【Daily Question: Pump Equipment】Short Answer Question 2019.3.21
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This post was last edited by 3983596_FPPZ on 2019-3-21 at 20:24. For bk14.jpg: Rules for short-answer questions: 1. If the answer is incorrect, +2 wealth for active participation; if the answer is somewhat reasonable but not specific enough, +5 wealth; if the answer is correct, +8 wealth. 2. Rewards for answers are available once per person only. 3. Each reply allows scoring for only one person. 4. The answer and its explanation will be visible after responding. 5. The reward is valid for 48 hours; no reward will be given after that period. Studying* and winning awards again; come by here every day. Briefly describe the advantages and disadvantages of centrifugal pump impellers with a large number of blades compared to those with a small number of blades Answer: 1. It affects the flow pattern between the blades; the more blades there are, the more stable the flow becomes, tending toward laminar flow, while fewer blades result in turbulent flow. Additionally, the backflow from the working surface to the back side at the blade exit increases hydraulic losses ； 2. It affects the contact area; the more blades there are, the larger the contact area between the liquid and the blades, and thus the greater the wear loss, while less wear occurs in contrast ； 3. It affects the degree of crowding at the inlet; the more blades there are, the greater the crowding at the impeller inlet, which results in a smaller flow area and a worse net positive suction head. Conversely, a better net positive suction head is achieved ； 4. It affects the connection strength; the more blades there are, the greater the strength of the connection between the front and rear covers, which is particularly suitable for high-speed pumps. Conversely, the strength is lower, making the component more prone to damage, especially due to the material used ； 5. It affects casting: a large number of blades and narrow flow channels make casting difficult, resulting in many casting defects ； 6. A larger number of blades enables more efficient work, which can slightly increase the head pressure, but the improvement is limited. In short, each type of pump has an optimal number of blades; too many or too few have negative effects.
1. It affects the flow pattern between the blades; the more blades there are, the more stable the flow becomes, tending toward laminar flow, while fewer blades result in turbulent flow. Additionally, the backflow from the working surface to the back side at the blade exits increases hydraulic losses； 2. It affects the contact area; the more blades there are, the larger the contact area between the liquid and the blades, and thus the greater the wear loss, while less wear occurs in contrast ； 3. It affects the inlet crowding factor; the more blades there are, the greater the crowding at the impeller inlet, and the smaller the area through which the fluid can pass. This leads to a worse net positive suction head, while conversely, it results in a better net positive suction head for the pump ； 4. It affects the connection strength; the more blades there are, the greater the strength of the connection between the front and rear covers, which is particularly suitable for high-speed pumps. Conversely, the strength is lower, making the component more prone to damage, especially due to the material used ； 5. It affects casting: a large number of blades and narrow flow channels make casting difficult, leading to numerous casting defects. In short, there is an optimal number of blades for each type of pump; too many or too few blades have negative effects.
For impellers with the same diameter, an increase in the number of blades leads to an increase in head, while the flow rate remains almost unchanged. Centrifugal pump impellers typically have 6 to 8 blades; for pumps used to transport liquids containing impurities, the number of blades is lower, ranging from 2 to 4. Additionally, the shape of the blades also changes significantly
Without considering flow losses, the greater the number of blades, the higher the theoretical head. This is because an impeller with a finite number of blades can deliver less energy to the liquid compared to an impeller with an infinite number of blades.
1. It affects the flow pattern between the blades; the more blades there are, the more stable the flow becomes, tending toward laminar flow, while fewer blades result in turbulent flow. Additionally, the backflow from the working surface to the back side at the blade exits increases hydraulic losses； 2. It affects the contact area; the more blades there are, the larger the contact area between the liquid and the blades, and thus the greater the wear loss, while less wear occurs in contrast ； 3. It affects the inlet crowding factor; the more blades there are, the greater the crowding at the impeller inlet, and the smaller the area through which the fluid can pass. This leads to a worse net positive suction head, while conversely, it results in a better net positive suction head for the pump ； 4. It affects the connection strength; the more blades there are, the greater the strength of the connection between the front and rear covers, which is particularly suitable for high-speed pumps. Conversely, the strength is lower, making the component more prone to damage, especially due to the material used ； 5. It affects casting: a large number of blades and narrow flow channels make casting difficult, leading to numerous casting defects. In short, there is an optimal number of blades for each type of pump; too many or too few blades have negative effects.
For impellers with the same diameter, an increase in the number of blades leads to an increase in head, while the flow rate remains almost unchanged
More leaves result in poor performance; fewer leaves lead to better cavitation resistance
Too few blades result in a relatively short blade channel, increasing its diffusivity; this in turn leads to the formation of vortices within the channel, reducing the pump’s efficiency. An excessive number of blades can cause excessive compression as the fluid flows into the impeller, increasing the friction area and thus raising hydraulic losses and reducing efficiency. It also deteriorates the cavitation performance of the impeller and causes a hump in the pump head curve.
1. It affects the flow pattern between the blades; the more blades there are, the more stable the flow becomes, tending toward laminar flow, while fewer blades result in turbulent flow. Additionally, the backflow from the working surface to the back side at the blade exits increases hydraulic losses； 2. It affects the contact area; the more blades there are, the larger the contact area between the liquid and the blades, and thus the greater the wear loss, while less wear occurs in contrast ； 3. It affects the inlet crowding factor; the more blades there are, the greater the crowding at the impeller inlet, and the smaller the area through which the fluid can pass. This leads to a worse net positive suction head, while conversely, it results in a better net positive suction head for the pump ； 4. It affects the connection strength; the more blades there are, the greater the strength of the connection between the front and rear covers, which is particularly suitable for high-speed pumps. Conversely, the strength is lower, making the component more prone to damage, especially due to the material used ； 5. It affects casting: a large number of blades and narrow flow channels make casting difficult, leading to numerous casting defects. In short, there is an optimal number of blades for each type of pump; too many or too few blades have negative effects.