Impeller Characteristics Research Articles

Numerical study of the equivalent roughness effect on the low-flow centrifugal compressor impeller characteristics

The article presents the results of a numerical study of the effect of equivalent sandgrain roughness on the characteristics of a low-flow centrifugal compressor stage. Low-flow stages are widely used in high-pressure compressors as the last stages. These compressors are used for natural gas booster compressor stations, as well as in technological processes for the production of methanol, ammonia, high - pressure polyethylene, etc. The efficiency of the low-flow stages is lower than that of medium-and high-flow centrifugal compressors stages. Stages operate at high pressure and have low gas volume flow rates. For this reason they have narrow channels of the flow part, significant friction and leakage losses. The study was conducted in the Ansys CFX 19.2 software package. In the first part of the study, the low-flow stage numerical model is validated with the test results. Full-scale tests of the stage were carried out at the LPI-SPbPU earlie. In the second part of the study, impeller equivalent sand-grain roughness numerical study carried out. As a result, the characteristics of the stage were obtained at four different values of equivalent sand-grain roughness ks. The impeller losses were estimated. It is established that when the ks values increase, the polytropic head and efficiency values do not decrease equally over the entire characteristic. Characteristics are significantly reduced in areas of high expenditure and change slightly with minimal expenditure. The internal head coefficient varies slightly depending on ks.

Effects of Impeller Diameter on High-Speed Rescue Pump

Impeller diameter is a crucial design parameter of high-speed rescue pumps because it affects the performance and inner flow characteristics of these pumps. In this study, a pump with an impeller diameter of 248 mm was modeled and its performance was tested. Numerical simulations were conducted under steady and unsteady states, in which the sizes of the impeller diameters were designated as 248 mm (original), 235.6 mm (5% trimmed), 223.2 mm (10% trimmed), and 210.8 mm (15% trimmed). ANSYS software was used to test the shear stress transport (SST k-ω) of the four models, and results agreed well with experimental data. Diameter size affected impeller characteristics in both steady and unsteady states. Subsequently, the differences in performance, hydraulic loss, pressure pulsation, and radial force of the impellers were evaluated. In the performance test, the head and efficiency of the pump decreased as impeller diameter was reduced. The result trends are in accordance with the trim law within the acceptable error range. In terms of hydraulic loss, the impeller and diffuser vane components presented opposite trends with flow rate increase. Finally, in terms of pressure pulsation and radial force, the amplitude diminished while periodicity improved as impeller diameter decreased.

Underwater Machinery Source Identification by Signal Demodulation

Sound from underwater machinery systems like boats, small ships, ships, submarines, submersible pumps, etc. possess information about the systems. Usually, sound identification and extraction of required information from the passive sound source environment have been a challenging task in underwater acoustics. This paper deals with identification of noise source by carrying out experiments for various impeller speeds and different hydrophone locations. In turn, these experiments paved way to identify impeller signal in single sound source and multiple sound source scenarios. In single sound source scenario, impeller signal has been studied through spectrum analysis. In multiple sound source scenario, amplitude demodulation technique has been proposed to identify noise sources for further examination of impeller in this work. The results shown in this work shed light about the influence of impeller characteristics through various parameters like speed of the impeller, location of hydrophone, etc. The result also shows amplitude demodulation is an effective technique to distinguish noise sources and impeller characteristics in noisy environments.

Mixed-Flow Impeller Characteristics in Baffled Mixing Tank

In recent times, impellers have been designed and modified to combine unique hydrodynamic features to overcome redundancy during mixing. One of such impeller is the mixed-flow impeller which displays a unique combination of radial and axial flow. In this paper, the flow characteristic of a mixed-flow impeller is reported. The main focus is to compare the axial and radial characteristic of the velocity component using experimental and numerical study. The continuity and momentum equation were solved using the Reynold’s stress model (RSM). The field of view away from and below the impeller compared better with the numerical solution for the mean, radial and axial velocity component. Although the RSM was used at a higher computational cost, associated power number and energy of the impeller was also observed to be better predicted.

Experimental investigation of a direct driven radial compressor for domestic heat pumps

The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a.

Suppression of Unstable Flow at Small Flow Rates in a Centrifugal Blower by Controlling Tip Leakage Flow and Reverse Flow

The effects of the inlet recirculation arrangement on inducer stall and the diffuser width on diffuser stall in a high-specific-speed-type centrifugal impeller with inducer were analyzed by numerical simulation and also verified experimentally. It was found that the incipient unstable flow occurs due to a rolling-up vortex flow, resulting from an interaction between the tip leakage flow and the reverse flow accumulated at the pressure side immediately downstream of the inducer tip throat, in which a strong streamwise component of vorticity is included. By forming the inlet recirculation flow, the tip leakage vortex is effectively sucked into the suction ring groove, and the flow incidence is decreased simultaneously. The unstable flow range of the test blower was reduced significantly by about 45% without deteriorating the impeller characteristics by implementing optimally both the ring groove arrangement and the narrowed diffuser width.

The effects of impeller characteristics in the hydrogenation of aniline on Ru/C catalyst

Effects of impeller characteristics have been studied in the hydrogenation of aniline on Ru/C catalyst. Dual impellers were employed and the experiments were performed at 300 rpm using a lab-scale reactor. Reaction with disk turbines (DT) resulted in the higher cyclohexylamine (CHA) selectivity and higher reaction rate compared to that with pitched blade turbines (PBT). When a combination of PBT and DT impellers was employed, high product selectivity and reaction rate were obtained and the selectivity was maintained constant. Changes in the product selectivity with the impeller geometry were explained in terms of the relative rates of the side reactions depending on the hydrogen concentration in the reaction mixture.

Effects of Inlet Passage Width Contraction of Low-Solidity Cascade Diffusers on Performance of Transonic Centrifugal Compressor.

Low-solidity circular cascades have been applied successfully as a part of the diffuser system of a transonic centrifugal compressor. Three types of diffusers with and without an inlet passage width contraction or a pinch upstream of a cascade were tested. An appropriately contracted diffuser realized high compressor efficiency at high rotor speed due to the decrement in input power. Effects of a pinch on surge and choke were also discussed. Choke occurred at the throat of cascades of a pinched-type diffuser at lower flow rate than the inducer choke flow in spite of a low-solidity cascade. A pinched diffuser had a stabilizing effect on the diffuser characteristics but only a small amount of gain in the surge margin was obtained owing to the change in impeller characteristics.

Effects of splitter blades on centrifugal impellers. 2nd, The change of the impeller characteristics.

The characteristics of the centrifugal impellers with splitter blades were derived from flow measurements within the impeller passages shown in the first report. The effects of the splitter blades on the characteristics of an unshrouded and a shrouded impeller were investigated in comparison with the impellers removed splitter blades. In the impeller with splitter blades, the pressure difference between the suction and the pressure surface of the passage tends to be smaller, and the absolute circumferential velocity and the total pressure at the impeller exit become considerably larger than that in the impeller removed splitter blades. By the addition of splitter blades, the static pressure at the impeller exit increases in the unshrouded impeller, and decresases in the shrouded impeller.

Non-linear analyses of cavitating flows through a centrifugal impeller by a singularity method.

Cavitating flows through a centrifugal impeller were analysed by using a singularity method. The location of cavity surface was determined by an iterative method and the cavity surface boundary conditions were applied exactly on the surface. The closed cavity model of the present calculation gives a thicker face cavity and a thinner back cavity as compared with the results of linear cavity models which assume that the boundary condition can be applied approximately on the vane surface. In case of back cavities, which have smaller thickness, the impeller characteristics are close to those obtained by using the linear cavity model ; higher head was obtained for face cavities. Models assuming a cavity wake with constant displacement thickness or a wake filled with dead water gave significantly lower head compared with that obtained by the closed model. Thus, it was found that, for centrifugal impellers, the cavity wake has a large effect on the characteristics.

The performance of a high head reversible pump-turbine (1st report, Effect of impeller characteristics on the pump performance in low flow rate range)

In order to find a factor to determine the minimum head point in the pump low flow rate range of a pump-turbine, characteristics of an impeller are studied by using a casing, which has a wide annular room at the outlet of the impeller are studied by using a casing, which has a wide annular room at the outlet of the impeller and no guide vanes and stay vanes. The investigation shows the reverse flow at the inlet of the impeller at the minimum head point. The occurance of the reverse flow depends on the deceleration ratio of flow velocity on the band of the impeller which is analysed by quasi three dimensional method.