So...
Basically only one subject left, that of "how to extend operation time"...
It was pretty clear from the beginning that even with the improvements to the engine, operating time was fairly short: 15 minutes at best in reality, and for that I had to control myself and use the throttle fairly conservative.
So I first wanted to install an engine driven pump as offered by Microcosm. I ordered it, received it, but heck, by the time I got around to it I realized that this was not a plug&play option, and what was more, adjusting the feedrate was going to be an issue: I simply did not see how I was going to arrange that. It would entail either constructing an excenter with an adjustable stroke, or an adjustable bypass/return valve, additional piping, possibly a servo, and that was more effort and investment than I was willing to make.
So I looked around on the internet and found the Regner electric pump with speedcontrol. I will get back on that pump because there's something horribly wrong with that thing quality wise that I'd like to warn everybody of. But that is for later.
In itself, the pump is straightforward and I installed the pump. I posted this pic before.
https://www.modelbouwforum.nl/attachments/img-20230623-wa0001-1-jpg.544492/The next problem was going to be a feedwater tank: There was nothing commercially availlable that would make any sense, at least not to me.
As I said in my introduction, I am a marine engineer, and somehow "stuck in a certain train of thought" when it comes to operating steamsystems:
The Microcosm boiler has a steamable quantity of about 180 ml (6 oz) of water. I can deal with that. You boil the water, and when its gone its gone.
Things change when you add a tank. In my mind it suddenly becomes a "system" and in my mind, systems are operated a certain way, you don't deviate from that. My brain is conditioned by 30 years of dillidallying around in engine rooms. When one operates a boiler with a feed system, then that feed system has to run continuous and the operating time becomes the time it takes for the feed tank to be empty. A feedwater pump being switched off while a boiler is kept running is a no-no to me, and a feedwater pump being allowed to suck air against a pressurized boiler, even worse.
Call me silly, call me autistic (I am, so don't feel shy), but that was how it was going to be... A tank, a pump, boiler at constant level, and the operating time determined by the tank reaching low level.
I am, as you all have seen in the pics of the wick feed lubricator, a horribly poor metal sheet worker, so making a feedwater tank myself would not be very succesful.
Regner (at the timethe only supplier I was familiar with that could deliver in reasonable time, because in early August I was a total newbie in the world of model steam) only had a cylindirical 300 ml tank that would not fit in the boat, and a rectangular tank that would fit, but only held about 75 ml of water... So my autistic brain hit a snag: If the boiler has a steamable content of 180 ml, but a feedpump set-up would only be 70 ml of "consumable water", I would be going to LOOSE operating time.
Heck, I was fully aware that I could run the feedpump as long as the tank lasted, then continue emptying the boiler and I would gain maybe 6 or 7 minutes of operating time, but... To me, that would be a total turn-off. A bandaid, a non-solution. A patch. I could not envision deriving joy from that type of "solution".
I searched high and low in all kinds of non modelling related shops for suitable larger containers I could adapt, but no luck.
So I decided to make the feed tank out of plywood. Sounds silly, but... I normally build planes and such, I knew I could knock a tank out in mere hours, and to basically any shape I wanted. Waterproofing is easy: one or two coats of pore filler and sealing it up with the type of polyurethane laquer as used for hardwood flooring.
I ended up with a wedgeshaped tank, 12 cm long, 7 cm wide narrowing to 5 cm, and 5,5 cm in depth, theoretical almost 400 ml.
Open top with anti-sloshing baffles, practical tests showed it would safely hold 375 ml in actual running conditions...
https://www.modelbouwforum.nl/attachments/20230623_200420-1-jpg.544502/So.... NOW we're talking... this brought the boat to about 25 minutes of operating time, 30 if I took it really slow...
By this time, I started realizing that feeding from a tank
will introduce dissolved gasses in the boiler, and these non-condensable gasses will end up in the level glass eventually, but... the Microcosm boiler has its feedwater connection at the bottom of the level glass, so this immediately presented the problem that as soon as the feed is in operation, boiler level becomes hard to read.
This issue with dissolved gasses can be reduced significantly by keeping an eye on water quality, I might spend an episode on that later, but for now the problem was there and had to be dealt with.
What good is it to have a controllable pump, but no means to visually check the level?
I solved this by installing a blow-off valve in the top of the glass.
https://www.modelbouwforum.nl/attachments/20230930_101117-1-jpg.555012/The discharge line of this valve ends up at the bottom of the feed tank. Initially I was a bit worried that this might lead to accidents with the steam pressure blowing out the contents of the feedwater tank, but practical tests showed this to be a non-issue: Even with only 1 cm of water in the feed tank, and the blow-off valve fully open at full boiler pressure (max 2 bar in my case) the heat absorption of the feedwater is so strong that steam does not even reach the surface of the water. It's 100% safe.
As it is right now, I fire up the boiler from cold with this valve open, during warm up the air escapes (with a funny "gloop gloop" sound) and as soon as steam is raised the sound changes to the percolating noise of a coffeemaker. Very convenient.
Enough about the level glass...
By now I had achieved an operating time of about 25 minutes before I had to come in to refill the feedwater tank, which due to the open construction could be done "on the fly" with the boat in the water. The gas tank allowed for about 50~55 minutes of operation (including the firing up from cold) on a charge of 60 grammes of propane/butane mix.
Although now absolutely acceptable, I still wasn't really satisfied with the fact that I had to come in for water while obviously the fuel quantity allowed for much longer operating time, and overthinking things, I also thought that feeding a boiler with cold water is not the most eficient way of feeding a boiler. But what good is it to save on fuel when you don't have the water to evaporate with it?
Hmmm.... How if...?
How if I would utilize the exhaust steam to pre-heat the boiler feedwater? It would improve the operation of the boiler (in more than just "lower fuel consumption" by the way), but it would ALSO produce condensate. Condensate that MIGHT be usable for return to the feedwater tank, thus extending operating time, right?
A quick calculation showed that the condensate generated by the pre-heating of the feedwater alone, would yield at best 15% of the water feedrate.
That's a simple calculation, water per gramme requires a certain amount of heat to raise temperature from ambient to 100 deg C, and condensing steam delivers a certain amount of heat per gramme of condensed steam, and that ratio is roughly 1:7
Since we're talking here about a feedrate in the order of magnitude of 10 ml/min, the heat dissipation for preheating the feedwater is approx 50 Watt.
and a condensate return of maye 1,5~2ml/min
Disapointingly low yield. Would it be worth it?
Then it struck me: the condenser/preheater would be a shell to which steam is supplied, with a coil running through it conducting the feedwater. But the shell on the outside has exposed surface, dissipating heat to the ambient air.
A quick google search on the subject of radiator heat transfer combined with the expected dimensions of the condenser, hinted at a radiated heat of approx 80 Watt, which would probably generate another 2~2,5 ml/min.
OK... now we're talking, because that would reduce feedwater consumption from roughly 10 ml/min to 6 ml/min, and a quick estimate it would reduce fuel consumption by about 10% as well... Meaning I should be able to extend times between water refill, and possibly reduce the filling charge of the gas tank to 50 grammes.
The condenser was made with a coil of 1 metre copper tube 3 mm OD, fitted in a piece of vacuum cleaner tube, capped with two discs of aluminium, held together by a threaded rod.
https://www.modelbouwforum.nl/attachments/20230929_194756-1-jpg.554978/https://www.modelbouwforum.nl/attachments/20230929_200229-1-jpg.554979/Since exhaust steam can contain traces of cylinder oil, a condensate cleaner was built into the feedwater tank.
https://www.modelbouwforum.nl/attachments/20230924_093948-1-jpg.554374/https://www.modelbouwforum.nl/attachments/20230924_155120-1-jpg.554435/https://www.modelbouwforum.nl/attachments/20230924_155126-1-jpg.554436/https://www.modelbouwforum.nl/attachments/20230924_155131-1-jpg.554437/The condensate cleaner consists of a compartment of approx 25 ml, with a dividing bulkhead that forces the condensate to pass underneath.
The large side of the division is where the condensate enters, and in this part, oil absorbing material is floating on the water.
To make absolutely sure, a single sheet of oil absorbing cloth is floating on the feedwater tank as well.
https://www.modelbouwforum.nl/attachments/20230925_110235-1-jpg.554563/Condensate enters, possible oil traces are trapped in the absorbing material, water passes underneath the divider, and flows over into the feedwater tank.
The first test:
https://www.youtube.com/watch?v=rqYJdb_I7AMThis test showed that the single steam/condensate exhaust was a mistake, because the condensate ended up where it was intended, but the escaping steam caused unwanted condensation everywhere else in the boat.
WOW! First test at varying power settings (emulating normal use as good as possible) immediately resulted in an operating time of 50 minutes with some gas and water to spare...
NOW we're talking...
But I still had to solve the issue with steam all over the boat. First step: a separate exhaust.
https://www.modelbouwforum.nl/attachments/20230930_013649-1-jpg.554999/This did not solve the problem, it relocated it, because yes, the steam vented out, but it also sprayed condensate drops everywhere, so the boat still got wet all over. So a moisture trap with drain back to the feedwater tank was fitted. I don't have a pic, only a video:
https://www.youtube.com/watch?v=YxztgtuN-ZIand now that problem was solved as well.
The white "cap" on the condensate drain is an orifice, intended to allow condensate to pass but limit the escaping steam to a minimum.
It also serves to make the outflow of condensate a bit less abrupt, giving the filter more time to absorb any oil traces.
But... although I had clean condensate for about 30 minutes, then the condensate turned turbid and dirty, too dirty for the condensate cleaner to keep up... Damn, what happened?
I found out that the oil separator vessel as supplied with the machine, would be full after approx 30 minutes, and after that, oil would pass the separator and enter the condenser. I first tried to reduce condensation in the oil separator by thermally isolating it:
https://www.modelbouwforum.nl/attachments/20231003_230559-1-jpg.555625/This did NOT make any measurable difference. So I had to figure out a way to remove this water "automatically".
I messed around a bit with designing a float valve, but the numbers are not there: in the dimensions availlable (max diameter 7 mm) and the materials and methods at hand, it turned out impossible to make a float with sufficient displacement to actually
float...
If difficult and complicated solutions won't work, the only option is to go simple, and I solved this by simply fitting a 2 mm OD (1 mm ID) copper tube in the oil separator, all the way to the bottom.
https://www.modelbouwforum.nl/attachments/20231004_171543-1-jpg.555648/https://www.youtube.com/watch?v=TUNN3FOJzQM&t=18s(in the pic, the tube is still 3 mm OD, flattened at the end, as demonstration of principle only, the tube is now 2 mm OD, and the receptacle has been replaced with a stainless steel bottom part of a coco shaker)
This tube allows the very dirty crap that collects in the oil separator to discharge to a larger collecting reservoir. Now the oil separator stays dry inside, the condensate remains clean, and the condensate cleaner easily lasts 10 or more operating hours.
the receptacle for the crud from the oil separator suffices for about 2 hours.
Technically, this is what I have done to the installation.
I started with 10~15 minutes operating time, a waterconsumption of around 700~800 ml/hr and a fuelconsumption of 75 grammes per hour (average values, give or take, applying to average running conditions), and ended up with 50 minutes of operating time, about 400 ml of water per hour and 55 grammes of fuel per hour.
I grouped these posts by subject, but in reality everything went kriss-kross, all at the same time and in WAY more time than it took me to write these posts. I actually learned a LOT, despite having been involved in operatiing steam plants professionally, for many many years.
I freely admit that my "professional deformation" caused me to do things different than probably 99% of model steamers, and I am not sure if any of this is useful for other steam enthousiasts.
For me, the experimenting, the testing, the overthinking, the solving puzzles and the search for ways to achieve results with absolute minimum means, the "McGyvering" so to say, absolutely was worth it.
I ended up with an extremely userfriendly, easy to operate and reliable set-up despite the use of Micky Mouse methods and materials.
https://www.youtube.com/watch?v=3NY6Gr5_aiwA bit outside the scope of the subject of "modifications" but still maybe interesting for some, is the subject of "feedwater quality" and the experiences and observations I gathered in that respect while doing this project.
I might post about that as well.
