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Originally Posted by
Ralph1Malph
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I have printed your drawing from a few pages ago and it seems clear but...(the side view link is bruck)
Ta!,... I'd better look at that.
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1. How 'airtight' does the pan and the lid need to be? (We have spent hours drawing Bernoullis principal and associated math on the whiteboard and ended up just yelling at each other - quite funny aside actually, I'm the engineer so just build it I said, it's magic:p....We're the tradies and it won't work they say :D).
Righto Ralph, I'll do my best.
As airtight as possible without the need for gaskets etc. Mine was a good metal to metal fit, but now has a gap of about 1mm around 10cms of the pan edge (slight heat distortion) it still works OK. Any tradie worth his salt can build it and make it work,... considering that a Public Servant built one in about three nights after work and has been using it in his home for about four years now. [ame="http://www.youtube.com/watch?v=FvcgokYbpAg"]YouTube - ‪Waste oil heater‬‏[/ame]
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2. Detail as to the design and what's inside the primary pan is a little confusing (to me anyway). Are there any particular specs for the fuel feed trough?
The feed/preheat trough is all that is in the pan, it should extend to the centre if possible, mine is slightly shorter, but still works OK. This has a twofold purpose, 1. It acts as an oil heater negating the use of a preheating coil, these are a pain, as they usually coke up when the heater is running at high temperatures and there is no convenient way to clean them. 2. It dribbles the oil into the centre of the pan where it gets the most heat, both from the primary burning and also radiated heat from the flame in the secondary burner above it.
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3. Whilst I consider myself smart, the theory of these critters does my head in. Here's how I think it works: oil in the pan just plain ol' dirty burns, but when drawn through the secondary burner, the extra oxygen forces a cleaner hotter burn. But it actually should vapourise in the primary, not burn.....'pleeease explayn'.
Close,... The oil in the pan partially burns in a low oxygen environment providing heat that vapourises the remainder. This vapour in turn rises through the primary flame and radiated heat from above, forming a hot carbon rich vapour which in turn rises into the secondary burner where it is vigourously mixed with fresh air, this supports the secondary flame where most of the heat is generated.
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4. Is there any reason I can't just weld the two rims together rather than use throughbolts?
Welding large cast steel parts can be problematic requiring pre heating and temperature control whilst the welding is done with low hydrogen electrodes or similar. It could also make your assembly/disassembly more difficult depending on how you are going to hold the rest of it together. It would also make the firebox assembly bloody heavy and awkward to handle, should you ever need to do any maintenance.
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5. I actually intend to adapt your fine design and use it to heat my pool! Any modifications or changes you'd recommend at the pre build stage to achieve this?
Regards and pardon the questions
Ralph
I believe that there is already one being used in WA to heat a lap pool in the home of a paralegic gentleman somewhere down around Margaret River.
If you can find one use a large cast iron camp oven as a primary pan as the come with a close fitting lid, they are also cast iron and resist burning and distortion.
Drill all of your airholes undersize to start with and enlarge them as needed.
Use 15cm flue and a similar sized secondary burner tube, preferrably on old cylinder liner. They are soft and easy to work and also resistant to distortion.
The height of the secondary tube is not important, but for maximum efficiency it should be about "square" (similar height as the internal diameter)
One large row of holes near the bottom for radiant heat into the pan and another row about half way up. (32 holes x 10mm dia in each row) This combination seems to work well.
Not everyone is a masochist, and questions and answers may save you a lot of frustration. :D