# Playing with the calcs

Discussion in 'Reverse Flow' started by wombat, Jun 27, 2015.

1. ### wombatNewbie

Hi all. I'm Aussie based so don't get to see too many home built or even commercial reverse flows here. I'm about to embark on a build of a 120gal 30" diameter by around 48" propane tank. I have played around with some of the calculators and come up with some numbers but I'm still not sure of the height of the RF plate for ideal performance. My firebox is around 23" square but I can adjust this to suit the ideal RF plate height. That's assuming the FB and RF plate are meant to be the same height

Cheers

Neil

2. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

here is an excerpt that describes the RF plate......

When you open the "Circle Calculator" link, Click on the "bullet" to the left of Radius & Segment Height ED....

Circle Calculator

Click on the 2 variables you know

......Chord AB & Segment Height ED................Chord AB & Apothem OE
......Segment Height ED & Apothem OE...........Chord AB & Arc AB

You should have opened the circle calculator and a bunch of boxes will appear below..
and a box called [CALCULATE]..

Enter the radius in the box so marked.... If you tank is 24" OD, and has a 3/8" thick steel wall, the ID of the tank 23.25".... the radius is 11.625"..... these numbers need to be accurate if you want stuff to fit... ALSO, take into account the thickness of the FB steel when cutting out the tank...

Enter a guess for the Segment Height ED... I'd start with 6.0

Click on [CALCULATE]....

The other boxes will fill with numbers....

The [Segment Area] box is what you area going to compare with the FB/CC opening in square inches...

If the FB/CC opening number is smaller, change the number in the Segment Height ED box to 5.... continue changing that number until the [Segment Area] matches the FB/CC number.....

Now look at the colored circles above.... Segment height ED is how tall the green area is and corresponds to the area to be cut out.....

Also, [Chord AB] corresponds to the width of the RF plate... NOTE... for ease in fitment, the FB should be at least as wide as the RF plate..

3. ### wombatNewbie

Thanks Dave

The calculations are doing my head in at the moment. I haven't picked the tank up but going on a nominal 30" diameter I'm looking at a radius of 15" giving a cord at around 25" with a segment height of 8". This will give me a FB that is around 26" wide by 22" high and 22" long. Am I on the right track?

4. ### daveomakSmoking GuruOTBS MemberSMF Premier Member

Without crunching the numbers, sounds correct....Thumbs Up