Upstream Straight Pipe Research Articles

Numerical simulation of heat transfer characteristics of supercritical liquid hydrogen through triangular U-tube in moderator

In this study, the heat transfer characteristics of supercritical hydrogen in triangular U-tubes with different radius were investigated. In order to compare the heat transfer capacity of triangular U-tubes, and to explore the heat transfer characteristics of supercritical liquid hydrogen inside them, a three-dimensional numerical simulation was carried out by Fluent. The unstructured grid and RNG k-ε turbulence model were used to encrypt the grid. Meanwhile, the grid independence and the effectiveness of the turbulence model are verified. The Tw, Tf and Nu along the triangular U-tube at different q and Re were compared. The result shows that Tw, Tf and Nu increase with the increase of q and Re. The change of Re was found to be largest for Nu. The effect of secondary flow on Nu was similar to the entrance effect of upstream straight pipe, and the effect of secondary flow on Nu was slightly larger than the entrance effect. This work provides a useful technical guidance for thermal design and thermal management of neutron source and target station, as well as novel ideas for flow and heat transfer of supercritical liquid hydrogen in U-tube.

Sedimentation effects on particle position and inertial deposition in 90° circular bends

Laminar fluid-particle flows in bend geometries are present in many industrial, pharmaceutical, and biomedical applications. Particle deposition has been studied extensively; however, little attention has been paid to the effect of particle sedimentation on particle position and deposition in different pipe geometry combinations. This study presented a comprehensive analysis of sedimentation effects on particle flow behaviour in 90° circular pipe bends of micron particles in laminar pipe flows. Pipe geometry combinations consisted of eight pipe diameters, nine bend radii, and 30 particle diameters in a range of 1 to 100 μm. The results demonstrated the locations of particles that sedimented to the bottom half of the straight pipe section, and the particle positions upstream from the pipe bend entrance, which was no longer in a fully developed profile. These new locations represent the effects of gravity, pulling the particles down. While obtaining these positions can be found through CFD analysis, we proposed an analytical solution to predict the particle trajectory from different release locations that would help to identify the initial particle distribution at locations upstream to the bend, to obviate the need for long upstream straight pipe sections in the CFD analysis.

Numerical investigation of the valve-induced disturbance of the performance of a swirl meter

Abstract Flow through a swirl meter is numerically simulated and experimentally investigated to learn the effects of flow disturbance induced by an upstream valve on the performance and internal flow characteristics of the swirl meter. Investigations are performed for five valve openings and three upstream pipe lengths, as the two main influencing factors. Simulation results show that the valve affects the measuring accuracy of the swirl meter by increasing the inlet velocity and thus the internal flow acceleration and vortex precession. Experimental results show that the valve affects the flow rate measurement by as much as 35.7%, falling to ~1% when the valve is opened to 50% or the upstream pipe length is increased to 5 times the pipe diameter. To ensure the effectiveness and accuracy of flow rate measurements, the length of upstream straight pipe between the valve and swirl meter should be at least 5 times the pipe diameter.

Influence of flow velocity and temperature on flow accelerated corrosion rate at an elbow pipe

Abstract Flow accelerated corrosion (FAC) is one of the important issues that must be considered for aging fossil and nuclear power plants. To understand the effect of thermal flow field on FAC, FAC rates at an elbow pipe were measured under different flow velocity and temperature conditions. The elbow test section was made of stainless steel (diameter D = 49.5 mm) and FAC rates were measured using corrosion sensors made of carbon steel. The dissolved oxygen concentration was kept under 0.1 μg/kg, and pH was nearly neutral (about 7.0) at room temperature. The mean cross-sectional velocity was changed from 0.39 to 5.74 m/s (Reynolds number, about 1.0e6). When the water temperature was about 150 °C, the FAC rate was smaller at the intrados of the elbow pipe than at other circumferential locations. This tendency continued downstream. The FAC rates at the elbow pipe were larger than those upstream and downstream from the elbow pipe and the FAC rates downstream from the elbow pipe decreased along the flow direction. FAC rates increased as flow velocity increased and their relationship was not linear. The ratios of the maximum FAC rate at the elbow to the FAC rate in the upstream straight pipe ranged from about 1.7 to 2.9. When temperature decreased to 100 °C, FAC rate at the intrados became the largest of the other circumferential sensors. When temperature decreased further to 50 °C, FAC rate also decreased, but the value was not negligible. The influence of flow velocity was negligibly small at 50 °C and remarkable at 100 °C and 150 °C. The combination effect of flow velocity and temperature was different from place to place and particularly strong at the elbow.

Performance optimization of ultrasonic flow meter based on computational fluid dynamics

As a common nature gas measuring tool, ultrasonic flow meter is more and more put into use. Therefore, the accuracy of measurement is what we concern the most. The performance of ultrasonic flow meter is closely related to fluid state which flows through it. This article identified the evaluation method of rectification effect of gasotron and its implementation steps. It proposed an assessing index Lmin based on dichotomy. Computational fluid dynamics method is used to simulate the model of an upstream straight pipe section with a header and plate gasotron, which obtained the assessing index Lmin in five different transmission conditions. Finally, the feasibility of the gasotron is validated against comparing indication errors in different installation conditions: with a header, benchmark, with a header and gasotron.

Eksperimentalna analiza višeportnog uređaja za osrednjavanje i uticaj oblika tela na koeficijent protoka

This paper deals with the experimental results obtained using different shapes of multi-port averaging device at different gauge pressure. The cross-section of the multiport averaging device is essential factor which effects the meter performance. A closed loop air test facility(CLATF) is used for testing and calibration of the flowmeter, which is used to measure the air flow rate or velocity of flow. The circular probe is a commercial design while the diamond shape with slight modification is analyzed for providing better performance and appreciable result with less disturbance in the flow line. The prototype test of the flowmeter is done at a defined length of upstream straight pipe after an elbow bend, for a condition of well defined turbulent flow profile. The calibration is done at 2 and 5 gauge pressure while the flow rate varied from 0.0283 to 0.1121m3/s. As a result, the diamond shaped probe with curved edges provided appreciable differential pressure and flow coefficient compared to circular probe keeping the same blockage to both the probe facing the flow.

CFD-Aided Investigation of Sound Path Position and Orientation for a Dual-Path Ultrasonic Flowmeter With Square Pipe

This paper discusses the issues with a dual-path ultrasonic flowmeter with square-shaped pipe using CFD simulations, which include the sound path position, installation orientation, and effect of straight pipe length on the performance of the meter. By analyzing the flow field inside a single-elbow pipeline and T-shaped pipeline, the correction factor for the dual-path square-shaped ultrasonic flowmeter with respect to the change of Reynolds number is calculated. The optimal sound path position and orientation are investigated. Simulation results indicate that the optimal sound path position is located at the position of 0.65 times the half side length of square pipe cross-section. The upstream straight pipe length requirements for a single-elbow pipeline and a T-shaped pipeline are determined, which are at least 20-D and 50-D, respectively. Preliminary experiments are carried out and validate the simulations. The results are helpful for the design and practical applications of square-shaped ultrasonic flowmeter.

Large-eddy simulations of velocity and temperature fluctuations in hot and cold fluids mixing in a tee junction with an upstream straight or elbow main pipe

Thermal striping resulting in thermal fatigue is an important safety issue for nuclear power plants. In this work, temperature and velocity fluctuations in hot and cold fluids mixing in a tee junction with the main pipe connected either to an upstream straight or elbow pipe have been numerically predicted using large-eddy simulations (LES) on the FLUENT platform with the assumption of fully-developed velocity at both main and branch pipe inlets. The numerical results for the case with an upstream straight pipe were found to be in reasonable agreement with the available experimental data. The reason for the small discrepancy between the numerical results and experimental data can be attributed to the turbulence velocity being 10% of the fully-developed velocity at the main and branch pipe inlets in the LES calculations, while in the experiments the turbulence velocity was about 10% of the average velocity upstream of the tee junction. The simulated normalized mean and root-mean square (RMS) temperatures and the velocities at both straight and elbow tees were then compared, as well as the power spectrum densities (PSD) of the temperature fluctuations. The elbow pipe upstream of the main pipe has a significant influence on the mixing, resulting in increased temperature and velocity fluctuations. The flow pattern of the elbow tee deviates from the wall jet due to the secondary flow in the upstream elbow pipe.

Comparison of predicted and experimental erosion estimates in slurry ducts

Computational models for the impact velocity and impact angle in a bend have been successfully applied to the flow field and validated by electrical resistance tomography (ERT) to confirm the position of particle burdens. Particle impact parameters from this work have been used as inputs to erosion models to predict wall wastage rates in a R c/ D=1.2 bend and a upstream straight pipe section. The location of damage and the levels of wall wastage agree well with those obtained from erosion trials conducted on a full scale loop rig with AISI 304 stainless steel pipework. Well-distributed but asymmetric particulate flows of sand in water have been studied at average flow velocities of 3 m s −1. Predicted erosion damage levels and locations are compared to non-destructive ultrasonic and gravimetric measurements as well as wall thickness measurements made with a micrometer after cutting the pipe and bends sections.

배관구조에 따른 속도분포 변형과 선회가 오리피스 유량계의 압력차에 미치는 영향에 대한 수치적 연구

Three-dimensional pipe flows with elbows, tees and headers in three different pipe systems are calculated to estimate the effect of asymmetry of axial velocity profile and swirl on measuring accuracy of an orifice flowmeter. It is evaluated how the pressure difference across the orifice is dependent on the upstream straight pipe length and how swirl intensity, swirl angle, and axial velocity distribution affect the measuring error of the orifice flowmeter. From the results, it is found that variation of the pressure difference across the orifice is negligible in case that maximum swirl angle is less than 2°, and also that the pressure difference across the orifice is more sensitive to the asymmetry of axial velocity profile rather than the swirl intensity.

Investigations of sand–water induced erosive wear of AISI 304L stainless steel pipes by pilot-scale and laboratory-scale testing

The repair costs of erosion damage caused by solid particle impingement from transporting slurries and other particle-laden liquids in pipes can be extremely high. In the absence of accurate predictive models, routine monitoring of the pipe wall thickness or the use of sacrificial coupons are required to warn of erosion damage or impending loss of containment. Apart from advantages for plant maintenance, the environmental, safety and production implications are enormous. Identification of critical pipe components susceptible to high levels of damage, and innovative ways to ameliorate the damage, has been an active topic of research for decades. Recent work at University of Nottingham and University of Southampton [Wear 250 (1–12) (2001) 771] has sought definitions of flow fields and particle dispersions and their relationship to erosive wear to facilitate the development of new designs and geometries for slurry handling equipment. This paper covers research that has been aimed at determining the distribution of erosion rates and the erosion mechanisms that occur over wetted surfaces within pilot-scale pipe systems handling water–sand mixtures at 10% by volume concentrations and at a mean fluid velocity of approximately 3 m/s. Experiments are presented which have been conducted on a test section consisting of an upstream straight pipe section followed by a bend (with a radius of curvature of 1.2 bore diameter) within a 78 mm diameter pipe test loop. The whole loop and test section was manufactured from AISI 304L stainless steel. The wall wear rates, obtained by gravimetric measurements, as a function of time are discussed. Circumferential erosion penetration and mechanisms at discrete locations have been measured by surface profilometry on replicas and scanning electron microscopy after cutting-up the pipe sections. The erosion rates and patterns are compared to those predicted by erosion models linked to computational models for the impact velocity and impact angle in bend and straight sections. Bend wear patterns are further compared to flow visualisation results from a transparent flow loop and electrical resistance tomography (ERT) to confirm the placement of particle burdens. The erosion rates, expressed as volume loss per impact (determined gravimetrically and via computer models) in bends are found to agree well with simple laboratory-scale water–sand jet impingement tests on planar stainless steel samples. The pipe loss data alone represents a significant resource for future erosion researchers to reference.

Cleaning in place: effect of local wall shear stress variation on bacterial removal from stainless steel equipment

Local wall shears stress analysis as well as cleanability experiments on different pieces of equipment in various circuit arrangements were performed. Pieces of equipment used in this work, stainless steel made, were representative of production lines: straight pipes of different diameters, sudden or gradual contraction or expansion pipes. Local wall shear stress values, obtained by an electrochemical method, were shown to be influenced by the loop arrangement. Geometry as the gradual expansion pipe had an effect on the upstream straight pipe where the wall shear stress values were two times lower than in other configurations as with a sudden expansion. In sudden geometry, the bacterial removal during cleaning was improved by the increase of the flow rate, corresponding to the increase of the mean local wall shear stress. However, in gradual expansion or contraction pipe, cleanability was not improved by the increase of flow rate. The effect of the mean wall shear stress on the removal has been confirmed. Moreover, this work demonstrated a clear positive effect of an increase of the fluctuation rate on the spore detachment. Low mean wall shear stress zones as in sudden expansion (around 0.15 Pa ) could be cleanable because of the high fluctuation rate (around 21%). These results underline the importance of the design and the flow configuration.

Swirling Flows in a Circular-Sectioned 90.DEG. Bend.

Three components of mean velocities and wall static pressure have been measured in swirling flows through a circular-sectioned 90°bend with a curvature radius ratio of 4.0 under the Reynolds number of 60000. The complicated correlation between internal flow behavior and wall pressure distribution has been clarified from a region of upstream straight pipe through a bend to a down-stream one. Also, the shift of axial flow, the movement of the swirl center and the streamwise decay of swirl intensity have been investigated.

Installation effects on vortex shedding flowmeters

Numerous measurements of the effects of pipe fittngs on vortex shedding flowmeters are carried out as a contribution to flow metering standards. A water test line of 150 mm diameter is used in the experiments covering a Reynolds number range of about 2 × 10 5 to 10 6. The effects of six kinds of piping configurations are examined at various upstream straight pipe lengths and all four kinds of liquid vortex shedding flowmeters, which were commercially available in Japan, are tested. The vortex shedding flowmeters are compared with a turbine meter in experiments designed to evaluate reproducibility of measurements. The uncertainty of the measured data is estimated at about 0.1%. It is found that the magnitude of each installation effect strongly depends on the design of the flowmeter. The experimental results are presented in detail and a table is given of the minimum upstream straight pipe lengths needed to suppress the effects to less than 0.5% for each of the tested flowmeters. This can be used as guidance in the installation of vortex shedding flowmeters.