The invention relates to a tube for measuring heat con¬ sumption comprising a tubular member that is closed at a first extremity and open at a second extremity, and wherein an evaporative liquid filling is present in said tubular body, and wherein the lumen in the liquid-filled region of the tubular body has a cross-sectional area which is smaller than the area of a circle having a di- ameter of 3.5 mm.

In devices for measuring heat consumption of the evapora¬ tion type, liquid-filled tubes are used to record con¬ sumption. The tube is transparent, and the liquid con- tained therein has such colouring that the liquid level can be perceived and read off a calibration scale on the device for measuring heat consumption in which the tube has been arranged.

DK 41024 discloses a tube for measuring heat consumption comprising a tubular body with a lumen that substantially exceeds the area of a circle having a diameter of 3.5 mm. The tube is, at its one end, provided with a mouth region with a smaller area than the tubular body itself. This constriction serves to limit the evaporation from the tube. Owing to the relatively large diameter of the tubu¬ lar body, there is a risk that air may pass the liquid and enter the tube when the tube is arranged in a hori¬ zontal position, and a subsequent increase in temperature will cause an increase in the volume of this air and con¬ sequently liquid is pressed out of the tube. Following this partial or complete discharge, the tube is useless, since, if the tube was in use, the discharged liquid would be recorded as consumption.

A tube of the type described m the introductory part is known from DK patent No. 156,331. Tubes of this kind with a lumen where the area is smaller than the area of a cir¬ cle having a diameter of 3.5 mm has the effect that the liquid is withheld m the tube by a capillary effect. The capillary effect is associated with a variety of substan¬ tial advantages m connection with such tubes. Examples include the option of positioning the tube m any posi¬ tion without the liquid flowing out of the tube, and without air flowing into the tube past the liquid fill¬ ing. Furthermore, tubes of this type yield a far more ac¬ curate result, due to a small meniscus compared to tubes with a larger lumen area. In most cases such tubes can be stored and transported in bags with diffusion-proof coat- ing irrespective of the orientation of the tubes.

However, it has been found that certain combinations of lumen areas and liquid types are less advantageous. The impact of rough handling of tubes with a lumen having a cross sectional area which is approximately equivalent with the upper area limit, viz. the area of a circle hav¬ ing a diameter of 3.5 mm, may cause certain types of liq¬ uid to leave through the tube opening. In this context, the liquids concerned are those having a relatively small surface tension. In order to ensure that such liquid does not, upon rough handling, e.g. by impacts, leave through the open end of the tube, it is necessary to configure the liquid-filled portion of the tube with a substan¬ tially smaller lumen area or optionally to mount a clo- sure device, e.g. a plug, in connection with the mouth region. However, a smaller lumen area is associated with a drawback m the form of poor readability caused by the poor thickness of the liquid column with its usual col¬ ouring. In case of a more intensive colouring of the liq- uid, the colour contained m the liquid will deposit on

the tubular wall and thus add to the obstruction of the reading.

Mounting of a closure device is a further manufacturing process that aggravates the production procedure and in¬ creases the costs thereof. The required removal of a clo¬ sure device prior to mounting of the tubes involves a more time-consuming and difficult working routine for the fitters .

Moreover, there is a risk that a mounted closure device can oe left on the tube thereby preventing evaporation ana thus recording of consumption. Therefore, the ar ^¬ rangement of closure devices on tubes is undesirable.

It is thus the object of the present invention to provide a tube of the type described m the introductory part that allows the use of a wider range of liquids for fill¬ ing thereof.

According to the invention this is obtained by providing the tubular body with a constriction of its lumen above the liquid filling.

By this measure it is possible to combine substantially more liquid types and cross sectional dimensions for the tube while maintaining adequate readability without the rough handling of the tubes that occur m connection with their manufacture and transport causing leakage from said tubes. Leakage-preventing measures, such as plugs, are hereby rendered superfluous by the tube according to the invention and transport m bags is still an option.

According to a preferred embodiment of the invention the area of the constricted portion of the lumen m the tubu¬ lar body constitutes less than three quarters, preferably

less than half of the lumen in the liquid-filled portion of the tubular body.

Above the constriction a tubular portion may conveniently be provided which has a cross sectional area that is smaller than the area of a circle having a diameter of 3.5 mm.

Preferably the extent of the constriction in the axial direction of the tubular body is less than 10 mm, pref¬ erably less than 6 mm. Hereby the constriction will have only a small or non-existing impact on the diffusion out through the mouth region.

Examples of a measurement liquid which is suitable in connection with the tube according to the invention in¬ clude 1-hexanol. However, there will be numerous other alternatives available for use as measurement liquid, where said combinations of tube and liquid have not pre- viously been possible.

In the following, preferred embodiments of the tube for measuring heat consumption according to the invention are described with reference to the drawings, wherein

Figure 1 is a longitudinal sectional view of a first tube for measuring heat consumption,

Figure 2 is a longitudinal sectional view of a second tube for measuring heat consumption

Figure 3 is a sectional view of the tubes for measuring heat consumption shown in Figures 1 and 2.

The sectional view shown in Figure 1 comprises a tubular body 1 closed at the one end 2 and having at its opposite

end an opening 3. From the closed end 2 and until shortly before the mouth region at the opening 3, the tubular body 4 has an approximate cross sectional shape with an internal diameter D. Shortly before the mouth region a constriction is provided in connection with which a down¬ wardly oriented edge 6 is provided. The constricted area around the mouth region at the opening 3 has an internal diameter C. The area with the constriction extends in the axial orientation of the tube over a distance D. The tube has a total length A.

The tube for measuring heat consumption shown in a longi¬ tudinal sectional view in Figure 2 comprises constructive elements corresponding to the elements described in con- nection with the tube shown in Figure 1. Moreover the space above the constriction has a tubular region 7 hav¬ ing a lumen dimensioned in accordance with the same cri¬ teria as the lumen below the constriction.

Figure 3 clearly illustrates the circular cross sectional profile of the tube, and also the diameters of the liq¬ uid-filled area 5 and the constricted region at the mouth region 3 are subject to more detailed description therein.

In Figures 1 and 2, the liquid filling is shown as a dot¬ ted area.

The liquid-filled area has a sufficiently large diameter to allow the liquid level for a liquid with usual colour¬ ing to be clearly read on a calibration scale in a hous¬ ing intended therefor, wherein one or more tubes are ar¬ ranged. The constriction makes it possible to use measur¬ ing liquids in cases where a previously known tube would involve a high risk of waste during use, e.g. in case of

impacts, due to the small capillary constant of these liquids .

Such tubes are filled with liquid in a vacuum process de- scribed in detail in DK patent Nos 116,969 and 156,331. In this connection the construction shown in Figure 2 is advantageous in that it is desirable to fill the tube to a level immediately below the constriction and in that the magnitude of the required vacuum is desirably moder- ate. It is hereby possible to fill the tube to a distance above the constriction where the liquid volume above the constriction corresponds to the air-filled volume at the bottom of the tube and the volume in the constriction area, and subsequently by centrifuging force the liquid towards the bottom of the tube.