WO2001035035A1

WO2001035035A1 - Bath evaporator

Info

Publication number: WO2001035035A1
Application number: PCT/NL2000/000818
Authority: WO
Inventors: Titus Maria Christiaan Bartholomeus
Original assignee: Grasso Products B.V.
Priority date: 1999-11-10
Filing date: 2000-11-10
Publication date: 2001-05-17
Also published as: NL1013544C2

Abstract

Bath evaporator for cooling a refrigeration-transfer medium by evaporation of a refrigerant, the bath evaporator comprising a pressure vessel (1) having an internal bottom part (15) provided with a heat exchanger (2), which during operation is immersed in the refrigerant (5). An outlet (7) for evaporated refrigerant (2) and an inlet (13) for refrigerant, which opens out into the pressure vessel (1), in which evaporator at least one excess-pressure chamber (20), which opens downwards, is provided. When the excess-pressure chamber (20) is completely full with gaseous refrigerant, surplus gaseous refrigerant can flow through and/or along (23) the heat exchanger (2) to the internal top part.

Description

Bath evaporator

The present invention relates to a bath evaporator for cooling a refrigeration-transfer medium by evaporation of a refrigerant, the bath evaporator comprising a pressure vessel having: an internal bottom part provided with a heat exchanger, which during operation is immersed in a bath of refrigerant, for passing refrigeration-transfer medium which is to be cooled through the bath evaporator; an internal top part for separating gaseous and liquid refrigerant; - a recirculating system for returning liquid refrigerant from the top side of the heat exchanger to its bottom side; an outlet for evaporated refrigerant, which opens out into the top part of the pressure vessel; an inlet for refrigerant, which opens out into the pressure vessel. Bath evaporators of this type are generally known. They are used, inter alia, in the industrial refrigeration industry in order to cool refrigeration-transfer media, such as water, glycol, salt solutions, silicone oils, etc. The bath evaporator comprises a pressure vessel in which a heat exchanger, such as a cooling coil, a set of pipes, an assembly of plates, etc., is fitted. The pressure vessel is filled with a refrigerant, such as ammonia, Freon or another refrigerant which is able to take up heat, in particular by evaporation, until the heat exchanger is immersed in a bath of liquid refrigerant. The refrigeration-transfer medium flows through the heat exchanger and, in the process, releases heat to the bath of refrigerant, which is caused to evaporate under the influence of the heat absorption. The evaporated refrigerant is extracted by a compressor and is compressed in order then to be condensed in a condenser. The condensate is throttled from high pressure to low pressure with the aid of an expansion valve. The high- pressure and high-temperature liquid refrigerant in the process cools, through self- evaporation, to the saturation temperature associated with low pressure. Downstream of the expansion valve, the cooled, reduced-pressure refrigerant contains, depending on the type of refrigerant and the conditions in general, between 15 and 20% by mass vapour, known as the flash gas, with the remainder being liquid. This two-phase mixture of vapour and liquid passes at high speed into the gas space of the bath evaporator, the so-called vapour separator space, which is referred to in the claims as the internal top part. This internal top part/separator space is designed in such a manner that gas and liquid can separate inside it. The liquid falls back into the bath, and the gas, together with the gas which has evaporated out of the bath, as described above, is extracted via a compressor and is compressed, and is then condensed, throttled from high pressure to low pressure and returned as a high-speed two-phase mixture to the separator space/internal top part.

According to a first aspect, the object of the present invention is to provide an improved bath evaporator in which the process is smoother and can be controlled better.

According to the invention, this object is achieved by the fact that at least one excess-pressure chamber, which opens downwards, is provided in the pressure vessel, into which chamber the inlet for refrigerant opens out and which excess- pressure chamber is in fluid communication with the bottom side of the heat exchanger, in such a manner that, when the excess-pressure chamber is completely full with gaseous refrigerant, surplus gaseous refrigerant can flow through and/or along the heat exchanger to the internal top part. An excess-pressure chamber of this type has a number of advantages: a) one advantage of introducing the two-phase mixture of liquid and gaseous refrigerant which has come successively from compressor, condenser and expansion valve into the excess-pressure chamber is that the high velocity at which this mixture is fed into the refrigerant bath is considerably reduced, being, as it were, neutralized or even lowered to zero, before the liquid and/or gaseous constituent of this mixture enters the bath. This is because the two-phase mixture first enters the pressure chamber, where it loses a considerable part of its velocity and will enter the bath relatively gradually. The refrigerant bath, in particular that part of this bath which is situated beneath and, if appropriate, next to the heat exchanger, then remains much calmer than if, for example, the two-phase mixture were to be injected directly into the bath. The calmer refrigerant bath makes the process in the bath evaporator easier to control. If the liquid refrigerant has a lower specific gravity than the conventional lubricating oils and these components are not soluble in one another, which is the case, for example, if ammonia is used as the refrigerant, the calm refrigerant bath has the considerable additional advantage that the lubricating oils can sink to the bottom of the bath so that they can be removed from the system; b) another advantage is that as a result of gas being allowed to flow upwards through and/or along the heat exchanger which is immersed in the bath of liquid refrigerant, or at least through and/or along the immersed section of this heat exchanger, the heat transfer from refrigeration-transfer medium to refrigerant via heat exchanger can be improved considerably. It should be clear that the gaseous refrigerant, after it has been fed in at the bottom side of the heat exchanger, automatically rises upwards in the bath in the form of gas bubbles; - c) yet another advantage is that an excess-pressure chamber of this type can be positioned completely or partially in the refrigerant bath which is present at least during operation, leading to a reduction in the amount of refrigerant required, since the excess- pressure chamber will become completely filled with gas, while the liquid refrigerant will escape from the excess-pressure chamber via the open bottom side of the excess- pressure chamber.

To ensure that sufficient liquid refrigerant is supplied to the bottom side of the heat exchanger, and if appropriate to promote the sinking of lubricating oil, it is advantageous, according to the invention, if the heat exchanger is positioned above the base of the pressure vessel, leaving clear a liquid space which during use is filled with liquid refrigerant. Positioning the heat exchanger approximately 2 to 3 cm (or if appropriate more) above the base is sufficient in this context. This also promotes the flow of liquid refrigerant through the heat exchanger, since in this way it becomes possible, if the excess-pressure chamber is completely filled with gas, for further filling of the excess-pressure chamber with liquid and/or gaseous refrigerant to automatically lead to vertical upwards flow through the heat exchanger.

According to the invention, it is furthermore advantageous if the excess- pressure chamber opens out at the level of the bottom side of the heat exchanger. In this way, it is possible, in a simple manner, to ensure a transfer of in particular bubbles of gaseous refrigerant out of the excess-pressure chamber to the heat exchanger. According to another advantageous embodiment, the fluid communication between the excess-pressure chamber and the bottom side of the heat exchanger runs via the liquid space. This has the advantage that the entire process in the bath evaporator can be managed, in particular regulated or controlled, more successfully.

According to another advantageous embodiment, a preferably metal partition, such as a wall of the excess-pressure chamber, is provided in the excess- pressure chamber, which partition continues into, and preferably into the bottom of, the liquid space; the inlet for refrigerant has an opening which is designed, in particular positioned and directed, in such a manner that, during operation, at least the oily constituents which escape from the said opening and are contained in the refrigerant come into contact with the said partition; and oil-discharge means are provided in the bottom of the liquid space. It is thus possible for lubricating oil which is present in the refrigerant which has been returned to the excess-pressure chamber to come into contact with the partition and fall, as a film or in drops, along the partition into the refrigerant which is present in the liquid space. On account of the relatively high specific gravity with respect to the refrigerant and the fact that the refrigerant is relatively calm in the liquid space, the lubricating oil can sink to the bottom of the liquid space, in order to be discharged therefrom. Since as a result there is no lubricating oil, or at least less lubricating oil, in the refrigerant passed through the heat exchanger, the heat transfer between heat exchanger and refrigerant is improved considerably, since adhesion of lubricating oil to the heat exchanger, which leads to a reduction in the heat transfer coefficient, is prevented. The fact that the partition opens out into the liquid space reduces the risk of lubricating oil being entrained into the heat exchanger by gas bubbles.

Particularly if the excess-pressure chamber is arranged next to the heat exchanger, according to the invention it is advantageous if the partition is a side wall, remote from the heat exchanger, of the excess-pressure chamber. In this way, it is virtually impossible for lubricating oil which has come into contact with the partition to be entrained into the heat exchanger.

According to a further advantageous embodiment of the invention, the refrigerant in liquid form will have a specific gravity which is lower than that of the lubricating oil used, and the lubricating oil used will preferably not be soluble in the refrigerant. According to a second aspect, the invention is based on the object of reducing the amount of refrigerant in the pressure vessel and therefore the total amount of refrigerant required. According to the invention, this second object can be achieved by positioning the pressure chamber according to the first aspect of the invention in the bath of liquid refrigerant, or at least the bath of refrigerant which is present during operation, and thus replacing a smaller or greater part of the volume of the bath with a space which is filled with gas. According to a second aspect of the invention, however, this object can be achieved in a broader sense, independently of the first aspect, using a bath evaporator (which may therefore correspond with the bath evaporator according to the first aspect of the invention) for cooling a refrigeration-transfer medium by evaporation of a refrigerant, the bath evaporator comprising a pressure vessel having: an internal bottom part provided with a heat exchanger, which during operation is immersed in a bath of refrigerant, for passing refrigeration-transfer medium which is to be cooled through the bath evaporator; - an internal top part for separating gaseous and liquid refrigerant; a recirculating system for returning liquid refrigerant from the top side of the heat exchanger to its bottom side; an outlet for evaporated refrigerant, which opens out into the top part of the pressure vessel; - an inlet for refrigerant, which opens out into the pressure vessel, the pressure vessel, preferably being a cylindrical vessel such as a substantially horizontally positioned cylindrical vessel, and the heat exchanger being positioned centrally in the bottom part, with a space on either side of or around the heat exchanger, between the heat exchanger and the wall of the pressure vessel, characterized in that the said space contains filler means which, at least during use, are substantially free of liquid refrigerant and substantially fill the said space.

According to the invention, the filler means may comprise one or more bodies of neoprene. In practice, neoprene is well able to withstand numerous refrigerants, such as ammonia and Freon, and furthermore can be cut into a desired shape relatively easily. Bodies of this type made from neoprene are consequently relatively easy to use in bath evaporators which already exist and have already been built, in order to enable the volume of refrigerant required to be reduced considerably. According to the invention, it is also eminently possible to provide filler means in the form of one or more hollow filler-means chambers. Hollow filler-means chambers of this type may, for example, be obtained by welding steel sheet so as to form a hollow chamber and positioning this sheet in a bath evaporator, if appropriate a bath evaporator which is to be converted. The filler-means chambers may, as will be obvious, also be the excess-pressure chambers according to the first aspect of the invention.

According to a further advantageous embodiment, which relates in particular to the first aspect of the invention but is also advantageous with regard to the second aspect of the invention, the outlet for refrigerant, which opens out into the top part of the vessel, comprises a pipe part which extends through this top part and is provided with suction openings which are distributed over the length of the said pipe part and preferably face upwards. A pipe part with suction openings of this type makes it possible to extract gas from the entire top part uniformly and at a relatively low suction velocity. Since the suction can take place uniformly and at a relatively low velocity throughout the entire top part, the risk of drops of liquid refrigerant being entrained towards the compressor is reduced considerably. In this context, it should also be pointed out that, on account of gaseous refrigerant being blown in at the bottom side of the heat exchanger, significantly more drops of liquid refrigerant come out of the bath at the top side of the heat exchanger. If the suction velocity were to be too great, it would be impossible for these drops to fall back into the bath and they would be entrained. It should be clear that a pipe with suction openings of this type can also advantageously be used in other bath evaporators which are known from the prior art or are yet to be developed. On the one hand, a pipe with suction openings of this type allows reliable suction without drops of liquid being entrained, and on the other hand a pipe with suction openings of this type also allows the internal top part to be of much more compact design. The suction openings will advantageously be slots or perforations.

Particularly with regard to the first aspect of the invention, it is advantageous according to the invention if the excess-pressure chamber and the top part can be connected to one another via a valve. The valve may in this case be a stop valve, such as a solenoid valve. It thus becomes possible, if desired, to collect the surplus liquid refrigerant in the excess-pressure chamber while the evaporator is not operating. This is because opening the valve allows the excess pressure to escape, so that the excess-pressure chamber will fill up with liquid refrigerant. The valve could also be a control valve which is used to reduce the excess pressure in the chamber, which is required for feeding the refrigerant to the heat exchanger, and thus the feed of refrigerant to the heat exchanger. Therefore, the surface area of the heat exchanger which is used can be reduced, in particular regulated, in order, in this way, to very accurately regulate the refrigeration capacity of the bath evaporator.

According to another advantageous embodiment, the bath evaporator according to the invention will be provided with: - a temperature sensor for measuring the temperature of the refrigeration-transfer medium emerging from the heat exchanger; and control means designed to actuate the valve in order to control the level of the bath of refrigerant as a function of the temperature detected by the temperature sensor. If the temperature of the refrigeration-transfer medium emerging is/becomes lower, the refrigeration capacity can be lower, and therefore the level of the bath can be lower, in order thus to reduce the surface area of the heat exchanger which is used.

The present invention will be explained in more detail below with reference to the drawings, in which: Fig. 1 diagrammatically depicts a bath evaporator according to the prior art;

Fig. 2 shows a very diagrammatic view of a first embodiment of a bath evaporator, according to the first aspect of the invention;

Fig. 3 shows a very diagrammatic view of a second embodiment of a bath evaporator, according to the second aspect of the invention; and Fig. 4 shows a very diagrammatic view of a third embodiment of a bath evaporator, according to the first and second aspects of the invention, in which figure Fig. 4a shows a diagrammatic cross section; Fig. 4b shows a diagrammatic longitudinal section; and Fig. 4c diagrammatically depicts a detail of Fig. 4a. Fig. 1 diagrammatically depicts a bath evaporator according to the prior art.

The bath evaporator comprises a cylindrical pressure vessel 1, which is generally positioned horizontally (as shown), but may be positioned vertically or at an angle. This pressure vessel 1 holds a heat exchanger 2, for example a cooling coil, a set of pipes or an assembly of plates, to which a refrigeration-transfer medium which is to be cooled, such as water, glycol, a salt solution, silicone oils, etc., is fed via an inlet 3 in order to be cooled in the heat exchanger and then be discharged again via line 4. For the purpose of cooling, the heat exchanger 2 is immersed, preferably completely immersed, but if appropriate partially immersed, in a bath 5 of substantially liquid refrigerant, such as ammonia, Freon or another suitable refrigerant. On its sides, the heat exchanger 2 may, if appropriate, be shielded from the remainder of the bath by means of a shielding plate 6. The warm or hot refrigeration-transfer medium which is to be cooled heats the liquid refrigerant 5, which as a result begins to evaporate, forming large numbers of gas bubbles. Since the refrigerant in the heat exchanger 2 is being heated, a rising movement will occur there, as indicated by the arrows, and a falling movement (see arrows) will arise in the bath outside the heat exchanger 2, i.e. a circulating movement is imposed on the liquid refrigerant. To ensure that the bath 5 does not evaporate dry or at least does not evaporate down, gaseous refrigerant is discharged via line 7 to a compressor 8, where it is compressed, in order then to be passed on, via line 9, to a condenser, where the gaseous refrigerant is condensed, after which the condensate and any remaining gaseous refrigerant is passed, via line 11, to an expansion valve 12, where the condensate is throttled from high pressure to low pressure. The high-pressure and high-temperature liquid refrigerant is cooled during this throttling through self- evaporation to the saturation temperature associated with the low pressure. In the process, the condensate is partially evaporated to form gas, the so-called "flash gas". The two-phase mixture of liquid refrigerant and gaseous refrigerant which remains downstream of the expansion valve 12 is returned to the pressure vessel via line 13, in order to be introduced into the internal top part 14 of the pressure vessel.

Fig. 2 shows a second embodiment of a bath evaporator, in accordance with the first aspect of the invention. The same reference numerals as in Fig. 1 are used for corresponding parts.

The bath evaporator illustrated in Fig. 2 comprises a vertically positioned pressure vessel 1. In the bottom part 15 of this pressure vessel 1 there is a cylindrical plate-type heat exchanger 2 with a compartment 20 centrally inside, which compartment is closed in the circumferential direction and at the top and is open at the bottom. In view of the cylindrical shape, it is also possible to use a helically wound tube or assembly of tubes for the heat exchanger. The outlet 21 of the line 13 opens out into this compartment 20, which is referred to as the excess-pressure chamber. In this way, the cooled refrigerant, in the form of a two-phase mixture of gaseous refrigerant and liquid refrigerant, is passed into this pressure chamber 20. In the process, the velocity of the two-phase mixture is reduced, possibly even virtually to zero. The liquid constituent drops downwards, and the gaseous constituent will fill the compartment until the latter is completely filled with gas, in which case the pressure in the excess-pressure chamber 20 will be such that the fluid refrigerant 22 which is substantially in liquid form will be pressed out of this compartment 20. If the pressure in the compartment 20 then increases further, surplus gas will, as indicated by arrow 23, escape from the compartment 20 at the bottom side and will flow upwards via the plate-type heat exchanger 2. These gas bubbles 18 will improve the heat transfer of the heat exchanger 2 since the intensity of bubbles is increased. It should be clear that this improved heat transfer can be used not only to cool the refrigeration-transfer medium which is to be cooled to a lower temperature, but also to reduce the dimensions of the bath evaporator as such if, for example, cooling to a lower temperature is not necessary. The refrigerant which remains at the top side of the heat exchanger 2 and is substantially in liquid form is returned via return line 19 to the bottom side of the heat exchanger 2. This line 19 runs around the outside of the pressure vessel 1, but may equally well run through it, for example through the central compartment 20. A column of liquid 24 will form in the line 19 as a function of the pressure in the excess-pressure chamber 20 and the pressure in the separator space 16. Compartment 20 is in communication with the separator space 16 via a line 25 which projects above the bath and in which there is an actuable valve. During operation, this valve will generally be closed. If, when the evaporator is not operating, this valve is then opened, the excess pressure can be released from the excess-pressure chamber 20, and the excess-pressure chamber will fill up with liquid refrigerant from the bottom. If appropriate, it is also conceivable for this valve to be designed as a control valve, in order to control the refrigeration capacity of the bath evaporator by influencing the level of the bath of refrigerant.

According to an advantageous, but optional, embodiment, the excess- pressure chamber 20 also contains a partition 42. The partition 42 extends as far as into the bottom of the fluid refrigerant 22 which is substantially in liquid form. More particularly, the partition 42 extends as far as into a collection chamber 43 for lubricating oil. The collection chamber 43 may, for example, comprise a welded-on pipe connection stub 40, to which an oil-discharge line 41 is connected. The partition 42 advantageously ends at a lower level than the wall 44 of the excess-pressure chamber 20 which directly adjoins the heat exchanger. The outlet opening 21 is directed towards the partition 42, in such a manner that oily constituents which are contained in the refrigerant supplied via line 13 collide with the partition and adhere to the latter. The adhesion of oily constituents is promoted in particular if the partition has a metal surface.

In accordance with the second aspect of the invention, Fig. 3 shows a third embodiment of a bath evaporator. In Fig. 3, corresponding parts are denoted by the same reference numerals as in Figs. 1 and 2. Fig. 3 is substantially identical to the embodiment shown in Fig. 1, except that filler means 26 are positioned in the bath 5, in the form of cut-to-size bodies of neoprene or another material which is suitable for this purpose and is sufficiently refrigerant-, temperature- and pressure-resistant. These neoprene bodies 26 take up a very substantial part of the volume of the bath 5 and, as a result, save a considerable amount of refrigerant. As a result of a space being left clear at the ends of the pressure vessel 1, between the neoprene bodies 26 and the corresponding end wall, and/or leaving some space between the neoprene bodies 26, it is possible to ensure that the liquid refrigerant can flow back into the bottom of the bath in order to be recirculated through the heat exchanger 2.

Fig. 4 diagrammatically depicts a cross section (Fig. 4a) and a longitudinal section (Fig. 4b) through a particularly preferred embodiment of a bath evaporator according to the invention in which both the first aspect of the invention and the second aspect of the invention are employed. For corresponding parts, the same reference numerals are used as in Figs. 1-3. The embodiment shown in Fig. 4 differs from that shown in Fig. 2 substantially by virtue of the fact that the pressure vessel 1 is in this case a horizontal cylindrical vessel and excess-pressure chambers 20 are formed on both sides of the heat exchanger 2. These excess-pressure chambers 20 are obtained by, in the pressure vessel 2, fixedly welding two plates 27 which, although this is not really essential to the invention, are shown in horizontal form, by means of a longitudinal edge, to the top longitudinal edge of a respective protective plate 6, and by fixedly welding these plates by means of their other longitudinal edge and transverse edges to the inner wall of the pressure vessel 1.

Fig. 4 also shows that a filler layer, for example of neoprene, is arranged between the protective plate 6 and the heat exchanger 2 or, if appropriate, on that side of the protective plate 6 which is remote from the heat exchanger. This prevents the gas bubbles from rising up between the protective plates and the heat exchanger. It will be clear that a filler layer 28 of neoprene, for example, of this type may also be provided on one or other side of the protective plates 6 in the embodiments shown in Figs. 1 , 2 and 3.

A major advantage of the embodiments shown in particular in Figures 3 and 4 is that the amount of refrigerant required is very small. This has the advantage that almost immediately after the injection of two-phase mixture via line 13 is stopped, there is no longer any liquid refrigerant in the heat exchanger, so that the evaporation in the heat exchanger and the extraction of heat from the refrigeration-transfer medium which is to be cooled also stop almost immediately once the injection of the two-phase mixture is stopped. This is not the case in standard bath evaporators, where the remaining large amount of refrigerant continues to extract considerable amounts of heat. On account of this almost immediate cessation of cooling of the refrigeration- transfer medium when the injection of the two-phase mixture is stopped, it is possible, for example, to cool water to close to freezing point without there being any risk of freezing, i.e. without damage to the heat exchanger. In the event of freezing, the heat exchanger can easily spring a leak. A further drawback of the heat exchanger freezing is that the process stream of the refrigeration-transfer medium then stops, leading to the possibility of the line in which the refrigeration-transfer medium is incorporated coming to a standstill.

Fig. 4 also shows a suction pipe 29 which extends over the entire length of the cylindrical pressure vessel 1 and forms the inlet nozzle of line 7. The suction pipe 29 is provided, on its top half, with a series of slots 30 which extend in the transverse direction of the pipe 29. Via the suction pipe 29 with slots 30, it is possible for gaseous refrigerant to be extracted uniformly over the entire length of the pressure vessel 1 , at a relatively low velocity. Keeping the suction velocity at a relatively low level at least when the gas passes through the slots 30 prevents drops of liquid refrigerant being entrained, which could be very damaging to the compressor 8. This is furthermore also counteracted by providing the slots 30 in the top half of the suction pipe 29.

In accordance with the embodiment shown in Fig. 2, in the embodiment shown in Fig. 4 it is also highly advantageous, though optional, for a partition 42 to be provided, extending into the bottom of the fluid refrigerant 22 which is in liquid form, and for the opening 21 to be directed towards this partition 42. However, in the embodiment shown in Fig. 4 the partition 42 is not a separate component, but rather is formed by that wall of the excess-pressure chamber 20 which is remote from the heat exchanger 2 and as such also forms part of the wall of the cylindrical pressure vessel 1. The opening 21 is in this case formed by a tube which extends in the longitudinal direction of the cylindrical vessel 1 and has outlet openings directed towards partition 42. As illustrated more extensively in the detailed Figure 4c, a film 47 of lubricating oil forms on the partition 42. On account of its adhesion to the partition 42, this film 47 will move downwards relatively slowly, so that it can collect in the chamber 43 formed by a pipe connection stub 40. Compared to the film 47, drops 46 of refrigerant in liquid form will flow or roll downwards to the bath 22 much more quickly. It should be clear that the principle which has been explained with reference to Fig. 4c also applies to the embodiment shown in Fig. 2.

Claims

1. Bath evaporator for cooling a refrigeration-transfer medium by evaporation of a refrigerant, the bath evaporator comprising a pressure vessel having: - an internal bottom part provided with a heat exchanger, which during operation is immersed in a bath of refrigerant, for passing refrigeration-transfer medium which is to be cooled through the bath evaporator; an internal top part for separating gaseous and liquid refrigerant; a recirculating system for returning liquid refrigerant from the top side of the heat exchanger to its bottom side; an outlet for evaporated refrigerant, which opens out into the top part of the pressure vessel; an inlet for refrigerant, which opens out into the pressure vessel; characterized in that at least one excess-pressure chamber, which opens downwards, is provided in the pressure vessel, into which chamber the inlet for refrigerant opens out and which excess-pressure chamber is in fluid communication with the bottom side of the heat exchanger, in such a manner that, when the excess-pressure chamber is completely full with gaseous refrigerant, surplus gaseous refrigerant can flow through and/or along the heat exchanger to the internal top part.

2. Bath evaporator according to one of the preceding claims, characterized in that the excess-pressure chamber opens out at the level of the bottom side of the heat exchanger.

3. Bath evaporator according to Claim 1 or 2, characterized in that the heat exchanger is positioned above the base of the pressure vessel, leaving clear a liquid space which during use is filled with liquid refrigerant.

4. Bath evaporator according to Claim 3, characterized in that the fluid communication between the excess-pressure chamber and the bottom side of the heat exchanger runs via the liquid space.

5. Bath evaporator according to Claim 3 or 4, characterized in that a preferably metal partition, such as a wall of the excess-pressure chamber, is provided in the excess-pressure chamber, which partition continues into, and preferably into the bottom of, the liquid space; in that the inlet for refrigerant has an opening which is positioned in such a manner that, during operation, at least the oily constituents which escape from the said opening, are in liquid form and are contained in the refrigerant come into contact with the said partition; and in that oil-discharge means are provided in the bottom of the liquid space.

6. Bath evaporator according to Claim 5, characterized in that the said partition is a side wall, remote from the heat exchanger, of the excess-pressure chamber.

7. Bath evaporator according to one of the preceding claims, characterized in that the refrigerant comprises ammonia, and in that the lubricating oil used is preferably not soluble therein.

8. Bath evaporator, preferably according to one of the preceding claims, for cooling a refrigeration-transfer medium by evaporation of a refrigerant, the bath evaporator comprising a pressure vessel having: an internal bottom part provided with a heat exchanger, which during operation is immersed in a bath of refrigerant, for passing refrigeration-transfer medium which is to be cooled through the bath evaporator; an internal top part for separating gaseous and liquid refrigerant; a recirculating system for returning liquid refrigerant from the top side of the heat exchanger to its bottom side; - an outlet for evaporated refrigerant, which opens out into the top part of the pressure vessel; an inlet for refrigerant, which opens out into the pressure vessel, the pressure vessel being a cylindrical vessel, preferably a substantially horizontally positioned cylindrical vessel, and the heat exchanger being positioned centrally in the bottom part, with a space on either side of or around the heat exchanger, between the heat exchanger and the wall of the pressure vessel, characterized in that the said space contains filler means which, at least during use, are substantially free of liquid refrigerant and substantially fill the said space.

9. Bath evaporator according to Claim 8, characterized in that the said filler means comprise one or more bodies made from neoprene or at least a suitable refrigerant-, temperature- and pressure-resistant material.

10. Bath evaporator according to Claim 8 or 9, characterized in that the said filler means comprise one or more hollow filler-means chambers.

11. Bath evaporator according to Claim 10, in combination with one or more of Claims 1-7, characterized in that the at least one excess-pressure chamber forms one or more of the hollow filler-means chambers.

12. Bath evaporator according to one of the preceding claims, characterized in that the outlet for refrigerant, which opens out into the top part of the vessel, comprises a pipe part which extends through this top part and is provided with suction openings which are distributed over the length of the said pipe part and preferably face upwards.

13. Bath evaporator according to Claim 12, characterized in that the suction openings are slots or perforations.

14. Bath evaporator according to one of the preceding claims, characterized in that the excess-pressure chamber and the top part can be connected to one another via a valve.

15. Bath evaporator according to Claim 14, characterized in that it is provided with control means which control the level of the bath of refrigerant by actuation of the valve as a function of the exit temperature of the refrigeration-transfer medium, which is measured by means of a sensor.