Constant Diameter Pipe Research Articles

Effects of flow rate variation on solute transport in a karst conduit with a pool

To investigate the effects of flow rate variation on solute transport in a karst conduit, three pipe structures of a constant diameter pipe, the pipe connected to a symmetrical pool and an asymmetrical pool respectively were chosen, and several tracer experiments were conducted separately in each of the three pipe structures at nine flow rates. Experimental results show that the peak of the breakthrough curve (BTC) increased and the tailing decreased with increasing discharge. Three models, the advection–dispersion equation (ADE), the two-region nonequilibrium model (TRNM) and the transient storage model (TSM), were used to simulate BTCs and explore the change of transport parameters with increasing flow rate. Simulations show that ADE was capable of replicating the almost symmetrical BTCs of the single pipe but incapable of fitting the appreciable BTC tails for the pools. Nevertheless, TRNM and TSM can reproduce all BTCs of single pipe and pipe with a pool very well. The research demonstrates the significant effect of the pool on solute transport. The parameters in the two models (TRNM and TSM) exhibited similar trends with increasing discharge in either pool. In the TRNM, a clear positive correlation with discharge emerged for the partition coefficient and mass transfer coefficient. Meanwhile, the main channel cross-sectional area and exchange coefficient in TSM increased gradually with discharge. The storage zone area decreased generally with increasing flow rate. The relationship between solute transport and the flow rate is more complex in the asymmetrical pool than in the symmetrical pool.

Numerical and experimental investigation of leaks in viscoelastic pressurized pipe flow

Abstract. This paper extends the analysis concerning the importance in numerical models of unsteady friction and viscoelasticity to transients in plastic pipes with an external flow due to a leak. In fact recently such a benchmarking analysis has been executed for the cases of a constant diameter pipe (Duan et al., 2010), a pipe with a partially closed in-line valve (Meniconi et al., 2012a), and a pipe with cross-section changes in series (Meniconi et al., 2012b). Tests are based on laboratory experiments carried out at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy, and the use of different numerical models. The results show that it is crucial to take into account the viscoelasticity to simulate the main characteristics of the examined transients.

Transient hydrodynamics of in-line valves in viscoelastic pressurized pipes: long-period analysis

The literature contains few reports devoted to the analysis of the effects of a partially closed in-line valve on the characteristics of transients in viscoelastic pressurized pipes. In this paper a contribution to the analysis of the long-period behavior of pressure is offered from both the experimental and numerical modeling point of view. In the first part, laboratory tests and the related results—noticeably extensive with respect to the existing literature—are examined. More precisely, the dependance of the damping of the dimensionless pressure maximum values on the initial conditions and in-line valve local head loss coefficient is shown. In the second part, a 1-D numerical model is developed by determining its parameters within a physically based procedure. Model parameters are obtained by considering transients in a constant-diameter pipe (single pipe) and then exported to the case of pipes with a partially closed in-line valve (in-line valve pipe). Moreover, particular attention is devoted to the modalities of specifying boundary conditions. In particular, the quasi-steady-state approach is followed for determining the transient local head loss due to the partially closed in-line valve and the actual supply conditions and characteristics of the maneuver are taken into account. Finally, the effect of unsteady friction and viscoelasticity is examined in both single and in-line valve pipes.

Structures of confined vortex breakdown in constant diameter pipe flow

Numerical solutions of three-dimensional, incompressible and unsteady Navier-Stokes equations for constant diameter swirling pipe flows are used to study vortex breakdown, including the detailed flow structures in the bubble domain and the “tail” behind the bubble during the vortex breakdown, and a comparison is made between the numerical solutions and the experimental results.

Vortical flow. Part 2. Flow past a sphere in a constant-diameter pipe

This paper describes an experimental and numerical investigation of concentrated vortex flow past a sphere in a constant-diameter pipe. As the swirl was increased at a fixed sphere Reynolds number of approximately 1100, the length of the mean downstream separation bubble decreased. For a small range of swirl intensity, an almost stagnant separation bubble formed on the upstream hemisphere. A further increase in swirl caused the bubble to become unstable and develop into an unsteady spiral disturbance. At very high swirl the downstream separation bubble was eliminated and an unsteady separation zone extended far upstream. Calculations of the vorticity field from surface fits to azimuthal and axial velocity data suggest that upstream separation is caused by the distortion of vortex filaments in the diverging flow approaching the sphere. Numerical solutions of steady inviscid axisymmetric flow past a sphere exhibit a fold in the vicinity of upstream separation. It is suggested that this accounts for the extreme sensitivity encountered in the experiments.

Vortical flow. Part 1. Flow through a constant-diameter pipe

This paper describes an exploration of the behaviour and properties of swirling flow through a constant-diameter pipe. The experiments reveal a complicated transition process as the swirl intensity Ω is increased at fixed pipe Reynolds number Re ≈ 4900. For Ω [les ] 1.09, the vortex was steady, laminar, axisymmetric, and developed slowly with streamwise distance. The upstream velocity profiles were similar to those commonly appearing in the literature in similar apparatus. Spiral vortex breakdown appeared in the test section for 1.09 [les ] Ω [les ] 1.31 and was associated with a localized transition from jet-like to wake-like mean axial velocity profiles. Further increase in Ω caused the breakdown to move upstream of the test section. Downstream, the core of the post-breakdown flow was unsteady and recovered toward jet-like profiles with streamwise distance. At Ω = 2.68, a global transition occurred in which the mean axial velocity profiles suddenly developed an annular axial velocity deficit. At the same time, disturbances began to appear in the outer flow. Further increase in Ω eventually led to an annulus of reversed axial flow and a completely unsteady vortex.

Transient Behavior of Vortical Flow through a Constant Diameter Pipe

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Enhancement of Heat Transfer with Swirling Flows Issued into a Divergent Pipe

Experiments have been performed to study the heat transfer process of swirling e ow issued into a heated divergent pipe with a divergent angle of 7 deg with respect to the pipe axis. A e at vane swirler situated at the entrance of the pipe is used to generate the swirling e ow. The heat transfer results along the pipe wall demonstrate that at low Reynolds numbers without the swirl, the separation point of the recirculation e ow caused by the divergence of the pipe makes a minimum in the heat transfer. The presence of the swirler itself can have a signie cant effect on the heat transfer. The minimum disappears and the heat transfer results approach the case of a constant diameter pipe when the e ow is swirled. The enhancement of the heat transfer is small and is mostly caused by the swirl velocity. At high Reynolds numbers, the large turbulence intensity generated by the impingement of the e ow stream on the swirl vane can signie cantly enhance the heat transfer. A qualitative e ow structure can be inferred from the heat transfer measurements. During the experiments, the Reynolds number ranges from 10 4 to 2 3 10 5 , and the swirl number from 0 to 0.65. Because the increase of the heat transfer with the swirl number is monotonic, correlations of the Nusselt number in terms of the swirl number and the Reynolds number are obtained.

Study of the flow properties of slurries using the refractive index matching technique LDV

Modern light scattering instrumentation cannot be applied to many concentrated slurries because they are opaque. In this study Laser Doppler Velocimetry is used to measure liquid solid axial velocity profiles for refractive index matched slurries with solids loadings as great as 25 vol.%. Since measurements in flow geometries more complex than straight horizontal pipe are of interest in many applications, axial velocity profiles through a concentric contraction are reported. The usefulness of these measurements from an experimental perspective a modeling perspective is discussed. The theoretical analyses of Hanks and Dadia Hanks and Ricks were applied to the flow data through the constant-diameter pipe. Flow regimes are identified where these theories are appropriate.

Effects of pipe elbows and tube bundles on selected types of flowmeters

This paper presents experimental results for the decay of pipe elbow-produced swirl in pipeflows and its effects on flowmeter measurement accuracy. Experiments include the decay of swirl produced by single and double elbow configurations for pipe diameter Reynolds numbers of 10 4 to 10 5 using water in a 50 mm diameter facility at NIST in Gaithersburg, MD. Results show that different types of swirl are produced by the different piping configurations. The swirl decay is found to be dependent on the type of swirl and the pipe Reynolds number. At high Reynolds number very long lengths of straight, constant diameter pipe are required to dissipate the single eddy type swirl that is produced by the two elbows out-of-plane configuration. Without flow conditioning, it is concluded that the specifications of upstream pipe lengths in the current flowmetering standards may not be sufficient to achieve the desired flow metering accuracy. Experimental results are also presented for the effects produced by tube bundle-type flow conditioners. These results show shifts in orifice meter discharge coefficients that are both positive and negative depending upon pertinent conditions. A range of orifice geometries, Reynolds numbers and meter locations are studied and explanations are put forth to explain these shifts. Results are also presented for a specific type of turbine meter. These show meter factor shifts that are also both positive or negative depending upon the type of swirl pattern entering this meter. An example is given in which the insertion of a tube bundle flow conditioner between a single elbow and the turbine meter produces a larger disturbance to the meter factor than would occur without the conditioner.

Particle Velocities in a Swirling, Confined Flow

Abstract Abstract— Measurements of velocity have been obtained by laser-Doppler velocimetry in the isothermal flow of liquid in an axisymmetric vessel of geometry similar to that of a quarl burner and furnace. The arrangement comprised a co-axial jet, a diffusing quarl, a sudden expansion, a length of constant-diameter pipe and a contraction to the exit pipe. The liquid was a mixture of tetraline and turpentine with concentration and temperature arranged to match its refractive index to that of the plexiglass vessel and to plexiglass beads. with mean diameters of 510 and 700 μm, used to allow examination of two-phase flows. With single-phase flow, the swirl number of the annular jet was 1.38 and the ratio of the mass-flows in the central pipe and annulus was varied from zero to 0.77 to allow examination of the resulting flow characteristics with emphasis in the quarl region. The results quantify the decrease in size of the toroidal vortex with increasing mass-flow in the central jet and the correspondingly more uniform velocity distribution in the down stream region. The plexiglass beads were added separately to the core and annulus flows for the case of equal bulk mean axial velocity (a mass-flow ratio of 0.25 in the central pipe) and the single refractive index of the vessel, liquid and beads allowed measurements with mean volume concentration up to 0.113 and limited by the depth of field and inclusion of gas within the beads. With beads in the central jet and a volume concentration of 0.004, the bead velocities are higher than that of the single-phase flow by up to 15% up to the axial location where the swirl and geometry induce the toroidal vortex and low centreline velocities after which the beads tend to lag. With beads in the annulus of mean concentrations up to 0.113, the swirl causes locally high concentrations with a less uniform annulus velocity profile and considerable suppression of turbulence. In both cases, the profiles of mean and rms velocities were similar for beads and single-phase flow in the downstream region.

An experimental investigation of blade element theory for wind turbines. Part 1. Mean flow results

This paper describes an investigation of blade element theory, which is commonly used to describe the flow through wind turbine blades. A two-bladed model turbine was shrouded by a constant-diameter pipe. The tip clearance was sufficiently small to minimise and localise the tip clearance losses. By passively heating the wake of one of the turbine supports, it was found that supports did not produce any significant circumferential non-uniformity in the mean axial and circumferential velocities. These velocities were measured using a conventional three-hole yawmeter and an X-probe hot-wire anemometer. The agreement between the two methods was good. The turbine's power output was also determined by two independent methods; again with good agreement. The major finding was that blade element theory underestimated the power contribution as a function of radius wherever the local angle of attack exceeded the angle that gives the maximum lift/drag in two-dimensional flow. Several possible causes of the discrepancy are discussed.

An experimental study on the flows in the jet pump.

An experiment on the mixing flows in the suction port of the jet pump was made analogically, using air in place of water. The mixing took place in a converging bell-mouth inlet and in a successive constant-diameter pipe. Measurements were made on (1) the wall static pressure, (2) the mean velocity prefiles, and (3) turbulence for different velocity ratios and nozzle-throat spaces. The mean static pressure distribution on the throat inlet section was obtained by integrating Reynolds equation in a radial direction.

Confined Jet Mixing for Nonseparating Conditions

The mixing of an air jet with a lower-velocity air stream is described. The mixing takes place in a constant diameter pipe, and the flow is investigated from the inlet where the jet and secondary velocities are uniform (but different) to a location downstream where the flow is fully developed. Measurements are made of (1) the wall static pressure, (2) the mean velocity, (3) the turbulence velocities and Reynolds stress throughout the flow field for different velocity ratios and diameter ratios. This work differs from previous investigations in that a wider range of flow conditions is considered, i.e., different diameter and velocity ratios in addition to the flow in the latter stages of mixing. Also, the turbulence velocities and Reynolds stress as determined throughout the flow are described.