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Goddess of Whatever · 17-03-2006, 01:42 PM

I am looking for a velocity meter to measure air flow rate in refrigerator. The question is, I want to conver the unit from RPM (Round Per Minute) to m/s (Mater/Second) but I can't find it. I need to know the range I want before I call suppliers.

Anyone can help me? Please....ja...

GoW

lom · 17-03-2006, 02:35 PM

Don't think you can do that easily. RPM = Revolutions Per Minute , that is for the compressor motor. But how much air (actually gas) it can showel depends on the compressor size/construction and is not directly related to the speed of the motor.

friscofrankie · 17-03-2006, 02:36 PM

this an air pump? Fluid?
generally you' take the swept volume of the pump "sv" multiplied by the RPM revolutions per minute divide by 60 this will give you the volume pumped. if the Swept volume is measured in cubic centimeters "cc" then you'd divide by ... a million
go give a pump witha volume of say300 cc operatng at 2500 RPM
we'd get
300 x 2500 / 60 =12500 cubic centimeters
12500/ 10^6 = 0.0125 cubic meters
is that what you're after?

Goddess of Whatever · 17-03-2006, 03:12 PM

RPM = revolutions per minute, yes.

Goddess of Whatever · 17-03-2006, 03:18 PM

In the back side of freeze room, there's a motor fan which blow cold air from evaporator then flow to freeze room and from freeze room, there's small holes that cold air can flow through Ref room.

I don't know velocity of the air from that motor fan or fan motor. I know only its RPM (round per minute) then I just want to know its flow rate that how fast cold air can flow through freeze room.

So?

friscofrankie · 17-03-2006, 04:19 PM

Gotta measure the flow, or displacement of the fan. Fans are not static movers of whatever medium. but a rough estimate would be to measure teh diameter of the fan and depth of blade twist and multiply the number of blades this will give yu theoretic displacement and if you use that number for your opening you'd not restrict the flow in any way. fans are inefficient movers. there will be alot of slip and a ratio of 50 - 75% wouldn't be a bad guesstimate.
This problem is loaded with way to many variables. Is the fan inclosed in a duct? Then a anemometer could measure the velocity of the air movng in that duct to figure the volume.
To summarize:
Take your fan blade; measure it's pitch, and radius. Measure the diameter of the hub (the part that don't move air). Calculate the area of the entire fan, Deduct the area of the hub. Multiply by the depth (pitch)of the blade and the number of blades. This will give you the theoretic 'volme' of the fan. Now use the above formula "sv".
Things like shrouding, pitch angle, blade width, and shape have large influences on the efficiency of the fan. We are now in the realm of fluid dynamics. The calculations become extrremely complicated and beyond the scope of my pea brain. The formulas are out there fr the findng and they are biguns. If this is just for an aircon unit or one off icebox, take the product ofthe above formula, halve it, and call it ball-park good enough.
are you confused yet?

NickA · 17-03-2006, 05:56 PM

Have a look at these pages GoW....

http://www.vent-axia.com/sharing/fanlaws.asp

http://www.electronics-cooling.com/R...6/may96_01.htm

They might help, but they might not!

friscofrankie · 17-03-2006, 06:17 PM

wellthere ya go! everything you need to work that little bugger out!
interestng site Nick

hillbilly · 17-03-2006, 07:20 PM

Damn ya all. I grew up with one bull plus cows make a herd...

Ya smart bastards.

NickA · 17-03-2006, 07:25 PM

Quote:

Originally Posted by friscofrankie

wellthere ya go! everything you need to work that little bugger out!
interestng site Nick

I haven't actually read the sites, but I think the problem might be that you need to find a constant, K, or something like that, which might be the difficult bit.

Amazingly I found the sites by googling "fan flow rate"

friscofrankie · 17-03-2006, 07:40 PM

actually there are them constant but fluid dynamics is very mathematically complicated. there are so many vairables thatwould need to be measured. to be very accurate you'd have to get info on just too many things even then it's still an approximation dependent on a shit load of variables. My 50% rule of thumb will get her in the ball park i think. or if the fan is a unit designed fo this application she jst needs to get the specs from the mfr. then do tha arithmetic. Guesstimates work for me most he time, It ain't the space shuttle.

Goddess of Whatever · 17-03-2006, 09:40 PM

Thank you.

NickA · 17-03-2006, 09:46 PM

Did you get an answer then?

Goddess of Whatever · 17-03-2006, 09:50 PM

Apparently, yes.

Also a korean guy just sent me a test report before I left work. So I know the average flow rate in da fridge already. Then I can use that data to talk with the suppliers.

And, information in the links you gave me, helped me understood things better.

Thanks again, NickA and ff.

NickA · 17-03-2006, 09:51 PM

It was a pleasure to pleasure you

Goddess of Whatever · 17-03-2006, 09:52 PM

If I got a new job, we should have some drinks together.

NickA · 17-03-2006, 09:55 PM

A nice cup of tea would do me nicely!

Goddess of Whatever · 17-03-2006, 10:03 PM

Beer mate, beer!

dirtydog · 18-03-2006, 02:18 AM

A good way of course is to tape a plastic carrier bag over one of the vents, see how long it takes to blow up, and then see how many litres of water it takes to fill it, then multiply that by the number of vents there are, may not be suitable for the UK and testing there, but I feel sure you could get away with it in Thailand

Curious George · 18-03-2006, 11:48 PM

^
Dog, after observing the kind of logic you apply, you can build a house for me anytime!!!

17-03-2006, 01:42 PM	#1 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	Unit converstion needed! Help!! I am looking for a velocity meter to measure air flow rate in refrigerator. The question is, I want to conver the unit from RPM (Round Per Minute) to m/s (Mater/Second) but I can't find it. I need to know the range I want before I call suppliers. Anyone can help me? Please....ja... GoW __________________ To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

17-03-2006, 02:36 PM	#3 (permalink)
friscofrankie Northern Hermit Last Online: 16-03-2010 02:53 PM Join Date: Jul 2005 Location: Chiangmai, Thailand Posts: 7,399	this an air pump? Fluid? generally you' take the swept volume of the pump "sv" multiplied by the RPM revolutions per minute divide by 60 this will give you the volume pumped. if the Swept volume is measured in cubic centimeters "cc" then you'd divide by ... a million go give a pump witha volume of say300 cc operatng at 2500 RPM we'd get 300 x 2500 / 60 =12500 cubic centimeters 12500/ 10^6 = 0.0125 cubic meters is that what you're after? __________________ For art to exist, for any sort of aesthetic activity to exist, a certain physiological precondition is indispensable: intoxication. insanity... To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

17-03-2006, 03:12 PM	#4 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	RPM = revolutions per minute, yes. Last edited by Goddess of Whatever : 17-03-2006 at 03:14 PM.

17-03-2006, 04:19 PM	#6 (permalink)
friscofrankie Northern Hermit Last Online: 16-03-2010 02:53 PM Join Date: Jul 2005 Location: Chiangmai, Thailand Posts: 7,399	Gotta measure the flow, or displacement of the fan. Fans are not static movers of whatever medium. but a rough estimate would be to measure teh diameter of the fan and depth of blade twist and multiply the number of blades this will give yu theoretic displacement and if you use that number for your opening you'd not restrict the flow in any way. fans are inefficient movers. there will be alot of slip and a ratio of 50 - 75% wouldn't be a bad guesstimate. This problem is loaded with way to many variables. Is the fan inclosed in a duct? Then a anemometer could measure the velocity of the air movng in that duct to figure the volume. To summarize: Take your fan blade; measure it's pitch, and radius. Measure the diameter of the hub (the part that don't move air). Calculate the area of the entire fan, Deduct the area of the hub. Multiply by the depth (pitch)of the blade and the number of blades. This will give you the theoretic 'volme' of the fan. Now use the above formula "sv". Things like shrouding, pitch angle, blade width, and shape have large influences on the efficiency of the fan. We are now in the realm of fluid dynamics. The calculations become extrremely complicated and beyond the scope of my pea brain. The formulas are out there fr the findng and they are biguns. If this is just for an aircon unit or one off icebox, take the product ofthe above formula, halve it, and call it ball-park good enough. are you confused yet? Last edited by friscofrankie : 17-03-2006 at 04:22 PM.

18-03-2006, 02:18 AM	#19 (permalink)
dirtydog The Dog Last Online: Today 07:48 AM Join Date: Jun 2005 Location: Pattaya Jomtien Posts: 44,951	A good way of course is to tape a plastic carrier bag over one of the vents, see how long it takes to blow up, and then see how many litres of water it takes to fill it, then multiply that by the number of vents there are, may not be suitable for the UK and testing there, but I feel sure you could get away with it in Thailand __________________ To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

17-03-2006, 02:35 PM	#2 (permalink)
lom #&§~ Last Online: Today 02:23 AM Join Date: Jan 2006 Location: Dark side of the room Posts: 5,234	Don't think you can do that easily. RPM = Revolutions Per Minute , that is for the compressor motor. But how much air (actually gas) it can showel depends on the compressor size/construction and is not directly related to the speed of the motor.

17-03-2006, 03:18 PM	#5 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	In the back side of freeze room, there's a motor fan which blow cold air from evaporator then flow to freeze room and from freeze room, there's small holes that cold air can flow through Ref room. I don't know velocity of the air from that motor fan or fan motor. I know only its RPM (round per minute) then I just want to know its flow rate that how fast cold air can flow through freeze room. So?

17-03-2006, 05:56 PM	#7 (permalink)
NickA This is not my avatar Join Date: Oct 2005 Posts: 11,396	Have a look at these pages GoW.... http://www.vent-axia.com/sharing/fanlaws.asp http://www.electronics-cooling.com/R...6/may96_01.htm They might help, but they might not!

17-03-2006, 06:17 PM	#8 (permalink)
friscofrankie Northern Hermit Last Online: 16-03-2010 02:53 PM Join Date: Jul 2005 Location: Chiangmai, Thailand Posts: 7,399	wellthere ya go! everything you need to work that little bugger out! interestng site Nick

17-03-2006, 07:20 PM	#9 (permalink)
hillbilly Still trailer trash Last Online: Today 07:50 AM Join Date: Jun 2005 Location: BKK & 'D&G Resort' Posts: 6,610	Damn ya all. I grew up with one bull plus cows make a herd... Ya smart bastards.

17-03-2006, 07:40 PM	#11 (permalink)
friscofrankie Northern Hermit Last Online: 16-03-2010 02:53 PM Join Date: Jul 2005 Location: Chiangmai, Thailand Posts: 7,399	actually there are them constant but fluid dynamics is very mathematically complicated. there are so many vairables thatwould need to be measured. to be very accurate you'd have to get info on just too many things even then it's still an approximation dependent on a shit load of variables. My 50% rule of thumb will get her in the ball park i think. or if the fan is a unit designed fo this application she jst needs to get the specs from the mfr. then do tha arithmetic. Guesstimates work for me most he time, It ain't the space shuttle.

17-03-2006, 09:40 PM	#12 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	Thank you.

17-03-2006, 09:46 PM	#13 (permalink)
NickA This is not my avatar Join Date: Oct 2005 Posts: 11,396	Did you get an answer then?

17-03-2006, 09:50 PM	#14 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	Apparently, yes. Also a korean guy just sent me a test report before I left work. So I know the average flow rate in da fridge already. Then I can use that data to talk with the suppliers. And, information in the links you gave me, helped me understood things better. Thanks again, NickA and ff.

17-03-2006, 09:51 PM	#15 (permalink)
NickA This is not my avatar Join Date: Oct 2005 Posts: 11,396	It was a pleasure to pleasure you

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17-03-2006, 09:52 PM	#16 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	If I got a new job, we should have some drinks together.

17-03-2006, 09:55 PM	#17 (permalink)
NickA This is not my avatar Join Date: Oct 2005 Posts: 11,396	A nice cup of tea would do me nicely!

17-03-2006, 10:03 PM	#18 (permalink)
Goddess of Whatever A bladdy woman Last Online: 29-04-2009 05:13 PM Join Date: Jul 2005 Location: Somewhere I belong but it won't be last long Posts: 4,273	Beer mate, beer!

18-03-2006, 11:48 PM	#20 (permalink)
Curious George Kamphaeng Phet Join Date: Aug 2005 Location: Florida Posts: 316	^ Dog, after observing the kind of logic you apply, you can build a house for me anytime!!!