efficiency is achieved at design flow coefficient for both SVD and BCB 05 and slightly lesser efficiencies at off-design flow coefficients for BCB 05. The performance characteristics of BCB 05 are lesser in terms of energy coefficient, specific work, as well as static pressure rise.

Comparison of Periodic Flow Fields in a Radial Pump among CFD, PIV, and LDV Results

The interaction between the impeller and the diffuser is considered to have a strong influence on the unsteady flow in radial pumps. In this paper, the unsteady flow in a low specific speed radial diffuser pump has been simulated by the CFD code CFX‐10. Both Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements have been conducted to validate the CFD results. Both the phase‐averaged velocity fields and the turbulence fields obtained from different methods are presented and compared, in order to enhance the understanding of the unsteady flow caused by the relative motion between the rotating impeller and the stationary diffuser. The comparison of the results shows that PIV and LDV give nearly the same phase‐averaged velocity fields, but LDV predicts the turbulence much clearer and better than PIV. CFD underestimates the turbulence level in the whole region compared with PIV and LDV but gives the same trend.

Numerical simulation of 3D turbulent flow through an entire stage in a multistage centrifugal pump

A three-dimensional turbulent flow through a multistage centrifugal pump is numerically simulated using a commercial CFD software package. The simulation and analysis include flow fields in rotating impeller and stationary diffuser and is completed in a multiple reference frame. The standard k–ϵ turbulence model is applied. The analysis of the simulation reveals that the reverse flows exist in the zone near the impeller exit and diffuser entrance, resulting in asymmetric and unsteady flow field. There is a considerable interference on the velocity field at the impeller exit due to the interaction between impeller blades and diffuser vanes. The hydraulic performance is connected and evaluated with the 3D computational flow field. The current computation is verified by comparing predicted and measured head.

Qualification and performance of a reverberation chamber equipped with lightweight diffusers

A study was conducted in the reverberation chamber of the Integrated Acoustics Laboratory at Georgia Tech to evaluate the efficacy of lightweight (1.3 kg/m 2 ), fiberglass diffusers in increasing room diffusion while affording easy chamber reconfiguration. To this end, performance and qualification tests were conducted in accordance with the American Society of Testing and Materials (ASTM) standard C423-02a, the American standard for sound absorption measurements in reverberation chambers. Also, comparative absorption tests were conducted per the standard for comparison with other laboratories. Preliminary performance testing per C423-X1 included determining the optimum diffuser surface area and quantifying variation of sound decay rate with loudspeaker position. During performance testing, the sound absorption coefficient of a specimen increased with increasing diffuser area until the coefficient reached a maximum. The configuration that yielded this maximum, identified in Appendix X1 of the standard as optimum, had a diffuser-to-chamber surface area ratio of 19%; the diffusers were stationary for these tests. With respect to loudspeaker position, the decay rate was relatively independent of position. Qualification testing per C423-A3 required demonstration that decay rate was sufficiently independent of measurement location and specimen position. With the optimum stationary diffuser configuration the chamber did not qualify per ASTM C423-A3. In five of eighteen frequency bands, variation of decay rate with respect to measurement location exceeded the qualification limitations; likewise, variation with respect to specimen position exceeded the limits in five bands. However, a combination of rotating and stationary lightweight diffusers produced a sound environment that was diffuse enough to qualify per ASTM C423 in all frequency bands. To compare performance to other laboratories, absorption testing of round robin specimens was replicated in the IAL chamber. It should be noted that all specimens were Amounted according to ASTM Practices E795-00 (to chamber floor); the results of this paper apply to this mounting only. With both diffuser configurations, the measured absorption coefficients and their repeatabilities were within the confidence interval developed by the round robin testing. Interestingly, the absorption coefficients measured with the diffuser configuration that did not qualify the chamber were statistically no different from those from qualified laboratories. These results call into question the assumption that dense diffusers and strict diffusion requirements are necessary for sound absorption measurements in reverberation chambers.

Aeroacoustic characteristics and noise reduction of a centrifugal fan for a vacuum cleaner

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 3000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB(A) and the 2nd BPF is reduced about 20 dB(A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

Mechanical Sealing Technology Used in Multiphase Production

Abstract This paper describes various successful mechanical seal arrangements in positive displacement twin screw pumps most often used in multiphase applications. Introduction Among the technologies having been developed for oil and gas production in the last 15 years, multiphase pumping can be seen as one of the most promising. The significant reduction of capital investment either on- or offshore together with an increased production rule has led 10 a growing demand for systems to be installed. Meanwhile the following advantages for using multi phase pumps are well known:reduced equipment capital cost and complexity:elimination of separate oil/water und gas lines:profitable production of marginal fields;increased production rates:reduced weight and space requirements (for offshore applications);prolonged reservoir life:, and,reduced wellhead hack pressure. The bigges1 challenge to be overcome by a piece of rotating equipment in multiphase service is the variation from 100% liquid to 100% gas at the inlet of the fluid to be moved. FIGURE: 1: Example of compression cell.(Available in full paper) This variation provides very difficult operating conditions for the pump, as well as for the mechanical seals, since this content is unpredictable. The transient nature of the wellhead stream creates pressure surges, slugs of liquid, and gas locks. A multiphase pump must be able to withstand all these rather harsh operating conditions. This kind of pump must be insensitive to changing liquid density and gravity and resistant to the corrosive effects of the well fluid impurities, such as H2S.CO2 (= scaling), and wax. The sand content of the fluid is an additional challenge for the pump. Multiphase pumps can be subdivided into two general groups, each with their own benefits and limitations. These are rotodynamic and positive displacement pumps. Rotodynamic pumps rely on the concept of helico-axial hydraulics. A multistage rotodynamic pump can employ up to 15 compression cells on a single shift. Each compression cell (Figure 1) comprises a rotating helico-axial flow impeller and a stationary diffuser. The produced effluent can thus be boosted over long distances without the need for prior separation and with no limitation regarding gas void fractions. These kind of pumps are compact, produce high flow rates, and have high sand handling capacity. Industrial rotodynamic multiphase pumps are available through two licensed manufacturers: Sulzer Pumps and Framo Engineering. Positive displacement pumps, known as "twin screw pumps" (Figure 2) could already handle gas void fractions up to 70%. In this respect, only some minor improvements had to be made to an existing pump design. The Twin Rotor Screw Pump consists of two contra-rotating screws. A certain amount of liquid is needed to seal the gaps between the screws and the liner. These kind of pumps can handle large amounts of gas and are less susceptible to pressure fluctuations. Industrial screw pumps are available from Bornemann, Leistritz, or Flowserve. FIGURE 2: Example of twin screw pump design.(Available in full paper)

청소기의 공력소음 특성 파악 및 저소음화에 관한 연구

The aeroacoustic characteristics and noise reduction method of a centrifugal fan for a bagless vacuum cleaner were studied. The major noise source of vacuum cleaner is the centrifugal fan. The impeller of the fan rotates over 30000 rpm and generates very high-level piercing noise. It was found that the dominant noise source of the fan is generated from the aerodynamic interaction between the highly rotating impeller and stationary diffuser. In order to reduce the high tonal sound generated from the aerodynamic interaction between the impeller and diffuser, tapered impeller was carefully designed and tested. The trailing edge of the tapered impeller was inclined and this reduces the flow interactions between the rotating impeller and the stationary diffuser because of some phase shift. The static efficiency of the new impeller is slightly lower than the conventional one. The overall SPL is reduced about 3.6 dBA. The SPL of blade passing frequency(BPF) is reduced about 6 dBA and the <TEX>$2^{nd}$</TEX> BPF is reduced about 20 dBA. The vacuum cleaner with the tapered impeller has lower noise level than that of the previous impeller and the strong tonal sound was dramatically reduced.