A Study on the Unstable Coupling Between Pumps and Hydraulic Circuits With Entrapped Gas Pockets

2002 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Juan Antun˜a-Schu¨tze ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaqui´n Ferna´ndez-Francos
Keyword(s):  
Critical Conditions ◽  
Pressure Amplitude ◽  
Hydraulic Systems ◽  
Positive Slope ◽  
One Dimensional ◽  
Numerical Resolution ◽  
Air Pocket ◽  
Entrapped Air ◽  
Fundamental Equations ◽  
Oscillation Instability

A theoretical and experimental study has been conducted on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. The theoretical study was composed of an analysis of the critical conditions for the instability to develop, followed by the numerical resolution of the fundamental equations that govern the phenomenon, assuming unsteady one-dimensional flow, in order to simulate the limit cycle oscillations of the unstable system. Additionally a series of laboratory tests was conducted on a conventional centrifugal pump, with variation of the initial volume of an entrapped air pocket in the circuit. As expected from the predictions of the theoretical model, instability was found to developed with pressure amplitude oscillations and frequency dependent on the amount of entrapped air.

Computation of the Unstable Behavior of a Hydraulic Circuit With a Centrifugal Pump Coupled to an Air Pocket

2005 ◽  
Author(s):  
Jorge Parrondo ◽  
Juan Antun˜a ◽  
Jose´ I. Prieto
Keyword(s):  
Centrifugal Pump ◽  
Compressible Liquid ◽  
Hydraulic Systems ◽  
Calculation Algorithm ◽  
Trapped Air ◽  
Air Pocket ◽  
Dead End ◽  
Entrapped Air ◽  
The One ◽  
Oscillation Instability

A theoretical and experimental study is presented on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. In order to simulate these systems, the one-dimensional unsteady equations for compressible liquid flow were solved by means of a suitable calculation algorithm, based on the method of characteristics. Additionally, a series of laboratory tests was conducted on a conventional centrifugal pump that operated in a circuit with a dead end and different amounts of entrapped air. In accordance with the predictions of the theoretical model, instability was found to develop with limit cycle pressure oscillations of frequency dependent on the trapped air amount.

Experimental Validation of Existing Numerical Models for the Interaction of Fluid Transients With In-Line Air Pockets

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Jane Alexander ◽  
Pedro J. Lee ◽  
Mark Davidson ◽  
Huan-Feng Duan ◽  
Zhao Li ◽  
...  
Keyword(s):  
Time Delay ◽  
Wave Speed ◽  
Numerical Models ◽  
Diagnostic Process ◽  
Air Pocket ◽  
Fluid Transients ◽  
Entrapped Air ◽  
Air Pockets ◽  
The Given ◽  
Potential Tool

Entrapped air in pipeline systems can compromise the operation of the system by blocking flow and raising pumping costs. Fluid transients are a potential tool for characterizing entrapped air pockets, and a numerical model which is able to accurately predict transient pressures for a given air volume represents an asset to the diagnostic process. This paper presents a detailed study on our current capability for modeling and predicting the dynamics of an inline air pocket, and is one of a series of articles within a broader context on air pocket dynamics. This paper presents an assessment of the accuracy of the variable wave speed and accumulator models for modeling air pockets. The variable wave speed model was found to be unstable for the given conditions, while the accumulator model is affected by amplitude and time-delay errors. The time-delay error could be partially overcome by combining the two models.

scholarly journals Some numerical experiments on firn ventilation with heat transfer

1993 ◽  
Vol 18 ◽  
pp. 161-165 ◽  
Author(s):  
M.R. Albert
Keyword(s):  
Heat Transfer ◽  
Surface Pressure ◽  
Thermal Effects ◽  
Numerical Experiments ◽  
Temperature Gradients ◽  
Pressure Amplitude ◽  
Two Dimensional ◽  
One Dimensional ◽  
Thermal Signature ◽  
Spatially Varying

Preliminary estimates of the thermal signature of ventilation in polar firn are obtained from two-dimensional numerical calculations. The simulations show that spatially varying surface pressure can induce airflow velocities of 10−5m s−1at 1.5 m depth in uniform firn, and higher velocities closer to the surface. The two-dimensional heat-transfer results generally agree with our earlier one-dimensional conclusions that the thermal effects of ventilation tend to decrease the temperature gradient in the top portions of the pack. Field observations of ventilation through temperature measurements are most likely to be observed when the firn temperature at depths on the order of 10 m is close to the air temperature, since steep temperature gradients can mask the thermal effects of ventilation. Preliminary indications are that, as long as surface-pressure amplitude is sufficient to move the air about in the top tens of centimeters in the snow, the resulting temperature profile during ventilation is fairly insensitive to the frequency of the surface-pressure forcing for pressure frequencies in the range 0.1–10.0 Hz.

scholarly journals One-dimensional dislocations. I. Static theory

1949 ◽  
Vol 198 (1053) ◽  
pp. 205-216 ◽  
Keyword(s):  
Critical Conditions ◽  
Dislocation Model ◽  
Physical Parameters ◽  
Spontaneous Generation ◽  
Static Theory ◽  
One Dimensional ◽  
Lennard Jones ◽  
Regular Sequences ◽  
Crystalline Substrate ◽  
Made In

The theory of a one-dimensional dislocation model is developed. Besides acting as a pointer to developments of general dislocation theory, it has a variety of direct physical applications, particularly to monolayers on a crystalline substrate and to conditions in the edge row of a terrace of molecules in a growing crystal. Allowance is made in the theory for a difference in natural lattice-spacing between the surface layer or row and the substrate. The form and energy of single dislocations and of regular sequences of dislocations are calculated. Critical conditions for spontaneous generation (or escape) of dislocations are determined, and likewise the activation energies for such processes below the critical limits. Various physical applications of the model are discussed, and the physical parameters are evaluated with the aid of the Lennard-Jones force law for the above-mentioned principal applications.

On the Hydraulics of Downward Sloping Pipes With Entrapped Air Pockets

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
H. A. Warda ◽  
E. M. Wahba ◽  
E. N. Ahmed
Keyword(s):  
Hydraulic Jump ◽  
Open Channel ◽  
Numerical Results ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Dynamics Model ◽  
Computational Fluid Dynamics Model ◽  
Air Pocket ◽  
Entrapped Air ◽  
Air Pockets

Abstract In this study, air–water flow in a downward sloping pipe subsequent to the entrapping of an air pocket is investigated both numerically and experimentally. A transient, two-dimensional computational fluid dynamics model is applied to study the different possible flow regimes and their associated phenomena. The numerical model is based on the Reynolds-averaged Navier–Stokes (RANS) equations and the volume of fluid (VOF) method. Both numerical and experimental investigations provide visualization for the hydraulic jump, the blowback regime, and the full gas transport regime. The numerical results predict that the flow structure in the pipe downstream the toe of the hydraulic jump is subdivided into three distinct regions including the jet layer, the shear zone, and the circulation region, which agrees qualitatively with the previous investigations of the hydraulic jump characteristics in open channel flow. Numerical results are in reasonable agreement with the experimental measurements of the circulation length and the hydraulic jump head loss.

Modeling and Control of a Supercritical CO2 Water Cooler in an Indirect-Fired 10MWe Recompression Brayton Cycle Near Critical Conditions

2019 ◽  
Author(s):  
Eric Liese ◽  
Priyadarshi Mahapatra ◽  
Yuan Jiang
Keyword(s):  
Supercritical Co2 ◽  
Cooling Water ◽  
Critical Conditions ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Modeling And Control ◽  
One Dimensional ◽  
Exit Temperature ◽  
Flow Pressure ◽  
And Control

Abstract A one-dimensional design and dynamic model of a microtube heat exchanger is presented for cooling supercritical CO2 to near critical conditions (35°C and ∼90 bar) with water. A control strategy is designed and implemented to achieve a desired hot-side CO2 outlet temperature, while the cooling-water exit temperature is monitored (ideally kept below 50°C). The control responses during drastic process changes at the boundaries such as sCO2 inlet flow/pressure and cooling water inlet temperature are presented.

scholarly journals Quasi-static Flow Model for Predicting the Extreme Values of Air Pocket Pressure in Draining and Filling Operations in Single Water Installations

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 664 ◽  
Author(s):  
Óscar E. Coronado-Hernández ◽  
Vicente S. Fuertes-Miquel ◽  
Daniel Mora-Meliá ◽  
Yamisleydi Salgueiro
Keyword(s):  
Flow Model ◽  
Extreme Values ◽  
Internal Diameter ◽  
Algebraic Equations ◽  
Flow Models ◽  
Numerical Resolution ◽  
Air Pocket ◽  
Water Pipelines ◽  
Thermodynamic Variables ◽  
Static Flow

Inertial models have been used by researchers to simulate the draining and filling processes in water pipelines, based on the evolution of the main hydraulic and thermodynamic variables. These models use complex differential equations, which are solved using advanced numerical codes. In this study, a quasi-static flow model is developed to study these operations in hydraulic installations. The quasi-static flow model represents a simplified formulation compared with inertial flow models, in which its numerical resolution is easier because only algebraic equations must be addressed. Experimental measurements of air pocket pressure patterns were conducted in a 4.36 m long single pipeline with an internal diameter of 42 mm. Comparisons between measured and computed air pocket pressure oscillations indicate how the quasi-static flow model can predict extreme values of air pocket pressure for experimental runs, demonstrating the possibility of selecting stiffness and pipe classes in actual pipelines using this model. Two case studies were analysed to determine the behaviour of the quasi-static flow model in large water pipelines.

Sign in / Sign up

Export Citation Format

Share Document