Rainer Haas, Andreas Tairych, Bernhard Manhartsgruber,
"Adiabatic and isothermal fluid bulk modulus - common theories and model verification"
, in M. Milani, L. Montorsi and F. Paltrinieri: Proceedings of the 7th FPNI PhD Symposium on Fluid Power, June 27-30, 2012, Reggio Emilia, Italy, Seite(n) 385-398, 2012, ISBN: 978-88-7559-069-7
Adiabatic and isothermal fluid bulk modulus - common theories and model verification
Sprache des Titels:
Proceedings of the 7th FPNI PhD Symposium on Fluid Power, June 27-30, 2012, Reggio Emilia, Italy
The aim of this paper is to give the reader well-founded information about the fluid bulk modulus (BM). The adiabatic respectively the isothermal BM is of practical interest because they define the physical bounds, the ?actual? value can reach.
This paper consists of a brief literature survey and measurements of the BM of a commonly used fluid (Shell Tellus S32). It provides detailed information about the test rig design, the measuring and the post processing procedure. The result of these measurements is used to validate the theoretical relation between the adiabatic and isothermal bound.
The first part of the paper contains some well known theoretical considerations as well as a short literature survey about this topic. Here the reader will find common definitions, references to other papers and a phenomenological comparison between the lower and upper BM-bound. This phenomenological part uses oil temperature measurements for different compression/decompression times, to show the influence of the heat expansion to the BM. It is followed a thermodynamic part in which the theoretical relation between the adiabatic and the isothermal BM is derived.
Following, the design and the capabilities of the test rig are discussed. E.g. ensuring repeatable initial conditions of the oil after refilling, a proper sealing strategy (compressibility of sealings and its influence to the measurement) and the actuation of the piston of the test rig. Moreover a critical view on the choice of sensors (e.g. temperature and pressure) and their geometrical placement is done to ensure reliable measuring results.
In the last part the post processed adiabatic and isothermal BM is discussed. Measured data is used for validation of the theoretical relation between them. It will be done in a way that the calculation of the upper bound is based on a combination of theory and the measurement of the lower bound. This result is compared to a separately measured upper bound of the BM.