When centrifugal booster irrigation vortex pumps have insufficient NPSH, optimizing the impeller design to reduce cavitation risk requires a comprehensive approach encompassing flow field control, structural optimization, and material reinforcement.
For flow field control, geometric parameter adjustments are necessary to minimize pressure drop caused by fluid acceleration. The impeller inlet shape is crucial. Increasing the impeller inlet area can reduce flow velocity, but excessive suction speed should be avoided, which can lead to inlet backflow. Thinning the back of the blade head improves inlet displacement, allowing fluid to enter the impeller more smoothly and reducing local pressure drop. A swept-back blade inlet edge allows the hub-side liquid to be exposed to the blades earlier, increasing pressure and delaying cavitation. Furthermore, the blade inlet edge is extended and tilted, creating a spatially distorted shape. This aligns the relative flow angle at each point with the flow conditions, minimizing impact losses and reducing cavitation risk.
For structural optimization, a balance must be struck between impeller performance and cavitation resistance. Using a double-suction impeller increases inlet flow, reduces inlet velocity, and minimizes bubble generation. An inducer is installed at the front end of the impeller. Its spiral structure pre-increases pressure on the liquid flow, increasing the flow pressure, reducing low-pressure areas, and mitigating the risk of cavitation. Care should also be taken when selecting the number of blades. Excessive blades reduce the flow area, increase flow velocity and friction losses, and worsen cavitation performance. Centrifugal booster irrigation vortex pumps typically use 5 to 7 blades. A combination of long and short blades improves pump efficiency, effectively prevents the development of wake flow, and reduces the risk of cavitation. Twisted blades offer higher efficiency near the pump's design operating point and in high flow rates than rounded blades, resulting in higher dead-point head and improved cavitation resistance.
For material reinforcement, the impeller should be constructed from high-strength, high-hardness, and high-wear-resistance materials. Dense, cavitation-resistant materials such as copper alloy and stainless steel can extend impeller life. Impellers welded from rolled steel plates offer greater cavitation resistance than cast impellers. Non-metallic coatings such as epoxy, nylon, and polyurethane can also be used to improve the impeller's surface finish, reduce drag losses, and mitigate the risk of cavitation.
In addition, the overall operating conditions of the pump must be considered. Properly control the pump flow rate to avoid operating beyond the rated flow rate to prevent localized pressure drops that increase the risk of cavitation. Maintain a suitable liquid temperature, using a cooling system to control the liquid temperature, to avoid excessive temperatures that increase vapor pressure and reduce the risk of cavitation. Optimize the piping system design by reducing the length and diameter of the suction pipe, reducing unnecessary valves and elbows, and reducing suction line losses. This increases the liquid pressure upstream of the pump and reduces the likelihood of cavitation.
