Note: Descriptions are shown in the official language in which they were submitted.
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Heating device for motor vehicles
The invention relates to a heating device for
motor vehicles, in which the engine has an exhaust for com-
bustion gases which communicates with at least one duct of
a heat exchanger, which duct is separated from a medium to be
heated by a partition.
Ileating devices of the kind described are known
from the United States Patent Specifications, 3,656,2~5
(=PEIN 4128) and 3,753,462. --
The heat exchanger may be constructed as a
radiator in which the combustion gases deliver their therminal
ener~y directly to the air inside the passengers compartment.
It is also possible, for example, to construct the heat .
exchanger as a counter-current heat exchanger in which the
combustion gases supply their thermal energy to a medium
(for example water) circulating in a closed circuit or to air
which, after having been heated in the counter-cuttent heat
exchangerj can frffly flow into the passengers compartment.
Known devices of the type described have tl~e
- drawback of being ratiler complicated,.because, for controlling
: 2~ the heating, bypass pipes which are provided with valves for
the hot combustion gas and the medium to be heated, respective-
ly, are used. In addition, the use of combustion gases for
heating vehicles involves the danger that, in the case of
leakage of the heat exchanger as a result of corrosion by the
combustion gases or by other.factors, the occupants of the
vehicle are exposed to detrimental exhaust gases. This ma~
necessitate extra structural measures which further complicate.
the he~ting device and make it more e~pensive (Unitcd States ~
q~
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Patent Specification 3,656,295).
According to the present invention there is provided a heat
exchanger comprising: at least one duct for a hot gas bounded by a first
heat transferring wall; a second heat transferring wall surrounding the
first heat transferring wall and spaced therefrom so as to form a space
between the said walls, the second heat transferring wall separating the
space from a body of medium to be heated during operation; at least one
radiation screen in the space; hydrogen in the space; a reversible hydrogen
getter communicating with the space; and heating means for controllably
heating said getter so as to control the pressure of hydrogen within the
space and thereby the heat transmitted through the space.
In this manner a device is obtained in which the heat transfer
of the combustion gas to the medium to be heated and hence the extent of
heating of the vehicle is controlled in a simple manner.
Should a leakage due to corrosion occur in the wall part adjoin-
ing the combustion gas duct, the wall part which is in contact with the
medium to be heated still prevents combustion gas from getting in said
medium and via said medium in the passengers compartment.
The radiation screens may be thin foils which consist at least
at the surface of a material having a good reflection for thermal radiation,
for example, copper, nickel, aluminum, silver, gold, lanthanum hexaboride,
and the like.
When a vacuum prevails in the space bounded by the two wall parts,
said space together with the thin foils constitutes an excellent heat insula-
tion, in practice sometimes
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referred to as "superinsulation". Such a heat insulation is
compact and of light weight.
Hydrogen presents the advantage that, compared
with other gases, it has the greatest tllermal conductivity.
Below a~given pressure, namely that pressure at which the
average free path length o~ the hydrogen molecules is equal
to the dlstance between the radiation screens, the heat
transport from radiation screen to radiation screen is a
function of the hydrogen pressure. With a distance between
two radiationscreens of 0.1 mm and a temperature difference
- of 700 (725C - 25~), for example, at a hydrogen pressure
of approximately 10 torr the heat flow rate is approximately
300 W/sq.cm, at a pressure of approximately 10 3 torr the
heat flow rate is approximately 4.10 W/sq.cm.
The advantage of the use of partially hydrated
hydrogen getters is that those parts of the metal not saturat~l
with hydrogen, can getter residual gases-in the space, for
example oxygen ~nd nitrogen, up to 1000C without the hydrogen-
metal equilibrium`being essentially influellced thereby. Mor~-
over, by means of the degree of hydration, the course of the
.
hydrogen dissociation pressure ~ith the tc~perature can be
-chosen arbitrarily within wide limits because the hydrogen
pressure above the meta; hydride is both a function of the
temperature and of the hydrogen concentration in the metal.
As partially hydrated reversible hydrogen
getters may be used metals from the group formed by titanium,
zirconlum, hafnium, lanthanum, cerium and other rare earth
metals, vanadiurn, niobium~ tantalurn, 1;horium and alloy5 and
mixtures of these metals in a partially hydrated state. The
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.
hydrogen dissociation pressure of the hydrides of said metals
varies at temperatures between 25C and 8000C between smaller
than 10 3 torr and approximately 10 torr. Particula~ly
suitable for the present purpose have proved to be titanium,
~irconium and hafniulll in a parti,ally hydrated state.
The getters may be used as fine powders or in
the forn~ of compressed porous mouldings.
For evacuating a space with a volume of a
, few litres of filling it with hydrogen up to a pressure of
,10 approximately 100 torr, approximately 5~to 50 g of metal
hydride are required in accordance with the molecular weight.
The metals may be obtainecl in a partially hydrated state and
starting from hydrogen-saturated metal hydride by pumping a
part of the dissolved hydrogen (5 to 60~ by weight) at
elevated temperature (for zirconium hydricle, for example,
between 200 and 700C).
The quantity of, hydrogen,getter and hydrogen is
--, , proportioned so that, wher,eas the hydrogen getter is at
normal ambient temperature, the hydrogen pressure in the space
, is 10 3 torr or less. I~ these'circ~mstances substantiall~r no
``heat t`ransport from'the combus`tion gas`duct to the medium
takes place. If now the medium is to be heated, the getter
is heated to a temperature at which the hydrogen pressure
in the space between combustion gas and medium has reached a
value at which the desired heated transfer is obtained.
In a favourable embodiment of the hea-tin~
device according to the invention the space is subdividecl into
severa~ mutually separated sub-spaces which each individua]
communicate with an associated reversib:Le hydrogen ge~ter
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having a controllable heat source.
This presents an additional possibility of
controll:ing the heat transfer between combustion gas and m4div~
A furt;her favourable embodiment of the heating
device according to the invention is characterized in that
the heat source consists of an electric resistance heating
element which is fed by an accumulator battery of the vellicle.
In a further favourable embodiment of the
heating device according to the invention the hea~ source is
formed by a part of the flow of combustion gas through the
exhaust.
The invention will be described in greater
detail with reference to the drawing which show~s diagrammatical
ly and not to scale a few embodiments of the heaiing device.
~5 Figure la is a longitudinal sectional view of
a heating device in which the combustion gases originate
from a hot-gas reciprocating engine.
Fi~gure lb is a cross-sectional view taken on
the line Ib-Ib of Figure ~a.
.
Figure 2a is a longitudinal sectional view of
a heatl~g device in association with a-four-cylinder internal
combustion engine.
Figure 2b is a cross-sectional view of the
heating device taken on the line IIb-IIb of Figure 2a.
Figure 3 is a longitudinal sectional view of a
heating device in which thermal energy of combustion gas is
also used to heat a hydroge~ getter.
Reference numeral lJn Fi~re 1 denotes a
cylinder in which a piston and a displacer 3 reciprocate with
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a mutual phase difference. The piston 2 and the displacer 3
are connected to a driving mechanism (not shown) by means of
a piston rod 4 and a displacer rod 5, respectively. Present
between the piston 2 and the displacer 3 is a compression
space 6~ while above the displacer 3 there is an expansion
space 7. The compression space 6 and the expansion space 7
communicate with each other via a cooler 8, a regenerator 9
and a heater 10. The heater 10 is cDnstructed from a number
of pipes 11 which communicate at one end with the regenerator
9 and at the other end with an annular duct 12~ and a number
of pipes 13 which communicate at one end with the annular
duct 12 and ~ the other end with the expansion space 7.
The ho~-gas en8ine furthermore comprises a burner device 14
with which a fuel inlet 15 communicates. The burner device 14
furthermore comprises an inlet 16 for air of combustion and
an outlet 17 for combustion gases communicating with the
said device via the heater 10. The outlet 17 communicates
with a pipe 19.
The engine comprises a preheater 18 which communicates
with the outlet 17 via pipe 19 and communicates with the inlet
16 via a pipe 20. In this preheater, combustion gases can
exchange heat with the combustion air. For supplying combus-
tion air a controllable fan 21 is present.
A heat exchanger 22 serving as a radiator is
incorporated in the pipe 19.
The heat exchanger 22 comprises an inner tube 22a and an
outer tube 22b arranged c~ncentrically herewith. The hot
combustion gases flow through the central space 22c during
operation. Rad$ation screens 23, for example copper
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foils, which are kep~ spaced mutually and with respect to
the tubes 22a and 22b by spacing members, no-t shown, are
arranged in the annular space 22d.
The annular space 22d in which the radiation
' .screens 23 are present communicates w~h a container 24 in
which partially hydrated zirconium 2~ and an electric heater
element 26 are present. The heater element 26 is connected
to an accumulator battery 28 ~ia a slide resistor 27.
. During operation of the hot-gas engine, the
hot combustion gases first flow through the central space 22c
of heat exchanger 22 and then through preheater 18.
When the heating device is not in operation,
the temperature of the zirconium 25 in container 24 is equal
to the ambient temperature, so that the pressure of the
hydrogen in the spaco 22d is smaller than 10 3 Torr and the
combustion gases in .space 22c do not supply thermal energy
' ' to the atmosphere'but o~y to.the combustion air in preheater,l8
. . When thermal energ~ should be supplied to the
' atmosphere indeed, in.this case the passengers compartment,
: 20 the part'ially hydrated zirconium 25 in container 24 is heated,
. by-means of electric heater element 26, to a temperature at
which the hydrogen pressure in space 22d is sufficiently high
to realize the desired heat transfer of combustion ga.s to the
atrnosphere. The adjusted temperature may b'e kept constant,
for example, by means of a thermostat which alternately
,
switches on and off the heater element 26.
Reference nurneral 30 in ~igure 2a denotes a
4-cylinder internal combustion engine the cylinder spaces of
which communicate, ~ia an exhaust manifold 31, with a common
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exhaust 32 for combustion gases in which a heat exchang~er
33 is incorporated. As is shown also in Figure 2b, the heat
exchanger 33 consists of three concentric jackets 33a, 33b
' and 33c within which the spaces 33d, 33e and 33f are formed.
, ~xhaust gases of engine 30 Plow through
space 33d.
Space 33f forms part of a closed system of
ducts 3l~ in which a medium, for example water, can circulate
by means of a pumping device 35. The system of ducts further-
more comprises a radiator 36.
, Space 33e again comprises radiation screens
which are re~erred toby reference numeral 37. Space 33e
communicates with a container 38 in which a hydrogen getter 39)
' for example partially hydrabed zirconium, is present. Conta;n2r '
,15 38 has an elect~ic heater element 40 which is connected to`a ''~~-
supply source (not shown).
When hydrogen getter 3~ is heated from room
,, temperature to a higher temperature, a certain hydrogen
pressure will prevail in space 3je so that said ,space no'
longer forms a hea,t insulator and the~nal energy of the
.
' , comb,~stion gases is transferred to the water circulàting in
the system of ducts 34. Counter-current heat exchange takes
place in heat exchanger 33. The thermal energy absorbed by
the water is delivered~ via radiator 36, to the passengers
compartment 41 of the vehicle denoted diagrammatically.
Figure 3 shows an engine 50 having an inlet 51
for an air-fuel mixture and an exhaust 52 for combustion
gases. A heat'exchanger 53, structurally equal to heat
exchanger 33 of Figure 2, is incorporated at one cnd in the
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e~haust 52, at the other end in a duct 54 to which air is
supplied by a fan 55, which air, after heating in heat
exc}lclllger 53, flows into the passengers compartment 56.
I-iydrogen getter 57 in container 58 is heated
by means of a part of the combustion gases flowing through
the exhaust 52. For that purpose, a branch-pipe 59 in which
a controllable ~al~e 60 is incorporated communicates with
exhaust 52. Combustion gases which reach container 58 via
branch-pipe 59 are guided in said container through ducts 61
and dissipated to the atmosphere after ha~ing given off
thermal energy to hydrogen getter 57.
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