Minimum Static Pressure Research Articles

Numerical and Experimental Investigation of the Aerodynamic for the IceWind Blades VAWT

The main aim of the present work is the numerical and experimental investigation carried out in, for the IceWind blade type with two heights (Model 1=250 mm) and (Model 2=125 mm). In this study a computational fluid dynamic CFD is used to simulate the aerodynamic characteristics modelled medals at 10 m/s. The finite volume method and SST (k-ω) turbulent model were used in this simulation. In the experimental part the models are manufactured by three dimensions printing machine (3D printing) using Polylactic acid (PLA), and the experimental work was implemented by using low speed wind tunnel that is available at University of Baghdad/College of Engineering/Mechanical Engineering Department/Fluid Mechanics Laboratory. The finding results from the numerical simulation show that the maximum static pressure at (Model 1) was 69.39 (pa) and the maximum velocity was 13.5 (m/s). For (Model 2) it was 62.58 (pa) and the maximum velocity was 12.69 (m/s). The minimum static pressure at (Model 1) was -66.69 (pa) and the minimum velocity was 1.04 (m/s). For (Model 2) it was -47.94 (pa) and the minimum velocity was 0.98 (m/s). The experimental results showed that (Model 1) give high performance in comparison with (Model 2) , because rotational speed 610 RPM and the power coefficient was 0.0688 also the tip speed ratio was 0.4533, when (Model 2) give rotational velocity were 265 RPM and the power coefficient was 0.03551 also the tip speed ratio was 0.2601.

Boil-Off Gas Generation in Vacuum-Jacketed Valve Used in Liquid Hydrogen Storage Tank

The boiling point of liquid hydrogen is very low, at −253 °C under atmospheric pressure, which causes boil-off gas (BOG) to occur during storage and transport due to heat penetration. Because the BOG must be removed through processes such as re-liquefaction, venting to the atmosphere, or incineration, related studies are required to estimate the heat transfer of storage and transport devices and to improve insulation to reduce BOG generation. In this study, a vaporization analysis was performed on a vacuum-jacketed valve used in liquid hydrogen storage and transport devices to calculate the amount of BOG generation considering the flow characteristics at the vena contracta and the saturation temperature. At a pressure of 1 bar in the liquid hydrogen storage tank, the maximum fluid flow velocity and minimum static pressure occurred at the vena contracta, with values of 62.9 m/s and −0.4 bar, respectively, and the BOG generation rate was estimated as 0.132 m3/h, where the saturation temperature was minimized at 19.3 K. Furthermore, through case studies, when the pressure in the liquid hydrogen storage tank increased to 1.5 and 2 bar, the static pressure and saturation temperature decreased, and the BOG generation rate increased to 0.221 and 0.283 m3/h, respectively.

Flow field and convective heat transfer of small-scale Taylor-Couette flow induced by end leakage

More and more researchers have paid attention to Taylor-Couette flow whose axial dimension is much larger than other dimensions. However, featured by the limited axial length of the bearing, its flow field and convective heat transfer between the rotator and the stator are highly conglutinated with the leakage at the end of the clearance. An investigation was conducted on the flow field and convective heat transfer of small-scale Taylor-Couette flow induced by end leakage through means of numerical simulation and experimental measurement. The static pressure and temperature of the stator were captured by a micromanometer and a time-resolved infrared camera, respectively. Large Eddy Simulation (LES) was performed to reveal the instantaneous and mean flow field of the shearing flow. Results show that the flow field and convective heat transfer are tightly associated with the presence of end leakage. As approaching the end of the clearance, the flow is dominated by the axial flow induced by the end leakage, and then a series of Taylor vortices gradually distorts and tilts as moving downstream. Along the angular direction, the maximum and minimum static pressures take place near minimum clearance height, respectively. The static pressure along the angular direction and the axial velocity near the minimum clearance height as well as the Nusselt number increase with increases of the rotational Reynolds number and the eccentricity ratio while decreasing with an increase of the dimensionless clearance height. Both natural convection by buoyancy and forced convection by the shearing flow play a significant role in convective heat transfer. Compared with classic Taylor-Couette flow, the occurrence of leakage decreases the maximum static pressure while increasing the minimum static pressure. The formation and evolution of the Taylor vortex are dominated by the axial flow.

Numerical Optimization of Mechanical Air-Oil Cyclone Separator for Air Compressor

Air-oil separator is used to recover oil from the air leaving the compressor. The air-oil separator design is based on the minimum diameter of capturing oil droplet and the separation efficiency of the separator. The available air-oil separators are Cyclone, Labyrinth, wire and oil filter. In this work cyclone separator is proposed due to its higher separation efficiency for wide range of droplet size. The proposed model C1 to C6 is analysed using CFD tool and maximum separation efficiency is obtained for C4 model and minimum residence time and static pressure is obtained for C3 model. It is concluded that C3 model is finalized model due to least residence time and back pressure with acceptable separation efficiency.

Contribution for the roadmap of hydraulic short circuit implementation: Case of Grand-Maison pumped storage power plant

The objectives of the 2050 energy policy based on the decarbonization of the electric power networks generate drastic changes for grid balancing with a massive integration of non-dispatchable Renewable Energy Sources. Hydroelectric power plants already significantly support electricity power system flexibility with innovative solutions such as variable speed units, fast frequency control, fast generating to pumping modes transition, high ramping rate, inertia emulation, etc.For pumped storage power plants (PSP), a quick solution to increase the flexibility without large investment is to operate the power plant in hydraulic short circuit (HSC) mode. This technological solution is simple to implement, but requires an in-depth study of various technical aspects among which the hydraulic transients of the new operating modes is of high importance from the installation’s safety perspective. In the framework of XFLEX HYDRO H2020 European research project, the exploitation of this solution is under implementation at Grand-Maison PSP. Located in the French Alps, Grand-Maison PSP is equipped with 8 reversible multi-stage Francis pump-turbines and 4 Pelton turbines, for a total installed capacity of 1800MW, thus being the largest PSP in Europe and one of the major PSP in the world. The waterway includes a headrace tunnel, a headrace surge tank, 3 parallel penstocks feeding the 12 units operated under a maximum gross head of 955mWC.In this paper, after a description of the general HSC considerations, the 1D model of the Grand Maison PSP and the related validation are presented. Finally, the most critical load cases in HSC operation are described to identify the potential hydraulic transient issues, such as extreme water levels in the upstream surge tank, maximum static pressure along the pressure shaft and minimum static pressure along the tunnels. The analysis performed for Grand Maison PSP is a contribution to the roadmap for the implementation of HSC operation in pumped storage power plant and will be made available as a public deliverable of the XFLEX HYDRO H2020 European research project.

Novel wave-shaped tip-shroud contours towards reducing turbine leakage loss

For axial turbines, tip leakage vortex and passage vortex flow are responsible for a large part of the aerodynamic loss. To pursue higher turbine efficiency, many methods are undertaken to eliminate the tip leakage loss. In this work, by experimental and numerical methods, novel wave-shaped tip-shroud contours on the unshrouded turbine cascade were proposed. In a low-speed large-scale linear turbine cascade facility, a traditional flat tip was first conducted to comprehensively validate the numerical tool, especially the inlet conditions and the total pressure loss due to the tip leakage loss. The numerical settings were kept the same as the experimental facility. It achieved a satisfactory agreement between the CFD and experiments. It was found that in a flat tip case, a large, integral tip leakage vortex structure was identified and responded to the aerodynamic loss within the tip leakage core. Then a series of novel wave-shaped tip-shroud contours were considered in the current turbine cascade. The overtip flow exited the suction side tip gap, and the peak mass flow rate was concentrated around the troughs of the wave tip. Several small-sized, but stronger-vorticity-magnitude vortex structures were identified. By breaking down a large, integral vortex structure into several smaller-scale vortices, the vortex evolution was beneficial for the turbine efficiency. Although a slight enhancement of passage vortex was identified, the overall loss reduction of 3.0% was achieved by reducing the tip leakage loss, which dominated the loss contribution. According to the real working condition, axial displacement for the blade was considered. Within the current scope, the maximum reduction of tip leakage loss coefficient was reduced by 14.6% compared to the flat tip case. It was mainly contributed by the smaller contraction coefficient within the tip gap, which reduced the overtip leakage mass flow. Meanwhile, the vena contracta within the tip gap was altered, as well as static pressure distribution on the tip surface. As a result, the minimum static pressure was re-distributed at the throat of the tip gap. It was proven that this novel wave-shaped tip-shroud contour was an efficient way to improve the aerodynamic performance at a larger tip gap.

Aerodynamic characteristics in upper airways among orthodontic patients and its association with adenoid nasopharyngeal ratios in lateral cephalograms

BackgroundAdenoid hypertrophy among orthodontic patients may be detected in lateral cephalograms. The study investigates the aerodynamic characteristics within the upper airway (UA) by means of computational fluid dynamics (CFD) simulation. Furthermore, airflow features are compared between subgroups according to the adenoidal nasopharyngeal (AN) ratios.MethodsThis retrospective study included thirty-five patients aged 9–15 years having both lateral cephalogram and cone beam computed tomography (CBCT) imaging that covered the UA region. The cases were divided into two subgroups according to the AN ratios measured on the lateral cephalograms: Group 1 with an AN ratio < 0.6 and Group 2 with an AN ratio ≥ 0.6. Based on the CBCT images, segmented UA models were created and the aerodynamic characteristics at inspiration and expiration were simulated by the CFD method for the two groups. The studied aerodynamic parameters were pressure drop (ΔP), maximum midsagittal velocity (Vms), maximum wall shear stress (Pws), and minimum wall static pressure (Pw).ResultsThe maximum Vms exhibits nearly 30% increases in Group 2 at both inspiration (p = 0.013) and expiration (p = 0.045) compared to Group 1. For the other aerodynamic parameters such as ΔP, the maximum Pws, and minimum Pw, no significant difference is found between the two groups.ConclusionsThe maximum Vms seems to be the most sensitive aerodynamic parameter for the groups of cases. An AN ratio of more than 0.6 measured on a lateral cephalogram may associate with a noticeably increased maximum Vms, which could assist clinicians in estimating the airflow features in the UA.

Performance assessment of solar chimney power plants with the impacts of divergent and convergent chimney geometry

Abstract Influence of area ratio (AR) on main performance parameters of solar chimney power plants (SCPPs) is investigated through a justified 3D axisymmetric CFD model. Geometric characteristics of Manzanares pilot plant (MPP) are taken into consideration for the numerical model. AR is varied from 0.5 to 10 to cover both concave and convex (convergent and divergent) solar chimney designs. Following the accuracy verification of the CFD results and proving mesh-independent solution, main performance oriented parameters are assessed as a function of AR such as velocity, temperature and pressure distribution within MPP, temperature rise of air in collector, mass flow rate of air around the turbine area, dynamic pressure difference across the turbine, minimum static pressure in the entire plant, power output and system efficiency. The results reveal that AR plays a vital role in performance figures of MPP. Mass flow rate of air ($\dot{m}$) is found to be 1122.1 kg/s for the reference geometry (AR = 1), whereas it is 1629.1 kg/s for the optimum AR value of 4. System efficiency (η) is determined to be 0.29% for the reference case; however, it is enhanced to 0.83% for the AR of 4.1. MPP can generate 54.3 kW electrical power in its current design while it is possible to improve this figure to 168.5 kW with the optimal AR value.

A thorough performance assessment of solar chimney power plants: Case study for Manzanares

Solar chimney power plants (SCPPs) are promising systems for clean energy generation. SCPPs are ideal for the large-scale harnessing of solar energy. They operate efficiently without auxiliary energy and do not cause any environmental pollution. There are several theoretical, numerical and experimental attempts to date for performance assessment of SCPPs, however, there are still contradictions in the findings, and a thorough performance evaluation is still missing. Therefore, in this study, a novel three-dimensional axisymmetric computational fluid dynamics (CFD) approach is proposed by considering the pioneer plant in Manzanares region. For a realistic approach, actual geometric parameters of the pilot plant are utilised in the CFD model, and the performance assessments are done regardless of time. Pressure, temperature and velocity distributions within the SCPP from collector inlet to chimney outlet are numerically modelled with respect to changes in solar radiation and atmospheric temperature. For model validation, the numerical findings are compared with the typical experimental findings performed in pilot plant, and a good agreement is obtained. For a certain value of solar radiation (1000 ​W/m 2 ), maximum air velocity in the pilot plant is found to be 14.24 ​m/s, which is compatible with the experimental data of 15.00 ​m/s. Static pressure is found to sharply decrease from chimney ground to turbine inlet, and then steadily rises to the chimney outlet. Minimum static pressure is observed to be −100.18 ​Pa ​at 21.92 ​m from the ground. Output power of SCPP linearly increases with the solar intensity whereas it steadily reduces with ambient temperature. Available power is determined to be 49059 ​W for the case of 1000 ​W/m 2 , and the atmospheric temperature of 293 ​K. • Manzanares pilot plant is analysed in terms of performance parameters. • For G ​= ​1000 ​W/m 2 , V m is found to be 14.24 ​m/s. • Minimum static pressure is −100.18 ​Pa ​at a height of 21.92 ​m from the ground. • Temperature rise in collector is found to be 20.4 ​°C for G ​= ​1000 ​W/m 2 . • P o is 49663 ​W for T a of 290 ​K while it is 41274 ​W for 320 ​K.

Numerical Simulation of Axial Inflow Characteristics and Aerodynamic Noise in a Large-Scale Adjustable-Blade Fan

Numerical simulation are conducted to explore the characteristics of the axial inflow and related aerodynamic noise for a large-scale adjustable fan with the installation angle changing from −12° to 12°. In such a range the maximum static (gauge) pressure at the inlet changes from −2280 Pa to 382 Pa, and the minimum static pressure decreases from −3389 Pa to −8000 Pa. As for the axial intermediate flow surface, one low pressure zone is located at the junction of the suction surface and the hub, another is located at the suction surface close to the casing position. At the outlet boundary, the low pressure is negative and decreases from −1716 Pa to −4589 Pa. The sound pressure level of the inlet and outlet noise tends to increase monotonously by 11.6 dB and 7.3 dB, respectively. The acoustic energy of discrete noise is always higher than that of broadband noise regardless of whether the inlet or outlet flow surfaces are considered. The acoustic energy ratio of discrete noise at the inlet tends to increase from 0.78 to 0.93, while at the outlet it first decreases from 0.79 to 0.73 and then increases to 0.84.

Numerical Simulation of Flow between Two Parallel Co-Rotating Discs

The study of fluid flow between two rotating discs aims to predict flow characteristics. In this paper numerical simulation is used to investigate axisymmetric swirling flow between two parallel co-rotating discs. Methodology entails, firstly, inputing parameters from CFD software are into previos study developed dimensionless radial velocity model for flow between two discs to obtain dimensional radial velocity of the model. Secondly, previous study parameters are used to perform numerical simulation on laminar and turbulent flows between two parallel co-rotating discs. The numerical simulation results are compared to previous study results. Then comparative numerical simulations was carried out on laminar and turbulent flows using CFD software. Results obtained showed that for the this study dimensional radial velocity and previous study dimensionless radial velocity, radial velocity distribution increase proportionately from the disc surface at 0m/s to 2208.00m/s and 0 to 0.0002396 respectively, at the domain centre. And both results satisfy initial inlet and boundary conditions with resultant parabolic profiles. In the study, it is shown that turbulent flow radial velocity profile is smoother than for laminar flow. The radial velocity increases from 0 at the walls to 0.15m/s before decreasing to - 0.2m/s at the mid-centre for laminar flow while for turbulent flow the radial velocity intitially increases from 0 at the walls to 0.15m/s before decreasing to -0.06m/s at the discs centre; while for laminar flow, swirl velocity decrease from approximately 2.55m/s to 0.55m/s and for turbulent flow the swirl velocity decrease from approximately 2.84m/s to 1.62m/s. The turbulent flow swirl velocity profile seen to be smoother than for laminar flow around the discs centre. The study further showed that for fluid near the discs surfaces radial velocity net momentum is radially towards the outlet with flow laminar in the boundary layer region and the velocity turbulent towards the domain centre. For static pressure, laminar flow maximum and minimum static pressure 2.48pa and -0.033pa respectively, while for turbulent flow maximum and minimum static pressure were 0.00 and -0.0024pa. The developed previous study model can therefore be used to predict radial velocity distribution between steady axisymmetric flow between two parallel co-rotating discs.

Performance Analysis and Cavitation Prediction of Centrifugal Pump Using Various Working Fluids

Background: The application of centrifugal pumps is found in domestic and petrochemical industries. Industrial centrifugal pumps are designed and tested using water as working fluid before supplied to industries, as water is commonly available. However, centrifugal pumps are used in industries for various applications, which involve the handling of fluids other than water- like saline-water, crude oil, gasoline, etc. Consequently, hydraulic performance of the pump differs from the designed and tested values and pump performance becomes unpredictable. Cavitation characteristics of the pump handling different fluids other than water are also changed and many a time, cavitation starts prematurely. As a result, the operating cost of pump is increased. Objective: A CFD based computational analysis of a single-stage, single-entry industrial centrifugal pump having double-volute casing is carried out to compare the performance and cavitation characteristics for various working fluids, namely water, saline water with varying salinity, gasolene and crude oil. Methods: Multiple Reference Frame method (MRF) available in Reynolds-Averaged Navier-Stokes (RANS) equations based CFD solver Ansys-CFX is used in the present study. CFD simulation is carried out for five flow rates with Standard k-ε turbulence model. Rayleigh-Plesset equation describing the growth of a single vapor bubble in a liquid is used for predicting the cavitation flow behaviour. Results: Minimum static pressure is computed at the suction side of saline water as compared to the other working fluids studied here. Hydraulic efficiency of crude oil is found to be the lowest as compared to other fluids. Supercavitation (excessive formation of vapor bubbles and sudden drop in head up to 3%) starts early for saline water with 40g/kg salinity. Conclusion: The results show little variation in pump efficiency when water and saline water are used as working fluids. However, cavitation characteristics differ considerably with the working fluids. Recent patents filed/published in this area revealed that efforts are needed to develop effective cavitationresistant centrifugal impellers and pumps.

Modeling, air balancing and optimal pressure set-point selection for the ventilation system with minimized energy consumption

Traditional static pressure reset control strategies commonly use a feedback indicator to reset the static pressure; this results in under-ventilation in certain zones and over-ventilation in others. Based on this issue, the objective of this study was to develop a model-based, improved, static pressure reset control strategy, providing a well-balanced system to eliminate under-ventilation and over-ventilation, while consuming minimal energy. In the study reported here, a comprehensive mathematical model was established to simulate the non-linear behavior of the ventilation system, and a supervised machine learning algorithm for a support vector machine was used to obtain values for unknown parameters in the model. The resulting model was then used as the basis for development of a damper position control method and to determine the damper position, given a desired airflow rate. An optimal, static pressure set-point selection method was also proposed using the developed model to calculate the minimum static pressure set-point in a closed-form. As a result, the revised system consumed less energy owing to the better-balanced system and optimized pressure set-point selection. Moreover, through the application of the damper position control method, the ventilation system was well-balanced and eliminated both under-ventilation and over-ventilation. Experimental tests were carried out to validate the performance of the proposed method in comparison with the conventional static pressure reset strategy, data from which were collected to train the proposed model.

Effect of Blade Wrap Angle on Performance of a Single-Channel Pump

To study the effect of blade wrap angle on energy performance and unsteady characteristics of the single-channel pump, a single-channel pump with specific speed of 140 was selected as experimental test model and three impeller models with blade wrap angle of 290°, 340° and 390° were respectively designed. The performance of different single-channel pumps with blade wrap angle of 290°, 340° and 390° respectively were tested. Based on the experimental study, the effect of blade wrap angle on the energy characteristics, head pulsation, pressure fluctuation and radial force of the single-channel pump was obtained and analyzed. The results show that with blade wrap angle increases from 290° to 390°, the maximum pump head and efficiency gradually increases and the maximum increase amplitude is 7.3% and 7.79% respectively. The minimum static pressure at impeller outlet under three schemes all occurs at 1.0Qd and bigger blade wrap angle can reduce the mixing loss at impeller outlet. With the increase of blade wrap angle, the head pulsation and pressure fluctuation all decrease gradually. The maximum eighth section under the small flow rate and under the big flow rate occurs at the volute second the section. A higher pressure fluctuation exists around volute tongue. The time-averaged radial force decreases as the blade wrap angle increases and its increase amplitude decreases as the flow rate increases. The research fruits can provide some reference and theoretical basis for the optimization of single-channel pumps.

Cavitation limits on tidal turbine performance

Blockage effects are currently not accounted for in cavitation analyses of tidal turbine rotors. At higher blockage ratios, rotors are more heavily loaded and have potentially stronger suction peaks, so cavitation inception is more likely. In this paper, blade resolved computations are used to carry out a cavitation analysis over a range of blockage ratios and tip-speed-ratios. Our analysis suggests that increasing the blockage ratio from 0.01 to 0.197 reduces the minimum static pressure head in the fluid by approximately 0.5 m. To mitigate this reduction, either the submersion depth of the rotor can be increased or the maximum permissible tip speed ratio reduced. However, reducing the maximum permissible tip speed ratio is shown to severely restrict the rotor thrust and power. Spanwise flow effects are shown to reduce the strength of the suction peak on the outboard blade sections, reducing the likelihood of cavitation inception. Blade element based methods are shown to inadequately account for spanwise flow effects and thus are overly-conservative. Hence, rotors designed with these methods could potentially be operated at higher tip-speed-ratios or reduced submersion depths.

Investigation on a vertical radial flow adsorber designed by a novel parallel connection method

Abstract Due to the increasing global demand for industrial gas, the development of large-scale cryogenic air separation systems has attracted considerable attention in recent years. Increasing the height of the adsorption bed in a vertical radial flow adsorber used in cryogenic air separation systems may efficiently increase the treatment capacity of the air in the adsorber. However, uniformity of the flow distribution of the air inside the adsorber would be deteriorated using the height-increasing method. In order to reduce the non-uniformity of the flow distribution caused by the excessive height of adsorption bed in a vertical radial flow adsorber, a novel parallel connection method is proposed in the present work. The experimental apparatus is designed and constructed; the Computational Fluid Dynamics (CFD) technique is used to develop a CFD-based model, which is used to analyze the flow distribution, the static pressure drop and the radial velocity in the newly designed adsorber. In addition, the geometric parameters of annular flow channels and the adsorption bed thickness of the upper unit in the parallel-connected vertical radial flow adsorber are optimized, so that the upper and lower adsorption units could be penetrated by air simultaneously. Comparisons are made between the height-increasing method and the parallel connection method with the same adsorber height. It is shown that using the parallel connection method could reduce the difference between the maximum and minimum radial static pressure drop by 86.2% and improve the uniformity by 80% compared with those of using the height-increasing method. The optimal thickness ratio of the upper and lower adsorption units is obtained as 0.966, in which case the upper and lower adsorption units could be penetrated by air simultaneously, so that the adsorbents in adsorption space could be used more efficiently.

Radial Nozzles for Non-Cavitating Flow of Water at High Pressure Drops

We analyze the conditions under which radial nozzles can be used to measure or regulate the flow of water at high pressure drops. Using the URANS model, numerical simulation of water flow in radial nozzles was carried out. We find a dependence that establishes a relationship between the minimum static pressure on the geometric contour of a radial nozzle and the pressure drop across the nozzle, which leads to an estimate of conditions for the onset of cavitation.

Numerical methodology for evaluating the effect of sleepers in the underbody flow of a high-speed train

This paper presents an innovative numerical methodology based on dynamic meshes that allow for the 3D simulation of the motion of a high-speed train, reproducing the real movement and including the geometry of the sleepers in the calculation. The objective of this strategy is to provide a more accurate analysis of the underbody flow, which has become a matter of concern, especially because of the rising problem of the ballast flight. The proposed methodology, without sleepers, has been compared to the conventional procedure, consisting of a static train and a moving wall condition on the ground, with satisfactory results. Subsequently, the inclusion of the sleepers in the simulation revealed an increase in the drag coefficient of approximately 15%. Regarding the underbody flow, lower values of the minimum static pressure were observed in the entire profile from the ballast layer to the train and some strong peaks of the vertical component of the velocity were identified near the sleepers. Both factors could affect the process of ballast flight, which is estimated to be favoured by the presence of the sleepers. The results obtained demonstrated the applicability of the proposed methodology.

Cavitating nozzle flows in micro- and minichannels under the effect of turbulence

The cavitation phenomenon inside micro- and minichannel configurations was numerically investigated. The simulations for each channel were performed at different upstream pressures varying from 1 to 15 MPa. Two microchannel configurations with inner diameters of 152 and 254 μm and two minichannel configurations with inner diameters of 504 and 762 μm were simulated. To validate the numerical approach, micro-jet impingement from a microchannel with an inner diameter of 152 μm was first simulated at different Reynolds numbers. Then, the mixture model was used to model the multiphase flow inside the channels. The results of this study present major differences in the cavitating flows between the micro- and miniscale channels and show that the pressure profile and vapor phase distribution exhibit different features. The static pressure drops to negative values (tensile stress) in microchannels, while the minimum static pressure in minichannels is found to be equal to vapor saturation pressure, and higher velocity magnitudes especially at the outlet are visible in the microchannels. It is shown that for higher upstream pressures, the cavitating flow extends over the length of the micro/minichannel, thereby increasing the possibility of collapse at the outlet. The effect of energy associated with turbulence was investigated at high Reynolds numbers for both micro/minichannels and its impact was analyzed using wall shear stress, turbulence kinetic energy and mean velocity at various locations of the micro/minichannels.

원자로 압력 및 체적제어계통의 다단 오리피스 설계

다공 및 다단오리피스열을 해석할 수 컴퓨터코드를 사용하여 원자력발전소 내 공급 및 배출장치의 수축오리피스를 설계하였다. 원래 단공 오리피스가 설치되었으나 다공 오리피스 설치가 필요하여 설계 변경되었다. 오리피스 사이 거리는 충분한 압력회복거리로 유지되었다. 최소 정압은 공동현상 방지를 위하여 그 온도에 상응하는 증기압 이하로 유지되도록 설계하였다. 오리피스 설치 배관의 직경은 운전시 강성을 유지할 수 있도록 원래 크기보다 증가시켰다. Restriction orifices in the feed and bleed circuit of nuclear power plant are designed using computer program capable of handling multiple hole cascade orifice assembly. Single hole stages of orifice assembly are alternated with multihole stages where necessary. The distance between stages is such that it allows full pressure recovery. The minimum static pressure is higher than vapor pressure at the operating temperature so that cavitation does not occur. Piping sizes are reviewed and increased if necessary to improve rigidity.