Design of Hydraulic Machinery Working in Sand Laden Water
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4.4.2 Hydraulic Design of Solid-Liquid Flow Pumps
The new hydraulic design method of solid-liquid two-phase flow pumps has
been put forward in Ref. [4.20, 4.21] on the basis of experiences of test and
design of a series of the new type of liquid-solid flow pumps. Their theoretical
considerations for the design are as follows:
(1) Velocities of solid-liquid two-phase mediums are different all along
because of the difference of the inertial forces.
(2) The fluid machine can only transfer the energy of the liquid phase and
by no means can change the energy of the solid phase. The energy of solid
phase is indirectly converted by the liquid phase in fact. Solid particles are in
a by-force motion of liquid flow.
(3) The water flow is a function with respects of all kinds of physical
characters and boundary conditions of flow domain. The pattern of the
function depends upon mutual effects of the characters and the function
solution is based on the boundary and initial conditions.
The new hydraulic design method of solid-liquid flow pump is based on
the velocity distributions of the two phase flow structure in the pump. It is
assumed that there exists a certain relation between the two-phase velocity
fields. If the variation rate of
the
two-phase velocities gets a certain value and
then most of solid particles may move along the streamlines of
the
liquid flow
in the pump, the impact erosion of particles to pump walls may be reduced
greatly and the friction erosion on the walls may increase, resulting in the
extension of the service life of
the
solid-liquid pump. Therefore, the blade and
flow passage designed according to the two-phase velocity distributions, not
only can transfer the energy more effectively, but also can avoid the damage
caused by the two-phase flow cavitation. And so far, the slurry pumps
designed by using the new method has a higher efficiency and longer service
time,
as well as there is not any the erosion patterns, such as 'fish-scale pits'
and 'honeycomb', but these pumps walls become brighter and smoother, as
the results of frictional erosion, than those in the erosion pattern of other
common slurry pumps.
It is possible that in the new method we do not need to change the design
procedure and the design calculation method for conventional pumps, but
need to add the consideration of
the
solid phase as movable and noncontinual
boundary conditions in the liquid flow. The distortion of the velocity field of
the liquid flow at the liquid-solid flow is the results of these boundary