Manual for the Design of Pipe Systems and Pumps - GEA ...

6.4 Pumping of
viscous media
6.4.1 Correction for
high viscosities
In the previous example (Chapter 6.1) water served as pumping medium.
In practice media other than water are conveyed. In this respect viscosity is a factor that
must be taken into account for the calculation and design of the pump.
Conveying liquids of higher viscosity (ν) at constant speed (n), reduce the flow rate (Q), flow
head (H) and the efficiency (η) of the pump, while power consumption Pz of the pump (see
Fig. 28) increases tt the same time. According to the method of approxima-tion, (6.4.2) the
suitable pump size can be determined, starting from the operating point for viscous liquids
via the operating point for water. The pump’s power
consumption depends on the efficiency of the complete
H
unit.
Annexed are tables used for the determination of
pressure drops in dependence of viscosity and pipe
diameter. In this connection it is worthwhile to mention
that the pressure drop in dependence of viscosity is
irrelevant for centrifugal pumps and can therefore be
neglected. Centrifugal pumps are suitable for liquids
up to a viscosity of 500 mm2/s. picture 5
If it is the question of pumping viscous media such as Fig. 28
quarg, butter or syrup, rotary piston pumps will be used due to their higher
efficiency in this respect.
The following page shows an example that explains the calculation and design of a pump
used for viscous media. Decisive in this connection are the correction factors for the flow
head (K H), flow rate (K Q) and the pump efficiency (K η).
The correction factors are found in the diagram on page 31, by proceeding in the
following steps:
1. Find out the kinematic viscosity of the medium in mm 2/s
2. Determine product of Q x √H (m 3/h √m)
3. Set up a vertical at the intersection of Q x √H with the corresponding viscosity
4. Reading the intersections with the three correction lines at the vertical
5. Enter these values into the equations and calculate the corrected value
On the basis of the obtained values, the pump can be desigend by means of the pump
characteristic for water, (see Chapter 6.2).
30
GEA Tuchenhagen
H z
P z
P
h
h z
Q