Concentric heat exchanger having hydraulically expanded flow channels

A cylindrical heat exchanger assembly has a plurality of spaced cylindrical heat exchangers having bulge formed circumferential passageways spiraling along the cylindrical surface of each to form a passageway for heat transfer fluid flow therethrough and for allowing a second fluid to sealably flow in the spaces therebetween to establish heat transfer between the two fluids thereby.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to heat exchangers generally and particularly 
to concentric heat exchanger having one media flowing internally within 
the heat exchanger and another heat transfer media flowing externally 
therethrough. 
2. Description of the Related Art 
There are a variety of heat exchangers using various designs of heat 
transfer surfaces. Air-cooled heat exchangers are known which consist of a 
bundle of smooth or finned tubes through which process fluid flows and is 
cooled by air blown over the tubes. 
Shell-and-tube type heat exchangers are known which contain a number of 
tubes (smooth or finned) that are contained within a shell. Heat transfer 
tubes are placed between one fluid flowing inside the tubes with another 
fluid flowing outside the tubes and contained by the shell. 
Plate heat exchangers consist of a series of parallel plates that are 
corrugated both to increase heat transfer and to give mechanical rigidity. 
They normally have flow paths in all four corners and are clamped together 
in a frame that has nozzles for line up with the plate ports. The nozzles 
are connected to external pipes that cover the two-fluid stream. 
None of the above described heat exchangers have the strength and increased 
heat transfer characteristics of bulge formed heat exchanger surfaces. 
The technique for forming such surfaces is known. One such hydraulic 
expansion technique is described in U.S. Pat. No. 4,295,255. Another 
method or technique is described in U.S. Pat. No. 5,138,765 as being used 
only on the internal surface of the flow channel. The specific application 
of the above hydraulic-expansion technique is applied to a stored chemical 
energy propulsion system. Therein the heat transfer effectiveness is 
improved both on the internal surface and is further enhanced by the flow 
channels. Strength is provided by a plate having the formed flow channels 
which are not bulge formed while the cover plate is bulge formed to 
provide added heat transfer surface and induce turbulent flow for 
increased heat transfer. 
To date there are no known cylindrical heat exchangers that have 
hydraulically expanded or bulge formed flow channels on either one side or 
both sides of the heat transfer surfaces to provide strength and turbulent 
flow around these surfaces to increase heat transfer thereby. Clearly such 
designs are needed and would be beneficial to the art. 
SUMMARY OF THE INVENTION 
The present invention uses hydraulic expansion manufacturing technique to 
form cylindrical heat transfer surfaces. The flow channels within the 
surface are hydraulically expanded or bulge-formed on both sides as is 
described in U.S. Pat. No. 4,295,255 or are bulge formed on one side as 
described in U.S. Pat. No. 5,138,765. FIG. 1 shows an example of a cross 
section of such a hydraulically-expanded cylinder 10 having bulge-formed 
flow passage 18. 
The cylindrical heat exchanger of the present invention has a series of 
concentric cylinders which are bulge-formed to provide an internal flow 
passage spiral formed around each of the series of cylinders. Flue gas is 
supplied at one end and exhausted out the other end of the cylindrical 
heat exchanger to cool the gas thereby. 
An inlet header supplies each of the internal passages of the cylinders 
while an outlet header connects all the cylinder internal passage exhausts 
to thus have the bulge-formed flow passages of all the cylinders act as 
one fluid inlet and one fluid outlet connection. While the heat exchange 
fluid thus flows inside of the bulge-formed passages of the cylinders the 
flue gas flows outside the bulge-formed passages with turbulent flow 
around the bulge formed passages to provide an increased heat transfer 
rate between the flue gas and the heat exchange fluid flowing through the 
internal passages of the cylinders cooling the flue gas thereby. 
In another embodiment, instead of the inlet and outlet headers connecting 
the bulge-formed passages of each cylinder, an interconnection between 
concentric cylinders is used with the fluid outlet of one concentric 
cylinder becoming the inlet to another concentric cylinder. 
In yet another embodiment, different heat exchange fluids are passed 
through each cylinder of the plural cylinder bulge-formed heat exchanger 
while the annular spaces between the cylinders is sealably ducted to also 
have different fluids passed through each annulus which fluids are also 
different from the fluids passing through the bulge formed passages of 
each cylinder. 
In view of the foregoing it will be seen that one aspect of the present 
invention is to provide a cylindrical heat exchanger having 
circumferentially formed spiral bulged passageway along a series of 
concentric cylinders of differing radius having a central axis. 
Another aspect of the present invention is to provide a cylindrical heat 
exchanger having bulge formed heat transfer fluid passageways to induce 
turbulent fluid flow of the gas passing through the heat exchanger 
externally of the bulge formed passageways. 
Yet another aspect of the present invention is to provide a cylindrical 
heat exchanger of plural cylinders having different heat exchange fluids 
flowing through each cylinder and the annular passageways formed between 
each cylinder. 
These and other aspects of the present invention will be more fully 
understood after considering the following description of the preferred 
embodiment in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention resides in a cylindrical heat exchanger fabricated 
with a hydraulic expansion manufacturing technique such as the coiled tube 
boiler (10) shown in FIG. 1. In fabricating the coiled tube boiler (10), 
one cylinder (12) is placed inside a second cylinder (14). It is seen that 
the two cylinders are of approximately the same diameter except for the 
inside cylinder (12) being than smaller outside cylinder (14). A high 
speed welding process, such as electron beam welding, welds in a spiral 
weld path (16) the two cylinders (12, 14) together. After welding, a 
pressure fitting (not shown) is attached and hydraulic pressure is applied 
between the welds (16) and the two cylinder sheets (12, 14). As the 
hydraulic pressure is slowly increased, the cylinders (12, 14) deform 
between the helical welds (16) to create a flow channel (18) therebetween. 
The manufacturing parameters are taught in U.S. Pat. No. 4,295,255 which 
is assigned to the present Assignee and is hereby incorporated by 
reference. 
Further, the thickness of plate could be made significantly thicker and 
stronger to allow the bulge to form on only one side as is taught in U.S. 
Pat. No. 5,138,765. 
In the present invention, best seen with reference to FIG. 2, a cylindrical 
heat exchanger 20 is formed from a plurality of cylindrical heat 
exchangers 22(a); 22(b); 22(c) each having a significantly different 
radius r.sup.1 ; r.sup.11 ; r.sup.111 but each being located 
concentrically within axis 24. This concentric relationship is maintained 
by any one of known structural supports such as radial struts (not shown). 
The central cylindrical heat exchanger 22(a) has a tubular opening 26 for 
passing fluid therethrough while the adjoining heat exchangers 22(b) and 
22(c) form annular openings 28, 30 for passing fluid therethrough. 
It will be understood that each cylindrical heat exchanger 22(a); 22(b); 
22(c); is formed according to the bulge forming process described with 
reference to FIG. 1 and has a circumferential spiral formed bulged fluid 
passageway 32(a); 32(b); 32(c) and a bottom fluid outlet 36(a); 36(b); 
36(c). Although each cylindrical heat exchanger was shown as having both 
sides bulged, it will be understood that single side bulge could also be 
used when manufactured as per the teachings of U.S. Pat. No. 5,138,765. 
Also, while three concentric heat exchangers are shown, any number could 
be used as needed by the design parameters. 
The heat exchanger 20 formed with the hydraulically-expanded flow channels 
can be used in industrial and utility boilers as the heat transfer surface 
for the superheat and reheat sections. Steam flow will then be in the 
inside of the bulge-formed flow channel 32(a); 32(b); 32(c) and flue gas 
flow will be in the central and annular flow passages 26; 28; 30. The 
steam is fed from a header 38 connected to the inlets 34 and is exhausted 
into a header 40 from outlets 36 to thus provide a single steam inlet 42 
and outlet 44. 
The construction of the present cylindrical heat exchanger provides certain 
advantages over prior art heat exchanger. 
Flat plate may be used to make each cylinder. This allows the use of exotic 
and/or high-strength materials which are not available in tube form. 
The size or compactness of the heat exchanger can be changed by varying the 
space between the concentric cylinders and the size of the bulge-formed 
flow channels. 
The external surface of the bulge-formed flow passage is tube-like, which 
increases flow turbulence in the fluid flowing in crossflow between each 
concentric cylinder. The increase in flow turbulence increases the heat 
transfer effectiveness of the heat exchanger. 
Turning now to FIG. 3, it will be seen that the headers 38 and 40 of FIG. 2 
can be replaced with an interconnection between concentric cylinders 22 
where the fluid outlet 36 of one cylinder 22 becomes the inlet of the 
adjoining cylinder 22 to allow cross current steam flow through cylinder 
22(b). 
Steam is passed to the inlet 34(a) of cylinder 22(a) and passes through the 
bulge formed passageway 32(a) to exit at outlet 36(a). A connection 46 
then passes the steam to fluid outlet 36(b) of cylinder 22(b) where it 
flows counter current to cylinder 22(a) through passageways 32(b) to be 
exhausted at inlet 34(b). A second connection 48 then passes the steam to 
inlet 34(c) of cylinder 22(c) where it is passed through passageway 32(c) 
to exhaust 36(c). 
Turning next to FIG. 4, it will be seen that since each concentric cylinder 
22 is a containment wall that can isolate the annular flow passages, 
different fluids can be used for each annular flow passage 26, 28, 30 with 
a different but common fluid on the inside of the bulge-formed passages. 
Two other combinations can be provided by not using the inlet and outlet 
manifolds 38, 40 or headers to interconnect the bulge-formed flow passages 
32. Separate tubes (not shown) on the inlets 34 and outlets 36 will allow 
use of different fluids on the inside of the bulge-formed flow passages 32 
of each concentric cylinder 22 along with a common fluid in the annular 
flow passages 26, 28, 30 or different fluids in the annular flow passages 
26, 28, 30. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that certain modifications and additions 
would be obvious to those of ordinary skill in this art. Such 
modifications have been deleted herein for the sake of conciseness and 
readability but are intended to fall within the scope of the following 
claims.