In medium and low head cooling pumps, there is a close quantitative relationship between flow and head, which can generally be described by the pump performance curve and related formulas.
From the perspective of the pump performance curve, the flow-head curve (Q-H curve) is the most intuitive reflection of the relationship between the two. For medium and low head cooling pumps, usually, as the flow increases, the head will gradually decrease, showing an inverse proportional change trend. This is because the working principle of cooling pumps is mostly based on centrifugal force. When the flow increases, the flow rate of the liquid in the pump increases, and the flow resistance of the fluid in the impeller and pump casing also increases accordingly, so that the energy obtained by the liquid has more losses in the process of overcoming the resistance, resulting in a decrease in head. For example, when the flow of the cooling pump increases from 50% of the design flow to 100%, the head may drop from 80% of the rated head to about 60%.
From the theoretical formula, under ideal conditions, the head and flow of the pump conform to the similarity law. For the same medium and low head cooling pump, when the speed remains unchanged, the relationship between flow and head can be approximately expressed by the following formula: H1/H2 = (Q1/Q2)², where H1 and H2 are the heads corresponding to two different flow rates Q1 and Q2 respectively. However, it should be noted that this is a formula under the ideal condition of no energy loss. The actual medium and low head cooling pump will be affected by various factors during operation, such as fluid viscosity, friction loss in the pump, impeller wear, pipeline resistance, etc.
In practical applications, accurately grasping the quantitative relationship between the flow and head of the medium and low head cooling pump is crucial for pump selection, system design and operation optimization. Engineers can reasonably select cooling pumps based on the required cooling flow and the resistance to be overcome (i.e. head), and adjust the flow during operation to meet the cooling needs under different working conditions, while avoiding the pump from operating in the inefficient or overloaded area to extend the service life of the pump.
