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Understanding static pressure in fans
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Source：Internet Author：Unknow Pubdate：2010-02-19
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jaydigs (Mechanical)
9 Apr 09 12:52
This may be a trivial question to those in the industry, but, can anyone help me understand the concept of static pressure in terms of fan design and operation. From some works I've read they make it seem like something present in the environment (ie atmospheric press), and some describe it more as something produced by the fan. As say a customer sitting under a ceiling fan I know what "more air" feels like, but is this just faster moving air, or air moving at higher pressure?
Thanks
rb1957 (Aerospace)
9 Apr 09 13:03
static pressure and dynamic pressure add together to give you total pressure; alittle like potential energy and kinetic energy.
so faster moving air has lower static pressure, and the experimental subject sitting under the ceiling fan is feeling the higher dynamic pressue (faster moving air, applies more force to a object (the subject) standing in the airflow)
字串6
Compositepro (Chemical)
9 Apr 09 13:12
A ceiling fan generates almost zero static pressure. It is simply moving air. However all fans and blowers operate on the same basic principles. The impart motion into the air (or, more generally, "fluid"). This can be looked at as puting momentum or kinetic energy into the fluid. If you suddenly stop this momentum the energy is converted into pressure ("static pressure"). The greater the velocity initially given to the fluid the greater the pressure that can be generated. "Fans" are designed just to move air at very low pressure. Blowers are designed for generating higher pressure.
jaydigs (Mechanical)
9 Apr 09 13:47
Adding the static and dynamic components makes sense, but how does a fan generate static pressure? I keep wanting to think of static pressure as just the air pressure when nothing is moving, ie..atmospheric pressure. The rotation of the blades generating pressure makes sense, but that would just be the dynamic component?
字串2
Compositepro (Chemical)
9 Apr 09 14:02
If you place a pitot tube in front of the fan the air that hits the open end of the tube comes to a stop and generates a pressure that can be measured and used to calculate the air velocity. The measured pressure will be less than 0.1" w.c. (water column). 24" w.c. is about one psi.
rb1957 (Aerospace)
9 Apr 09 14:08
i don't think it does ... for much the reasons you mention.
the fan does useful work on the air, by giving it a velocity, increasing the total pressure. ceiling fans don't have much power, so they don't create a hurricane, but more like a gentle breeze.
FeX32 (Mechanical)
9 Apr 09 18:21
Static pressure is exactly that, STATIC. It's nice to think of it like rb1957. (in terms of kinetic and potential energies, because that is EXACTLY what they are). 字串7
Fe
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