Report COST STSM
COST STSM Reference Number: COST-STSM-FP1005-16744
Period: 2014-03-02 00:00:00 to 2014-03-11 00:00:00
COST Action: FP1005
STSM type: Regular (from France to Italy)
STSM Applicant: Dr SALAHEDDINE SKALI LAMI, Lorraine university LEMTA,
Nancy(FR) , salaheddine.skali-lami@univ-lorraine.fr
STSM Topic: Flocculation measurements in pulp flow
Host: Marina Campolo,University of Udine,Udine(IT), marina.campolo@uniud.it
Work Plan Summary:
The purpose of this exchange is to make measurements of flocculation of a paper pulp flow in
pipes. Since the flocculation varies with the flow rate, it is then possible to evaluate the influence of
the rate of flocculation on the pressure losses and in particular in the case of drag reduction regime.
UVP is the technique which we have retained it is often implemented to measure the velocity
profiles in the flow of pulp at medium concentrations commonly used in industry. We intend to use
this technique by analyzing simultaneously two signals of two ultrasonic probes placed along a
generatrix of the tube and spaced at a controlled length. This would allow, by a spacetime
processing and a convolution of the two signals, to measure the size of flocs convected by the flow
and their different radial position.
Introduction
This work investigating the flocculation of the pulp flowing was done in collaboration with Marina
Campolo and Mattia Simeoni at the University of Udine.
The first task was to validate measures of UVP in common use on an experimental loop = 100 mm
for flow of water at different velocities. All experiments were performed in the turbulent regime.
The second work, performed on the same loop, involved the study of a suspension of nylon fibres
(0.5% by weight). In both cases measures of velocity profiles at different velocities were coupled to
measures of pressure losses.
Finally the last work was especially focused on the use of UVP provided with two probes disposed
in parallel on a pipe of 30 mm diameter to assess the rate of flocculation in a flow of pulp.
1) Conventional measurements using UVP
The experimental tests made on the experimental loop (diameter =100mm and length L=8.99m)
are summarized in Table below.
Water (T=17°C, =998.4 kg/m3, µ=1,05 10-3 Pa.s)
Q (m3/h)
11,58
22,51
31,08
58,86
88,92
105,80
V (m/s)
0,41
0,80
1,10
2,08
3,14
3,74
p mbar
1,74
5,43
9,77
30,86
66,12
93,00
p/L mbar/m 19,59
61,14
110,07
347,72
745,06
1047,93
Fibre (C=0,5% L/d=120, T=21°C, =997.6 kg/m3, µ=9,84 10-4 Pa.s)
Q (m3/h)
5,37
18,51
27,67
57,14
88,25
105,80
V (m/s)
0,19
0,65
0,98
2,02
3,12
3,74
0,89
4,39
8,73
30,58
67,35
93,00
p mbar
10,08
49,49
98,40
344,57
758,90
1047,93
p/L mbar/m
Table1. Pressure losses at different flow rates for water and nylon fibre suspension
These results allow the calculation of the friction factors which are shown in figure below
7.0E-03
Cf
6.0E-03
Water
5.0E-03
Karman
fibre C=0.5%
Blasius
4.0E-03
3.0E-03
2.0E-03
1.0E-03
0.0E+00
1.0E+04
1.0E+05
Re
1.0E+06
Figure1. Fiction factors of flow of water and nylon fibre suspension vs Reynolds number
The Fiction factors show good agreement with Blasius equation. The Reynolds number for the fibre
suspension was calculated with a viscosity according to the Dinh & Armstrong model for an
isotropic fibre suspension (Dinh & Armstrong,1984):
𝑙 2
4𝐶0 ( )
𝑑
𝜇 = 𝜇0 (1 +
)
𝜋𝑑
90𝑙𝑛 (𝐶 )
0 𝑙
µ0 : viscosity of water
l/d , C0: aspect ratio and volumetric concentration of fibres.
The UVP are used for measurements of the velocity profiles at the different flow rates. The average
profiles are shown in Figures 2 and 3).
We can notice these velocity profiles strongly deviate from the theoretical profiles for distances to
the wall less than 6 mm. Theses variances are known for velocity investigation by ultrasound in the
areas close to the wall (no particles, multiple echoes ...).
Turbulent flow of water (pipe 100mm)
5
4.5
4
Re=38830
Re=75489
Re=104240
Re=197430
Re=298270
Re=357620
U*=0.024m/s
U*=0.0.42m/s
U*=0.054m/s
U*=0.097m/s
U*=0.142m/s
U*=0.165m/s
Velocity (m/s)
3.5
3
2.5
2
1.5
1
0.5
0
0
10
20
30
radius (mm)
40
50
Figure 2. Velocity profiles of flow of water at different Reynolds number
Turbulent flow or fibre suspension (L/d=120 C=0.5%)
5
4.5
Re=68476
Re=102360
Re=211370
Re=326440
Re=391870
U*=0.034m/s
U*=0.05m/s
U*=0.093m/s
U*=0.137m/s
U*=0.165m/s
4
Velocity (m/s)
3.5
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
radius (mm)
Figure 3. Velocity profiles of flow of nylon fibre suspension at different Reynolds number
Despite this difference of velocity values close to the wall, the flow rate calculation from these
profiles gives deviations with the flowmeter measurements between 2 and 12% (see Table below)
Water
Re
Q (flow meter) (m3/h)
Q (UVP) (m3/h)
Deviation (%)
38830
11,58
10,91
5,8
75489
22,51
22,00
2,3
104240
31,08
28,73
7,6
197430
58,86
55,91
5,0
298270
88,92
99,83
-12,3
357620
105,80
104,40
1,3
Fibre
Re
68476 102360 211370 326440 391870
3
Q (flowmeter) (m /h)
18,51 27,67
57,14
88,25
105,80
3
Q (UVP) (m /h)
19,40 29,23
59,00
84,28
109,37
Deviation (%)
-4,8
-5,6
-3,3
4,5
-3,4
Table 2. Deviations of flow rate calculation with the flowmeter measurements
2) Using the UVP with two coupled probes
One objective was to evaluate the flocculation rate and scale of flocs in a pipe paper pulp flow. The
final aim is to see if there is a correlation between the flocculation rates of the cellulose fibres and
drag reduction observed in the flow of paper pulp at certain flow rates (drag reduction regime).
To validate measurement of flocculation obtained by two coupled ultrasound probes, we used a pipe
of =30mm diameter for fibres suspension in water at concentration in the range 0.4 to 0.6 % by
mass. Flow rates and pressure drops were not measured in these preliminary tests.
The instantaneous coupling signals of two ultrasonic sensors can discriminate the Doppler shift
(principle of ultrasonic velocity measurement) emanate from rigid structures (identical for both
probes transmission) or a fluid structure (different velocity for both probes transmission).
For example, in Figure 4 (velocity profile given by two coupled signal provided by probes) one can
easily see the discontinuity in the velocity profile (aberrant values) in the areas between flocs within
the pipe.
Velocity profile with 2 probes (mean velocity 0.4m/s)
1.4
velocity
floc1
floc2
floc3
1.2
Velocity (m/s)
1
0.8
0.6
0.4
0.2
0
0
5
10
15
Radial position (mm)
20
25
30
Figure 4. An example of the velocity profile given by two coupled signal provided by probes
The exploitation of successive profiles delivered by the two probes by using signal processing based
on image processing (see the algorithm in the Appendix) then allows a mapping of flocs in the flow
(see figure 5).
For the same signal processing applied to these three experiments substantially at different rates,
this figure shows in fact the existence of a network of fibers in the small flow rate (V=0.2m/s). This
network begins to break up in large flocs (V=0.6m/s) and small flocs thereafter (V=0.8m/s).
Nevertheless, these first results are qualitative because the flow rates used were not very stable.
V=0.2 m/s
V=0.6m/s
V=0.8m/s
Figure 5. Mapping of flocs in the pipe flow (=3cm, 0.4%<C0<0.6% and 0.2m/s<V<0.8m/s)
Conclusion
The objectives defined in the context of this exchange have only been partially achieved. We
wanted to correlate the flocculation rate to drag reduction phenomenon in of the pulp of paper flow.
Nevertheless, we carried out preliminary tests to qualify flocculation by ultrasonic technique UVP
using two coupled probes. The results obtained in this framework are new and promising to
determine the 3D floc size in the pulp flow. In this context one should probably use more than 2
ultrasonic probes arranged along the pipe and around a diameter thereof.
Bibliography
B. Ouriev, E. J. Windhab, Rheological study of concentrated suspensions in pressure-driven shear
flow using a novel in-line ultrasound Doppler method. Experiments in Fluids, 32:204-211, 2002.
D.M. Pfund, M.S. Greenwood, J.A. Bamberger and R.A. Pappas, Inline ultrasonic rheometry by
pulsed Doppler.Ultrasonics, 44:477-482, 2006.
J. Wiklund, M. Stading, Application of in-line ultrasound Doppler-based UVP-PD rheometry
method to concentrated model and industrial suspensions. Flow Measurement and Instrumentation,
19(3-4):171-179, 2008.
Dinh, S.M. and Armstrong, R.C. “A rheological equation of state for semiconcentrated fiber
suspensions.” J. Rheol., 28, (1984): 207-227.