Rotating disks separators, mounted on single and double hollow shafts, are investigated experimentally. The shaft and disks were enclosed in stainless steel housing. Many parameters were measured to study their influence on the performance of single and double shaft disk filters at various rotation speeds. These parameters are pressure inside the housing, permeate flux, and electrical power consumption. The average velocity coefficient

Shear-enhanced or dynamic filtration consisting of
rotating disks relies on the presence of a shear stress at the filter media
surface to reduce the accumulation of the particles. The reason for its good performance is that very high shear rates are
produced with a low inlet flow, thereby resulting in low pressure drop in the
module. In the classical cross flow filtration with membrane modules, the
shear stress is linked to the feed flow rate which leads to the pressure drop.
High shear stress is produced by increasing the tangential flow along the
membrane surface and continuous circulation of the feed flow. In rotating
filters, the shear stress and flow rate are unlinked because the shear stress
is a function of the rotating filter disk. Dynamic filters which create
relative motion between the filter media and the suspension producing high
shear rate are compared with conventional cross flow filtration [

With relatively large axial gap between the disk and a
stationary wall, the boundary layers are separated by a core of fluid moving at
an angular velocity of (

The main objective of this study is to estimate andvalidate the average velocity coefficient, both for single and double shaft disk separators and the dynamic filtrationperformance, respectively. Additionally, we want to assess the contribution of filter overlapping by estimating the average shear stress based on electrical powerconsumption. Lastly, we would like to compare the single and double shaft disk separators based on filtration experiments.

Two different
geometries have been used as shown in Figure

Single shaft disk separator (a) double shaft disk separator (b).

The filtration
experiments are carried out using asuspension of sphere glass (mean particle size
10

The clearance inside
the filter disk where the filtrate collects is small and divided in radial flow
channel (about 2 mm). Therefore, the filtrate rotates as a solid body at
the same rotation speed of the filter, that is,

Comparison of measured permeate flux rate for single and double shaft disk separator.

In order to
check the consistency of the filtration data with the averaged pressure
difference (

Comparison of measured and calculated permeate flux rate for single and double shaft disk separator.

The variation of
the measured filtrate flux rate with rotation speed is represented in Figure

It is important
to estimate the energy that is necessary to drive the disk especially in an industrial
sized system.Therefore, we have measured the electrical power consumed by the
single and double shaft disk separators under consideration. In our small scale
device, a large part of the electrical power supplied is consumed by friction
of the rotating shaft. Thus, to eliminate the shaft friction, we have
subtracted the electrical power necessary to drive the system without disks from
the power at the same speed in the filtration test (with filters). The power
difference corresponds to the friction forces (shear stress) exerted by the
fluid on the disks, which, in a large scale system, will be the most dominating
forces. This power difference is shown in Figure

Electrical power consumed for variable rotation speed by single and double shaft
disk separator (0.057 m^{2} filter media area, 5 disks).

The power difference consumed by single and
double shaft disk separators is converted into shear forces exerted on the
disks. Thus, we were able to estimate the average shear stress over the filter
surface for single and double shaft disk separators
according to (

Average shear stress at different rotation speed using single and double shaft disk
separator (0.057 m^{2} filter media area, 5 disks).

We have shown that
the average shear stress for the filter disk overlapping is almost twice as
large as compared to the single shaft disk separator. Thus, it is legitimate to
investigate its ability in avoiding cake formation under filtration process.
Therefore, filtration experiments were carried out using single and double
shaft disk separators at

Variation of filtrate flux rate with time for single and double shaft disk separator using
sphere glass at TMP = 7 kPa,

Filter cake shape after using double shafts (a) single shaft (b).

The performance
of single and double shaft disk separators has been investigated. Permeate flux rate is found
to decrease as the rotation speed increases for both configurations. The
average velocity coefficient

Pore diameter of the filter media (

Average velocity coefficient

Velocity coefficient

Concentrate pressure (Pa)

Filtrate pressure (Pa)

Electrical power (W)

Mechanical power (W)

Radius (m)

Inner radius (m)

Outer radius (m)

Membrane resistance (1/m)

Axial clearance between the disk and

wall (mm)

Axial gap between two rotating discs (mm)

Axial shear gap between two overlapped

discs (mm)

Shaft torque (

Transmembrane pressure (Pa)

Filtrate flow rate (

Shear stress (Pa)

Average shear stress (Pa)

Fluid dynamic viscosity (Pa

Output efficiency without discs

Disk angular velocity (rpm)

Fluid angular velocity (rpm)

Fluid density (kg/m^{3})

Fluid kinematics viscosity (m^{2} s^{−1})