Note: Descriptions are shown in the official language in which they were submitted.
~OS~;~8
The present invention relates to a low pressure
vapour lamp particularly a mercury low pressure vapour lamp
having a lamp tube designed as a flat discharge tube encom-
passed by an encasing tube.
Such low pressure vapour lamps usually consist of
a quartz tube filled with metal vapour having a vapour pres--
sure of, e.g., 0.1 torr and two electrodes at the ends. The
lamp tube has an oblong flat cross section. The term "flat
discharge tube" is used for this reason.
In operation a light emitting arc discharge is creat-
ed between the elecirodes. Mercury low pressure lamps are
most widely used, since they are very suitable devices for
producing UV radiation. In fact, the light emitted by them
is a pure line sp~ctrum having a high proportion of UV radia-
tion with particularly strong lines at 254 nm.
Carrying out photochemical reactions with the aid
of UV radiation has been increasingly gaining in importance
recently, and photochemical disinfecting and sterilizing pro-
; cesses constitute a particularly important field. A number
of these reactions and primarily also the disinfecting andsterilizing processes show a marked dependence on the radia-
tion intensity, so that a radiation intensity and power as
high as possible are important. That is due to the fact that
the correspondin~ reactions require a simultaneous presence of
a specific minimum number of photons (for example, 4 or 5)
at the location of the moiecule to be reacted and therefore
cannot proceed when radiation of lower intensity is employed
which cannot supply simultaneously this minimum number of
photons. This situation cannot be improved, for example, by
extending the time of irradiation.
The flat discharge tube is customarily encompassed
~y an encompassing tube consisting of quartz. The assembly
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consisting of the encompassing tube and flat discharge tube
can then be immersed in water for sterilization. In contrast
to the oblong flat cross section of the flat discharge tube
the encompassing tube is a circular tube, since optimal pro-
tection against the surrounding water pressure can thus be
provided. The flat discharge tube in the encompassing tube
can be constructed with relatively ~hin walls.
The flat discharge tube produces, in addition to the 254 nm
line mentioned above, a line, which is not so intensive, i.e.,
at 183 nm, so that ozone, which supports the disinfecting and
sterilizing process, can be produced.
However, even today the fact that the radiation
intensity required for effective disinfection and steriliza-
tion cannot be attained directly confronts the ever increasing
importance of conventional low pressure vapour lamps. An
increased radiation intensity by means of an increased energy
supply can only be attained by simultaneously providing ade-
quate cooling of the low pressure lamp. In fact, a reasonably
erfective cooling with a resulting increase of radiation in-
tensity is known from German Offenlegungsschrift 2,825,018.
This cooling is attained by providing special cooling tubes
along the narrow sides of the discharge tube, but this is a`
case of separate cooling requiring additional expenditure at
the discharge tube. Attempts have also been made to concen-
trate the radiation of several lamps into the same reaction
volume with the aid of reflectors. However, this also is
costly and results in a poor energy e~uilibrium.
It is an aim of the present invention to provide a
low pressure vapour lamp in which an increase of the radiation
intensity can be attained by simple means while avoiding the
disadvantages described hereinbefore.
According to the present invention there is provide~
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a low pressure vapour lamp, comprising a flat discharge tube
mounted with in anencompassing tube having an inside wall so
as to be capable of being brought at least partially into con-
tact with the inside wall of said encompassing tube.
The invention is based on the surprising fact that
by bringing the flatdischarge tube into contact with the encom-
passing tube, cooling can be provided by the medium which en-
compasses the encompassing tube and is to be disinfected and
sterilized. Tests have shown that a substantial increase in
radiation intensity can be attained by this so-called contact
cooling. This is all the more surprising since both the en-
compassing tube and the jacket of the flat discharge tube
are made of quartz, i.e., a poor heat conductor. The gas in
the flat discharge tube cools at the points of contact of the
flat discharge tube with the encompassing tube to such an extent
that a higher supply of energy and thus a higher emitted radi-
ation intensity are attained.
Particularly favourable values can be attained with
a low pressure vapour lamp according to the present invention
when the medium surrounding the encompassing tube, usually
water, does not exceed a maximum temperature of 25 C.
By the simple measure of bringing the flat discharge
tube into contact with the encompassing tube the separate
1, S~oc~s
cooling required by conventional arrangements can be dis~e~3
ed with In fact the desired increase of the radiation in-
tensity can also be attained by separate cooling, but this
would involve a substantial expenditure for additional parts
and thus increased costs, while in the case of the proposed
cooling by contact, merely contact of the discharge tube with
the encompassing tube is required.
In a preferred embodiment of the present invention
the contact is so designed that it is linear in the direction
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of the longitudinal axes of both the flat discharge tube and
the encompassing tube so that one contact line exits along
the surface of the flat discharge tube. However, in many
cases this kind of linear contact with the encompassing tube
cannot always be realized for production-related reasons, since
both the inside wall of the encompassing tube and the outside
wall of the flat discharge tube might be slightly uneven. In
this case the contact is limited to a plurality of discrete
points of contact. However, corresponding tests gave the
surprising result that adequate cooling by contact is attained
even in such cases, so costly separate cooling can be dispens-
ed with.
Another way of achieving cooling by contact is to
provide t'ne flat discharge tube with several sleeves disposed
around the outside wall and brought into contact with the en-
compassing tube.
In order to avoid possible damage to the low pres-
sure lamp during transportation, another embodiment provides
a flat discharge tube disposed within the encompassing tube
so as to be slidable at right angles to its longitudinal
axis and fi~able in various positions. In one of its posi-
tions, i.e., in the transportation position, the flat discharge
tube is disposed centrally within the encompassing tube so
that contact with the encompassing tube is avoided. After
transportation, and, when putting the flat dischar~e tube into
operation, it is then shifted into the other position and
fixed so that it makes the desirèd contact with the encompass-
ing tube.
The novel cooling-by-contact provided by the present
invention can be so effective that under certain conditions,
when switching the low pressure vapour lamp on, the optimal
operating temperature of the gas in the flat discharge tube
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is not reached. In anotner suitable embodiment the cooling by
contact comes into effect only when a specific temperature is
reached. For this purpose a bimetal strip can be used. On reach-
ing a predetermined temperature value said bimetal strip causes the
flat discharge tube to shift into a position in which it is
in contact with the encompassing tube.
The invention will now be described in more detail,
by way of example only, with reference to the accompanying
drawings, in which:-
Figure 1 and 2 show a diagrammatic cross sectional
view, taken along the line A-B in Figure 3, of a low pressure,
vapour lamp according to one embodiment of the present inven-
tion, illustrating two different positions of a flat discharge
tube within an encompassing tube;
Figure 3 shows a part cross sectional view of a
reactor containing several low pressure vapour lamps; and
Figure 4 is a diagrammatic representation of a flat
discharge tube with sleeves disposed on the outer jacket.
The low pressure lamp 1 shown in the drawing com-
prises a flat discharge tube 2 having an oblong flat crosssection. The flat discharge tube 2, whose outer wall consists
of quartz, is encompassed in the usual manner by a circular
encompassing tube 4, also made of quartz.
Externally a reaction space 28 (see Fig. 3) adjoins
the encompassing tube. This reaction space receives the
medium, for example, water, to be subjected to UV radiation
for the purpose of disinfection and sterilization. In Figure
3 a total of four encompassing tubes 4 with flat discharge
tubes 2 disposed therein are provided. The encompassing tubes
3a 4 are disposed at an angle of 90 with respect to each other. Only
two of the encompassing tubes can be seen in the cross sectional
drawing. Approximately at the centre of the reaction space 28
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~2OSg~i~B
there is disposed a sensor 1~ for the UV radiation at this
point.
The reactor 30 has a cover 32 and a casing 40. The
encompassing tubes 4 are retained within a flange 34, which
communicates with a shroud ring 36 via a screw connection 38.
Gaskets 24 and 26 are provided for sealing the reaction space
28.
As is further evident from Figure 3 and 4 each flat
discharge tube 2 has on its outer ends a socket 20 with elec-
trodes 22 for the flat discharge tube 2. (Only one end of
the falt discharge tubes 2 is shown in the Eigures so that
only one socket 20 can be seen in each case).
The flat discharge tubes 2 within the encompassing
tubes 4 are retained by a disc-shaped discharge tube support
10 disposed at the two ends of the encompassing tube 4. Via
the electrodes 22, which engage corresponding orifices of
the discharge tube support 10, the flat discharge tube 2 com-
municates with the two discharge tube supports 10 at their
outer ends~
As is evident from the drawings in Figure 1 and 2
the discharge tube supports 10, and thus of course also the
flat discharge tubes 2 communicating therewith, are slidable
in a direction indicated by the arrow 12 both towards the
left and towards the right. The sliding direction is prefer-
ably chosen at right angles to the direction in which the
flat discharge tube 2 with its oblong cross section extends.
Each ~ischarge tube support 10 is provided with two
oblong holes 14 extending in the direction o~ the arrow 12.
A pin 16 engages each oblong hole 14 whereby a well-defined
guide is obtained during the shifting of the discharge tube
supports 10. Furthermore because of the pins 16, which are
fixed with respect to the discharge tube supports 10, differ-
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ent end positions of the discharge tube supports 10 are mark-
ed when the pins 16 are at one end of the oblong hole or at
the other. The discharge tuhe supports 10 can be fixed in
the two end positions by means of screws (not shown) so that
the flat discharge tube is also fixed in the two different
positions.
According to Figure 1 the discharge tube supports
10 are in a first fixed position, to which a central arrange-
ment of the flat discharge tube 2 within the tube 4 has been
assigned. In this position of the flat discharge tube 2 (the
only position used heretofore~ it can also be transported
without difficulty, since the flat discharge tube 2 is not
in contact with the encompassing tube 4.
By shifting the discharge tube supports 10 in the
direction of the arrow 12 the position shown in Figure 2 is
attained. Since the flat discharge tube 2 moves together
with the discharge tube supports 10 while the encompassing
tube 4 and the pins 16 retain their positions. The flat dis-
charge tube 2 comes into contact with the inside wall of the
encompassing tube 4 at the points of contact 6 and 8. In
the ideal case the two contact points extend in a line along
the entire length of the flat discharge tube 2.
Taking into account the diameters of the pins 16,
the length of the oblong holes 14 is so chosen that, starting
from the position in Figure 1, when shifting the discharge
tube supports 10 in the direction of the arrow 12, the flat
discharge tube 2 comes into contact with the encompassing tube
4 without any damage.
In the embodirnent shown in Figure 4 (the encompass-
ing tube is not shown in this case) the flat discharge tube 2is surrounded by sleeves 42, which are spaced apart. In this
case, too, the flat discharge tube 2 can be shifted by means
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of the discharge tube supports 10 to such an extent that
the sleeves 42 rest against the inside wall of the encompass-
ing tube 4, whereby the desired cooling by contact is also
obtained.
In the Figures 1 and Z it has been assumed that the
discharge tube supports 10 are shifted by hand. It is of
course also possible to use mechanical means for this purpose.
The use of a bimetal strip which has the property of mechani-
cal deformation on exceeding a specific temperature, is
particularly favourable. When this kind of bimetal strip is util-
ized for shifting the discharge tube supports 10 and the flat
discharge tube 2 until contact with the encompassing tube
4 is made, the advantage is attained that the cooling by
contact does not start immediately on starting the low pres-
sure vapour lamp 1. The low pressure vapour lamp 1 can then
reach its optimum operating temperature without cooling and
the cooling by contact is produced only thereafter with the
aid of a bimetal strip.
