fan blades affect fan air volume.
Blade number of cooling fan have related relationship with blade space. The more leaf number, leaf spacing is less, which will appear disturbing between each blade expect growing friction,along with growing turbulent flow,space for each blade will affect the Pneumatic sex and noise of fan,small space each leaf will increasing the friction chance of blade surface,thus lead to low efficiency,when space is too big,relative blade spacing is too large, produce the separation phenomenon of pressure loss is bigger.
performance influence of blade number & impeller mainly shows as below:
1. blade number too little, divergence Angle increases, lead to high pressure gradient, boundary layer thickening, makes a cooling fan efficiency decline.
2.leaf number increased, single blade load down, reduced deviation of the impeller outlet flow Angle, under other conditions being the same slip coefficient increases, the energy coefficient increase accordingly.
3. blade number is overmuch, increase air flow friction loss, cause the clogging in port imported, which resulted in the reduction efficiency of the cooling fan.
Then what is the best leaf number? For example one test,original model of five blades, rotating speed is 3000 RPM, by changing the number of the blade to make analysis of the effect of blade number on the fan performance.By compare the effect of 4, 5, 6, 7 blades , through the experiment, we can see that for each type of fan is with the increase of flow rate, efficiency is the trend of increase to decreases.When the flow rate is less than 0.006 cubic meters per second, blade for 5 and 6 of the two cooling fans, compared with other two kinds of model is high, this is because the blade number is less, less flow of gas, fan total pressure is low, thus lead to low efficiency, when the number of leaves increased, intensify the generation of eddy current.Cause blade lift coefficient decreased, flow loss increases rapidly, making the flow passage efficiency decline.
When the flow rate is between 0.006 to 0.008 cubic meters per second,a few cooling fan model’s efficiency is very close, so in this small flow rate the static characteristics of leaf number of 7 is the best.When the flow rate is greater than 0.008 cubic meters per second, on the contrary, the leaf number 7 and 4 more efficiency than 5 and 6,that is becasue the efficiency is related with the total pressure in the flow, 7 and 4 of the total pressure is higher, so the efficiency is high.
Thus we can make a conclusion: when flow is large the 7 leaf number has the best fan performance.
