ISO 21630:2007

INTERNATIONAL ISO
STANDARD 21630
First edition
2007-08-15
Pumps — Testing — Submersible mixers
for wastewater and similar applications
Pompes — Essais — Mélangeurs immergés pour eaux usées et
applications similaires
Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Terms and definitions. 1
3 Symbols and abbreviated terms . 3
4 Guarantees. 4
4.1 Subjects of guarantees . 4
4.2 Conditions of guarantees . 5
5 Execution of tests. 5
5.1 Subjects of tests . 5
5.2 Organization of tests . 6
5.3 Test arrangements. 8
5.4 Test conditions . 8
6 Analysis of test results. 11
6.1 Translation of the test results to the guarantee conditions. 11
6.2 Measurement uncertainties. 12
6.3 Values of tolerance factors. 13
6.4 Verification of guarantees. 14
7 Measurement of thrust . 15
7.1 Flow conditions of mixer thrust measurement. 15
7.2 Mixer thrust measurement method. 18
7.3 Uncertainty of measurement . 18
8 Measurement of mixer electric power uptake. 19
Annex A (informative) Checklist . 20
Bibliography . 21

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 21630 was prepared by Technical Committee ISO/TC 115, Pumps, Subcommittee SC 2, Methods of
measurement and testing.
iv © ISO 2007 – All rights reserved

Introduction
This International Standard prescribes acceptance test methods for submersible mixers for wastewater and
other applications. It is intended for performance measurements relevant to submersible mixers bearing in
mind the similarities to, and crucial differences from, submersible pumps. Hence head (pressure) and flow rate
measurements are not included. The basic output performance parameter is the thrust. As continuous
operation is commonplace, electric power consumption is important for the Life Cycle Cost, and is put forward
as an important parameter. It is acknowledged that the present International Standard draws heavily on
ISO 9906:1999 in the generalities.
The major objectives of this International Standard are to
⎯ increase uniformity/compatibility in equipment performance characterization, enabling a comparison of
mixers,
⎯ simplify communication between customer and supplier and protect customers,
⎯ reduce the need for documentation,
⎯ increase quality and efficiency in both machinery and process.

INTERNATIONAL STANDARD ISO 21630:2007(E)

Pumps — Testing — Submersible mixers for wastewater and
similar applications
1 Scope
This International Standard prescribes acceptance test methods for submersible mixers (hereafter “SM” or
“mixer”) used for mixing in wastewater and other applications where at least one system component is a liquid.
“Submersible mixer” is taken to mean a fully submersible aggregate consisting of a drive unit and an axial flow
type impeller, and optional parts, such as shrouds, supporting the basic functions.
“Liquid” is taken to mean a body without capacity to accommodate shear stresses when at rest. This includes
suspensions and dispersions (liquid/solid, gas/liquid and gas/liquid/solid), and non-Newtonian liquids, provided
that a possible small yield stress does not prevent the liquid from flowing when agitated.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
thrust-to-power ratio
ratio of mixer thrust force to mixer power consumption
R = F / P
FP 1
NOTE 1 The ratio of minimum required mixing system power dissipation to mixer power consumption is an (end-user
oriented) system efficiency. To understand the importance of the thrust-to-power ratio, consider the case of an SM
generating a longitudinal flow velocity u in a recirculation channel such as a wastewater oxidation ditch. This is in fact a
common application of the SM, and the following argument is in principle possible to generalize to other applications.
The momentum loss of the flow over one circulation equals the rate of momentum provided by the SM at quasi-steady
state. This is given by the mixer thrust F. The power dissipated as a result of this momentum loss is P = F u, and this is the
minimum required mixing system power to maintain the velocity u. Hence, the system efficiency is P / P = F u / P .
1 1
It is possible to isolate the mixer properties from the system requirement in this expression, and this leads to the thrust-to-
power ratio, R , as the most relevant efficiency-related parameter of the SM. It should be noted that it is dimensional, and
FP
hence it depends on the impeller diameter and speed, not only on the impeller geometry. Other considerations than
energetic efficiency of generation of longitudinal flow provide for the multitude of impeller diameters and speeds available
in practice.
NOTE 2 An impeller efficiency, defined as the ratio of power of axial motion of the impeller discharge to the electric
power uptake of the mixer, can be defined. The definition draws on the assumption that the approaching velocity, u, is
small enough to have negligible influence on the mixer impeller characteristics. The hydraulic discharge power P = p Q
h
can be expressed in thrust using the relations
p = F / A and F = 2 ρ Q / A
which are approximately valid for the mixer test established herein. The conventional area of the vena contracta A / 2 is
used, as this discharge section best fulfils the flat velocity profile requirement. With A = π D / 4, one obtains
1/2 3/2 1/2
P = (F / A) (A F / 2 ρ) = F / [D (π ρ / 2) ]
h
Hence the impeller efficiency can be written
3/2 1/2
η = F / [(π ρ / 2) D P ]
It can be noted that, often correct to within 1 %, the efficiency is conventionally given as (assuming SI units [F] = Newton,
[P ] = Watt, [D] = meter, and clean cold water as defined in 5.4.5.2)
3/2
η = F / (40 D P )
Although the derivation given here is not based on completely correct assumptions, the approximate expression for the
efficiency may be derived in more rigorous ways.
The value of the impeller efficiency alone is not deemed to be of primary interest because of the dependency of mixer-
system efficiency on the impeller diameter and speed.
2.2
advance ratio
ratio of propeller traversing speed or mean liquid ambient speed to (essentially) tip speed
J = u / nD
2.3
impeller Reynolds number
ratio between inertial and viscous forces prevailing at impeller
1/2
Re = (F / ρ ) / ν
NOTE F is the thrust for the same mixer running at the same speed in clean cold water as defined in 5.4.5.2. Also
note that this is not the same as the blade Reynolds number, nor is it identical, but akin to the impeller Reynolds number
used for dry-installed agitators in the process industries.

2 © ISO 2007 – All rights reserved

3 Symbols and abbreviated terms
Table 1 summarizes the symbols in alphabetical order and SI units used.
Table 1 — Alphabetical list of letters used as symbols
Symbol Quantity Unit
A Area swept by impeller m
D Diameter of impeller m
e Uncertainty, relative (pure number), %
−1
f Frequency s , Hz
F Thrust N
J Propeller advance ratio (pure number)
L Length of lever m
−1
n Speed of rotation s , Hz
p Pressure Pa
P Power W
Q Flow rate m /s
R Thrust-to-power ratio N/W
FP
Re Impeller Reynolds number (pure number)
t Tolerance (pure number), %
T Time s
u Mean velocity in the axial or m/s
longitudinal direction
U Voltage V
x Generic measured entity
Time average of x
η Efficiency (pure number), %
ν Kinematic viscosity m /s
ρ Density kg/m
σ Standard deviation
Table 2 summarizes the subscripts used for the symbols.
Table 2 — Alphabetical list of letters and figures other than above used as subscript
Subscript Meaning
1 electric (power)
G guaranteed
L/L length ratio
h hydraulic (power)
LC load cell related
m measured
M mixer related
FP see R
FP
sp specified
Tr translated
TS time series
4 Guarantees
4.1 Subjects of guarantees
4.1.1 General
Terms used herein such as “guarantee” or “acceptance” should be understood in a technical but not in a legal
sense. The term “guarantee” therefore specifies values for checking purposes determined in the contract, but
does not say anything about the rights or duties arising if these values are not reached or fulfilled. The term
“acceptance” does not have any legal meaning here, either. Therefore, an acceptance test carried out
successfully alone does not represent an “acceptance” in the legal sense.
A procedure for verifying the guarantees is given in 6.4.
4.1.2 Thrust guarantee
One guarantee point shall be defined by a guarantee thrust
...