'WIDE A WAKE' a steam launch tale

[derekwarner]

Ramon....

. from an engineering placement point of view....the radial array of the 12 cross tubes appears brilliant
. from a thermal transfer question....will the heat from the gas flame be less effective on the tubes outby [furthest away] from the flame?

Derek

[Bezalel]

Nice job Ramon
 
Question for my edification; My understanding is that 2 flute slot drills are designed to plunge into solid material, so I am wondering, was there a particular reason you run a pilot hole ahead of the slot drill?
 
 
 
Bez 

[Ramon Wilson]

Hi guys, Thanks for your input - just a quick reply before getting going for the day.

Derek, I'm afraid I don't know. I have done as suggested by the CBI. When I first laid it out (and did a first test piece) I had twelve tubes at 30 degrees to each other which gave two spirals. To me that 'looked right' the hot gases, not just the flame having plenty to work round but it did leave gaps as you looked straight down the flue which is not what CBI Paul recommended. What you now see is a result of the discussion over that first test. As you can see there is just one spiral straight through to the uptake but with the tubes much closer. Again - to me - that does not look as effective as the first but having no experience of this kind of matter I have taken his advice at face value.

Sandy has done me proud again and sent me some more calculations on the steam required and the likely output with ten tubes which just falls short of requirements at 500rpm. Given that the engine will very unlikely be required to do anything more than push this boat along at a very sedate pace I'm hoping that whats been done will be more than sufficient.  One things absolutely for sure - having drilled this pricey bit of tube - pretty or functional - it's going in 

Bez - yes two (and three) flute slot drills are designed to cut on the end but by removing the centre the cutting (plunging) pressure is much reduced. Given the material I wanted to reduce the stresses on the work/set up (as well as  me ) as much as possible.

Regards - Ramon

[steamer]

Ramon....

. from an engineering placement point of view....the radial array of the 12 cross tubes appears brilliant
. from a thermal transfer question....will the heat from the gas flame be less effective on the tubes outby [furthest away] from the flame?

Derek

Interesting question Derek.   Flue gases don't always behave like they are "envisioned" to...but I'd bet it works better than straight or 90 degrees though....which I can provide absolutely no technical proof on....without a couple of weeks of analysis.   Even then I'd want to test it.

Dave

[derekwarner]

Guys....one of my  tutors of thermodynamics [in boilers] suggested simplistically.............

1. heat is like an arrow 
2. it will be adsorbed ~~~in the first pass
3. little if any of the arrow will continue on past the first point of contact

Adding more arrow  / heat in a stationary boiler gas flue will not necessarily assist in any proportionate increase of the outby tubes transfer of energy [heat to water to steam]

...    having said this I will naturally accept  an opinion from a more qualified person...........Derek

[Jasonb]

So that would be why the inspector did not want to see any gaps, the arrows of heat would fly straight through the gaps without making any contact.

I would hazard a guess that the gentle spiral gives a better draught than the more turbulent flow that the other pattern Ramon came up with would produce so helping to draw the fire through the flue.

J

[Ramon Wilson]

Thanks for your explanation Derek but I'm afraid I don't have the background to comment further

I would say however that, excluding 'Meccano',  its 58 years since I made my first working (flying) model. Since then I think I can honestly say that I have enjoyed every single moment I have spent making something whatever it may be. Throughout that time however I have tried very hard not to allow the fact that I do not have any academic qualifications in the various subjects tackled to spoil that enjoyment.

That is not to appear dismissive - if this works then great, if it doesn't work so well (unlikely I feel) then it's still a 100% improvement on what it was before setting out but I'm afraid I don't have the mental energy to be concerned whether or not this is not going to work to it's most efficient potential - I'm just getting too old for that 

I would like to add that I hope this thread is not going to be a catalyst for heated (pun intended) debate - it's just about building a boat and rebuilding the boiler 

Regards - Ramon

[steamer]

So that would be why the inspector did not want to see any gaps, the arrows of heat would fly straight through the gaps without making any contact.

I would hazard a guess that the gentle spiral gives a better draught than the more turbulent flow that the other pattern Ramon came up with would produce so helping to draw the fire through the flue.

J

YUP...that's the picture in my head also...and I agree Derek...you want contact with radiant heat based on line of sight.....Temp difference to the 4th power and all.

It will certainly not promote laminar flow so  from a convective and conductive perspective..it's got to help the heat transfer if you can get the boundary layer scrubbed off.     But the latter forms of heat transfer are really secondary.....

Dave

[steamer]

Thanks for your explanation Derek but I'm afraid I don't have the background to comment further

I would say however that, excluding 'Meccano',  its 58 years since I made my first working (flying) model. Since then I think I can honestly say that I have enjoyed every single moment I have spent making something whatever it may be. Throughout that time however I have tried very hard not to allow the fact that I do not have any academic qualifications in the various subjects tackled to spoil that enjoyment.

That is not to appear dismissive - if this works then great, if it doesn't work so well (unlikely I feel) then it's still a 100% improvement on what it was before setting out but I'm afraid I don't have the mental energy to be concerned whether or not this is not going to work to it's most efficient potential - I'm just getting too old for that 

I would like to add that I hope this is not going to be a catalyst for heated (pun intended) debate - it's just about building a boat and rebuilding the boiler 

Regards - Ramon

Sorry Ramon...you're right of course!     You see being an engineer is a personality trait...not a profession....we just can't let it be...we poke at it...scribble down numbers.......open up books....ect.....and we end up taking it all too damn seriously....your right Ramon......it's a model ..........if it has a fire under it...it'll push the boat around just fine....Have fun....My apologies.....closing the text book now

[Ramon Wilson]

Apologies simply not required Dave - just saying it as it is.

I love - have always loved - making things. Apart from Sue I guess that's my 'raison d'etre' (is that how you bloody spell that) and I don't think there's anything better than sharing what you've done and helping someone - something that's been a character trait for far too long a time.

I'd love to be able to say I had a better education but I didn't - I haven't done too bad because of it though so I don't beat myself up about it  Of course there are times when I think 'I wish I knew more' but I don't have the grey matter left in which to store a whole lot more of new facts - Hell the lot I've got is fast running out

Now, I'm back off to that workshop to enjoy myself and practice contentment

Ramon

[steamer]

Now, I'm back off to that workshop to enjoy myself and practice contentment





Glad to hear it!.....and thank you for sharing!

Dave

[K.B.C]

Ramon,
The best education is getting off of your butt and doing it, you will learn more by doing so, just as you are doing.
Remember that our small boilers and engines don't always relate to full size practice but on boilers and pressure vessels they must be tested to the insurance companies, Model club and Societies requirements.

Great job of your boiler making.

George.

[Ramon Wilson]

Thanks George,

Two lengths of tube just arrived 

With fifty knot winds forecast for Norwich tomorrow the boats, and us, are confined to barracks.
Guess it's a day in the workshop then  

Back soon!

[SandCam]

Hi Guy's,

Derek posted: -

1. heat is like an arrow 
2. it will be adsorbed ~~~in the first pass
3. little if any of the arrow will continue on past the first point of contact

Theoretically correct Derek, however adsorption is related to surface area of the first point of contact and thermal transfer characteristics of the material ... if this area is small and the amount of heat high then the amount of heat capable of being adsorbed at first point of contact will be altered accordingly... the remaining heat will then pass on to the next point of contact and so on... in reality it is never possible to extract all the applied heat and there are also heat losses to be considered... it is these facts which gives rise to a particular boilers evaporation/conversion constants (be it a model or full size)... the majority of model boilers are around 40 - 50 % efficient and a centre flue arrangement, such as this one, has an evaporation capability of approx 1.5 cu in water per 100 sq in heated surface per minute.

It does get interesting though, albeit a very complex subject.


Ramon,

The spiral suggested by your inspector is correct (my apologies for not making this clear in our previous discusions), I usually arrange for my cross tubes to make one complete turn.
So long as you have the correct tube to tube clearance then you will achieve MAX possible heat extraction.
The other effect of having the tubes in a spiral is to promote a rotation in the gas flow... which speeds up the gas flow at the periphery and promotes a scavenging effect on the flue wall... helping to strip away any boundary layer, which would reduce adsorption.

Nice job getting round the mills spindle height issue.

The only thing I would have done differently would have been to reduce the OD of the cross tubes a small amount at one end... for just enough length to pass through the flue wall and provide the required outside projection.
I would then have drilled straight through both walls using a drill for the reduced end size... followed by opening up the upper end holes to suit the OD of the cross tubes.
This helps when soldering, as it prevents the tubes falling straight through when heated.

You need to think about which end to open up though

A small countersink on the outside of all holes is beneficial in achieving a good solid joint with adequate penetration.

Keep up the good work.

Best regards.

Sandy.

[Ramon Wilson]

Hi Sandy - no need for apologies you have done more than one could ask or expect for this build 

It's some relief to hear that both designer and inspector are in agreement  and that things are on the right track -  though to get twelve tubes in I had to close the gap between tubes from 2.5 to 2mm so hope that won't be too detrimental.

I like the tip about reducing the diameter on the tube end but as you say it's a bit late now. I have filed shallow grooves across each hole with the corner of a three square file and my intention is to gently swage each tube as it's fluxed and fitted enough to hold it in situ. To maximise heat it's going to have to be done horizontally so I need the tubes to hold enough against its own weight. There's a good chamfer on both sides of each hole so hopefully the solder will flow through the grooves and provide a strong fillet inside and out.

All being well I shall be able to get the uptake turned and fitted to the flue tomorrow ready to solder 

Thanks again for the input - it's much appreciated.

Regards - Ramon