scholarly journals Optimization of the critical overlap length of hudraulic distributors regarding cavitation inception

2021 ◽  
Vol 3 (10) ◽  
Author(s):  
Mahamadou Adama Maiga ◽  
Olivier Coutier-Delgosha ◽  
Daniel Buisine
Keyword(s):  
Strong Influence ◽  
Rotation Speed ◽  
Critical Length ◽  
Slide Valve ◽  
List Type ◽  
Hydraulic Systems ◽  
Significant Development ◽  
Cavitation Inception ◽  
Pressure Losses ◽  
Different Types

Abstract The present paper is focused on the optimization of the overlap length in various types of distributors in hydraulic systems. It has been shown that this length has a strong influence on cavitation in rotating distributors, so its optimization would be beneficial to reduce the detrimental effects of cavitation, such as noise, vibrations, and instabilities. The objective of the present study is to generalize the modelling of the overlap length to different types of distributors and to determine the critical length at cavitation inception. The results show that the pressure losses in rotating distributors and in other types of distributors are similar, including the slide-valves that are the vast majority of distributors in hydraulic systems. It is confirmed that the overlap length has a stronger influence on the cavitation development than the distributor rotation speed. A critical overlap length of 0.071 mm is obtained, below which no significant development of cavitation is obtained, at all rotation speeds. Article Highlights The pressure losses in a rotating distributor and in a slide-valve can be expressed similarly. The overlap length has a large influence on the cavitation development, much larger than the rotation speed. A critical overlap length of 0.071 mm was obtained, below which there is almost no cavitation, for any rotation speed.

Effect of semi-open impeller side clearance on centrifugal pump cavitation inception

2018 ◽  
Vol 1 (2) ◽  
pp. 24-39
Author(s):  
A. Farid ◽  
A. Abou El-Azm Aly ◽  
H. Abdallah
Keyword(s):  
Centrifugal Pump ◽  
Static Pressure ◽  
Rotation Speed ◽  
Centrifugal Pumps ◽  
Severe Condition ◽  
Cavitation Inception ◽  
Total Input ◽  
Input Pressure ◽  
Pump Head ◽  
Pump Pressure

Cavitation in pumps is the most severe condition that centrifugal pumps can work in and is leading to a loss in their performance.  Herein, the effect of semi-open centrifugal pump side clearance on the inception of pump cavitation has been investigated.  The input pump pressure has been changed from 80 to 16 kPa and the pump side clearance has been changed from 1 mm to 3 mm at a rotation speed of 1500 rpm. It has been shown that as the total input pressure decreased; the static pressure inside the impeller is reduced while the total pressure in streamwise direction has been reduced, also the pump head is constant with the reduction of the total input pressure until the cavitation is reached. Head is reduced due to cavitation inception; the head is reduced in the case of a closed impeller with a percent of 1.5% while it is reduced with a percent of 0.5% for pump side clearance of 1mm, both are at a pressure of 20 kPa.   Results also showed that the cavitation inception in the pump had been affected and delayed with the increase of the pump side clearance; the cavitation has been noticed to occur at approximate pressures of 20 kPa for side clearance of 1mm, 18 kPa for side clearances of 2mm and 16 kPa for 3mm.

Bejan’s Constructal Theory Analysis of Gas-Liquid Cooled Finned Modules

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Giulio Lorenzini ◽  
Simone Moretti
Keyword(s):  
Thermal Behavior ◽  
Heat Exchangers ◽  
High Performance ◽  
Numerical Study ◽  
Constructal Theory ◽  
Electronic Components ◽  
Theory Analysis ◽  
Pressure Losses ◽  
Different Types ◽  
Overall Performance

High performance heat exchangers represent nowadays the key of success to go on with the trend of miniaturizing electronic components as requested by the industry. This numerical study, based on Bejan’s Constructal theory, analyzes the thermal behavior of heat removing fin modules, comparing their performances when operating with different types of fluids. In particular, the simulations involve air and water (as representative of gases and liquids), to understand the actual benefits of employing a less heat conductive fluid involving smaller pressure losses or vice versa. The analysis parameters typical of a Constructal description (such as conductance or Overall Performance Coefficient) show that significantly improved performances may be achieved when using water, even if an unavoidable increase in pressure losses affects the liquid-refrigerated case. Considering the overall performance: if the parameter called Relevance tends to 0, air prevails; if it tends to 1, water prevails; if its value is about 0.5, water prevails in most of the case studies.

scholarly journals Finding the Perfect Match: Different Heavy-Duty Mobile Applications Call for Different Actuators

Proceedings ◽  
2020 ◽  
Vol 64 (1) ◽  
pp. 22
Author(s):  
David Fassbender ◽  
Tatina Minav
Keyword(s):  
Mobile Applications ◽  
State Of The Art ◽  
Perfect Match ◽  
The Novel ◽  
Hydraulic Systems ◽  
Heavy Duty ◽  
Different Types ◽  
Evaluation Algorithm ◽  
Novel Concept ◽  
Valve Control

For the longest time, valve-controlled, centralized hydraulic systems have been the state-of-the-art technology to actuate heavy-duty mobile machine (HDMM) implements. Due to the typically low energy efficiency of those systems, a high number of promising, more-efficient actuator concepts has been proposed by academia as well as industry over the last decades as potential replacements for valve control—e.g., independent metering, displacement control, different types of electro-hydraulic actuators (EHAs), electro-mechanic actuators, or hydraulic transformers. This paper takes a closer look on specific HDMM applications for these actuator concepts to figure out where which novel concept can be a better alternative to conventional actuator concepts, and where novel concepts might fail to improve. For this purpose, a novel evaluation algorithm for actuator–HDMM matches is developed based on problem aspects that can indicate an unsuitable actuator–HDMM match. To demonstrate the functionality of the match evaluation algorithm, four actuator concepts and four HDMM types are analyzed and rated in order to form 16 potential actuator–HDMM matches that can be evaluated by the novel algorithm. The four actuator concepts comprise a conventional valve-controlled concept and three different types of EHAs. The HDMM types are excavator, wheel loader, backhoe, and telehandler. Finally, the evaluation of the 16 matches results in 16 mismatch values, of which the lowest indicates the “perfect match”. Low mismatch values could be found in general for EHAs in combination with most HDMMs but also for a valve-controlled actuator concept in combination with a backhoe. Furthermore, an analysis of the concept limitations with suggestions for improvement is included.

Hydraulic Components Contribution to Total Power Losses and Acceleration of an Open Loop System With Long Hose

2004 ◽  
Author(s):  
Michael Westman ◽  
Ove Isaksson
Keyword(s):  
Open Loop ◽  
Total Power ◽  
Hydraulic Systems ◽  
Power Losses ◽  
Hydraulic Motor ◽  
Hydraulic Pump ◽  
Pressure Losses ◽  
Forest Logging ◽  
Pipe Line ◽  
Valve Block

This paper is concerned with forest logging machinery. A great deal of final felling in cut-to-length method done by harvester, which fells, delimbs and cuts the trees to pre-selected lengths. Two important criteria of a harvester head are that it has to be energy efficient and it has to be as fast as possible. To minimize losses in hydraulic systems the main demand is to reduce pressure losses in high power valves and outer components as much as possible. Each orifice in the flow path results in power losses. This work is an experimental study on power losses and acceleration of hydraulic motor in a system with long hoses. Main hydraulic components included are hydraulic pump, cartridge valve, pipe line and hydraulic motor. The results show that pre-activating the pump improves the system speed. To reduce losses, optimization of valve block, cartridge valve orifices are needed. Accumulators are favourable if combined with high stand-by pressure.

scholarly journals Cavitation Inception in Spool Valves

1981 ◽  
Vol 103 (4) ◽  
pp. 564-575 ◽  
Author(s):  
C. Samuel Martin ◽  
H. Medlarz ◽  
D. C. Wiggert ◽  
C. Brennen
Keyword(s):  
Reynolds Number ◽  
Hydraulic Systems ◽  
Cavitation Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Annular Jet ◽  
Directional Control ◽  
Valve Opening ◽  
Response Pressure ◽  
Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

The Choice of the Propeller

1966 ◽  
Vol 3 (02) ◽  
pp. 158-171
Author(s):  
J. D. van Manen
Keyword(s):  
Test Data ◽  
Model Test ◽  
Testing Technique ◽  
Full Size ◽  
Cavitation Inception ◽  
Different Types

In this paper the four main requirements for a propeller are dealt with. These requirements concern efficiency, cavitation, propeller-excited forces and stopping abilities. In a propeller diagram the characteristic efficiency curves for different conditions are explained. A comparison of the optimum efficiencies for various types of propulsors is given, and the applications on a 130,000-dwt tanker are considered. Cavitation-inception curves both for a specific propeller and for systematic propeller series are discussed. Predicted torque and thrust fluctuations, based on model-test data, and the results of measurements on the full-size ship are compared. Finally a quasi-steady testing technique, developed to analyze different types of stopping maneuvers, is described.

Bilingualism and cognition: A focus on mechanisms

2014 ◽  
Vol 18 (1) ◽  
pp. 47-50 ◽  
Author(s):  
VIRGINIA VALIAN
Keyword(s):  
Young Adults ◽  
Executive Function ◽  
Executive Functions ◽  
List Type ◽  
Type Number ◽  
Old People ◽  
Daily Lives ◽  
Different Types ◽  
Children And Young Adults ◽  
Underlying Mechanisms

The goal of my keynote article, “Bilingualism and Cognition” (Valian, 2014), was to resolve the inconsistencies in effects of bilingualism on executive functions, whether the individuals were children, young adults, or old people. To summarize (and sharpen) my argument: 1.Especially in children and young adults, benefits of bilingualism for executive functions are not reliable. In old people, there are benefits for executive functions but contradictory results on delay of cognitive impairment, depending on whether studies are retrospective or prospective.2.All experiences that have benefits for executive functions and aging – and there are many – yield inconsistent effects. Bilingualism is not alone.3.Three reasons for inconsistencies in bilingualism and other experiences are: a.Executive function and cognitive reserve are broad cover terms for a variety of mechanisms, most of which are ill-understood. Because we mean different things by ‘executive function’ from one experiment to the next, we can both think we don't have an effect when we do and think we have an effect when we don’t.b.Tasks are impure: apparently similar tasks measure different aspects of executive function and measure other aspects of cognition as well. Because we lack a good analysis of tasks, we too often do not know what we are measuring. I encourage readers to examine the demos in the supplementary materials of the keynote article to see for themselves what the tasks are like.c.Individuals engage in many different activities that may be on a par with bilingualism in their benefits.4.Different types of bilingual experience are unlikely to explain the variability of findings, given the inconsistencies in extant data on varieties of bilingualism.5.There is a benefit of bilingualism, but bilingualism competes with other sources of benefits. Especially for children and young adults, whose daily lives are full of cognitively enriching and challenging experiences, we should expect variability in effects of being bilingual.6.The way forward is to focus on underlying mechanisms.

The effect of the valence of sponsorship information on consumers’ attitudes toward the sponsor brand

2019 ◽  
Vol 20 (4) ◽  
pp. 603-616 ◽  
Author(s):  
Christopher Dick
Keyword(s):  
Boundary Condition ◽  
Experimental Research ◽  
Design Methodology ◽  
Strong Influence ◽  
Content Type ◽  
Different Types ◽  
Negative Condition ◽  
Practical Implications ◽  
Practical Recommendations ◽  
Better Than

Purpose To date, research on sponsorship considers the effects of only positive or only negative sponsorship information on consumers’ attitudes toward the sponsor brand. However, in practice, sometimes mixed information (positive and negative) is available that influences consumers’ sponsor evaluations. To mirror the information situation of the real world, the purpose of this paper is to investigate how the valence of sponsorship information (only positive vs mixed vs only negative) and the strength of sponsorship information (weak vs strong) influence the consumers’ attitudes toward the sponsor brand. Design/methodology/approach This research uses an experimental research design (n=210). Data were collected among students of a German university. Findings The results reveal that when the strength of information was weak, attitudes in the mixed information condition were not significantly worse than in the only positive condition and significantly better than in the only negative condition. In addition, when the strength of information was strong, attitudes in the mixed information condition were significantly worse than in the only positive condition and significantly better than in the only negative condition. Practical implications This study offers several practical recommendations regarding the sponsors’ evaluation of their investments and the decision to maintain or exit the sponsorship of a controversial object. Originality/value This study expands the research on the effects of available sponsorship information on consumers’ sponsor evaluation. The present research highlights the effects of different types of sponsorship information on consumers’ attitudes and considers the strength of information as a boundary condition of these effects.

scholarly journals Tip Vortex Cavitation on an Oscillating Hydrofoil

1997 ◽  
Vol 119 (4) ◽  
pp. 752-758 ◽  
Author(s):  
O. Boulon ◽  
J. P. Franc ◽  
J. M. Michel
Keyword(s):  
Steady State ◽  
Vortex Core ◽  
Oscillation Frequency ◽  
Strong Influence ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Time Required ◽  
Oscillation Frequencies ◽  
The University

This paper discusses tests conducted in the hydrodynamic tunnel of the University of Grenoble on a 3D oscillating hydrofoil. Visualization of unsteady tip vortex cavitation indicates a strong influence of the water nuclei content. The investigation was focused on the influence of the oscillation frequency on tip vortex cavitation inception. For very low nuclei content, cavitation inception is strongly delayed as compared to the steady-state results at very small oscillation frequencies. This delay is significantly reduced by nuclei seeding. The results can be explained by assuming that the time required for the inception of cavitation in the tip vortex corresponds to the time necessary for a cavitation nucleus to be captured by the vortex core.

Simulation of Flow and Heat Transfer in the MTPV Systems

2013 ◽  
Vol 448-453 ◽  
pp. 3291-3295
Author(s):  
Ge Ping Wu ◽  
Jun Wang ◽  
Ping Lu
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Friction Factor ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Transfer Characteristics ◽  
Pressure Losses ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Different Types

Flow and heat transfer characteristics in the microchannel cooling passages with three different types of the MTPV systems are numerically investigated. Reynolds ranged from 100 to 1000 and hydraulic diameter from 0.4mm to 0.8mm. The steady, laminar flow and heat transfer equations are solved in a finite-volume method. The local heat transfer characteristics, thermal resistance, Nusselt numbers, friction factor and pressure losses of the different types are analyzed. A comparison of the heat transfer coefficient, pressure losses and friction factor of the different microchannels are also presented. The heat transfer performance of the rob bundles microchannel is found to be much better than others. However, the rectangular passage has the lowest thermal resistance than the other types of microchannels.

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