The cavitation characteristics for the head drop in a mixed-flow pump were investigated with the steady- and unsteady-state analysis. Two mixed-flow pump models exhibiting a different incidence angle were analyzed under the cavitation condition. The model with a larger incidence angle obtains relatively poor suction performance. Moreover, the steady-and unsteady-state analysis indicate different head level under the cavitation condition. The results of the unsteady-state analysis are more accurate to the experimental results. The head of a fully convergent steady-state analysis is not even distributed in the head fluctuation range of the unsteady-state analysis. However, the head drop due to the decrease of inlet pressure has almost the same distribution and gradient. In addition, the amount and shape of the bubbles were presented with the time variation, which were also compared with the averaged result of steady-state analysis. The bubbles show a larger oscillation in the model which has a larger incidence angle. The oscillation of the bubbles is related to the magnitude of the head fluctuation.

Micro hydro turbines are getting renewed research interest in recovering unused energy from systems like water supply pipelines, sewage treatment and transportation plants, chemical and oil refineries, etc. and making them energy efficient for sustainable development. The present work dealt with this aspect wherein the unused energy of the hot water transportation pipelines, which was earlier throttled by pressure differential control valve (PDCV), was harvested and used elsewhere. A special class of multipurpose micro hydro turbine known as the positive displacement turbine was developed for the present application which involved very low flow rates with high heads and very low specific speeds and to replace the PDCV which was frequently failing due to cavitation causing loss of energy. A framework was developed for designing such turbines and predicting their performance using CFD. The reasons for the occurrence of cavitation and flow pulsations were also examined and remedial measures were incorporated for their elimination. At the rated condition during experimental study, the base design generated 7.31 kW power with an overall efficiency of 67.7%. The socio-economic analysis was also carried out which concluded that the PDT will aid in energy conservation and reduction in CO2 emissions. (C) 2019 Elsevier Ltd. All rights reserved.

This paper presents detailed analyses on the steady and unsteady internal flow characteristics of a three-stage centrifugal pump under design and off-design conditions. A numerical analysis is conducted by solving three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model. The results of the steady and unsteady numerical analyses throughout the flow region are analyzed and compared with experimental data. A reattachment modification is used in the SST turbulence model to better capture the characteristics of flow separation due to boundary layer reattachment under the design and off-design conditions. The unsteady numerical results are in reasonable agreement with the experimental data, whereas they differ from the steady numerical results when it comes to the internal flow fields at each component stage. In particular, the time-averaged internal flow phenomena obtained from the unsteady analysis are close to the real field conditions of this pump at low flow rates. The hydraulic performances with and without the reattachment modification are similar throughout the flow region, whereas the respective flow characteristics in each impeller component are considerably different, particularly at low flow rates.

Positive displacement turbines (PDT) find their use in applications with low flowrate, high head and having lower specific speed requirement, which is below the operational range of the conventional turbines. In the present work, an initial PDT was designed using the governing equations of fluid flow to extract the unused energy from the hot water transportation pipelines. The turbine was of lobe type with two rotors each having four lobes. The tip clearance, side clearance and other leakage losses were considered while designing using fundamental principles coupled with the empirical co-relations from the literature. The initial design's performance analysis had been carried out numerically using commercial computational fluid dynamics (CFD) code ANSYS CFX. The objective of the present study was to reveal the performance of the preliminary design for the given conditions and examine the causes of pulsations in torque, pressure and flow rate from the fluid flow characteristics.

Positive displacement turbine (PDT) is a special class of hydraulic turbine which finds its usage in the applications involving very low flow rates with high heads and very low specific speeds. In the present case, a PDT was designed and developed to replace the pressure differential control valve (PDCV) and to harness the unused differential pressure energy from the water supply pipeline system. The turbine was designed considering the on-site available head and flowrate. The rotors were twisted to damp the fluctuations in pressure, flow rate and torque. The primary objective of the present study was to analyze the effect of the stator shape on the performance of PDT using Computational Fluid Dynamics approach. The governing equations of the fluid flow were solved using an unsteady approach to capture accurately the pulsating nature of the flow using ANSYS CFX v17.1. Initially a circular stator turbine was used for transporting the working fluid to and from the turbine rotors and later the effects of square and rectangular shaped stator designs were also checked. It was observed that the performance of the PDT slightly improved with rectangular and square stators in terms of hydraulic efficiency than with circular stator with low flow fluctuations.

This paper presents a detailed analysis of the internal flow characteristics of a three-stage centrifugal pump at design and off-design conditions. Numerical analysis is conducted by solving three-dimensional steady and unsteady Reynolds-averaged Navier – Stokes equations with the shear stress transport (SST) turbulence model. The results of steady and unsteady numerical analyses are analyzed and compared with experimental data throughout the flow region. Moreover, a reattachment modification in the SST turbulence model is applied to better capture the characteristics of flow separations arising from boundary layers reattaching at design and off-design conditions. The results show that the unsteady numerical results are in good agreement with the experimental data. Additionally, hydraulic performance with and without the reattachment modification is similar throughout entire flow region whereas the respective flow characteristics for each impeller component are considerably different, especially at low-flow-rate conditions.

논문에서는 사류펌프의 성능을 향상시키는 최적화 방법을 개발하였다. 본 연구에서 개발한 최적화 방법은 유동해석코드인 CFX 와 최적화 소프트웨어인 HEEDS 를 연계하는 프로세스로 이루어진다. CFX 는 유체기계해석 분야에서는 잘 알려진 소프트웨어로 해석결과의 신뢰성은 이미 검증되었으나, 새롭게 소개되고 있는 HEEDS 는 주로 구조해석 분야에서 최적화를 수행한 사례가 보고되어 있다. 이에 본 논문을 통해 유체기계에 적용하여 최적화 결과를 검토하였다. HEEDS 에는 SHERPA 라는 최적화 기법이 탑재되어 있으며, 다수의 설계변수를 설정할 수 있어 변수간의 교호작용 등을 효율적으로 검토할 수 있다. 본 논문에서는 DOE 방법으로 최적화가 이루어진 사류펌프 임펠러에 대해 개발된 방법을 적용하여 최적화 결과의 타당성과 안정성을 검토하였으며, 같은 방법을 디퓨저에 적용하여 최적화 형상을 검토하였다. 본 논문에서 개발된 최적화 방법을 이용하여 사류펌프 최적화를 수행한 결과, DOE 방법을 이용한 설계보다 개선된 결과를 적절한 시간 내에 얻을 수 있음을 확인하였다.

Abstract — The crude oil in an oil well exists in various phases such as gas, seawater, and sand, as well as oil. Therefore, a phase separator is needed at the front of a single-phase pump for pressurization and transfer. On the other hand, the application of a multiphase pump can provide such advantages as simplification of the equipment structure and cost savings, because there is no need for a phase separation process. Therefore, the crude oil transfer method using a multiphase pump is being applied to recently developed oil wells. Due to this increase in demand, technical demands for the development of multiphase pumps are sharply increasing, but the progress of research into related technologies is insufficient, due to the nature of multiphase pumps that require high levels of skills. This study was conducted to verify the reliability of pump performance evaluation using numerical analysis, which is the basis of the development of a multiphase pump. For this study, a model was designed by selecting the specifications of this study. The performance of the designed model was evaluated through numerical analysis and experiment. The results of the performance evaluation were compared to verify the reliability of the result using numerical analysis.

The crude oil produced from well contains a mixture of oil, gas and water. The existing pump system that uses a single phase pump requires a separator to separate the crude oil. Changing from a single phase pump to a multiphase pump significantly reduces costs because a multiphase pump does not require a separator. Therefore, most wells currently being developed apply the multiphase pump system. In this study, a multiphase pump was designed using a multi objective optimization technique. To conduct research, a base model was chosen and its performance was evaluated through numerical analysis. The design variables and variable ranges were set for the impeller and the diffuser. Based on the selected variables, experiment sets were produced. The experiment sets were also evaluated for their performance using numerical analysis. Based on the performance evaluation results of each experiment set, the optimization model for a multiphase pump was derived using Response Surface Method (RSM). In addition, each model's performance for multiphase flow was also evaluated according to changes in Gas Volume Fraction (GVF) using multiphase numerical analysis. Furthermore, the internal flow characteristics of each model were analyzed.

A PWR design incorporates a passive auxiliary feedwater system equipped with one passive condensation heat exchanger (PCHX) which consists of inclined V-shaped tube bundles submerged in a water pool of which the top is open to the atmosphere. During the PCHX operation, saturated steam flows into the PCHX where steam is condensed inside of the tubes by cooling the outer side with the pool water. Then, the condensate flows out passively by gravity. Because the thermal-hydraulic characteristics in the PCHX determine the condensation mass rate and the possibility of thermal stratification-induced fatigue of the pool tank wall, system instability and waterhammer, it is important to understand the phase change flow in the PCHX. In this paper, the complex phase change heat transfer and multi-phase flow in a PCHX tube model were numerically simulated. The single fluid multi-component flow model with the equilibrium phase change model was employed for the condensation phase change flow inside the tube and the two-fluid model with the wall boiling model and the equilibrium phase change model was used for the boiling-induced natural convection outside the tube in the pool. Based on the present numerical simulation, the characteristics of the heat transfer and flow in the PCHX are discussed and illustrated for some typical results.

Temperature of pressurized water reactor (PWR) core is a key parameter used widely for judging the initiation of emergency operating procedures and severe accident management. Since direct measurement of the fuel cladding surface temperature using thermocouples is not practicable currently, the coolant temperature at the core exit locations is monitored instead. Several experimental researches showed that the CET rise during a loss of coolant accident (LOCA) and its magnitudes were always lower than the actual fuel rod cladding temperature at the same time. In this regard, a theoretical analysis of the transient heat transfer of coolant flow in a PWR core is needed to confirm the findings from the previous experimental works. This paper addresses numerical simulation of the transient boiling-induced multiphase flow through a simplified PWR core model during a LOCA by a commercial computational fluid dynamics (CFD) code. The calculated results are discussed to understand the transient heat transfer mechanism in the core and to provide useful technical information for reactor design and operation.

For the initiation of emergency operating procedures and severe accident management of most commercial nuclear reactors worldwide, monitoring of the core temperature is required. Currently, it is not practicable to directly measure the temperature of fuel cladding surface temperature due to some technical limitations.Thus, measurement of the coolant temperature by using thermocouples at the core exit locations is widely used. However, the core exit temperature (CET) may not represent the core temperature properly because the measurement locations are somewhat distant from the heat generating part of fuel rod assembly. In this regard, it is important to assess the difference between the fuel cladding temperature and the CET.The objective of this study is to get the general insight and understanding of the boiling-induced multiphase flow inside fuel rod bundle during an abnormal operation mode following a loss-of coolant accident by comparing the calculation results of the CET deviation from the fuel cladding (or in-core) temperature for the two different cases of the present analysis model subjected to a coolant flowrate of either 100% or 50% of the nominal value.To do this, three-dimensional multi-phase computational fluid dynamics (CFD) calculations of a simplified pressurizer water reactor (PWR) core model were performed for both reactor operating modes.As a result, it was found that the calculated CETs are much lower than the maximum fuel rod cladding temperatures during both operating modes. Consequently, it is considered that the temperature deviation should be taken into account carefully to use the measured CETs for the initiation of emergency operating procedures and severe accident management of commercial nuclear reactors.

This paper addresses the numerical simulation of two-phase flow heat transfer in the helically coiled tubes of an integral type pressurized water reactor steam generator under normal operation using a computational fluid dynamics code. The shell-side flow field where a single-phase fluid flows in the downward direction is also calculated in conjunction with the tube-side two-phase flow characteristics. For the calculation of tube-side two-phase flow, the inhomogeneous two-fluid model is used. Both the Rensselaer Polytechnic Institute wall boiling model and the bulk boiling model are implemented for the numerical simulations of boiling-induced two-phase flow in a vertical straight pipe and channel, and the computed results are compared with the available measured data. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. Both the internal and external turbulent flows are simulated using the standard k-ε model. From the results of the present numerical simulation, it is shown that the bulk boiling model can be applied to the simulation of two-phase flow in the helically coiled steam generator tubes. In addition, the present simulation method is considered to be physically plausible in the light of discussions on the computed results.

Numerical studies have been conducted to predict the solid-liquid separation efficiency of turbulent flow in a hydrocyclone using a commercial CFD code. To validate the CFD code, several preliminary numerical calculations are carried out to determine the influence of parameters such as grid systems, numerical schemes, and turbulence models. The numerical studies have been performed on the hydrocyclones with the different vortex finder geometries by changing the mass flow rate, and the results were compared with the experimental data. The results show that the CFD code can be used as a design tool to improve the performance of hydrocyclones.

A commercial CFD code is used to compute the 3-D viscous flow field within the impeller of a centrifugal pump. Several preliminary numerical calculations are carried out to determine the influence of the parameters such as the grid systems, the numerical schemes, the turbulence models and the shape of the vaneless diffusers at the design flow rate. The results of the preliminary study are used for the calculation of the off-design flow conditions. The circumferentially averaged results such as the radial and tangential velocities, the exit flow angle, the slip factor, the static pressure and the total pressure are compared with the experimental data at the impeller exit to discuss the influence of the prescribed parameters.