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This study investigates the flow characteristics of pulp suspensions flowing through a 90° bend, which is used in the production system of an actual paper making machine, e.g., for transporting the pulp suspensions from its stock...
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This study investigates the flow characteristics of pulp suspensions flowing through a 90° bend, which is used in the production system of an actual paper making machine, e.g., for transporting the pulp suspensions from its stock reservoir to the header. Experiments were conducted on pulp suspensions with a fiber concentration Cs of 0.3 and 0.6 wt% and a bend with a diameter of 22 mm and a curvature radius ratio of 4.0. Flow visualization and measurements of the distributions of time-averaged fiber concentration Ca and axial velocity U were performed with a light section method and the particle image velocimetry (PIV) method, respectively, at representative bulk velocities and at various longitudinal stations. The influence of the flow rate on the changes of their distributions in the streamwise direction was examined. The flow characteristics of the pulp suspension depend on the flow pattern in the upstream straight tube and are greatly different from those of the single-phase water flow. For a low flow rate, the flocculated pulp fibers move without getting disentangled in the bend and the distribution of Ca shows a shape bias towards the inner wall side. As the flow rate is increased, Ca becomes larger in the outer part of the bend, and it changes into a rather flat distribution in the downstream tangent.
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摘要 :
In this study, we analyze the flow characteristics of pulp suspensions in a sudden expansion channel, which is used as a tube bank in papermaking machines. Flow visualization using a light section method and measurements of time-a...
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In this study, we analyze the flow characteristics of pulp suspensions in a sudden expansion channel, which is used as a tube bank in papermaking machines. Flow visualization using a light section method and measurements of time-averaged and fluctuating fiber concentrations, Ca and C’, and pressure, were performed. The experiments were carried out on pulp suspensions with a bulk fiber concentration (Cs) of 0–2.0 wt% in a channel with an expansion ratio of ? ? 2 at varied average velocities (Ua) of 0.04?6.6 m/s. We examined the effect of flow velocity on the changes in concentration and pressure distributions along the channel axis. The distribution of the pulp fiber concentration behind the sudden expansion significantly changes depending on the flow state in the upstream channel before the expansion. In particular, for low and moderate velocities, the flow field is characterized in the main flow region consisting of flocculated plug fibers and a recirculation region with a low concentration near the expansion corner by a type of streamline originated from the thin water-layer in the upstream channel. The distribution of Ca shows a tongue-shaped structure in the central part of the cross section, and C’ is large near the annulus streamline. As the velocity is further increased, the flocculated fibers gradually disperse, and the distributions of Ca and C’ become almost uniform. In addition, the uniformity of fiber concentration does not change much in the section downstream from a distance 10 times the step height from the sudden expansion plane.
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In this study, the flow characteristics of a pulp suspension in a modeled headbox channel containing a screen-type circular cylinder were examined experimentally. The distributions of the pulp fiber concentration and the axial vel...
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In this study, the flow characteristics of a pulp suspension in a modeled headbox channel containing a screen-type circular cylinder were examined experimentally. The distributions of the pulp fiber concentration and the axial velocity of downstream wake of the cylinder were obtained using the transmitted light attenuation method and particle image velocimetry, respectively. The influence of flow velocity and the degree of pulp fiber dispersion were explained. From this information, we explored the feasibility of improving the efficiency of the hydraulic headbox of a papermaking machine.
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This paper presents the results of an experimental study on a pulsating turbulent flow through conical diffusers with total divergence angles (2θ) of 12°, 16°, and 24°, whose inlet and exit were connected to long straight pipe...
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This paper presents the results of an experimental study on a pulsating turbulent flow through conical diffusers with total divergence angles (2θ) of 12°, 16°, and 24°, whose inlet and exit were connected to long straight pipes. To examine the effects of the divergence angle and the nondimensional frequency on flow characteristics, experiments were systematically conducted using a hot-wire anemometry and a pressure transducer. Moreover, the pressure rise between the inlet and the exit of the diffuser was analyzed approximately under the assumption of a quasi-steady flow and expressed in the form of simple empirical equations in terms of the time-mean value, the amplitude, and the phase difference from the flow rate variation. The expressions are in good agreement with the experimental results and very useful in practice. With the increase in the Womersley number, α, and 2θ, the sinusoidal change in the phase-averaged velocity, W, with time becomes distorted, and the W distributions show a more complicated behavior. For the flow at α=10 in the diffusers with large 2θ, the distributions of W are depressed on the diffuser axis. In contrast, for the flow at α=20, W has a protruding distribution on the diffuser axis.
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This paper presents the results of an experimental study on the developing pulsatile flow in curved pipes with a long, straight pipe upstream. In order to examine the dependence of flow-field development on the governing parameter...
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This paper presents the results of an experimental study on the developing pulsatile flow in curved pipes with a long, straight pipe upstream. In order to examine the dependence of flow-field development on the governing parameters, LDV measurements were conducted systematically for six cases of flow, where the Womersley number α was varied from 5.5 to 18, the mean Dean number D m was 200 and 300, the flow rate ratio η was 0.5 and 1, and the curvature radius ratio Rc was 10 and 30. Peculiar flow phenomena, such as flow reversal for all values of α and a depression in the axial velocity profile for α = 10, were analyzed by decomposing the axial velocity into a time-mean and a varying component, as well as by obtaining the bias of their profiles. The velocity distributions abruptly change with the phase at turn angles Ω of 15–30°, corresponding to the nondimensional axial length z′ ? 1–2 from the bend entrance, and their development along the pipe axis is the most complicated for the flow at a moderate α of 10 and large η of 1. The entrance length in the case of pulsatile flow is shorter than that for steady flow with the same flow rate as the maximum pulsatile flow rate.
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An experimental investigation was performed for the pulp-suspension flow in a channel with a partition plate, which is an extremely simplified model of the dispersion part of the hydraulic headbox of papermaking machines. This stu...
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An experimental investigation was performed for the pulp-suspension flow in a channel with a partition plate, which is an extremely simplified model of the dispersion part of the hydraulic headbox of papermaking machines. This study was tried to make the papermaking system most suitable and was conducted to obtain the fundamental findings. To do it, flow visualization and optical measurements of the fiber concentration were made in the wake region of a flat plate. Characteristics of the pulp-suspension flow were examined for five flow cases based on the flow patterns found in the authors' previous report (2010) for a channel. The behavior of the pulp fibers and flow in the wake is strongly related to the flow states in the passages of the partition plate and also depends on the shear layer generated at the trailing edge of the plate. The partition plate is slightly effective for obtaining a uniform time-averaged fiber concentration distribution and for making the fluctuating fiber concentration lower.
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An experimental study has been made to investigate the secondary stream in an oscillatory laminar flow in the entrance region of curved pipes. The experiments were performed under the conditions of the Womersley numbers α=5.5～30...
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An experimental study has been made to investigate the secondary stream in an oscillatory laminar flow in the entrance region of curved pipes. The experiments were performed under the conditions of the Womersley numbers α=5.5～30, the Dean numbers D= 100～300, and the curvature radius ratios of R_c=4 and about 10. The secondary flow was visualized and was recorded photo- graphically at several sections near the bend inlet. Development of the secondary flow is discussed mainly for D=300 and influences of the Womersley number on the characteristics are made clear. The classification found by authors to describe the secondary flow pattern in the fully-developed region is also useful in doing the problem in the entrance region. For α~2/D < 0. 655, the secondary flow forms a Dean type and grows up at Ω = 20～50°around the curved turn at the inflow phase, particular- ly its intensity showing drastic increase for a moderate a of α~2/D＝0.41, while the secondary flow in the tangent at the outflow phase almost breakes down at the section of four times diameter from the bend inlet. For high α of α~2/D >0.655, the secondary flow in a kind of Lyne type, which consists of two pairs of vortices, is induced even at the bend inlet. The steady streaming is generated near the bend inlet and the fluid drifts in the axial direction depending on the secondary flow patterns.
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360-degree bend flowmeters were applied to determine pulsatile flow rates in water. Experiments were performed using bend flowmeters with curvature radius ratios of 7, 10 and 30 under the conditions of Womersley numbers of α=2.1?...
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360-degree bend flowmeters were applied to determine pulsatile flow rates in water. Experiments were performed using bend flowmeters with curvature radius ratios of 7, 10 and 30 under the conditions of Womersley numbers of α=2.1?18, mean Reynolds numbers of Reta=800?5×104 and oscillatory Reynolds numbers of Reos=600?1.6×104. The pressure difference across the bend was found to be independent of the pulsation frequency and to conveniently vary with almost the same phase as the instantaneous flow rate. A method for measuring the instantaneous flow rate is proposed as well as a method for estimating the time-mean and amplitude values of the pulsatile flow rate. It is concluded that 360-degree bend flowmeters can be used to measure the pulsatile flow rate.
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A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition...
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A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition of a moderate Womersley number a=10, which is a physiologically interesting nondimensional frequency, and a Dean number D=300. The secondary flow motion was rendered visible by means of a tracer method using nylon particles, and photographs were taken at four phases in one cycle and at axial locations from the upper stream tangent to the downstream in the curved pipe.
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An experimental study was performed on the fiber-concentration distributions of wood pulp liquid flowing through a divergent tube at a divergence angle of θ = 12°. The study was conducted to verify the tube’s effectiveness for ...
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An experimental study was performed on the fiber-concentration distributions of wood pulp liquid flowing through a divergent tube at a divergence angle of θ = 12°. The study was conducted to verify the tube’s effectiveness for application to the tube banks of papermaking machines. Experiments were conducted at bulk pulp-fiber concentrations of Cs = 0.2 - 0.6 wt % and inflow velocities of Ua = 0.1 - 2 m/s. The flow in the horizontal plane that contained the tube axis was visualized using the light-section method. In addition, the distributions of the time-averaged and fluctuating fiber concentrations (Ca and C’, respectively) were measured. We then investigated the effect of the average flow rate on the variations in the directions of flow of the concentration distributions. At a low flow rate (Ua < 0.3 m/s), the fluid of the annular water layer formed in the upstream tube divided the flow into two in the divergent tube, and the Ca and C’ distributions exhibited shapes that had considerable differences in the cross-section. When the flow velocity was increased to Ua ≥ 0.5 m/s, the shape of the Ca distribution flattened, and C’ reduced gradually in the flow direction. The results related to the non-uniformity of fiber concentration demonstrated that the divergent tube is suitable for use in a tube-bank channel of the headbox of a papermaking machine.
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