• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.36-44
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• 2000

The flow at the impeller exit is important to validate engineering design and numerical analysis of pumps. We installed axisymmetric collector instead of the volute casing, so there is no interaction between the impeller and casing. A hot-film probe and a high response pressure transducer are used to investigate the flow at impeller exit and vaneless diffuser region for design and off design flow rate. For a single suction centrifugal pump of low specific speed, the flow field such as velocity, flow angle, and total pressure are measured by traversing the probe across the vaneless diffuser. These data can be used for performance prediction, design, and numerical analysis of pumps.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.391-396
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• 2000

The present experimental study is focused on the application of multi-point simultaneous measurement by PIV(Particle Image Velocimetry) to guide vane region within a diffuser pump. Various different kinds of clearance were selected as experimental conditions. Optimized cross correlation identification to obtain velocity vectors was implemented with direct calculation of correlation coefficients. Fine optical setup important in PIV performance is arranged for the accurate PIV measurement of high-speed complex flow. Various flow patterns are represented quantitatively at the stator passages.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2002.05a
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• pp.161-166
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• 2002

The resent experimental study is focused on the application of multi-point simultaneous measurement by PIV Particle Image Velocimetry) to guide vane region within diffuser pump. Various different kinds of rotational veto ity and changing clearance between Guide Vane and Impeller were selected as experimental condition. Optimized ross correlation identification to obtain velocity vectors is implemented with direct calculation of correlation coeffi cients. Fine optical setup concerned with PW performance is arranged for the accurate PW measurement of high peed complex flow. Variable flow pattern are represented quantitatively at the stator region.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.234-241
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• 1999

The flow at the impeller exit is important to validate engineering design and numerical analysis of pumps. However, it is not easy to measure the flow at the impeller exit and evaluate the impeller performance since there is usually strong interaction between the impeller and the volute casing. We installed axisymmetric collector instead of the volute casing, so there is no interaction between the impeller and casing. A 3-hole Cobra probe is used to investigate the flow at impeller exit and vaneless diffuser region for design and on design flow rate. For a single suction centrifugal pump of low specific speed, the flow field such as velocity, flow angle, and total pressure are measured by traversing the probe across the vaneless diffuser. These data can be used for performance prediction, desist and numerical analysis of pumps.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.727-736
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• 2016

In this study, a high-pressure multistage pump used in the combined cycle power plants is analyzed. The pump performance characteristics (differential head and efficiency) are numerically analyzed for different shapes of the radial diffuser. The design variables selected for the radial diffuser are, number of vanes, diameter ratio ($D_4/D_3$), return channel outlet angle(${\alpha}_6$), and pressure recovery factor ($C_p$). The numerical analysis results showed that the differential head and efficiency are the highest when the diameter ratio is the highest. Further, it was observed that the differential head was lower when the return channel outlet angle was $60^{\circ}$ than when it was $90^{\circ}$, because of pre-swirl at the diffuser outlet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.789-795
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• 2014

In this study, the distribution characteristics of diffusers with various shapes that are installed in an open-type thermal storage system are numerically investigated. Four diffusers are designed to distribute a working fluid evenly through the holes on bifurcated pipes. Three-dimensional steady simulations of incompressible laminar flow are conducted using commercial software (ANSYS-FLUENT). The simulation results show that both the bidirectional header-type diffuser and the H-type diffuser distribute the working fluid evenly whereas both the unidirectional and the bidirectional diffusers distribute the working fluid unevenly. The results also show that the H-type diffuser requires a higher head of pump than the bidirectional header-type diffuser. Therefore, the bidirectional header-type diffuser is recommended for use because it enables even distribution of the working fluid and requires a low head of pump.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1147-1155
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• 2002

Discharge flows from a centrifugal pump impeller with a specific speed of 150 [rpm, m$^3$/min, m] were experimentally investigated. A large axisymmetric collector instead of a volute casing was installed to obtain circumferentially uniform flow, i.e. without interaction of the impeller and the volute. The unsteady flow was measured at the impeller exit and vaneless diffuser using a hot film probe and a pressure transducer. The flow at impeller exit showed pronounced jet-wake flow patterns. The wake, which was on the suction/hub side at high flow rate, became enlarged pitchwisely on both the hub and the shroud side as the flow rate decreases. The pitchwise non-uniformity of the flow rapidly decreased along the downstream and the non-uniformity almost disappeared at radius ratio of 1.18 for medium flow rate. The mean vaneless diffuser flow was reasonably predicted using a one dimensional analysis when an empirical constant was used to specify the skin friction coefficient. The data can be used for a centrifugal pump impeller design and validation of CFD codes and flow modeling.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.544-551
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• 2005

The flow characteristics have been numerically investigated for various shapes of the diffuser/nozzles which are used for a valveless micro-pump. The important parameters considered in this study are the throat width ($15\~120\mu$m), the taper angle ($3.15\~25.2^{\circ}$), and the diffuser length ( $600\~4,800\mu$m), and the size of the middle chamber ($1\~16mm^2$). To find the optimal values for these parameters, steady state calculations have been performed assuming the constant pressure difference between the inlet and exit of the flow For the taper angle and the throat width, it is found that there exists an optimum at which the net flow rate is the greatest. The optimal taper angle is in the range of $10\~20^{\circ}$ for all the pressure differences; and the throat width indicates an optimal value near $75\mu$m for the case of 35 kPa pressure difference. The net flow rate is also influenced by the size of the middle chamber. With decreasing chamber size, the net flow rate is reduced because of the interference between two streams flowing into the middle chamber. The unsteady pulsating flow characteristics for a micro-pump with a given diffuser/nozzle shape have been also investigated to show the validity of the steady state parametric study.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.520-524
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• 2000

A ejector system is one of the fluid machinery, which has been mainly used as an exhaust pump or a vacuum pump. The ejector system has often been pointed out to have only a limited efficiency because it is driven by pure shear action and the mixing action between primary and secondary streams. In the present work, numerical simulations were conducted to investigate the effects of the geometry and the mass flow ratio of supersonic ejector-diffuser systems on their mixing performance. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations, and the standard ${\kappa}-{\varepsilon}$ turbulence model was used to close the governing equations. The flow fields of the supersonic ejector-diffuser systems were investigated by changing the ejector throat area ratio and the mass flow ratio. The existence of the second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle, and served to enhance the mixing performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1059-1065
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• 2010

An analysis was conducted to predict the hydraulic performance of a reactor coolant pump (RCP) of SMART at the off-design as well as design points. In order to reduce the analysis time efficiently, a single passage containing an impeller and a diffuser was considered as the computational domain. A stage scheme was used to perform a circumferential averaging of the flux on the impeller-diffuser interface. The pressure difference between the inlet and outlet of the pump was determined and was used to compute the head, efficiency, and break horse power (BHP) of a scaled-down model under conditions of steady-state incompressible flow. The predicted curves of the hydraulic performance of an RCP were similar to the typical characteristic curves of a conventional mixed-flow pump. The complex internal fluid flow of a pump, including the internal recirculation loss due to reverse flow, was observed at a low flow rate.