Somebody asked this and I promised to ask my friendly physics major. Here
was the answer.
Here was the question. When we increase from one 2.5 inch pipe to two 2.5
inch pipes does it carry the same volume as if we went from one 2.5 inch
pipe to a single 5 inch pipe? NO is the answer and here is why.
OK, what you need to notice here is that the cross-sectional area of the
pipe (hence, the volume of gas you can push through per second) is
proportional to the radius squared (since area = pi * (radius^2)).
Area is PI times Radius squared or in a 2.5 inch pipe it's
3.14159 * (1.25 * 1.25) = Area
3.14159 * (1.5625) = Area
or 4.908 square inches For a single 2.5 inch pipe.
Then two 2.5 inch pipes would be 4.908 times 2 or 9.816 square inches.
Now lets do the math for a 5 inch pipe!
3.14159 * (2.5 * 2.5) = Area
3.14159 * (6.25) = Area
or 19.6349 square inches of area.
So;
by doubling the diameter (2.5 -> 5 inches), the area increases by a factor
of four.
By using two pipes, the area has increased by a factor of two.
Of course, the flow of air is also a factor (remember, we were talking about
volume of gas earlier, now we're onto flow, that's (say) molecules per
second (which is dependent on pressure)) - you can get the same flow for
both pipes simply by making the air go through the pipe with the smaller
area faster - although this might mean;
less ventilation/circulation within the car (or whatever is causing the air
flow), so higher temperatures, higher concentrations of gases, etc... This
is a "Bad Thing" (tm)
faster, hotter gases expelled by the narrower pipe. This is also a "Bad
Thing" (tm)
Hope this (quick answer) answers you question, get back to me if you want to
discuss further.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:53:44 EDT