What is the correlation between the air pressure and ventilation resistance of a cooling fan?

Has the device encountered such an awkward situation when using a cooling fan

Despite being equipped with a high air volume fan, the temperature of the equipment remains high?

The fan rotates vigorously, but there is almost no wind at the air outlet;

The equipment eventually experienced overheating, crashes, and even burnout Wait a minute.

What are the reasons for the above situation?

Actually, it may not be that the fan is broken, but that the wrong air pressure was selected.

1. What is wind pressure

Wind pressure refers to the pressure difference generated by a fan during operation, which is the driving force behind the flow of air.

High wind pressure=strong fan thrust, capable of blowing through channels with high resistance;

Low wind pressure means that the fan can only freely ventilate in open environments and will 'deflate' when encountering resistance.

2. What is ventilation resistance?

Ventilation resistance refers to the resistance generated by various obstacles encountered by air during the flow process, including friction on pipeline walls, obstacles on bends, and obstacles on filters.

The wind pressure generated by the fan needs to overcome ventilation resistance in order to allow air to flow smoothly and achieve the purpose of heat dissipation.

If the wind pressure is insufficient, the air cannot overcome the ventilation resistance, resulting in a decrease in air flow and poor heat dissipation effect.

If your system has narrow air ducts, many bends, and dense filters, the resistance will naturally be high;

At this point, the fan must have higher air pressure to 'push' the air.

3. The air pressure and ventilation resistance of a cooling fan are interrelated and mutually influential

Ventilation resistance affects wind pressure demand: The greater the ventilation resistance, the higher the wind pressure that the fan needs to generate in order to ensure sufficient air flow through the cooling system.

For example, when the air ducts in the cooling system are long, there are many bends, or dense filters are installed, the ventilation resistance will significantly increase. At this time, it is necessary to choose a high-pressure fan to ensure good cooling effect.

On the contrary, if the ventilation resistance is small, a fan with lower air pressure may be able to meet the requirements.

Mutual constraints determine system performance: In actual heat dissipation system design, wind pressure and ventilation resistance need to be matched with each other. If the wind pressure of the fan is too high and the ventilation resistance is low, it may cause the air flow rate to be too fast, resulting in loud noise and energy waste. On the contrary, if the wind pressure is too low to overcome ventilation resistance, it will result in insufficient air flow and unsatisfactory heat dissipation effect.

Therefore, it is necessary to achieve a balance between air pressure and ventilation resistance through reasonable design of heat dissipation ducts, selection of suitable fans, and other measures, in order to achieve efficient and stable operation of the heat dissipation system.

4. Will the relationship between wind pressure and ventilation resistance be affected by environmental temperature?

The answer is affirmative. The relationship between wind pressure and ventilation resistance will be affected by the ambient temperature, as follows:

The impact on air density: Changes in ambient temperature can cause changes in air density. According to the ideal gas state equation \ (PV=nRT \) (where P is pressure, V is volume, n is the amount of substance, R is a universal gas constant, and T is thermodynamic temperature), at a certain pressure, as the temperature increases, the volume of air expands and the density decreases; The temperature decreases and the air density increases. The air density is related to both air pressure and ventilation resistance. The air pressure generated by a fan is directly proportional to the air density. Under constant conditions such as fan speed, the higher the air density, the greater the air pressure. And ventilation resistance is also related to air density. The higher the air density, the greater the ventilation resistance, because air molecules with higher density collide more frequently with the surface of objects.

So, when the ambient temperature changes, the air density changes, which in turn affects both wind pressure and ventilation resistance, causing a change in their relationship. For example, in a high-temperature environment, as the air density decreases, the wind pressure generated by the fan will decrease, and the ventilation resistance will also decrease, but the magnitude of the decrease may vary, which will change the balance between wind pressure and ventilation resistance.

The impact on thermal expansion of objects: Changes in ambient temperature can also cause thermal expansion or contraction of objects in the cooling system. For example, the material of the heat dissipation duct may expand due to temperature rise, causing changes in the shape and size of the duct. If the air duct expands and becomes more spacious, the ventilation resistance may decrease;

On the contrary, if the deformation of the air duct leads to local narrowing, the ventilation resistance will increase. And the components of the fan itself may also affect its performance due to thermal expansion, thereby affecting the air pressure. For example, the blades of a fan may change shape or angle due to thermal expansion, causing a change in the wind pressure generated by the fan at the same speed. In this way, the ambient temperature indirectly changes the magnitude and relationship between wind pressure and ventilation resistance by affecting the thermal expansion of objects.

The impact on air viscosity: As the temperature increases, the viscosity of the air will increase. An increase in viscosity means an increase in the internal friction between air molecules, which increases the resistance that air experiences during flow, i.e., an increase in ventilation resistance. In this situation, the fan pressure needs to be increased accordingly to maintain the same air flow and overcome the increased ventilation resistance. So, environmental temperature affects the relationship between wind pressure and ventilation resistance by changing air viscosity.

5. Important scenarios that require attention to 'wind pressure'

High density heat sinks or filters are used for air supply;

The space inside the chassis is enclosed and there are few ventilation holes;

Ventilation for equipment with long pipes, corners, and partitions;

Medical equipment, industrial power supplies, laser modules, LED drivers, and other "windless" systems.

Capital Technology Co., Limited is the chief agent of SANYO DENKI, one of the leading enterprises of the cooling fan industry. We are a factory who also have our own independent brand CAPITAL product series. The main products are cooling fan, DC/AC fan, radiator, filter, reactor etc. We can provide customer with the most professional and perfect technical support, welcome to contact me at anytime at rainlee@szcpt.com.