How do you determine which air delivery method a cooling fan uses?
Category:
Industry Trends
Release time:
2020-11-30
An axial-flow fan, or simply a fan, is a type of fan in which the blades propel air to flow in the same direction as the shaft during operation.
This classification method, which categorizes blades based on the direction in which they propel air relative to the axis, can... Cooling fan They are classified as follows: axial-flow fans, centrifugal fans (where air intake is along the axis but air discharge is perpendicular to the axis), cross-flow (or tangential-flow) fans (in which both air intake and discharge are perpendicular to the axis), and mixed-flow fans (where air intake is along the axis, but air discharge occurs diagonally—both along the axis and perpendicular to it).
Axial-flow fans—this is the common air-delivery configuration for fans. The most widely used form involves axial-flow fans that blow air downward. This design has become so popular because it offers excellent overall performance at a low cost. In addition, there’s also a growing trend of reversing the direction of axial-flow fans to create an upward-exhausting airflow configuration.
The difference between the two ventilation modes lies in the distinct airflow patterns: during blow-in, turbulent flow is generated, resulting in high wind pressure but greater susceptibility to resistance losses; during pull-in, laminar flow is produced, offering lower wind pressure but more stable airflow. Theoretically, turbulent flow has much higher heat-transfer efficiency than laminar flow, which is why it has become the mainstream design approach. However, in certain fin designs—such as those with excessively close fins—airflow can be significantly obstructed by the fins themselves. In such cases, using pull-in ventilation may yield better performance.
How do we determine which ventilation method to use? When heat within the equipment is relatively dispersed and evenly distributed, and the air resistance on the cooling surfaces is relatively low, exhaust ventilation is typically employed. On the other hand, when heat distribution within the equipment is uneven, air resistance is high, and there are many components, blow-through ventilation is usually preferred. If necessary, fans can be connected in series (to increase air pressure), in parallel (to boost airflow), or in a combination of both.
A cross-flow fan is also known as a through-flow fan—so they refer to the same thing, just with different names!
The cross-flow fan, also known as the transverse-flow fan, was proposed in 1892 by the French engineer Mottier. Its impeller features multiple blades arranged in a long, cylindrical shape with numerous forward-leaning blades at the front. As the impeller rotates, air flows into the blade passage through the impeller’s opening, passes through the interior of the impeller, and is discharged from the opposite side of the blade passage into the volute, thereby forming the working airflow. The flow within the impeller is highly complex and characterized by an unstable velocity field. Inside the impeller, a vortex forms, centered near the tongue of the volute. The presence of this vortex induces circulating flow at the impeller’s outlet. Outside the vortex, the streamlines within the impeller take on an arc-shaped configuration. Consequently, the velocities at various points along the outer periphery of the impeller are not uniform. The closer one gets to the center of the vortex, the higher the velocity; conversely, the closer one is to the volute wall, the lower the velocity.
The velocity and pressure of the air flow at the fan outlet are uneven; therefore, both the flow coefficient and the pressure coefficient of the fan are averaged values. The location of the vortex significantly affects the performance of a cross-flow fan. When the vortex is positioned closer to the inner circumference of the impeller and near the volute tongue, the fan exhibits better performance. Conversely, when the vortex is located farther from the volute tongue, the area of circulating flow increases, leading to reduced fan efficiency and increased flow instability.
The above are the other categories of fans. For more details and information, please visit our company’s website!
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