homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam

The Geek Culture Forums


Post New Topic  New Poll  Post A Reply
my profile | directory login | | search | faq | forum home
  next oldest topic   next newest topic
» The Geek Culture Forums   » Other Geeky Stuff   » Ask a Geek!   » Physics Geeks: Here's One for You! (Page 1)

 - UBBFriend: Email this page to someone!  
This topic comprises 2 pages: 1  2 
 
Author Topic: Physics Geeks: Here's One for You!
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 5 posted June 02, 2006 18:36      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
Okay, so if I take two fans and put them inside of some sort of ducting, will it actually increse the total flow of the system?

How about this... If one fan's blades spin one way (say clockwise), and the second fan's blades spin another way (say, anti-clockwise)? I've heard that this setup will create a vortex and propel the air much faster than if the blades both spin the same direction... is this correct?

If I know the CFM ratings of each fan, how can I calculate the CFM rating of the system?

FYI, this all relates to my VW's heating system. I'm trying to get hot air down a 5 foot piece of PVC pipe as fast as possible with as much volume as possible.

Thanks in advance. [Smile]

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
Ashitaka

SuperFan!
Member # 4924

Member Rated:
4
Icon 1 posted June 03, 2006 02:19      Profile for Ashitaka     Send New Private Message       Edit/Delete Post   Reply With Quote 
Is the size of the pipe fixed? Increase it's radius for less drag. Making the pipe straight but also lacking laminar flow will also increase the speed. As for the fan questions i don't know,I know more about fluid flow through pipes (pumps and so on).

--------------------
"If they're not gonna make a distinction between Muslims and violent extremists, then why should I take the time to distinguish between decent, fearful white people and racists?"

-Assif Mandvi

Posts: 3089 | From: Switzerland | Registered: Feb 2006  |  IP: Logged
Ugurcan

Member # 4746

Member Rated:
5
Icon 1 posted June 03, 2006 07:58      Profile for Ugurcan   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
As far as I know, that's how the jet engines work. Blades spin to different directions,but they also have different angles on each fan disk.

--------------------
"Constants aren't, Variables won't..."

Posts: 219 | From: Under a 110 ft satellite dish... | Registered: Dec 2005  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 04, 2006 03:51      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK_________________________If you are refering to a Micro bus there is not much that you can do, The heater source as Dr. Porshe designed it was to cool the engine and it does a fine job of doing that, the rub is that the air as it exits the engine shroud is just too cool to be of much good in heating the inside of the car. Your idea of using a round pvc pipe does sound promising as it would lose less heat than the previous metal duct. For your porpuses try two ducts and squirrel cage fans, ducted axial flow fans woun't give you enough help for the effort.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 1 posted June 04, 2006 18:57      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
MoMan, you're aparently not familiar with the concept of the "Heater Box," a.k.a. Heat Exchanger. Allow me to elaborate.

To heat the interior of the vehicle, hot air is extracted from the hottest part of the engine, the exhaust headers. There are metal boxes that wrap around the headers and inside are radiator fins. Cooling air from the enigne, along with air from a blower in the engine compartment blow into the heater boxes, where it passes over the fins and acts like a heatsink for the headers, removing the heat from the headers and transferring the heat energy into the air. The air comes out the front of the heater boxes and into the ducting (or in a beetle, into the rocker panels) and heads toward the front of the vehicle. The air, unfortunately, cools severely as it makes it's trip forward and the once heated air becomes quite chill again by the time it gets to the front.

This gives me two ideas for improving the system: 1) insulate it more, which the PVC pipe will do and 2) move the air faster, as the faster it reaches the front the less time it will have to dissapate the heat. The problem is that the blower fan in the back just doesn't have enough gusto to get the air up to the front efficiently, so I want to add some fans to SUCK the air forward....

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
The Famous Druid

Gold Hearted SuperFan!
Member # 1769

Member Rated:
4
Icon 1 posted June 04, 2006 19:48      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
Um, not that I know much about cars, but I did study a bit of thermodynamics many moons ago, so here goes....

The idea of insulating the duct is a good one, no complaints there.

The 2-fan approach I'm not so sure about.

If you increase the air-flow through the heat exchanger, you'll get a larger volume of hot air, but it'll be cooler, as the air has less time to heat up on the way through. If the objective was to cool the engine this would be a good thing, but if the objective is to heat your van, you might find that vast amounts of luke-warm air doesn't really do the job.

--------------------
If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

Posts: 10680 | From: Melbourne, Australia | Registered: Oct 2002  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 05, 2006 04:07      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK______________________I am familier with exhaust heaters I drove a Model A ford to high school now that heater worked too well. The heaters as VW used on the micro bus and the bugs just had too far to push the air. My Corvair also had the same problems. I do not know how you are going to get the PVC into the original duct work or if you are going to run beside the original. axial flow fans are too expensive I would see about getting some squrril cage 12 volt such as used in automotive app. Try these people

http://www.surpluscenter.com/sort.asp?UID=2006060506011451&catname=electric&keyword=EBSD

Have their prices ever gone up!

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
Ashitaka

SuperFan!
Member # 4924

Member Rated:
4
Icon 1 posted June 05, 2006 07:28      Profile for Ashitaka     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by TheMoMan:
I drove a Model A ford to high school

Too easy [evil]

--------------------
"If they're not gonna make a distinction between Muslims and violent extremists, then why should I take the time to distinguish between decent, fearful white people and racists?"

-Assif Mandvi

Posts: 3089 | From: Switzerland | Registered: Feb 2006  |  IP: Logged
canadiangeek
Geek
Member # 4946

Member Rated:
3
Icon 1 posted June 05, 2006 17:15      Profile for canadiangeek     Send New Private Message       Edit/Delete Post   Reply With Quote 
The turbine blades all rotate in the same direction (sometimes).... but there are stator blades (blades that don't spin) in between each set. these blades take the air that exits the moving blades (at an angle), and re-align the air's direction to the angle of the leading edge of the next set of blades.

The compressor end may operate with counter-rotating rotors (I'm not entirely sure), but they would still likely use a stator assembly to re-align the air flow's direction.


Here's a simple rule for the pumps (or fans)...

if you want a higher flow rate, add a pump in parallel
If you want higher pressure, add a pump in series.

--------------------
-whenever you build something that's idiotproof, someone comes out with a better idiot-

Posts: 161 | From: Nova Scotia | Registered: Mar 2006  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 05, 2006 17:35      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK__________________While out on the tractor today I was thinking about your problem. Dr. Porshe just designed the cooling system for the flat four too well, it had the capability to cool the engine in air temps from 110 F to -20 F. He did this by having an in take air shutter that was modulated by a small bellows, when the engine was cold the shutter was closed as the engine warmed up to proper temp the shutter let in more air, this was good for the engine but bad for the passengers. When the air was very cold the passengers wanted heat so did the engine so the shutter remained closed, as the engine warmed it opened the shutter some but not enough for the passengers, just enough to keep the engine temp in line.

So the air flow is inverse to your wishes as an ocupant of the car. I do remember there were after market heaters that went in the trunk for the bugs but I do not know about the micro bus.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 1 posted June 05, 2006 18:10      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
MoMan, yes, but, on the later busses anyway, there's the secondary blower (squirrel cage fan) that feeds directly into the heater boxes, independant of the engine cooling air.

Also... I need one of these... 436CFM Fan. That would probably do the trick. [Smile]

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
CommanderShroom
BlabberMouth, a Blabber Odyssey
Member # 2097

Member Rated:
4
Icon 1 posted June 05, 2006 18:41      Profile for CommanderShroom     Send New Private Message       Edit/Delete Post   Reply With Quote 
Since you do have a squiirel cage blower. I would see about modifying a more powerful one into your system.

The squirrel cage fan is still used in HVAC systems for cars because they efficient and powerful. Much more so than the standard case arial fans.

So you have everything sealed up and now? All the tin is closed up and the gaps closed?

--------------------
Does he know our big secret?
Has one of us confessed?
'Bout the wires circuits and motors
Buried in our chest

Posts: 2465 | From: Utarrrrggggghhh!!!!!!!! | Registered: Mar 2003  |  IP: Logged
Colonel Panic
BlabberMouth, the Next Generation
Member # 1200

Icon 1 posted June 05, 2006 18:48      Profile for Colonel Panic         Edit/Delete Post   Reply With Quote 
Kris,

A can of Sterno and a match work OK, and they're cheaper.

In my old VW van a bottle of Southern Comfort and the promise of Grateful Dead concert tickets to an enchanting woman named Wanda kept the van quite warm.

CP

--------------------
Free! Free at last!

Posts: 1809 | From: Glacier Melt, USA | Registered: Mar 2002  |  IP: Logged
Chesty
Assimilated
Member # 2460

Member Rated:
2
Icon 1 posted June 05, 2006 21:49      Profile for Chesty         Edit/Delete Post   Reply With Quote 
See it's like this - Germans are a hearty people that live through cold winters in old stone buildings. The VW was never meant to be heated well. Because in Hitler's Opinion, Aryans don't need good heaters because they have all those big coats!

get one of these: these

If you have a 6volt then get one of these: these

Posts: 416 | From: The Beach | Registered: Nov 2003  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 06, 2006 03:35      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK__________________Now some of your idea makes more sense. Before shelling out that much money go to a place that repairs Campers (RVs) and see if you can get a fan out of a RV furnace for much less, they use one motor and usually have a fan on each end one for draft one to spread the heat.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 06, 2006 17:39      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Ashitaka_____________

.. _.. ___ .._ _... _ _ .... ._ _

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 1 posted June 06, 2006 17:42      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
Chesty: those suck, I have like a million of them.... okay, so I have 3 or 4.. some 200W, some 300W, and a 500W... the thing is, 500Watts just isn't enough heat to get ANYTHING warm.

You need at least 1600 watts, which just isn't possible with a 12 volt system. Volts * Ampres = Watts (EI=P) 12 volts * n amps = 1600 watts.. 1600/12 = n = 133 1/3 amps! The stock alternator gives 35 amps, max. My alternator, from a 1987 Pontiac Grand Am, cleverly rigged, pumps out 90 amps, max. You just can't generate that much power and there's more then plenty of heat coming off the enigne, the problem is just harnessing it.

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 1 posted June 06, 2006 17:59      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
yes, double post...

I have two fans, 12cm case fans that I got from macmcseboy that are capable of 152CFM each, and one that will do 102CFM. My orig. plan was to use them inline, then I found out about the potential advantages of using two fans with opposite rotations but like flow directions. That seems to have proven a dead end...

Now I'm left wondering if 152CFM will be enough. I don't know the flow rate of the stock squirrel cage fan, I've tried looking but can't find any info on it. I need to get a flow meter, I guess. [Smile]

I'm tempted by the usually male attitude of "more is always better", which is why the 436CFM squirrel cage fan (linked above) seems like such a good idea... the exhaust headers have plenty of heat to give, but there's the chance that I'll max out the energy transfer potential of the heater boxes, which will just make it colder... then again, I can always put a pot on the fan and slow it down, but I can't make a 200CFM fan blow harder....

Can anyone give me an idea of an expected CFM rating for your average automotive squirrel cage fan? Or have any other ideas?

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 06, 2006 18:07      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK_____________________I wasn't going to suggest it, but CP does have an idea only you both have to not smoke. Get one of those propane fueled heaters, and a twenty pound bottle. With all the air leaks a micro bus has you would not have to worry about depleating the oxygen. I use a dual burner out in the barn/radio shack and it warms up the work area quite nicely. Mine has three flame settings and the choice of how many burners are on, so 7000-28000 BTU just don't close the windows and shut off the engine while using the heater.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 06, 2006 18:12      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK___________________The makers of most air moving equipment cite best case air flows not how much you will get against this ammount of back pressure, to get the perfomace charts out of some venders is like getting two income tax return checks for one year. KrisK if the motor is about 2 and one half inches in diameter it is low output, over three, I'm guessing but near 500 CFM.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
MacManKrisK

Gold Hearted SuperFan!
Member # 955

Member Rated:
5
Icon 1 posted June 06, 2006 18:22      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post   Reply With Quote 
MoMan, too dangerous. I might as well fix/rebuild the OEM gasolene-powered heater if I'm going to do that. That's dangerous too, though. I don't want to subject myself to any more danger then is already inherent in driving a microbus. [Smile]

--------------------
"Buy low, sell high
get rich and you still die"


Posts: 2331 | From: Southwest Michigan, USA | Registered: Oct 2001  |  IP: Logged
CommanderShroom
BlabberMouth, a Blabber Odyssey
Member # 2097

Member Rated:
4
Icon 1 posted June 06, 2006 18:31      Profile for CommanderShroom     Send New Private Message       Edit/Delete Post   Reply With Quote 
I would pull out your old fan and just do a prowl around for fans at your local FLAP (friendly local auto parts) store. IMO a blower from a late 70's American built car would do the trick. They were built for large spaces and pushing air out as quickly as possible.

I am not too certain how you have things routed. But if you are piping heat to the rear of the cabin I would try to close those off when you are running solo. Better to pump the heat to the front and let it drift to the rear.

If you can try to hunt out a blower assembly from a GM vehicle. They kept the same general design for almost 30 years, down to the placement of the mounting screws. So they are relatively cheap. Also if you hunt around some places sell the squirrel cage fans made out of plastic. So are much lighter than a stock steel fan.

edit: You have a stock gasolene heater?!

Fix it and fix it well. Those things will get you nice and toasty much faster than anything we are sitting here and trying to design.

And something of note. The horro stories you hear about gas heaters are mostly due to improper care and feeding of the units. Not from any true flaws in the system. Mostly clogged vents and gas leaks would be the main culprits. Othersise they are very reliable and not high on fuel consumption. I have heard that they averaged about 1/10 of a gallon per hr on high.

--------------------
Does he know our big secret?
Has one of us confessed?
'Bout the wires circuits and motors
Buried in our chest

Posts: 2465 | From: Utarrrrggggghhh!!!!!!!! | Registered: Mar 2003  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 07, 2006 02:46      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK______________________You have a Northwind and are trying to cobble together something else. I was going to tell you to try finding one of those.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted June 07, 2006 08:34      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
MacManKrisK_________________Lets get back to basics, does the thermostat on your VW work correctly? On a cool morning the air intake shutter should be closed, If it is open the engine will never make opperating temp. This is bad for the oil and engine life.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
olivetti
Single Celled Newbie
Member # 5247

Icon 1 posted June 07, 2006 14:36      Profile for olivetti         Edit/Delete Post   Reply With Quote 
HI was wondering if you could tell me the size of the pipe your using thats coming off the heaterbox? I'm thinking of copying your idea of using plastic tubing. Just installing heaterbox and new exhaust and was wondering how to improve on the stock parts. I live in scotland and my bus is so cool most of the months of the year.
Posts: 1 | From: uk scotland | Registered: Jun 2006  |  IP: Logged


All times are Eastern Time
This topic comprises 2 pages: 1  2 
 
Post New Topic  New Poll  Post A Reply Close Topic    Move Topic    Delete Topic next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:

Contact Us | Geek Culture Home Page

2015 Geek Culture

Powered by Infopop Corporation
UBB.classicTM 6.4.0



homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam