Proposição de um novo dispositivo para alívio de golpe de aríete: tubo de admissão e expulsão bidirecional (TAEB)

Abstract

This study aims to evaluate the performance of the Bidirectional Intake and Exhaust Tube (TAEB) as a water hammer protection device, a new device proposed for hydraulic transients’ mitigation. The TAEB consists of an extended vertical tube equipped with an Air Valve at its upper end. Its operating principle is based on the hypothesis that the addition of this water-filled tube can regulate the uncontrolled air intake promoted by the Air Valve, while preventing negative pressures at its installation point. The modeling of the TAEB was performed by integrating two other relief devices: the Surge Tank and the Air Valve. Furthermore, the transient calculation considering the device employed the Method of Characteristics (MOC) model that accounts for the presence of air in the system, specifically the cavitation model. It is understood that the liquid column within the TAEB varies during the hydraulic transient as a function of air intake and expulsion governed by the Air Valve. The advantages of using the TAEB include its effectiveness in protecting against negative pressures, thereby avoiding cavitation and liquid column separation, in addition to its significantly lower cost compared to Surge Tanks and One-Way Surge Tanks, which perform similar functions. To support this work, a literature review was conducted on hydraulic transients, the MOC solution (the primary numerical model for one-dimensional hydraulic transient analysis), main water hammer protection devices, cavitation-related issues and an overview of the UFC System. The methodology is subsequently presented, detailing the Surge Tank and Air Valve models, as well as their integration. The methodology’s equations were implemented in the UFC System – Module 7, the specific module for hydraulic transient calculations. Model validation utilized water level drawdown data measured during an experiment at the Santa Maria Farm Pipeline in Presidente Olegário, Minas Gerais. A TAEB was constructed at this site, and its protective efficiency against transients was tested following the pump set shutdown. Using the collected data, a sensitivity analysis was performed based on the results generated in UFC 7, varying specific parameters to match the experimental field results. Following validation, the TAEB was tested in other pipelines, consistently positioned at the point of lowest negative pressure identified in unprotected transient simulations. The simulation results indicated that the TAEB successfully elevated the minimum pressure envelope at the installation node to the ground level plus the maximum water drawdown reached within the device. Additionally, pressure graphs showed that the TAEB limited the pressure to the value corresponding to the minimum water height reached during simulation. For the Santa Maria Farm Pipeline case, the TAEB also impacted positive pressures across the entire system; in other cases, this effect was restricted to the vicinity of the installation node, primarily due to differences in the geometric profiles of the simulated pipelines. Simulations were also conducted using only an Air Valve at the same node where the TAEB was installed. These simulations showed that the Air Valve promotes greater instability in pressure peaks and, in some cases, leads to higher negative and positive pressures. To provide a comparative sensitivity between devices, comparisons were also made between the TAEB and the conventional Surge Tank, demonstrating that while the Surge Tank is a highly reliable device for relieving maximum and minimum pressures, it requires massive structural dimensions to fulfill this function. Finally, it is observed that the TAEB effectively fulfilled its function of attenuating minimum pressures in the pipeline. However, its efficiency must be verified in software such as UFC 7, as its conception relies on accurate simulations and correct sizing to function effectively.