- Jun 18, 2020
- Reaction score
as I noted I spilled a full glass of water on my entire pile of notes. I had a big mess of drying papers of course the super fine black marrrs I used sonic an readily see are now some kind of artwork don’t laugh too hard my kitty was running all over probably thinking I was sbout to explode. So I’m rebuilding the mess the aluminum is quite strong enough when you consider water pressure is around 45-50 psi in RV WATER TANKS THAT ARE PRETTY THIN WALLED AN INEXPERIENCED GUY ONCE BLEW ONE UP WITH 120 psi air very lucky nobody got hurt. It was a 5?gallon tank . I have no idea what he was doing testing with shop air . I did some basic stress calculation observing that the screws holding the end caps in might subject the end of the main tube to to a testing effect which is where overlapping plates you see in bridge construction comes from. By using the through to tod I was able to load its bolts in tension preventing any real bending ofvthe end cap which is unlikely anyway we often lift race care engine with a 4 bolt plate on the carb studs. These are 1/4 inch to 5/16” engines can weigh 1,000 pounds And I’ve never seen any of these bolts pull out or break the lifting plates are often just loosely held on with hand installed nuts so the things are poorly mounted a 1/4” gr 8 bolt is amazingly strong so I’m pretty confident ther won’t be issues there are no closed copper tubes so collapse as you pointed out won’t happen they are the just to help circulation and provide heating surface area. As far as heater go they are stainless tubes surrounding the elements . I don’t have a way of measuring wall thickness but I have to go with previous experience here the same things were used to heat platic mold in molding while not submerged or pressurized at lest not measurable I don’t see any problems . I know it seems like a low heating capacity and I may be taken to task here we will se . This boiler holds less than 3/4 gallon subtracting volumes of all the submerged parts there just it’s is not a lot of water in it which is why I need to come up with a good fill pump . I have the parts to do it I just have not got that far yet . It’s hard to believe how fast and how far this hobby has advanced for me . I “0” when I made the decision yet 50+ years of model airplanes and who bows how many years in sports I played senior base ball untill I was 72 And of course my life career. I appreciate any challenges and comments . I consider them learning experiences. Every spect of this hobby is new and bears investigating . I’m trying to document things I do if for no reason other than have w page to look at and say yep I considered that and here is what I did . When you say hey you need to calculate this or that , I most certainly will look into it . Because it’s part of learning sbout this hobby. I’m building on your experiences. As I noted I’m open to debate and out right challengesHi Byron, You sound to be very productive with your ideas. Just a couple I want to debate:
- If you are planning on just balsa wood for insulation, that will be all you need for conductive losses, if around 1/2" or more. So I can't see any reason for the car exhaust stuff? But your choice. However, you should consider radiation losses (the radiant heat shines straight through the balsa or other until it hits the stainless steel). So if you polish the aluminium tube that will be excellent, or wrap in aluminium foil. Either will reduce radiant losses significantly compared to doing nothing with the surface of the tube.
- My biggest issue is the use of aluminium with steam. I thought this was always a "NO! NO!" because water doesn't corrode aluminium rapidly, yet STEAM does, especially at elevated temperature. And when it does it gives off hydrogen, which has the potential of being very explosive... So although domestic pressure cookers with steam at up to 15psi exist and are safe to use, please check what higher temperature steam will do to your boiler.
- A quick check suggests you need >5.2kW of steam to extract if the engine needs 50psi at1000rpm (and a generator to load the engine). Of course, at 20psi you'll only need 3kW... of steam power. Allowing for losses (maybe a couple of hundred W if well lagged?) you'll need more than those figures from the heaters. Unless I have screwed-up the calculations? (I had to correct some glitches in my spreadsheet). What did you calculate?
- What "penetrations" will you make in the outer shell cylinder? (If any?) I can see a design where all the safety valves, water gauge connections, steam extraction, water-feed, etc. is done via the end plates, so the boiler shell is "without penetrations". but that is unusual. Mostly there is a steam dome (to collect steam high above the spraying surface of water), water feed, connection for safety valve, etc. so that affects the hoop stress calculations and comparison of the design with permissible safety limits. ASME uses a "Standard" value of 3.3 for the SCF if ANY penetrations exist in a boiler shell or tube. With this SCF (assuming at least 1 penetration) for your boiler at 50psi, I get a hoop stress of 1902psi and I think the permissible stress will only be 1141psi for aluminium..? which I reckon is a FOS of less than 5. But the regulations normally require a FOS of 8? But I may be wrong? If there are no penetrations in the shell tube, then the FOS is over 15 - which is good. - What have you calculated? - I am keen to be sure my calcs are sensible, and if you have close results I'll be happy.
I’m just having a good time already . Sorry I got carried away. I have an INT blood yet so I must go for now . The engine is supposed to be delivered today I just checked tracking and it’s out for delivery . I’ll get back later thanks