Precautions for Correct Use of Axial-flow Fans

Leakage Flux

Leakage flux from an Axial-flow Fan may distort the image on nearby CRT screens. Measures to prevent this problem include:

1. Keeping CRTs at least 30 cm away from the Axial-flow Fan

2. Shielding the Axial-flow Fan side with metal mesh.

The leakage flux from a Fan with metal blades is less than with plastic blades. The leakage flux distribution curves are shown below as examples.

Noise Countermeasures

The cooling effect and noise levels of Axial-flow Fans are greatly affected by the mounting conditions. Take the points listed below into account when installing the Fans.

Maintain as much clearance as possible between the Fan inlet and the cooled object. (If the cooled object occupies about the same surface area as the Fan on a flat surface, a istance of approximately 10 cm is appropriate.)

The diameter of the Fan installation hole (D₂) should be larger than the diameter of the Fan (D₁).D₁:Fan installation hole diameter D₂: Fan diameter D₁ > D₂

Cooling Effect

Avoid rapid changes in air flow direction or air-flow cross-section which reduce the cooling effect.

When installing the Fan, keep the clearance at the outlet side as small as possible. (If there is a large clearance at the outlet side,it may not be possible to obtain a sufficient cooling effect.)

Axial-flow Fan Installation

The Fan can be mounted with bolts through only one flange (singleflange mounting) or with through-bolts through both flanges (double-flange mounting). Take care not to distort the frame when using double-flange mounting.Tighten the bolts to a torque of approximately 0.44 Nm when installing the Fan.

Box Fan Installation

As shown in the figure, line the Box Fan up with the screw holes,insert it into the panel cut-out, and firmly secure it with the enclosed mounting screws and nuts.

The cover can be mounted either upward or downward. Use whichever direction is convenient.

Flow Rate and Static Pressure

The characteristic graphs provided for each of the models represent the average of actual measurement data obtained under the measurement conditions given below. They are provided as reference for determining the Fan most suitable for the type of cooling required; the actual characteristics may differ from the values represented in the graphs. The graphs are not intended to guarantee these characteristic values.

A simple explanation of the flow rate/static pressure characteristics and the methods of measuring them is given below.

Fully close the damper. Take the pressure difference between chamber B and ambient pressure (Ps). The maximum value of the pressure difference (Ps) is the maximum static pressure (Ps max).

Adjust the auxiliary blower to change the static pressure (Ps).Measure the pressure difference between chamber A and chamber B (Pd). Calculate the flow rate (Q).

Fully open the damper and adjust the auxiliary blower to set the static pressure to zero (0). Measure the pressure difference between chamber A and chamber B (Pd). Take the flow rate (Q) calculated at this point as the maximum flow rate (Q max).

Fan Operating Point:

A Fan installed in equipment operates near the point where the Fan characteristic curve crosses the system impedance curve.

Note: The maximum flow rate and maximum static pressure do not indicate the Fan operating point when it is installed in equipment. However, these characteristics are important for comparing Fan performances and for selecting Fans.

Measurement Conditions

Flow Rate Measurement Device

Flow Rate/Static Pressure Characteristic Model

Selecting a Fan

Procedure

1.Estimate the amount of heat generated (W) inside the Unit.

2.Set the maximum permitted temperature rise limit (ΔT) inside the Unit.

T1: Temperature of the inlet air (°C).
T2: Temperature of the outlet air (°C).

3.Calculate the required flow rate.

4.Estimate the system impedance from the air flow through the Unit or from previous data.

5.Select the Fan according to the P - Q characteristics.

6.Measure the temperature rise in an installed Unit.

7.Reappraise the Fan if the measured cooling effect is insufficient.

The procedure to select a Fan is described above. It is difficult, however, to obtain the actual system impedance.
In general, therefore, select a Fan with a maximum flow rate of from 1.3 to 2 times the flow rate required.

As a rough guide, 1.3 times for a small system impedance, 1.5 times for medium, and 2 times for large.

Reconsider the Fan if the cooling effect is insufficient after the selected fan has been installed in the Unit and the temperature rise has been measured.

Serial and Parallel Fan Operation

The characteristics of two identical Fans operated in series or parallel are determined as shown in the following diagrams.

Serial Operation:

Noise Measurements

The following two methods are available for measuring Fan noise. These are used interchangeably by Fan manufacturers so that the measurement method is not standardized.

JIS B 8330: Testing and Inspection Methods for Fans
JIS C 9603: Extractor Fans

OMRON conducts testing according to JIS (Japan Industrial Standard) C 9603 because of the small size and low noise levels of the Fans and because of their similarity in shape to extractor fans. This standard prescribes that the noise be measured at a distance of 1.5 m (A characteristics) from the side of the Fan.