Information
-
Patent Grant
-
6575227
-
Patent Number
6,575,227
-
Date Filed
Tuesday, October 26, 199924 years ago
-
Date Issued
Tuesday, June 10, 200321 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
- Hochberg; D. Peter
- Vieyra; Katherine R.
- Mellino; Sean
-
CPC
-
US Classifications
Field of Search
US
- 165 44
- 165 41
- 165 173
- 165 174
- 440 88
-
International Classifications
-
Abstract
A keel cooler having a beveled bottom wall, with orifices on the inner wall of the exterior tubes extending into the header, the orifices being in the natural flow path of coolant flow. The orifices are sufficiently large so as not to restrict the flow of coolant. The anode assemblies and drain plugs are mounted on the beveled bottom wall.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to heat exchangers, and more particularly to heat exchangers for cooling engines, generators, gear boxes and other heat generating sources in industrial apparatuses having fluid cooled heat sources, such as marine vessels. The invention more particularly relates to open heat exchangers (where heat transfer tubes are exposed to the ambient cooling or heating fluid, rather than being in a shell to shell container holding the cooling or heating fluid) used for cooling heat sources, where the heat exchangers are efficient, and thus have lower weight and volume compared to other heat exchangers known in the art. Alternatively, the heat exchanger according to the invention could be used as heater, wherein relatively cool fluid absorbs heat through the heat transfer tubes.
2. Description of the Prior Art
Heat generating sources in industrial applications such as marine vessels are often cooled by water, other fluids or water mixed with other fluids. For example, in marine vessels used in fresh water and/or salt water, the cooling fluid or coolant flows through the engine or other heat generating source where the coolant picks up heat, and then flows to another part of the plumbing circuit. The heat must be transferred from the coolant to the ambient surroundings, such as the body of water in which the vessel is located. For small engines, such as outboard motors for small boats, ambient water pumped through the engine is a sufficient coolant. However, as the vessel power demand gets larger, ambient water pumped through the engine may continue to provide good cooling of the engine, but also serves as a source of significant contamination damage to the engine. If raw, ambient water were used to cool the engine, the ambient water would carry debris and, particularly if it is salt water, corrosive chemicals to the engine. Therefore, there have been developed various apparatuses for cooling engines and other heat sources. One apparatus for cooling the engine of a vessel is channel steel, which is basically a large quantity of shaped steel which is welded to the bottom of the hull of a vessel for conveying engine coolant and transferring heat from the coolant to the ambient water. Channel steel has severe limitations: it is very inefficient, requiring a large amount of steel in order to obtain the required cooling effect; it is very expensive to attach to a vessel, since it must be welded to the hull—a very labor intensive operation; since channel steel is very heavy, the engine must be large enough to carry the channel steel, rendering both the initial equipment costs and the operating costs very high; the larger, more powerful engines of today are required to carry added channel steel for their cooling capacity with only a relatively small amount of room on the hull to carry it; the payload capacity is decreased; the large amount of channel steel is expensive; and finally, channel steel is inadequate for the present and future demands for cooling modem day, marine vessels. Even though channel steel is the most widely used heat exchanger for vessels, segments of the marine industry are abandoning channel steel and using smaller keel coolers for new construction to overcome the limitations cited earlier.
A keel cooler was developed in the 1940's and is described in U.S. Pat. No. 2,382,218 (Femstrum). The Femstrum patent describes a heat exchanger for attachment to a marine hull structure which is composed of a pair of spaced headers secured to the hull, and a plurality of heat conduction tubes, each of whose cross-section is rectangular, which extend between the headers. Cylindrical plumbing through the hull connects the headers to coolant flow lines extending from the engine or other heat source. Hot coolant leaves the engine, and runs into a heat exchanger header located beneath the water level (the water level refers to the water level preferably below the aerated water, i.e. below the level where foam and bubbles occur), either beneath the hull or on at least one of the lower sides of the hull. The coolant then flows through the respective rectangular heat conduction tubes and goes to the opposite header, from which the cooled coolant returns to the engine. The headers and the heat conduction tubes are disposed in the ambient water, and heat transferred from the coolant, travels through the walls of the heat conduction tubes and the headers, and into the ambient water. The rectangular tubes connecting the two headers are spaced fairly close to each other, to create a large heat flow surface area, while maintaining a relatively compact size and shape. Frequently, these keel coolers are disposed in recesses on the bottom of the hull of a vessel, and sometimes are mounted on the side of the vessel, but in all cases below the water line.
The foregoing keel cooler is referred to as a one-piece keel cooler, since it is an integral unit with its major components welded or brazed in place. The one-piece keel cooler is generally installed and removed in its entirety.
There are various varieties of one-piece keel coolers. Sometimes the keel cooler is a multiple-pass keel cooler where the headers and heat conduction tubes are arranged to allow at least one 180° change in the direction of flow, and the inlet and outlet ports may be located in the same header.
Even though the foregoing heat exchangers with the rectangular heat conduction tubes have enjoyed wide-spread use since their introduction over fifty years ago, they have shortcomings which are corrected by the present invention.
The rectangular heat exchangers of the prior art have the outward shape of a rectangular parallelepiped having headers at their opposite ends. These headers have opposing end walls which are perpendicular to the hull of the vessel and parallel to each other, and act as a barrier to ambient water flow relative to the keel cooler as the vessel with the heat exchanger travels through the water. The perpendicular header walls are responsible for the creation of dead spots (lack of ambient water flow) on the heat exchanger surfaces, which largely reduce the amount of heat transfer occurring at the dead spots. In addition, the perpendicular walls diminish the flow of ambient water between the heat conduction tubes, which reduces or diminishes the amount of heat which can be transferred between the coolant in the tubes and the ambient water.
The ability of a heat exchanger to efficiently transfer heat from a coolant flowing through heat conduction tubes depends, in part, on the volume of coolant which flows through the tubes and its distribution across the parallel set(s) of tubes, and on whether the coolant flow is turbulent or laminar. The volume flow of coolant per tube therefore impacts heat transfer efficiency and pressure drop across the heat exchanger. In the present heat exchanger with rectangular tubes, the ends or extensions of the outermost rectangular tubes form exterior walls of the respective headers. Coolant flowing through the heat exchanger, has limited access to the outermost tubes as determined from data obtained by the present inventors. At the present time, the outermost tubes have a solid outer wall, and a parallel inner wall. In order for coolant to flow into the outermost rectangular tubes, orifices, most often circular in shape, are cut through the inner wall of each of the outer tubes for passing coolant into and out of the outer tubes. The inlet/outlet orifices of the exterior tubes are presently disposed centrally in a vertical direction and endwardly of the respective headers of the keel coolers. However, an analysis of the flow of coolant through the foregoing keel cooler shows that there is a larger amount of coolant per tube flowing through the more central tubes, and much less coolant per tube through the outermost tubes. A graph of the flow through the tubes has a general bell-shaped configuration, with the amount of flow decreasing from the central portion of the tube array. The result is that heat transfer is lower for the outermost tubes, and the overall heat transfer for the keel cooler is also relatively lower, and therefore, the pressure drop across the keel cooler is higher than desired.
The flow of coolant through the respective orifices into the outermost rectangular tubes was found to be inefficient, causing insufficient heat transfer in the outermost tubes. It was found that this occurred because the orifices were located higher and further towards the ends of the respective headers than is required for optimal flow. It has been found by the inventors that enlarging the orifice size and moving it closer to the natural flow path of the coolant flowing through the headers, i.e. its optimal path of flow, coupled with the modification to the design of the header as discussed below, further increased the flow to the outer tubes and made the flow through all of the tubes more uniform, reducing the pressure drop across the cooler while increasing the heat transfer.
The current keel cooler with rectangular heat conduction tubes has an anode and a drain plug or plugs located on the bottom portion of the respective headers, which increases the overall height of the header and which may render these devices subject to potential damage from debris in the water and underwater structures. In order to reduce the likelihood of damage, shrouds have been provided to protect the keel coolers against damage. In addition, the anode(s), and the drain plug(s), by projecting into the ambient water, impede the relative flow of the ambient water as the vessel moves therethrough which increases drag. As explained below, the location of the anode(s) and drain plug(s) so as to minimize the increase height of the header and the keel cooler, reduces the foregoing problems.
As discussed below, the beveled header, and the relocation of the anode assemblies and drain plugs, also contribute to the increase of the overall heat transfer efficiency of the keel cooler according to the invention, since the ambient water is caused to flow towards and between the respective heat conduction tubes, rendering the heat transfer substantially higher than in the keel cooler presently being used. This increase in heat transfer is due at least in part to the increase in turbulence in the flow of ambient water across the forward header and along and between the coolant flow tubes.
One of the important aspects of keel coolers for vessels is the requirement that they take up as small an area on the vessel as possible, while fulfilling or exceeding their heat exchange requirement with minimized pressure drops in coolant flow. The area on the vessel hull which is used to accommodate a keel cooler is referred to in the art as the footprint. In general, keel coolers with the smallest footprint and least internal pressure drops are desirable. One of the reasons that the keel cooler described above with the rectangular heat conduction tubes has become so popular, is because of the small footprint it requires when compared with other keel coolers. However, keel coolers according to the design of rectangular tubed keel coolers presently being used have been found by the present inventors to be larger than necessary both in terms of size and the related internal pressure drop. By the incorporation of the various aspects of the present invention described above (and in further detail below), keel coolers having smaller footprints and lower internal pressure drops are possible. These are major advantages of the present invention.
Some of the shortcomings of heat exchangers with rectangular heat conduction tubes presently being used relate to the imbalance in the coolant flow among the parallel tubes, in particular in keel coolers which lead to both excessive pressure drops and inferior heat transfer which can be improved according to the present invention. The unequal distribution of coolant flow through the heat conduction tubes in present rectangular tube systems has led to inferior heat transfer in the systems. In order to attend to this inferior heat transfer, the designers of the present keel coolers on the market have been compelled to enlarge or oversize the keel cooler which also may increase the footprint, through additional tube surface area, to overcome the poor coolant distribution and inferior heat transfer in the system. This has resulted in the present one piece keel coolers which are unnecessarily oversized when compared with the invention described below. In some instances, the invention described below would result in fewer keel coolers in cooling circuits which require multiple keel coolers.
The unequal distribution of coolant flow through the heat conduction tubes in present rectangular tube systems also results in higher internal pressure drops in the systems. This higher pressure drop is another reason that the prior art requires oversized heat exchangers. Excessive oversizing compensates for poor heat transfer efficiency and excessive pressure drops, but this requires added costs and a larger footprint.
When multiple pass (usually two pass) keel coolers are specified for the present state of the art, an even greater differential size is required when compared with the present invention, as described below.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a heat exchanger for fluid cooled heat sources which is smaller than corresponding heat exchangers having the same heat exchange capability.
Another object of the present invention is to provide an improved heat exchanger for industrial applications which is more efficient than heat exchangers presently known and used.
It is yet another object of the present invention to provide an improved one-piece heat exchanger for vessels which is more efficient in heat transfer than presently known one-piece heat exchangers.
It is an additional object to produce a one-piece heat exchanger and headers thereof which generally equalizes the flow of coolant through each of the tubes of the keel cooler.
A further object is to provide an improved one-piece heat exchanger which reduces the pressure drop of coolant flowing therethrough.
A further object of the present invention is to provide an improved one-piece heat exchanger having heat conduction tubes which are rectangular in cross-section having a length which is reduced in size from the current heat exchangers due to improved coolant flow distribution inside the heat exchanger and enhanced ambient water flow across the keel cooler.
Another object is to provide an improved one-piece heat exchanger having a reduced size from present one-piece heat exchangers of comparable heat transfer capability, by reducing the length of the heat transfer tubes, the number of tubes and/or the size of the tubes.
A still further object of the present invention is to provide a new one-piece heat exchanger having rectangular shaped heat conduction tubes which has enhanced durability compared to keel coolers presently on the market.
A related object of the invention is to provide an improved heat exchanger and headers thereof which is capable of deflecting debris more readily, and for presenting a smaller target to debris in the ambient water.
It is another object to provide a keel cooler and header thereof which projects into the water from the hull by a lesser amount than the corresponding one-piece keel coolers and headers thereof.
Another object of the present invention is to provide an improved one-piece keel cooler which is easier to install on vessels than corresponding keel coolers presently on the market.
It is still another object of the invention to provide a one-piece heat exchanger having a reduced pressure drop and a more uniform distribution of coolant flowing therethrough than heat exchangers presently on the market, for increasing the amount of coolant flowing through the heat exchanger to improve its capacity to transfer heat.
Yet a further object of the present invention is to provide a one-piece heat exchanger and a header having a lower weight, and therefore lower cost, than corresponding one-piece heat exchangers presently in use.
Another object of the present invention is to provide a one-piece heat exchanger and headers thereof having rectangular heat conduction tubes having a lower pressure drop in coolant flowing through the heat exchanger than corresponding heat exchangers presently known.
Another object of the present invention is the provision of a one-piece heat exchanger for a vessel, for use as a retrofit for previously installed one-piece heat exchangers which will surpass the overall heat transfer performance and provide lower pressure drops than the prior units without requiring additional plumbing, or requiring additional space requirements, to accommodate a greater heat output.
It is another object of the invention to provide an improved header for a one-piece heat exchanger having rectangular coolant flow tubes.
Another object is to provide an improved header for a one-piece heat exchanger with rectangular coolant flow tubes which reduces the dead spots which have heretofore reduced the heat transfer capabilities of one-piece heat exchangers, the dead spots reducing the flow of ambient water around and between the coolant flow tubes.
A further object of the invention is to provide an improved header for a one-piece keel cooler with rectangular coolant flow tubes, by reducing the likelihood of damage to the header from striking debris and underwater objects which could damage the keel cooler.
It is still another object for the provision of a header for effecting increased turbulent flow of the ambient water flowing between and around the heat transfer tubes.
It is an additional object to provide an improved header for one-piece keel coolers which enables the anode for such keel coolers to be less likely to strike debris and underwater objects.
Another object is the provision of a keel cooler having a smaller, and more streamlined profile to reduce drag as the vessel with the keel cooler moves through the ambient water.
Another object is to provide a header for a one-piece heat exchanger which provides for enhanced heat exchange between the coolant and the ambient cooling medium such as water.
Yet a further object is to provide a header for a one-piece heat exchanger which provides for more uniform flow of coolant through all tubes of the keel cooler, to improve the heat transfer as compared to equivalent, current headers.
A general object of the present invention is to provide a one-piece heat exchanger and headers thereof which is efficient and effective in manufacture and use.
Other objects will become apparent from the description to follow and from the appended claims.
The invention to which this application is directed is a one-piece heat exchanger, i.e. heat exchangers having two headers which are integral with coolant flow tubes. It is particularly applicable to heat exchangers used on marine vessels as discussed earlier, which in that context are also called keel coolers. However, heat exchangers according to the present invention can also be used for cooling heat generating sources (or heating cool or cold fluid) in other situations such as industrial and scientific equipment, and therefore the term heat exchangers covers the broader description of the product discussed herein. The heat exchanger includes two headers, and one or more coolant flow tubes integral with the header.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic view of a heat exchanger on a vessel in the water.
FIG. 2
is a side view of an engine for a vessel having a one-piece keel cooler according to the prior art installed on the vessel and connected to the engine;
FIG. 3
is a pictorial view of a keel cooler according to the prior art;
FIG. 4
is a partial pictorial view of a partially cut-away header and a portion of the coolant flow tubes of a one-piece keel cooler according to the prior art;
FIG. 5
is a cross-sectional view of a portion of a keel cooler according to the prior art, showing a header and part of the coolant flow tubes;
FIG. 6
is a side, cross-sectional, partial view of a portion of one-piece keel cooler according to the invention, showing a header and part of the coolant flow tubes;
FIG. 7
is a pictorial view of a portion of a one-piece keel cooler according to the invention, with portions cut away;
FIG. 8
is a pictorial view of a header and part of the coolant flow tubes of a one-piece keel cooler according to the invention;
FIG. 9
is a side view of part of the apparatus shown in
FIG. 8
;
FIG. 10
is a front view of the apparatus shown in
FIG. 8
;
FIG. 11
is a partial bottom view of the apparatus shown in
FIG. 8
;
FIG. 12
is a side view of a portion of a header according to the invention showing the flow lines of ambient water;
FIG. 13
is a pictorial view of a keel cooler according to the invention;
FIG. 14
is a cross-sectional view of a portion of a keel cooler substantially according to the prior art, but the orifice for the flow of coolant between the header and the outermost coolant flow tube, is constructed according to the invention;
FIG. 15
is a cross-sectional view of a portion of a keel cooler, having several variations of the orifice(s) for the flow of coolant between the header and the outermost coolant flow tube, according to an aspect of the invention;
FIG. 16
is a pictorial view of a two pass keel cooler system according to the invention;
FIG. 17
is a cut away view of a portion of the header shown in
FIG. 16
;
FIG. 18
is a pictorial view of a multiple systems combined, having two single pass portions, according to the invention;
FIG. 19
is a pictorial view of a keel cooler according to the invention, having a single pass portion and a double pass portion; and
FIG. 20
is pictorial view of two double pass systems according to the invention;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fundamental components of a heat exchanger system for a water going vessel are shown in FIG.
1
. The system includes a heat source
1
, a heat exchanger
3
, a pipe
5
for conveying the hot coolant from heat source
1
to heat exchanger
3
, and a pipe
7
for conveying cooled coolant from heat exchanger
3
to heat source
1
. Heat source
1
could be an engine, a generator or other heat source for the vessel. Heat exchanger
3
could be a one-piece keel cooler (since only one-piece keel coolers are discussed herein, they are generally only referred to herein as “keel coolers.”) Heat exchanger
3
is located in the ambient water, below the water line (i.e. below the aerated water line), and heat from the hot coolant is transferred through the walls of heat exchanger
3
and expelled into the cooler ambient water.
FIG. 2
shows a heat exchanger
11
mounted on a vessel, for transferring heat from the coolant flowing from an engine or other heat source
13
to the ambient water. Coolant flows from one of lines
14
or
15
from engine
13
to keel cooler
11
, and back through the other flow pipe from keel cooler
11
to engine
13
. Keel cooler
11
is attached to, but spaced from the hull of vessel.
A keel cooler
17
according to the prior art is shown in FIG.
3
. It includes a pair of headers
19
,
21
at opposite ends of a set of parallel, rectangular heat conductor tubes
23
, having interior tubes
25
and two exterior tubes (discussed below). A pair of nozzles
27
,
28
conduct coolant into and out of keel cooler
17
. Nozzles
27
,
28
have cylindrical threaded connectors
29
,
30
, and nipples
31
,
32
at the ends of the nozzles. Headers
19
,
21
have a generally prismatic construction, and their ends
34
,
35
are perpendicular to the parallel planes in which the upper and lower surfaces of tubes
23
are located. Keel cooler
17
is connected to the hull of a vessel through which nozzles
27
and
28
extend. Large gaskets
36
,
37
each have one side against headers
19
,
21
respectively, and the other side engages the hull of the vessel. Rubber washers
38
,
39
are disposed on the inside of the hull when keel cooler
17
is installed on a vessel, and metal washers
40
,
41
sit on rubber washers
38
,
39
. Nuts
42
,
43
, which typically are made from metal compatible with the nozzle, screw down on sets of threads
44
,
45
on connectors
29
,
30
to tighten the gaskets and rubber washers against the hull to hold keel cooler
17
in place and seal the hull penetrations from leaks
Turning to
FIG. 4
, a partial, cross section of the current keel cooler according to the prior art and depicted in
FIG. 3
, is shown. Keel cooler
17
is composed of the set of parallel heat conduction or coolant flow tubes
23
and the header or manifold
19
. Nozzle
27
is connected to header
19
as described below. Nozzle
27
has nipple
31
, and connector
29
has threads
44
as described above, as well as washer
40
and nut
42
. Nipple
31
of nozzle
27
is normally brazed or welded inside of a connector
29
which extends inside the hull. Header
19
has an upper wall or roof
47
, outer back wall
34
, and a bottom wall or floor
48
. Header
19
includes a series of fingers
52
which are inclined with respect to tubes
23
, and define spaces to receive ends
55
of interior tubes
25
.
Referring also to
FIG. 5
, which shows keel cooler
17
and header
19
in cross section, header
19
further includes an inclined surface or wall
49
composed of fingers
52
. End portions
55
of interior tubes
25
extend through surface
49
. Interior tubes
25
are brazed or welded to fingers
52
to form a continuous surface. A flange
56
surrounds an inside orifice
57
through which nozzle
27
extends and is provided for helping support nozzle
27
in a perpendicular position on the header
19
. Flange
56
engages a reinforcement plate
58
on the underside of wall
47
.
In the discussion above and to follow, the terms “upper”, “inner”, “downward”, “end” etc. refer to the heat exchanger, keel cooler or header as viewed in a horizontal position as shown in FIG.
5
. This is done realizing that these units, such as when used on water going vessels, can be mounted on the side of the vessel, or inclined on the fore or aft end of the hull, or various other positions.
Each exterior side wall of header
19
is comprised of an exterior or outer rectangular tube, one of which is indicated by numeral
60
in FIG.
4
. The outer tubes extend into header
19
.
FIGS. 4 and 5
show both sides of outside tube wall
61
. Both sides of interior wall
65
are shown in
FIGS. 4 and 5
. A circular orifice
69
is shown extending through interior wall
65
of the outside rectangular tube of keel cooler
17
, and is provided for carrying coolant flowing through the outside tube into or out of header
19
. In this regard, nozzle
27
can either be an inlet conduit for receiving hot coolant from the engine whose flow is indicated by the arrow A in
FIG. 5
, but also could be an outlet conduit for receiving cooled coolant from header
19
for circulation back to the heat source. It is important to note that in the prior art, the location and size of orifice
69
limits the amount of flow which can pass through orifice
69
. More particularly, the orifice has heretofore been mounted too high, is too small, and too far away from the natural flow path of the coolant, resulting in reduced flow through the outer rectangular tubes, non-uniform coolant flow through tubes
23
, and a disadvantageously high pressure drop as the coolant flows through the orifices, and at higher rates through the less restricted inner tubes—even though the outermost tubes have the greatest ability to transfer heat.
FIG. 4
also shows that keel cooler header
19
has a drainage orifice
71
for receiving a correspondingly threaded and removable plug. The contents of keel cooler
17
can be removed through orifice
71
.
Orifice
57
is separated by a fairly large distance from the location of orifice
69
, resulting in a reduced amount of flow through each orifice
69
, the reduction in flow being largely due to the absence of the orifice in the natural flow path of the coolant. Although this problem has existed for five decades, it was only when the inventors of the present invention were able to analyze the full, flow characteristics that they verified the importance of properly locating and sizing the orifice. In addition, the configuration of the header in both single pass and multiple pass systems affects the flow through the header as discussed below.
Still referring to the prior art header
19
shown in
FIGS. 3-5
, it can be seen that outer back wall
34
and floor
48
are formed at right angles. This configuration has led to a number of disadvantages, previously unrecognized by those designing and working on keel coolers. First, by having wall
34
perpendicular to the direction of flow of the coolant through the tubes, greater pressure drops occur inside of header
19
as the coolant becomes chaotically turbulent and is forced through the coolant flow tubes at varying flow rates depending on resistance. This coupled with the poor location and size of orifice
69
leads to a net reduction in flow and thus of heat transferred from the coolant through outer tubes
60
of keel cooler
17
. With respect to the outside of wall
34
, the vertical wall acts as an obstruction to the flow of ambient water, and diminishes the amount of ambient water which is able to flow between and around tubes
23
. In addition, vertical wall
34
serves as an obstruction to debris in the ambient water and absorbs the full impact of the debris leading to potential damage to the keel cooler. Moreover, having wall
34
and floor
48
defining a right angle increases the amount of material used for keel cooler
17
, which adds to its expense. Most keel coolers are made from 90-10 copper-nickel (or some other material having a large amount of copper), which is a relatively expensive material. In addition, significant drag is created by the resistance which the vertical wall presents to ambient water, as well as the protruding anode(s) and drain plug(s) (discussed below) mounted on floor
48
. This restricts the flow of ambient water to the heat exchange tubes of the keel cooler, increases the required depth of the keel cooler which may increase the likelihood of it being hit by debris, as well as lowering the depth of the vessel and increasing the probability of damage by underlying structures, and adds to the drag of the vessel as it moves through the water.
Still referring to
FIGS. 3-5
, gaskets
36
,
37
are provided for three essential purposes: (1) they insulate the header to prevent galvanic corrosion, (2) they eliminate infiltration of ambient water into the vessel, and (3) they permit heat transfer in the space between the keel cooler tubes and the vessel by creating a distance of separation between the heat exchanger and the vessel hull, allowing ambient water to flow through that space. Gaskets
36
,
37
are generally made from a polymeric substance. In typical situations, gaskets
36
,
37
are between one quarter inch and three quarter inches thick. Keel cooler
17
is installed on a vessel as explained above. The plumbing from the vessel is attached by means of hoses to nipple
31
and connector
29
and to nipple
32
and connector
30
. A cofferdam or sea chest (part of the vessel) at each end (not shown) contains both the portion of the nozzle
27
and nut
42
directly inside the hull. Sea chests are provided to prevent the flow of ambient water into the vessel should the keel cooler be severely damaged or torn away, where ambient water would otherwise flow with little restriction into the vessel at the penetration location.
Referring next to
FIGS. 6-11
, the invention in the preferred embodiment is shown. The embodiment includes a keel cooler
200
with coolant flow tubes (or heat transfer fluid flow tubes, since in some instances the fluid may be heated instead of cooled)
202
having a generally rectangular cross section. A header
204
is an integral part of keel cooler
200
. Tubes
202
include interior or inner coolant flow tubes
206
and outermost or exterior tubes
208
. A nozzle
27
having nipple
31
and threaded connector
29
, are the same as those described earlier and are attached to the header. Header
204
includes an upper wall or roof
210
, a beveled closed end portion
212
having an end wall
214
transverse to (and preferably perpendicular to) upper wall
210
and a beveled, bottom wall
216
beginning at end wall
214
and terminating at a generally flat lower wall
217
. Beveled wall
216
should be greater in length (from end wall
214
to lower wall
217
) than the height of end wall
214
. An interior wall
218
(
FIGS. 6-7
) of exterior or outermost rectangular flow tube
208
has an orifice
220
(one per header for each tube
208
) which is provided as a coolant flow port for coolant flowing between the chamber of header
204
and outer flow tubes
208
(The chamber is defined by upper wall
210
, an inclined surface or inner end or inlet end portion
229
, beveled bottom wall
216
, lower wall
217
and end wall
214
). Header
204
also has an anode assembly
222
(shown in
FIG. 6
) for reducing corrosion of the keel cooler.
Anode assembly
222
includes a steel anode plug(s)
223
which is connected to an anode insert(s)
224
which is part of header
204
, an anode mounting screw(s)
242
, a lockwasher(s)
246
(
FIG. 11
) and anode bar
228
, which is normally made of zinc. The anode insert, the anode plug and the anode bar have not changed from the prior art, but were omitted from
FIGS. 3 and 4
for the sake of clarity. However, the location of the anode assembly has changed as explained below.
Considering specifically cut away
FIG. 7
, keel cooler
200
includes rectangular tubes
202
with interior tubes
206
and outermost tubes
208
, and inner wall
218
(with orifice
220
) of the outermost tubes. The open ends or inlets or ports for interior tubes
206
are shown by numerals
227
. Tubes
206
join header
204
through inclined surface
229
(
FIG. 6
) on the opposite part of header
204
from beveled wall
216
. Exterior tubes
208
have outer walls
230
, part of which are also the side walls of header
204
. A gasket
232
, similar to and for the same purpose as gasket
36
, is disposed on roof
210
.
An important part of the present invention is the beveled closed end portion
212
. Beveled closed end portion
212
, with beveled bottom wall
216
, provides a number of important advantages to the keel cooler. First, being beveled as shown, it enhances the continuous flow of coolant either from heat conduction tubes
202
into nozzle
27
, where nozzle
27
is an outlet nozzle, or from nozzle
27
into tubes
202
, where nozzle
27
is an inlet nozzle. When nozzle
27
is an inlet, beveled wall
216
in cooperation with the angled surface
229
acts to direct the flow of coolant into orifice
220
and openings
227
, i.e. beveled wall
216
directs the natural flow of coolant from the nozzle
27
to orifices
220
and tube openings
227
. It can be seen that the beveled end portion
212
either distributes the coolant more uniformly across inlets
227
to each of tubes
202
(including orifices
220
in interior wall
218
of exterior tubes
208
, or from tubes
202
for discharge of coolant into nozzle
27
where nozzle
27
is an outlet nozzle). The increased coolant flow in the outermost tubes results in improved coolant flow distribution among all the tubes, which provides a lower pressure drop across the entire system and greater heat transfer between the coolant, through tubes
202
and through the walls of header
204
, and the ambient water. For example, for a keel cooler having eight rectangular tubes whose external dimensions are 2½ inches in height and ½ inch in width, and the keel cooler is mounted on a vessel with a 2 knot speed, the coolant flow to the outer tubes increased by about 35% over the flow under corresponding heat exchange conditions using the prior art heat exchanger of the same size (i.e. the numbers of tubes and lengths of the tubes) as shown in
FIGS. 3-5
, which had poor flow distribution. In addition, the heat transferred by the exterior tubes increased by 45% over the corresponding heat transfer under corresponding conditions using the prior art keel cooler shown in
FIGS. 3-5
. The total heat transfer of the entire system increased by about 17% in a particular instance over the corresponding unit of
FIGS. 3-5
. As explained below, the improvement over the prior art is expected to be even greater for two pass systems. Also, as discussed later, the deficiencies of the prior art for higher coolant flows, are not experienced to the same extent by the keel cooler according to the invention.
The angle of beveled wall
216
is an important part of the present invention. As discussed herein, the angle, designated as θ (theta), is appropriately measured from the plane perpendicular to the longitudinal direction of coolant flow tubes
202
and located at the part of the closed end portion of header
204
spaced furthest from the set of open ends or ports
227
of tubes
206
, i.e. from end wall
214
, to beveled wall
216
. Angle θ is described as an exterior angle, since it is exterior to end wall
214
and beveled bottom wall
216
; it is measured from a plane perpendicular to the longitudinal axes of the flow tubes
202
and roof
210
, and it is along end wall
214
at the beginning of beveled bottom wall
216
. The factors for determining angle θ are to maintain the center to center distance of the nozzle spacing, to maintain the overall length of the keel cooler, to provide vertical drop beneath the roof of the header so that the header can hold the anode insert, to keep the anode assembly from extending longitudinally beyond wall
214
, and to allow for the maximum length of heat transfer tubing (and the associated reduction of the length of the header). Angle θ could be affected by the size of orifice
220
, but generally the other factors limit angle θ before the orifice would affect it.
Another important aspect to beveled wall
216
is the manner in which it directs the flow of ambient water over and between the exterior walls of coolant flow tubes
202
, to increase the heat transfer between the coolant inside the tubes and the outside ambient water. It will be recalled that under the prior art as shown in
FIGS. 3-5
, vertical wall
34
diverted the ambient water as the vessel passed therethrough, so that the ambient water to a significant extent went around rather than between and over the separated rectangular tubes
27
.
It is desirable not to increase the depth of a keel cooler any more than necessary, to make it less likely to strike debris in the water, and less likely to strike underwater objects or the ground beneath the vessel, i.e. the bottom. For this reason, anode assembly
222
is preferably mounted on beveled wall
216
. As shown in
FIGS. 6 and 11
, anode bar
228
of anode assembly
222
is attached to beveled wall
216
, by anode screws
242
which extend through lockwashers
246
and into anode insert
224
. Anode insert
224
extends from wall
216
into header
204
. This decreases the depth of anode assembly according to the prior art, under which anode assembly
222
would have extended from lower wall
217
.
As shown most clearly in
FIGS. 10 and 11
, drain plug
244
is also preferably located on beveled wall
216
to avoid plug
244
from striking debris in the water or hitting bottom. More importantly, the drain plug and anode located on the beveled surface have less interference with the ambient water flow pattern (
FIG. 12
, arrows B). Drain plug
244
extends into a drain plug insert which is part of the header. Under the prior art, drain plug
244
would otherwise have extended from lower wall
217
.
Referring to
FIG. 12
, which shows a side view of keel cooler
200
, arrows B show the flow pattern of ambient water across keel cooler
200
as the keel cooler moves to the right through the ambient water. Arrows B show that the water impinges on beveled wall
216
, flows around the beveled wall, and, due to the drop in pressure, along inclined surface
229
and up and between coolant flow tubes
202
. This flow is turbulent which greatly increases the transfer of heat from the heat conduction tubes as compared to the prior art shown in
FIGS. 3-5
, yielding a more efficient and effective heat exchanger than those of the prior art. Additionally, having drain plug
244
and anode bar
228
on beveled wall
216
causes less interference with the ambient water flow pattern shown by arrows B. They contribute to the improved heat transfer efficiency.
Keel coolers according to the invention are used as they have been in the prior art, and incorporate two headers which are connected by an array of parallel coolant flow tubes. A common keel cooler according to the invention is shown in
FIG. 13
, which illustrates a keel cooler
200
′ having opposing headers
204
like the one shown in FIG.
7
. The headers shown have the identical numbers to those shown in FIG.
7
. Heated coolant fluid flows into one nozzle
27
from a heat source in the vessel, then flows through one header
204
, the coolant flow tubes
202
, the other header
204
, the other nozzle
27
, and the cooled coolant flows back to the heat source in the vessel. While flowing through headers
204
and coolant flow tubes
202
, the coolant transfers heat to the ambient water. All of the advantages of the beveled wall
216
apply to keel cooler
200
′.
As mentioned above, the size of orifice
220
is an important part of the new keel cooler and the new header. It is desirable to have the orifice be sufficiently large to not impede the amount of coolant flow to exterior heat conduction tubes
208
of the keel cooler, and to implement a balanced flow near the juncture of beveled wall
216
and the interior of surface
229
and ports
227
. It has been found that a distance of about ⅛ of an inch between orifice
220
and walls adjacent its lower edge (the interior of the lower parts of wall
216
, wall
217
and surface
229
, as shown in
FIG. 6
) be provided for manufacturing tolerance as it is fabricated, which is advantageously done by drilling or cutting orifice
220
into wall
218
. It is important that the coolant flow into exterior tubes
208
be near the bottom of walls
218
, rather than closer to their top. The distance between the top of orifice
220
and roof
210
is not as crucial. The proper size and placement of orifice
220
thus reduces the pressure drop of the coolant in the entire system of keel cooler
200
, balances the flow among the multiple tubes, and thus increases the heat transfer through the outer tubes and therefore the entire unit.
While the embodiment under discussion is a beveled keel cooler, the size and location of the orifice to the outermost tubes in a one-piece keel cooler according the prior art as shown in
FIGS. 3-5
is significantly improved according to the present invention.
FIG. 14
shows a keel cooler header and an outermost coolant flow tube much as was shown in
FIG. 5
(and corresponding parts have corresponding numbers), except that orifice
69
has been replaced by orifice
221
. Orifice
221
has been moved closer to the openings of the inner coolant flow tubes, has been moved lower, and its size has been increased significantly, so that it is as large as possible within the area permitted on wall
67
. Relocated and enlarged orifice
221
enables more coolant fluid to flow into the outermost coolant flow tubes (or from it if the flow were to proceed out of nozzle
27
). As explained in the preceding paragraph, the use of orifice
221
reduces the pressure drop of the coolant and balances the flow of coolant amongst the coolant flow tubes, thus increasing heat transfer for the keel cooler (or other heat exchanger).
As a practical matter, it has been found that a circular orifice having a diameter as large as possible while maintaining the orifice in its wall within the header provides the desired coolant flow into the outermost tubes while enabling the proper amount of flow into the inner tubes as well. More than one orifice can also be provided, as shown in
FIG. 15
, where all of the members have the same numerical designators shown in
FIGS. 6-12
, except that some have a prime (′) designation since angle θ has been changed to 40°, wall
214
′ is larger than wall
214
, beveled wall
216
′ is shorter than wall
216
and the configuration of wall
218
′ has been modified from wall
218
. Orifice
220
has been replaced by two orifices
220
′ and
220
″. Also, the anode assembly
222
and drain plug have been moved to a lower wall
217
′ of header
204
′. Tubes
202
have also been moved along with the change in header
204
′.
The orifice has been shown as one or more circular orifices, since circular orifices are relatively easy to provide. However, non-circular orifices are also within the scope of the invention, and a length of wall
218
could be dispensed with (as shown at
218
′ in FIG.
15
).
The importance of the size and location of orifice
220
has other advantages as well. So far, only single pass keel cooler systems have been described. The problems with the size and location of the orifice to the outside tubes may be magnified for multiple pass systems and for multiple systems combined, as explained below. In two pass systems, the inlet and outlet nozzles are both disposed in one header, and coolant flows into the header via an inlet nozzle, through a first set of tubes from the first header into the second header (with no nozzles), and then back through a second set of tubes at a lower pressure—and finally out from the header via an outlet nozzle. Referring to
FIGS. 16 and 17
, a two pass keel cooler
300
according to the invention is shown. Keel cooler
300
has two sets of coolant flow tubes
302
,
304
, a header
306
and an opposite header
308
. Header
306
has an inlet nozzle
310
and an outlet nozzle
312
, which extend through a gasket
314
. Gasket(s)
314
is located on roof
316
of header
306
. The other header
308
has no nozzles, but rather has one or two stud bolt assemblies
318
,
320
for connecting the portion of the keel cooler which includes header
308
to the hull of the vessel. The hot coolant from the engine or generator of the vessel enters nozzle
310
as shown by arrow C, and the cooled coolant returns to the engine from header
306
through outlet nozzle
312
shown by the arrow D. Outer tubes
322
,
324
are like outer tubes
208
in
FIGS. 7
,
8
and
11
in that orifices corresponding to orifice
220
directs coolant into tube
322
and from tube
324
. In addition, a tube
326
serves as a separator tube for delivering inlet coolant from header
306
to header
308
, and it has an orifice (not shown) for receiving coolant for separator tube
326
under high pressure from a part of header
306
as discussed below. Similarly, a tube
327
which is the return separator tube for carrying coolant from header
308
, also has an orifice
328
in header
306
.
For space limitations or assembly considerations, sometimes (as noted above) it is necessary to remove the inner wall or a section of the inner tube instead of one or the other of the orifices. Other times, a separator plate is used and the standard angle interior tubes are used instead of separator tubes.
Keel cooler
300
has one set of coolant flow tubes
302
for carrying hot coolant from header
306
to header
308
, where the direction of coolant flow is turned 180° by header
308
, and the coolant enters a second set of tubes
304
for returning the partially cooled coolant back to header
306
. Thus, coolant under high pressure flows through tubes
302
from header
306
to header
308
, and the coolant then returns through tubes
304
, and subsequently through nozzle
312
to the engine or other heat source of the vessel. Walls
334
and
336
(shown in
FIG. 17
) of tubes
326
and
327
in header
306
are solid, and act as separators to prevent the mixing of the hot coolant going into coolant flow tubes
302
, and the cooled coolant flowing from tubes
304
. There is a fairly uniform rate of flow through the tubes in both directions. Such efficient systems have been unable to be produced under the prior art, since the pressure drop across all six (or as many as would be realistically considered) orifices made the prior keel coolers too inefficient due to poor coolant distribution to be operated without a substantial additional safety factor. That is, in order to have two pass systems, prior one piece keel cooler systems having two pass arrangements are up to 20% larger than those required pursuant to the present invention to provide sufficient heat exchange surfaces to remove the required amount of heat from the coolant while attempting to maintain acceptable pressure drops.
The keel cooler system shown in
FIG. 16
has 8 flow tubes. However, the two pass system would be appropriate for any even number of tubes, especially for those above two tubes. There are presently keel coolers having as many as 24 tubes, but it is possible according to the present invention for the number of tubes to be increased even further. These can also be keel coolers with more than two passes. If the number of passes is even, both nozzles are located in the same header. If the number of passes is an odd number, there is one nozzle located in each header.
Another aspect of the present invention is shown in
FIG. 18
, which shows a multiple systems combined keel cooler which has heretofore not been practically possible with one-piece keel coolers. Multiple systems combined can be used for cooling two or more heat sources, such as two relatively small engines or an after cooler and a gear box in a single vessel. Although the embodiment shown in
FIG. 18
shows two keel cooler systems, there could be additional ones as well, depending on the situation. As explained below, the present invention allows multiple systems to be far more efficient than they could have been in the past. Thus,
FIG. 18
shows a multiple systems keel cooler
400
. Keel cooler
400
has a set of heat conducting or coolant flow tubes
402
having outer tubes
404
and
406
, which have orifices at their respective inner walls which are similar in size and position to those shown in the previously described embodiments of the invention. For two single pass, multiple systems combined, keel cooler
400
has identical headers
408
and
410
, having inlet nozzles
412
,
416
respectively, and outlet nozzles
414
,
418
respectively. Both nozzles in respective headers
408
and
410
could be reversed with respect to the direction of flow in them, or one could be an inlet and the other could be an outlet nozzle for the respective headers. The direction of the coolant flow through the nozzles are shown respectively by arrows E, F, G and H. A set of tubes
420
for conducting coolant between nozzles
412
and
418
commence with outer tube
404
and terminate with separator tube
422
, and a set of tubes
424
extending between nozzles
414
and
416
, commencing with outer tube
406
and terminating with separator tube
426
. The walls of tubes
422
and
426
which are adjacent to each other are solid, and extend between the end walls of headers
408
and
410
. These walls thus form system separators, which prevent the flow of coolant across these walls, so that the tubes
420
form, in effect, one keel cooler, and tubes
424
form, in effect, a second keel cooler (along with their respective headers). Keel cooler
400
has beveled closed end portions
428
,
430
as discussed earlier. This type of keel cooler can be more economical than having two separate keel coolers, since there is a savings by only requiring two headers, rather than four. Multiple keel coolers can be combined in various combinations. There can be two or more one pass systems as shown in FIG.
18
.
There can be one or more single pass systems and one or more double pass systems in combination as shown in FIG.
19
. In
FIG. 19
, a keel cooler
500
is depicted having a single pass keel cooler portion
502
, and a double pass keel cooler portion
504
. Keel cooler portion
502
functions as that described with reference to
FIGS. 6-11
, and keel cooler portion
504
functions as that described with reference to
FIGS. 16 and 17
.
FIG. 19
shows a double pass system for one heat exchanger, and additional double pass systems could be added as well.
FIG. 20
, shows a keel cooler
600
having 2 double pass keel cooler portions
602
,
604
, which can be identical or have different capacities. They each function as described above with respect to
FIGS. 16 and 17
. Multiple coolers combined is a powerful feature not found in prior one-piece keel coolers. The modification of the special separator/tube design improves heat transfer and flow distribution while minimizing pressure drop concerns.
The keel coolers described above show nozzles for transferring heat transfer fluid into or out of the keel cooler. However, there are other means for transferring fluid into or out of the keel cooler; for example, in flange mounted keel coolers, there are one or more conduits such as pipes extending from the hull and from the keel cooler having end flanges for connection together to establish a heat transfer fluid flow path. Normally a gasket is interposed between the flanges. There may be other means for connecting the keel cooler to the coolant plumbing system in the vessel. This invention is independent of the type of connection used to join the keel cooler to the coolant plumbing system.
The invention has been described with particular reference to the preferred embodiments thereof, but it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains.
Claims
- 1. A header for a heat exchanger, the heat exchanger having a plurality of parallel tubes extending in a longitudinal direction and having generally rectangular cross sections, the tubes including a pair of outermost tubes and at least one inner tube located between the outermost tubes, the outermost tubes having an outside wall and a parallel inside wall, and the inner tubes having coolant ports, said header comprising:an upper wall having an upper end portion, opposing side portions and an upper inner portion, said upper end portion and said upper inner portion being located in a plane, and an inlet/outlet opening for permitting the flow of coolant between an inlet/outlet and said header, said upper wall having a length extending between said upper end portion and said upper inner portion; a lower wall located below said upper wall, said lower wall having a lower end portion, opposing side portions and a lower inner portion, said lower wall having a length extending between the lower end portion and the lower inner portion, said length being less than the length of said upper wall and disposed inwardly from both the upper end portion and the upper inner portion of said upper wall; an end wall extending transversely from the end portion of said upper wall and terminating below said upper wall and above said lower wall; an inclined surface extending between the inner portions of said lower wall and said upper wall, and including the open end(s) of the at least one inner tube to said header; outside side walls extending between the side portions of said upper wall and said lower wall, said outside side walls each being an extension of the outside wall of the outermost tube of the heat exchanger; inside side walls parallel to said outside side walls, said inside side walls each being an extension of the inside wall of the outermost tube; and a beveled wall extending between the termination of said end wall and the end portion of said lower wall and beveled with respect to said longitudinal direction from said upper wall to said lower wall towards said tube to reduce the turbulence of coolant flow to and/or from said parallel tubes and increase ambient fluid flow to the exterior surfaces of said parallel tubes compared to a non-beveled wall; the inner surfaces of said inside side walls, upper wall, end wall, bottom wall, beveled wall and inclined surface forming a header chamber; said inside side walls each having an orifice for permitting the flow of coolant between said header chamber and the respective outermost tube; said orifice being disposed at least partly over said inclined surface when viewed in a transverse direction with respect to the longitudinal direction and at least partly beneath said inlet/outlet opening.
- 2. A header according to claim 1 wherein said orifice is a circular orifice.
- 3. A header according to claim 1 wherein said orifice is a circular orifice generally tangent to said bottom wall.
- 4. A header according to claim 1 wherein said orifice is a circular orifice whose size is the maximum size that will fit on said inner wall in said header chamber.
- 5. A header according to claim 1 wherein the parallel tubes have an internal cross sectional area, and wherein said orifice has an area of at least 1½ times the internal cross sectional area of each of the parallel tubes.
- 6. A header according to claim 5 wherein the area of said orifice is about twice the area of each of the parallel tubes.
- 7. A header according to claim 1 wherein the side walls having said orifice have an internal cross sectional area, and wherein said orifice has an area of at least 1½ times the internal cross sectional area.
- 8. A header according to claim 1 wherein said orifice has an area substantially as large as the largest circular orifice which will fit in said side walls at the location of said orifice.
- 9. A header according to claim 1 wherein said orifice is one of a plurality of orifices.
- 10. A header according to claim 1 wherein each of said orifices covers substantially the respective inside side walls.
- 11. A header according to claim 1 and further including an anode assembly located on said beveled wall.
- 12. A header according to claim 11 wherein said beveled wall has an interior side and an exterior side, and wherein said anode assembly has an anode bar located on the exterior side of said beveled wall, and said anode bar does not extend beyond said end wall.
- 13. A header according to claim 1 and further including a drain assembly including a drain hole located in said beveled wall, and a drain plug locatable in said drain hole, said drain plug extending outwardly from said beveled wall.
- 14. A header according to claim 13 wherein said drain plug does not extend below said lower wall.
- 15. A one-piece heat exchanger comprising:a plurality of coolant flow tubes extending in a longitudinal direction for carrying coolant fluid and for transferring heat from the coolant fluid to a fluid heat sink, said coolant flow tubes having inner tubes and exterior side tubes, said inner tubes having at least one set of open ends in proximity to each other; and a header connected to said coolant flow tubes at said set of open ends of said tubes, said header having an inlet end portion for receiving coolant from and/or delivering coolant to said coolant flow tubes through said open ends, a generally flat upper wall having an opening for the flow of coolant into and/or out of said header, a closed end portion opposite said inlet end portion having an end wall transverse to said upper wall and a beveled bottom wall having a beveled portion terminating in a generally flat bottom wall generally parallel to said upper wall, said beveled portion being beveled with respect to said longitudinal direction of said coolant flow tubes to reduce the turbulence of coolant flow to and/or from said coolant flow tubes and increase ambient fluid flow to the exterior surfaces of said coolant flow tubes compared to a non-beveled inlet end portion, and side walls comprising extensions of said exterior side tubes, each of said side walls including an outermost wall and an inner wall, said inner wall having an orifice for the flow of coolant between said header and said exterior tube of which said inner wall is an extension, said orifice being disposed at least partly over said inlet end portion and at least partly beneath said opening as viewed in a transverse direction with respect to the longitudinal direction, said beveled portion serving to direct internal coolant flow to and/or from said orifices.
- 16. A one-piece heat exchanger according to claim 15 wherein said orifice has an area substantially as large as the largest circular orifice which will fit in said side walls at the location of said orifice.
- 17. A one-piece heat exchanger according to claim 15 wherein said orifice is one of a plurality of orifices for the flow of coolant between said header and said exterior tube of which said inner wall is an extension.
- 18. A one-piece heat exchanger according to claim 15 wherein each of said orifices covers substantially the respective inside side walls.
- 19. A one-piece heat exchanger according to claim 15 and further including an anode assembly located on said beveled portion of said beveled bottom wall.
- 20. A one-piece heat exchanger according to claim 19 wherein said beveled portion has an interior side and an exterior side, and wherein said anode assembly has an anode bar located on the exterior side of said beveled portion, and said anode bar does not extend beyond said end wall.
- 21. A one-piece heat exchanger according to claim 15 and further including a drain assembly including a drain hole located on said beveled portion of said beveled bottom wall, and a drain plug locatable in said drain hole, said drain plug extending outwardly from said beveled portion.
- 22. A one-piece heat exchanger according to claim 21 wherein said drain plug does not extend below said flat bottom wall.
US Referenced Citations (7)