P-Q curve: More significant than parameters,
The air volume and static pressure of the fan are not fixed but vary with changes in system impedance. The actual air volume and static pressure are determined by the impedance. By obtaining different air volumes under varying static pressures (impedances), a P-Q curve can be plotted to depict the relationship between static pressure (P) and air volume (Q). This curve is commonly used to describe the characteristics of a cooling fan."
The given sentence has been polished to enhance its professional expression while maintaining the original meaning: "In the provided diagram, fan A and B exhibit identical maximum static pressure and maximum air volume. However, A outperforms B as evidenced by its curve completely 'enclosing' that of B. Whether it is at the same air volume or static pressure, A consistently demonstrates superior performance compared to B. Although it is unlikely to find two such 'perfect' curves, what constitutes a better curve? Generally speaking, a larger area enclosed by the P-Q curve and both axes indicates better performance. Nevertheless, this criterion does not guarantee 100% accuracy; incorporating system impedance curves for selection and analysis would provide a more reasonable approach."
The figure above displays six curves, among which three colored lines represent characteristic curves of the three fans, while the other three dotted lines depict curves representing different system impedances (simulating the system impedances of the fans in three application scenarios: chassis fan, air-cooled radiator fan, and water-cooled exhaust fan). The intersection point between the P-Q characteristic curve of each fan and the corresponding system impedance represents its operating point. In other words, the fan will operate at a static pressure and air volume corresponding to this operating point (as static pressure is utilized to overcome impedance).
It can be observed that the cold row has the highest impedance, followed by the air-cooled radiator; meanwhile, the chassis exhibits relatively lower impedance. Amongst these scenarios, NF-F12 provides maximum static pressure while NF-S12A offers larger air volume.
So how should one choose a suitable fan? In fact, it is quite simple - on a given impedance curve, select a product with maximum air volume at its working point. Therefore, in all three scenarios mentioned above,NF-A12 proves to be an optimal choice despite not having either highest maximum air volume or best maximum static pressure. This also emphasizes that specifications alone are merely for reference purposes; instead,the P-Q characteristic curve holds greater significance when selecting a suitable fan. Fortunately,various brands provide P-Q curves for their fans.
