heat exchanger welds, 6013, need advice

[gaz1]

you can improve it if you weld direct to a steel wood stove top

if your based on a normal wood stove and you come out of the rear you can then flow the fireboxes flue exhaust back to the front and up to the next level via tubes again before the final lift with the chimney

the pic is for a pellet boiler but can be used with a normal wood stove



for sizing of the tubes you have to match the stoves flue pipe so how many of your tubes equal the stoves flue size 5" or 6" should be about 7-8, 2" tubing

but you still need ash collection boxes at the rear of the stove so you can brush the steel tubes clean

if your intending a seperate boiler you can connect it at the rear or from the top of the stove but you need your boiler stood above the fire stove

but it will chew through wood using secondary air will conserve on wood even more so if you preheat the secondary air released above the fire itself as it gasifys rather well and you burn this whist the stove is set at a lower level

 

[Turbo]

Is is just me or does this thread remind you of this one.

https://www.mig-welding.co.uk/forum...acket-heat-exchanger-for-a-wood-stove.142899/

At least this time the op is sticking around. In the other thread the op made one post and was never seen again.

 

[VanMarco]

gaz, my idea is indeed to mount the belly of this exchanger over my existing firebox. wether or not i will have exhaust do that in out in out, i don't know, it can be arranged with simple baffles after.
About sizing, yes in theory 7 8 tubes should be the exact area for 5-6", but i will use about 20. On the other forum, someone even used 30+. It's too complex engineering calculattion for me. Reasoning is, Existing pipes
if too many can be capped. non existent pipes, it's another issue

I also apologize if some things I say may be profoundly wrong, I did also get help on the welding of this from.. chatpgpt
I understood about denlow diagram, sorry about earlier, well isn't it what i said, root pass and 7018 cap on top? even though in the diagram there's no bevel?
Infact, what's confusing me now is that i was told here that I could use 7018s, yet chatgpt says these are only for capping? (yes i know they're low hydrogen and need to be baked, don't worry about that)

Ty!

 

[addjunkie]

gaz, my idea is indeed to mount the belly of this exchanger over my existing firebox. wether or not i will have exhaust do that in out in out, i don't know, it can be arranged with simple baffles after.
About sizing, yes in theory 7 8 tubes should be the exact area for 5-6", but i will use about 20. On the other forum, someone even used 30+. It's too complex engineering calculattion for me. Reasoning is, Existing pipes
if too many can be capped. non existent pipes, it's another issue

I also apologize if some things I say may be profoundly wrong, I did also get help on the welding of this from.. chatpgpt
I understood about denlow diagram, sorry about earlier, well isn't it what i said, root pass and 7018 cap on top? even though in the diagram there's no bevel?
Infact, what's confusing me now is that i was told here that I could use 7018s, yet chatgpt says these are only for capping? (yes i know they're low hydrogen and need to be baked, don't worry about that)

Ty!

Never forget if you ask 50 people for an opinion on how to do a job, you will get at least 100 different answers.
As you mention efficiencies earlier….if you do your research you will find that fire tube boilers in the generation of steam have been pretty much superseded by water tube boilers as they were far more efficient. Addition of a waste heat recovery unit ( which is what your building) adds a bit to the efficiency, but not a great lot, as it only really preheats the water. In your design you will need to be careful not to actually reduce the efficiency by removing too much heat from the fire smoke on its travel through the waste heat recovery unit, reducing draw and therefore the efficiency of the heating in the primary heating.

 

[denlow60]

gaz, my idea is indeed to mount the belly of this exchanger over my existing firebox. wether or not i will have exhaust do that in out in out, i don't know, it can be arranged with simple baffles after.
About sizing, yes in theory 7 8 tubes should be the exact area for 5-6", but i will use about 20. On the other forum, someone even used 30+. It's too complex engineering calculattion for me. Reasoning is, Existing pipes
if too many can be capped. non existent pipes, it's another issue

I also apologize if some things I say may be profoundly wrong, I did also get help on the welding of this from.. chatpgpt
I understood about denlow diagram, sorry about earlier, well isn't it what i said, root pass and 7018 cap on top? even though in the diagram there's no bevel?
Infact, what's confusing me now is that i was told here that I could use 7018s, yet chatgpt says these are only for capping? (yes i know they're low hydrogen and need to be baked, don't worry about that)

Ty!

VanMarco@I understood about denlow diagram, sorry about earlier, well isn't it what i said, root pass and 7018 cap on top? even though in the diagram there's no bevel?​

If you look at example image 7.1.4.
you will see at the top left that you need to bevel.

 

[VanMarco]

VanMarco@I understood about denlow diagram, sorry about earlier, well isn't it what i said, root pass and 7018 cap on top? even though in the diagram there's no bevel?​

If you look at example image 7.1.4.
you will see at the top left that you need to bevel.

View attachment 495985

oh, apologies, i see it now!

 

[gaz1]

if your just sitting the unit to the rear of the stove you want a bypass door for starting the stove so you can get the chimney flowing it also helps in stopping your tubes getting creosoted with klinkers

putting more tubes in is for the likes of coal being used and well loaded unless your using smaller tubes as long as it equals the 5-6" exhaust

you want the exhaust to flow through the tubes whilst the water is kept within a water jacket its also the easiest to clean out if you flow it the other way using baffles you wont clean those pipes even with baffles fitted whilst an access port can be built on the side

whilst a square to rectangle water system is the prefered method due to heating up the water faster compared to the external round tube system that would take longer to heat up that amount of water

 

[gaz1]

now since im aware of the lithuania ( i think ) vertical boilers this one below uses preheated secondary air



the sides of that stove is the boiler water system

for the secondary air it uses an electric fan to blow preheated air above the fire i also have the video
the name on youtube is this

primulfoc-centralapelemnesicarbu its also known as a candle wood boiler

if that top box was fitted with tubes like the old vertical steam boilers




if your tubes was set in the rocket stove method the top tubes would become really hot whilst the lower tubes ( downdraft ) are used to preheat the water boiler system compared to follow the flow of exhaust but both systems still need a chimney bypass system

 

[VanMarco]

wow so many cool info, thanks!
I did 2.5mm 7018 elekroda zagreb. rods not dried. they seem to "bite" more, even though i see some undercut. Don't mind the point where the two meet, yes, i could've made the holes not that close, i know

this is 6013 again, it's more fluid, but it doesn't give the same effect.

so to do the second pass i would grind this flat, not bevelled, and weld again?
Thanks so much guys!!!

 

[gaz1]

a bit of advice for you if the tubes are too close to each other they are not heating the water up equal

best to have them with enough space between them 1" is more than ample to heat the water between them or even 3/4" space between them both tubes will equal warm between them but that also allows 1" spacings between the lower level but those tubes have to equal out at the same spacings but stepping the tubes between each other its still 1" between 2 tubes

the posted one above works on a 24hr heating system

 

[VanMarco]

ehehem thanks for the concern, I know it very well. this is just a test plate. the project will have 50mm spacing

 

[VanMarco]

hmm, also, as tomorrow I go and order the pipes for the firetubes, I'm still confused a bit, even though this isnt the ideal forum to ask this to, as this is more design rather than just welding, I think i would like to put 20 pipes that are 48mm OD. I thought about putting more, but 42mm OD, but I'm not sure how would this impact it. the exhaust of my firebox is currently 6" but I built this, so I don't know if as it is it's big enough, if i were to match this to the firetubes as gaz1 mentioned, they should be 7 or 8. But i also read that it's ok to use twice the size of the exhaust, but not more. So what would it be best? I find these 48mm ones easier to weld, and i also predict it'll be much easier to do "chim chim roo" with this size than the smaller ones.

Thanks again!!!

 

[addjunkie]

As long as the cross section area of your tubes is bigger than the current exhaust cross sectional area of exhaust you wont restrict the gas flow. However more tube surface area will give you more heat transfer.

 

[gaz1]

theres more involved than what you know of

your stoves output is only 5-6" even the dynamics of most wood stove is the same whilst it collects all of the heat to output at 5-6" it still goes through 2 baffle plates the front and rear baffle plate roughly 1, 1/2" wide x 500mm wide

you can add another row onto it as a backup incase some tubes block up

heres the different tube pics



on each of those systems it uses mass of fire and mass of air pushing through the system you only have one flow output of 6" yes you can add another layer or 2 layers but your better off adding something so all 4 sets of tubes are heated per each pass

the first one would work better with it and the second one and also the third and 4th one

the rule of thumb is heat rises on the first one heat rises and rushes towards the top tubes and out through the exhaust fast but the mass of coal and flames and heat from that type of system creates more than enough flow through all the tubes and exits via the exhaust

the flame thrower ( fuel ) with air blower uses the same principle

 

[knighty]

I don't know any numbers for it, and I guess they'll depend a lot on the rest of the system, what you're burning, if you have a fan, fire box design etc. etc.

but... you don't want loads more surface area through the heater tubs than the exhaust - too much and you'll cool and slow the smoke through them too much so they'd end up covered in tar/soot deposits

I think it's one of things where you just have to guess it

are you having the tubes horizontal or vertical?

 

[addjunkie]

Id suggest having a baffel in the head section of the exchanger so the hot gasses get two passes.
The big difference between your system and the fire tube boilers shown is the boilers have forced air. Where as you are just using a naturally aspirated fire. Forced air allows you to burn much more fuel, and fuels with a higher calorific value, therefore generating higher flame temperature and more heat inthe system providing you keep the stoichiometric ratio correct. This is where you need to be very careful with your economiser design, last thing you want to be doing is superheating any steam you generate.

In a past life before I got old, I used to be all intimate with the big sums required to work all this stuff out! Enthalpy, Entropy, superheat, heat transfer through composite walls and such things

 

[VanMarco]

are you having the tubes horizontal or vertical?

it's going to be horizontal.


Also, i did plan to do like, 10 lower pipes exhaust in, top 10 pipes exhaust out like in picture #3 (IQSdirectory).
I just believe it'll take a bit to start sucking up exhaust from cold.
And yes i'm all aware about creosote, thats why i wanted to bigger pipes so they'll be easier to clean periodically.
Im not going to make steam, just hot water though.

I'm still convinced that whatever is that I do, will definitely be more efficient than what I have. I will find pictures, but it's quite shameful. essentially, most of the heat is just dispersed
and not recovered, exhaust temp is close to 300+C, so albeit coal being quite cheap, this cannot continue.

Thanks so much for all yoru kind help!!!

 

[gaz1]

its better to use a bypass to the flue at the start up so your chimney is preheated before you redirect it to the boiler as the chimney is preheated

for steam or just hot water its basically the same process

whatever you can do can also can fail my advice here draw what you intend to build and get some advice on the subject

ive already given you pointers but i havent told you directly as you havent provided any drawing of your attempted build

wait until you get the system has failed as you havent factored the speed or flow through your system

 

[VanMarco]

its better to use a bypass to the flue at the start up so your chimney is preheated before you redirect it to the boiler as the chimney is preheated

for steam or just hot water its basically the same process

whatever you can do can also can fail my advice here draw what you intend to build and get some advice on the subject

ive already given you pointers but i havent told you directly as you havent provided any drawing of your attempted build

wait until you get the system has failed as you havent factored the speed or flow through your system

Oh I see what you mean, I would have a valve that at start up bypasses the heat exchanger, gets the chimney well warm, then it's closed and gases go through the exchanger!

I will provide with the drawing thanks for the help!

 

[gaz1]

another thing i will say on a first build or test build i would build it in thin material first and test that model

that gives me chance to adjust the system before the final build in thick material however they will be a slight difference as the material is thicker and takes longer to warm up compared to thin material

theres more things that you havent thought out access doors for clean outs as ash does want cleaning out

windows 7 has a paint program easy enough to draw with that you want 2 drawings one side view and one tube view also best to consider the bypass way as well via a drawing

theres simple sluce door or a door that closes

ive gone the exact opposite way with a difference purple flame

this is whats possible

but high temps within the firebox means high temps with the secondary air so def hitting 2000f

boiler temps are acheiveable with a rocket stove