Why Does Choking Off Airflow to a Fan Damange the Motor

Do you know how to use up this graph?

Siamese to a motor's speed-torque curve, this graph is how manufacturers show the performance of their fans, and where the air flow and unchanging pressure specifications come from.

For any customers, this may wait completely foreign.  Many an customers I've dealt with in my past animation as a technical support engineer selected fans based on dimensions and air flow.  Withal, a deeper understanding is necessary to determine how the winnow will in reality perform in a real life scenario.

Therein post, I will follow discussing the definitions of air flow vs electricity pressure, the relationship between them, and the grandness of impedance.

Airflow vs Static Pressure level

In the above fan specifications table, "Goop. Airflow" and "Max. Still Pressure" are listed as specifications.

Flow of air is the volume of air that is produced by the fan metric past time.  In that case, the air flow of a fan is measured in isometric meters per minute (m³/min) in metric function units, operating room cubic feet per little (CFM) in imperial units.  In simplest terms, if you accept a 5 foot x 5 ft x 5 foot enclosure, and a fan that produces 5 CFM, it will likely take 25 minutes for the fan to air out the calefactory air in the enclosure.  (In actuality, it's non that easy.)

Static blackmail is the amount of air pressure that can be produced by the sports fan in an enclosure.  In this case, the static insistence is measured in Pascals (Pa), or inches of water (inH ₂ O).  The pascal (Pa) is the SI derived unit of pressure exploited to measure internal imperativeness, punctuate...etc.  The unit is named after Blaise Pa and is defined as single Isaac Newton per square meter.  Inches of water (isoniazid₂O) is characterized as the pressure exerted by a column of water of 1 inch in height at defined conditions.  At a temperature of 4 °C (39.2 °F) stark piddle has its highest density (1000 kg/m³). At that temperature and the standard quickening of gravity, 1 inH₂O is approximately 249.082 pascals.

It's important to get laid that level though maximum values for airflow and static pressure are specified, the lover will not output some upper limit values simultaneously.

The family relationship between airflow and atmospherics pressure of a fan is shown in the graph above. A you can see, air flow and static pressure have a indirect correlation.  When transmit flow increases, static pressure decreases; and when static pressure increases, flow of air decreases.  The 3 points depict possible scenarios where the fan will perform.

To visualize the 3 scenarios, you may have to imagine an electronics enclosure being ventilated by the fan. Refer to the graph to a higher place with the 3 designated points 1), 2), and 3).

In example 1), we have an enclosure that is all open on one end.  There is nothing that obstructs the air be due the fan, and all air flow rate is expelled retired the other destruction.  This example creates a scenario where maximum air flow would take plac, and we have zero static pressure.

In example 2), we have an enclosure that is enclosed except with a small exhaust hole, or air outlet, on the other oddment.  The size of it of the exhaust hole out is smaller than the airwave intake hole, which hinders air menses.  The constant build-up of air inside the enclosure not beingness able to escape increases the static pressure inside.  This creates a scenario where bare flow is limited away the increased unchangeable pressure.  The air flow bequeath represent less than its uttermost value.

In deterrent example 3), the enclosure is totally closed.  In this scenario, the airflow artesian into the enclosing causes the unmoving blackjack to rise since there's nary spot for the broadcast to escape.  Once the static pressing specification has been exceeded, even if the lover continues to operate, the high static pressure level will not let whatever more air in.  In other words, the maximum static hale has been reached, and air flow volume drops to null.

In real life, examples 1) and 3) are not realistic.  In a practical example of ventilating an electronics enclosure, almost fans would perform close to example 2). However, in order to farm the graph, a similar method is exploited (also known A the double chamber method acting).

Installation Density

OK at present that we understand air flow and static pressure by using an electronics enclosure As an example, Lashkar-e-Tayyiba's make information technology more realistic.  An electronics enclosure houses desperate electrical devices, so much as PLCs, power supplies, and drivers for motion control within automated machines.  Since it's an enclosure with heat generating elements, a fan is necessary to lower the temperature and keep the electronics running.  The come of components inside an enclosure determines the "installation denseness".

With fewer components (crushed installation concentration), there is more board for the air to infiltrate.  This scenario would be somewhat nearby to exemplar 1) above where the winnow would create high air flow.

With more components (high gear installation density), there are more obstructions in the path of the airflow.  This scenario would be akin to example 2) above, which is the most standard.  In this case, the high static pressure could decrease the flow of air to below its maximum value.

The Importance of Impedance

How are the true flow of air and unchangeable pressure requirements determined?  The answer is impedance. Impedance is definite as resistance to air flow, and it could be in the physique of electronic components, walls, or anything that impedes the path of the air flow. The actual air flow and static insistency is determined aside impedance.

Let's assure how this is done.  For most nonvoluntary air temperature reduction lotion, impedance is calculated by the "square law," which means that static pressure changes equally a square function of changes in the CFM.

P = KrQⁿ

where:

P = inactive pressure
K = warhead factor (here's some reference info)
r = Fluid Denseness
Q = Flow
n = constant; Let n=2; approximating a turbulent system.

In the graph below, we show 3 dishonorable lines to depict 3 different levels of impedance (A, B, and C).

The Green Line depicts some air flow and static pressure.  Point A depicts high electrical resistance spell point C depicts miserable impedance. The actual impeded breeze hang and static pressure are set where the impedance curve (fearful) intersects the performance curve (green).

Sometimes, it can be difficult to determine system impedance.  In this case, information technology can be safe to seize that the actual flow of air will beryllium about half of the buff's maximum air flow, so select a lover that can produce double the obligatory air run.

For a flourishing enclosure external respiration design, in addition to devotee selection, other factors such as intake/exhaust hole size of it, location of holes, and placement of components, should beryllium considered.  In the following video, we use smoking to demonstrate how air flow can be affected by opposite enclosure designs, such as contrastive ingestion hole diameters and the use of dividers.

Using accessories such as filters, screens, or finger guards bum increment the dependableness and life of fans in dust-covered surgery wet environments, but they will also bear upon the flow of air and static pressure characteristics.

The above graph shows data regarding pressure loss caused aside fan accessories for a physical body size 119 mm (4.69") sports fan.  The filter causes the most significant pressure loss, patc the finger safeguard causes flyspeck loss.	The above graph shows how characteristics English hawthorn switch with installation of accessories while using the MU1225S-21 fan as an example.  Greater pressure loss causes greater reduction of airflow and atmospherics pressure characteristics.

Topics: VIDEOS, Cooling Fans, Motion Verify Basics

Written by

Johann Tang is a Mathematical product Specialist at Oriental Motor USA Corp. with over 15 years of knowledge and experience supporting applications of respective types of electric motors, gearheads, actuators, drivers, and controllers.

Why Does Choking Off Airflow to a Fan Damange the Motor

Source: https://blog.orientalmotor.com/fan-basics-air-flow-static-pressure-impedance