Common FRQ for axial fans and cross-flow fans

1. What is a cross-flow fan?

The main feature of a cross-flow fan is that the fluid passes through the fan impeller twice, flowing radially in and then radially out, with the intake and exhaust directions in the same plane, resulting in a uniform distribution of the exhaust gas along the width of the fan. Due to its simple structure, small size, and high dynamic pressure coefficient, it achieves a longer distance and is widely used in fitness equipment, air conditioning, air curtain devices, air purifiers, hair dryers, household appliances, and smart clothes drying racks.

Features:

(1) Under the same working conditions, the higher the speed, the more likely it is to experience surge, and the surge cycle is also longer. When surge occurs, the readings at high speed are stable but lower than expected, resulting in a heavy noise inside the fan; when the speed decreases, the readings become unstable and vary greatly, with the fan first 'surging' and then 'vibrating' within the same cycle, alternating thereafter. The 'vibration' phenomenon is characterized by a significant increase in readings, intensified belt shaking, and increased vibration of the test system, with noise changing from dull to sharp.

(2) Under the same speed but different working conditions, the smaller the resistance, i.e., the larger the ventilation area, the more likely surge phenomena will occur.

(3) Under the same suitable working conditions, when surge occurs at high speed, the actual value deviates significantly from the ideal normal value, while the difference compared to the stable value at low speed is not large.

2. What are the differences in gas flow direction between centrifugal fans, axial fans, and cross-flow fans?

In terms of gas flow direction, centrifugal fans draw air axially and exhaust radially, axial fans draw and exhaust air axially, while cross-flow fans draw and exhaust air radially.

3. Is there a difference between a cross-flow fan and a through-flow fan?

A through-flow fan is also called a cross-flow fan, so they refer to the same thing, just different names!

The through-flow fan, also known as a cross-flow fan, was first proposed by French engineer Mortier in 1892. The impeller is multi-blade and cylindrical, featuring forward multi-wing blades. Its structure is shown in the right diagram. When the impeller rotates, the airflow enters the blade grid from the open side of the impeller, passes through the inside of the impeller, and is discharged from the other side of the blade grid into the volute, forming a working airflow. The flow of air within the impeller is quite complex, and the airflow velocity field is unsteady, with a vortex present, centered near the tongue of the volute. The presence of the vortex causes a circulating flow at the output end of the impeller; outside the vortex, the airflow streamlines within the impeller are arc-shaped. Therefore, the flow velocity at various points on the outer circumference of the impeller is inconsistent; the closer to the vortex center, the higher the speed, and the closer to the volute, the lower the speed. At the fan outlet, the airflow velocity and pressure are not uniform, thus the flow coefficient and pressure coefficient of the fan are average values. The position of the vortex significantly affects the performance of the cross-flow fan; if the vortex center is close to the inner circumference of the impeller and near the tongue, the fan performs better; if the vortex center is far from the tongue, the area of circulating flow increases, reducing fan efficiency and increasing flow instability.

4. Where are cross-flow fans generally used? In what situations would a cross-flow fan be needed?

The cross-flow fan, also known as a through-flow fan, has the main feature of a cylindrical impeller, where the airflow enters the impeller from one side of the rotor through the blade grid, then passes through the inside of the impeller and is discharged from the other side of the rotor, with the airflow direction always perpendicular to the rotor axis. The intake and exhaust airflow is organized uniformly over a large return air plane, maintaining high efficiency even at low power, with low noise. Therefore, it is particularly suitable for small space return air situations. Due to the slender and long structural characteristics of the cross-flow fan, a single cross-flow fan can perform the functions of multiple axial or centrifugal fans, making it suitable for installation in various flat, elongated, or compact refrigeration and air conditioning equipment, such as cold air machines, air conditioners, and warm air machines.

5. What is the difference between a capacitor-type cross-flow fan and a shaded-pole cross-flow fan?

Capacitor-type motors use the phase-shifted current from the capacitor and the power supply voltage to achieve phase operation. Shaded-pole motors use a short-circuit ring to surround part of the magnetic pole area on the main magnetic pole as a mechanism for phase starting. If the power is the same, the only difference is the starting method; shaded-pole motors are generally less efficient and are typically used only for low power.

6. Is the noise from a through-flow fan very loud? What are the reasons?

There are several reasons:

(1) Dust accumulation on the through-flow impeller;

(2) The through-flow impeller hitting the casing;

(3) Wear of the through-flow motor bearings.

7. Can a dirty through-flow fan cause the blades to break?

A poor operating environment for the through-flow fan, with excessive dust accumulation, can affect the fan speed, reduce its lifespan, and cause the motor to overheat. It should be cleaned in a timely manner.

8. What are the common reasons for a cross-flow fan in an elevator control cabinet not to rotate?

Common reasons include:

(1) A thermal resistor controls the fan; when the temperature reaches a certain level, the fan does not rotate;

(2) Without a thermal resistor, the fan operates when the elevator is running, but generally does not rotate when the elevator stops;

(3) The wiring of the cross-flow fan has come loose;

(4) Excessive dust accumulation on the cross-flow fan, causing damage to the fan.