scholarly journals Impact pressure on an orifice plate by a rising water column driven by an air pocket in a vertical riser

2020 ◽  
Vol 81 (5) ◽  
pp. 1029-1038 ◽  
Author(s):  
Yu Qian ◽  
David Z. Zhu
Keyword(s):  
Water Column ◽  
Peak Pressure ◽  
Current Model ◽  
Strong Relationship ◽  
Water Hammer ◽  
Orifice Plate ◽  
Minor Effect ◽  
Initial Water ◽  
Air Pocket ◽  
Riser Height

Abstract Occurrences of storm geyser events have attracted significant attention in recent years. Previous studies suggest that using an orifice plate can reduce the intensity of a geyser event but may induce a water-hammer type of pressure on the orifice plate. This study was conducted to explore the factors that influence the pressure transients when an orifice plate was installed in a vertical riser. A novel model was developed to simulated the movement of a rising water column driven by an air pocket in a vertical riser with an orifice plate on the top. Water-hammer type of pressure occurs when the water column reaches the orifice plate. The current model accurately simulates the dynamics of the water column considering its mass loss due to the flow along the wall of the riser (film flow) and the existence of the orifice plate. It was found that the initial water column length and the driving pressure, as well as the riser material, have a strong relationship with the peak pressure. The riser diameter and riser height have minor effect on the peak pressure. The water-hammer induced peak pressure reaches the maximum when the orifice opening is around 0.2 times the diameter of the vertical riser.

scholarly journals Pressure oscillation of an air pocket beneath a water column in a vertical riser

2020 ◽  
Author(s):  
Yu Qian ◽  
David Z. Zhu
Keyword(s):  
Water Column ◽  
Film Flow ◽  
Pressure Oscillation ◽  
Pressure Head ◽  
Oscillation Period ◽  
Column Length ◽  
Filling Process ◽  
Initial Water ◽  
Air Pocket ◽  
Significant Attention

Abstract Storm geysers have received significant attention lately due to its more frequent occurrences and the induced severe local flooding and infrastructure damages. Previous studies suggested that the air pocket pressure oscillated during geyser events especially in rapid filling process, but only the peak values were studied and the oscillation period was not discussed in detail. In this paper, a theoretical model was developed focusing on the period of the pressure oscillation induced by the expansion/compression of the air pocket below a water column in a vertical riser with film flow. It was found that the oscillation period was a function of the initial air pocket volume, initial air pocket pressure head, the riser diameter, and the initial water column length. The oscillation period increased with the air pocket pressure head and the air pocket volume, but decreased with the riser diameter and the polytropic coefficient. The oscillation period increased then decreased with an increasing water column length. Further, when considering the film flow along the riser, the oscillation period decreased slightly from the analytical solution. It was also found that the inflow rate change did not significantly influence the oscillation period.

scholarly journals Numerical modelling of pipelines with air pockets and air valves

2016 ◽  
Vol 43 (12) ◽  
pp. 1052-1061 ◽  
Author(s):  
Vicente S. Fuertes-Miquel ◽  
P. Amparo López-Jiménez ◽  
F. Javier Martínez-Solano ◽  
Gonzalo López-Patiño
Keyword(s):  
Numerical Modelling ◽  
Water Column ◽  
Water Hammer ◽  
Extreme Conditions ◽  
Residual Velocity ◽  
Air Pocket ◽  
Air Valve ◽  
Air Pockets

This work considers the behaviour of air inside pipes when the air is expelled through air valves. Generally, the air shows isothermal behaviour. Nevertheless, when the transient is very fast, it shows adiabatic behaviour. In a real installation, an intermediate evolution between these two extreme conditions occurs. Thus, it is verified that the results vary significantly depending on the hypothesis adopted. To determine the pressure of the air pocket, the most unfavourable hypothesis (isothermal behaviour) is typically adopted. Nevertheless, from the perspective of the water hammer that takes place when the water column arrives at the air valve and abruptly closes, the most unfavourable hypothesis is the opposite (adiabatic behaviour). In this case, the residual velocity with which the water arrives at the air valve is higher, and, consequently, the water hammer generated is greater.

scholarly journals Modulation of transient pressure by an air pocket in a horizontal pipe with an end orifice

2018 ◽  
Vol 77 (10) ◽  
pp. 2528-2536 ◽  
Author(s):  
Lin Li ◽  
David Z. Zhu
Keyword(s):  
Open Channel ◽  
Peak Pressure ◽  
Water Hammer ◽  
Sudden Increase ◽  
Transient Pressure ◽  
Horizontal Pipe ◽  
Air Pocket ◽  
Large Orifice ◽  
Air Pockets ◽  
End Wall

Abstract In urban drainage systems, a sudden increase in the flow rate can cause the transition of the flow from open channel to pipe flow, and the entrapment of large air pockets in sewers, which might result in serious geysers and water-hammer like pressure events. This paper presents a numerical analysis of flow processes associated with the pressurization and release of an air pocket in order to study its influence on transient pressure in a horizontal pipe with an end orifice. The influence of the air pocket inside the pipe on the peak pressure can be described in two distinct regimes. In regime I for the pipe with a small orifice, the peak pressure is modulated by the pressurization and expansion of the air pocket and its subsequent damping. In regime II for the pipe with a large orifice, air can be quickly expelled, and the water column directly impinges on the pipe end wall and causes water-hammer like pressure. With the increase of the orifice size, the peak pressure decreases due to the change in the water velocity. In the study cases, the peak pressure in regime I is about two times the inlet pressure, while it can be more than forty times in regime II.

scholarly journals Development of Pant-Type Harness with Fabric Air-Pocket for Pain Relief

2019 ◽  
Vol 9 (9) ◽  
pp. 1921
Author(s):  
Dongwoo Nam ◽  
Miyeon Kwon ◽  
Juhea Kim ◽  
Bummo Ahn
Keyword(s):  
Contact Area ◽  
Peak Pressure ◽  
Applied Pressure ◽  
The Body ◽  
Area Measurement ◽  
Medical Applications ◽  
Air Pocket ◽  
Long Time ◽  
Developed Pressure ◽  
Air Pockets

Harnesses can be used in various applications, such as entertainment, rescue operations, and medical applications. Because users are supported on the harness for a long time, they should feel comfortable wearing the harnesses. However, existing commercial harnesses are uncomfortable to wear and cause continuous serious pain. Therefore, in this study, a new pant-type harness with a fabric air pocket to reduce the applied pressure on the body, especially in the groin, is proposed. Keeping this in mind, we have designed and developed the pant-type harness. In addition, we performed pressure and contact area measurement experiments using the harness developed, pressure sensor, and a human mannequin. Peak and mean pressures and contact areas near the groin and waist were measured in the experiments. From the results, when air is injected in the air pockets, the peak pressure and contact area near the waist increased, and the peak pressure near the groin decreased. This means that the pressure applied on the human mannequin near the groin reduces because of the increased contact area near the waist, which is achieved by multi-layered air pockets. In this study, we proposed the optimal design of a novel pant-type harness that can address the limitations of existing harnesses. The proposed harness can be used for a prolonged time in applications, such as virtual reality entertainment, rescue operations, and rehabilitation.

Large Scale Experimental Wave Impact on Walls in the Québec Coastal Physics Laboratory

2015 ◽  
Author(s):  
Jannette B. Frandsen ◽  
Francis Bérubé
Keyword(s):  
Large Scale ◽  
Peak Pressure ◽  
Vertical Wall ◽  
Test Series ◽  
Vertical Force ◽  
Wave Impact ◽  
Physics Laboratory ◽  
Air Pocket ◽  
Jet Velocity ◽  
Plunging Breaker

The present tests are conducted in the new Québec Coastal Physics Laboratory, Canada. The flume has a depth and a width of 5 m and is 120 m long. This paper presents large scale experiments of water wave impact on a vertical wall following wave runup on a mixed sand-gravel-cobble beach. This present study is concerned with advancing knowledge on rapidly varying pressure magnitude and distributions on different types of sea/river/harbor walls. Protection against extreme events and subsequent coastal erosion is a key theme of application. Herein is presented preliminary test series which has focus on forces on vertical walls. Specifically, 27 pressure sensors are mounted on the vertical wall with a total test area of 1.2 m wide and 2.4 m high and is a stiffened aluminum plate. The outer regions of the wall are made of steel to span the entire width of the tank. The wall is designed to behave as a rigid plate. The geometric model to full scale is about 1:4. The incoming waves evolve on a flat bed to climb the final 25 m on a beach with slope with constant slope of 1:10. A small regular wave train forms the basis for investigations of force patterns on the wall. Herein, our preliminary findings reported are based on selected 6 test series (18 impacts out of 150 impacts). In general, wall pressures greater than 1 MPa and 10 m run-up are easily developed even with moderate amplitude waves at the inlet. We will discuss some details of the underlying mechanism of various types of breaking and impact on the wall. The peak pressure identified on the wall with the mixed gravel beach surface was 1.23 million N/m2 occurring in 0.2 milli seconds. It was cuased by a plunging breaker with a relatively large air pocket (∼0.11 m2). It was further identified that the maximum pressure on the wall does not necessarily give the maximum jet velocity (equivalent to vertical force considered in design of on parapets). They are independent quantities in these very random rapid processes. The maximum jet velocity was in the order of 35 m/s but could higher on a different beach surface. Further, it was found that the maximum waves are not necessarily the most critical ones as the waves break and therefore dissipates its energy before reaching the wall. A plunging breaker with a relatively large airpocket with a crest tip located at the top part of the wall resulted in max. peak wall pressure. One impact case caused a near simultaneous double peak pressure generated by a plunging breaker with two relatively small airpockets (0.003 m2 and 0.01 m2). This was the impact case responsible for the max. vertical jet velocity. We further found that the max. peak water pressure of the plunging breakers had a similar order of magnitude as the max. pressure within an air pocket.

Charts for water hammer in pipelines with air chambers

1977 ◽  
Vol 4 (3) ◽  
pp. 293-313 ◽  
Author(s):  
Eugen Ruus
Keyword(s):  
Water Column ◽  
Pipe Wall ◽  
Water Hammer ◽  
Wall Friction ◽  
Low Resistance ◽  
Discharge Line ◽  
Air Chamber ◽  
Basic Parameters ◽  
Computer Studies

Upsurges and downsurges are calculated and plotted for a simple pump discharge line provided with an air chamber. Basic parameters such as pipeline constant, air chamber parameter, pipe wall friction, and orifice resistance are used. The results of this paper can be used to determine the necessary volume of the air chamber. Computer studies indicate that the assumption of the rigid water column and the concentration of pipe friction at the pump end of the pipeline yields reasonably good results at the pump end; however, because of these assumptions, large errors in estimation of both upsurges and downsurges occur at the midpoint and particularly at the quarter point of the pipeline. Pipe friction has a substantially different effect on surges than that of the orifice resistance; these two effects should therefore be considered separately. A differential orifice is recommended and considered; this orifice should have a low resistance to flow out of the chamber.

scholarly journals Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling

2021 ◽  
Vol 8 ◽  
Author(s):  
Patricia Grasse ◽  
Kristin Haynert ◽  
Kristin Doering ◽  
Sonja Geilert ◽  
Janice L. Jones ◽  
...  
Keyword(s):  
Water Column ◽  
Silicic Acid ◽  
Isotope Composition ◽  
Size Fraction ◽  
Strong Relationship ◽  
Silicon Isotope ◽  
Main Driver ◽  
Subsurface Waters ◽  
Minimum Zone ◽  
Si Isotope

The upwelling area off Peru is characterized by exceptionally high rates of primary productivity, mainly dominated by diatoms, which require dissolved silicic acid (dSi) to construct their frustules. The silicon isotope compositions of dissolved silicic acid (δ30SidSi) and biogenic silica (δ30SibSi) in the ocean carry information about dSi utilization, dissolution, and water mass mixing. Diatoms are preserved in the underlying sediments and can serve as archives for past nutrient conditions. However, the factors influencing the Si isotope fractionation between diatoms and seawater are not fully understood. More δ30SibSi data in today’s ocean are required to validate and improve the understanding of paleo records. Here, we present the first δ30SibSi data (together with δ30SidSi) from the water column in the Peruvian Upwelling region. Samples were taken under strong upwelling conditions and the bSi collected from seawater consisted of more than 98% diatoms. The δ30SidSi signatures in the surface waters were higher (+1.7‰ to +3.0‰) than δ30SibSi (+1.0‰ to +2‰) with offsets between diatoms and seawater (Δ30Si) ranging from −0.4‰ to −1.0‰. In contrast, δ30SidSi and δ30SibSi signatures were similar in the subsurface waters of the oxygen minimum zone (OMZ) as a consequence of a decrease in δ30SidSi. A strong relationship between δ30SibSi and [dSi] in surface water samples supports that dSi utilization of the available pool (70 and 98%) is the main driver controlling δ30SibSi. A comparison of δ30SibSi samples from the water column and from underlying core-top sediments (δ30SibSi_sed.) in the central upwelling region off Peru (10°S and 15°S) showed good agreement (δ30SibSi_sed. = +0.9‰ to +1.7‰), although we observed small differences in δ30SibSi depending on the diatom size fraction and diatom assemblage. A detailed analysis of the diatom assemblages highlights apparent variability in fractionation among taxa that has to be taken into account when using δ30SibSi data as a paleo proxy for the reconstruction of dSi utilization in the region.

scholarly journals Numerical study on dynamic behavior of entrapped air in a partially filled pipe

2021 ◽  
Vol 83 (4) ◽  
pp. 771-780
Author(s):  
Hengliang Guo ◽  
Ye Guo ◽  
Biao Huang ◽  
Jiachun Liu
Keyword(s):  
Dynamic Behavior ◽  
Peak Pressure ◽  
Numerical Study ◽  
Relative Length ◽  
Time Duration ◽  
Initial Water ◽  
Pipe Length ◽  
System Parameters ◽  
Air Volume ◽  
Entrapped Air

Abstract Rapid filling in horizontal partially filled pipes with entrapped air may result in extreme pressure transients. This study advanced the current understanding of dynamic behavior of entrapped air above tailwater (the initial water column with a free surface in a partially filled pipe) through rigid-column modeling and sensitivity analysis of system parameters. Water and air were considered as incompressible fluid and ideal gas, respectively, and the continuity and momentum equations for water and a thermodynamic equation for air were solved by using the fourth order Runge-Kutta method. The effects of system parameters were examined in detail, including tailwater depth, entrapped air volume, driving head, pipe friction, and relative length of entrapped air and pipe. The results indicate that the presence of tailwater can mitigate the peak pressure when with identical initial volumes of entrapped air, as it can be considered to reflect a certain amount of loss of the net driving head. However, the peak pressure can increase as much as about 45% for the cases with fixed pipe length, due to the reduction in the initial entrapped air volume. The rise time for the first peak pressure was closely related to pipe friction, whereas the oscillation period (defined as the time duration between the first and second peaks) was virtually irrelevant. The applicability of the rigid-column model was discussed, and a time scale relevant indicator was proposed. When the indicator is larger than 20, the relative difference between the peak pressure estimation and experimental measurements is generally below 5%.

Analysis of Passive Water Hammer

1999 ◽  
Author(s):  
Syed M. Husaini ◽  
Asif H. Arastu ◽  
Riyad Qashu
Keyword(s):  
Flow Velocity ◽  
Water Column ◽  
Power Plants ◽  
Cold Water ◽  
Water Hammer ◽  
Saturated Water ◽  
Pipe Segment ◽  
Pressure Surge ◽  
Active Flow

Abstract This paper presents a methodology for the calculation of the severity a type of water hammer called “passive water hammer”. The passage of a cold water column followed by hot saturated water through a restricting orifice causes a reduction in flow velocity and a corresponding increase in pressure. The term passive water hammer was given to this mechanism because there is no active flow intervention required for its initiation. This type of water hammer has been observed in heater drain systems of power plants. An example is given for the calculation of pressure surge and pipe segment forces due to this mechanism.

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