Air Flow Through Pipe

[SlowLearner]

What would be the approximate volume of air ( if any) flowing OUT of the 4 inch pipe and into the house over the course of one hour if the outside air temperature was 90 degrees Fahrenheit ( 32C )?

At a depth of approximately 10 feet (3 meters) below the surface of the earth here the temperature is about 72 degrees Fahrenheit ( 22 C) year round. (Goswami and Biseli 1993). 4" PVC pipe extends 400 feet below grade. Inside 4" pipe is 2" PVC pipe filled with 72 degree water.

4" pipe enter house and is vented through roof 15 feet above grade.

2" pipe provides water to plumbing fixtures in house.

4" pipe is also vented inside house 1 foot above grade.

How much cool air would flow from this open 4" pipe without using any mechanical means to move air? Sketchup Model (requires Sketchup software to to be installed) https://docs.google....QU9ScTM1Q05KMlE Images from model

Exterior view

https://lh3.googleus...ng_Exterior.JPG

Interior view

https://lh3.googleus...ng_Interior.JPG

[CaptainPanic]

Slowlearner,

There are 2 reasons why you didn't get an answer to this question yet:

1. It is really difficult to calculate. I know how to do these kinds of calculations, but for me it goes too far to do this for a hobby on the forum... it would take too long, and my answer might still be wrong. If you want to learn more about it, some useful keywords are "free convection", which is also called "natural convection".

 

2. The explanation of the pipes is not 100% clear. We need a better (but more simple!) picture. There is no need to make the picture in 3D. Just a 2D explanation is probably enough.

[Enthalpy]

The throughput would be very low if resulting only from the temperature difference. But wind impinging at the roof would change it a lot.

 

Some very open buildings use natural convection - seen one at the 1992 universal expo - and they achieve a wind of around 0.1m/s; friction in a pipe would reduce this speed to nothing and the small section would cut the throughput to zero.

 

If you weren't convinced, you can compute the pressure difference from the density difference, then estimate the speed versus pressure in the pipe from experimental relationships - or even from laminar regime computation, as speed will be so low. Even neglecting all angles will tell you "too slow".

 

Or consider a flame or a chimney: with several 100K temperature difference they achive only 1m/s.

 

An excellent book is "Technische Fluidmechanik" bei Herbert Sigloch but it's in German and I don't have mine here.

http://www.amazon.de/Technische-Fluidmechanik-Herbert-Sigloch/dp/3540220089