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Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1577

Posted: 10:12am 03 Apr 2022

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After spending some hours to trying to find an answer and every one I come up with being in the wrong terms or measurements, I default to the brains trust here for help.
2, I hope simple questions.

1. I want to burn 1 Liter of oil. How many Cubic feet of air does that Require?
Backyard level accuracy only needed.
My ball park calculation is 388?

2. I wish to burn up to 2 L of oil in one hour. Using a Centrifugal blower or inline fan ( IE, very low air pressure) is it going to be feasible to put that much air down a 25MM tube about 1.5M all up. Don't need any real numbers, just a Yes / no with a margin for inevitable inefficiency. There should only be 1 90o bend in the pipe.

I am thinking this should not be a problem with something like a 12V marine Bilge blower. O have one which has a 3" outlet and rated at 90 CFM. Thinking if I can get 20 CFM down a 1" Tube, that will be 1200 CFM.

-IF- my first guess is near correct and oil needs 390 CF to combust, then that would be say 800 CF an hour and I would therefore have a reasonable margin to do this. Excess air is probably desirable.

Oh, a bonus question for extra points....

If the combustion chamber is in effect sealed, would a 2" exhaust/ Flue of 3-4 Meters handle the expanded hot air (Which hopefully will be well under 200o C and cooled further) be adequate to not cause to much of a restriction?

Just trying to explore the practicality of a design I have in mind before I start welding it all up and buying near expensive materials.

Anyone can correct or confirm my inevitable poor calculations would be much appreciated.

Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1577

Posted: 09:51am 04 Apr 2022

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Might be a bit out of the scope of people experience here.
I asked a mate about heat transfer of metal in area and although he works in heating and cooling, He didn't know. For him a matter of working out the load and matching the pre built product with sufficient capacity.

I got a gas pool heater off him on the weekend which is 94 KW capacity. Going to remove the gas burner and put in an oil burner instead.
Was watching a Vid on something else last night and the brain wheels began to creak.
I only want maybe 20 KW max so I thought of doing a submerged heater.

Pretty much a sealed tube sunk in a drum of water with the oil burning in the bottom though forced air and blowing onto the sides of the tube.
A gas water heater I have has a 70MM flue running through the middle and is 800mm long. The rated output is 7 KW. I have another with the same Diameter though the tank only a little longer and that is rated at just over 8Kw.

The tube I have is about 165MM and I have an 800 MM length I'm going to try and a couple of 1700MM length mate gave me. I figure that the larger size should give 4-6X the surface area so should transfer the heat I want pretty easy. Going to go with a 35MM sq air feed tube cause I have plenty of that up the back so pretty sure I'll have plenty of air for the output I need. Really thinking I can ramp the heat a LOT higher but then efficiency may fall off. I do plan to set the air up in stages in the burner so it radiates out and is forced onto the sides of the fire tube so as to break up and disrupt the boundary layer gasses and ensure a totally clean and hopefully blue flame burn from the oil.

I am going to test the burner design tomorrow and if all goes as well as I fully expect, I'll install it in the 6" Pipe and drop it in a drum and see how I go.
I was thinking to use the pool heater as the "Boiler" and then transfer the water to an IBC I'll insulate so I have about 60 KWH heat capacity for the night.
If the submerged boiler works out, I'll put that direct in the IBC and save heat loss through the pipes and make it more compact.

I am hoping I can run the thing at at least 20 KW for heat up and providing house heat at the same time and then throttle it back down to maintain heat as well.
I have achieved greater than 10:1 turn down ratios on other burners so hopefully this one will be good for that too.

Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 961

Posted: 12:40pm 04 Apr 2022

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Haven't had much time lately but, will add a little previous experience.

Quote A gas water heater I have has a 70MM flue running through the middle �and is 800mm long. The rated output is 7 KW.

Had one of those given to us, not all that good.........so ended up cutting a hole in the side and in the center tube and plugged the bottom hole....Made an excellent muffler for a friends 68Kva genset.

More surface area is great for a boiler but a bugger size heat tube you can waste heat up the centre of it, the reason why Loco boilers have a lot of tubes.

The boiler/water heater Dad and I built years ago is 1100mm high and had I think 26 or more tubes 25mm OD steam pipe, this was very efficient at heating water, by the time the hot gases from the fire got to the top of the tubes it was the same temp as the water, the flew you could still hold your hand on it...until it all heated up
This worked for heating but had a really big downfall, being wood fired it would clog the tubes all the time and the flew being cold would also tare up.
Put up with cleaning tubes for years...eventually got the sh$ts, cut all the tubes out and put in 3X 60mm ID �tubes, only clean it mid winter now, but it will waste a lot of heat with the large tubes.

I would like to try it with an oil burner for those times we get a week or so of rain and I Couldn't bother with wood.
So more surface area is good but large diameter can waste some of it, although collecting the heat from the flue by another method would beneficial.
I haven't worked out exactly how you have it rigged up, but will see how it works out.....Going to need some heating this winter I,m sure.

Edited 2022-04-04 22:42 by Revlac

Cheers Aaron
Off The Grid

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