This is how it used to work, the flue gasses just loop back on itself to pass on to the exhaust.
Here's what I am completed as a mod to improve heat transfer. This was a major improvement.
If I make a chamber a bit smaller then the coil diameter and seal off the back end it would force the exhaust gasses to flow over the tubes and around the sides to transfer more heat rather then just go straight up the chimney.
I'll lose a bit of interior space for the crucible but I don't think it will matter much as I don't usually make large castings. Only problem I can see here would be lack of fresh combustion air, I may have to add a port through the back of the stove to get more air in, but hey, that's what experimenting is all about...
Apr 17/03
Made a quick chamber to test out my theory before installing
more 1/2 copper tubing. Wow what a difference. Immediately there
was a 50°F temp rise of the water at full flow, took almost no time
to boost the holding tank temps to 180°F. This is definitely the way
to go. My temporary heat exchanger I use to blow off the heat cant flow
enough water to blow off the heat generated so I have to Tee in a second
exchanger today.
Still running on the first tank with another 5 hrs of burning.
Need to locate or build a small heat exchanger to pre-warm
my household hot water. ;-)
Apr 18/03
Well I finally ran out of oil in the small tank. I refilled
it with a mix of stuff I had around the garage and made a bad discovery.
Automatic transmission fluid makes a lousy fuel! I had a mix of about
60% ATF and it went through it at about half the time that that the waste
crankcase oil lasted. I still have about 2 gallons left and will try it
in lesser quantities.
Also had to add a filter before the needle valve. was getting a lot of fluctuations in the flame due to small contaminates, it plugged up the nozzle pretty tightly and I ended up having to remake the nozzle. With the current mix of oils and the new nozzle I have the atomizing air pressures tuned down to about 3-4 psi now and the compressor kicks on about once every hour and a half for just under 1 min of run time..
Apr 22/03
We actually had a nice warm Easter weekend. I Didn't have to fire up the
stove at all till tonight. Ran for a few hours and ran out of oil again,
That ATF really goes fast. So far I have been running on the initial
50Ft coil in the stove trying to optimize my settings, I still have a flow
restriction in the coils I am using to blow off the heat and with the flow
passing so slowly I am getting a 90°F drop across the exchanger cores.
Until I can find a proper multi-pass core I picked up another of the
single pass cores and will Tee it in this week.
I spent a few hrs today optimizing these pages a bit so they're a little easier on slower connections.
Apr 28/03
Best laid plans go to waste, its been a few days but I managed to make
some improvements in the stove and on these pages.
I installed an
additional 40Ft of 1/2" copper tubing inline with the first for
improved heat transfer. Also added was
another inch of refractory to the rear wall, I had noticed it was getting
a little hotter then I would like to see. The water reserve tank I
was using was also removed and replaced with a smaller modified propane
tank, the larger tank was taking way too long to come up to stable temps.
I really expected to see a dramatic temp change with the added tubing,
such was not the case. At first I was quite disappointed till I noticed
that the temp rise didn't slow down at all at 200°F like it previously
did. I hit 209°F before I got the flame low enough to keep the temps
below boiling, then trimmed the flame to hold a steady 185°F. Definite improvement
I think!
One of the delays that kept me from my tasks was picking up a refrigerated water chiller that a friend offered me. turns out its a 15hp 15 Ton cooling capacity unit weighing in at about 1500 lbs.. Any one want to guess how I unloaded it off my pickup without a fork lift?
Any how I now have some more thermal controls and heat exchanger parts to create with. My next project, make a R-22 reclamation machine..
May 12/03
Well our weather was holding out well till today. The winds have been
blowing like mad for the last two days and the house temp took a nose dive. I
was down to my last gallon of oil so I called up a friend and he offered me a
few (25!) gallons of surplus hydraulic oil he had. This friend was also the one
who we built the original stove with so I took the opportunity to see what mod's
he has made. He changed from the home brew nozzle to adapting a pressure washer
tip to the end of the tube. Generously he gave me one of the tips to try out.
His pressures are much higher for operating then mine, but he's got more air in
the shop then he knows what to do with. All the parts are pretty much the same
still from when it was first built.
This hydraulic oil is a bit tricky to dial in. there's either smoke, or smell, I couldn't seem to dial both out at the same time till I moved the heat sink steel a little further away from direct flame. This seemed to give the oil a little more room to combust. I think my next mod is to add the new nozzle tip and make the inner chamber a little larger so the flame has more room to breath.
Also donated by my friend was a nice air to liquid heat exchanger radiator. This unit measures approximately 22" by 19" by 2 1/2" which is just about perfect for my duct, and with 3/4" NPT inlet and outlets it's flow capability is more then enough.
I might even have to restrict the flow a bit to tune the system to get the 120°F return temps that I need if I want to run it through a liquid to liquid heat exchanger for my hot water needs.
Looks like the ambient temps are on the steady rise so I wont have much to update till fall.
In the meantime I have added another page with some Air Conditioning mods I intend to make.
May18/03
Best laid plans put to rest, seems the exchanger has a leak in it. I might be
able to fix it with this aluminum rod I purchased years ago. I kind of doubt it
though, I never had luck with the stuff yet and the hole looks to be in an
awkward place. I guess I have nothing to lose by trying, at worst I should be
able to take it in to a radiator shop and let them try to patch it.
Feb 2004 Successes and blow outs.
Finally have a chance to update the page a bit. Basic breakdown of the system configuration
is as follows;
The System is now sealed and pressurized to about
15psi with a 4 gallon expansion tank.
Added 1 gallon of No Burst (c) propylene antifreeze but still froze up 3 times!
Tried
out the pressure washer nozzle with higher pressures on the oil. Wow! With 80psi
on the oil and less then 5psi on the air the burn is much hotter and cleaner and
oil consumption is super low.
Attempted to add a flameout control but need to make a proper bracket in
the flame area to hold the probe.
Added a nice digital thermometer
to monitor the outgoing water temp from in the house (see
"Thermometer" below).
Overheated the stove a the first time
and popped a line nothing serious.
Overheated it again a few weeks later, this time much
more dramatically, popped a line and melted the inner liner on the Kitec line
for about 15ft and steamed out the entire garage.
Switched to Prestone (c) poly antifreeze, $15/gallon vs. $35/gallon for the No Burst (c)
Thermometer
Now this project was well worth the time and effort. Till I built
this I had to keep going to the stove to monitor the temps. It consists of an
Atmel 2313 and a DS18S20 digital thermometer chip and 4 digit LED display. The original Project
design was taken from Wichit Sirichote's Web Page at http://chaokhun.kmitl.ac.th/~kswichit/avrthermo/avrthermo.html
Its details you can get from the preceding address.
Unfortunately it
didn't contain some functionality I desired so the hardware was reworked and
thanks to a good friend of mine on IRC "zchrist" the code was heavily
modified to add relays on 2 I/O ports of the Atmel. The only real hardware
addition were the 4 switches shown in the original schematic, The relays are
tripped based on user programmable limits of high and low temp settings. For the
low temp setting I have one of the micro controllers I/O ports running a small
TRIAC board controlling the pump shutdown, when I am done burning its necessary
to let the pump run for a bit to soak off some of the heat remaining in the
stove so the water doesn't boil. The circuit will let the pump remain running
till the water drops to a temp of 26°C saving me the trouble of manually
shutting it off. The second I/O is tripped at about 90°C which controls a relay
to switch the furnace fan on high speed to move a little more air past the A
coil in the furnace ducts.
I plan on adding a few more controls and pictures soon so bear with me for a bit.