Heat exchanger and method of making same

A heat exchanger is provided which has a heat exchanger coil made from a continuous length of tubing arranged in an alternating series of conical helical and reverse conical helical winds wherein the medium to be heated flows downwardly through the coil and the heated medium from which heat energy is to be transferred flows upwardly around the coil in counter flow fashion to provide for a compact and efficient heat exchanger. Two methods of constructing such a coil are disclosed which utilize one or more mandrels to form the tubing into the approximately shaped coil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to heat exchangers and more particularly to 
helical wound tubing heat exchangers and methods of making such 
exchangers. 
2. Description of the Prior Art 
Heat exchangers known and used for transferring heat energy from one medium 
to another sometimes consist of an array of tubes positioned within a 
housing. A medium to be heated and a medium giving up the heat are on 
opposite sides of the flow restricting paths. Oftentimes the flow through 
the tubes is split such that the tubes form a plurality of independent 
paths through the interior of the heat exchanging unit with each tube 
making one or more passes through the heat exchanging zone. Many of these 
prior heat exchangers are relatively inefficient in transferring heat 
energy from one medium to another because of an insufficient amount of 
surface area presented to the heated medium or else require an 
extraordinary amount of space in order to achieve efficient levels of heat 
transfer. 
SUMMARY OF THE INVENTION 
The present invention provides for a compact heat exchanger in which the 
medium to be heated passes through the heat exchanging zone through a 
continuous tube which provides a large surface area in a compact format. 
To achieve this, the single tube is wound in an alternating series of 
conical helical winds forming a coil having a maximum outside diameter and 
a minimum inside diameter. A plurality of alternating series of conical 
helical winds are provided to increase the heat transfer. 
The medium to be heated flows through the coil at a continuous downward 
slant of approximately 0.5.degree. to the outlet at the bottom of the 
coil. This makes the coil self draining when a liquid is used as the 
medium to be heated. 
The coil may be made from a plurality of equal length pipes welded together 
or from a single length of pipe. If the heat exchanger is made of a 
plurality of equal length pipes, the method of manufacture would include 
using a single mandrel to form the conical helical winds and then welding 
the conical coils together in alternating fashion. If the heat exchanger 
is made of a continuous length of tubing, all conical helical winds are 
made on one machine without the need for any welding. To perform this 
method of manufacture, a plurality of mandrels are required.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 there is shown a heat exchanger generally at 10 which is 
comprised of a generally cylindrical housing 12 having a vertically 
disposed axis with an inlet opening 14 near a bottom end 15 and an outlet 
opening 16 at a top end 17. The housing 12 has a generally open chamber 18 
at the bottom end 15 communicating with the inlet opening 14 and being 
disposed below a heat exchanging chamber 20 positioned directly below the 
outlet opening 16. A source of heated fluid being the medium from which 
heat energy is to be transferred is shown generally at 22, which in the 
embodiment shown in FIG. 1 comprises a burner and fan device which directs 
fuel and air for combustion into the chamber 18 interior of the housing 12 
through the inlet opening 14. Heated mediums, other than combustion 
products, which are capable of flowing can be utilized in the present 
invention. This includes generally any type of fluid, either liquid or gas 
which can flow from the inlet opening 14 through the interior of the 
housing 10 and out through the outlet opening 16. 
A coil arrangement is shown generally at 24 which is comprised of a 
plurality of alternating conical helical winds of tubing having an inlet 
end 26 positioned near the top end 17 of the heat exchanging chamber 20 
and an outlet end 28 positioned near the bottom end 29 of the heat 
exchanging chamber 20. 
As seen in greater detail in FIGS. 2 and 3, the coil 24 comprises an 
alternating series of windings having an innermost winding 30 forming an 
interior diameter 30a of the coil and an outer winding 32 forming an outer 
diameter 32a of the coil. Intermediate windings 33 are formed between the 
interior winding 30 and the exterior winding 32. Secured, for instance by 
welding, to the interior diameter of the interior coil 30 is a baffle 
plate 34 which prevents the heated medium from flowing primarily up 
through the relatively large space within the interior diameter 30a of the 
inner coil 30. The heated medium is thus forced to flow between the 
individual windings 33, which are maintained in spaced relationship, 
presenting a plurality of flow paths. The tubing is arranged in a series 
of alternating helical winds which have reversing conical shapes such that 
there is a continuous and constant downward slope or slant from the inlet 
end 26 of the tubing to the outlet end 28. It has been found that a slant 
of approximately 0.5.degree. is sufficient to allow a liquid type fluid 
having a viscosity approximately that of water to flow downwardly through 
the tubing so that the coil is self draining while also allowing for a 
compact format for the coil. Auxiliary pumps may be used to pump the 
liquid through the coil depending on coil size, slant and liquid flow rate 
desired. The slant of the coil can be more or less than the 0.5.degree. 
specified, as required. 
The downward slope or slant of the coil is maintained by using a plurality 
of reinforcing members 36 such as elongated bars which are attached, for 
instance by welding, to the underside of each of conical winds. The 
reinforcing means not only maintain the tubing at the appropriate slant 
angle, but also maintain an optimum spacing between adjacent winds 
enhancing uniform flow of the heated medium through the heat exchanging 
zone 20 around each of the individual winds. 
As seen in FIG. 2, the outside diameter 32a of the outer winding 32 is 
slightly smaller than the inside diameter of the cylindrical wall 12 of 
the housing such that virtually the entire lateral cross section within 
the heat transfer zone is provided with tubing thereby maximizing the 
surface area of the tubing within the heat transfer zone 20. The baffle 
plates 34 are welded to the inner diameter 30a of the inner winding 30 to 
prevent the heated medium from flowing up through the inner diameter 
space. Because the windings are constructed in a continuous and downward 
slant, the baffle plates 34 cannot be welded in a continuous manner around 
the entire interior diameter 3a, but rather are attached along a portion 
of their circumference. Thus, some heated medium does flow up through the 
inner diameter 30a, but most of it flows up around the intermediate 
windings 33. 
The medium to be heated is introduced into the coil 24 through the inlet 
end 26 near the top of the heat transfer zone 20 where it is relatively 
cool and it flows downwardly through the coil in alternating inward and 
outward spiral fashion as is shown by the schematic view in FIG. 4 at 38 
to where it exits from the heat transfer chamber 20 through the outlet end 
28 having attained a relatively high temperature. The heated medium is 
introduced through the chamber 18 at a relatively high temperature and 
then flows upwardly through the heat transfer chamber 20 to the exit 
opening 16 at the top of the chamber. Thus, there is provided a counter 
flow heat exchanger which further enhances the efficiency of the heat 
transfer. The number of series of alternating conical helical winds can be 
selected based upon the amount of heat transfer desired and space 
availability. 
The heat transfer housing 12 is provided with an insulating layer 40 around 
the entire periphery which is increased in thickness in the inlet chamber 
18 due to the high temperatures there. The insulation retains heat energy 
within the interior of the housing 12 and permits an outer wall 41 of the 
housing to remain relatively cool. 
The heat exchanger coil which is disclosed above can be manufactured by at 
least two methods. A first method of manufacturing, shown in FIGS. 5 and 
6, is relatively simple from a tooling aspect, but it does require 
considerable labor. In this method, numerous conical helical winds are 
made from identical lengths of tubing pipe, using one mandrel 42 (FIGS. 5 
and 6) to form the winds. The mandrel 42 is shaped as a cone with ribs or 
channels 44 formed on an exterior surface 46 to hold and guide the tubing 
48 as it is wound around the mandrel. Preferably the mandrel 42 is rotated 
as shown by arrow A and the tubing 48 is biased against the mandrel by a 
roller means R shown in phantom. The tubing used, for instance A53 pipe, 
is flexible enough to be wound on the mandrel 42, yet rigid enough to 
retain its shape once wound. A clamp 49 secures a first end of the tubing 
48 during the winding process. The tubing 48 can be carried on a roll 50 
from which it is drawn by rotation of the mandrel 42. The mandrel can be 
rotated manually or automatically for instance by a driving means 51 such 
as a motor. 
A second method of manufacture requires more complex tooling. All of the 
conical helical winds are made on one machine from one continuous length 
of tubing. With this method, there is not a requirement for any welding of 
the individual winds. However, by this method, numerous mandrels are 
required. The mandrels 52 (FIGS. 7 and 8) are cone shaped and have ribs or 
channels 54 formed on an outer surface with a slope in excess of the slope 
desired for the conical winds, for instance a 5.degree. slope instead of a 
0.5.degree. slope for the winds. 
The mandrels 52 are arranged in front-to-front and back-to-back assembly on 
a square shaft 55 to present the conical and reverse conical shape. A 
continuous length of tubing 56 is then wound or wrapped around the 
assembly of mandrels 52 in a manner similar to that described above. The 
conical angle or slope of the tubing is exagerated as described above to 
allow for removal of the mandrels. The mandrels 52 are retained in 
appropriate rotational registry with each other by locating means 53 to 
ensure that the continuous length of tubing 56 will have the necessary 
slope throughout its length, particularly where the two mandrels are 
joined. After the winds have been formed in the tubing, the shaft 55 is 
removed and adjacent winds are separated longitudinally at each wide 
diameter as at 58 in FIG. 8 so that the mandrels 52 may be laterally 
removed one at a time from the interior of the tubing. The entire coil is 
then compressed axially until the desired final slope is attained and then 
the retaining means 36 are secured to the winds which retain the coil in 
the desired shape. The coil is then placed within the heat exchanging 
chamber 20 and the inlet end 26 and outlet end 28 are inserted through 
appropriate openings in the housing 12. 
Therefore, it is seen that there is provided a heat exchanging device in 
which heat energy is transferred from a first heated medium to a second 
medium to be heated within a heat transfer zone which can be compact and 
in which there is a conduit carrying the medium to be heated which 
exhibits a large surface area relative to the volume of the heat 
exchanging zone so as to maximize the transferring of heat energy. 
As is apparent from the foregoing specification, the invention is 
susceptible of being embodied with various alterations and modifications 
which may differ particularly from those that have been described in the 
preceding specification and description. It should be understood that we 
wish to embody within the scope of the patent warranted hereon all such 
modifications as reasonably and properly come within the scope of our 
contribution to the art.