Hydraulic modeling during filling and emptying processes in pressurized pipelines: a literature review

Abstract

Filling and emptying processes are common maneuvers while operating, controlling and managing water pipelines systems. Currently, these operations are executed following recommendations from technical manuals and pipe manufacturers; however, these recommendations have a lack of understanding about the behavior of these processes. The application of mathematical models considering transient flows with entrapped air pockets is necessary because a rapid filling operation can cause pressure surges due to air pocket compressions, while an uncontrolled emptying operation can generate troughs of sub-atmospheric pressure caused by air pocket expansion. Depending on pipe and installation conditions, either situation can produce a rupture of pipe systems. Recently, reliable mathematical models have been developed by different researchers. This paper reviews and compares various mathematical models to simulate these processes. Water columns can be analyzed using a rigid water column model, an elastic water model, or 2D/3D CFD models; air-water interfaces using a piston flow model or more complex models; air pockets through a polytropic model; and air valves using an isentropic nozzle flow or similar approaches. This work can be used as a starting point for planning filling and emptying operations in pressurized pipelines. Uncertainties of mathematical models of two-phases flow concerning to a non-variable friction factor, a polytropic coefficient, an air pocket sizes, and an air valve behavior are identified.

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

“…The air phase is typically modelled using the polytropic formulation of an entrapped air pocket, where an air pocket can exhibit an adiabatic evolution, isothermal behaviour, or intermediate thermodynamic process [8,9]. An adiabatic evolution is produced when fast manoeuvres of regulating or draining valves are performed in water distributions systems; by contrast, an isothermal evolution is generated for slow manoeuvres [10]. Typically, an intermediate thermodynamic process is considered in actual water pipelines.…”

Simplified Mathematical Model for Computing Draining Operations in Pipelines of Undulating Profiles with Vacuum Air Valves

“…Draining processes are periodically repeated for cleaning and maintenance purposes in hydraulic installations [1,2]. These processes involve drops of sub-atmospheric pressure pulses because entrapped air pockets are expanded when water columns are coming out of drain valves located at downstream ends of pipelines [3,4].…”

“…Vacuum air valves should be installed in the highest points of water installations [5][6][7], as well as other positions recommended by the American Water Works Association (AWWA) [8] in order to prevent extreme values of sub-atmospheric pressure occurring. An optimal selection of air valves [9,10] considers not only the analysis of mathematical models for predicting hydraulic and thermodynamic variables but also stiffness class pipe and burial conditions (type of soil and backfill, and cover depth) of water installations [1].…”

Maniobras de llenado y vaciado en grandes conducciones. Aplicación a una tubería de fundición DN400 en Massamagrell (Valencia, España)

“…Es importante seleccionar un correcto tamaño de las válvulas de aire, debido a que, si el orificio de la ventosa no es el adecuado para cada instalación, cabe la posibilidad de que no cumpla con su objetivo de permitir el paso del aire y evitar sobrepresiones o depresiones en el interior. El sobredimensionamiento de las ventosas durante un proceso de llenado puede generar sobrepresiones incluso superiores a cuando no se utilizan estos dispositivos (Fuertes-Miquel, 2019b). Sin embargo, en los procesos de vaciado, el sobredimensionamiento de las ventosas siempre reducirá las depresiones ocurridas al interior de las tuberías.…”

“…El modelo matemático permite predecir de manera adecuada el comportamiento de la velocidad del agua, la presión de la bolsa de aire, la densidad del aire, la velocidad de salida o de entrada del aire por la ventosa y la longitud de la columna de agua. Para la modelación de la columna de agua se suelen utilizar modelos elásticos o de columna rígida (Fuertes-Miquel, 2019b). No obstante, las aproximaciones usando modelos CFD (Computacional Fluid Dynamics) también han sido empleadas para estudiar este comportamiento, necesitando en este caso largos tiempos de cálculo para la resolución numérica de las variables hidráulicas y termodinámicas (Besharat, 2018.…”