• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.76-80
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• 2015

The purpose of this study is to understand the cavitation phenomena in centrifugal pumps through computational fluid dynamics method. NPSH characteristic curve is measured from different flow operating conditions. Steady state, liquid-vapor homogeneous method with two equations transport turbulence model is employed to estimate the NPSH curve in centrifugal pumps. The Rayleigh-Plesset cavitation model is adapted as source term for inter-phase mass transfer in order to understand cavitation phenomena in centrifugal pumps. The cavitation incipient curve is clearly estimated at different flows operating conditions. A relationship is made between cavitation incipient and NPSH curve. Also the effects on water vapor volume fraction and pressure load distributions on the impeller blade are also described.

• International Journal of Fluid Machinery and Systems
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• v.9 no.3
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• pp.277-286
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• 2016

The development of heavy-duty process pumps, usually based on various design criteria, depends on the pump's application. The most important criteria are Q-H, efficiency and NPSH characteristics. Cavitation due to inlet recirculation is not often one of the design criteria, although many problems in pump operation appear because of inlet recirculation, when the operation range is from 0.5-0.8 $Q_{opt}$. The present paper shows that steady state CFD analysis of inlet recirculation can give quite good results for the design of new hydraulic shapes, which have been developed to expand operating range and to minimize the harmful influence of recirculation at part load. In this paper, the structures of inlet recirculation are presented, as well as detailed shapes of vortices between the blades for various operating regimes, axial velocity distribution at the impeller inlet, the experimental results of NPSH and efficiency characteristics of an existing and newly designed pump.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.637-642
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• 2001

Performance and cavitation characteristics of a turbo pump inducer which is designed for oxygen pump is experimentally investigated. It is found that the static performance of inducer is dependent on the location of inlet pressure measurement and that enough distance from inducer is ensured for accurate evaluation of performance. With the increase of flow rate. NPSH tends to decrease as opposed to pump characteristics, which seems to be due to the cavitation region.

• Atmosphere
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• v.27 no.3
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• pp.277-290
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• 2017

Characteristics of precipitation in South Korea during the 2016 Changma period (6/18~7/30) are analyzed in great details. El $Ni{\tilde{n}}o$-induced tropical Indian Ocean (IO) basin-wide warming lasts from spring to early summer and induces the western North Pacific subtropical high (WNPSH) circulation anomaly through an equatorial Kelvin wave during the 2016 Changma period. Along the northern edge of the WNPSH, strong precipitation occurred, in particular, over eastern China and southern Japan. During the Changma period, South Korea had the near-normal mean precipitation amount (~332 mm). However, about 226 mm of rain fell in South Korea during 1 July to 6 July, which amounts to 67% of total Changma precipitation in that year. Upper-level synoptic migratory lows and low-level moisture transport played an essential role, especially from 1 July to 3 July, in triggering an abrupt development of fronts over the Korean Peninsula and the eastern continent China. The front over the eastern China migrates progressively eastward, which results in heavy rainfall over the Korean peninsula from 1 to 3 July. In contrast, from 4 to 6 July, the typhoon (NEPARTAK) affected an abrupt northward advance of the North Pacific subtropical high (NPSH). The northward extension of the NPSH strengthens the Changma front and induces the southerly flows toward the Korean peninsula, giving rise to an increase in heavy rainfall. The NEPARTAK is generated due to interaction of the Madden-Julian Oscillation (MJO), equatorial Rossby wave and Kelvin waves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.858-865
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• 2006

SMART Pilot is a multipurpose small capacity integral type reactor. Main coolant pump (MCP) of SMART Pilot is a canned-motor-type axial pump to circulate the primary coolant between nuclear fuel and steam generator in the primary system. The reactor is designed to operate under condition of $310^{\circ}C$ and 14.7MPa. Thus MCP has to be tested under same operating condition as reactor design condition to verify its performance and safety. In present wort a test apparatus to simulate real operating situations of the reactor has been designed and constructed to test MCP. And then functional tests, performance tests, and endurance tests have been carried out upon a prototype MCP. Canned motor characteristics, homologous head/torque curves, coast-down curves, NPSH curves and lift-time performance variations were obtained from the qualification test as well as hydraulic performance characteristics of MCP.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.382-388
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• 2004

The hydraulic and suction performance of an inducer varies sensitively with the inducer geometry and this paper deals with solidity as the inducer geometry parameter. The typical performance characteristics of a basic inducer was investigated and tests with another three inducers of which the solidity is different from each other were performed, so the effect of solidity on the inducer performance was experimentally investigated. For a fixed flow coefficient, required NPSH of the inducer did not follow the conventional similarity rule, so this paper suggested another empirical formula. The hydraulic and suction performance was measured at four cases of the tip solidity ranged from 1.32 to 2.76. As long as the tip solidity had the value above 1.84, the hydraulic and suction performance of the inducer increased with decrease in the tip solidity. With further decrease in the tip solidity up to 1.32, however, inducer head decreased and the suction performance dropped sharply.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.185-190
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• 2001

The cavitation causes suction performance and efficiency of the high-speed pump to be reduced significantly To diminish these effects, the inducer has been used. Most of the inducer is designed at a maximum efficiency point of the pump, therefore suction performance drop due to effects of flow separation and inlet inverse flow is often observed at off-design point. The objective of this study is to find out the cavitation modes at various conditions by applying event detection technique and to design an inducer reducing cavitation. The pressure fluctuations at each cavitating condition were measured at inducer inlet and outlet locations using pressure transducers, which were located 90 degrees apart from each other to identify the cavitation modes. The time-frequency characteristics were analyzed by using Choi-williams distribution. In the second part of this paper, the inducer design method which uses nominal performance characteristic and onset condition of cavitation is introduced and applied to real situation.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.509-514
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• 2005

Main coolant pump (MCP) is a canned-motor-type axial pump to circulate the primary coolant between nuclear fuel rods and steam generators in an integral type reactor. The reactor is designed to operate under condition of 310 oC and 14.7 MPa. Thus MCP has to be tested under same operating condition as reactor design condition in order to verify its performance and safety. In present work, a test loop to simulate real operating situation of the reactor has been designed and constructed to test MCP. And then, as a part of qualification test, canned motor functional test and pump hydraulic performance test have been carried out upon a prototype MCP. Canned motor efficiency and pump hydraulic characteristics including homologous curves and NPSH curves were obtained from the qualification test.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.306-313
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• 2005

The performance of a regenerative pump is affected by many parameters, especially blade shape of impeller, leakage flow in the clearance and head losses at the inlet & outlet. An impeller with J-shape blade was designed and 5 times scale up model was tested at similarity conditions to evaluate the performance. Performance variations with clearance change were executed. The amounts of leakage flow through the clearance were estimated using the one-dimensional leakage flow models and analysis. Main leakage flow is generated through the gap between the impeller and casing. The inlet & outlet head losses were also estimated. Such corrections are very important to evaluate the final performance of the impeller and pump. Cavitation test was also performed at 1,200 rpm. NPSH of the regenerative pump was obtained and growth of cavity within blades was visualized.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2434-2439
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• 2008

This paper was studied on the cavitation instability of a Solution Pump Inducer in an absorption chiller-heater. Inlet pressure of LiBr and rotational speed at nominal mode are 2,800 Pa and 3,500 rpm respectively. Due to the marginal operation of available NPSH, the cavitation performance of the inducer is critical for the stable operation without the deterioration of head performance. In the study, cavitation performance and its mode of instability was investigated experimentally. Water was used as the working fluid and the test inducer was scaled up as 1.75 times for detail measurements and flow visualization. Inlet pressure was controlled by a vacuum pump. This research focused on types of cavitation instability and phenomena to investigate the possibility of harmful damage due to cavitation instability. Casing wall pressure and instantaneous inlet pressure was measured to observe the unsteady flow characteristics. Through the visualization and spectrum analysis of pressure, the occurrence region and intensity of asymmetric cavitation and cavitation surge are analyzed in the test inducer.