HEAT EXCHANGER FOR COOLING AN ELECTRONIC ENCLOSURE

Abstract

In order to reduce the dimensions of a heat exchanger it is suggested to configure the heat exchanger in such a way that it has a heat exchanging element comprising a condenser unit and an evaporator unit. The evaporator unit comprises a lower end area, an upper end area and a plurality of channels for transporting a refrigerant from the lower end area to the upper end area, said refrigerant comprising liquid and gas. The upper end area is connected to the lower end area by a first line which is configured to transfer only liquid from the upper end area to the lower end area.

Claims

1. A heat exchanger for cooling an electronic enclosure, comprising a condenser side and an evaporator side, wherein the heat exchanger comprises a heat exchanging element having a condenser unit and an evaporator unit, wherein the evaporator unit comprises an upper end area, a lower end area and a plurality of channels for transporting a refrigerant from the lower end area to the upper end area, said refrigerant comprising liquid and gas, wherein the upper end area is connected to the lower end area by a first line, said first line being configured to transfer only liquid from the upper end area to the lower area.

2. The heat exchanger according to claim 1, wherein the upper end area is configured to let liquid and gas being transported to the upper end area by means of the plurality of channels separate from each other to form a continuous liquid phase and a continuous gas phase so that liquid can flow back to the lower end area by means of the first line.

3. The heat exchanger according to claim 1, wherein the upper end area of the evaporator unit is configured basin-shaped, wherein the first line is configured as a drain.

4. The heat exchanger according to claim 1, wherein the condenser side is located higher than the evaporator side.

5. The heat exchanger according to claim 1, wherein the condenser unit and the evaporator unit are arranged such that the condenser unit and the evaporator unit overlap vertically.

6. The heat exchanger according to claim 1, wherein the condenser unit has an upper end area, a lower end area and a plurality of channels, wherein the heat exchanging element has a second line for transporting gas from the upper end area of the evaporator unit to the upper end area of the condenser unit.

7. The heat exchanger according to claim 6, wherein the heat exchanging element has a third line for transporting liquid from the lower end area of the condenser unit to the lower end area of the evaporator unit.

8. The heat exchanger according to claim 1, wherein the heat exchanging element is a thermosiphon.

9. The heat exchanger according to claim 1, wherein the condenser side and the evaporator side are separated from each other by a barrier.

10. The heat exchanger according to claim 1, wherein the heat exchanger comprises an evaporator fan configured to produce a first air stream on the evaporator side and a condenser fan configured to produce a second air stream on the condenser side, wherein the barrier is configured to separate the first air stream and the second air stream.

11. The heat exchanger according to claim 1, wherein the channels have a cross dimension of 0.1 mm to 12 mm.

12. The heat exchanger according to claim 1, wherein the channels are partially filled with a refrigerant.

13. The heat exchanger according to claim 1, wherein the heat exchanger comprises metal plates being disposed between neighboring channels.

14. The heat exchanger according to claim 1, wherein the condenser unit is configured larger than the evaporator unit.

15. The heat exchanger according to claim 1, wherein the heat exchanger is adapted for cooling an electronic enclosure.

16. The heat exchanger according to claim 1, wherein the channels have a cross dimension of 0.2 mm to 10 mm.

17. The heat exchanger according to claim 1, wherein the channels have a cross dimension of 0.4 mm to 6 mm.

18. The heat exchanger according to claim 1, wherein the channels have a cross dimension of 2 mm to 5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The above-mentioned and the other features of the invention disclosed herein are described below with reference to the drawings of the preferred embodiments. The illustrated embodiments are intended to illustrate, but not to limit the inventions. The drawings contain the following figures:

[0062] FIG. 1 a longitudinal sectional view of a heat exchanger according to the invention being attached to an electronic enclosure;

[0063] FIG. 2 a longitudinal sectional view of the evaporator unit and the condenser unit of the heat exchanger according to FIG. 1;

[0064] FIG. 3 a cross sectional view along the line A-A of FIG. 2;

[0065] FIG. 4 a schematic view of the refrigerant flow between the evaporator unit and the condenser unit; and

[0066] FIG. 5 an enlarged cross sectional view of a mini-channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] FIG. 1 shows a longitudinal sectional view of a heat exchanger (10) which is configured as an air-to-air heat exchanger (11). The heat exchanger (10) is attached to an electronic enclosure (90). For this purpose, the heat exchanger (10) comprises a casing (21) which is attached to the respective casing (91) of the electronic enclosure (90). The casing (91) defines an inside (55) and an outside (56) of the electronic enclosure (90).

[0068] The heat exchanger (10) comprises a condenser side (15) and an evaporator side (12). The condenser side (15) of the heat exchanger (10) is located higher than the evaporator side (12). The condenser side (15) is separated from the evaporator side (15) by a barrier (18) which is configured as a metal plate (19), namely an inner wall (20) in the casing (21). The condenser side (15) and the evaporator side (12) are both disposed in the inside (53) of the heat exchanger (10). The heat exchanger (10) comprises on its evaporator side (12) an evaporator fan (13) configured to produce a first air stream (14). Furthermore, the heat exchanger (10) has a condenser fan (16) on the condenser side (15) configured to produce a second air stream (17). The barrier (18) is configured to separate the first air stream (14) and the second air stream (17).

[0069] The heat exchanger (10) comprises a heat exchanging element (30) which is configured as a thermosiphon (30a). The heat exchanging element (30) comprises an evaporator unit (31) as well as a condenser unit (32). The evaporator unit (31) is disposed on the evaporator side (12) of the heat exchanger (10), while the condenser unit (32) is disposed on the condenser side (15). The evaporator unit (31) has an upper end area (31a) and a lower end area (31b). Also, the condenser unit (32) has an upper end area (32a) and a lower end area (32b).

[0070] The evaporator unit (31) has a longitudinal direction (31c) and a cross direction (31d) as well as a length (31e) in the longitudinal direction (31c) and a width (31f) in the cross direction (31d). The condenser unit (32) also has a length (32e) in a longitudinal direction (32d) as well as the width (32f) in a cross direction (32d). The longitudinal direction (31c) of the evaporator unit (31) corresponds to the longitudinal direction (32c) of the condenser unit (32). The same applies to the cross directions (31d, 32d). Furthermore, the longitudinal directions (31c, 32c) correspond to the vertical direction (52), whereas the cross directions (31d, 32d) correspond to the horizontal direction (51).

[0071] In vertical direction (52) the evaporator unit (31) and the condenser unit (32) overlap with each other by an overlap (34). Thus, the length (10a) of the heat exchanger is smaller than the sum of the lengths (32e, 31e) of the condenser unit (32) and the evaporator unit (31).

[0072] Due to the overlap (34), the barrier (18) has one part (namely the second part (18b)) which has an angle to the vertical direction (52). The second part (18b) is formed oblique. Furthermore, the barrier has a first part (18a) and a third part (18c) extending in the horizontal direction (51). The second part (18b) is disposed between the first part (18a) and the third part (18c). Each part (18a, 18b, 18c) amounts to about one third of the entire length of the barrier (18) projected on the horizontal direction (51).

[0073] The heat exchanging element (30), in particular the evaporator unit (31) and the condenser unit (32), comprises an extruded metallic material (35) which is aluminum (36). The connections for fluid transfer between the evaporator unit (31) and the condenser unit (32) penetrating the barrier (18) are not shown in FIG. 1.

[0074] On the condenser side (15) the casing (21) of the heat exchanger (10) comprises a first opening (22) for letting cool ambient air (26) from an outside (54) of the heat exchanger (10) enter the inside (53) of the heat exchanger. The cool ambient air (26) is drawn in through the first opening (22) on the condenser side by means of the condenser fan (16). The cool ambient air (26) enters the inside (53) through the first opening (22) and passes through the condenser unit (32) towards the condenser fan (16).

[0075] At the location of the condenser fan (16) the casing (21) of the heat exchanger (10) comprises a second opening (23) for letting hot air (27) exit the inside (53) of the heat exchanger (10) at its condenser side (15) to the outside (54). By hot air the ambient air which is heated by means of passing through the condenser unit (32) is meant. The cool ambient air (26) passing through the condenser unit (32) and exiting by the second opening (23) to the outside (54) of the heat exchanger (10) in form of hot, i.e. heated, air (27) forms the second air stream (17).

[0076] On the evaporator side (12) the casing (21) of the heat exchanger comprises a third opening (24) for letting hot air (28) from an inside (55) of the electronic enclosure (90) enter the inside (53) of the heat exchanger (10). The hot air (28) is drawn in from the electronic enclosure (90) to an inside (53) of the heat exchanger (10) by means of the evaporator fan (13) which is disposed at the third opening (24). The drawn in hot air (28) passes through the evaporator unit (31) and returns back through a fourth opening (25) in the casing (21) in form of cool air (29), i.e. cooled by means of passing through the evaporator unit (31), air to the inside (55) of the electronic enclosure (90). The evaporator unit (31) is disposed in the fourth opening (25). The hot air (28) from the electronic enclosure (90) travelling through the evaporator unit (31) and returning to the electronic enclosure (90) in form of cool air (29) forms the first air stream (14) which is produced by the evaporator fan (13). After passing the evaporator fan (13) and before returning to the inside (55) of the electronic enclosure (90) the first air stream (14) is deflected on an inner wall of the casing (21), in particular the barrier (18), most preferred its second part (18b).

[0077] All in all, for allowing the first air stream (14) and the second air stream (17) the casing (21) of the heat exchanger (10) comprises two openings respectively on the evaporator side (12) and the condenser side (15).

[0078] The first air stream (14) and the second air stream (17) can be reversed in their respective flow direction. To reverse the flow direction, the rotational direction of the evaporator fan (13) as well as the condenser fan (16) can be reversed. In detail, the condenser fan (16) draws in cool ambient air (26) through the second opening (23) at which the condenser fan (16) is disposed. The cool ambient air (26) enters the inside (53) of the heat exchanger (10) at its condenser side (15), passes through the condenser unit (32) and exits to the outside (54) of the heat exchanger (10) by means of the first opening (22) within the casing (21) in the form of hot, i.e. heated, air (27).

[0079] On the evaporator side (12) hot air (28) from the inside (55) of the electronic enclosure (90) enters the inside (53) of the heat exchanger (10) by means of the fourth opening (25), travels through the evaporator unit (31) and exits the inside (53) of the heat exchanger (10) to the inside (55) of the electronic enclosure (90) through the third opening (24) in the form of cool, i.e. cooled, air. At the third opening (24) the evaporator fan (13) is disposed.

[0080] The condenser fan (16) is therefore able to either push air through the condenser unit (32) or pull air through it. The same applies to the evaporator fan (13) with regard to the evaporator unit (31).

[0081] The two-phase refrigerant (45) is present within the channels (38) in a gaseous state, thus gas (59), and a liquid state, thus liquid (58) (see also FIG. 4). This means that the channels (38) are filled with liquid parts (58a) and gaseous parts (59a) of the two-phase refrigerant (45) which do not form a continuous phase respectively. Rather, the liquid parts (58a) and gaseous parts (59a) are intermixed. The gaseous parts (59a) are formed by gas bubbles, while the liquid parts (58a) are formed by drops or larger accumulations of liquid (58).

[0082] In the evaporator unit (31) the refrigerant (44) is heated by means of the first air stream (14). As a consequence of the heating, the refrigerant (44), especially its liquid parts (58a), evaporates partially. The gaseous parts (59a), i.e. the gas bubbles, coalesce into larger bubbles which eventually occupy the respective entire channel (38) trapping liquid parts (59a) of the refrigerant (44) in between them. Due to the bubbles rising, they take the trapped parts of liquid (58) with them. This bubble pumping action serves to move the refrigerant (44) from the lower end area (31b) to the upper end area (31a) of the evaporator unit (31) (see also FIG. 4).

[0083] In FIG. 2 the evaporator unit (31) and a condenser unit (32) of the heat exchanging element (30) is shown. In particular, the thermosiphon (30a) is shown.

[0084] The upper end area (31a) and the lower end area (31b) of the evaporator unit (31) are both designed as manifolds (33). The same applies to the condenser unit (32), in particular its upper end area (32a) and its lower end area (32b). The evaporator unit (31) and the condenser unit (32) overlap in vertical direction (52) by the overlap (34) since the upper end area (31a) of the evaporator unit (31) is located higher than the lower end area (32b) of the condenser unit (32).

[0085] The evaporator unit (31) and the condenser unit (32) have a plurality (37) of channels (38) which are formed as micro-channels (39). The channels (38) of the evaporator unit (31) have a first end (38a) disposed in the lower end area (31b) as well as a second end (38b) disposed in the upper end area (31a). In particular, the second ends (38b) of the channels (38) are disposed as openings (62) in a bottom (60a) of the upper end area (31a) which is formed as a basin (60). In particular, the upper end area (31a) comprises a bottom wall (60b) to which the channels (38) lead. The second ends (38b) of the channels (38) are thus formed as openings (62) in the bottom wall (60b) of the upper end area (31a). Furthermore, the first end areas (38a) of the channels (38) are formed as openings (62) in a top wall (60c) of the lower end area (31b) of the evaporator unit (31).

[0086] Also the condenser unit (32) comprises a plurality (37) of channels (38) with a first end (38a) and a second end (38b) which are designed in the same way as described above for the evaporator unit (31).

[0087] The liquid parts (58a) and the gaseous parts (59a) of the refrigerant (44) arriving in the upper end area (31a) of the evaporator unit (31a) are allowed to separate by gravity and form respective continuous phases (58b, 59b), namely a continuous liquid phase (58b) covering the bottom wall (60b) of the upper end area (31a) and a continuous gas phase (59b) (see also FIG. 4).

[0088] The liquid (58), namely the continuous liquid phase (58b), travels through a first line (41) of the heat exchanging element (30). The first line (41) is configured as a tube (46). The first line has a first end (41a) disposed in the upper end area (31a) of the evaporator unit (31) and a second end (41b) disposed in the lower end area (31b) of the evaporator unit (31) (see also FIG. 4).

[0089] The first line (41) is configured as a drain (61) of the upper end area (31a). The first end (41a) is particularly designed as an opening (62) in a side wall (60d) of the upper end area (31a) being in close proximity to the bottom (60a). While liquid (58), namely liquid from the continuous liquid phase (58b), is allowed to flow back to the lower end area (31b) of the evaporator unit (31), gas (59) which has traveled to the upper end area (31a), namely gas from the continuous gas phase (59b), travels to the upper end area (32a) of the condenser unit (32) by means of a second line (42) of the heat exchanging element (30) being configured as a tube (46). The second line (42) has a first end (42a) being disposed in the upper end area (31a) of the evaporator unit (31) and a second end (42b).

[0090] The gas (59) arriving in the upper end area (32a) of the condenser unit (32) is cooled by means of the second air stream (17). After having cooled down the gaseous parts (59a) of the refrigerant (44) condense again and the refrigerant (44) travels back to the lower end area (32b) of the evaporator unit (32) by means of the channels (38) of the condenser unit.

[0091] For returning accumulated liquid (58) from the lower end area (32b) to the lower end area (31b) of the evaporator unit the heat exchanging element (30) comprises a third line (43) configured as a tube (46) extending from the lower end area (32b) of the condenser unit (32) to the lower end area (31b) of the evaporator unit (31). Therefore, the third line (43) has a first end (43a) being disposed in the lower end area (32b) of the condenser unit (32) and a second end (43b) disposed in the lower end area (31b) of the evaporator unit (31). The second end (41b) of the first line (41) mouths in the third line (43).

[0092] Between neighboring channels (38) metal plates (47) in the form of fins (48), namely pleated aluminum fins (49), are disposed. The metal plates (47) facilitate the heat transfer between the air streams (14, 17) and the refrigerant (44) within the channels (38) via conduction. The metal plates (47) form an angle (50) towards the direction in which the channels (38) extend, especially to the vertical direction (52). The pleated aluminum fins (49) are arranged in a V-shaped configuration between the neighboring channels (38).

[0093] FIG. 3 shows a cross sectional view along the line A-A of FIG. 2. The channels (38) have a cross dimension (40) and a substantially oval shape. The channels (38) are formed as ports of mini-channels (57) which are substantially rectangular-shaped. In particular, six channels (38) form the ports of one mini-channel (57), wherein the evaporator unit (31) comprises ten mini-channels (57) (see FIG. 5). In between the mini-channels (57) the metal plates (47) in the form of pleated aluminum fins (49) are disposed.

[0094] In FIG. 4 a schematic overview of the flow of the refrigerant (44) between the evaporator unit (31) and the condenser unit (32) of the heat exchanging element (30) is shown.

[0095] Of the evaporator unit (31) an over-dimensioned channel (38) is exemplarily shown. Within the channel (38) the two-phase refrigerant (45) is present, namely liquid (58) in the form of liquid parts (58a) and gas (59) in the form of gaseous parts (59a). Due to the heating, liquid parts (58a) evaporate so that larger gaseous parts (59a) in the form of bubbles are formed. All in all, the refrigerant (44) travels from the lower end area (31b) to the upper end area (31a) of the evaporator unit (31) through the channels (38) via the bubble pumping action.

[0096] Due to the much larger dimensions, namely cross dimensions of the upper end area (31a), compared to the cross dimensions of the channels (38), the gaseous parts (59a) and the liquid parts (58a) are allowed to separate and form a continuous liquid phase (58b) and a continuous gas phase (59b). The continuous liquid phase (58b) covers the bottom (60a) of the upper end area (31a). The first end (41a) of the first line (41) forms an opening (62) in the side wall of the upper end area (31a) so that liquid (58) from the continuous liquid phase (58b) can flow back to the lower end area (31b). The second end (41b) of the first line (41) ends in the third line (43) of the heat exchanging element (30) from where the liquid (58) flows back to the lower end area (31b).

[0097] The continuous gas phase (59b) in the upper end area (31a) travels by means of the second line (42) to the upper end area (32a) of the condenser unit (32). Exemplarily, an over-dimensioned channel (38) of the condenser unit (32) is shown. Liquid parts (58a) are formed by condensation and due to gravity travel to the lower end area (32b) of the condenser unit (32). From there, the liquid (58) is transported to the lower end area (31b) of the evaporator unit (31) by means of the third line (43).

[0098] FIG. 5 shows an enlarged cross sectional view of a mini-channel (57) of the heat exchanger (10). The mini-channel (57) has a substantially rectangular shape, while the channels (38) have are substantially oval-shaped. The channels (38) are formed as ports of the mini-channel (57).