Who's good at maths???

I need to convert a round duct to the equivalent oval duct...the only dimension I have is the round duct is 55mm OD (c.53mm ID)
I'd like to figure out 'a' and 'b' in the diagram below...

So, who remembers how to do simultaneous equations? I'm borderline discalculic so this may as well be in Chinese.....

Oval Equivalent Diameter (Ellipse)
The equivalent diameter of a oval duct or tube (ellipse) can be calculated as (Heyt & Diaz)

de = 1.55 A0.625 / P0.25 (2)

where

A = cross-sectional area oval duct (m2, in2)

P = perimeter oval duct (m, inches)



The cross-sectional area of an oval duct can be expressed as

A = π a b / 4

where

a = major dimension of the flat oval duct (m, in)

b = minor dimension of the flat oval duct (m, in)

The perimeter of an oval duct (ellipse) can be approximated to

P ≈ 2 π (1/2 ((a / 2)2 + (b / 2)2))1/2 (2b)
​

 

dont you mean flat oval duct ?

 

flat oval is two end diameters and a rectangle , vent duct is normally flat oval ?

 

I don't get any of that, surely you need to know either A or B first?
For example if you want B to be 20mm, you can then figure A using B and the diameter.

 

long story short: Air cleaner box outlet to carb (rubber elbow) is 55mm ID.....I want an oval spigot fitting that a 55mm ID rubber (or aluminium) round duct will fit over, with the same equivalent dimensions....if that makes sense

 

Just squash the fecking round one to make it oval. You're being too scientific. Think outside the box. The blokes on Apollo 13 survived by using their pants and dirty socks as CO filters FFS

 

I know the diameter of the circle (55mm) so you'd do a simultaneous equation and work backwards to find a and b (I fink)

 

Pencil and paper time!

 

I would do, but the inlet pipe has to have something to fit onto....
think of it like this.....the ducting is round and flexible.....this can be squeezed to form an oval...i need to make ta spigot onto which this oval will fit....

 

The pants will tell you

 

But A and B are variable, you change A and B will change, and vice versa.

 

You need to know what either a or b needs to be to figure out the other dimension.

 

Colly is correct, I believe.

 

Doesnt look difficult but you do need to decide on what dimension you actually want - either a or b as they are variable as the shape isnt regular.

 

Squash the round flexible tube you've got into the shape you want, draw round it on cardboard, cut it out and use it as a template!!

 

I didn't even understand the original question.
Mathematics, never one of my stronger subjects.

 

that's what i've just done