Centrafugal pump coeficients question

[woops]

Hi everyone. I am having a slight issue with part of a question regarding an experiment that i had to do as part of my course. Basically we were calculating the coeficients and characteristics of a basic centrafugal pump. We used the pump to pump water round a simple system and recorded the values for input power, flow rate and discharge pressure while varying the apiture of a valve to control flow rate but kept the pump speed constant. We took 8 different readings each at a different valve setting and then repeated the experiment 3 times each with a different pump speed.

From the results we calculated the head coefficient and flow rate coefficient and plotted them against each other for each of the 4 speeds. It was found that the head coefficient against flow rate coefficient was dependant on pump speed and decreased with increasing pump speed. We were then asked to explain why this has happened as opposed to them being independent of pump speed as should be the case. The only explanation i can think of is that at higher pump speeds there is a higher pressure in the system which causes an increase in head loss due to friction on the pipe walls hence a reduction in the flow rate which results in a lower than expected value for flow coefficient at higher pump speeds.

Im not sure if I am on the correct lines and simply can’t think of what else could account for these experimental findings. I really need some help with this as i have been going round in circles for hours now and simply don’t know what else to do. Please help

 

[Valkarie]

.One possible explanation is that the increased pump speed causes an increase in turbulence, which can lead to higher head loss due to friction. This means that more energy is lost when the fluid passes through the pipe, leading to a lower flow coefficient at higher pump speeds. Another factor that could be influencing the results is cavitation. When the pump speed increases, the pressure in the system drops below vapour pressure, leading to the formation of vapour bubbles. These bubbles can create additional turbulence and reduce the efficiency of the pump, resulting in a reduced flow coefficient.