Water Vapour Cavitation in Hydraulic Fluids

2018 ◽  
Author(s):  
Filipp Kratschun ◽  
Tobias Mielke ◽  
Katharina Schmitz
Keyword(s):  
Base Fluid ◽  
Cavitation Erosion ◽  
Simultaneous Occurrence ◽  
System Failure ◽  
Hydraulic Systems ◽  
Test Rig ◽  
Release Rates ◽  
Pressure Drops ◽  
Hydraulic Fluids ◽  
Dissolved Air

Cavitation in hydraulic systems leads to cavitation erosion which ultimately results in system failure [1, 2] and the reduction of the systems’ stiffness. There are three types of cavitation known: gas, vapour and pseudo cavitation [3]. In previous gas-cavitation studies enormous air release rates in hydraulic fluids have been discovered which could not be explained just by the diffusion of dissolved air through bubble’s boundary. A possible explanation is the simultaneous occurrence of vapour cavitation in conjunction with gas-cavitation. However, this requires drastic pressure drops below several Pa, which is hard to achieve in hydraulic systems. This article introduces a further hypothesis for the unexplainable air release rates as fourth type of cavitation. Technical fluids can dissolve other fluids, such as water, to a degree which evaporate at much higher pressures compared to the base fluid. Based on a standard HLP 46 hydraulic oil and water as dissolved fluid, the presented hypothesis is verified. Firstly, a phenomenological mathematical model is developed. Subsequently, a test rig is presented to prove the hypothesis.

Comparison of Different Methods for the Evaluation of Cavitation Damaged Surfaces

2005 ◽  
Author(s):  
B. Bachert ◽  
G. Ludwig ◽  
B. Stoffel ◽  
S. Baumgarten
Keyword(s):  
Mass Loss ◽  
White Light ◽  
Cavitation Erosion ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Special Device ◽  
Test Rig ◽  
Rotating Disc ◽  
White Light Interferometer ◽  
Initial Stage

The experimental data which will be presented in this paper are the results of the comparison between different methods for evaluating damaged surfaces by cavitation erosion. The different methods are partly working in the initial stage of cavitation erosion and partly at developed cavitation erosion, where mass loss occurs. The used test rig consists basically of a rotating disc with a diameter of 500 mm on which four holes are located. Each hole generates a cavitation zone while the disc is rotating. The test objects are material specimens made of copper. Copper was used as test material in respect to reasonable durations for the tests. The specimen can be implemented in the casing of the test rig directly across the rotating disc on the diameter where the holes are located. This rotating disc test rig generates a very aggressive type of cavitation, so that mass loss, of course depending on the tested material, will appear after relatively short durations. Also the initial stage of cavitation erosion can be observed. The used test rig is very interesting regarding the possibility to apply different measuring techniques to characterize the erosive aggressiveness of cavitation. These techniques are at first the so-called Pitcount-Method, which allows investigations of cavitation erosion in the initial stage. The second one is an acoustic method, which is based on a structure-borne noise sensor and a specially developed signal processing system. The third method is the measuring of mass loss of the material specimen after several time steps. With the help of a CCD-camera and special digital image processing software, images of different cavitation conditions were recorded. The information obtained from these images should serve as support for the evaluation of the other used methods. After the evaluation with the above mentioned methods, the specimens were evaluated with a special device which works with the help of a white light interferometer. With this evaluation method three-dimensional information can be obtained in respect to the actually eroded volume of the specimens. With this information the lost mass of the specimens could be calculated directly. Especially the comparison of the results obtained from the Pitcount-Method, which is a two-dimensional evaluation method, and the three-dimensional results of the white light interferometer is an important point of the work within this paper.

An Effect of Air Content on the Occurrence of Cavitation

1960 ◽  
Vol 82 (4) ◽  
pp. 941-945 ◽  
Author(s):  
J. W. Holl
Keyword(s):  
Pressure Coefficient ◽  
Cavitation Number ◽  
Experimental Results ◽  
Simultaneous Occurrence ◽  
Minimum Pressure ◽  
Air Content ◽  
The Difference ◽  
Dissolved Air

The simultaneous occurrence of vaporous and gaseous cavitation on hydrofoils is considered. The experimental results show that gaseous cavitation occurs at much higher ambient pressures than that for the vaporous cavitation resulting in desinent-cavitation numbers twice the minimum-pressure coefficient of the hydrofoil. The analysis indicates that the difference between the desinent-cavitation number for the gaseous cavitation and that for the vaporous cavitation is proportional to the dissolved air content and inversely proportional to the square of the velocity.

Design Parameters of Brush Seals and Their Impact on Seal Performance

2012 ◽  
Author(s):  
H. Schwarz ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Steam Turbine ◽  
Gas Turbine ◽  
Large Scale ◽  
Design Parameters ◽  
Test Rig ◽  
Pressure Drops ◽  
Seal Design ◽  
Brush Seal ◽  
Extreme Load ◽  
Brush Seals

Brush seals, which were originally designed for gas turbine applications, have been successfully applied to large-scale steam turbines within the past decade. From gas turbine applications, the fundamental behavior and designing levers are known. However, the application of brush seals to a steam turbine is still a challenge. This challenge is mainly due to the extreme load on the brush seal while operating under steam. Furthermore, it is difficult to test brush seals under realistic conditions, i.e. under live steam conditions with high pressure drops. Due to these insufficiencies, 2 test rigs were developed at the University of Technology Braunschweig, Germany. The first test rig is operated under pressurized air and allows testing specific brush seal characteristics concerning their general behavior. The knowledge gained from these tests can be validated in the second test rig, which is operated under steam at pressure drops of 45 bar and temperatures up to 450 °C. Using both the air test rig and the steam test rig helps keep the testing effort comparably small. Design variants can be pre-tested with air, and promising brush seal designs can consequently be tested in the steam seal test rig. The paper focuses on a clamped brush seal design which, amongst others, is used in steam turbine blade paths and shaft seals of current Siemens turbines. The consequences of the brush assembly on the brush appearance and brush performance are shown. The clamped brush seal design reveals several particularities compared to welded brushes. It could be shown that the clamped bristle pack tends to gape when clamping forces rise. Gapping results in an axially expanding bristle pack, where the bristle density per unit area and the leakage flow vary. Furthermore, the brush elements are usually assembled with an axial lay angle, i.e. the bristles are reclined against the backing plate. Hence, the axial lay angle is also part of the investigation.

Influence of Cathodic and Anodic Currents on Cavitation Erosion

CORROSION ◽  
1993 ◽  
Vol 49 (11) ◽  
pp. 910-920 ◽  
Author(s):  
J. G. Auret ◽  
O. F. R. A. Damm ◽  
G. J. Wright ◽  
F. P. A. Robinson
Keyword(s):  
Corrosion Rate ◽  
Cavitation Erosion ◽  
Loss Rate ◽  
Mechanical Damage ◽  
Bubble Collapse ◽  
Volume Loss ◽  
Test Rig ◽  
Anodic Current ◽  
Cathodic Current ◽  
Geometrical Effects

Abstract A vibratory-type cavitation test rig was constructed to study the effect of polarizing currents applied to a cavitating body. The generation of gas by electrolysis reduced mechanical damage suffered by a cavitating body because of bubble collapse cushioning. However, the net effect on overall damage depended on several factors, including the intensity of mechanical attack, corrosion rate, and surface geometrical effects. A cathodic current was shown to always decrease of the total volume loss rate, but the volume loss rate sometimes was increased and sometimes was reduced in the anodic current range.

Research on a novel flow rate inferential measurement method and its application in hydraulic elevators

2016 ◽  
Vol 231 (2) ◽  
pp. 372-386 ◽  
Author(s):  
Bing Xu ◽  
Pengpeng Dong ◽  
Junhui Zhang ◽  
Jinjin Yao
Keyword(s):  
Mathematical Modeling ◽  
Flow Rate ◽  
Measurement Method ◽  
Sensitivity Analyses ◽  
Hydraulic Systems ◽  
Rate Measurement ◽  
Flow Rate Measurement ◽  
Test Rig ◽  
Flow Meters ◽  
Inferential Measurement

Measuring and controlling the flow rate is a widely concerned problem in engineering fields. The direct flow rate measurement employing conventional flow meters and the indirect flow rate measurement using speed/position transducers or other particular techniques would result in inevitable pressure drop in hydraulic circuits, more energy consumption for pumping fluid, and higher cost of hydraulic systems. This paper presents a novel flow rate inferential measurement method and its application in hydraulic elevators. Mathematical modeling of the proposed method is deduced. The key component of the hydraulic elevator circuit, a two-stage proportional flow rate valve, is verified by experiments as one of the contributions of this paper. Based on the mathematical modeling and the valve validation test, the feasibility and validity of the proposed method are verified by the experiments performed on a test rig which is designed to imitate work situations of a hydraulic elevator. Moreover, sensitivity analyses of the proposed flow rate inferential measurement method are carried out to find the ways how to improve the accuracy of the proposed method. It is believed that this method can be applied in various engineering devices.

Cavitation in Hydraulic Machines: Measurement, Numerical Simulation and Damage Patterns

2020 ◽  
Author(s):  
Helmut Benigni
Keyword(s):  
Single Phase ◽  
Rapid Assessment ◽  
Vapor Bubbles ◽  
Test Rig ◽  
Liquid Media ◽  
Histogram Method ◽  
Pressure Drops ◽  
Physical Limit ◽  
Hydraulic Machines ◽  
Multi Phase

Abstract Cavitation is a phenomenon that occurs in liquid media when the pressure drops below the vapor pressure. Cavitation is accompanied by damage when the imploding vapor bubbles implode in the vicinity of components. Cavitation is known in all hydraulic machines, be it a pump or a turbine, and it can occur within all components that are flowed through and have a low-pressure side or area. In the last 100 years, a lot has been done to understand the damage caused by cavitation, and cavitation has been classified within the entire range of component-damaging mechanisms. Nevertheless, users are now interested in the behavior of different machine types and different specific speeds and need information for a particular installation situation, while hydraulic developers are interested in a methodology for the rapid assessment of CFD results. This paper presents examples of damage to all kinds of hydraulic machines as well as numerical simulations of cavitation. Cross-comparisons between single-phase numerical calculations are realized with the histogram method, and multi-phase calculations are carried out and then compared with test rig investigations. Often, it is not possible or economically feasible to completely avoid cavitation. With the help of dimensionless values and the assumption of complete cavitation, a generally valid physical limit curve can be specified for turbines.

Cavitation Erosion in the Portion of an Oil Passage Through Which Bubbles Pass

2017 ◽  
Author(s):  
Kento Kumagai ◽  
Toshiharu Kazama
Keyword(s):  
Hydraulic System ◽  
Cavitation Erosion ◽  
Dynamics Simulation ◽  
Hydraulic Systems ◽  
Computational Fluid Dynamics Simulation ◽  
Construction Machinery ◽  
Cavitation Bubbles ◽  
Experimental Apparatus ◽  
Research Findings ◽  
Pass Through

Cavitation erosion is a serious problem in the hydraulic system of construction machinery. In particular, the erosion which occurs even when cavitation bubbles only pass through oil passages, occurs at a connecting portion between the hydraulic components and piping, and the erosion causes oil leakage, which is a serious problem for hydraulic systems. However, it is difficult to predict the eroded area and to prevent the erosion because of a lack of research findings. The present study investigated erosion in the portion through which cavitation bubbles passes using a basic experimental apparatus that simulates an oil passage of hydraulic components, and by conducting a computational fluid dynamics simulation. The following results were obtained. Erosion occurs near the outlet of the oil passage, cavitation bubbles frequently disappear rapidly near the area of erosion, and the cause of bubble disappearance is the pressure distribution and amplification of the pressure wave of cavitation jets at the outlet of the oil passage. These results help explain the erosion generation mechanism and the characteristics of erosion in oil passages of hydraulic components, and can be used to design methods of reducing erosion.

Assessment of resistance of non-metallic coatings to silt abrasion and cavitation erosion in a rotating disk test rig

Wear ◽  
1996 ◽  
Vol 194 (1-2) ◽  
pp. 149-155 ◽  
Author(s):  
J. Zhang ◽  
M.O.W. Richardson ◽  
G.D. Wilcox ◽  
J. Min ◽  
X. Wang
Keyword(s):  
Cavitation Erosion ◽  
Rotating Disk ◽  
Metallic Coatings ◽  
Test Rig ◽  
Disk Test

Experimental Investigations Concerning Erosive Aggressiveness of Cavitation at Different Test Configurations

Volume 3 ◽  
2004 ◽  
Author(s):  
B. Bachert ◽  
M. Dular ◽  
S. Baumgarten ◽  
G. Ludwig ◽  
B. Stoffel
Keyword(s):  
Mass Loss ◽  
Cavitation Erosion ◽  
Evaluation Method ◽  
Experimental Investigations ◽  
Cavitating Flows ◽  
Test Rig ◽  
The Third ◽  
Long Duration ◽  
Initial Stage ◽  
Test Objects

The experimental results, which will be presented in this paper, demonstrate the significant influence of the flow velocity, respectively the rotational speed, on the erosive aggressiveness of cavitating flows. On two of the three investigated test objects, cavitation erosion can only be observed in the initial stage by the so-called pit-count evaluation method. Developed erosion with mass loss is impossible to measure because of the very long duration until mass loss appears. The third test rig generates a very aggressive type of cavitation, so that mass loss, depending on the tested material, will appear after relatively short durations. In addition, the initial stage of cavitation erosion can be observed. Three different techniques were applied to investigate cavitation erosion in the initial and developed stage. Thereby, the capability of methods to quantify erosive effects in dependence of influencing operating parameters has been proven.

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