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Fundamental Issues and Canonical Flows

Measurement of Effective Bulk Modulus for Hydraulic Oil at Low Pressure

[+] Author and Article Information
Sunghun Kim1

 Institute for Fluid Power Drives and Controls, RWTH Aachen University, Aachen, Germanysung-hun.kim@ifas.rwth-aachen.de

Hubertus Murrenhoff

 Institute for Fluid Power Drives and Controls, RWTH Aachen University, Aachen, Germanypost@ifas.rwth-aachen.de

1

Corresponding author. Present address: Steinbachstr. 53, 52074 Aachen, Germany.

J. Fluids Eng. 134(2), 021201 (Mar 06, 2012) (10 pages) doi:10.1115/1.4005672 History: Received May 31, 2011; Revised December 15, 2011; Published March 06, 2012; Online March 06, 2012

Oil properties are very important input parameters for the simulation of hydraulic components. Precise values of effective bulk modulus at low pressures are especially required to improve the simulation accuracy of the pumps suction side or of cavitation in pumps or valves. So far, theoretical equations to compute the effective bulk modulus of hydraulic oil have not been experimentally verified, and only poor measured data are available to calculate the effective bulk modulus at low pressure. Therefore in this paper, the theoretical equation was verified for effective bulk moduli based on measurements of pressure change as a function of volume change at low pressures, varying temperature, entrained air content, and type of state change. Furthermore, the comparison of effective bulk moduli calculated with three different methods (mass-change, volume-change, and sound-speed method) shows that the effective bulk modulus can be calculated well from the measurement results of all three methods. The calculated effective bulk moduli values show little variation among the methods. Additionally, the release pressure of dissolved air in oil and the change of the polytropic gas constant depending on the speed of volume change rate were identified in this study.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Theoretical E-Moduli depending on the entrained air content

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Figure 2

Schematic diagram of mass-change method

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Figure 3

Schematic diagram of volume-change method

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Figure 4

Schematic diagram of test bench

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Figure 5

Test bench for measurement of E-Modulus

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Figure 6

Test chamber block for measurement of E-Modulus

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Figure 7

Exemplary measurement by mass-change method

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Figure 8

Exemplary measurement by volume-change method

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Figure 9

Exemplary measurement below 1 bar by volume-change method

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Figure 10

Exemplary measurement by sound-speed method

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Figure 11

Exemplary diagram for calculation of entrained air content in oil by measurement

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Figure 12

Calculated E-Moduli above 1 bar depending on temperature with three methods

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Figure 13

Change of E0 depending on temperature

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Figure 14

Measurements and calculated E-Moduli below 1 bar depending on temperature

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Figure 15

Measurements and calculated E-Moduli above 1 bar depending on entrained air content

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Figure 16

Measurements and calculated E-Moduli below 1 bar depending on entrained air content

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Figure 17

Pressure change depending on speed of volume change with entrained air content of 0.45%

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Figure 18

Measurements and calculated E-Modulus depending on state change with entrained air content of 0.45%

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Figure 19

Effect of state change

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Figure 20

Estimation of polytropic gas constant depending on the speed of volume ratio change

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