Analysis of the propagation velocities of hydraulic transients between a radial centrifugal pump and an amphibious pump using CFD software
In this paper, we will compare the behavior of the velocities in the transport of hydraulic transients from a conventional radial centrifugal pump to that of an amphibious pump, using the computational model created through the CFD program. The information was obtained from presentations and technical articles produced by the engineering department of Higra (manufacturer of amphibious pumps), as well as from the Federal University of Itajubá — UNIFEI, whose article was published in RBRH — Revista Brasileira de Recursos Hídricos, where both used the aforementioned computational model.
CFD (Computational Fluid Dynamics) technology has become a fundamental part of the design and analysis of products and processes in many companies, due to its ability to predict the performance of these equipment and processes before they are even produced or implemented, allowing for correction and improvement of the design, even before the prototype is built.
For the analysis of the radial centrifugal pump, we will take as a basis a flow rate of 60 m3/h (figure 01). According to the study conducted, some small areas of recirculation and areas without water flow are noted along the empirical operation of the pump. These are areas of detachment, that is, the water detaches from the wall of the rotor with the movement of the initial mass of the fluid from the center of the rotor to its end, forming a vacuum, which is the point of lowest pressure load of the pump. These areas can be detrimental to the efficiency of the equipment. The highest velocities observed in this simulation are in the center of the volute and the lowest velocities are presented in the suction piping, where the fluid has not yet been influenced by the centrifugal force.
For the analysis of amphibious pumps, we will take as a basis the range of flows between 2000 m³/h and 2400 m³/h (figure 05). We can observe that at the beginning of the hydraulic modeling, empty spaces occurred, with higher speed at the beginning of the process and low speed until the flow was uniformized, as the initial mass moved from the center of the rotor to its tip.
Using the Computational Fluid Dynamics (CFD) technique for hydraulic modeling of the amphibious pump, it was possible to note a significant improvement in the uniformity of the flow during its operation. The empty spaces at the beginning of the operation were considerably reduced, resulting in a low variation between the initial and final speed throughout the entire process.
Comparing the design of the equipment, we observe that the conventional centrifugal pump has several points of pressure loss, through its numerous transmission components, both from the pump and the motor (Figure 06).
These components, exposed to numerous efforts throughout operation, inclement weather, pressure variation, due to different consumption demands, provide loss of alignment, heating of the pump and motor, and consequently, wear and loss of efficiency.
On the other hand, the amphibious pump was designed to minimize these problems as much as possible, presenting a low number of parts in its design, without the need for alignment, with its motor always being cooled, resulting in low maintenance and high energy efficiency (Figure 07).
The word "amphibious", of Greek origin (amphi 'both' and bio 'life'), means "double life" and defines animals that are able to live in both terrestrial and aquatic environments. Amphibious pumps are those that are able to work underwater, like submersible pumps, vertical pumps, and also capable of working outside of water, like conventional pumps, such as horizontal, bi-parted, multistage pumps, and others. This equipment can have its flange mounted inline with the piping for "booster" systems, fixed on the flange of the suspended piping. It can be installed on rafts or adapted to a wide variety of structures, such as bases, rails, and pump houses (HIGRA, 2018). The liquid enters the pump longitudinally, is driven by the rotor, passes through the diffuser, circulating the pump motor. By circulating the motor, the heat exchange is optimized, since the fluid remains in contact with the motor for a longer time, preventing its temperature from exceeding 55°C (experimental data).
CONCLUSION
According to the study presented, the conventional centrifugal pump has an initial higher speed in its operation, which is reduced over the course of the process, resulting in empty spaces that can cause efficiency problems over time. Its construction includes several components susceptible to heating, wear, and loss of alignment. These factors directly affect the speed variation and, consequently, the efficiency of the equipment over time.
On the other hand, amphibious pumps, after their start-up, present a uniformity in the flow with low speed variations until the end of their process, significantly reducing the empty spaces during the hydraulic transient. Their construction characteristics contribute to obtain a high efficiency, including low internal pressure loss and constant cooling of the motor, which helps to minimize the need for maintenance. The uniformity in the operating speed contributes to a better energy efficiency during its operation.
Although it is expected that higher flows will result in greater pressure losses and, consequently, greater problems to uniformize the operating speeds, it was found that amphibious pumps were efficient, even with different flows between the equipment. This is due to the constructive design of these pumps.
It is important to consider that each technology is developed to meet a specific need for use and that, depending on the project, one technology may be more suitable than the other. In the case of amphibious technology, its differential is to seek to meet demands for projects with specific difficulties. Therefore, it is essential to consider its use from the beginning of the studies, instead of comparing it directly to other technologies, since they are quite distinct.
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