175
Chapter 5
Performance Measurement
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_5
Abstract Experimental performance analysis of turbomachines requires pressure
measurement, temperature measurement and flow rate measurement at the flow
side and torque and rotational speed measurement at the shaft side. The present
chapter deals with the principles of the most fundamental measurement techniques
for these variables and describes three laboratory set-ups for performance measurement: a hydraulic turbine, a fan and a pump. Measurement results are discussed.
5.1 Pressure Measurement
5.1.1 The Metal Manometer
Figure 5.1 shows a sketch. A hollow curved tube with an elliptical section is connected with the fluid (liquid or gas). The tube bends outwards due to positive pressure difference with respect to the atmospheric pressure and inwards due to negative
pressure difference. The displacement of the end point of the tube is transferred to
a measuring needle. The linkage allows zero and scale adjustment. The measured
pressure is called gauge pressure, which means that it is relative to the atmospheric
pressure: above (+) or below (−). Absolute pressure is determined by adding the
atmospheric pressure read from a barometer. Metal manometers are not suitable for
values changing quickly in time.
5.1.2 The Pressure Transducer
Figure 5.2 shows a sketch. Two diaphragms bend by the pressure difference with
the atmosphere. In the example, the bending is detected by a strain gauge with variable electrical resistance, mounted in a Wheatstone bridge. The voltage output of
the bridge is a measure of the pressure. The electronic circuit of the transducer incorporates a compensator for the temperature-related resistance change of the strain
gauge. Similar pressure transducers exist with diaphragm movement detected by
Chapter 5
Performance Measurement
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_5
Abstract Experimental performance analysis of turbomachines requires pressure
measurement, temperature measurement and flow rate measurement at the flow
side and torque and rotational speed measurement at the shaft side. The present
chapter deals with the principles of the most fundamental measurement techniques
for these variables and describes three laboratory set-ups for performance measurement: a hydraulic turbine, a fan and a pump. Measurement results are discussed.
5.1 Pressure Measurement
5.1.1 The Metal Manometer
Figure 5.1 shows a sketch. A hollow curved tube with an elliptical section is connected with the fluid (liquid or gas). The tube bends outwards due to positive pressure difference with respect to the atmospheric pressure and inwards due to negative
pressure difference. The displacement of the end point of the tube is transferred to
a measuring needle. The linkage allows zero and scale adjustment. The measured
pressure is called gauge pressure, which means that it is relative to the atmospheric
pressure: above (+) or below (−). Absolute pressure is determined by adding the
atmospheric pressure read from a barometer. Metal manometers are not suitable for
values changing quickly in time.
5.1.2 The Pressure Transducer
Figure 5.2 shows a sketch. Two diaphragms bend by the pressure difference with
the atmosphere. In the example, the bending is detected by a strain gauge with variable electrical resistance, mounted in a Wheatstone bridge. The voltage output of
the bridge is a measure of the pressure. The electronic circuit of the transducer incorporates a compensator for the temperature-related resistance change of the strain
gauge. Similar pressure transducers exist with diaphragm movement detected by