Analytical solutions for predicting the maximum pressure drop after pump failure in long-distance water supply project

2018 ◽  
Vol 18 (6) ◽  
pp. 1926-1936 ◽  
Author(s):  
Cheng-yu Fan ◽  
Jian Zhang ◽  
Xiao-dong Yu
Keyword(s):  
Pressure Drop ◽  
Water Supply ◽  
Safety Assessment ◽  
Water Hammer ◽  
Maximum Pressure ◽  
Long Distance ◽  
Pump Failure ◽  
Pipe System ◽  
Protection Scheme ◽  
Maximum Pressure Drop

Abstract The water hammer caused by pump failure in a long-distance pressurized pipe system generally poses a severe threat to the safety of the whole system. The maximum pressure drop at the pump end of the discharge line is significant for the safety assessment of the pipelines. In this study, the characteristics of the pump-stopping water hammer and its propagation in the pipelines are analyzed. The formula for predicting the maximum pressure drop is deduced based on the Method of Characteristics and the complete characteristics of the pumps. The application conditions of the formula and the solution procedures are presented as well. In addition, two engineering cases are introduced and the results calculated by the formula are compared with those resulting from the numerical simulation, and the agreement is satisfactory. The formula presented in this study is of simple form, practical and of high precision, and can provide a theoretical basis for the water hammer protection scheme of a long-distance water supply project.

Effect of multi-valve closure on superposed pressure in a tree-type long distance gravitational water supply system

2019 ◽  
Vol 68 (6) ◽  
pp. 420-430
Author(s):  
Xingtao Wang ◽  
Jian Zhang ◽  
Xiaodong Yu ◽  
Sheng Chen ◽  
Wenlong Zhao ◽  
...  
Keyword(s):  
Water Supply ◽  
Pressure Rise ◽  
Water Hammer ◽  
Supply System ◽  
Water Supply System ◽  
Maximum Pressure ◽  
Valve Closure ◽  
Long Distance ◽  
Maximum Water ◽  
Tree Type

Abstract Valves are installed at the end of each branch pipeline in a tree-type long distance gravitational water supply system to regulate flow. However, the sequential closing of all valves may cause a tremendous superposed pressure rise, even larger than the pressure rise under simultaneous valve closure. In this paper, the effects of sequential valve closure on the superposed maximum water hammer pressure rise in a pipeline were investigated. By using the wave superposition principle, a sequential valve closure formula leading to maximum water hammer was proposed and verified using numerical simulation based on a practical project. In addition, the superposed maximum pressure rises in the pipeline were compared under single, simultaneous and sequential valve closure, respectively. The results show that the sequential valve closure formula agrees well with the numerical results and the pressure rise in the pipeline under the sequential closing was the largest. Moreover, compared with the superposed maximum pressure rises at the main pipeline, the effect of sequential valve closure on superposed maximum pressure rise at the branch pipeline is more sensitive.

scholarly journals Computational and Experimental Study on Pressure Drop in a Fluidised Bed with Different Air Distributor Designs

2020 ◽  
Vol 17 (2) ◽  
pp. 8043-8051
Author(s):  
A. S. M. Yudin ◽  
A. N. Oumer ◽  
N. F. M. Roslan ◽  
M. A. Zulkarnain
Keyword(s):  
Pressure Drop ◽  
Perforated Plate ◽  
Area Ratio ◽  
Maximum Pressure ◽  
Fluidised Bed ◽  
Key Factor ◽  
Minimum Number ◽  
Maximum Pressure Drop ◽  
Free Area ◽  
Distributor Plate

Fluidised bed combustion (FBC) has been recognised as a suitable technology for converting a wide variety of fuels into energy. In a fluidised bed, the air is passed through a bed of granular solids resting on a distributor plate. Distributor plate plays an essential role as it determines the gas-solid movement and mixing pattern in a fluidised bed. It is believed that the effect of distributor configurations such as variation of free area ratio and air inclination angle through the distributor will affect the operational pressure drop of the fluidised bed. This paper presents an investigation on pressure drop in fluidised bed without the presence of inert materials using different air distributor designs; conventional perforated plate, multi-nozzles, and two newly proposed slotted distributors (45° and 90° inclined slotted distributors). A 3-dimensional Computational Fluid Dynamics (CFD) model is developed and compared with the experimental results. The flow model is based on the incompressible isothermal RNG k-epsilon turbulent model. In the present study, systematic grid-refinement is conducted to make sure that the simulation results are independent of the computational grid size. The non-dimensional wall distance,  is examined as a key factor to verify the grid independence by comparing results obtained at different grid resolutions. The multi-nozzles distributor yields higher distributor pressure drop with the averaged maximum value of 749 Pa followed by perforated, 45° and 90° inclined distributors where the maximum pressure drop recorded to be about one-fourth of the value of the multi-nozzles pressure drop. The maximum pressure drop was associated with the higher kinetic head of the inlet air due to the restricted and minimum number of distributor openings and low free area ratio. The results suggested that low-pressure drop operation in a fluidised bed can be achieved with the increase of open area ratio of the distributor.

Mountain-Top Vortices as Causes of Large Errors in Altimeter Heights

1949 ◽  
Vol 30 (2) ◽  
pp. 39-44 ◽  
Author(s):  
F. A. Brooks
Keyword(s):  
Pressure Drop ◽  
Ground Surface ◽  
Maximum Error ◽  
Maximum Pressure ◽  
Strong Wind ◽  
High Mountains ◽  
Pressure Drops ◽  
Pressure Distributions ◽  
Maximum Pressure Drop ◽  
Vortex Axis

There have been uncontradicted reports of large altimeter errors in the vicinity of high mountains. A brief survey of pressure distributions over an airfoil with flaps shows a maximum pressure drop below static pressure of twice the velocity head. Applying this ratio to a 14,000-foot mountain in a 100-mph wind a maximum error of 700 feet is indicated. This is important, but not enough to explain the occasional reports of 2 to 3,000-foot errors. Pressure drops of this magnitude exist in tropical cyclones, and even greater depression is known in tornadoes. The pressure drop at the ground surface is seen to have an axial connection with the natural low pressure aloft. The strength of the vortex is shown to depend on the outside tangential input by the wind where the whirl velocity can be very moderate, and the superspeed spin inside a vortex is shown to be dependent on radial inflow of air which is discharged along the vortex axis. Procedures are suggested for locating mountain tornadoes and thorough investigation urged so that the great hazards of mountain vortices in a strong wind will become generally known.

Polyline Closure Law Design and Realization in Long-Distance Water-Supply Project

2010 ◽  
Author(s):  
Jian Zhang ◽  
Xiaodong Yu ◽  
Jianfeng An ◽  
Arash Hazrati
Keyword(s):  
Water Supply ◽  
Theoretical Basis ◽  
Temporal Distribution ◽  
Break Point ◽  
Water Hammer ◽  
Long Distance ◽  
Closure Time ◽  
Water Conveyance ◽  
Flow Inertia ◽  
Application Scope

Long-distance water-supply project is an effective way to solve the uneven spatial and temporal distribution of water resources, but the safety of water conveyance system is threatened seriously by water-hammer. Based on the research of the characteristic of water-hammer with pipe friction considered, the formula of indirect water-hammer is deduced and the application scope of the formula is also discussed, which is the theoretical basis for the design of polyline closure law. To the defects that valve closure time is long and response of accident is slow in the long-distance water-supply project, polyline closure law is designed with consideration of valve overflowing property, which greatly reduces the closure time and water-hammer. At the same time, the flow inertia is large in long-distance water-supply project and break point of polyline closure law is hard to fix. In order to improve the reliability of the mechanical operating system, locking device is installed, which make the polyline closure law carry out successfully and provide a new idea for water hammer protection in long-distance water-supply project.

scholarly journals Analytical and numerical study of entropy generation in small scale heat exchangers

2019 ◽  
Author(s):  
Mahyar Pourghasemi
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Energy Harvesting ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Optimum Operating ◽  
Maximum Pressure ◽  
Channel Height ◽  
Maximum Pressure Drop

In present work, the entropy generation minimization technique (EGM) is applied to study the performance of a microchannel heat sink combined with a new proposed parameter called irreversibility index and energy harvesting concept. Three different cases have been investigated using geometry of a microchanel heat sink selected from experimental work in the literature. The constraints considered in this study, are fixed channel height and maximum pressure drop. It has been observed that with fixed channel height constraint, while the aspect ratio changes from 1 to 10, the optimum operating condition fall in the range of Reynolds number equal to 2000 and aspect ratio of 2.25. Moreover, the extra constrain on maximum pressure drop imposes a limitation on applicable aspect ratio range. The maximum aspect ratio of the channel for stable flow field in this case cannot be higher than 5 imposed by criteria of laminar flow regime. The obtained optimum values are Reynolds number of 1850 and aspect ratio of 2. Using a combined new defined irreversibility index and Energy Harvesting Concept (EHC), it has been shown that the optimum design values for industrial applications are not necessary ones obtained from EGM method and may shift to a new operating point based on the method considered for energy harvesting.

scholarly journals Research on the water hammer protection of the air vessel caused by underground pipe burst in long distance water supply system

2018 ◽  
Vol 246 ◽  
pp. 01066 ◽  
Author(s):  
Xingtao Wang ◽  
Jian Zhang ◽  
Xiaodong Yu ◽  
Lin Shi
Keyword(s):  
Water Supply ◽  
Check Valve ◽  
Water Hammer ◽  
Supply System ◽  
Water Supply System ◽  
Safe Operation ◽  
Long Distance ◽  
Underground Pipe ◽  
Pipe Burst ◽  
The Mathematical Model

The conventional air vessel installation is usually installed behind the check valve at the upstream end of the pipeline to effectively control the water hammer pressure due to pump trip. However, the water hammer pressure caused by underground pipe burst has been neglected. The water hammer protection of air vessel due to pipe burst in long distance water supply system was discussed in this paper. According to analysis of the process of the pipe burst, the mathematical model of underground pipe burst and air vessel were established. A new air vessel installation that was installed in the middle of the pipeline was proposed. The new air vessel installation was simulated by method of characteristics. Then it was compared with the conventional air vessel when the pump trip and the pipe burst occur respectively. The results show that both the conventional air vessel and the new air vessel can effectively protect the water hammer duo to the pump trip. Moreover, when pipe burst occurs, the conventional air vessel cannot achieve the safe operation of the long distance water supply system. However, under the same air vessel type parameters, the new air vessel installation can effectively protect the water hammer pressure.

In Vitro Pressure Flow Relationship in Model of Significant Coronary Artery Stenosis

2004 ◽  
Author(s):  
Abhijit Sinha Roy ◽  
Lloyd H. Back ◽  
Ronald W. Millard ◽  
Saeb Khoury ◽  
Rupak K. Banerjee
Keyword(s):  
Coronary Artery ◽  
Pressure Drop ◽  
Power Law ◽  
Flow Rate ◽  
In Vitro Model ◽  
Maximum Pressure ◽  
Vitro Model ◽  
Maximum Pressure Drop

Simultaneous measurement of pressure and flow rate has been found to be helpful in evaluating the physiologic significance of obstructive coronary artery disease and in the diagnosis of microvascular disease. This experimental study seeks to find important pressure-flow relationship in an in-vitro model of significant coronary artery stenoses using a non-Newtonian liquid, similar to blood showing a shear thinning behavior, using significant stenotic in-vitro model (minimal area stenosis = 90%). The geometry for the stenotic model is based on data provided in an in vivo study by Wilson et al., (1988). For 90% area stenosis, the maximum recorded pressure drop for steady flow rate of 55, 79 and 89 are 14, ~24 and ~32 mmHg respectively. The maximum pressure drop at flow rate of 115 ml/min (the physiological limit) is 50.3 mmHg respectively. Using a power law curve fit, the maximum pressure drop (in mmHg) related with flow rate (in ml/min) provided a power law index of 1.72. Shorter distal length than required in the in-vitro model did not allow the recording of complete pressure recovery. This preliminary data provides reference values for further experimentation both in vitro with pulsatile flow as in physiological conditions, and in vivo.

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