Axial Flow Fans and Altitude

5 comments

Rate

keyur_197 Associate Join Date: Jan 2007 Location: Pune / India Posts: 48	Axial Flow Fans and Altitude 05/26/2009 8:20 AM
	Hi.. I am selecting an axial flow fan. My system requirement is 6700 cmh at 75 pa, at 0 ft altitude. Now, altitude is changed from 0 ft to 10,000 ft. Is there any impact on flow as altitude increases? if yes, please suggest at what parameters I shall design a fan at 0 ft so that it can deliver 6700 cmh at 75 pa and 10,000 ft altitude. Regards, Keyur __________________ First do it and then talk about it
	Register to Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Codemaster Guru Join Date: Jul 2005 Location: Stoke-on-Trent, UK Posts: 4496 Good Answers: 137	#1 Re: Axial Flow Fans and Altitude 05/26/2009 11:00 AM
	Hello keyur According to my calcs, at 10000 ft atm pressure is down from 1000 to 680mbar. With your fan as it stands ΔP drops to 750.68Pa = 51Pa, as ΔP is proprtional to inlet density (hence pressure). Actual flow (i.e. measured at the lower pressure) remains unchanged. If you increase fan speed by 1/√0.68 = 1.21, ΔP goes back to 75Pa (1.21²51 = 75) and actual flow to 6700*1.21 = 8110 cmh, and power drawn will (I think, haven't quite decided) increase by factor 1.21. Cheers........Codey __________________ Give masochists a fair crack of the whip
	Register to Reply

keyur_197 Associate Join Date: Jan 2007 Location: Pune / India Posts: 48	#2 In reply to #1 Re: Axial Flow Fans and Altitude 05/26/2009 11:57 AM
	Hi.. thanks for explanation but I am bit confused. As you mentioned, as altitude increases pressure drops but this is system pressure and I think it should remain constant. If I am wrong, please explain... Regards, Keyur Shah __________________ First do it and then talk about it
	Register to Reply

Codemaster Guru Join Date: Jul 2005 Location: Stoke-on-Trent, UK Posts: 4496 Good Answers: 137	#3 In reply to #2 Re: Axial Flow Fans and Altitude 05/27/2009 7:02 AM
	Hello keyur Not sure what you mean by system pressure. I assumed the 75Pa requirement is a dynamic loss and after the system the air discharges to atmosphere. So at sea level the fan suction pressure and the system discharge pressure are both 1000mbar, at 10000ft they are both 680mbar. Is this correct? If so, then my figures are :- Sea level. Actual inlet flow 6700cmh. Fan inlet pressure 1000mbar = 100000Pa. Fan ΔP 75Pa. Fan discharge pressure 100075Pa. System ΔP 75Pa. System discharge pressure 100000Pa. Power drawn W. 10000ft - speed unchanged. Actual inlet flow 6700cmh. Fan inlet pressure 680mbar. Fan ΔP 51Pa. Fan discharge pressure 68051Pa. System ΔP 51Pa. (Fan and system ΔP both proportional to inlet density, sea level figure x 0.68). System discharge pressure 68000Pa. Power drawn 0.68W (flow as at sea level, ΔP x 0.68). 10000ft - speed x 1.21. Actual inlet flow 6700 x 1.21 = 8110cmh (proportional to fan speed). Fan inlet pressure 680mbar. Fan ΔP 75Pa (proportional to speed²). Fan discharge pressure 68075Pa. System ΔP 75Pa. System discharge pressure 68000Pa. Power drawn 1.21 x W (flow x 1.21, ΔP as at sea level). Cheers.........Codey __________________ Give masochists a fair crack of the whip
	Register to Reply

GLB Commentator Join Date: Oct 2006 Location: Pacific Northwest, USA 45.952N -123.976W Posts: 73 Good Answers: 3	#4 Re: Axial Flow Fans and Altitude 06/02/2009 1:43 PM
	Hello Keyur... ... A quick query: Are you attempting to move a volume of air as in an exhaust stack? Or, is this volume of air intended for another purpose such as equipment cooling? Sorry to be so late into the thread... ... out of town. Regards __________________ “Any sufficiently advanced technology is indistinguishable from magic.” Sir Arthur Charles Clarke
	Register to Reply

keyur_197 Associate Join Date: Jan 2007 Location: Pune / India Posts: 48	#5 In reply to #4 Re: Axial Flow Fans and Altitude 06/04/2009 7:36 AM
	Hi, This is for equipment cooling. __________________ First do it and then talk about it
	Register to Reply

Copy to Clipboard

Codemaster (2); GLB (1); keyur_197 (2)

You might be interested in: Axial Flow Pumps, Gas Flow Meters, Flow Meters

	Got Something to Say?
	Ask a Question Start a Discussion

	Aerospace
	BioMech & BioMed
	Chemical & Material Science
	Civil Engineering
	Communications & Electronics
	Education and Engineering Careers
	Electrical Engineering
	General Discussion
	Instrumentation
	Manufacturing
	Mechanical Engineering
	New Technologies & Research
	Software & Programming
	Sustainable Engineering
	Transportation

	Site Directories
	Forum Directory Blog Directory User Group Directory RSS Feeds CR4 Rules of Conduct CR4 FAQ Site Glossary Who's Online (93 right now) Show Members