The Transient Response of Orifices and Very Short Lines

1972 ◽  
Vol 94 (2) ◽  
pp. 483-489 ◽  
Author(s):  
J. E. Funk ◽  
D. J. Wood ◽  
S. P. Chao
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
System Analysis ◽  
Transient Flow ◽  
Transient Behavior ◽  
Short Term ◽  
State Equations ◽  
Steady State Condition ◽  
Orifice Flow ◽  
Flow Through

It is generally assumed that orifices and valves follow closely their steady-state characteristics during transient operation. However, this assumption of quasisteady behavior may lead to errors in predicting transient flow conditions under certain circumstances. In order to evaluate the transient behavior of an orifice, a differential equation relating the flow through and the pressure drop across an orifice was derived. An extension was made to include an axial dimension for the orifice. The solution of this equation for transient flow through an orifice subjected to a step change in pressure drop across the orifice is significantly different than that obtained using the steady state relationship. An experiment was designed to evaluate the theoretical results in which an orifice on the end of a line was subjected to a sudden pressure change and the resulting transient pressures were observed. It was found that a significant short term transient occurs before the orifice flow reaches the new steady state condition. The observed short term transient agrees well with that predicted by the theory. It is concluded that the behavior of an orifice can deviate considerably from that predicted by steady-state equations during periods of rapid pressure or flow changes. The dynamic description of orifice flow may be combined with a larger system analysis (e.g., using the method of characteristics) to more accurately predict the overall transient performance of flow systems.

A New Emergency Stop and Control Valve Design: Part 2 — Validation of Numerical Model and Transient Flow Physics

2014 ◽  
Author(s):  
Christian Musch ◽  
Frank Deister ◽  
Gerta Zimmer ◽  
Ingo Balkowski ◽  
Peter Brüggemann ◽  
...  
Keyword(s):  
Steady State ◽  
Mass Flow ◽  
Transient Flow ◽  
Control Valve ◽  
Transient Behavior ◽  
Complex Flow ◽  
Stop Valve ◽  
Turbine Inlet ◽  
Flow Through ◽  
Emergency Stop

In order to enhance steam mass flow through a turbine it becomes necessary to reduce the flow resistance of the turbine inlet valves. Consequently, a replacement of the high pressure turbine inlet valves is required. The valve combination described in this paper consists of a control valve and an emergency stop valve, opposite to the control valve. Both valves share a common valve seat. The control valve is a single-seat valve with integral pilot disc. A pre-stoke is introduced to allow for moderate opening forces. The emergency stop valve closes in countercurrent with the steam mass flow. The flow through the valve is analyzed by steady state and transient computational flow simulations. In addition to the steam mass flow, the forces acting upon the valve are determined. Transient behavior will be investigated by means of analyzing pressure fluctuations. Therefore frequencies caused by the steam flow are determined in the range up to 2000Hz. It will be shown that neither steady state nor transient simulations with a simple eddy viscosity turbulence model are capable to correctly predict the complex flow inside the valve. More sophisticated turbulence modeling like Large-Eddy simulation is thus inevitable. Furthermore, the physical phenomena causing the transient behavior are discussed. All findings are verified by comparison of the CFD with the measurements.

scholarly journals Pressure Analysis in the Draft Tube of a Pump-Turbine under Steady and Transient Conditions

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4732
Author(s):  
Jing Yang ◽  
Yue Lv ◽  
Dianhai Liu ◽  
Zhengwei Wang
Keyword(s):  
Steady State ◽  
Pressure Pulsation ◽  
Transient Flow ◽  
Draft Tube ◽  
Simulation Method ◽  
Wall Pressure ◽  
Pump Turbine ◽  
Steady State Condition ◽  
Transient Conditions ◽  
Pumped Storage

Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.

scholarly journals Maximal Flow Through a Network

1956 ◽  
Vol 8 ◽  
pp. 399-404 ◽  
Author(s):  
L. R. Ford ◽  
D. R. Fulkerson
Keyword(s):  
Steady State ◽  
The Other ◽  
State Condition ◽  
Maximal Flow ◽  
Steady State Condition ◽  
Rail Network ◽  
Two Cities ◽  
Flow Through

Introduction. The problem discussed in this paper was formulated by T. Harris as follows:“Consider a rail network connecting two cities by way of a number of intermediate cities, where each link of the network has a number assigned to it representing its capacity. Assuming a steady state condition, find a maximal flow from one given city to the other.”

An Effect of Fractal Flow Conditioner Thickness on Turbulent Swirling Flow

2013 ◽  
Vol 315 ◽  
pp. 93-97 ◽  
Author(s):  
Bukhari Manshoor ◽  
N.F. Rosidee ◽  
Amir Khalid
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Pressure Drop ◽  
Swirling Flow ◽  
Plate Thickness ◽  
Flow Characteristics ◽  
Space Filling ◽  
Flow Through ◽  
Experimental Fluid ◽  
Good Agreement

Fractal flow conditioner is a flow conditioner with a fractal pattern and used to eliminate turbulence originating from pipe fittings in experimental fluid flow applications. In this paper, steady state, incompressible, swirling turbulent flow through circle grid space filling fractal plate (Fractal flow conditioner) has been studied. The solution and the analysis were carried out using finite volume CFD solver FLUENT 6.2. The turbulence model used in this investigation is the standardk-εmodel and the results were compared with the pressure drop correlation of BS EN ISO 5167-2:2003. The results showed that the standardk-εmodel gave a good agreement with the ISO pressure drop correlation. Therefore, the model was used further to predict the effects of circle grids space filling plate thickness on the flow characteristics.

A Fast and Reliable Dynamic Tyre-Road Contact Model for ABS Braking Manoeuvre Simulations

2006 ◽  
Author(s):  
Francesco Braghin ◽  
Federico Cheli ◽  
Emiliano Giangiulio ◽  
Federico Mancosu ◽  
Daniele Arosio
Keyword(s):  
Differential Equation ◽  
Steady State ◽  
Order Differential Equation ◽  
Transient Behavior ◽  
Slip Angle ◽  
Relaxation Length ◽  
Steady State Condition ◽  
Tyre Model ◽  
First Order ◽  
Significant Parameter

Due to the dimensions of the tyre-road contact area, transients in a tyre last approximately 0.1s. Thus, in the case of abrupt maneuvers such as ABS braking, the use of a steady-state tyre model to predict the vehicle’s behavior would lead to significant errors. Available dynamic tyre models, such as Pacejka’s MF-Tyre model, are based on steady-state formulations and the transient behavior of the tyre is included by introducing a first order differential equation of relevant quantities such as the slip angle and the slippage. In these differential equations the most significant parameter used to describe the transient behavior is the so-called relaxation length, i.e. the distance traveled by the tyre to settle to a new steady–state condition once perturbated. Usually this parameter is assumed to be constant.

A Series Pressure Drop Representation for Flow Through Orifice Tubes

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
T. A. Jankowski ◽  
E. N. Schmierer ◽  
F. C. Prenger ◽  
S. P. Ashworth
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Simple Model ◽  
Pressure Drop ◽  
Diameter Ratio ◽  
Pressure Drops ◽  
In Series ◽  
Orifice Flow ◽  
Flow Through ◽  
Length To Diameter Ratio

A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number. The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories.

Thermal Management of Electronic Chips in a Channel Using Input Power to Control Flow Velocity

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
Thermal Management ◽  
Heat Generation ◽  
Electronic Device ◽  
Thermal Characteristics ◽  
Input Power ◽  
Control Flow ◽  
Steady State Condition ◽  
Average Temperature

In this research, thermal management of an electronic device using the input power is investigated numerically using the finite element method. The considered geometry consists of a horizontal channel with three volumetrically heated chips mounted on the bottom wall of the channel. The magnitude of the channel’s inlet velocity is varied with the variation of heat generation in the chips. The thermal characteristics of the system are presented, and compared with thermal characteristics of a system at a steady state condition. The effect of the Reynolds number and the oscillating period of the heat generation on the chips’ average temperature and Nusselt number is presented. The pressure drop in the channel is also calculated. The results indicated that the transient operating condition causes temperature to be higher than steady state by more than 45%, and difference between the transient and steady operations is reduced if the frequency is high. However, flow frequency has nearly no effect on the pressure drop in the channel.

Steady and Transient Flow of a Non-Newtonian Chemically Reactive Fluid in a Twin-Screw Extruder

2001 ◽  
Author(s):  
W. Zhu ◽  
Y. Jaluria
Keyword(s):  
Steady State ◽  
Response Time ◽  
Transient Flow ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Twin Screw Extruder ◽  
Screw Extruder ◽  
Twin Screw ◽  
Calculated Velocity ◽  
Screw Extruders

Abstract The flow of chemically reactive non-Newtonian materials, such as bio-polymers and aciylates, in a fully intermeshing, co-rotating twin-screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single- and twin-screw extruders. The effect of a time-dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single-screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the fluid, materials, and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The numerical results show that not all desired operating conditions are feasible. The calculated results for transient transport agree with the few experimental observations available on this system. These results will be useful in the design, control and optimization of polymer extrusion processes.

Air Flow Through Compressed and Uncompressed Aluminum Foam: Measurements and Correlations

2006 ◽  
Vol 128 (5) ◽  
pp. 1004-1012 ◽  
Author(s):  
Nihad Dukhan ◽  
Rubén Picón-Feliciano ◽  
Ángel R. Álvarez-Hernández
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Pressure Drop ◽  
Wind Tunnel ◽  
Aluminum Foam ◽  
Forchheimer Equation ◽  
Open Cell ◽  
Inertia Coefficient ◽  
Flow Through ◽  
Darcian Velocity

Wind-tunnel steady-state unidirectional pressure-drop measurements for airflow through nine compressed and uncompressed isotropic open-cell aluminum foam samples, having different porosities and pore densities, were undertaken. The compressed foam produced significantly higher pressure drop, which increased with increasing Darcian velocity following the quadratic Forchheimer equation. The permeability and the inertia coefficient data for the compressed foam showed less scatter compared to those for the uncompressed foam. Both were correlated using an Ergun-like equation, with the correlation being better for the permeability. The permeability correlation predicted the results of some previous studies very well. The friction factor correlated well with the Reynolds number.

Two-Phase Pressure Drop Characteristics During Low Temperature Transients in PEMFCs

2014 ◽  
Author(s):  
Rupak Banerjee ◽  
Satish G. Kandlikar
Keyword(s):  
Fuel Cells ◽  
Steady State ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Transient Behavior ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Four Levels ◽  
Phase Pressure

Proton Exchange Membrane fuel cells are being considered as the powertrain of choice for automotive applications. Automotive fuel cells experience transients during start-up, shut-down and changing load conditions, which constitute a significant part of the drive cycle. Transient behavior of PEMFCs can be classified into three categories: electrochemical, thermal and two-phase flow. Two-phase transients require a longer time to return to steady state than the electrochemical transient (which typically requires less than 1 second). Experiments have shown two-phase transients to be more prominent at the lower temperatures due to the increased presence of liquid water. Overshoot / undershoot behavior of current and voltage has been observed during investigations of electrochemical transients. This study investigates similar overshoot / undershoot behavior in the two-phase pressure drop in the reactant channels. An increase in the current drawn from the PEMFC is accompanied by larger air flow rates and greater water generation. An in situ setup is utilized to measure the pressure drop in the reactant channels across the length of the channel, when the electrical load drawn from the PEMFC is changed. This pressure drop measurement along the length of the reactant channels is used to characterize the overshoot / undershoot behavior. A parametric study is conducted to identify the factors which influence the overshoot / undershoot in two-phase flow pressure drop. The transient behavior is explored at the temperatures of 40, 60 and 80°C. Transient behavior is more pronounced at the lower temperature. Five different ramp rates have been used to show that faster ramp rates results in larger overshoot. The effect of magnitude of current change is investigated using four levels of load change. It was observed that increased magnitude of change results in increased overshoot behavior. However, no direct relationship has been observed between the magnitude of overshoot and the time required to return to steady state.

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