Air Speed

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SYED MD. ANWAR UL ISLAM Commentator Join Date: Nov 2010 Posts: 72 Good Answers: 2	Air Speed 12/19/2012 8:31 AM
	I need an air speed of 20ft/sec. I am not an engineer. Can a ceiling fan (56"), which is generally used in domestic houses in summer season (rated 80W, 220VAC) provide this speed 7 feet away from it? Is there any instrument easily available in market (e.g. scientific store) to measure the air speed? What is the name of the instrument? If not, is there any way to DIY?
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#1 "Re: AIR SPEED" by JPool on 12/19/2012 8:41 AM (score 2)
#4 "Re: Air Speed" by JPool on 12/19/2012 9:17 AM (score 2)
#6 "Re: Air Speed" by JRaef on 12/19/2012 9:24 AM (score 2)
#7 "Re: Air Speed" by Codemaster on 12/19/2012 10:43 AM (score 2)

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#3 "Re: AIR SPEED" by lyn on 12/19/2012 8:51 AM (score 1)

JPool Guru Join Date: Apr 2012 Location: Detroit MI, USA Posts: 2496 Good Answers: 271	#1 Re: AIR SPEED 12/19/2012 8:41 AM
	Air Velocity Meters will measure air speed. Googling them comes up with many different models from many different manufacturers. __________________ How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
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SYED MD. ANWAR UL ISLAM Commentator Join Date: Nov 2010 Posts: 72 Good Answers: 2	#2 In reply to #1 Re: AIR SPEED 12/19/2012 8:49 AM
	Thanks.
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#3 Re: AIR SPEED 12/19/2012 8:51 AM
	Air Velocity Indicators-Buy Cheap Air Velocity ... - Aliexpress.com Economical Air Velocity Meter
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JPool Guru Join Date: Apr 2012 Location: Detroit MI, USA Posts: 2496 Good Answers: 271	#4 Re: Air Speed 12/19/2012 9:17 AM
	We can't answer your question about the ceiling fan with the information given, I would need to know the rated CFM. If you have CFM then got to : http://www.hansenwholesale.com/ceilingfans/reviews/ceiling-fan-wind-speed.asp Convert the MPH to FPS. 20 FPS = 13.6 MPH. A typical industrial 56" ceiling fan is rated at 34,500 cfm, this is about 22 MPH or 33 FPS __________________ How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
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Joshi Guru Join Date: Oct 2007 Location: India Posts: 1246 Good Answers: 34	#5 Re: Air Speed 12/19/2012 9:19 AM
	*What is the name of the instrument?* An anemometer is a device for measuring wind speed, and is a common weather station instrument. Anemometer - Wikipedia, the free encyclopedia
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#6 Re: Air Speed 12/19/2012 9:24 AM
	The official name for an air speed instrument is an "anemometer" by the way. Common household fans are designed to move air WITHOUT increasing air speed as much as possible, because air speed comes with noise. You will need something more powerful and less domestic to get that kind of speed at that distance. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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Codemaster Guru Join Date: Jul 2005 Location: Stoke-on-Trent, UK Posts: 4496 Good Answers: 137	#7 Re: Air Speed 12/19/2012 10:43 AM
	Can a ceiling fan (56"), which is generally used in domestic houses in summer season (rated 80W, 220VAC) provide this speed 7 feet away from it? No. Even if velocity is 20 ft/s in the fan area (and higher vel needed to get 20ft/s 7 ft away) velocity pressure P_v = 0.5ρV² ~ 23 Pa. Power = P_vVarea and it comes to ~ 220W. And that's ignoring losses. __________________ Give masochists a fair crack of the whip
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Fredski Guru Join Date: Feb 2011 Posts: 7025 Good Answers: 207	#8 Re: Air Speed 12/19/2012 12:11 PM
	why do you need this? does it have to be exact?? what volume of air do you need moved? help us out here
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#9 In reply to #8 Re: Air Speed 12/19/2012 12:20 PM
	Not to speak for the OP, but I know that he is a doctor in Bangladesh and has had other questions posed here.
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Brave Sir Robin Guru Join Date: May 2007 Location: Annapolis, Maryland Posts: 7940 Good Answers: 458	#10 Re: Air Speed 12/20/2012 11:20 AM
	You could drive down the road at 13.636 miles per hour.
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SYED MD. ANWAR UL ISLAM

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#11

Re: Air Speed

12/20/2012 1:43 PM

Thank you all those who have responded & helped me. The matter is cooling effect of speedy air. Human body sweats when the ambient temperature & humidity is high. When air flows over the body (e.g. by fan or natural speedy air) the sweat evaporates absorbing heat from our body & we feel cool to some extent. This is called COOLING EFFECT. There is a chart of cooling effect. e.g. at 90 deg F & at various air speed what shall we feel:

Air speed (ft/min)	Temp. will be felt (deg F)
20	90
50	89
100	85
200	80
300	77
400	75
500	73

Yesterday when I posted the thread there was a serious mistake. I found that in a book. After posting it seemed to me that the speed is very high & I had to spend almost two hours today to make myself clear (being not an engineer). That was wrong. That would be 20 ft/minute. At this speed no cooling effect would occur but would drive away gases from a closed house when air is blown out by special fan in winter.

Industrial fans those I have seen run on 3-Phase AC supply & they have almost 900 rpm as I was told. A 3-Phase supply is not always available & costly. In so many places we have to rely on 230V AC supply & a general ceiling fan/table fan is the only way in summer.

The ceiling fans found in the market are not always labeled how much (volume) air they supply (cft/min). Even if that was written I cannot calculate the air speed driven by the fan at 7ft distance with full speed setting without an anemometer, which an engineer can. A ceiling fan is generally fixed at 7ft height (safe distance) from the floor. So, I had to seek support from CR-4.

In my child hood I knew/saw anemometer in weather stations. Yesterday I had forgotten.

HiTekRedNek Guru Join Date: Oct 2006 Location: 44.56024"N 15.307971E Posts: 8277 Good Answers: 270	#12 Re: Air Speed 12/20/2012 6:12 PM
	Here is a link to high velocity fans that will blow your socks off, literally. These are meant to be mounted high,but you can adjust length of down rod to suit application, adjust speed to suit flow. You will need more flow on humid days, less on dryer days to achieve the same effect. Air temp will never be lower than wet bulb temperature. Good luck. http://www.teksupply.com/contractor/supplies/prod1;ts_cooling_exhaust_fans-ts_ceiling_fans;pg101483_101486.html __________________ "A man never stands so tall as when he stoops to help a child." "Never argue with a stupid person.They will drag you down to their level and beat you with experience" "To create an apple pie from scratch, first you must create a universe"
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