scholarly journals STUDI EKSPERIMENTAL PERFORMANCE KAVITASI WATERJET PROPULSI

2021 ◽  
Vol 4 ◽  
pp. 112-120
Author(s):  
Wulfilla M. Rumaherang ◽  
J. Louhenapessy ◽  
Mesak F. Noya ◽  
Cendy S. Tupamahu
Keyword(s):  
Critical Point ◽  
Performance Studies ◽  
Energy Performance ◽  
Critical Value ◽  
Performance Curve ◽  
Test Rig ◽  
Thrust Coefficient ◽  
Working Zone ◽  
Cavitation Performance ◽  
Hydraulic Machines

Cavitation is a complex phenomenon of dynamic processes in hydraulic machines that can cause a decrease in energy performance, vibration and damage the blade surfaces. Analysis of cavitation symptoms in hydraulic machines is carried out through cavitation performance studies, namely the relations between energy parameters. Each hydraulic machine has a critical value on a different cavitation performance curve. Therefore, a study of the effect of cavitation changes is needed to determine the working zone of hydraulic machines without cavitation. In this study, cavitation performance analysis was carried out on a waterjet propulsor model with 5 impeller blades and 7 stator blades using experimental methods. The cavitation coefficient was varied at σ = 2.25 to 0.25 by setting and controlling the inlet pressure on the cavitation test rig. The critical point value will be observed at the point where the thrust coefficient decreased to 3.28%.  The results showed that cavitation begins at σ = 1, the critical point is obtained at σ = 0.75. From these studies, we find that waterjet must be operated at conditions where is σ > 0.75.

scholarly journals Role of thermal field in entanglement harvesting between two accelerated Unruh-DeWitt detectors

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Dipankar Barman ◽  
Subhajit Barman ◽  
Bibhas Ranjan Majhi
Keyword(s):  
Mutual Information ◽  
Critical Point ◽  
Thermal Field ◽  
Narrow Range ◽  
Critical Value ◽  
Critical Values ◽  
Parallel Motion ◽  
Field Temperature ◽  
The Right

Abstract We investigate the effects of field temperature T(f) on the entanglement harvesting between two uniformly accelerated detectors. For their parallel motion, the thermal nature of fields does not produce any entanglement, and therefore, the outcome is the same as the non-thermal situation. On the contrary, T(f) affects entanglement harvesting when the detectors are in anti-parallel motion, i.e., when detectors A and B are in the right and left Rindler wedges, respectively. While for T(f) = 0 entanglement harvesting is possible for all values of A’s acceleration aA, in the presence of temperature, it is possible only within a narrow range of aA. In (1 + 1) dimensions, the range starts from specific values and extends to infinity, and as we increase T(f), the minimum required value of aA for entanglement harvesting increases. Moreover, above a critical value aA = ac harvesting increases as we increase T(f), which is just opposite to the accelerations below it. There are several critical values in (1 + 3) dimensions when they are in different accelerations. Contrary to the single range in (1 + 1) dimensions, here harvesting is possible within several discrete ranges of aA. Interestingly, for equal accelerations, one has a single critical point, with nature quite similar to (1 + 1) dimensional results. We also discuss the dependence of mutual information among these detectors on aA and T(f).

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.

scholarly journals Airtightness Analysis of the Built Heritage–Field Measurements of Nineteenth Century Buildings through Blower Door Tests

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6727
Author(s):  
Alexander Martín-Garín ◽  
José Antonio Millán-García ◽  
Juan María Hidalgo-Betanzos ◽  
Rufino Javier Hernández-Minguillón ◽  
Abderrahmane Baïri
Keyword(s):  
Performance Studies ◽  
Architectural Design ◽  
Field Measurements ◽  
Energy Performance ◽  
Historical Buildings ◽  
Change Rate ◽  
Built Heritage ◽  
Air Change Rate ◽  
Wide Range ◽  
Energy Behaviour

Airtightness is a major issue in architectural design and it has a significant impact on the energy performance of buildings. Moreover, the energy behaviour of built heritage is due, to its singular characteristics, still a great unknown. The aim of this study is to establish a better knowledge of the airtightness of historical buildings, based on an in depth field study using blower-door tests. A set of 37 enclosures were analyzed inside eight buildings located in historical areas of a Spanish city with a significant built heritage. They were constructed between 1882 and 1919 and include diverse construction typologies applied for many building uses such as residential, cultural, educational, administrative and emblematic. The results indicate lower values compared to other previous airtightness studies of historical buildings. The average air change rate was found to be n50 = 9.03 h−1 and the airtightness of the enclosures presented a wide range of between 0.68 and 37.12 h−1. Three main levels of airtightness were identified with two thirds of the tested samples belonging to the intermediate level between 3–20 h−1. To conclude, several correlations have been developed which provide a method to estimate air leakage and could serve as a basis for energy performance studies of these kinds of building.

scholarly journals On optimization of flow passages of impellers of centrifugal pumps

2019 ◽  
Vol 11 (4) ◽  
pp. 311-318
Author(s):  
A. V. Volkov ◽  
A. G. Parygin ◽  
A. A. Vikhlyantsev ◽  
A. A. Druzhinin
Keyword(s):  
High Efficiency ◽  
Modular Design ◽  
Energy Performance ◽  
High Energy ◽  
Experiment Planning ◽  
Centrifugal Pumps ◽  
Hydraulic Machines ◽  
Specific Speed ◽  
Conventional Solution ◽  
Turbine Mode

The conventional solution for HAPPs is the use of reversible hydraulic machines operating both in the pump mode as well as in the turbine mode. At the same time, for example, a blade system of a hydraulic machine designed for the pumping mode has a high efficiency. However, in the turbine mode, the energy characteristics of such machine are far from optimal. Considering different patterns of micro- and mini-HAPPs (up to 100 kW) of modular design, it is most appropriate to use a pump and a turbine separately, since the efficiency of hydraulic machines is very important in the case of such low power. To date, approaches to the design of hydraulic turbines are quite developed and allow to achieve high energy performance [1, 2]. According to different data sources the level of axial turbine efficiency with power less than 100 kW is about 80÷91%. At the same time, for centrifugal pumps, especially those of low specific speed, the problem of increasing energy efficiency is very urgent. E.g., for pumps with a specific speed ns< 80 the efficiency level is usually 40 to 65%. The aim of the presented research is the development of methods of synthesis and optimization of the flow passages of centrifugal pumps using the approaches of the theory of optimal control and increasing energy performance of hydraulic machines. Various ways of local correction of geometry of flow passages are presented in the paper. As an alternative to empirical approaches, methods based on the control of the circulation distribution are considered in detail. Various mathematical dependences of the flow circulation on the coordinate of the point lying on the surface of the blade are analyzed. Possibilities of application of the theory of experiment planning in relation to the problems to be solved are considered.

THE BAROMETRIC FORMULA FOR REAL GASES AND ITS APPLICATION NEAR THE CRITICAL POINT

1933 ◽  
Vol 9 (6) ◽  
pp. 637-640 ◽  
Author(s):  
R. Ruedy
Keyword(s):  
Molecular Weight ◽  
Critical Temperature ◽  
Temperature Gradient ◽  
Critical Point ◽  
Van Der Waals ◽  
Critical Value ◽  
Uniform Density ◽  
Van Der Waals Equation ◽  
Other Substances ◽  
Separation Of Isotopes

According to the theory of the continuity of liquid and gaseous states, as expressed for instance in van der Waals' equation, pronounced density differences may exist in a short column of fluid maintained, throughout its length, at the critical temperature. The point in the tube at which the density of the contents has decreased a given percentage from the critical value is the higher the larger the ratio of the critical temperature to molecular weight. For substances like neon the variations are so large that a measurable separation of isotopes may be expected at or near the critical point; for other substances the computed results are at least of the magnitude found by experiment. Also, according to the theory, in order to obtain, at or near the critical point, a column of gas of uniform density a temperature gradient must be allowed to exist along the column.

Polymerisation processes with intrapolymer bonding. II. Stratified processes

1980 ◽  
Vol 12 (1) ◽  
pp. 116-134 ◽  
Author(s):  
P. Whittle
Keyword(s):  
Critical Point ◽  
Reaction Rates ◽  
Critical Value ◽  
Unstable Stratification ◽  
Local Fluctuations ◽  
Polymer Size ◽  
Spatially Homogeneous ◽  
New Feature ◽  
Size And Structure

We consider a polymerisation process stratified in that space is divided into regions, between which migration occurs, but with bonding occurring only within a region. In the case of a process whose specification is spatially homogeneous, criticality (gelation) is then easily detectable as the point at which statistical equidistribution over regions becomes unstable. Stratification does import a new feature, however, in that the equipartition solution can become metastable below criticality; local fluctuations of density can induce ‘gelational collapse’ at a density below the critical value. We derive also detailed results for the inhomogeneous case, both below and above criticality. Statistics of polymer size and structure are also easily determined in the stratified case, although one can locate the critical point without recourse to these. Finally, one can to a large extent treat the case in which inter- and intrapolymer reaction rates differ, and show that such difference affects the onset of metastability rather than of instability.

MINI-MAX MODEL OF MOTIVATION: AN INITIAL PRESENTATION

2007 ◽  
Vol 35 (8) ◽  
pp. 1139-1148 ◽  
Author(s):  
Darhl M. Pedersen
Keyword(s):  
College Students ◽  
Critical Point ◽  
Cost Benefit ◽  
Cost Effective ◽  
Low Achievers ◽  
Initial Presentation ◽  
High Achievers ◽  
Performance Curve ◽  
Class Session ◽  
Motivational Model

A cost/benefit motivational model is presented based on the discrepancy between a benefits equals costs line and a negatively accelerated performance curve. The model posits that people attempt to maximize benefits while minimizing costs and that the critical point is where the lines cross. Performance increments beyond that point are seen as not cost effective. It was proposed that high achievers expend additional effort in spite of a lower benefits to costs ratio, whereas low achievers do not. In an application of the model, 119 college students (47 men and 72 women) were studied. Those who remained in a 2.5 hour long class session following an examination administered in the first 45 minutes had significantly higher achievement in the course than did those who left.

scholarly journals HUBUNGAN ANTARA NILAI KRITIS DERIVATIF- F^\alpha DENGAN DIMENSI-\gamma DARI SUATU KURVA

2012 ◽  
Vol 4 (1) ◽  
pp. 233
Author(s):  
Supriyadi Wibowo
Keyword(s):  
Critical Point ◽  
Critical Value ◽  
Fractal Set ◽  
Irregular Structure

Continue function that defined on fractal set  is a function which has irregular structure, that can not be an ordinary differentiable on F. In this paper will be explored the correlation between critical point of the derivatif  with dimension-  of a curve. By using the properties of the derivative  , Holder’s continue function in rank of  and dimension , has been obtained the correlation between critical value of derivative and the dimension  of a curve.

Behavior of Point Thermal Bridges from Mechanical Anchoring of Flat Roofs

2014 ◽  
Vol 1041 ◽  
pp. 117-120
Author(s):  
Markéta Bogárová
Keyword(s):  
Thermal Flux ◽  
Software Tool ◽  
Energy Performance ◽  
High Energy ◽  
Critical Value ◽  
Ansys Software ◽  
Mechanical Anchoring ◽  
Thermal Bridges ◽  
Flat Roof ◽  
Flat Roofs

Building of structures with high energy performance is topical. To achieve this, it is necessary to have processed besides other thing a detailed design. Thermal bridges have to be eliminated in the design period. Thermal bridges occur as point, linear and 3-dimmensional ones. Mechanical anchoring creates point thermal bridges too. In this paper will be described only the mechanical anchoring to stabilize a flat roof. In the space with anchoring elements there is increased the thermal flux. This flux depends on the composition of the flat roof and kind of anchoring elements. It could lead to the condensation of water vapour in these locations upon attainment of the critical value of surface temperature in the room. This issue has another not-less interesting side. It is behaviour in summer season, when the anchoring conducts heat to the interior of objects. These thermal bridges caused by the anchoring elements described in this article will be modelled with the Ansys software tool.

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