Is the air volume the same for the forward-curved and backward-curved blades of a centrifugal fan?
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When disassembling and cleaning the heater cooling fan on site, the direction was not taken into account, which led to problems during installation; the bending direction of the blades was sometimes the same as that of the impeller’s rotation direction, and other times it was opposite. Current measurements taken on site showed little difference. Under such circumstances, can it be concluded that the effect of forward-bending and backward-bending blades on air volume is minimal? According to the Euler equation for blades, the only thing that changes is the total pressure at the same flow rate... PS. For small fans with short, straight blades that are welded in just one direction, the rated current is only 4.5A
The blades of centrifugal fans can be classified into three types based on the size of their outlet installation angle: backward curved, forward curved, and radial. The curvature direction of the backward-curving blades is opposite to the rotation direction of the impeller, and the outlet installation angle is less than 90 degrees ； The exit direction of the radial blades is radial, and the exit installation angle is 90 degrees ； In the forward-curved blade type, the blade bends in the same direction as the rotation of the impeller, and the outlet installation angle is greater than 90 degrees. Under identical other conditions, forward-curved blades generate a higher total pressure head compared to radial and backward-curved blades; however, their dynamic pressure head accounts for a larger proportion of the total pressure head, resulting in greater energy loss in the flow channel and lower efficiency. Blades with a backward curvature produce a lower total pressure head, but the static pressure head accounts for a larger proportion of this total head; as a result, energy loss in the flow channel is low and efficiency is high. Therefore, rear-curved blades are commonly used in boiler fans.
Forward-curved blades generate a higher total pressure head compared to radially curved or backward-curved blades, but their dynamic pressure head accounts for a larger proportion of the total pressure head; as a result, there is greater energy loss in the flow channel and the efficiency is lower. Blades with a backward curvature produce a lower total pressure head, but the static pressure head accounts for a larger proportion of this total head; as a result, energy loss in the flow channel is low and efficiency is high. Therefore, rear-curved blades are commonly used in boiler fans.
Even if the current and so on are the same, the air volume will differ; conversely, installing it in the opposite direction should reduce the air volume.
I can’t figure out whether it should be a forward curve or a backward curve – TvT. Since it’s a ventilator with low power and low pressure, the books state that a forward curve is generally used for low-pressure ventilators. I’m at a loss; for now I’ve installed them all with a forward curve, and the air volume shouldn’t differ much. So I don’t understand what determines the air volume in this situation...
Rear curved blade: high efficiency, low pressing head； Radial: Moderate efficiency, moderate head pressure ； Forward curved blade: low efficiency, high pressure head ； Impeller diameter: The larger the diameter, the greater the head pressure ； Impeller width: The wider the impeller, the greater the air volume ；
Did you install the impeller incorrectly? You can check the fan’s nameplate to find out whether it is forward-curved or backward-curved; this has an impact on performance, and getting it wrong can easily lead to motor damage
The last edit to this post was made by shenconan on 2015-10-21 at 15:19. It’s the cooling fan for the tank heating element… There is no name plate on it; OJZ. All I could find was the motor’s name plate. It’s 5.5 kw. I tried both ways of installing it, and the current level remained similar – around 2.9–3A, even when operating at its rated capacity of 4A. It shouldn’t burn out the motor
Then check the temperature of the heater; if it’s also within the normal range, there’s no problem
It’s completely the opposite. Blades with a forward curvature result in a low pressure head but high flow rate, while blades with a backward curvature use centrifugal force to increase the dynamic pressure head of the gas.