[0001] The invention relates to a heating appliance having a radiator tube which is acted
upon internally by heating gases from a gas burner connected to the tube at one end.
[0002] Heating appliances of this type are used, in particular, for large area or open places
of work in which a temperature-stabilization of the (room) air would be difficult
or impossible. It has been found that heating a place of work with heat radiators,
particularly with low-temperature heat radiators with internal heating by gas, is
not only effective but also economical.
[0003] In case of heating appliances of the type here under consideration, a particular
advantage lies in the fact that a long radiator tube with relatively low temperatures
produces a long-wave and therefore gentle radiation of heat which can be well apportioned
and purposefully directed in a place of work without heavy losses of waste gas or
heat occurring.
[0004] A particular difficulty in this case, however, is to adhere to an optimum working
range wherein the tube temperature is sufficiently high for the required heat output
but not so high that, with common materials such as steel, it leads to destruction
of the tube or exceeds a limiting temperature of 500°C for example prescribed for
such installations. Accordingly, it can happen that the radiator tube is above the
desired or prescribed temperatures near the gas burner but carries a temperature which
is ineffectual for the radiation at the other end as a result of cooling down.
[0005] To mitigate this problem it has been proposed e.g. in U.S. - A - 4,529,123 to provide
a first longitudinal portion of the radiator tube with internal shielding limiting
the heating of the radiator tube.
[0006] The object of the invention is to provide a radiant heating appliance which is heated
by a gas burner and which renders possible the most effective and large-area radiation
possible without dropping below or exceeding preset limiting temperatures of the tube
surface.
[0007] According to the invention, this problem is solved starting from a heating appliance
in accordance with the preamble to Claim 1 with the characterising features of Claim
1.
[0008] With shielding in a first portion of the radiator tube, in part by room air conveyed
through the tube, the heat transfer to the tube surface and hence its temperature
can be reduced so that overheating above the temperature range to be regarded as particularly
favourable and particularly also above prescribed temperature values is avoided in
this part of the tube. At the same time, the effect can thus be achieved that, in
the further course of the tube, the heating gases supplemented by the conveyed air
cause a higher surface temperature and so also better activate the rear end of the
radiator tube.
[0009] Whereas the radiator tube is preferably of thick-walled design so that, with great
thermal inertia, it ensures a uniform temperature radiation even when the gas burner
is adjusted to an average preset heating power in intermittent operation, the inner
tube can be thin walled in construction. In order to avoid oxidizing, it is preferably
formed of stainless steel.
[0010] Further features and advantages of the invention are apparent from the Claims and
the following description in which two examples of embodiment of the subject of the
invention are explained in more detail with reference to a drawing. In the drawing:
Figure 1 shows a view of a heating appliance from below,
Figure 2 shows a side view of the heating appliance of Figure 1,
Figure 3 shows a section through a radiator tube on the line III-III in Figure 1 and
Figure 4 shows a section corresponding to Figure 3 through a modified radiator tube.
[0011] A heating appliance 1 as shown in Figures 1 and 2 comprises an elongated radiator
tube 2 of U-shape which is mounted in a shell-shaped reflector 3 and is connected
at one end to a gas burner 4 which projects with its combustion chamber out of a combustion
housing 5 in which a solenoid valve is also accommodated to control the supply of
gas, and at the other end to a waste-gas blower 6.
[0012] Such a heating appliance, heated by the heating gases supplied by the gas burner
4 and drawn through the radiator tube 2 by the waste-gas blower 6, acts essentially
as a radiator even if the heating gases also deliver a residual proportion of heat
as warm air which can be used for the heating. Operation of the radiator tube at relatively
low temperatures of 300°C for example, is particularly advantageous, with low-frequency
heat radiation which can be directed, without great dispersion losses and convention
losses, onto a place of work where it acts with a satisfactory consistency.
[0013] The radiator tube may, for example, be constructed in the form of a thick-walled
steel tube in order to provide a heat storage capacity which can bridge the intervals
in combustion even in intermittent operation with periodic switching-on times of the
gas burner and even out the radiation.
[0014] The temperature drop of the heating gases and the resulting temperature drop of the
radiator tube may stand in the way of an effective and uniform utilization of the
radiator tube. Thus, at the beginning of the radiator tube, for example, shortly behind
the gas burner, no temperature of more than 500°C should occur which would stress
the tube material, shift the heat radiation into a shorter wave range which is already
no longer desirable and in addition may be contrary to the building regulations. On
the other hand, the end at the blower side should not be cooled down too much to be
able to contribute appreciably to the total radiation.
[0015] Here this is met by a partial internal shielding of the radiator tube 2 in the form
of an inner tube 7 which lies coaxially to an outer tube 8 as a continuation of the
rest of the radiator tube in this region and forms in cross-section, in relation to
the outer tube, a free annular gap which extends over the whole length of the inner
tube.
[0016] The inner tube 7 is connected directly and tightly to the gas burner 4 so that the
gas burner only feeds into the inner tube 7. In the region of the gas burner 4, the
annular gap between inner tube and outer tube is open to the ambient air; it is also
open continuously as far as the rest of the radiator tube 2 so that the waste-gas
blower 6 can draw in additional air through the annular gap. Thus relative cooling
of the first, thermally highly stressed region of the tube and an extension of the
emission of heat over the radiator tube 2 are achieved.
[0017] Because of the high temperature loading, the inner tube 7 is preferably made of stainless
steel. It may, however, since it is only intended to have a shielding function and
not a heat storage function, be of thin-walled construction with a view to a saving
in costs, for example having a wall thickness of 0.8 to 1.22 mm, while the annular
gap between the tubes has a gap width of preferably 3 to 3.5 mm. The length of the
inner tube 7 is 45% to 55% of the length of the straight portion of the radiator tube
in which it is disposed and accordingly constitutes about 1/4 of the total length
of the radiator tube.
[0018] Figure 3 illustrates the cross-sectional relationships between inner tube 7, outer
tube (and radiator tube) 8 and an annular gap 9 situated in between. In comparison
Figure 4 shows a modified form of embodiment wherein a hexagonal inner tube 10 is
disposed in an identical outer tube 8. It is understood that other polygonal cross-sections
may also be provided in order to obtain exteriors favourable to flow or simple possibilities
for centering the inner tube.
[0019] It will be understood that the shielding aimed at here is achieved in the first instance
by the multi-wall construction in a first longitudinal portion 11 determined by the
length of the inner tube 7 while the conveying of additional air round the shielding
inner tube further distributes the heating along the radiator.
[0020] It will further be understood that the inner tube may also be formed from another
material, such as ceramic.
1. A heating appliance having a radiator tube which is acted upon internally by heating
gases from a gas burner connected at one end, wherein the radiator tube (2) is provided,
in a first longitudinal portion (11), with internal shielding (7, 10) limiting the
heating of the radiator tube characterised in that the shielding (7, 10) is provided
by a portion of tube of multi-walled construction wherein an inner tube (7, 10) is
disposed in the longitudinal portion (11), coaxially to and with radial spacing from
an outer tube (8), and only the inner tube (7, 10) is acted upon by heating gases
from the gas burner (4) there being a continuous gap (9) formed between inner tube
(7, 10) and outer tube (8) that opens freely into the outside air at one end.
2. A heating appliance as claimed in Claim 1, characterised in that inner tube (7,
10) and the outer tube (8) change over openly into a common run of tube.
3. A heating appliance as claimed in Claim 1 or 2, characterised in that the inner
tube (7, 10) is made thin-walled from stainless steel.
4. A heating appliance as claimed in any preceding Claim, characterised in that the
inner tube (10) has a polygonal cross-section.
5. A heating appliance as claimed in any preceding Claim, characterised in that the
outer tube (8) continues with the same cross-section in the further radiator tube
(2).
6. A heating appliance as claimed in any preceding Claim, characterised in that the
longitudinal portion (11) occupies about a quarter of the total length of the radiator
tube (2).
7. A heating appliance as claimed in any preceding Claim, characterised in that the
radiator tube (2) has a U-shaped longitudinal course with two straight uniform tube
portions and one elbow portion.
8. A heating appliance as claimed in any preceding Claim, characterised in that the
radiator tube (2) is a thick-walled steel tube.
9. A heating appliance as claimed in any preceding Claim, characterised in that the
radiator tube (2) is connected to a blower offtake (6) at the end.