DE69007709T2 - Stack evaporator. - Google Patents

Description

The present invention relates to a stack evaporator for car cooling systems or the like, in particular to a stack evaporator having many plate-shaped tube elements with internal coolant paths, wherein many air paths are formed by and with a cooling fin member arranged between the one tube element and the next tube element.

In general, the stack evaporators used for the above purpose comprise tube elements whose internal refrigerant paths are in fluid communication with one another so as to form a refrigerant loop between a refrigerant inlet and a refrigerant outlet. A refrigerant mist enters the inlet and flows through the refrigerant loop so that heat exchange takes place between the refrigerant and the air passing through the air paths. The refrigerant is thus gradually evaporated and the refrigerant gas then flows out of the evaporator via the outlet.

Fig. 12 shows a known tubular member (as disclosed in Japanese Utility Model Application Sho. 53-32375) in which one end portion is formed as a discharge water box 10a and a return water box 10b. A coolant flow loop is formed such that the coolant flows through the discharge water box 10a into the interior of the tubular member, then passes to the other end portion of the tubular member where it makes a U-turn, and then flows back to the return water box. Such coolant flow is made turbulent by the existence of many projecting inner fins 70; these inner fins belong to each of the cup-shaped core plates 60 which are fixed to each other at their edges so as to form a space for the coolant loop therebetween, with the inner fins 70 being arranged in the space. The inner fins 70 are arranged obliquely to the coolant flow direction, and each inner fin 70 of a core plate 60 and each corresponding inner fin 70 of the other core plate fixedly coupled to the one core plate intersect. However, the U-turn of the coolant flow in the loop of the tubular element tends to cause a "channel" or uneven coolant flow in the loop, thereby causing a significant decrease in the effective heat transfer area.

It should also be noted that the mutually intersecting inner fins 70 arranged obliquely to the coolant flow are disadvantageous in that the coolant pressure loss in the tube elements near the evaporator exit increases unfavorably, despite the reduced heat transfer efficiency due to the increasing amount of gas in the coolant which reaches the vicinity of the evaporator exit. This disadvantage reduces the value of an expected advantage, namely an improved heat transfer efficiency which is obtained when vigorous coolant turbulence takes place in the tube elements arranged near an evaporator inlet.

A stack evaporator with cooling fin members arranged between many stacked plate-shaped tube elements with inlet and outlet water box parts is disclosed in DE-A-3536325. An evaporator with tube elements having coolant paths formed by alternating fins on the core plates is disclosed in US-A- 4371034.

An object of the invention, which was made in view of the problems of known evaporators, is to provide a stack evaporator which has a low refrigerant pressure loss but a high heat transfer efficiency.

The invention therefore relates to a stack evaporator with many plate-shaped tube elements of a certain thickness; the Tube elements are stacked side by side in the thickness direction with a cooling fin member disposed between two such tube elements, each composed of a pair of cup-shaped core plates; these core plates are provided with many fins projecting from a flat body and are fixed to one another at their edges so as to form coolant paths, the core plates facing each other with their fins disposed inside; the invention is characterized in that each tube element has an inlet water box part at one end and an outlet water box part at the other end, that the ribs of each core plate run parallel to the coolant flow direction and are arranged at regular intervals so that they form a row in a direction perpendicular to the flow direction, that each rib protruding from one of the paired core plates is arranged in the middle between two ribs protruding from the other core plate of the pair such that end surfaces of the ribs of one core plate are alternately connected to the flat body of the other core plate of the pair, the coolant paths running parallel to each other and straight from the inlet water box part to the outlet water box part, and that furthermore the ribs on the side surfaces of the tube elements have outer surfaces which each form many, open-topped, gutter-like drainage channels leading from one end of the tube elements to the other end, the water condensed on the side surface of each tube element flowing through the drainage channels to be drained at the other end, so that the occurrence of a water droplet flight process is effectively prevented.

The refrigerant flowing through the tube elements each provided with the inlet water box part at one end and the outlet water box part at the other end need not make a U-turn. Therefore, no uneven refrigerant flow occurs in the evaporator according to the invention, eliminating the problem that the effective heat transfer area decreases and the pressure loss increases due to the U-turn of the coolant in the known devices.

The refrigerant can flow smoothly through the refrigerant loop of the evaporator without being disturbed by the fins running parallel to the flow direction, so that the heat transfer takes place evenly across the loop leading from an inlet pipe to an outlet pipe for the refrigerant with a reduced pressure loss and with an improved overall efficiency.

Furthermore, such an alternate arrangement of the fins of the coupled core plates as used in the invention, with the end faces of each fin of one core plate pressing against the opposite flat body of the other core plate, not only improves the heat transfer efficiency but also bonds the core plates more firmly to each other, improving the pressure resistance of the evaporator. In order to improve the heat exchange efficiency, it is desirable to use a smaller "equivalent diameter" for the refrigerant paths, the equivalent diameter being such a value obtained by dividing a product of the cross-sectional area and "4" by an inner peripheral length of the refrigerant path. According to the invention, the equivalent diameter can be made small even though the fin pitch (that is, the distance between two adjacent fins) of the core plates is large. In other words, such a high fin spacing in the invention does not significantly reduce the equivalent diameter of the coolant paths, but it does facilitate the manufacture of the core plates in the invention. It is also advantageous that the flat outer surfaces of the core plates are so large that the contact area with the corrugated cooling fins is increased, so that the heat exchange efficiency is further improved.

A quantity of water that is in the respective between adjacent

The water condensed along the air passageways formed by the tube members can flow smoothly down along drainage recesses arranged between the fins. Therefore, the so-called "flying water drop" phenomenon is prevented from occurring in the evaporator according to the invention. In an embodiment in which a side plate is attached to the outermost fin member, internal channels extending vertically on the side plate help the condensed water to flow smoothly down so that the flying water drop is prevented even when a significant amount of water is condensed or flows in between the outermost tube member and the side plate.

The invention will now be explained in more detail using exemplary embodiments with reference to the drawings. They show:

Fig. 1 is a side view of a core plate of a first embodiment, seen from the side of the coolant paths,

Fig. 2 is an enlarged cross-section along the line 2-2 in Fig. 1,

Fig. 3 is a perspective view of two core plates forming a tubular element and a corrugated cooling fin member, with the core plates and cooling fin member being shown in a separated state,

Fig. 4 a front view of the assembled evaporator,

Fig. 5 is a perspective view of a side plate, corrugated fin members and tubular elements in a second embodiment, with all elements and members shown in the separated state,

Fig. 6 is a front view corresponding to Fig. 5,

Fig. 7 is a plan view corresponding to Fig. 5,

Fig. 8 is a side view of a tube element,

Fig. 9 a side view of a core plate,

Fig. 10 is a cross-section along the line 10-10 in Fig. 6,

Fig. 11 an enlarged front view of the evaporator and

Fig. 12 is a side view of a core plate of a known evaporator, seen from the side of the refrigerant paths.

Embodiments of the invention relating to stack evaporators made of aluminum or aluminum alloys and used in automotive cooling systems will now be described in detail.

Figures 1 to 4 show a stack evaporator of a first embodiment according to the invention.

This evaporator has many plate-shaped tube elements 1 arranged upright and stacked side by side in the horizontal direction. The evaporator also includes corrugated fin members 2, most of which are arranged between two adjacent tube elements 1 and the rest are arranged outside the outermost tube element. Each corrugated fin member 2 is fixed to the tube elements.

Each tube element 1 is, as shown in Figures 1 to 4, provided with an upper water box part 1a and a lower water box part 1b (which function either as an input water box or as an output water box, as shown in the following description), both of which are solid and arranged at opposite and longitudinal ends of the element. Coolant paths 1c running in the longitudinal direction of the element 1 are formed midway therebetween and are in fluid communication with the water box parts 1a and 1b, the coolant paths 1c forming a flat coolant path as a whole.

The adjacent tube elements 1 are watertightly connected to each other at their header parts 1a and 1b, which are in close contact and fluid communication with each other due to coolant flow holes 1d. As shown in Fig. 4, the upper header part 1a of the right (in the drawings) outermost tube element 1 is connected to a coolant inlet pipe 3, while on the other hand the upper header part 1a of the left (in the drawings) outermost tube element 1 is connected to a coolant outlet pipe 4. Narrow closure plates (not shown) are attached between the upper header parts 1a of the second and third tube elements near the coolant inlet and between the upper header parts 1a of the eighth and ninth tube elements near the coolant outlet, these closure plates closing the coolant flow holes 1d. Similarly, narrow closure plates (not shown) are arranged between the lower header portions 1b of the fifth and sixth tube elements and between those of the eleventh and twelfth tube elements, these closure plates closing the refrigerant flow openings 1d. These closure plates cause the refrigerant flowing into the evaporator via the inlet pipe 3 to continue to flow in a zigzag pattern, changing its flow direction at each boundary between adjacent groups of the tube elements. Heat exchange takes place between the refrigerant flowing in this manner and the air streams flowing through air paths formed between the adjacent tube elements and through the cooling fin members 2; the refrigerant then leaves the evaporator through the Outlet tube 4. A side plate 5 (Fig. 4) is arranged on the outside of the outermost corrugated cooling fin member 2.

The tube elements 1 are each formed by soldering two cup-shaped core plates 6 inside to inside at their edges 6a so that they form a unit. The core plates 6 are manufactured by pressing a suitable material, preferably by pressing a brazing sheet. The brazing sheet comprises an aluminum alloy core sheet, the front surface and rear surface of which are coated with a brazing metal which is applied by a plating technique. End parts of each core plate 6 project outwards to form expansion parts 9. A coolant flow opening 1d is formed by a groove-shaped opening in each expansion part in the longitudinal direction thereof. A flange 9a projects from a semicircular edge of the elliptical opening 1d.

On inner surfaces of the core plates 6, fins 7 are formed, which contribute to improving the heat transfer efficiency in the above-described evaporator. The fins 7 run parallel to the refrigerant flow direction, i.e. in the longitudinal direction of the core plate, and extend almost over the entire length of the core plate. The fins 7 are arranged at regular transverse intervals, although they are slightly curved as a whole toward a side edge of the core plate 6.

Two core plates 6, each provided with ribs 7, are brought into close contact and soldered together at their edges 6a. As can be seen from Figures 1 and 2, the rib 7 of one core plate 6 is shown in full, while that of another core plate is shown in dashed lines, with the ribs of the two core plates alternating with one another. End surfaces of the ribs 7 of one core plate 6 lie close to one another and are connected to a flat body 8 located between two adjacent ribs 7 of the other core plate. soldered, whereby many coolant paths 1c are created in a straight direction from the discharge water box 1a to the return water box 1b of the tube element 1.

These straight refrigerant paths increase the smoothness of the refrigerant flow because uneven flow or violent movement of the refrigerant in the tube element 1 is prevented. Furthermore, the refrigerant flows so evenly through all the paths that heat transfer is carried out effectively, thereby improving the heat transfer capacity of the evaporator.

In addition, extremely high precision is not required in the manufacture of this evaporator because the end surfaces of the fins 7 of one core plate do not have to be exactly in line with one another, but only have to be brought up to the relatively wide, flat bodies 8 of the other core plate and soldered to it, in such a way that, as previously described, the fins of two core plates alternate with one another in a direction perpendicular to the coolant flow direction. This structure is also advantageous because the two core plates 6 can be soldered easily and safely, increasing the mechanical bonding force and the pressure resistance of the tube elements 1 of the evaporator. Furthermore, with such a structure, the heat transfer area and the heat transfer efficiency are increased.

Another important feature of this design is the shape of the fins 7, which are wider at their ends, so that the coolant paths 1c are narrowed at their parts near the inlet and outlet. This allows the coolant to flow more evenly between the paths, avoiding any inadvertent reduction in the effective area of heat transfer.

In order to make the cross-section of the coolant path as large as possible, it is advantageous to set the width W1 of the ribs 7 so so that it falls within the range of two to four times the plate thickness "t", as shown in Fig. 2.

For greater heat exchange efficiency, the equivalent diameter of the coolant paths 1c is chosen to be as small as possible. In this design, each coolant path 1c has a width of 2.1 mm and a height of 1.9 mm and thus an equivalent diameter of approximately 1.99 mm, as can be seen from the following calculation:

1.99 = 4 x (2.1 x 1.9) / [2 x (2.1 + 1.9)].

A second embodiment of the invention will now be described with reference to Figures 5 to 11.

Although the basic features of the evaporator in the second embodiment are the same as in the first embodiment, there are some minor differences, for example, in the water box parts of the tube elements, the structure of the side plates or other members.

The evaporator of the second embodiment is also provided with tube elements 101 which are provided at their longitudinal ends with an upper water box part 101a and a lower water box part 101b of a bulky shape. The plate-like tube elements 101 stand upright and are stacked side by side with corrugated fin members 102, one of which is located between each two tube elements. A corrugated fin member 102 is arranged outside the outermost tube element 101 and covered with a side plate 105.

The fluid passages formed by coolant flow holes 101d are closed between the upper water box parts 101a of the fifth and sixth tube elements near the coolant inlet and between those of the fourteenth and fifteenth tube elements near the coolant outlet. Similarly, the passages are closed by the refrigerant openings 101d between the lower header parts 101b of the tenth and eleventh tube elements are closed. Such local passage closure causes the refrigerant to flow into the evaporator via an inlet pipe 103 and an inlet header 103a and then to flow in a zigzag fashion, changing its flow direction at each boundary between adjacent groups of the tube elements, before flowing out of the evaporator via an outlet header 104a and an outlet pipe 104.

A tube element 101 is constructed as in the first embodiment in such a way that two cup-like core plates 106 lie opposite one another and are soldered together. Ribs 107 protruding from the inner surfaces of the core plates 106 and arranged at regular intervals in the longitudinal direction of the core plates form coolant paths 101c which run straight in each tube element 101 from an upper water box part 101a to a lower water box part 101b.

Upper and lower expansion parts 109 of the core plates 106 have an elliptical shape as shown in Figures 5, 8 and 9. These expansion parts are each provided with three coolant flow openings 101d in series. Above and between the coolant flow openings 101d of the upper expansion parts 109 and also below and between the coolant flow openings 101d of the lower expansion parts 109 are recesses 109a. Projections 109b (of the core plate 109) are adapted to the recesses 109a and cooperate with them in such a way that additional soldering surfaces are created which increase the pressure resistance of the upper and lower water box parts 101a and 101b so that the coolant pressure is well resisted.

Mandrels 106b arranged on the surfaces of the core plates are used to position the corrugated cooling fin members. The mandrels 106b are located next to each other, but more inward than the expansion parts 109, and between the fins 107 and also outside the outermost fin 107 in such a formation that they form rows. The upper and lower rows of the mandrels 106b, as shown in Fig. 11, hold the upper and lower ends of the corrugated fin members 102, respectively, when the tube members 101 and the fin members 102 are alternately pre-assembled before they are brazed. Gaps are provided at predetermined intervals between the upper end surfaces of the fin members and the upper header parts 101a and between the lower end surfaces of the fin members and the lower header parts 101b. These gaps serve as drainage channels 125 when all the parts belonging to an evaporator are joined together in a single operation, for example, brazing.

As shown in Fig. 9, the inner width of the expansion parts 109 is preferably substantially equal to the width of a flat tube part 108. Side walls 121 comprising the parts 108 and 109 extend continuously in a straight direction from the inside of the flat tube part 108 to the upper and lower water box parts 101a and 101b, with all coolant paths 101c (Fig. 10) including the outermost coolant path forming straight fluid connections with the water box parts 101a and 101b.

As can be seen from Figures 5 and 6, the side plates 105 have many internal channels 128, for example, made by pressing a metal sheet, which extend vertically and are parallel to each other. The internal channels 128 provide vertical drainage guides 129 between the side plates 105 and the corrugated cooling fin members 102.

During operation of the evaporator described above, heat transfer takes place between the coolant flow and the air flow, with the coolant entering the evaporator via the inlet pipe 103, flowing through the evaporator and exits it via the outlet pipe 104, while the air flows through air paths formed by the corrugated fin members 102 arranged between two tube elements 101 or between a tube element 101 and the side plate 105. As a result of this heat transfer, the heat of the air flow is absorbed by the evaporator so that a considerable amount of condensed water is generated in the air paths between two tube elements 101 or between the outermost tube element 101 and the side plate 105 or so that this condensed water enters the air paths.

The amount of condensed water in the air paths between two tube members 101 flows down through the drainage guides 126 (Fig. 10) formed between the outer surface of the tube members and the corrugated fin members 102 due to the recesses formed by the fins 107. Then, the condensed water is drained into the channels 125 formed by the lower end surfaces of the fin members and the lower water box parts 101b.

On the other hand, another amount of condensed water in the air paths between the outermost tube member and the side plate 105 also flows down through drainage guides formed by the fins 107 arranged between the outermost tube member 101 and the corrugated fin member 102. Therefore, the drainage for the air paths in the mentioned area is improved, preventing the flying of water drops, which inevitably takes place in the air flow through known evaporators.

The depth "D2" of the inner channels 128 is such that the condensed water can flow smoothly and can be 0.5 mm or more.

The inner channels 128 are formed by corrugations of the side plates 105, thereby increasing their strength. Therefore, the load can be distributed across the entire width of a makeshift assembled evaporator consisting of the side plates 105 and pairs of alternating tube elements 101 and fin members 102, these pairs between the side plates 105 being in the "bandage" condition prior to the brazing operation.

The increased strength allows the side plates to be made thinner; they can have a thickness of about 0.5mm, while the thickness of known vaporizers is about 1.6mm.

As shown in Figures 5, 6 and 11, the lowermost parts of the side plates 105 are pressed into water box support tongues 130 which meet the end surfaces of the lower water box parts 101b. The inner channels 128 run continuously from the main parts of the side plates over the tongues 130. This structure of the end plates not only ensures the drainage of the condensed water, but also increases the mechanical strength on the outer surfaces of the lower water box parts 101b of the outermost tube element 101, to which water box parts neither the water box 103a nor the water box 103b is attached after all the evaporator parts are firmly connected to one another into a unit.

Claims (12)

1. Stacked evaporator with many plate-shaped tube elements (1) of a certain thickness stacked side by side in the direction of thickness with a cooling fin member (2) arranged between two such tube elements and each consisting of a pair of cup-shaped core plates (6) provided with many fins (7) protruding from a flat body (8) and fixed to one another at their edges in such a way that coolant paths are formed, the core plates facing one another with their fins arranged inside, characterized in that each tube element (101) has an inlet water box part (1a) at one end and an outlet water box part (1b) at the other end, that the fins (7) of each core plate (6) run parallel to the coolant flow direction and are arranged at regular intervals in such a way that they form a row perpendicular to the flow direction standing direction, that each rib (7) protruding from one of the paired core plates (6) is arranged in the middle between two ribs (7) protruding from the other core plate (6) of the pair in such a way that end surfaces of the ribs (7) of one core plate (6) are alternately connected to the flat body (8) of the other core plate (6) of the pair, the coolant paths running parallel to each other and from the inlet water box part (1a) straight to the outlet water box part (1b), and that furthermore the ribs (7) on the side surfaces of the tube elements have outer surfaces which each form many, open-topped, groove-like drainage channels (126) leading from one end of the tube elements to the other end, the water condensed on the side surface of each tube element flowing through the drainage channels to be drained at the other end, so that the occurrence of a water droplet flight process is effectively prevented. 2. Stack evaporator according to claim 1, characterized in that the tube elements (1) are arranged vertically and are stacked side by side in the horizontal direction. 3. Stack evaporator according to claim 1, characterized in that the core plates (6) are manufactured by pressing a metal sheet which has a core material made of an aluminum alloy and whose front surface and rear surface are coated with a solder by the plating process. 4. Stack evaporator according to claim 1, characterized in that the core plates (6) are equipped at their ends with elliptical expansion parts (9) which have back parts with a series of coolant flow openings. 5. Stack evaporator according to claim 4, characterized in that the expansion parts (9) of one core plate (6) have recesses on their outer surfaces which lie between the coolant flow openings and which are adapted to and connected to corresponding projections of the other core plate. 6. Stack evaporator according to claim 1, characterized in that the core plates (6) have mandrels which determine the positions of the upper and lower end surfaces of the corrugated cooling fin members. 7. Stack evaporator according to claim 4, characterized in that the core plates (6) are designed such that the expansion parts have the same inner width as the flat tube parts, whereby all coolant paths including the outermost coolant path are in straight fluid connection with the inside of the water box parts (1a, 1b). 8. Stack evaporator according to claim 1, characterized in that the fins (7) are wider at their ends than at their middle parts, the coolant paths being narrowed in the vicinity of the inlet water box parts (1a) and the outlet water box parts (1b). 9. Stack evaporator according to claim 1, characterized in that the ribs (7) have a width which falls within the range of twice the thickness of the core plates. 10. Stack evaporator according to claim 1, characterized in that one of the cooling fin members (102) is arranged outside each outermost tube element (101) and that a side plate (105) having vertical internal channels is arranged on the outside of a cooling fin member (102), wherein drainage guides (129) are provided along the internal channels (128) between the side plate (105) and a cooling fin member (102). 11. Stack evaporator according to claim 10, characterized in that the inner channels (128) run parallel to one another. 12. Stack evaporator according to claim 10 or 11, characterized in that the inner channels (128) have a depth of 0.5 mm or more.