Axial flow pumps are good at transferring fluids quickly and in large quantities, especially in situations where low head and high flow are required. Therefore, axial flow pumps are widely used in many industrial fields such as water treatment, irrigation and power generation.

Key Design Points

When designing an axial flow pump, you need to carefully balance several key factors to ensure that the pump can achieve optimal working conditions. The first consideration is flow rate, which is the total amount of fluid that the pump can handle per second or minute. Next is head, which reflects the maximum height the pump can lift the fluid to or the amount of pressure it can generate. In addition, the efficiency of the pump cannot be ignored. It directly reflects the pump's ability to convert input mechanical energy into hydraulic energy and is the core indicator for measuring the performance of the pump.The size and operating conditions of the pump directly determine the power required.

Net positive suction head (NPSH) is a critical parameter that is essential to prevent cavitation, which can cause serious damage to the pump. To ensure stable operation of the pump, we usually ensure that the actual NPSH value is higher than the required NPSH value of the pump. In addition, the overall geometry and performance characteristics of the pump are affected by its specific speed.

Three-Dimensional Characteristics Of The Flow Field

A comprehensive understanding of the three-dimensional characteristics of the flow field is crucial for optimizing the design of axial flow pumps. The fluid flow of axial flow pumps is extremely complex and exhibits a high degree of three-dimensional characteristics, especially in the diffuser and impeller areas, where the flow rate and pressure change dramatically.

The primary fluid flow of an axial flow pump remains parallel to the pump axis. However, secondary flows such as hub angle separation, tip leakage vortex, etc. can affect the performance of the pump. These secondary flows arise from the complex interaction between the fluid and the key components of the pump, such as the impeller blades, hub and pump casing.

Computational fluid dynamics (CFD) has become a key means of studying complex fluid flow patterns. Through CFD simulation, the flow field is predicted and optimized to identify areas where there may be inefficiencies or cavitation risks. Based on the three-dimensional flow characteristics, designers can better design blade shapes, impeller structures, and diffuser configurations to achieve the best results in improving pump efficiency and performance.

Pump Specific Speed

Pump specific speed is a dimensionless parameter that relates the pump's rotational speed to its flow rate and head.The specific speed is calculated using the formula:

Ns = (N * Q^0.5) / H^0.75

Where:

Ns = Specific speed

N = Rotational speed (rpm)

Q = Flow rate at best efficiency point (m³/s)

H = Head at best efficiency point (m)

Axial flow pumps often have specific speeds in excess of 10,000 (by U.S. standards). High specific speeds allow them to efficiently handle large flows at low heads. If designers understand the relationship between specific speed and pump performance, they can optimize pump geometry for specific needs.

As specific speed increases, the impeller diameter decreases relative to the flow path, while the blade angles become more gradual. This geometry is a hallmark of axial flow pumps, allowing them to efficiently handle large volumes of fluid at low heads.

Blades

The performance of an axial flow pump is greatly affected by the design of its impeller blades. Several factors need to be considered in blade design, such as the number of blades, thickness, and the angle of installation relative to the hub.

Number of Blades

As for the number of blades, axial flow pump impellers are usually equipped with three to six blades. When choosing the number of blades, a balance needs to be found between performance and manufacturing difficulty. More blades can improve flow guidance and reduce slip, thereby improving efficiency. However, too many blades increase manufacturing difficulty and may increase friction losses. When handling fluids containing suspended matter or debris, fewer blades can ensure a smoother flow path, but may affect production. Therefore, the optimal number of blades needs to be determined based on specific application requirements, flow rate, and speed.

Blade Thickness

The thickness of the blades affects the structural strength and hydraulic performance of the axial flow pump. Generally speaking, thicker blade designs help improve hydraulic efficiency and reduce energy losses caused by flow resistance and friction. In addition, the blades must be of sufficient thickness to withstand the impact of hydraulic pressure and possible debris in the fluid. The thickness of the blades is not uniform, but varies along their length: the tip of the blade is the thinnest, while the area close to the hub is the thickest. The purpose of this design is to provide the necessary structural support. Modern manufacturing technologies, such as CNC machining and investment casting, can accurately control the thickness distribution of the blades, thereby ensuring the performance and durability of the pump to the best state.

Blade-to-hub mounting angle

The angle at which the blades are tilted relative to the hub, called the blade stagger angle, is a core element in designing pump performance. This angle is related to the interaction between the blade and the fluid and the energy transfer efficiency of the pump. In the design, the installation angle of the blade is not fixed, but is flexibly adjusted according to the length of the blade: the angle is steep near the hub and gradually transitions to the tip of the blade. The design is intended to adapt to the velocity differences of the fluid at various radial points, and by precisely adjusting the blade angle, the pump can achieve the expected head and flow standards while effectively managing energy losses and preventing cavitation. In addition, using the latest technology in pitch and sweep design, we can further optimize the blade shape, improve work efficiency, and reduce the occurrence of secondary flow.

Pump casing

The core component of an axial flow pump is the pump casing, which not only contains the pressurized fluid, but also supports the internal components and guides the fluid flow. The pump casing design has a significant impact on the efficiency and overall performance of the pump. The diffuser, as part of the pump casing, is located behind the impeller and gradually expands, a typical feature of axial flow pumps, which can convert the kinetic energy of the impeller into pressure energy and improve the overall efficiency of the pump.

The finish of the inner surface of the pump casing is crucial to reducing friction losses. Smooth surfaces improve flow characteristics and reduce turbulence. When designing the pump casing, it is also necessary to consider its ability to withstand the working pressure and the potential impact of water hammer, while taking into account the convenience of assembly and maintenance.

Axial Flow Pump Manufacturer

Tianjin Kairun, a leader in the pump manufacturing industry, adheres to the bottom line of quality and performs strict quality inspections on each pump to ensure perfection. From material selection to finished products, every step has been carefully considered to create durable and high-performance pumps.

Welcome to contact us by email at catherine@kairunpump.com.

References

1. Gülich, J. F. (2014). Centrifugal Pumps. Springer-Verlag Berlin Heidelberg.

2. Karassik, I. J., Messina, J. P., Cooper, P., & Heald, C. C. (2008). Pump Handbook. McGraw-Hill Education.

3. Tuzson, J. (2000). Centrifugal Pump Design. John Wiley & Sons.

4. Brennen, C. E. (2011). Hydrodynamics of Pumps. Cambridge University Press.

5. Sulzer Pumps. (2010). Centrifugal Pump Handbook. Elsevier.