• Journal of computational fluids engineering
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• v.20 no.3
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• pp.35-40
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• 2015

Centrifugal pumps consume considerable amounts of energy in various industrial applications. Therefore, improving the efficiency of pumps machine is a crucial challenge in industrial world. This paper presents numerical investigation of flow characteristics in volutes of centrifugal pumps in order to compare the energy consumption. A wide range of volumetric flow rate has been investigated for each case. The standard k-${\varepsilon}$ is adopted as the turbulence model. The impeller rotation is simulated employing the Multi Reference Frames(MRF) method. First, two different conventional design methods, i.e., the constant angular momentum(CAM) and the constant mean velocity (CMV) are studied and compared to a baseline volute model. The CAM volute profile is a logarithmic spiral. The CMV volute profile shape is an Archimedes spiral curve. The modified volute models show lower head value than baseline volute model, but in case of efficiency graph, CAM curve has higher values than others. Finally for this part, CAM curve is selected to be used in the simulation of different cross-section shape. Two different types of cross-section are generated. One is a simple rectangular shape, and the other one is fan shape. In terms of different cross-section shape, simple rectangular geometry generated higher head and efficiency. Overall, simulation results showed that the volute designed using constant angular momentum(CAM) method has higher characteristic performances than one by CMV volute.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.165-171
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• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.309-312
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• 2007

The cryogenic fluid is the propellant for the liquid rocket engine. The design of space launcher vehicle is guided by minimum size and weight criteria, so the turbo pump solicits high impeller speed. Such high speed results in a zone of pressure drop below vapor pressure causing caivtation around inducer blades. The cryogenic fluid has different characters from isothermal fluid like water. The cryogenic fluid has very sensible thermodynamic properties and the phase change undergoes evaporative cooling. So, the developed code has to be modified cavitation modeling and it is added the energy equation for temperature sensitivity.

• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.234-241
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• 2004

Cavitation erosion properties of the Cu-9Al-4.5Ni-4.5Fe alloys (Al-bronze) surface-modified by flame quenching process have been investigated. After flame quenching at above $T_{\beta}$, the surfaces of Al-bronze with $\alpha$ + $\textsc{k}$ structure have been changed into the $\alpha$ + $\beta$' martensite phases by the eutectoid reaction of $\alpha$ + $\textsc{k}$\longrightarrow$\beta$ followed by the martensite transformation of $\beta$\longrightarrow$\beta$'. As a result of cavitation test, the measured incubation time and erosion rate of the $\alpha$ + $\beta$' alloy was 1.2 times higher and 1.5 times lower, respectively, compared to those of the conventional $\alpha$ + $\textsc{k}$ alloys, showing a remarkable increase of cavitation resistance with the formation of $\beta$' martensite. This is attributed to a preferential erosion of the $\textsc{k}$ precipitates that show the lowest resistance among the $\alpha$, $\textsc{k}$, $\beta$' phases under cavitation loading.ases under cavitation loading.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.290-298
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• 2005

A study of design and analysis for the POD type waterjet is conducted. The analysis and design of waterjet system are more difficult than that of conventional propulsor because waterjet is complicatedly composed of many parts which are impeller, stator, inlet, nozzle, etc. The streamline method is traditionally used in the design of pump whose characteristics are similar to those of waterjet. This streamline method, however, has some limitation in analysis of a viscous flow as well as the interaction of inlet part of hull. In the present study, the developed CFD program is applied to the analysis of POD type waterjet. The developed program is first validated by comparing the existed experimental results. The designed waterjet system is also analyzed by the developed CFD program and analyzed results show that the performance of the present POD type waterjet is above the requirement.

• Corrosion Science and Technology
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• v.21 no.6
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• pp.454-465
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• 2022

The objective of this study was to determine effects of temperatures and pH of sodium chloride solution with MgCl₂ ions on corrosion resistance of duplex stainless-steel X2CrNiMoN22-5-3 (DSS) and Ti 6Al 2Nb1Ta1Mo (Ti). Effects of sodium chloride concentration on corrosion resistance were also studied. Corrosion behavior and pitting morphology of duplex stainless steel (DSS) and Ti alloys were evaluated through potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). It was found that a decrease in pH significantly reduced the corrosion resistance of both alloys. Changes in chloride concentration and temperature had more substantial impact on corrosion behavior of DSS than on Ti alloys. Pitting corrosion was formed on DSS samples under all conditions, whereas crevice corrosion was developed on Ti samples with the presence of magnesium chloride at 90 ℃. In conclusion, magnesium chloride ions in an exceedingly strong acidity solution appear to interact with re-passivation process at the surface of these alloys and influence the resulting surface topography.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.5
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• pp.296-304
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• 2023

Cavitation tests for a waterjet propulsor of an amphibious vehicle are carried out in the Large Cavitation Tunnel. Waterjet pump performances and cavitation characteristics including thrust breakdown performances are investigated in the tests. In addition, cavitation characteristics for waterjet propulsors working inside the intake are calculated by using a commercial CFD code, Star-CCM+. Sliding mesh is implemented to a rotating impeller and the k-epsilon turbulence model is chosen. Cavitation bubble growth and collapse are estimated using the Schnerr-Sauer cavitation model based on Rayleigh-Plasset equation. Calculated results agree fairly well with experimental results. The re-design of the waterjet propulsor is performed to enhance waterjet cavitating performances and calculated results show that waterjet thrust breakdown characteristics are significantly improved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1191-1198
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• 2011

The use of a ventricular assist device (VAD) can raise the one-year survival rate without cardiac transplantation from 25% to 52%. However, malfunction of the VAD system causes 6% of VAD patients' deaths, which could possibly be avoided through the development of new VADs in which VAD malfunctions do not affect the patient's heart movement or hemodynamic state. A conventional VAD has an impeller or vane for propelling blood that can allow blood to regurgitate when the propelling force is weaker than the aortic pressure. In this paper, we developed a new pulsatile conduit-shaped VAD that has two valves. This device removes the possibility of blood regurgitation and has a small stationary area even when the pumping force is extremely weak. We estimated the characteristics of the device by measuring the outflow and the pressure of the pump in in-vitro and in-vivo experiments.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.11-18
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• 1998

This study describes sea trial tests for a waterjet propulsion system attached in the hybrid super high speed cargo ship named "Narae". A measuring technique of jet velocity, gross thrust and impeller torque for the waterjet system is explained. From the measured data in sea trial test, performance of the waterjet propulsion system is analyzed and compared with model test results of a similar waterjet system which was carried out in 1996. The erective horse power estimated from sea trial tests shows a good agreement with resistance test results of the model ship. The optimum rising height is estimated as 0.75 m, and the overall efficiency of the waterjet system is predicted as 0.315 at 15 knots. Useful data such as the pump performance, the jet efficiency, the losses of inlet duct and nozzle were obtained. Test results show a similar behavior to the model test results.

• Clean Technology
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• v.27 no.1
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• pp.39-46
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• 2021

A road structure washing vehicle equipped with a 4 HP, 80 LPM ultrafine bubble generator was used to clean a tunnel wall and the surface of the surrounding structure, consisting of concrete and tiles, in a heavy traffic area around an apartment complex in the city. Ultrafine bubbles were generated by supplying air at 2 to 3 LPM and using a specially designed nozzle, whereas fine bubbles made by an impeller in a gas-liquid mixing self-priming pump were produced with an average diameter of 165.4 nm and 6.81 × 107 particles mL-1. Using a high pressure washer gun that can perform high-pressure cleaning at 150 bar and 30 LPM, ultrafine bubbles were used to wash dust adsorbed on the surface of the road structures. The experimental analysis was divided into before and after washing. The samples were analyzed by applying ISO 8502-3 to measure surface contamination of dust adsorbed on the surface. Using the transparent tape attached to the surface, the removal rate was calculated by measuring the weight of the dust, and the number of particles was calculated using the gravimetric method and the software, ImageJ. The results of the experiment showed that the number of dust particles adsorbed on the tile wall surface before and after washing were 3,063 ± 218 particles mL-1 and 20 ± 5 particles mL-1, respectively, with weights of 580 ± 82 mg and 13 ± 4 mg. Particles on the surface of the concrete structure before and after washing were 8,105 ± 1,738 particles mL-1 and 39 ± 6 particles mL-1, respectively, with weights of 1,448 ± 190 mg and 118 ± 32 mg.