Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION HEAT RECOVERY SYSTEM -
Technical Field
My invention is a system of mechanical apparatus for the recovery of
waste heat from smokepipes, chimneys or stacks using natural draft.
Background Art
Prior means for improving the heat output of natural draft stoves,
boilers, furnaces or fireplaces, have made use of: air blown through tubular
grates set in the fire; heat exchanger and fan units have been mounted in the
smokepipe (Magic Heat); literature describes the horizontal phase-change heat
pipes. Prior art is all limited by the need to keep the stack temperatures
hot enough to maintain adequate draft, and are thus wasteful.
I know of no use or disclosure which anticipates my key discovery of
locating an exchanger at the very apex of the stack in such a manner that the
draft is not impaired.
Disclosure of Invention
My invention uses a special heat exchanger mounted on a stack or chim-
ney and baffled so that the gases go up through the core and down through the
exchanger before release to the atmosphere.
Condensibles are trapped out and their latent heats recovered. The
column of hot gases still exists in the stack below and its normal draft is
not impaired. The reclaimed heat is transferred to liquid which ~s circulated
to just those areas where it is desired. The heat obtained from fireplaces and
stoves is greatly increased and without the aesthetic violence of blowers, heat
tubes, or the sheer physical bulk of surface area.
The fuel energy saved results in lesser environmental pollution and of ~;
course oil fuels conserved are available for other uses.
A number of problems arise when we install heat exchangers in various
gas streams. The products of combustion vary with the nature of the fuels
burned; the salient corrosives are pyroligneous acids with wood fuels and sul-
phur compounds with coal and oil.
We should avoid the use of dissimilar metals with their inherent galva-
nic vulnerability due to 'heir separation in the electrochemical series. This
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also argues against any use of brazed joints.
Some metals in the stainless steel series, while they are acid resis-
tant, have poor thermal conductivity and thus do not lend themselves well to
fabrication as finned tubing where the heat travel is a relatively long path.
Any exchanger in such service will eventually foul with soot and must
have a configuration which permits of access to its surfaces for cleaning.
Ideally, it should be possible to enable the exchanger to be varied in
capacity and function without the need for a large series of dies or die
changes for different production runs.
Thus to make the basic system invention practical and perform well, it
has been necessary to specifically design a heat exchanger for it which con-
siders these criteria.
Brief Description of Drawings
Sheet 1 of the drawings shows a vertical section through the equipment
and a schematic of the other elements in the system. The exchanger unit
either sits on top of a leveled masonry chimney or is supported so as to
embrace a round flue. The basic elements are: a torus shaped condensate pan
(1); a heat exchanger scroll (2); a jacket around the scroll (3); a hinged cap
(4); which is tensioned to open by a spring; the cap incorporates a dome (5)
and a filler cap (6); short flexible hoses lead from the exchanger outlet (7)
to the dome and from the dome (8) down to piping and to the pump; hose (9) runs
to tubing which leads to bottle (10).
The pump circulates the heated liquid through any conventional hot
water heating system or device, such as baseboard heaters, convectors, radia-
tors, unit heater, etc. or even to a hot water storage tank. This via supply
line (11) and return (12).
Bottle (10) is open and sized to hold the volume of liquid displaced
by expansion plus the small volume in dome (5). The liquid in the dome is
expelled automatically upon the generation of the slightest steam as would ~ ;
follow upon a power failure. The cap, now unloaded, is opened by the afore-
mentioned spring. Thus the exchanger is by-passed and no liquid boiled off
or wasted from the system.
Sheet 2 of the drawings shows the construction of the heat exchanger
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itself. This begins as a two ply sandwich of metal (figure 1); these are
embossed, fitted with liquid connections and rolled into a spiral scroll
(figure 3); the scroll is inserted into the jacket (figure 4) which pro-
tects the scroll from abuse and resists the "hoop stress" or the spring-back
of the scroll.
Best Mode For Carrying Out The Invention
Fabrication of the exchanger (see drawing sheet 2) starts with slitt-
ing suitable metal to width. For example for use with wood fires, a typical
choice would be type 304, stainless steel, fully annealed, in .007 inch (.2mm)
thickness. Two metal coils are each run through an embossing roll and laid
together in a sandwich. The embossing is in modular rows to permit varying
the width of the strips without change to the rolls. Note the skew pattern
across the strips (fig. 1).
One set of rolls impresses shallow tits to the interior of the sand-
wich (21); the other set of rolls impresses larger and wider spaced dimples
to the outside of the sandwich (22). The small tits establish a liquid
channel and will be on the concave face of the scroll; the larger dimples
maintain a uniform gap for the gases. Both patterns also serve to rigidize
and strengthen a metal gauge chosen for economy and light weight.
The edges of the lapped sheets are run through the wheels of a resis-
tance seam welder or a high frequency resistance welder. The total transfer
area desired fixes the length at which the sandwich is cut. The skew cut
(fig. 5) is parallel with the dimples and the liquid connection cuff (24) is
inserted here. This piece is bench welded by Tungsten Inert Gas with filler
metal or alternately, by Metal Inert Gas with wire feed to embrace the half-
nipple (23). This cuff wraps around the nipple but gradually blends off in a
tapering run until it is pinched flat at the other end (24). These two liquid
connection welds are the only manual welds required in the fabrication; others -
are made by machine and require lesser degree of skill.
A machine seam is run across the skew to join the thin skins to the
heavier cuff, with a temporary copper chill sheet inserted (25) through the
end of the sandwich and then withdrawn and the end welded shut. The top
nipple - the outlet - should not be inserted deeper than 1 cm. into the
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sandwich.
The whole rolled up spiral scroll is leak tested. If quality control
has been good, the scroll is better inserted into the jacket and then tested. -
The test is made of course, by admitting low air pressure to one of the ports - ~?
with the other capped, and submerged in tepid water with a wetting agent.
Referring to sheet 1 of the drawings: the construction of the conden-
sate pan (1) the cap (4) and the dome (5) are obvious and are made by conven-
tional spinning or stamping as is determined by volume and labor cost inter-
sects.
In the interests of clarity and simplicity, minor elements of construc- ;
tion are not shown on the drawings when they can better be conveyed in words,
which follow: ;~
The interior of the jacket should have no sharp edges or protrusions
to gouge the exchanger scroll which may be withdrawn for ease of cleaning.
Connection (13) is a stub tube inserted low so that condensate may
be drained off if desired.
A weatherproof, snap acting thermostat set for 140 F (60 C) is
surface mounted on the exterior of the jacket anywhere close under the cap -
preferably near the hinge. This is to actuate the pump when a manual-auto
swltch is set for automatic.
The dome (5) has three functions: it ~s an alr separation chamber ~;
where air swept out anywhere in the whole heating system will be trapped out;
it has a small superheating effect; it is an unloader to prevent boiling off
liquid if the power supply were interrupted or the heating system could not
use as much heat as the exchanger produced. If steaming occurs, the liquid
in the dome is forced out via hose (9) to small diameter tubing which runs
into bottle (10) through the check valve (14) which has a controlled leak in
the reverse direction. Vapor condensing in the dome allows the return of
liquid over a period of say half an hour, at which time the dome will close
and again test for excessive heat. Incidentally, the cap in an open position
when no firing is going on is a signal that air remains in the system to be ~ -
bled off.
Two large and one small tubes project from the dome and project out
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over the hinge area for the hoses to connect to. They are supported at the
outboard edge of the cap to withstand shipping abuse.
The liquid in the heating system can well be clean filtered rain
water with only enough ethylene glycol type anti-freeze added to protect
against minimum temperatures to be encountered. This does not preclude
other precautions against freezing which are possible.
The pump of choice selected for prototype models may be of interest.
It is not universally known that small pumps are available with magnetically
coupled drives which preclude weeps or leaks from stuffing boxes or mech-
anical seals. Such pumps also protect themselves in that the impeller
declutches should grit from a dirty piping system be entrained.
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