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Research Papers: Multiphase Flows

A Novel Approach for the Prediction of Dynamic Features of Air Release and Absorption in Hydraulic Oils

[+] Author and Article Information
Junjie Zhou

National Key Laboratory of Vehicular Transmission,
Beijing Institute of Technology,
Beijing 10081, China
e-mail: junjiezhou1987@gmail.com

Andrea Vacca

Maha Fluid Power Research Center,
Purdue University,
West Lafayette, IN 47905

Bernhard Manhartsgruber

Institute of Machine Design and Hydraulic Drives,
Johannes Kepler University,
Altenbergerstrasse 69, 4040 Linz, Austria

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the Journal of Fluids Engineering. Manuscript received November 19, 2012; final manuscript received June 17, 2013; published online July 11, 2013. Assoc. Editor: D. Keith Walters.

J. Fluids Eng 135(9), 091305 (Jul 11, 2013) (8 pages) Paper No: FE-12-1583; doi: 10.1115/1.4024864 History: Received November 19, 2012; Revised June 17, 2013

An accurate evaluation of fluid density and bulk modulus is essential for predicting the operation of hydraulic systems and components. Among the models reported in literature to describe fluid properties, of particular success in the fluid power field are the continuous methods that assume the gas and liquid phases to be the same fluid. However, these models are typically based on steady-state equilibrium relations and, consequently, they fail in correctly predicting the dynamic features of both air release and air absorption processes. These phenomena are particularly important for machines based on open-system hydraulic circuits, in which a significant part of the system can operate with a fluid below the saturation pressure. This paper addresses this topic by proposing a novel approach suitable to describe the dynamic features of both vaporization and air release processes. The approach is based on simplified transport equations to evaluate the phase change rate and the air release/dissolve rate. These transport equation are obtained from the well-known theoretical “full cavitation model” previously developed for computational fluid dynamics (CFD). Specific tests were performed to validate particularly as concerns the air release/absorption features using a standard ISO32 mineral oil. Comparisons between model predictions and measurement data are presented for compression/decompression cycles as concerns transient fluid density and bulk modulus, and a good agreement between the two trends is found, showing the potentials of the new approach to describe typical cavitation phenomena in hydraulic systems.

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References

Figures

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Fig. 1

(a) Description of Henry's law; (b) limitation of Henry's law

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Fig. 2

Hysteresis of fluid density with a measured cycle time 10 s [22]

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Fig. 3

Simplified section sketch of the test rig

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Fig. 4

Test results of the compression/decompression cycle: (a) chamber pressure; (b) chamber pressure—piston stroke

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Fig. 5

Evaluation of the free air content using the measurement data

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Fig. 6

Dynamic evolution of free air mass and volume content during a test cycle

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Fig. 7

Comparison of fluid density between: (a) measurement, a static model, and the proposed dynamic model; (b) dynamic model and static model using constant α values

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Fig. 8

Comparison of fluid bulk modulus between: (a) measurement, a static model, and the proposed dynamic model; (b) dynamic model and static model using constant α values

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Fig. 9

Predicted fluid density: (a) for a different initial air content; (b) for a different characteristic time

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