scholarly journals An Experimental and Numerical Analysis on the Dynamical Behavior of a Safety Valve in the Case of Two-Phase Non-Flashing Flow

2020 ◽  
Author(s):  
Mhd Ghaith Burhani ◽  
Csaba Hős
Keyword(s):  
Mass Fraction ◽  
Dynamical Behavior ◽  
Valve Lift ◽  
Test Facility ◽  
Maximum Pressure ◽  
Two Phase ◽  
Mixture Flow ◽  
System Pressure ◽  
Wide Range ◽  
The Stability

Pressure Relief Valves (PRVs) are key elements of any hydraulic system in the process industry, especially in chemical plants or hydraulic power transmission systems. Their task is to maintain the system pressure beneath a prescribed maximum pressure and vent the excessive fluid in an emergency scenario. This paper addresses the static and dynamic behavior of a Direct Spring-Operated PRV of conical shape in the presence of two-phase non-flashing flow, that is, water-air mixture. First, experimental results on the force and discharge characteristics of such a valve in a wide range of the air-to-water mass fraction are presented. Our test facility includes a custom-designed PRV with 42.5 mm inlet pipe diameter, an inlet pressure up to 6.6 bar(g) and a maximum lift of 10 mm. Additionally, the empirical results on the static characteristics, notably fluid force on the valve disc and discharge coefficients are reported as a function of the liquid mass fraction and valve lift. In the second part of the paper, we present the development of a Matlab-based simulation tool that is capable of predicting the dynamics and stability of such a valve in the case of two-phase, non-flashing, frozen-mixture flow. Moreover, the effect of system parameters, such as spring stiffness and reservoir capacity are recorded. Finally, we also present results on the stability of the opening and closing the multi-phase flow influence on the stability of the blowdown process.

Effects of Bubble on the Viscosity Properties of Lubricant

2005 ◽  
Author(s):  
W. S. Ng ◽  
M. C. Levesley ◽  
M. Priest
Keyword(s):  
Combustion Engine ◽  
Test Chamber ◽  
Gas Content ◽  
Oil Viscosity ◽  
Two Phase ◽  
Mixture Flow ◽  
Shear Rates ◽  
System Pressure ◽  
Wide Range ◽  
Shearing Motion

Air ingestion and entrapment is prevalent in the lubricant circulating around internal combustion engine and can lead to formation of two-phase flow system referred to as bubbly oil which affecting the oil viscosity and overall damping capability. Experimental work is conducted to study the effective viscosity of bubbly oil in a simple shear rheometer with the aim of gaining a general understanding of the two-phase mixture flow and developing lubrication models to be used in subsequent analysis. A laboratory simulator is used to produce bubbly oil by controlling the system pressure, temperature, and gas content entrained from atmosphere and an enclosed rheometer is employed to measure the mixture viscosity. A new detailed design is incorporated into the commercial rheometer with the purpose of maintaining the distribution of bubbles within the lubricant. The transparent test chamber is initially pressurized with air to control the bubbly oil level and the bubbly oil viscosity is tested over a wide range of shear rates. Under shearing motion, the viscosity of bubbly oil varies with time and the results obtained are compared to that of single-phase oil.

Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Peter A. Kottke ◽  
Thomas M. Yun ◽  
Craig E. Green ◽  
Yogendra K. Joshi ◽  
Andrei G. Fedorov
Keyword(s):  
High Heat ◽  
Heat Fluxes ◽  
High Mass ◽  
Two Phase ◽  
Worst Case ◽  
Pressure Drops ◽  
System Pressure ◽  
Performance Trends ◽  
Wide Range ◽  
Contraction And Expansion

We present results of modeling for the design of microgaps for the removal of high heat fluxes via a strategy of high mass flux, high quality, and two-phase forced convection. Modeling includes (1) thermodynamic analysis to obtain performance trends across a wide range of candidate coolants, (2) evaluation of worst-case pressure drop due to contraction and expansion in inlet/outlet manifolds, and (3) 1D reduced-order simulations to obtain realistic estimates of different contributions to the pressure drops. The main result is the identification of a general trend of improved heat transfer performance at higher system pressure.

On the Equilibrium of Cavitation Nuclei in Liquid-Gas Solutions

1981 ◽  
Vol 103 (3) ◽  
pp. 425-430 ◽  
Author(s):  
Y. S. Cha
Keyword(s):  
Stable Equilibrium ◽  
Thermodynamic Theory ◽  
Phase System ◽  
Saturated Liquid ◽  
Theoretical Justification ◽  
Two Phase ◽  
System Pressure ◽  
Two Component ◽  
Cavitation Nuclei ◽  
The Stability

The stability of a spherical bubble in a two-component two-phase system is examined by employing the thermodynamic theory of dilute solutions. It is shown that a bubble can remain in a state of stable equilibrium provided that the ratio of the total number of moles of the solute to the total number of moles of the solvent in the system is not extremely small and that the system pressure falls between an upper bound (dissolution limit) and a lower bound (cavitation limit). The results of the analysis provide a theoretical basis for the persistence of microbubbles in a saturated liquid-gas solution. Thus to a certain extent, the results also help to resolve the dilemma that exists in the field of cavitation due to (1) the necessity of postulating the existence of microbubbles; and (2) the lack of theoretical justification for the persistence of such bubbles in a liquid.

scholarly journals Numerical Investigation of the Pressure Drop Characteristics of Isothermal Ice Slurry Flow under Variable Ice Particle Diameter

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shehnaz Akhtar ◽  
Taqi Ahmad Cheema ◽  
Haider Ali ◽  
Moon Kyu Kwak ◽  
Cheol Woo Park
Keyword(s):  
Pressure Drop ◽  
Flow Velocity ◽  
Mass Fraction ◽  
Fluid Dynamic ◽  
Particle Diameter ◽  
Ice Slurry ◽  
Slurry Flow ◽  
Two Phase ◽  
Wide Range ◽  
Volumetric Loading

Ice slurry is an advanced secondary refrigerant that has been attracting considerable attention for the past decade due to the growing concerns regarding energy shortage and environmental protection. To stimulate the potential applications of ice slurry, the corresponding pressure drop of this refrigerant must be comprehensively investigated. The flow of ice slurry is a complex phenomenon that is affected by various parameters, including flow velocity, ice particle size, and ice mass fraction. To predict the pressure drop of ice slurry flow in pipes, a mixture computational fluid dynamic model was adopted to simulate a two-phase flow without considering ice melting. The numerical calculations were performed on a wide range of six ice particle sizes (0.1, 0.3, 0.5, 0.75, 1, and 1.2 mm) and ice mass fraction ranging within 5%–20% in the laminar range of ice slurry flow. The numerical model was validated using experimental data. Results showed that the ice volumetric loading and flow velocity have a direct effect on pressure drop; it increases with the increase in volumetric concentration and flow velocity. The findings also confirmed that for constant ice mass fraction and flow velocity, the pressure drop is directly and inversely related to the particle and pipe diameters, respectively. Moreover, the rise in pressure drop is more significant for large ice particle diameter in comparison to smaller size ice particles at high values of ice concentration and flow velocity.

scholarly journals A Discrete Fractional-Order Prion Model Motivated by Parkinson’s Disease

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
M. F. Elettreby ◽  
E. Ahmed ◽  
A. S. Alqahtani
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Fractional Order ◽  
Chaotic Behavior ◽  
Dynamical Behavior ◽  
Disease Model ◽  
Equation Model ◽  
Wide Range ◽  
The Stability ◽  
Uniqueness Of A Solution

A prion differential equation model motivated by Parkinson’s disease (PD) is studied. A fractional-order form of this model is proposed. After that, we discretized fractional-order Parkinson’s disease model. A sufficient condition for the existence and the uniqueness of a solution to the system is obtained. The stability of the fixed points of the system is achieved by using the Jury test. The impacts of varying the parameters of the system are examined. Under certain conditions, the system undergoes some kinds of bifurcations. We observe that the model loses its stability through double-period bifurcation to chaotic behavior as the growth rate increases. Also, the system stabilizes by increasing the memory parameter, and the contact rate between the two types of prions increases. The system shows rich dynamical behavior for a wide range of the values of the parameters.

Throttling Effect and Thermodynamic Characteristics of Supercritical CO2 Flowing Through Shut-Off Valve

2020 ◽  
Author(s):  
Xiaolu Guo ◽  
Peng Xu ◽  
Shuangqing Xu
Keyword(s):  
Gas Phase ◽  
Supercritical Co2 ◽  
Carbon Capture ◽  
Temperature Drop ◽  
Carbon Capture And Storage ◽  
Thermodynamic Characteristics ◽  
Large Temperature ◽  
Two Phase ◽  
System Pressure ◽  
The Stability

Abstract The supercritical flow of CO2 is widely applied in energy fields such as the carbon capture and storage technology and the Brayton cycle power generation technology. The shut-off valves are widely used in various systems of energy fields, and their use is related to the stability and safety of the system. Due to the throttling effect of supercritical CO2 flowing through the valve, the large temperature drop may cause the dry ice generation, the overpressure and the blockage, which have an important impact on the safety and stability of the whole system. At present, there are few researches on the throttling effect and thermodynamic characteristics of supercritical CO2 flowing through the shut-off valve. In this paper, the pressure and temperature changes before the valve inlet and after the valve outlet were studied, and the field of pressure, temperature and phase inside the valve were analyzed. It was found that the outlet pressure of the shut-off valve increased rapidly after the valve was opened, and the temperature decreased at the same time. With the decrease of system pressure, supercritical CO2 in front of the valve changed into gas-liquid two-phase and gas-phase successively, and CO2 after the valve changed into gas-phase, liquid-phase, gas-liquid two-phase and gas-phase successively. This study is of great significance to the stability and safe operation of energy systems.

On the Neuro-Muscular Control of Trochlean Joints

1996 ◽  
Vol 118 (3) ◽  
pp. 349-356 ◽  
Author(s):  
Muriel Balthazar ◽  
Irina Mountian ◽  
Pierre Y. Willems
Keyword(s):  
Dynamical Behavior ◽  
Calcium Balance ◽  
Golgi Tendon Organs ◽  
Stability Robustness ◽  
Wide Range ◽  
Transmission Of Information ◽  
Joint Dynamics ◽  
Tendon Organs ◽  
The Stability ◽  
Balance Dynamics

This paper presents a simplified dynamical model for the control of one-degree-of-freedom synovial joints considered as pure trochlean joints. This model considers the joint dynamics, the dynamics of the corresponding muscles and their calcium balance dynamics, as well as position and force feedbacks provided by the spindles and the Golgi tendon organs. Delays in the transmission of information are also taken into account as they proved to be of critical importance for the dynamical behavior of the considered systems. The linearized version of this model, which is valid for a rather wide range of movements, also allows us to investigate the stability of the system, as well as its stability robustness with respect to the feedback gains. Further, particular behaviors such as tremor are described.

Numerical Aspects on the Prediction of Stability Boundaries of Two-Phase Natural Circulation Circuits, Considering Flashing Evaluation

2005 ◽  
Vol 73 (6) ◽  
pp. 911-922
Author(s):  
P. Zanocco ◽  
D. Delmastro ◽  
M. Giménez
Keyword(s):  
Numerical Integration ◽  
Natural Circulation ◽  
Stability Limit ◽  
Linearization Method ◽  
Test Case ◽  
Implicit Methods ◽  
Two Phase ◽  
Circulation Circuit ◽  
Wide Range ◽  
The Stability

In this work, the stability of a two-phase, natural circulation circuit is analyzed, using a specially developed model. This thermohydraulic model results in a set of coupled, nonlinear, first-order partial differential equations, which are solved by means of the up-wind finite difference method, using combinations of explicit and implicit methods for the numerical integration of the different balance equations. An adaptive nodalization scheme is implemented, minimizing the error of the propagation of small perturbations through the discretized volumes and especially the ones having two-phase flow regime. A linearization method is implemented by means of numerical perturbations. Frequency domain calculations are carried out, allowing a rapid visualization of the stability of the linearized system. Two cases are analyzed: a test case, where the code is compared in a wide range of qualities with an analytical model, and an application case, where the model is used to analyze the stability of an integral reactor cooled by natural circulation. The CAREM prototype is taken as a reference. In both cases, the numerical diffusion and integration errors are analyzed in the stability limit prediction by means of a convergence analysis using different nodalization and numerical integration criteria.

Modeling and Numerical Prediction of Flow Boiling in a Thin Geometry

2004 ◽  
Vol 126 (1) ◽  
pp. 22-33 ◽  
Author(s):  
Ranganathan Kumar ◽  
Charles C. Maneri ◽  
T. Darton Strayer
Keyword(s):  
Flow Boiling ◽  
Bubbly Flow ◽  
Three Dimensional ◽  
Companion Paper ◽  
Two Phase ◽  
Void Fractions ◽  
Field Modeling ◽  
System Pressure ◽  
Wide Range ◽  
Inlet Conditions

An analysis capability to examine the two-phase bubbly flow in high pressure boiling systems has been developed. The models have been adapted from the literature for a narrow high aspect ratio geometry using the measurements obtained in a companion paper. Three-dimensional computational results have been compared with cross-section averaged and line-averaged void fractions measured with a gamma densitometer, and local void fraction measured with a hot-film anemometer. These comparisons have been made over a wide range of flow inlet conditions, wall heating and system pressure. Comparisons are found to be good when the flow is bubbly, but at high void fractions, where the flow is churn-turbulent or annular, the two-field modeling approach does not perform adequately. This result emphasizes the need for multiple field modeling.

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