Downstream Pipe Research Articles

Comparison of hinge microflow fields of bileaflet mechanical heart valves implanted in different sinus shape and downstream geometry

The characterization of the bileaflet mechanical heart valves (BMHVs) hinge microflow fields is a crucial step in heart valve engineering. Earlier in vitro studies of BMHV hinge flow at the aorta position in idealized straight pipes have shown that the aortic sinus shapes and sizes may have a direct impact on hinge microflow fields. In this paper, we used a numerical study to look at how different aortic sinus shapes, the downstream aortic arch geometry, and the location of the hinge recess can influence the flow fields in the hinge regions. Two geometric models for sinus were investigated: a simplified axisymmetric sinus and an idealized three-sinus aortic root model, with two different downstream geometries: a straight pipe and a simplified curved aortic arch. The flow fields of a 29-mm St Jude Medical BMHV with its four hinges were investigated. The simulations were performed throughout the entire cardiac cycle. At peak systole, recirculating flows were observed in curved downsteam aortic arch unlike in straight downstream pipe. Highly complex three-dimensional leakage flow through the hinge gap was observed in the simulation results during early diastole with the highest velocity at 4.7 m/s, whose intensity decreased toward late diastole. Also, elevated wall shear stresses were observed in the ventricular regions of the hinge recess with the highest recorded at 1.65 kPa. Different flow patterns were observed between the hinge regions in straight pipe and curved aortic arch models. We compared the four hinge regions at peak systole in an aortic arch downstream model and found that each individual hinge did not vary much in terms of the leakage flow rate through the valves.

Impact of Piping Impedance and Acoustic Characteristics on Centrifugal Compressor Surge and Operating Range

The performance of a centrifugal compressor is usually defined by its head versus flow map, limited by the surge and stall regions. This map is critical to assess the operating range of a compressor for both steady state and transient system scenarios. However, the compressor map does not provide a complete picture on how the compressor will respond to rapid transient inputs and how its surge behavior is affected by these events. Specifically, the response of the compressor to rapid transient events such as single or multiple (periodic) pressure pulses, is also a function of the compressor's upstream and downstream piping system's acoustic response and impedance characteristics. This unique response phenomenon was first described in the 1970 s and came to be known as the “compressor dynamic response (CDR) theory.” CDR theory explains how pulsations are amplified or reduced by a compression system's acoustic response characteristic superimposed on the compressor head-flow map. Although the CDR theory explained the impact of the nearby piping system on the compressor surge and pulsation amplification, it provided only limited usefulness as a quantitative analysis tool, mainly due to the lack of computational numerical tools available at the time. To fully analyze pulsating flows in complex centrifugal compressor suction and discharge header piping systems, the principles of the CDR theory should be implemented in a dynamic flow model to quantify the magnitude of the amplifications of pressure pulses near the surge region. When designing centrifugal compressor stations within a transmission piping system, it is critically important to have a full understanding of the impact of the station's piping system on compressor dynamic behavior. For example, if a compressor system's piping impedance amplifies the suction side pulsations, the compressor's operating range will be severely limited and will produce unacceptable discharge piping vibrations. Whereas it is usually desirable to limit the downstream volume between the compressor discharge and the check valve to reduce the potential for transient surge events, a small discharge volume results in high piping impedance. This will amplify pressure pulsations passing through the compressor. The small downstream volume provides limited ability for any transient peak (such as a pressure pulse) passing through the compressor to be absorbed quickly, and an amplified discharge pressure spike will be the result. Also, if any periodic pressure excitation from upstream vortex shedding or any other continuously varying flow disturbance couples with a pipe resonance length, the result can be high fluctuations of the compressor operating point on its speed line, effectively resulting in a reduced operating range and higher than expected surge margin (surge line moves to the right). Both acoustic resonance and system impedance are functions of pipe friction, pipe and header interface connections, valve/elbow locations, pipe diameter, and valve coefficients, i.e., the entire piping system connected to the compressor. Thus, a careful acoustic and impedance design review of a compressor station design should be performed to avoid impacting the operating range of the machine. This paper describes the methodology of such a design review using modern pulsation analysis software. Examples and parametric studies are presented that demonstrate the impact of system impedance and piping acoustics on the dynamic operating response of the compressor in a typical compressor station. Some recommendations to reduce the risk of pulsation amplification and unsteady operation are also provided.

Analytical Study of Cavitation Surge in a Hydraulic System.

In order to clarify effects of an accumulator, pipe lengths and gradients of pressure and suction performances on cavitation surge, one-dimensional stability analyses of cavitation surge were performed in hydraulic systems consisting of an upstream tank, an inlet pipe, a cavitating pump, a downstream pipe, and a downstream tank. An accumulator located upstream or downstream of the cavitating pump was included in the analysis. Increasing the distance between the upstream accumulator and the cavitating pump enlarged the stable region. On the other hand, decreasing the distance between the downstream accumulator and the cavitating pump enlarged the stable region. Furthermore, the negative gradient of a suction performance curve and the positive gradient of a pressure performance curve cause cavitation surge.

Simulation of supercritical water–hydrocarbon mixing in a cylindrical tee at intermediate Reynolds number: Formulation, numerical method and laminar mixing

The objective of this work is to study the flow dynamics and mixing of supercritical water and a model hydrocarbon (n-decane), under fully miscible conditions, in a small scale cylindrical tee mixer (pipe ID=2.4mm), at an intermediate inlet Reynolds number of 500 using 3-D CFD simulations. A Peng–Robinson EoS with standard van der Waals mixing rules is employed to model the near-critical thermodynamics with the mixture binary interaction parameter obtained from a Predictive Peng–Robinson EoS using group contribution theory (PPR78). The n-decane stream is introduced at the colder temperature of 700K to ensure operation above the Upper Critical Solution Temperature (UCST, 632K) of the water n-decane system while the water stream enters at a higher temperature of 800K. Under these conditions, the flow in the tee mixer remains laminar and steady-state is reached. Mixing occurs predominantly due to the circulating action of a counter-rotating vortex pair (CVP) in the body of the hydrocarbon jet entering from the top. This CVP is formed due to the reorientation of the streamwise vorticity pre-existing within the hydrocarbon jet as it flows down the vertical pipe of the tee junction. The advective transport is further assisted by a secondary flow of water from the bottom stream, around the hydrocarbon jet, toward the space vacated near the top of the downstream pipe section by the downward motion of the HC jet. The CVP becomes progressively weaker due to vorticity diffusion as it is advected downstream and beyond 10–12 diameter lengths downstream of the mixing joint, transport is mainly controlled by molecular diffusion. It was found that the variations of density and transport properties with temperature do not have a significant impact on the flow and mixing dynamics for a ΔT=100K between the two streams. Local cooling of the fluid mixture was also observed in the mixing of water and n-decane streams entering at the same temperature (initially isothermal). This cooling effect is due to the diffusion of species along a gradient in their partial enthalpy in the mixture. Such gradients in species partial enthalpies are non-zero under near-critical conditions even for initially isothermal flows due to the non-ideality of the fluid mixture under these conditions. This local heating/cooling effect at near-critical conditions could give rise to unexpected formation of phases when operating close to critical points.

Measurement of the oil holdup for a two-phase oil-water flow through a sudden contraction in a horizontal pipe

Oil-water two-phase flow experiments were conducted in a horizontal duct made of Plexiglas® to determine the holdup of oil by means of the quick closing valves technique, using mineral oil (viscosity: 0.838 Pa s at 20 °C; density: 890 kg m−3) and tap water. The duct presents a sudden contraction, with contraction ratio of 0.64. About 200 tests were performed by varying the flow rates of the phases. Flow patterns were investigated for both the up- and downstream pipe. Due to the relatively high value of the contraction ratio, it was not observed any relevant variation of the flow patterns across the sudden contraction. Data were then compared with predictions of a specific correlation for oil-water flow and some correlations for gas-water flow. A drift-flux model was also applied to determine the distribution parameter. The results agree quite well with flow pattern visualization.

Experimental testing and modeling analysis of solute mixing at water distribution pipe junctions

Flow dynamics at a pipe junction controls particle trajectories, solute mixing and concentrations in downstream pipes. The effect can lead to different outcomes of water quality modeling and, hence, drinking water management in a distribution network. Here we have investigated solute mixing behavior in pipe junctions of five hydraulic types, for which flow distribution factors and analytical equations for network modeling are proposed. First, based on experiments, the degree of mixing at a cross is found to be a function of flow momentum ratio that defines a junction flow distribution pattern and the degree of departure from complete mixing. Corresponding analytical solutions are also validated using computational-fluid-dynamics (CFD) simulations. Second, the analytical mixing model is further extended to double-Tee junctions. Correspondingly the flow distribution factor is modified to account for hydraulic departure from a cross configuration. For a double-Tee(A) junction, CFD simulations show that the solute mixing depends on flow momentum ratio and connection pipe length, whereas the mixing at double-Tee(B) is well represented by two independent single-Tee junctions with a potential water stagnation zone in between. Notably, double-Tee junctions differ significantly from a cross in solute mixing and transport. However, it is noted that these pipe connections are widely, but incorrectly, simplified as cross junctions of assumed complete solute mixing in network skeletonization and water quality modeling. For the studied pipe junction types, analytical solutions are proposed to characterize the incomplete mixing and hence may allow better water quality simulation in a distribution network.

Effects of pipe diameters on the pressures during delayed load rejection in high-head pumped storage power stations

High-head pumped storage power stations face serious problems related to the transient process, especially in the area of delayed load rejection in stations with annular piping layouts. The controlled pressures are adversely affected, which leads to many problems in the engineering design phase. In this study, we investigated this condition through theoretical analysis, numerical simulation, and actual engineering practice. We concluded that the root cause of the pressure issues is the flow switching resulted from the non-synchronous changes in pressure between each branch pipe. Moreover, we examined the impact of the diameters of the upstream main pipe and branch pipe on the controlled pressures and determined that the diameter of the branch pipe has a major influence on the pressures as it changes the flow switching rate. A similar investigation was conducted for downstream pipes. Our conclusions can be applied to actual engineering practice for high-head pumped storage power stations.

20317 超音速流により誘起される管の振動に関する研究

In the bifurcation area of high differential pressure regulating valve downstream piping, such as a petrochemical plant, piping may vibrate by high frequency and may result in fatigue breaking for a short time. "Flow excitation vibration" by the vibration of the super sonic speed style formed in a pipe by the one of these causes is pointed out. Flow field in the cross section immediate expansion subordinate style plumbing influences this vibration greatly. In addition, the sound to occur then is related to piping flow field and closeness. In this study, I supposed that flow patterns in the jurisdiction were represented by a sound released from a pipe edge and I compared it with the vibration form of the pipe and considered it.

Comparison of Experimental and Computational Fluid Dynamics (CFD) Studies of Slug Flow in a Vertical 90° Bend

This paper presents the results of comparison of experimental and CFD studies of slug flow in a vertical 90° bend using validated models. For the experimental part, Electrical Capacitance Tomography (ECT), Wire Mesh Tomography (WMS), and high-speed videos were used to monitor an air-silicone oil mixture flowing in a vertical 90o bend. The ECT probes were mounted before the bend whilst the WMS was positioned either immediately upstream or immediately downstream of the bend. The downstream pipe was maintained horizontal whilst the upstream pipe was maintained vertical. The bend (R/D = 2.3) was made of transparent acrylic resin. Parallel to the experiments, simulations were carried out for same experiment set-up using the commercial software package Star-CD and Star-CCM+. The condition was simulated with the Volume of Fluid (VOF) model. The simulation predictions were validated against the experimental data. A reasonably good agreement was observed for the results of the experiment and CFD.

Parasitic pressure losses in diffusers and in their downstream piping systems for fluid flow and heat transfer

The need for precise design of piping systems and of ducts which interconnect fluid flow and heat transfer equipment of different dimensional scales depends on the availability of basic fluid flow information. One of the most ubiquitous features in a system which transports fluids is the occurrence of changes in flow cross section. In particular, enlargements of the flow cross section give rise to parasitic pressure losses both in the enlargement fitting and in the piping system that is downstream of the enlargement. The most commonly used enlargement fittings are diffusers. Although there is some information about pressure losses that are caused by flows in diffusers, it is highly contradictory and, equally significant, the available information takes no account of the heightened pressure losses in the downstream piping which are due to the highly disturbed flow that exits the diffuser. This investigation was undertaken to provide definitive information on diffuser-created parasitic pressure losses that occur in response to all possible operating conditions, including the Reynolds number at the diffuser inlet, the diffuser opening angle, and the ratio of the exit and inlet diameters of the diffuser. This information is cast in dimensionless form and is presented as incremental departures from a simply calculated baseline case. In addition, the lengths of pipe downstream of the diffuser that are required to dampen the irregularities of the diffuser exit flow are presented as a necessary prerequisite for the proper use of the incremental pressure drop results. It was found that the incremental pressure drop increases monotonically with increasing diffuser opening angle. In general, the incremental pressure drop values for a given diffuser opening angle decrease with increasing Reynolds number and tend to level off as the Reynolds number further increases.

Study on flow pattern maps in hilly-terrain air–water–oil three-phase flows

Although three-phase flows are often encountered in offshore petroleum engineering, but there have been only a few comprehensive studies on flow pattern maps. In the present study, an experimental program was carried out to obtain flow pattern maps in hilly-terrain air–water–oil three-phase flows. Two elbows, including two symmetrical inclined pipes, were used at the peak and the valley respectively, with an inclination angle of 0–30°. The test section was made of transparent acrylic resin, with a total length of 10m and an inner diameter of 40mm. The superficial velocities were 0.01–15m/s, 0.01–2m/s, and 0.01–2m/s for air, water and oil, respectively.By using a high-speed camera and a single-wire capacitance probe, we recorded the flow processes and measured the water layer height in the pipe, and further identified different flow patterns. Similar to the flow patterns in horizontal pipes, eleven typical flow patterns were observed in the present study. However, the ranges in the flow pattern maps were extended for intermittent flow in uphill pipes, and also for stratified flow in downhill pipes. When each superficial velocity was low enough, elbows, causing accumulation at the peak and the valley of the hilly-terrain system, determined the flow pattern in the downstream pipes, and resulted in different flow patterns in the uphill and downhill pipes. Nevertheless, when superficial gas velocity was high enough, exceeding 10m/s, all the flows tended to be annular along the whole hilly-terrain pipes. It may be appropriate to simplify the air–water–oil three-phase flow into gas–liquid two-phase flow, where water fraction had an effect on oil–water distribution and changes the viscosity of the liquid mixture. As a result, water fraction was considered as a secondary factor to determine flow patterns when compared with pipe structures and superficial velocities.

Generation of monodispersed microdroplets by temperature controlled bubble condensation processes

This work introduces a microfluidic method for the generation of monodispersed microdroplets by using temperature controlled bubble condensation processes. In this method, the dispersed phase is first vaporized in the feeding pipe and ruptured to monodispersed bubbles in a coflowing stream. These bubbles are then condensed in the downstream pipe, where monodispersed microdroplets are obtained. This method ensures the narrow distribution of droplet diameters and prepares microdroplets less than 200 μm in sub-millimeter fluidic devices.

Interrogating the effect of 90° bends on air–silicone oil flows using advanced instrumentation

When gas/liquid mixtures flow around a bend they are subjected to forces additional to those encountered in a straight pipe. The behaviour of the flows at the inlet and outlet of the bend depends on the orientation of the pipes. Air/silicone oil flows around a 90° bend have been investigated using advanced instrumentation: Electrical Capacitance Tomography (ECT), Wire Mesh Sensor Tomography (WMS) and high-speed video. The first two provide time and cross-sectionally resolved data on void fraction. ECT probes were mounted 10 diameters upstream of the bend whilst WMS was positioned either immediately upstream or immediately downstream of the bend. The downstream pipe was maintained horizontal whilst the upstream pipe was mounted either vertically or horizontally. The bend ( R/ D=2.3) was made of transparent acrylic resin. From an analysis of the output from the tomography equipment, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability Density Function (PDF) plots of the time series of cross-sectionally averaged void fraction as suggested by Costigan and Whalley (1996). The superficial velocities of the air ranged from 0.05 to 4.73 m/s and for the silicone oil from 0.05 to 0.38 m/s. Bubble/spherical cap, slug, unstable slug and churn flows were observed before the bend for the vertical pipe and plug, slug, stratified wavy and annular flows when the pipe was horizontal. Bubble, stratified wavy, slug, semi-annular and annular flows are seen after the bend for the vertical 90° bend whilst for the horizontal 90° bend, the flow patterns remained the same as before the bend. Flow patterns for the vertical and horizontal 90° bends are shown on the diagram of the gas superficial velocity versus liquid superficial velocity. These results are confirmed by the high-speed videos taken around the bend. A previously proposed criterion, to determine stratification after the bend, based on a modified Froude number have been shown to be valid for a liquid different from that tested in the original paper.

Particle capture by turbulent recirculation zones measured using long-time Lagrangian particle tracking

We have measured the trajectories of particles into, and around, the recirculation zone formed in water flowing through a sudden pipe expansion with radius ratio 1:3.7, at Reynolds numbers between 5,960 and 41,700 over a range of particle Stokes number (here defined as $$ St = {\frac{{T_{\text{f}} }}{{\tau_{\text{p}} }}} $$ , where T f is an appropriate mean or turbulent timescale of the fluid flow and a particle relaxation time, τp,) between 6.2 and 51 and drift parameter between 0.3 and 2.8. The particles were thus weakly inertial but nevertheless heavy with a diameter about an order of magnitude larger than the Kolmogorov scale. Trajectories of particles, released individually into the flow, were taken in a Lagrangian framework by a three-dimensional particle tracking velocimeter using a single 25 Hz framing rate intensified CCD camera. Trajectories are quantified by the axial distribution of the locations of particle axial velocity component reversal and the probability distributions of trajectory angle and curvature. The effect of increasing the drift parameter was to reduce the tendency for particles to enter the recirculation zone. For centreline release, the proportion of particles entering the recirculation zone and acquiring a negative velocity decreased from about 80% to none and from about 66% to none, respectively, as the drift parameter increased from 0.3 to 2.8. Almost half of the particles experienced a relatively large change of direction corresponding to a radius of curvature of their trajectory comparable to, or smaller than, the radius of the downstream pipe. This was due to the interaction between these particles and eddies of this size in the downstream pipe and provides experimental evidence that particles are swept by large eddies into the recirculation zone over 1.0 < $$ Z^{*} $$ < 2.5, where $$ Z^{*} $$ is axial distance from the expansion plane normalized by the downstream pipe diameter, which was well upstream of the reattachment point at the wall ( $$ Z^{*} \approx 3. 5 $$ ). Once inside the recirculation zone, the particle motion was governed more by the drift parameter than by the Stokes number.

Char and char-supported nickel catalysts for secondary syngas cleanup and conditioning

Tars in biomass gasification systems need to be removed to avoid damaging and clogging downstream pipes or equipment. In this study, Ni-based catalysts were made by mechanically mixing NiO and char particles at various ratios. Catalytic performance of the Ni/char catalysts was studied and compared with performance of wood char and coal char without Ni for syngas cleanup in a laboratory-scale updraft biomass gasifier. Reforming parameters investigated were reaction temperature (650–850 °C), NiO loading (5–20% of the weight of char support), and gas residence time (0.1–1.2 s). The Ni/coalchar and Ni/woodchar catalysts removed more than 97% of tars in syngas at 800 °C reforming temperature, 15% NiO loading, and 0.3 s gas residence time. Analysis of syngas composition indicated that concentrations of H 2 and CO in syngas significantly. Furthermore, performance of the Ni/coalchar catalyst was continuously tested for 8 h. There was slight deactivation of the catalyst in the early stage of tar/syngas reforming; however, the catalyst was able to stabilize soon after. It was concluded that chars especially coal char can be an effective and inexpensive support of NiO for biomass gasification tar removal and syngas conditioning.

A Two-Dimensional Study of Transonic Flow Characteristics in Steam Control Valve for Power Plant

A steam control valve is used to control the flow from the steam generator to the steam turbine in thermal and nuclear power plants. During startup and shutdown of the plant, the steam control valve is operated under a partial flow conditions. In such conditions, the valve opening is small and the pressure deference across the valve is large. As a result, the flow downstream of the valve is composed of separated unsteady transonic jets. Such flow patterns often cause undesirable large unsteady fluid force on the valve head and downstream pipe system. In the present study, various flow patterns are investigated in order to understand the characteristics of the unsteady flow around the valve. Experiments are carried out with simplified two-dimensional valve models. Two-dimensional unsteady flow simulations are conducted in order to understand the experimental results in detail. Scale effects on the flow characteristics are also examined. Results show three types of oscillating flow pattern and three types of static flow patterns.

J0504-3-1 下流側曲がり管に設置された圧力容器内温度計ウェルの流力振動評価([J0504-3])流体関連の騒音と振動(3))

A lot of thermometers are used for monitoring the fluid and reactive conditions in thermal and nuclear power plants. From the experience of failure of the thermometer well due to flow-induced vibration in fast breeder reactor "MONJU" JSME proposed the guideline for the flow-induced vibration of a cylindrical structure. Its applicable scope is limited in structures subjected to homogeneous and cross flow. In some case of monitoring of reaction in pressure vessel, thermometer wells are installed downstream bend pipe and subjected to complicated flow. In the present study, the structural integrity of the thermometer well installed in pressure vessel was evaluated through scale tests with respect to flow-induced vibration. Lock in synchronization would not occur for the thermometer well. The predictable maximum fluctuating stresses induced by the turbulence and the Karman vortex shedding were bellow 1MPa and was satisfied the allowable level of fatigue limit.

Numerical analysis of soil pipe effects on hillslope water dynamics

Soil pipes are considered to drain off water from a hillslope and play an important role in the subsurface runoff generation process, thus reducing the slope failure susceptibility. However, soil pipes are also often detected on the collapsed slope suggesting that they might act to induce slope instability. To examine how the soil pipes act on pore-water pressure generation and on a slope failure processes, a numerical model was developed. The model was used to test the response of pore-water pressure in a hillslope with soil pipes of different cross-sectional areas, lengths, distances from the impermeable bed, roughness, and hillslope angles. The model was also tested to find the response of open soil pipe if blocked. The study reveals that pipes reduce pore-water pressure (measured closed to bed) around its upstream end and increase around its downstream end if compared with no pipe case. Pore-water pressure at downstream end is increased with increase in hillslope angle, pipe cross-sectional area, pipe length, or depth of soil pipe. Soil pipe, even if it is ended within the hillslope, increases the total discharge from hillslope. Location of rough soil also affects the discharge and pressure within the hillslope. If the less rough pipe is close to the source of water, discharge from hillslope matrix is greater regardless of its downstream pipe roughness. Blockage of small portion of open soil pipe increases the soil pressure around the region but not beyond the case if there is no soil pipe. However, complete collapse of soil pipe from a point to all along the downstream end of hillslope increases the pore-water pressure beyond the pressure if there were no soil pipes. Therefore, the position and type of soil pipe collapse might play an important role in shallow landslide initiation.

Unsteady Wall Shear Stress in Transient Flow Using Electrochemical Method

Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows.

The flow‐field downstream of a collapsible tube during oscillation onset

AbstractThe flow‐field immediately downstream of a collapsible tube during oscillation onset starting from the collapsed state was measured using two‐dimensional high‐speed particle image velocimetry. Both tube and fluid were chosen to produce oscillation at the lowest possible Reynolds number, of just over 300. The flow was examined in the plane formed by the tube axis extended into the downstream pipe and the major axis of the tube collapse cross‐section. The resulting time‐series of spatial fields of 2D velocity vectors was analysed by frequency content and by proper orthogonal decomposition. Areas of the flow where oscillation initially occurs were identified. Flow disturbances centred at various frequencies were identified, some associated with the growing oscillation arising from the instability of the fluid–structure interaction between the main flow and the tube and others associated with the instability of the confined twin jets emanating from the collapsed‐tube throat. Copyright © 2009 John Wiley &amp; Sons, Ltd.