The change in the conveying medium involves two main aspects: first, the variation in the density of the medium. When the density of the fluid being pumped differs from that of water at normal temperature, the pump’s head, flow rate, and efficiency remain essentially unchanged. However, the power required by the pump shaft will vary depending on the density of the liquid.
Second, the effect of viscous liquids on pump performance is significant. The viscosity of the liquid has a major impact on the pump's operation, influenced by factors such as the pump's internal structure, impeller design, and surface roughness. As the viscosity increases, the Reynolds number decreases, leading to higher hydraulic friction losses. This results in reduced head and flow rate, causing the Q-H curve to shift downward (although the shut-off head remains relatively constant). Additionally, increased friction leads to higher shaft power consumption, which drastically lowers pump efficiency and may increase the net positive suction head required (NPSHr).
When the viscosity of the liquid exceeds 20 mPa·s, it becomes necessary to adjust or convert the pump’s performance characteristics to ensure accurate and efficient operation. Understanding these effects is crucial for selecting the right pump and optimizing its performance under varying fluid conditions.
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