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Feedwater heater question
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: January 28, 2005 03:19PM

Iím fitting a smoke hood feedwater heater to my non-condensing Stanley, connected between the pumps and the main boiler check valve. There will be an extra check valve at the start of the coil.

Is it best to return the pump by-pass water cold before the heater coils? Or can it be by-passed after the coil so as to pre-heat the water in the tank? Would this make the water too hot to pump properly? It has a 24 gallon tank and usually does about 1.25 miles to a gallon of water.

Discuss!

Re: Feedwater heater question
Posted by: David K. Nergaard (---.bos.east.verizon.net)
Date: January 29, 2005 10:32AM

What you are trying to make is called an economiser, using flue gasses after they have passed through the boiler. Do you have an exhaust steam feed water heater?
In either case, the bypass should be right at the pumps, passing cold water. Especially so as non-condensing Stanleys have fast pumps running at engine speed.

Re: Feedwater heater question
Posted by: Mike Clark (---.winn.dial.virgin.net)
Date: January 29, 2005 06:00PM

David,

I stand corrected on terminology - economiser is what I meant - I'll consider a steam exhaust feed water heater after I make the economiser work! I do appreciate that heat is more efficiently recovered from steam than collected from hot gases but I have a rather nice free flowing steam exhaust which I prefer not to alter.

Thanks for the advice to by pass only cold water - rather as I thought.

Mike

Re: Feedwater heater question
Posted by: David K. Nergaard (---.bos.east.verizon.net)
Date: February 2, 2005 08:16AM

Build the feed water heater first, it will give you much more for the effort than the economizer.

Re: Feedwater heater question
Posted by: Nick Howell (---.in-addr.btopenworld.com)
Date: February 3, 2005 12:14PM

Hello Mike,
On my Toledo the excess heat from the flue gases and the exhaust steam are both used to heat the infeed water. An enclosed separate alluminium casting 20" diameter, 1 1/2" thick has coils of the copper inlet water feed, direct from the pump, inside. The exhausted steam folows a baffled maze around the water pipes before exiting below the car. The whole unit sits 4" above the boiler so it is also heated by the main burner. Mind you the Toledo boiler is a double cased, water filled affair with eight steam coils inside the inner shell. The burner is beneath and the heat exits through an 8" opening in the centre of the top of the outer shell. The exhaust encloses the 4" gap between the top of the boiler and the ali casting.

At present I cannot identify any by pass valve though I am sure there should be one after the pump and before the pre heater.

Re: Feedwater heater question
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: February 3, 2005 07:24PM

Thanks for the comments.

The Model H hasnít much room for a feedwater heater inside the gas flue so I have been thinking of making a muffler size heat exchanger to go underneath the flue. So as to make this short and shallow (it would be about 24 inches long by 5 wide by 2 deep, extending from the position of the exhaust manifold to just in front of the rear axle) I thought up the idea shown on this link. [photos1.flickr.com]
I might also insulate the outside of the case.

Steam would be directed up and down through the 3 loops of pipe by a pair of corrugated sheets placed above and below the pipe loops so as to trap and hold them in place. This should be much more effective than just letting the steam pass along the length of the loops.

I can get about 12 feet of pipe in - my question is would this be enough to be of use and secondly would it be better to go for 3/8 pipe instead of 5/16ths so the water remains exposed to the heat for longer (the surface/volume ratio would be less but the actual surface area would be greater).

Mike

Re: Feedwater heater question
Posted by: Nick Howell (---.in-addr.btopenworld.com)
Date: February 4, 2005 10:30AM


Looking at your drawing Mike it may be an even more effective heat transfer if you made the steam route as tortuous as possbible. The corrugated baffles would have some effect but through the middle is still quite a direct route. If you had full height baffles longitudinally between your pipes--not easy--with alternating gaps at either end, then the steam would have to travel three or four times the length of the casing before exiting, ideally at the opposite corner rather than in the middle. Just a thought
Nick H

Re: Feedwater heater question
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: February 4, 2005 03:57PM

Yes Nick I see what you mean but I am trying to retain a reasonably free flowing steam exhaust and the point of the corrugations is that the path through them for the steam is not too contorted, they also locate the water loops loosely so that pulsing and expansive movements donít strain anything. It will all come apart easily for cleaning and the oil and condensed water should be able to drain out of the tailpipe. I need to make it small as I want to hang it below the flue so I can see if it is leaking; also I donít want to restrict the gas flue which is dodgy enough as a chimney! It will be interesting to hear David's comment on whether such a heater will do enough to be useful.

I am not really trying to improve the economy of the car - letís face it the cost of fuel is the least of the expense involved in running a steamer - but aiming to get hot water feed which will be better for the boiler and will improve steam output climbing long hills where the pumping is are needed.

I originally had the steam exhaust coming out of the manifold, going forward through an elbow, a piece of flexible pipe and a couple more elbows into the flue then finally running back down the flue to the back of the car. This is the usual arrangement for a Model H. However, as an exhaust pipe it seemed awfully small (1.25Ē) and very convoluted so I dumped it and put a 2Ē pipe though one elbow and a long ďZĒ bend into the flue, shortening the whole thing by at least 2 feet. The result was a noticeable improvement in power so it does pay to let the steam out freely. The 2 inch exhaust suits the sporty nature of the car - it is actually quite loud and with plenty of throttle at 50 mph the chuffs blend to an impressive roar. The feedwater heater will no doubt silence it a bit but not too much.

Mike

Re: Feedwater heater question
Posted by: (---.cache.pol.co.uk)
Date: February 5, 2005 04:37PM

One point I think is worth considering with feed water heaters is avoiding loading up the pump and its drive too much. As you increase the length of feed pipe so you increase the loadings by flow resistance. So how about having two pipes (or more) in parallel, then you reduce the resistance and slow down the water and get better transfer of heat, the water is moving pretty quick through a single pipe----just another thought!

Jack.

Re: Feedwater heater question
Posted by: David K. Nergaard (---.bos.east.verizon.net)
Date: March 16, 2005 09:43AM

Don't worry about heat flow from steam to feed water tubes, steam will condense on anything cool! The typical Stanley feed water heater was a long tube just big enough to hold two loops of tubing in the feed water line. The heater diameter was set by how sharply one could make the bend at the end of the loop. Length was from 4 to 6 feet, depending on car model.
My home made heater has 12 feet of 3/8 tube carefully pretzallised in a 3 inch diameter tube less than 2 feet long.

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