Everything moves at a snails pace here, part of my imposed Zen training program.
Hope you're right about the outcome
My hearth isn't going to be enormous by any means Scott, especially with only 27" depth. I haven't even looked at what manufacturers are offering in Btus per sq ft but will check. Been searching the internet high and low to find out what size ports I should be using with what spacing. I think its going to be about .5 sq mm aperture per inch of burner if I'm using about 12' in total.
My thinking (sketchily) is that for 120,000 Btus/hour, 2000 Btus/min, I will need to burn about 1 cu ft of propane (2520 Btus). Therefore the jet orifice size for a 0.5 psi pressure would be about 3mm. Including an adequate amount of air (about 25 cu ft per ft of propane I will have 26 cu ft coming out of the ports per minute.
Here I'm not sure but I'm sort of assuming that the pressure in the burner will be the same as the propane pressure. So for the ports, where the mixed gas will be coming out, I need 26x as much area as the jet orifice, . ie 26x3=78mm over the entire run of the burner (12')
So 78/144 = .54 sq mm per inch of burner length.
Two ports be inch would be about 0.3mm diameter per hole.
If any one can follow what I've written and has any suggestions please let me know!!
I was thinking to use a steel plate under the hearth which would suppot the firebricks, act as a deflector and provide some thermal mass. I spoke to another chap recently and he thought that with flames directly onto 3mm mild steel that it would still warp. Frankly with the weight of the bricks on it I don'y know how much of an issue that would be. However I don't really need a steel plate considering I will be using 2" bricks. It was also suggested that 3mm mild steel checkered frame would warp less because the heat would dissapate more quickly. I'm sort of ready to make the frame for the bricks but I want to wait until I have the burner designed first so I can see where the flames will be. I don't think that the bricks would suffer if I had the flame directly on it but maybe I will design the frame to take the first brunt of the heat. What do you think? Not to worried about even heating at this point because I plan to have part of the burner under each brick.
I have also considered copper and thicker aluminium. There is a company that makes solid aluminium ovens, apparently they make a gift to the Whitehouse each time there is a new president.