EP3614086A1

EP3614086A1 - Evaporator and refrigeration system with evaporator

Info

Publication number: EP3614086A1
Application number: EP19192313.5A
Authority: EP
Inventors: Torfinn TORP; Knut Roger VÅGENES; John Magne GITMARK
Original assignee: Teknotherm Marine As Norway
Current assignee: Teknotherm Marine As Norway
Priority date: 2018-08-20
Filing date: 2019-08-19
Publication date: 2020-02-26
Also published as: NO345004B1; NO20181095A1

Abstract

Evaporator and a refrigerator system with evaporator comprising
a refrigerant circuit comprising first longitudinal hollow elements (10) with an inner cross section (CS1), and a fluid circuit comprising second longitudinal hollow elements (20) arranged inside respective first longitudinal hollow elements (10), where the second longitudinal hollow elements (20) has an outer cross section (CS2) smaller than the inner cross section (CS1), wherein the difference in the inner cross section (CS1) and the outer cross section (CS2) defines a first cavity (11), arranged to carry a refrigerant.

Description

TECHNICAL FIELD

The present invention relates to a refrigeration system, and an evaporator for a refrigeration system, and more specifically to a refrigeration system for cooling of fluids, such as a chiller. The system may be used in different applications, such as in marine applications for cooling of water filled tanks. Other applications may include, but are not limited to cooling other liquids, cooling of gases under pressure or condensing a secondary medium in a cascaded system.

BACKGROUND

Various types of refrigeration systems, such as compression systems are well known in the art, as is also the general construction components, their interaction and operating characteristics. However, depending on the application, the systems differ significantly.
A water chiller is a device used to extract heat from water to a refrigerant in a closed loop system. The refrigerant is then pumped to a location where the waste heat is transferred to the surroundings via a condenser.
Specific types of water chillers are employed in marine applications where waste heat is transferred to the sea.
Further, some marine vessels are equipped with water tanks that need temperature control and consequently refrigeration. When the tanks are filled up, different type of debris, minerals and algae flow into the tank with the seawater. This may be an advantage when the tanks are used to store sea animals, such as fish, but it may cause problems for the chiller system, since the evaporator tend to loose efficiency after a while because of growing of algae and fouling. Larger particles or debris, such as shellfish may also cause problems. Evaporator components may even brake if water is allowed to freeze as a result of blocked channels. The evaporator design should therefore allow easy maintenance.
Another problem with some of the prior art chillers, is that explosion-proof rooms are required because of the risks related to storage of the refrigerant. Such rooms are not always readily available.

SHORT SUMMARY

A goal with the present invention is to overcome the problems of prior art.
The invention solving the above-mentioned problems is an evaporator and a refrigerator system, such as a chiller according to the independent claims.
The evaporator and refrigerant system have a low refrigerant charge, i.e. the type and mass of refrigerant is low due to a small refrigerant volume. The small volume is made possible by the novel evaporator design.
Thus, the amount of refrigerant may be decreased while maintaining the capacity. The refrigerant is always well protected inside the evaporator itself, and explosion-proof rooms are not required on board ships for hosting the evaporator, according to at least some authorities like the Norwegian Maritime Directorate.
Further, the evaporator has an increased heat transfer rate compared to flooded evaporators. The increase is made possible by an increased velocity on the refrigerant side, again resulting from the design of the evaporator.
The evaporator is easy to clean and maintain and can be used in areas with a high fouling rate. Due to flow velocity, the evaporator may also be self-cleaned.
The evaporator is also suitable for refrigerants with a large difference between vapor and liquid density, such as Ammonia. In prior art systems has therefore been challenging to have a good distribution in the evaporator. The first longitudinal hollow elements help to maintain this distribution. Further the large vapor volumes may be easily ventilated due to the natural flow through the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates in a partly sectioned perspective view, an evaporator according to an embodiment of the invention.
Fig. 2 illustrates, in a cross sectional view where objects behind the cutting plane are omitted, an embodiment of the invention where inlet and outlet (3a, 3b) for the fluid to be refrigerated are arranged on the same end of the housing (1).
Fig. 3 illustrates in a cross sectional view, where objects behind the cutting plane are omitted, an embodiment of the invention where inlet and outlet (3c, 3d) for the fluid to be refrigerated are arranged on different ends of the housing (1). The enlarged section shows details of the interior of the evaporator.
Fig. 4 illustrates in a cross sectional view, where objects behind the cutting plane are omitted, an embodiment of the invention where refrigerant inlet and outlet (2c, 2d) for the fluid to be refrigerated are arranged on the same end of the housing (1). The fluid circuit is otherwise the same as in Fig. 2.
Fig. 5 illustrates in three different cross sections, where objects behind the cutting plane have been omitted in the upper cross section, the division of the evaporator in different chambers. The refrigerant is kept inside refrigerant inlet chamber (5a), the first cavity (11) and the refrigerant outlet chamber (5b), while the fluid to be refrigerated is kept within the fluid inlet chamber (4a), the second longitudinal hollow elements (20).
Fig. 6 illustrates schematically a refrigerator or chiller according to an embodiment of the invention.

EMBODIMENTS OF THE INVENTION

In the following description, various examples and embodiments of the invention are set forth in order to provide the skilled person with a more thorough understanding of the invention. The specific details described in the context of the various embodiments and with reference to the attached drawings are not intended to be construed as limitations. Rather, the scope of the invention is defined in the appended claims.
The embodiments described below are numbered. In addition, dependent or related embodiments defined in relation to the numbered embodiments are described. Unless otherwise specified, any embodiment that can be combined with one or more numbered embodiments may also be combined directly with any of the related embodiments of the numbered embodiment(s) referred to.
In a first embodiment, the invention is an evaporator comprising a refrigerant circuit comprising first longitudinal hollow elements (10), and a fluid circuit comprising second longitudinal hollow elements (20) arranged inside respective first longitudinal hollow elements (10), as illustrated in Fig. 1, 2, 3 and 4.
The evaporator is typically used in a refrigerator system, such as a chiller. The refrigerant circuit is arranged to carry the refrigerant, and the fluid circuit is used to carry the fluid to be refrigerated, such as water.
The first longitudinal hollow elements (10) has an inner cross section (CS1) and the second longitudinal hollow elements (20) has an outer cross section (CS2). The outer cross section (CS2) is smaller than the inner cross section (CS1), and the difference in the inner cross section (CS1) and the outer cross section (CS2) defines a first cavity (11), arranged to carry the refrigerant. Inner and outer cross sections (CS1, CS2) are illustrated in the enlarged part of Fig. 3.
In a second embodiment, that may be combined with the first embodiment, the evaporator comprises a fluid inlet (3a, 3c) and a fluid inlet chamber (4a, 4c), wherein the fluid inlet chamber (4a, 4c) is arranged as a manifold between the fluid inlet (3a, 3c) and at least a first set of the second longitudinal hollow elements (20). This is illustrated in Fig. 2 and 3.
A manifold is intended to mean a larger or wider channel, into which one or more smaller pipes or channels lead, intended to carry fluid in one direction or the other.
In a first related embodiment the evaporator comprises a first fluid end element (22a) providing fluid communication from the fluid inlet chamber (4a, 4c) to the least first set of the second longitudinal hollow elements (20), and arranged at the end of the at least first set of the second longitudinal hollow elements (20), wherein the fluid inlet chamber (4a, 4c) is delimited by the first fluid end element (22a).
In a second related embodiment that may be combined with the first related embodiment above, the first fluid end element (22a) is a plate with through holes.
In a third related embodiment that may be combined with the first or second related embodiment above, the second longitudinal hollow elements (20) and the through holes are arranged in rows.
In a third related embodiment that may be combined with any of the related embodiment above, the first fluid end element (22a) is arranged perpendicular to the second longitudinal hollow elements (20).
In a third embodiment that may be combined with the first or second embodiment, the evaporator comprises a refrigerant inlet (2a) and a refrigerant inlet chamber (5a) wherein the refrigerant inlet chamber (5a) is arranged as a manifold between the refrigerant inlet (2a) and at least a first set of the first longitudinal hollow elements (10).
The flow direction of the refrigerant relative to the fluid to be refrigerated may be the same as indicated in the drawings, or opposite. In the last case the inlet and outlet should change places.
In a first related embodiment the evaporator comprises a refrigerant end element (12a) providing refrigerator communication from the refrigerant inlet chamber (5a) to the at least first set of the first longitudinal hollow elements (10), and arranged at the end of the at least first set of the first longitudinal hollow elements (10), wherein the refrigerant inlet chamber (5a) is delimited by the refrigerant end element (12a).
In a second related embodiment that may be combined with the first related embodiment, the refrigerant end element (12a) is a plate with through holes.
In a third related embodiment that may be combined with the second related embodiment above, the second longitudinal hollow elements (20) are running through the refrigerant inlet chamber (5a) and the refrigerant inlet chamber (5a) is delimited by the second longitudinal hollow elements (20).
In a third related embodiment that may be combined with any of the related embodiment above, the refrigerant inlet chamber (5a) is further delimited by the fluid end element (12a).
In a fourth embodiment the evaporator comprises a housing (1), wherein the housing (1) delimits the fluid inlet chamber (4a, 4c) and the refrigerant inlet chamber (5a) from the exterior.
In a first related embodiment, the refrigerant inlet chamber (5a) is arranged inside, or behind, the fluid inlet chamber (4a, 4c) seen from a first end (1a) of the housing (1) as illustrated in the figures.
The housing (1) may e.g. have the form of a cylindrical tank with a cylindrical section between first and second housing ends (1a, 1b), as illustrated.
In the following, some additional possible embodiments of the features above are described.
The first longitudinal hollow elements (10) and/or the second longitudinal hollow elements (20) may be cylindrical or tubular as illustrated e.g. in Fig. 1. In this case the first cavity (11) will be an annulus.
Alternatively, or in combination, the first longitudinal hollow elements (10) and/or the second longitudinal hollow elements (20) are corrugated tubes, finned tubes or elements with other hollow shapes.
The first longitudinal hollow elements (10) and/or second longitudinal hollow elements (20) may be straight from end to end. This will facilitate maintenance and cleaning of the fluid circuit of the evaporator, which over time will be exposed to fouling.
As illustrated, the first longitudinal hollow elements (10) and/or the second longitudinal hollow elements (20) may be arranged in rows.
In order to reduce the size of the evaporator, the first longitudinal hollow elements (10) may in an embodiment be arranged in staged array where one row is offset by e.g. half the centre to centre distance between two first longitudinal hollow elements (10).
The first fluid end element (22a) and/or the refrigerant end element (12a) may be circular plates whose circumferences align with a wall of the housing (1) as seen in Fig. 2 and 3, to form cavities constituting the fluid inlet chamber (4a, 4c) and the refrigerant inlet chamber (5a) within the housing.
The plates may e.g. be welded or bolted to the housing (1), or fastened by other means, such as being a result of a molding or printing manufacturing process.
The refrigerant end element (12a) may be arranged in parallel to the first fluid end element (22a) as illustrated in Fig. 2 and 3. Further, both these elements may be arranged perpendicular to the first longitudinal hollow elements (10).
So far, only the elements in one end of the evaporator have been described.
However, the evaporator may in a fifth embodiment, that may be combined with any of the embodiments above, comprise a fluid outlet chamber (4b, 4d), wherein the fluid outlet chamber (4b, 4d) is arranged as a manifold between the fluid outlet (3b, 3d) and at least a first set of the second longitudinal hollow elements (20).
Two alternative embodiments are illustrated in Fig. 2 and 3. In Fig. 2, the fluid outlet chamber (4b) and the fluid outlet (3b) are arranged on the same end of the evaporator as the fluid inlet chamber (4a), while in Fig. 3, the fluid outlet chamber (4b) and the fluid outlet (3d) are arranged on the opposite end of the evaporator.
In Fig. 2 the fluid to be refrigerated will therefore enter through the fluid inlet (3a), be distributed in the fluid inlet chamber (4a) to a first subset of the second longitudinal hollow elements (20) in the upper half of Fig. 2, continue all the way through the longitudinal hollow elements (20) to the second end (1b) of the housing (1) comprising an internal cavity (4e) where all the longitudinal hollow elements (20) are terminated. The fluid will then return through a second subset of longitudinal hollow elements (20) in the lower half of Fig. 2, and exit through the fluid outlet (3b) via the fluid outlet chamber (4b). As understood, the fluid flow could also be in the opposite direction if inlet and outlets are interchanged.
In this case the cavity in the first end (1a) of the housing (1) is split into two sub-chambers, i.e. fluid inlet chamber and fluid outlet chamber (4a, 4b) by the divider (6). Two-pass evaporators may be advantageous when fluid flow rate is low or space is limited.
In Fig. 3 the fluid to be refrigerated will enter through the fluid inlet (3a), be distributed in the fluid inlet chamber (4a) to all the second longitudinal hollow elements, continue all the way through the longitudinal hollow elements (20) to the second end (1b) of the housing (1) comprising the fluid outlet chamber (4d) where all the longitudinal hollow elements (20) are terminated. The fluid will then exit through the fluid outlet (3d) via the fluid outlet chamber (4d).
In a first related embodiment illustrated in Fig. 3, the evaporator comprises a fluid second end element (22b) providing fluid communication from the least first set of the second longitudinal hollow elements (20) to the fluid outlet chamber (4d), and arranged at the end of the at least first set of the second longitudinal hollow elements (20), wherein the fluid outlet chamber (4d) is delimited by the fluid second end element (22b).
The evaporator may in an embodiment comprise a refrigerator outlet (2b) and a refrigerant outlet chamber (5b) wherein the refrigerator outlet chamber (5b) is arranged as a manifold between the at least a first set of the first longitudinal hollow elements (10) and the refrigerator outlet (2b).
The evaporator may also in an embodiment comprise a refrigerant end element (12b) providing refrigerator communication from the at least first of the first longitudinal hollow elements (10) to the refrigerator outlet chamber (5b), and arranged at the end of the at least first of the first longitudinal hollow elements (10), wherein the refrigerator outlet chamber (5b) is delimited by the refrigerant end element (12b).
As can be seen from Fig. 2 and 3, most of the elements, such as the fluid end element (12b), the refrigerant end element (22b), the first and second longitudinal hollow elements (10, 20), and the housing (1), except for the first and second housing ends (1a, 1b) may be similar in both ends, and the features already described for the elements located to the left in Fig. 2 and 3 may also be combined in the same way with the elements located to the right.
Although the refrigerant inlet and outlet (2a, 2b) are illustrated on the same side of the housing (1) in Fig. 2 and 3, the inlet and outlet could in other embodiments of the invention be arranged e.g. above and below in different ends, or above or below in the same end, such as illustrated in Fig. 4. In the latter case, the refrigerator will therefore enter through the refrigerant inlet (2c), be distributed in the refrigerant inlet chamber (5c) to a first subset of the first longitudinal hollow elements (10) in the upper half of Fig. 4, continue all the way through the first longitudinal hollow elements (10) to the second end (1b) of the housing (1) comprising an internal refrigerator cavity (5e) where all the first longitudinal hollow elements (10) are terminated. The fluid will then return through a second subset of first longitudinal hollow elements (10) in the lower half of Fig. 4, and exit through the refrigerator outlet (2d) via the refrigerator outlet chamber (5d).
In this case the chamber equivalent to the refrigerant inlet chamber (5a) of Fig. 2 is split into two sub-chambers, i.e. refrigerant inlet chamber and refrigerant outlet chamber (5c, 5d) by the refrigerator divider (7).
The evaporator in Fig. 3 is sometimes referred to as a single pass evaporator because the fluid flows only through one length of the housing (1), i.e. in in one end and out the other end. The evaporator in Fig. 2 is referred to as a double, or two-pass evaporator since fluid is passing through two lengths of the housing (1). According to the invention, the evaporator may also have more than two passes, e.g. 3, 4, 5.
Accordingly, the refrigerant circuit is illustrated only as single-pass, but may also have any number of passes.
The evaporator may successfully be used with different types of refrigerants, such as e.g. ammonia or CO₂. Ammonia has a normal boiling point of 28 degree centigrade, and a refrigeration system using ammonia may have certain advantages, such that the refrigerant being environmentally compatible. Ammonia and CO₂ as refrigerants have very good thermodynamic qualities, which may increase the efficiency of the system.
To improve refrigerant distribution the refrigerant inlet (2a) may in an embodiment be arranged below the refrigerant outlet (2b).
All the inlets and outlets may be equipped with flanges and/or couplings for connection to other elements of a refrigeration system.
In an embodiment the invention is also a refrigerator system or a chiller (100) comprising;

a condenser (102),
a compressor (103),
a thermal expansion valve (104), and

In a related embodiment the refrigerator system comprises a liquid separator (105) to release flash gases as illustrated in Fig. 6.
In the refrigerator system illustrated in Fig. 6, the liquid separator (105) is a container arranged in the refrigerant condenser circuit. The liquid separator (105) has an inlet for gaseous refrigerant from the refrigerant outlet (2b, 2d) of the evaporator, and an outlet for passing the gaseous refrigerant to the refrigerant condenser circuit comprising compressor (103), condenser (102) and thermal expansion valve (104). The liquid separator (105) further has an inlet for the liquid feed from the thermal expansion valve (104), and an outlet for passing liquid refrigerant to the inlet (2a, 2c) of the evaporator.
Passing the condensed refrigerant liquid feed via the liquid separator (105) removes essentially all flash gases that might be present in the condensed refrigerant, before the liquid refrigerant enters the evaporator. This is especially an advantage when ammonia is used as refrigerant since ammonia gives a relatively large amount of flash gases when the pressure is reduced. Removing essentially all flash gases from the refrigerant liquid provides an excellent and uniform liquid distribution in the evaporator according to the present invention. A good liquid distribution in the evaporator also leads to reduced overheating (i.e. the temperature difference between evaporating temperature and actual gas temperature). As is well known in the art, overheated gases may also negatively affect the compressor properties. The refrigerator system according to the present invention has shown significantly increased capacity of the chiller system compared to e.g. traditional RSW systems, it allows a low amount of refrigerant while maintaining a high capacity, and furthermore the refrigerant circuit may be self-circulating due to natural flow, which also provides a reliable operation.
Some applications of the evaporator and the chiller system with an evaporator according to the invention above have been mentioned initially. Further, such systems may be well suited for any application with limited space, such as mobile refrigeration where refrigeration is needed during transport and storage, e.g. refrigerator trucks, trailers etc. The evaporator according to the present invention may be arranged in a horizontal, inclined, or in a vertical position. A chiller system (100) may comprise more than one evaporator (101), e.g. two or more evaporators, which might be coupled in parallel, each evaporator (101) being in fluid communication with a liquid separator (105), and refrigerant condensing circuit as described above.
In the exemplary embodiments, various features and details are shown in combination. The fact that several features are described with respect to a particular example should not be construed as implying that those features by necessity have to be included together in all embodiments of the invention. Conversely, features that are described with reference to different embodiments should not be construed as mutually exclusive. As those with skill in the art will readily understand, embodiments that incorporate any subset of features described herein and that are not expressly interdependent have been contemplated by the inventor and are part of the intended disclosure. However, explicit description of all such embodiments would not contribute to the understanding of the principles of the invention, and consequently some permutations of features have been omitted for the sake of simplicity or brevity.

Claims

An evaporator comprising
- a refrigerant circuit comprising first longitudinal hollow elements (10) with an inner cross section (CS1),

- a fluid circuit comprising second longitudinal hollow elements (20) arranged inside respective first longitudinal hollow elements (10), where the second longitudinal hollow elements (20) has an outer cross section (CS2) smaller than the inner cross section (CS1), wherein the difference in the inner cross section (CS1) and the outer cross section (CS2) defines a first cavity (11), arranged to carry a refrigerant.
The evaporator of claim 1, comprising a fluid inlet (3a, 3c) and a fluid inlet chamber (4a, 4c), wherein the fluid inlet chamber (4a, 4c) is arranged as a manifold between the fluid inlet (3a) and at least a first set of the second longitudinal hollow elements (20).
The evaporator of claim 2, comprising a first fluid end element (22a) providing fluid communication from the fluid inlet chamber (4a, 4c) to the least first set of the second longitudinal hollow elements (20), and arranged at the end of the at least first set of the second longitudinal hollow elements (20), wherein the fluid inlet chamber (4a, 4c) is delimited by the first fluid end element (22a).
The evaporator according to any of the claims 1 to 3, comprising a refrigerant inlet (2a) and a refrigerant inlet chamber (5a) wherein the refrigerant inlet chamber (5a) is arranged as a manifold between the refrigerant inlet (2a) and at least a first set of the first longitudinal hollow elements (10).
The evaporator of claim 4, comprising a first refrigerant end element (12a) providing refrigerator communication from the refrigerant inlet chamber (5b) to the at least first set of the first longitudinal hollow elements (10), and arranged at the end of the at least first set of the first longitudinal hollow elements (10), wherein the refrigerant inlet chamber (5a) is delimited by the first refrigerant end element (12a).
The evaporator of any of claims 4 to 5, wherein the second longitudinal hollow elements (20) are running through the refrigerant inlet chamber (5a) and the refrigerant inlet chamber (5a) is delimited by the second longitudinal hollow elements (20).
The evaporator of any of claims 5 to 6, wherein the refrigerant inlet chamber (5a) is further delimited by the first fluid end element (22a).
The evaporator according to any of claims 4 to 7, comprising a housing (1), wherein the housing (1) delimits the fluid inlet chamber (4a) and the refrigerant inlet chamber (5a).
The evaporator according to any of the claims 5 to 8, wherein the first fluid end element (22a) and the refrigerant end element (12a) are circular plates whose circumferences align with a wall of the housing (1).
The evaporator of any of the claims above, wherein the second longitudinal hollow elements (20) are straight from end to end.
The evaporator of any of the claims above, wherein the first longitudinal hollow elements (10) are arranged in rows.
A refrigerator system (100) comprising;
- a condenser (102),

- a compressor (103),

- a thermal expansion valve (104), and
an evaporator (101) according to any of the claims 1 to 11.
The refrigerator system (100) of claim 12 comprising;
- a liquid separator (105).
The refrigerator system (100) of any of claims 12 to 13, wherein the evaporator (101) is arranged in a horizontal, inclined, or in a vertical position.
The refrigerator system (100) of any of claims 13 to 14, comprising two or more evaporators (101).