DE69413173T2 - Pipe element for a laminate heat exchanger - Google Patents

Description

The present invention relates to a layered heat exchanger in the form of an evaporator according to the preamble of claim 1.

GB-A-2223091 discloses a heat exchanger for use as a condenser comprising a plurality of planar tubes each formed with restrictors defining a flow path for a heat exchange fluid. Each tube has internal projections with defined dimensions for width and pitch but does not provide U-shaped passages with first and second passage legs on opposite sides of a connecting wall.

US-A-5111878 discloses an evaporator having a plurality of U-flow tubes arranged side by side therein. The tubes have a plurality of flow fins recessed and connected therein in a predetermined pattern, but the dimensions of the recesses are not defined. US-A-4800954 and US-A-5125453 also disclose evaporators having U-flows. In view of the significant prior art in evaporators having U-flows, the present invention has been developed from this art, and since condensers normally involve various conditions of refrigerant pressure and/or temperature and heat radiation or absorption, no one would have been motivated to adapt the evaporator of US-A-5111878 in accordance with a condenser without U-flow.

In a prior art heat exchanger formed by alternately layering fins and tube elements, beads are formed in the passages of the passage legs for the heat exchange medium to distribute the flow of the heat exchange medium and at the same time to increase the contact area with the heat exchange medium as a means of improving the heat exchange efficiency. The applicant also uses tubular members in which a plurality of round beads are press-molded into the molded plates constituting the tubular members, as disclosed, for example, in Japanese Unexamined Patent Publication S63-153397. The tubular member products of the relevant prior art typically have a bead diameter of 3.8 mm, a minimum bead pitch of 7.0 mm, a tubular member thickness of 2.9 mm, and a plate thickness of 0.57 mm for the molded plates. According to a study conducted by the inventor on the evaporators manufactured by other companies using either round beads or elliptical beads, the bead diameter or minor axis is in the range of 3.5 mm to 4.8 mm, the tube element thickness is in the range of 2.8 mm to 3.4 mm, and the plate thickness of the molded plates is in the range of 0.40 mm to 0.57 mm. Except for the bead pitch, for which we have no information, our tube elements fit within these ranges.

It is generally accepted in the art that the more beads there are in the tube element, the larger the contact area between the tube element and the heat exchange medium and, consequently, the better the heat exchange efficiency must be. However, if the number of beads is increased indiscriminately, the passage area of the heat exchange medium is reduced, thereby increasing the passage resistance and obstructing the flow of the heat exchange medium. On the other hand, if the beads are made smaller and their number is reduced to reduce the passage resistance, the area of contact with the heat exchange medium becomes insufficient, the heat transfer rate to the fins is reduced and the heat exchange performance is deteriorated. However, the need for a smaller heat exchanger with better performance must be answered while taking these conflicting factors into account. Further improvement of the tube elements is essential.

It is also understood that when a plurality of obstacles A are arranged one after the other in the direction of advance of a fluid, as shown in Fig. 13, the flow of fluid which has come into contact with the obstacle A is directed laterally back from the obstacle A and tends to flow between subsequent obstacles A without hitting them, thereby remaining in so-called stagnant water areas. It has been deduced that in tubular elements of the prior art described above there are a number of bulges which do not fully contribute to the heat exchange process because they are located in a stagnant water area. Such bulges in stagnant water areas are not only superfluous, but also contribute to the passage resistance and should be eliminated. It is preferable to promote heat exchange by allowing as much heat exchange medium as possible to pass through the passage with a minimum of passage resistance.

In addition to the problems of the areas of standing water described above, the flow of heat exchange medium tends to take the shortest path available and in a tubular element provided with a U-shaped passage 7 for heat exchange medium, such as the tubular element shown in Fig. 2, the heat exchange medium tends to run along the projection 10 in the middle. Since the prior art tubular element has beads of consistent density formed throughout the passage, there is no difference in passage resistance throughout the passage. As a result, the heat exchange medium runs along the projection, leaving areas where the heat exchange medium becomes motionless, such as on the upper sides of the tubular element.

All this indicates that there is room for improvement in the arrangement of beads in the tubular element.

It is an object of the present invention to provide a tube element which realizes an improvement in efficiency and also makes it possible to produce a smaller heat exchanger.

A further object is to provide a tubular element with an improved bead arrangement by taking into account the need to reduce the number of beads in areas of standing water and the need to distribute the fluid flow, thereby achieving an improvement in heat exchange efficiency.

The applicant of this invention has determined an optimum dimensional relationship among bead size, bead pitch, tube member thickness, and molded plate thickness by considering the following factors: (1) The larger the bead size, the larger the passage resistance, and the smaller the bead size, the smaller the passage resistance. However, if the bead size is too small, the heat exchange performance is correspondingly reduced. (2) The smaller the bead pitch, the larger the number of beads, thereby increasing the passage resistance. On the other hand, if the bead pitch is large, the number of beads is small, thereby reducing the heat exchange performance. (3) The smaller the thickness of the tube member, the narrower the passage for heat exchange medium, thereby increasing the passage resistance, and the larger the thickness of the tube member, the lower the passage resistance. However, in this latter case, the heat exchange medium passes through without performing sufficient heat exchange, thereby deteriorating the heat exchange performance. (4) The heat transfer rate is improved by reducing the thickness of the formed plates, but this results in reduced corrosion resistance and reduced strength. If the thickness of the formed plates is increased and the thickness of the tube element remains the same, the passage for heat exchange medium becomes narrower, which increases the passage resistance.

In summary, the present invention is a tube member for an evaporator in which tube members and fins are alternately layered over a plurality of rows, in which the fluid passage for the heat exchange medium is formed by joining two molded plates having beads which are formed in the above-mentioned tube member as projections in the above-mentioned fluid passage such that the width A of the beads and the pitch B of the beads are set at 2.0 mm ≤ A ≤ 3.0 mm and 3.5 ≤ B ≤ 6.3 mm, respectively.

In addition, the tubular element thickness H and the thickness T of the molded plates can be set in the ranges of 1.9 mm ≤ H ≤ 2.7 mm and 0.25 mm ≤ T ≤ 0.47 mm, respectively.

By determining an optimum dimensional relationship for the bead width A and the bead pitch B of the beads formed in the tube element, and also for the tube element thickness H and the thickness T of the formed plate in this way, an ideal tube element can be designed which provides the best possible combination of heat transfer rate, flow resistance and strength, thus achieving the highest possible heat exchange efficiency while making a smaller heat exchanger possible.

In addition to the structure described above, a plurality of bead rows may be provided which cross the direction of the fluid passage of the above-mentioned heat exchange medium at a right angle, the bead rows which are adjacent to each other having different distances between beads so that the beads in adjacent bead rows are arranged such that the low pressure zone generated behind each bead in the direction in which the fluid passage is formed does not affect the beads, which follow. Or, the tubular member may adopt a structure in which a plurality of bead rows are provided which cross the fluid passage direction at a right angle, the various bead rows which are adjacent to each other forming a continuum in the regions where no beads are present and in the regions where no beads are present in the above-mentioned bead rows which are adjacent to each other.

In such a structure, even though it may be outside the optimum dimensional ranges due to the areas where no beads are formed, the bead arrangement reduces the areas of standing water and the passage resistance, thereby eliminating stagnation by evenly distributing the heat exchange medium over the entire passage. As a result, the heat exchange efficiency is further improved due to the improvement in the areas where no beads are formed.

The above and other features of the invention and the attendant advantages will be better understood and appreciated by those skilled in the art to which the invention belongs, in view of the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments:

Fig. 1 shows an embodiment of a layered heat exchanger, wherein (a) is a front view and (b) is a bottom view;

Fig. 2 is a front view of the molded plate (Type 1) constituting the tube element used in the layered heat exchanger shown in Fig. 1 ;

Fig. 3 illustrates the flow of the heat exchange medium in the layered heat exchanger shown in Fig. 1;

Fig. 4 is an enlarged cross-section showing the beads in a tubular member;

Fig. 5 (a), (b) and (c) show the relationships between the bead shape, the bead size A and the bead pitch B of the beads formed in the tubular member;

Fig. 6 (a) is a behavior diagram showing changes in the relationship between heat exchange performance and volume resistance when the bead size is changed, Fig. 6 (b) is a behavior diagram showing changes in the relationship between heat exchange performance and volume resistance when the bead pitch is changed, and Fig. 6 (c) is a behavior diagram showing changes in the relationship between heat exchange performance and volume resistance when the tube element thickness is changed;

Fig. 7 shows an example of a molded plate (type 2) used in the tube element in the layered heat exchanger;

Fig. 8 shows another example of a molded plate (type 3) used in the tube element in the layered heat exchanger;

Fig. 9 shows the test equipment used to evaluate the performance of the tube element;

Fig. 10 shows the temperature distribution for the tube element when the flow rate of tap water is set to 5 cm³/s. Fig. 10(a) shows the temperature distribution for the tube element of type 1, Fig. Fig. 10(b) shows the thermodynamic distribution for the type 2 tube element and Fig. 10(c) shows the temperature distribution for the type 3 tube element;

Fig. 11 shows the temperature distribution for the tube element when the flow rate of tap water is set to 10 cm³/s, Fig. 10(a) shows the temperature distribution for the type 1 tube element, Fig. 10(b) shows the temperature distribution for the tube element type 2 and Fig. 10(c) shows the temperature distribution for the type 3 tube element;

Fig. 12 shows the thermodynamic distribution for the tube element when the flow rate of tap water is set to 20 cm3/s, Fig. 10(a) shows the thermodynamic distribution for the tube element of type 1, Fig. 10(b) shows the thermodynamic distribution for the tube element of type 2 and Fig. 10(c) shows the thermodynamic distribution for the tube element of type 3;

Fig. 13 shows the fluid flow past obstacles.

The following is an explanation of the embodiments of the present invention with reference to the drawings.

In Fig. 1, the layered heat exchanger 1 is an evaporator, e.g. of the 4-pass type, in which fins 2 and tube elements 3 are alternately layered over a plurality of rows. Each tube element 3 is formed by joining two molded plates 4, 4 at their peripheral edges and is provided with two reservoirs 5, 5 at one end on the upstream side of the air flow and the downstream side of the air flow. It is also provided with a passage 7 for heat exchange medium which Heat exchange medium flows from these reservoirs 5, 5 to the other end.

Each molded plate 4 is formed by press-forming an aluminum plate with two vessel-like bulged portions 8, 8 for forming reservoirs at one end and a bulged portion 9 for forming a passage formed as a continuation of the bulged portions 8, 8. The projection 10 extending from between two bulged portions 8, 8 for forming reservoirs to the vicinity of the other end of the molded plate is formed in the bulged portion 9 for forming a passage. Also, the mounting recess 11 for attaching the connecting pipe to be explained later is provided between the bulged portions 8, 8 for forming reservoirs, and a protruding part 12 (shown in Fig. 1) is provided at the other end of the molded plate 4 to prevent the fins 2 from falling off during assembly before brazing. Each bulged portion 8 for forming reservoirs bulges further than the bulged portion 9 for forming a passage. The projection 10 is connected to its opposite projection when the shaped plates 4 are connected at their peripheral edges, so that the projection 10 partitions the passage 7 for the heat exchange medium except in the region close to the other end of the tubular member 3, thereby forming an overall U-shaped passage.

The reservoirs of adjacent tube elements 3 are joined to one another at the bulged portions 8 for forming reservoirs of the respective molded plates 4 and, except for the blind type reservoir 5a located on one side approximately in the middle of the layering direction, are connected to one another via communication holes 13 formed in the bulged portions 8 for forming reservoirs.

In addition, the tube member 3a located at a specific position from the center to one side is not provided with the above-mentioned mounting recess 11, and one of its reservoirs 5b on the side where the dummy type reservoir 5a is provided is expanded so as to be adjacent to the opposite reservoir side. This expanded reservoir 5b is connected to the connecting pipe 15 installed in the mounting recess 11. Also, at one end of the heat exchanger in the layer direction that is furthest from the expanded reservoir 5b, the inlet/outlet port 16 is provided. This inlet/outlet port 16 is in turn provided with a connecting portion 17 for connecting an expansion valve, a connecting passage 18 provided between the connecting portion 17 and the reservoir on the side where the blind reservoir is provided, and a connecting passage 19 connected to the above-mentioned connecting pipe 15.

In this structure, heat exchange medium flows in through one of the communication passages, for example, the communication passage 16 connected to the inlet/outlet port 16. The heat exchange medium that has flowed in flows into a portion of the reservoir 5 which is approximately halved on the side of the blind type reservoir 5a via the communication pipe 15 and the expanded reservoir 5b, then flows upward through the heat exchange medium passage 7 along the projection 10, turns around at the tip of the projection 10 to make the downward journey, and finally reaches the reservoir located on the opposite side of the blind type reservoir 5a. After that, it flows horizontally to the other reservoir 5 which is approximately halved. Then, it flows again through the heat exchange medium passage 7 along the projection 10 and turns around at the tip of the above-mentioned projection 10 to make the downward journey. Finally, it flows out of the reservoir 5, which is located on the side where the reservoir 5a of the blind type is provided via the communication passage 18 (see the flow path shown in Fig. 3). Therefore, during the process in which the heat exchange medium flows through the heat exchange medium passage 7 to be heat exchanged with the air passing between the fins, heat in the heat exchange medium is transferred to the fins 2.

Furthermore, the beads 20 are press-molded as part of the above-mentioned molded plates 4. In the case of the molded plate 4 shown in Fig. 2, a plurality of rows are formed so as to be at a right angle to the direction of flow of the heat exchange medium passing through the heat exchange medium passage 7, and each bead row is provided with a plurality of beads 20 arranged at equal intervals. In the figure, when the row n is constructed with four beads, the row n + 1 is constructed with five beads, the row n + 2 is constructed with four beads, and so on. The beads are arranged in bead rows which are adjacent to each other so that the low-pressure zone generated behind each bead in the direction in which the fluid passage is formed (the vertical direction in the figure) does not affect the following beads. All of the beads of each row are arranged so that they interleave with the low pressure zones created behind the beads in the direction in which the fluid passage 7 is formed. Overall, the beads 20 are formed with a consistent density.

As shown in Fig. 4, the above-described beads 20 protrude from the inner surface of the molded plate to the inside of the fluid passage 7. They are connected to beads of the adjacent molded plate to improve the heat exchange efficiency across the heat exchange medium passage 7. In the tubular member 3, when the area of the lower portion of each bead, which is considered to start at the point where the molded plate 4 starts, is directed to the inside of the fluid passage 7. neren of the fluid passage 7 (hereinafter referred to as bead size) is denoted by A, the pitch of the adjacent beads closest to each other (hereinafter referred to as bead pitch) is denoted by B, the thickness of the portion of the tubular member constructing the passage for heat exchange medium is denoted by H, and the thickness of the molded plate is denoted by T, they fall within the following ranges: 2.0 mm ≤ A ≤ 3.0 mm, 3.5 mm ≤ B ≤ 6.3 mm, 1.9 mm ≤ H ≤ 2.7 mm, and 0.25 mm ≤ T ≤ 0.47 mm.

For example, when circular beads having an overall shape of a circular truncated cone are arranged as shown in Fig. 2 (the enlargement shown in Fig. 5(a)), i.e. when a plurality of beads are provided at specific pitches b in row n extending in the direction at right angles to the direction in which the heat exchange medium passage is formed, and the beads in row n + 1 are provided with the above-mentioned specific pitches b such that each of the beads in row n + 1 is equidistant from the next bead in row n, the diameter at the lower part of the bead is A and the specific pitch b is B. In the case shown in Fig. 5(b) where the beads in Fig. 5(a) at the top are replaced by oval-shaped beads, or when the beads are arranged as in Fig. 5(c), the shortest distance between the centers of the various beads (i.e., the position at which the minor axis and the major axis intersect in each bead) is B.

Generally speaking, it is desirable to have a heat exchange performance that is as large as possible and to minimize the passage resistance of the heat exchange passage 7 in the tube element. For example, if the bead size A increases, the passage resistance increases, and if the bead size A decreases, the passage resistance also decreases. However, if the bead size is excessively small, the heat exchange performance is correspondingly reduced. Also, when the bead pitch B is smaller, the number of beads becomes large, which increases the passage resistance, and when the bead pitch B becomes large, the number of beads becomes smaller, which correspondingly reduces the passage resistance but at the same time also reduces the heat exchange performance. Also, with the thickness of the tubular member 3, the smaller the thickness, the narrower the passage 7 for heat exchange medium, which increases the passage resistance, and the larger the thickness H, the smaller the passage resistance. Here, however, the heat exchange performance is again reduced because the passage through which air moves becomes smaller. In addition, when the thickness of the formed plate is made smaller, the passage 7 for heat exchange medium can be made wider, which improves the heat exchange performance. However, if the plate thickness is made too small, problems related to the strength and corrosion resistance properties arise. On the other hand, if the plate thickness is increased, the passage 7 for heat exchange medium becomes narrower, which increases the passage resistance. All this means that, except for the thickness of the formed plate, the relationship between the heat exchange performance and the volume resistance can be used as an index for evaluating the tubular element 3.

This evaluation can also be performed by assigning the heat exchange performance/volume resistance as the ordinate axis and each of the bead size, bead pitch and thickness of the tube member as the abscissa axis, and these are shown in Fig. 6. The index (heat exchange performance/volume resistance) is set to 100 when the bead size is 2.5 mm, the bead pitch is 4.8 mm and the thickness of the tube member is 2.4 mm.

Where bead size is concerned, the index becomes smaller if the size is either less or greater than 2.5 mm, as shown in Fig. 6 (a). However, since machining becomes more difficult as the beads are smaller and at the same time the performance deteriorates, it is necessary to ensure that A ≥ 2 mm. Also, it is noted that as the bead size is increased, the passage resistance also becomes larger, and if the bead size is increased to 3.8 mm, which is common in the prior art, a good index cannot be obtained. Consequently, the upper limit of the bead size is to be set by using an index equivalent to the lower limit of the bead size or using an index better than that, for example, at A ≤ 3.0 mm.

As for the bead pitch, as shown in Fig. 6(b), the index becomes smaller when the bead pitch is either smaller or larger than 4.8 mm. All in all, a good index is achieved in the pitch range of 3.5 mm to 6.3 mm. Since the smaller B is, the more difficult machining becomes and at the same time the passage resistance is greatly increased, it is necessary to set B to 3.5 mm or more. Preferably, it should be set to 3.8 mm or more to allow some tolerance in machining. Also, although the larger B becomes, the passage resistance becomes smaller, the heat exchange performance is also reduced. Therefore, by using an index equivalent to the lower limit (3.5 mm) of the bead pitch or an index better than that, the upper limit of the bead pitch is set to 6.3 or less. The upper limit of bead pitch is set at 5.8 or less by using an index equivalent to the lower limit (3.8 mm) of bead pitch or an index better than that.

Now, as shown in Fig. 6 (c), the index for the tubular element becomes smaller when the thickness H is set either smaller or larger than 2.4 mm. Since the smaller H is, the more difficult the machining becomes and the time, the performance is reduced, it is necessary to set H at 1.9 mm or more. Preferably, H should be set at 2.0 or more to allow for machining tolerance. It has also been found that the larger the thickness H is, the lower the volume resistance becomes and the heat exchange efficiency is also reduced. Therefore, using the index equivalent to the lower limit of the thickness or an index better than that, the upper limit is set at H ≤ 2.7 or preferably H ≤ 2.6.

As for the molded plate, as mentioned above, it is necessary to set the optimum plate thickness T by considering the relationship between the strength and corrosion resistance properties of the molded plate and the volume resistance. It is therefore necessary to set the lower limit at T ≥ 0.25 mm by considering the strength and corrosion resistance, and to set the upper limit at T ≤ 0.47 mm by considering the deterioration of the heat exchange performance caused by the increase in the volume resistance.

As a result, a tube element in which the above-agreed ranges are obtained will be the best possible tube element when considering and balancing the two requirements, i.e., an improvement in heat exchange efficiency and a reduction in passage resistance. Furthermore, when such factors as strength and the like are also taken into account, the tube element makes it possible to provide a more compact, lightweight heat exchanger compared with one employing the prior art tube elements.

Fig. 7 shows another example of the molded plate 4 (second embodiment) composing the tubular member 3.

Here, the beads 20 are formed in a plurality of bead rows that cross the direction in which the heat exchange medium passage is formed at a right angle, and the pitches at which the beads are arranged are different between bead rows that are adjacent to each other. In this embodiment, if 5 beads are provided on the surface at equal pitches L1 in row n, 3 beads are provided at equal pitches L2 in row n+1, 5 beads are provided at equal pitches L1 in row n+2, and three beads are provided at equal pitches L2 in row n+3, and so on. In short, bead rows in which beads are provided at equal pitches L1 and bead rows in which beads are arranged at equal pitches L2 are alternately formed. Further, each pitch L2 is twice the length of pitch L1.

All the beads in each bead row are arranged so as to interleave with the low pressure zones created behind the beads in the direction in which the fluid passage 7 is formed (in the vertical direction in the figure). In this embodiment they are arranged so that the bead closest to a given bead in an adjacent row is at an angle of 30 degrees from the given bead to the direction in which the passage for heat exchange medium is formed. As a result, a regular pattern of bead groups results when viewed in the direction of 30 degrees in which beads are arranged alternately at intervals a and intervals b.

The molded plate 4 constituting the tubular member 3 may take the structure shown in another embodiment (third embodiment) shown in Fig. 8, in which regions without beads 20 are provided at various locations in bead rows adjacent to each other, which determine the direction in which the passage 7 for heat exchange medium is formed at a right angle. Those portions in the bead rows adjacent to each other in which no beads are formed connect to form a passage 21 in which no beads are present in a direction different from the direction in which the heat exchange medium passage 7 is formed. In this embodiment, the portions in which no beads 20 are formed connect continuously in the direction which is at an angle of 30 degrees to the direction in which the heat exchange medium passage 7 is formed, in contrast to the prior art tube member in which beads are consistently formed.

As a result, in both the second and third embodiments, the number of beads located in areas of stagnant water is reduced, and areas where the passage resistance is small are created over the entirety of the heat exchange medium passage 7 without reducing the heat exchange efficiency. The distribution of the heat exchange medium to these areas with low passage resistance is promoted, thereby distributing the heat exchange medium over the entirety of the tube member and preventing stagnation. Moreover, by the very measure of reducing the number of beads, an improvement in the heat exchange efficiency can be achieved.

The applicant of this invention conducted the following tests to evaluate the tubular members having the bead arrangements described above in comparison with a tubular member in which beads are provided at a constant density.

The following tubular elements were tested: the tubular element of the type shown in Fig. 2, in which beads are provided with a consistent density (hereinafter referred to as type 1), the tube element in the second embodiment (hereinafter referred to as type 2), and the tube element in the third embodiment (hereinafter referred to as type 3). A heating plate 22 was placed over the entirety of one of the surfaces of the bulged portion 9 to form a passage. Then, adiabatic material 30 was laid over the entire structure, and an AC power source was connected to the heating plate 22 to evenly supply a consistent amount of heat to the tube element. Next, a specific amount of tap water was supplied to the tube element via a 500 mm long inlet pipe 23. The tap water flowed from one reservoir to the next through the heat exchange medium passage to be discharged from the outlet pipe 24. The tap water supplied via the inlet pipe 23 was monitored on a flow meter 25 and the flow rate of the tap water was set at 5 cc/s, 10 cc/s and 20 cc/s. The surface temperature of the tube elements at these various flow rates was measured. The results are shown in the thermographic diagrams in Figs. 10 to 12. Note that the values in Figs. 10 to 12 indicate temperature readings (degrees Celsius).

In addition, the flow rate of tap water was varied at 5 cm³/s, 10 cm³/s and 20 cm³/s, and a difference in water temperature (degrees Celsius) between the inlet and the outlet was measured at a temperature reader 28 from the thermocouple 26, 27 provided at the inlet and outlet of the molded plate 4 for each flow rate setting. The results are shown in Table 1. (Table 1)

The pressures at the inlet and outlet were also measured on the pressure gauge 33 through the static pressure inlet hole 31 formed in the inlet pipe 23 and the static pressure outlet hole 32 formed in the outlet pipe to determine the water flow resistance (mmHg) in the tube member 4. The results are shown in Table 2. (Table 2)

Furthermore, in order to determine the degree of inconsistency in heat exchange between the direction in which the heat exchange medium passage 7 is formed and the direction that crosses that direction at a right angle, the average value of the temperature differences (degrees Celsius) between the direction in which the fluid flows and the direction that crosses that direction at a right angle was measured with a group of thermocouples 29 provided at a plurality of specific locations (24 locations) on the surface of the tube member 4 (the surface on the side opposite to the side on which the heating plate is provided).

The results are shown in Table 3. (Table 3)

The temperature difference between the inlet and the outlet indicates that the greater the difference, the more actively the heat exchange is carried out, and our experiment shows that the temperature difference in Type 2 and Type 3 is slightly larger than in Type 1, although not significant. In Type 1, the temperature difference is larger at flow rates of 5 cm³/s and 20 cm³/s compared to Type 2.

As for the water flow resistance, it was larger at 5 cm³/s for both types 2 and 3 than for type 1, but it was smaller at 10 cm³/s and 20 cm³/s for both types 2 and 3. Therefore, considering that in an actual heat exchanger the flow rate is usually about 10 cm³/s, it can be concluded that types 2 and 3 have lower water flow resistance. It was also noted that the water flow resistance is lower for type 3 than for type 2.

It is desirable that the isotherm in Fig. 10 to 12 be horizontal (at right angles to the passage for heat exchange medium). In other words, it is desirable to minimize the temperature difference in Table 3, since this means that the heat exchange is carried out consistently. From this point of view, both Type 2 and 3 are superior to Type 1.

In summary, the data obtained by the tests indicate that the heat exchange properties of Type 2 and Type 3 are improved even though the number of beads in these types is less than in Type 1, and it can be safely said that in Type 2 and Type 3 tubular elements the number of beads in areas of standing water is reduced, thereby implementing bead arrangements that make it possible to distribute heat exchange medium more completely over the entire passage without stagnation than in Type 1.

All this leads to the conclusion that if the bead size A, the bead spacing B of adjacent beads that are closest to each other, the tubular element thickness H and the thickness T of the formed plate are set in the ranges 2.0 mm ≤ A ≤ 3.0 mm, 3.5 mm ≤ B ≤ 6.3 mm, 1.9 mm ≤ H ≤ 2.7 mm and 0.25 mm ≤ T ≤ 0.47 mm and the number of beads is reduced as shown in Fig. 7 or Fig. 8, although the beads in those areas where the number of beads is reduced are outside the dimensional ranges, the heat exchange properties are improved as proved in the tests described above, and an additional effect of this reduced number of beads further improves the heat exchange performance of the tube elements used in an evaporator. It is also to be noted that the present invention can be applied in a similar manner whether a reservoir section is formed as part of a tube element or as a separate unit and attached to the tube element.

Claims (9)

1. An evaporator (1) comprising a plurality of alternately layered tube elements (3) and fins (2), each tube element consisting of a pair of abutting shaped plates (4) and each tube element comprising: a passage section (9) having a first and a second end and a connecting wall (10) extending from the first end to a position adjacent to the second end to define a U-shaped passage with first and second passage legs on opposite sides of this connecting wall, respectively, and a connecting passage section connecting the first and second passage legs and located between the second end of the passage section and the position of the connecting wall adjacent to the second end of the passage section, first and second reservoir portions (5) provided at the first end of the passage portion and communicating with the first and second passage legs, respectively, the first and second reservoir portions being spaced apart from each other; wherein each of the shaped plates (4) has a plurality of beads (20) which project into the U-shaped passage, so that the beads which project from one of the shaped plates correspond to or touch the location of the beads projecting from the other shaped plate, and wherein these beads are arranged in a plurality of bead rows which extend perpendicular to the longitudinal direction of the passage legs, wherein the beads in the bead rows which are adjacent to one another are arranged so that a relative overlap in the longitudinal direction of the passage legs is avoided, characterized in that the width A of a base of each bead and the spacing B of the beads satisfy the relationships: 2.0 mm ≤ A ≤ 3.0 mm or 3.5 mm ≤ B ≤ 6.3 mm. 2. Evaporator according to claim 1, wherein the thickness H of the tube element and the plate thickness T of each of the shaped plates (4) satisfy the relationships: 1.9 mm ≤ H ≤ 2.7 mm or 0.25 mm ≤ T ≤ 0.47 mm. 3. Evaporator according to claim 1 or 2, wherein the beads (20) in each of the bead rows are arranged at equal intervals. 4. Evaporator according to claim 1 or 2, in which two rows of beads lying adjacent to one another in the longitudinal direction of the passage legs are located at different distances. 5. Evaporator according to one of claims 1 to 4 with sections which are not formed with the beads (20), and such sections in each two rows of beads lying adjacent to each other in the longitudinal direction of the passage legs are different from each other, with a section in one of the rows of beads and a section in another of the rows of beads being formed such that they partially overlap in the longitudinal direction. 6. Evaporator according to claim 5, wherein portions in which no beads (20) are provided form a continuum in a direction having an angle of 30° to the longitudinal direction. 7. Evaporator according to one of claims 1 to 4, in which rows of beads in which beads (20) with specific stands are provided, and bead rows in which beads (20) are provided with twice the specific pitch are alternately formed. 8. Evaporator according to one of claims 1 to 4, in which a bead (20) in a bead row closest to a given bead (20) in an adjacent row is arranged to form an angle of 30° with the given bead to the longitudinal direction. 9. Evaporator according to one of claims 1 to 8 with a coolant inlet (16) and a coolant outlet (16), in which a pair of reservoir groups consists of layered pairs of reservoir sections (5) of the tube element (3), wherein one reservoir group is divided into two reservoir subgroups by a blind reservoir (5a), another of the reservoir groups is provided with two reservoir subgroups in fluid communication with each other, wherein the one of the reservoir subgroups which is divided by the blind reservoir (5a) which is further away from the coolant inlet (16) and the coolant outlet (16) has a tube element with an extended reservoir (5b) which is connected to one of the coolant inlet and outlet (16) by a connecting pipe (15) which is provided between the pairs of reservoir sections (5) of the tube elements (3) between the coolant inlet and outlet (16) and the blind reservoir (5b), and wherein one of the coolant inlet and outlet (16), the connecting pipe (15), the extended reservoir (5b), the reservoir subgroup divided by the blind reservoir (5a) which is further away from the coolant inlet and outlet (16), passage sections (9) of the tube element (3) communicating with the reservoir subgroup which is further away from the coolant inlet and outlet (16), the two being in fluid communication with each other reservoir subgroups, with the reservoir subgroup closest to the coolant inlet and outlet (16) having passage sections (9) of the tube elements (3) in fluid communication, the reservoir subgroup closest to the coolant inlet and outlet (16) and another of the coolant inlet and outlet (16) being connected in fluid communication in series.