Rotary kinetic fluid motors or pumps – With control means responsive to non-cyclic condition... – Plural diverse condition responsive
Reexamination Certificate
1998-06-22
2001-06-05
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
With control means responsive to non-cyclic condition...
Plural diverse condition responsive
C417S030000, C417S047000, C417S026000
Reexamination Certificate
active
06241463
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for determining the operating level of a fan and a fan operated by that method.
BACKGROUND OF THE INVENTION
For many applications it is important to know the operating level, i.e. the flow rate V and the total pressure difference &Dgr;p
t
of a fan in its installed state. In refineries, in the chemical industry or in process technology the knowledge of the flow rate V is a requisite for establishing the material balance. In nuclear power plants fans and the like are integrated in the safety chain for keeping an underpressure. In the construction of installations and equipment, for instance in chip drying or the drying of plaster board, the knowledge of the operating levels of the fans improves the control of the installation or the equipment. When fans are used in building technology, the operating levels of the fans are needed for energy management. The conditions in the installed state do not allow for measuring methods which can be compared to measurements taken on the test stand.
A generic method and a generic device for determining the flow rate of a radial fan are known from EP-B 0 419 798. The radial fan has at least one inlet nozzle defining a cross flow opening and arranged upstream of the radial fan wheel. At least partially at one measuring point in the area of the inner periphery of the inlet nozzle and namely in the area preceding its cross flow opening a measuring device is arranged which is designed as a static pressure measuring device and connected via an opening in the nozzle wall close to the measuring point.
The static pressure prevailing in front of the cross flow opening of the inlet nozzle is measured with the static pressure measuring device at the measuring point and compared to the static pressure prevailing in the fan surroundings. The pressure difference &Dgr;p is proportional to the square of the flow rate V. From the measured difference of the pressures &Dgr;p the flow rate V is calculated, and with the aid of the flow rate V the operating efficiency of an already installed fan can be established. The proportionality factor depends on the mounting situation, so that each time it is necessary to include a calibration curve. As a rule in installations there are rarely sufficient working sections for calibrations, since the tendency is to build these installations as compact as possible. A drawback of this method is that fan influx disturbances are not noted. This can lead to wrong interpretations of the measurement results.
OBJECT OF THE INVENTION
It is the object of the invention to provide a method and a corresponding fan which make it possible to determine the operating level in the installed state, i.e. without an external measuring section and calibration, as well as an estimate about the quality of this determination, and which insure a high degree of safety against failure and thereby a high operational safety.
SUMMARY OF THE INVENTION
According to the invention an effective pressure difference &Dgr;p
M
w
between two planes of the inlet nozzle or between a plane in the inlet nozzle and a point of the surroundings is measured, as well as a total pressure difference &Dgr;p
M
t
between the suction side and the pressure side of the fan, and the shaft power P
M
w
. The shaft power P
M
w
is a good measure for the power exerted by the impeller for the displacement of the gas. Instead of the shaft power P
M
w
it is also possible to measure the motor power P
M
M
of the fan motor and to translate that measurement into the shaft power P
M
w
. The flow rate V is determined from the pressure difference &Dgr;p
M
w
according to
V=&agr;A{square root over (((2+L /&rgr;)&Dgr;
p
M
w
+L ))} (1)
whereby &agr; is a nozzle coefficient composed by the cross flow coefficient &agr;′ and the expansion coefficient &egr;, A the reference cross section of the inlet nozzle and &rgr; the density of the propelled gas when entering the fan. Subsequently from an available operational characteristic curve &Dgr;p(V) the target value of the total pressure difference &Dgr;p
s
t
is determined and compared with the measured total pressure difference &Dgr;p
M
t
. Optionally the target value of the shaft power P
s
w
pertaining to the flow rate V is determined from an available operational characteristic curve P
w
(V) and compared with the measured shaft power P
M
w
. Based on the coincidence or the deviations of the target values &Dgr;p
s
t
and P
s
w
, the measured values &Dgr;p
M
t
and P
M
w
the operating level and its quality are determined. If one or both values coincide closely with their measured values, then the operating level determined from the flow rate V and the total pressure &Dgr;p
M
t
is established with high precision. A corresponding class of accuracy is assigned.
An advantage of the method according to the invention is that the operating level of the fan in the installed state can be determined along with an indication of the class of accuracy. Unfavorable afflux conditions are recognized when the operating level is determined and generally lead to the finding of less accurate values. Also with this method of determination of the operating level it is possible to detect unacceptable operating levels. It is also possible to detect hidden failures or total failures of the measured-value receivers, for instance through the addition of measuring points. False alarms are avoided and can be intercepted through qualified warnings.
The target values &Dgr;p
s
t
and P
s
w
can be established with the help of transmitted configuration values, such as nominal diameter D of the fan or measurements of the inlet nozzle and measured physical parameters, such as the outer pressure Pa, the temperature T, the rotary motor speed n or the rotary impeller speed n* and from the model characteristics. Model characteristics are characteristics which have been established during the testing of a fan model and have been standardized, i.e. they are standardized type characteristics. Model characteristics for the pressure coefficient &psgr;(&phgr;), the efficiency &eegr;(&phgr;) and optionally the power coefficient &lgr;(&phgr;) depending on the cross flow coefficient &phgr;, are recorded. Finding the target values &Dgr;p
s
t
and P
s
w
from the model characteristics &psgr;(&phgr;) and &eegr;(&phgr;) for the current installed state makes possible the use of a fan with an integrated, correspondingly programmed microcomputer and a system interface.
Additionally, with the method of the invention for the determination of the operating level, a physical parameter, for instance the density &rgr; of the propelled gas can be determined, by measuring the shaft power P
M
w
in addition to an effective pressure difference &Dgr;p
M
w
between two planes in the inlet nozzle or between a plane of the inlet nozzle and a point in the surroundings, and the total pressure difference &Dgr;p
M
t
. Thereby after finding the flow rate V and the corresponding value of the model characteristic &psgr;(&phgr;), the physical parameter to be determined is found with the help of the value of the model characteristic &psgr;(&phgr;) and optionally of configuration and physical parameters, as well as of the measured total pressure difference &Dgr;p
M
t
. If, as in the case of the density &rgr;, the physical parameter to be found is necessary for determining the flow rate V, the determination of the flow rate V and of the physical parameter is performed in iteration steps. The comparison of the target value for the shaft power P
s
w
derived from the established flow rate V with its measured value P
M
w
makes possible the assignment of a class of accuracy.
In the determination of the flow rate V from the measured pressure difference &Dgr;p
M
w
, it is possible to take into account the dependence of the nozzle coefficient &agr; corresponding to this pressure difference &Dgr;p
M
w
on the Reynold's number Re in iteration steps. For this purpose at least one model characteristic curve &agr;(Re) measured on a model inlet nozzle int
Bahner Friedrich
Eichhorn Norbert
Moller Wilfried
Babcock-Bsh GmbH
Dubno Herbert
Ryznic John E.
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