U.S. patent number 3,662,542 [Application Number 04/854,923] was granted by the patent office on 1972-05-16 for engine exhaust gas heater.
This patent grant is currently assigned to Dynatherm Corporation. Invention is credited to Alan J. Streb.
United States Patent |
3,662,542 |
Streb |
May 16, 1972 |
ENGINE EXHAUST GAS HEATER
Abstract
An improved engine exhaust gas heater based on the heat pipe
principle is provided which is suitable for many applications,
including aircraft to supply warm air for cabin conditioning, and
also automobiles, trucks, and other vehicles. The heater is
preferably associated with the engine exhaust gas muffler, and the
resulting combination comprises a device or system of greater
safety and of increased effectiveness regarding heat transfer and
noise reduction capability.
Inventors: |
Streb; Alan J. (Baltimore,
MD) |
Assignee: |
Dynatherm Corporation
(Cockeysville, MD)
|
Family
ID: |
25319869 |
Appl.
No.: |
04/854,923 |
Filed: |
September 3, 1969 |
Current U.S.
Class: |
60/320; 123/543;
237/12.3R; 165/104.26; 237/12.3B |
Current CPC
Class: |
B60H
1/20 (20130101) |
Current International
Class: |
B60H
1/02 (20060101); B60H 1/20 (20060101); B60h
001/20 () |
Field of
Search: |
;60/31 ;165/105
;237/28,12.1,12.3,12.3A,12.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Hart; Douglas
Claims
I claim:
1. An engine exhaust gas heating system of improved safety and heat
transfer efficiency comprising a muffler to which exhaust gases
from an engine are brought for gradual expansion therein in order
to reduce exhaust gas noise, a heat exchanger adjacent and separate
from said muffler and disposed in end-to-end relation thereto, a
heat pipe connecting the muffler and heat exchanger and comprising
(1) a heat input section disposed in said muffler and heated by hot
exhaust gases, (2) a heat output section disposed in said heat
exchanger, and (3) a heat transfer member extending through opposed
ends of said exchanger and muffler and connecting said input and
output sections and serving to transport heat substantially
isothermally from the input to the output sections, said heat pipe
mechanically as well as thermally connecting said exchanger and
muffler, means for introducing hot exhaust gases to said muffler,
means for introducing air to said heat exchanger to be warmed by
said heat output section, means for passing said warmed air to a
space to be heated, said air circulating between the exchanger and
the space to be heated, means for discharging exhaust gases from
said muffler directly to atmosphere, said exhaust gases following a
pathway from engine to discharge which is separate from the pathway
followed by the air so that rupture of a wall of said muffler does
not present a danger of contaminating said circulating air with
said exhaust gases, and said muffler-heat exchanger-heat pipe
system being not significantly larger than, and having
substantially the same over all shape and diameter as, the muffler
alone.
2. System of claim 1 wherein said exhaust gas introducing means
comprises a pair of conduits which enter the muffler through
opposed ends thereof with one of said conduits extending through
the heat exchanger, and wherein means are present for supporting
said last-mentioned conduit in the heat exchanger and for providing
additional protection against contamination of the air by exhaust
gases.
3. An engine exhaust gas heating system of improved safety and heat
transfer efficiency comprising a muffler to which exhaust gases
from an engine are brought for gradual expansion therein in order
to reduce exhaust gas noise, a heat exchanger adjacent and separate
from said muffler, a heat pipe connecting the muffler and heat
exchanger and comprising (1) a heat input section disposed in said
muffler and heated by hot exhaust gases, (2) a heat output section
disposed in said heat exchanger, and (3) a heat transfer member
connecting said input and output sections and serving to transport
heat substantially isothermally from the input to the output
sections, said heat pipe mechanically as well s thermally
connecting said exchanger and muffler, means for introducing hot
exhaust gases from the engine to said muffler, means for
introducing air to said heat exchanger to be warmed by said heat
output section, means for passing said warmed air to a space to be
heated, said air circulating between the exchanger and the space to
be heated, means for discharging exhaust gases from said muffler
directly to atmosphere, and said exhaust gases following a pathway
from engine to discharge which is separate from the pathway
followed by the air so that rupture of a wall of said muffler does
not present a danger of contaminating said circulating air with
said exhaust gases.
4. System of claim 3 wherein said exhaust gas introducing means
comprises a pair of conduits which enter the muffler through
opposed ends thereof, and wherein said system has substantially the
same diameter and length as said muffler alone.
5. An engine exhaust gas heating system of improved safety and heat
transfer efficiency comprising a muffler to which exhaust gases
from an engine are brought for expansion therein in order to reduce
exhaust gas noise, a heat exchanger adjacent and separate from said
muffler, a heat pipe connecting the muffler and heat exchanger and
comprising (1) a heat input section adapted to be heated by hot
exhaust gases, (2) a heat output section for heating air, and (3)
heat transfer means connecting said input and output sections and
serving to transport heat substantially isothermally from the input
to the output sections, means for introducing hot exhaust gases
from said engine to said heat input section, means for introducing
air to be warmed by said heat output section, means for passing
said warmed air to a space to be heated, said air circulating
between the exchanger and the space to be heated, means for
discharging exhaust gases from said muffler to atmosphere, and said
exhaust gases following a pathway from engine to discharge which is
separate from the pathway followed by the air so that rupture of a
wall of said muffler does not present a danger of contaminating
said circulating air with said exhaust gases.
6. An engine exhaust gas heating system of improved safety and heat
transfer efficiency comprising a muffler to which exhaust gases
from an engine are brought for gradual expansion therein in order
to reduce exhaust gas noise, a heat exchanger adjacent and separate
from said muffler, a heat pipe connecting the muffler and heat
exchanger and comprising (1) a heat input section adapted to be
heated by hot exhaust gases, (2) a heat output section for heating
air, and (3) heat transfer means connecting said input and output
sections and serving to transport heat substantially isothermally
from the input to the output sections, said heat pipe being
disposed entirely within the heat exchanger and extending
longitudinally therein so as to form an annular passage
therebetween for the flow of air, said heat pipe having along the
longitudinal axis thereof a passageway which extends therethrough
for the flow of hot exhaust gases, means for introducing hot
exhaust gases from said engine to said passageway in the heat pipe,
means for introducing air to said annular passage in said heat
exchanger to be warmed by said heat output section, means for
passing said warmed air from the annular passage to a space to be
heated, said air circulating between the exchanger and the space to
be heated, means for discharging exhaust gases from said muffler to
atmosphere, and said exhaust gases following a pathway from engine
to discharge which is separate from the pathway followed by the air
so that rupture of a wall of said muffler does not present a danger
of contaminating said circulating air with said exhaust gases.
7. System of claim 6 wherein said heat exchanger and muffler are
disposed in end-to-end relation, wherein said heat pipe extends
from end to end of the heat exchanger, and wherein said
muffler-heat exchanger-heat pipe system has substantially the same
diameter as the muffler.
8. System of claim 6 wherein said heat exchanger encloses a part of
the muffler, wherein said muffler throughout a portion of its
length is a part of the heat pipe, and wherein said muffler-heat
exchanger-heat pipe system has substantially the same diameter as
the muffler.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
The heat pipe employed in FIGS. 4-7 is disclosed in copending
application Ser. No. 854,827, filed Sept. 3, 1969
BACKGROUND OF THE INVENTION
1 The field of the invention comprises engine exhaust gas
heaters.
2. So far as is known, the system described herein is new.
SUMMARY OF THE INVENTION
The system employs a heat exchanger adjacent the engine exhaust gas
muffler. Separate pathways are provided for the exhaust gas and the
heating air or other heating medium, with the exhaust gas passing
from the engine to the muffler to atmosphere, and the air
circulating between the heat exchanger and the space to be heated.
Thermal interconnection between the gaseous streams in the pathways
is achieved by using one or more heat pipes, described below. Thus,
physical failure, such as rupture, of either pathway will not
result in commingling of the two streams, such as may occur in a
conventional system and result in passage of toxic exhaust gases
into the heated space or cabin.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the accompanying drawings, which
are diagrammatic, and in which
FIG. 1 is a side view of the device with parts broken away to show
the interior construction;
FIG. 2 is a partial end view of the device of FIG. 1, looking in
the direction of arrow A;
FIG. 3 is a view like FIG. 1, but reduced, and showing a
modification;
FIG. 4 is a view like FIG. 3 but showing another modification in
which a heat pipe of different construction is used;
FIG. 5 is an enlarged fragmental sectional view of FIG. 4
illustrating the heat pipe construction;
FIG. 6 is an enlarged fragmental sectional view along line 6--6 of
FIG. 5; and
FIG. 7 is a view like FIG. 4, but showing another modification, and
employing the heat pipe illustrated in FIGS. 5 and 6.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Referring to FIG. 1, the heater system shown here is of particular
applicability in aircraft, especially light aircraft whose cabin
space is conventionally heated by means of the engine exhaust
gases. The system includes a chamber 10, which in a light aircraft
installation would comprise the muffler, to which engine exhaust
gases are brought by the exhaust gas conduits, the latter
termination in the baffles or perforated end pieces 11, 12 to which
the conduits are attachable. The chamber is defined by a
cylindrical wall 13 and end walls 14, 15 which are suitably
apertured to receive the baffles. Exhaust gases leave by conduit
16.
A heat exchanger 17, preferably of cylindrical shape, is disposed
adjacent the chamber as shown, and it will be noted that the baffle
11 is sufficiently elongated as to extend axially through the
exchanger 17. Baffle 11 is supported at 18 by a concentric inner
cylinder 19 which extends between, and is supported by, the
apertured end walls 20, 21 of the heat exchanger. Cylinder 19
provides additional protection against contamination of the cabin
heating air should the baffle 11, or its extension 11a, undergo
rupture. Air may be introduced to the exchanger by an inlet 22 and
leave by an outlet 23, for which suitable apertures are formed in
the cylindrical wall 24.
A heat pipe, generally indicated at 25, extends between the chamber
and the heat exchanger and provides a thermal interconnection
therefor. It comprises a heat input section 26 disposed in the
chamber 10, a heat output section 27 disposed in the heat exchanger
17, and a heat transfer member or element 28 which extends through
and connects both sections. Member 28 preferably is in the form of
a continuous tube which extends from one end of the heat pipe to
the other, while the sections 26 and 27 are characterized by the
presence of closely spaced fins 29, 30 at each end portion of the
tube. Heat input section 26 is heated by the hot exhaust gases
brought into the chamber 10 by the exhaust gas conduits and the
baffles 11, 12, and the heat thus picked up is transported
substantially isothermally by member 28 to the heat output section
27 where it is transferred by direct heat exchange to air flowing
over fins 29 on its way to the space to be heated.
Although heat pipes per se are known, a brief description of them
may be appropriate. Generally, each comprises a closed outer shell,
usually in the form of a long tube such as the member 28, although
other cross-sections are useful, in which a capillary structure or
porous wick (not shown in FIGS. 1 and 2) is tightly and uniformly
held against the inner surface of the shell throughout its length,
and a working fluid or heat transfer agent is present in an amount
sufficient to wet the entire wick. The shell may be formed of a
variety of materials, either metallic or non-metallic and including
ceramics and glass.
In operation, heat is added to the heat input section of the heat
pipe, causing the fluid to evaporate, and thus the fluid gains heat
by virtue of its latent heat of evaporation; fluid vapors then move
through the pipe to the heat output section where, since this
section is at a slightly lower temperature than the input section,
they condense, giving up latent heat of condensation. The condensed
fluid returns to the heat input section through the capillary
action of the wick, and the foregoing cycle is repeated. Since the
evaporation and condensation processes are isothermal, the
transport of heat from one section of the heat pipe to the other
takes place substantially isothermally, i.e., at a substantially
uniform temperature.
While the capillary structure, also termed a porous wick, may have
any suitable form, it should have pores of a sufficiently small
size as to produce a capillary action. Generally, the capillary
structure is an element separate from the tube, but it may also be
secured to the same, or made integral therewith. The structure may
comprise woven cloth, fiber glass, porous metal, porous ceramic
structures such as tubes, wire screens, perforated metal sheets,
and the like.
The working fluid of heat transfer agent includes practically any
organic or inorganic liquid, or a molten salt, or a molten metal;
some examples are hydrocarbons, fluorinated hydrocarbons, ketones
like acetone, alcohols like methanol and glycerin, water, molten
sodium chloride, molten elements like sodium, cesium, potassium,
lead, bismuth, etc. The agent should not be corrosive nor should it
decompose at operating temperatures. In the present case, an agent
is chosen which can be vaporized in the range of temperatures
prevailing in chamber 10. As these temperatures range from
800.degree. to 1,800.degree. F., the agent may be chosen from such
materials as sodium, potassium, cesium, and the like, which
evaporate at temperatures in the foregoing range.
Returning to FIG. 1, it will be seen that the heat pipe 25 is
supported on the end wall 20 of heat exchanger 17 by a bolt and
washer arrangement, one of which is indicated at 35; this comprises
a plug 35a suitably secured in the recessed end 35b of the heat
pipe, as by a weld, and having a threaded recess 35c into which the
bolt 35d extends, the latter being provided with one or more
washers 35e. The heat pipe is also supported on the end wall 21 by
means of a pair of abutting plates 36, 37; plate 36, which is
secured to member 28 as by welding, is disposed in an opening in
wall 21, whereas plate 37, which is of larger diameter that plate
36, abuts the outer side of wall 21 and also abuts plate 36. A
similar but reverse arrangement, involving plates 38, 39, is used
to support the heat pipe on end wall 14 of chamber 10. A spacer
sleeve 40 supports the plates 37 and 38. The entire heat pipe
assembly may be stabilized in place by tightening the bolts as at
35.
It will be noted that the heat pipe mechanically and thermally
connects the heat exchanger to the chamber. The elongated baffle
11--11a also acts to mechanically connect these structures, being
in physical contact with the end wall 21 and also, at the
stepped-up portion 41, being secured by means not shown, such as
seam welding, to end wall 14.
As may be apparent from FIG. 2, a plurality of heat pipes are used,
the configuration in FIG. 2 indicating the use of three heat pipes,
two of which are indicated at 25 and 25a. A greater or lesser
number may be used, as will be understood, and as is apparent, they
are radially disposed about the baffles 11, 12. By varying the
number of heat pipes, one can vary the amount of heat recovered
from the exhaust gases, more heat pipes producing more heated air
and vice versa. Of course, other conventional heat control means
may be used, such as a step of mixing the heated air with air of
different temperature. In general, the temperature of the heat pipe
is a function of the conditions of the exhaust gas, i.e.,
temperature and flow rate, and of the cabin air, and will vary
substantially over the range of operation.
By comparison with a conventional heating system, the present
system enables more of the exhaust gas energy to be made available
for heating the cabin space simply because a greater heat transfer
surface area can be provided in the chamber 10.
As FIG. 1 shows, the muffler-heat exchanger combination is not
significantly larger than the original muffler, considering the
latter to be as represented by the chamber 10. The over all shape
or envelope is substantially the same, enabling the new system to
replace the conventional without appreciable difficulty. If
required, other shapes or envelopes are possible simply by
relocating the position of the heat exchanger; for example, the
latter may be disposed angularly of the longitudinal axis of the
muffler, thus maintaining the length and diameter of the original
muffler while locating the heat exchanger in a selected position
outwardly of the cylindrical surface of the muffler. Or by altering
the construction of the heat pipe in a manner to be described, a
simplification of the system of FIG. 1 may be achieved. Or by using
the last-mentioned heat pipe of altered construction, the heat
exchanger may be placed in a position outwardly concentric of the
muffler so as to maintain the length of the original muffler while
only moderately increasing its diameter. These variations are
illustrated in FIGS. 3-7, which may now be described.
In FIG. 3, the heat exchanger 50 is disposed angularly of the
longitudinal axis 51 of muffler 52, and such disposition may be at
any suitable angle with respect to said axis. Hot exhaust gases
enter the muffler via inlets 53 and 54, flows over heat input
sections 55, 56, and 57 of heat pipes 58, 59, and 60, and leave the
muffler via exit 61. Air on its way to the space to be heated
enters heat exchanger 50 via inlet 62, is heated by heat output
sections 63, 64, and 65 of the heat pipes, and leaves by outlet
66.
In FIG. 4-6, the heat exchanger 70 and muffler 71 are disposed end
to end, as in FIG. 1, but the exhaust gas outlet in the muffler
(note 16 of FIG. 1) is eliminated, thus providing a muffler without
projections and improving the ease of installation of the system.
The heat pipe 72 is constructed differently from those of FIGS. 1-3
but its principle is the same. It comprises a pair of concentric
hollow structures, preferably the pipes or tubes 73, 74 (note FIG.
5 which is an enlarged view, in section, of the upper right hand
corner of the heat pipe 72 of FIG. 4), having therebetween a sealed
evacuated annular space 75 which is disposed a capillary structure
or porous wick 76 which is in contact with adjacent opposed
surfaces of said pipes. Ends of the annular space 75, in which is
disposed said wick, are sealed by rings, one of which is shown at
77 of FIG. 5. Suitably the capillary structure comprises, note
FIGS. 5 and 6, a porous layer 76a in contact with outer surfaces of
the inner of said pipes, another porous layer 76b in contact with
inner surfaces of the outer of said pipes, and porous means 76c
connecting said layers, and the entire structure may be made of
fine mesh screen. The means 76c may be of any suitable shape and
construction; in the form shown it is of cylindrical shape and is
in contact with the opposed screen layers 76a and 76b. It will be
understood that a plurality of cylinders 76c are circumferentially
disposed in the annular space 75, and they may extend for the
length of heat pipe 72, or they may be of shorter length and may be
staggered circumferentially of the annular space. Layers 76a and
76b, and cylinder 76c, may be secured in place in any suitable
way.
The capillary structure 76 may have other suitable forms, but in
any event it should contain pores of a sufficiently small size as
to produce a capillary action.
A heat transfer agent is represented at 78; it is one of the type
described and substantially fills the capillary structure 76.
As hot exhaust gases enter the system at 80, they heat the inner
tube at 74, which comprises the heat input section of the heat
pipe, and the absorbed heat serves to vaporize the agent 78. The
vapors pass toward the outer tube 73, which is at slightly lower
temperature, where they condense, giving up latent heat of
condensation. The condensed vapors are brought back toward the
inner tube by virtue of the capillary action effect exerted by the
capillary structure or wick 76, and they are re-vaporized, the
foregoing process being repeated over and over. Air entering the
heat exchanger 81 flows in the annular space or passage between the
exchanger and heat pipe and is heated by the uniformly heated heat
output section 73 of the heat pipe and leaves by outlet 82. Exhaust
gases leave the system via exit 83. It will be seen that the heat
transfer member or means of the heat pipe 72 comprises the wick and
working agent disposed in the annular space 75.
A heat pipe like 72 is described at greater length in said
copending application Ser. No. 854,827 filed Sept. 3, 1969.
The modification of FIGS. 4-6, in which the engine gas flows
lineally through the system, is of particular interest for
application in an automobile, truck, tractor, or other land
vehicle.
In FIG. 7, the heat exchanger 85 is disposed in a position
outwardly concentric of the muffler 86. Throughout most of its
length the muffler is a part of the heat pipe 87, with only a
portion 99 of the muffler extending beyond the heat pipe. The
latter is constructed as in FIGS. 4-6 and need not be further
described. Hot exhaust gases enter the system at 89 and 90 and
leave by 91, and during their passage they heat up the heat input
section of the heat pipe. Heat is transferred in the manner
described in FIGS. 4-6, thus uniformly heating the heat output
section, which in turn heats the air entering the heat exchanger
via inlet 92. The air leaves by exit 93 on its way to the space to
be heated.
In FIGS. 4-6 and 7, it will be noted that the heat pipe is hollow
and forms a a part of the flow path of the exhaust gases. Also, in
each case the heat exchanger is disposed outwardly concentrically
of the heat pipe.
As may be more or less apparent, the described heating system is of
use in any vehicle or installation employing an engine which
produces hot exhaust gases and in which there is a space to be
heated, including aircraft, automobiles, trucks, tractors, motor
cycles, motor bikes, scooters, motor boats, and the like. In
vehicles employing a muffler, the internal construction of the
muffler may be variable, as to provide a more or less tortuous
passageway and thus a greater noise level reduction, but even so,
the invention is applicable therein. The heating system may also be
of use in stationary installations, as illustrated by electric
power-producing stations where an engine is used to operate a
generator.
As indicated by the various views, the geometry of the heating
system, by which is meant its size, shape, and disposition of
parts, is variable to suit a given application.
The invention may be of further use in internal combustion engines
to more effectively preheat the fuel gas mixture in the intake
manifold on its way to the firing cylinders. Conventionally, such
preheating is done at a "hot spot", comprising a small chamber
surrounding the mid-point of the intake manifold through which
chamber a part of the hot exhaust gases is by-passed. According to
the invention, one or more heat pipes can be used to thermally
interconnect the hot exhaust gases in the exhaust gas manifold with
the cool fuel gas in the intake manifold. It may also be feasible
to use warm engine coolant instead of the hot exhaust gases, and in
such case the interconnection will involve the duct carrying such
coolant. It will be noted that the gas stream to be warmed
comprises an air-hydrocarbon mixture.
It will be understood that the invention is capable of obvious
variations without departing from its scope.
In the light of the foregoing description, the following is
claimed.
* * * * *