GB2284471A

GB2284471A - Flat condenser tube

Info

Publication number: GB2284471A
Application number: GB9324091A
Authority: GB
Inventors: Junji Sotani; Singoro Fukuoka; Katsuya Nagata; Masafumi Katsuta
Original assignee: Furukawa Electric Co Ltd; Waseda University
Current assignee: Furukawa Electric Co Ltd; Waseda University
Priority date: 1992-07-24
Filing date: 1993-11-23
Publication date: 1995-06-07
Anticipated expiration: 2013-11-23
Also published as: FR2694080A1; GB9324091D0; FR2694080B1; DE4325043A1; GB2284471B

Description

FLAT, POROUS CONDENSER TUBE This invention generally relates to a flat,

porous condenser tube, and more particularly, to a flat, porous condenser tube with a small diameter, which is suitable to be used for a small-sized heat exchanger (condenser) such as a car cooler and has a relatively small pressure loss and a high heat transfer performance.

A condenser shown in Fig. 18 has been proposed in, e.g., Japanese Patent Laid-open No. 62-175588 and its first US. Patent Application, namely, US. Pat. No. 4998580.

This condenser is provided with a pair of headers 8 and 9 facing to each other at a certain interval, a large number of flat, porous condenser tubes 7 communicating with the opposed side of the headers 8 and 9 and extending in parallel between the headers, and upper and lower parts 5 and 6 combined to the headers 8 and 9. A wave-formed radiation fin 70 is fixed between the mutually adjacent condenser tubes 7.

One header 8 acts as the supply side of vapor, and has one end provided with a vapor inlet 80 and the 2 other end closed by a cap 81.

The other header 9 acts as the exhaust side of a condensate, and has one end provided with a condensate outlet 90 for communicating with a conduit 92 and the other end closed by a cap 91.

In the internal portion of the flat, porous condenser tube 7 used in the above-mentioned condenser, a plurality of discrete refrigerant paths 72 respectively having an approximately triangular shape in cross section are formed in the length direction by inserting and fixing a wave-formed spacer 71 to the condenser tube, as shown in Fig. 19.

This sort of condenser has a far smaller heat transfer coefficient with the outside air around the radiation fins 70 in comparison with the condensation heat transfer coefficient of vapor in the condenser tube 7. Therefore, since the condenser tube 7 of the condenser relatively enlarges the heat radiative area of the radiation fins 70 by reducing the inflow sectional area of vapor in such a degree that the pressure loss within the refrigerant paths 72 might not become too large, the hydraulic diameter (what is defined by multiplying the sectional area of each of the refrigerant paths by 4 and then dividing this product by the wetted perimeter of the corresponding refrigerant path) of each refrigerant path 72 in the condenser tube 72 is set within the range of 0.015 to 0.040 inches (about 0.4 to 1.Omm).

When the hydraulic diameter of each refrigerant path is made small as described in the above-mentioned condenser tube 7, the heat radiative area of the radiation fins 70 is relatively enlarged to improve the heat transfer performance.

Recently, particularly in the field of smallsized heat exchangers such as a car cooler and the other, it is desirable, however, to improve such a condenser as is further of small size and has a heat transfer performance at a higher level. In order to cope with such a demand, the present inventors prepared various condenser tubes having refrigerant paths of 1. 0 mm or less in hydraulic diameter and then tested their heat transfer performance, similarly to the porous condenser tube 7 of the prior art described above. Then, it is understood that this condenser tube is not practical owing to its very large pressure loss, apart from its heat transfer performance.

In other words, the present inventors made various experiments with respect to flat condenser tubes having a large number of refrigerant paths of 1 mm or less in hydraulic diameter and have found the points to be improved in the following and achieved the present invention herein.

One of the points to be improved is the most important point, which is the following finding that the pressure loss in the refrigerant paths becomes smaller and at the same time. the heat transfer performance is further improved as well by removing part of the spacer for spacing the mutually adjacent refrigerant paths, increasing the width of each refrigerant path more than the internal height by a certain height and forming projections continuously extending in the length direction, instead of the removed spacer part described above.

Another point is the following finding that the heat transfer performance of the condenser tube gets at a higher level when the ratio of the height of each projection to the height of the internal portion of each refrigerant path is within a certain range.

A further point is the following finding that the heat transfer performance of the condenser tube gets at a further higher level when the groove adjacent to each projection has a smooth bottom surface (preferably, when the shape of the groove is an invert trapezoid).

A still further point is the following finding. that the heat transfer performance gets at a still further higher level when the pitch between the projections formed in the refrigerant path is within a certain range.

It would therefore be desirable to be able,to provide a flat, porous condenser tube which has a far smaller pressure loss in a refrigerant path in comparison with the flat, porous condenser tube of the prior art described above and enables its heat transfer performance to be further improved.

It would also be desirable to be able to provide a flat, porous condenser tube which achieves much more miniaturization of a small-sized condenser such as a car cooler and the other.

The present invention provides a flat, porous condenser tube, comprising a plurality of discrete refrigerant paths extending in parallel in the width direction and continuous in the length direction; wherein the external height of the condenser tube is set to be not more than 2 mm; the internal height of each refrigerant path is set to be not more than 1. 2 mm; the ratio of the width of each refrigerant path to the internal height thereof is set within the range of 1.8 to 6.0; a plurality of projections continuously extending in the length direction are provided in each refrigerant path; a groove adjacent to each projection has a smooth bottom; and the ratio of the projection height to the internal height of each refrigerant path is set within - 6 the range of 0.055 to 0.25.

It is preferable that the pitch of the projections is within the range of 0.25 to 0.6 mm in the flat, porous condenser tube of the present invention.

It is preferable that each groove between the mutually adjacent projections is formed in an approximately inverse trapezoid in cross section by forming the sectional shape of each projection, for example, in a triangle.

It is also preferable that the hydraulic diameter of the refrigerant path is within the range of 0.7 to 1.5 mm.

Further, each projection may be formed on both or either surface (the upper or lower surface when in use) of each refrigerant path in the width direction.

The flat, porous condenser tube according to the present invention is utilized by incorporating the condenser tube into a condenser in such a state that the condenser tube is placed to be long sideways.

In comparison with the prior art flat, porous condenser tube described above, the condenser tube of the present invention is constituted such that the width of each refrigerant path is larger than the height thereof, the projections extending in the length direction are provided each refrigerant path and each groove adjacent to the projections has a smooth bottom. Therefore, any refrigerant vapor brought into contact with the surfaces of the projections is efficiently condensed and the condensed refrigerant moves more promptly along the grooves in a certain direction.

Thus, the pressure loss within the tube is relatively small and the heat transfer performance is further improved.

Furthermore, the reason why the external height (total thickness) of the condenser tube of the present invention is set to be not more than 2 mm and the internal height of the refrigerant path is set to be not more than 1.2 mm is as follows. Namely, when the external and internal heights described above are not less than these values, the surface area proportion of the radiation fins mounted on the surface of the condenser tube becomes relatively small to the heat transfer area of the refrigerant path, so that the heat transfer performance of the heat exchanger is lowered, and the heat exchanger cannot be miniaturized.

In addition,- the reason why the ratio of the internal width to the internal height of each refrigerant path is set within the range of 1.8 to 6.0 is as follows. Namely, when the ratio described above is set to be not more than 1.8, the pressure loss of the refrigerant path is enlarged, whereas when the ratio described above is set to be not less than 6.0, the withstanding pressure of the condenser tube against the internal pressure when the refrigerant passes through the internal portion is remarkably lowered.

In accordance with the flat, porous condenser tube of the present invention, it is possible to provide the condenser tube, in which the pressure loss of the refrigerant path is relatively small and the heat transfer performance at a high level can be exerted, while much more miniaturized condenser can be prepared.

The foregoing and other objects and features of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which:

Fig. 1 is an enlarged sectional view showing a condenser tube as a first preferred embodiment of the present invention; Fig. 2 is an enlarged sectional view showing a projection within a refrigerant path in the condenser tube of Fig. 1; Fig. 3 is a fragmentary enlarged sectional view showing a condenser tube as a second preferred embodiment of the present invention; Fig. 4 is an enlarged sectional view showing a projection within a refrigerant path in the condenser tube of Fig. 3; Fig. 5 is an enlarged sectional view showing a modification of a projection within a refrigerant path; Fig. 6 is a fragmentary enlarged sectional view showing a condenser tube as a fifth preferred embodiment of the present invention; Fig. 7 is a fragmentary enlarged sectional view showing a condenser tube as a sixth preferred embodiment of the present invention; Fig. 8 is a fragmentary enlarged sectional view showing a condenser tube as a seventh preferred embodiment of the present invention; Fig. 9 is a fragmentary enlarged sectional view showing a condenser tube as an eight preferred embodiment of the present invention; Fig. 10 is a fragmentary enlarged sectional view showing a condenser tube as a ninth preferred embodiment of the present invention; Fig. 11 is an enlarged sectional view showing another modification of the projection within the refrigerant path; Fig. 12 is a fragmentary enlarged sectional view showing a comparative to the condenser tube as the preferred embodiment of the present invention; Fig. 13 is a fragmentary enlarged sectional view showing another comparative to the condenser tube as the preferred embodiment of the present invention; Fig. 14 is a bar graph showing the comparison in inside heat transfer rate among the condenser tubes as the preferred embodiments (in part) of the present invention and the condenser tubes as the comparatives of Figs. 12 and 13; Fig. 15 is a bar graph showing the comparison in pressure loss ratio among the condenser tubes as the preferred embodiment (in part) of the present invention and the condenser tubes as the comparatives of Figs. 12 and 13; Fig. 16 is a bar graph showing a relation between the projection pitch and the inside heat transfer rate in the condenser tube as a preferred embodiment of the present invention; Fig. 17 is a line graph showing a relation between the projection height and the inside heat transfer rate in condenser tube as a preferred embodiment of the present invention; Fig. 18 is a fragmentary exploded, perspective view showing a condenser using a prior art flat, porous condenser tube; and

Fig. 19 is an enlarged sectional view showing the flat, porous condenser tube in the condenser of Fig. 18.

Embodiment 1 A condenser tube 1 as a first preferred embodiment shown in Fig. 1 is a flat tube made of an aluminum alloy and prepared by means of conformal extrusion (precision extrusion).

The condenser tube 1 has discrete refrigerant paths 10 and 11 which have the internal width wl larger than the internal height hl and are formed so as to respectively extend in parallel in the width direction through spacers 14 and to be continuous in the length direction.

A large number of projections 12 are formed on the upper and lower surfaces of each of the refrigerant paths 10 and 11 at an approximately uniform pitch, respectively.

Since the sectional shape of each projection 12 is an approximate triangle as shown in Fig. 2, each groove 13 between the mutually adjacent projections 12 has an approximate inverse trapezoidal shape. Therefore, each groove 13 has a smooth bottom.

The dimension of the condenser tube 1 shown in Fig. 1 is as follows: Length: 850 mm Width w: 17 mm External height h: 1.8 mm Thickness t: 0.45 mm Width wl of the refrigerant path 10 in the central portion: 3.87 mm Internal width wl of the refrigerant path 11 on both sides: 3.755 mm Internal height hl of each of the refrigerant paths 10 and ll: 0.9 mm Thickness tl of each spacer 14: 0.25 mm Height h2 of each projection 12: 0.15 mm Width w2 of each projection 12: 0.15 mm P.f.tch p of each projection 12: 0.48 mm Width w3 of the smooth bottom of each groove 13: 0. 33 mm Ratio of the width wl to the internal height hl of the refrigerant path 10: 4.3 Ratio of the width wl to the internal height hl of the refrigerant path ll: nearly 4.2 Ratio of the height h2 of each projection 12 to the internal height hl: nearly 0.17 Hydraulic diameter of the refrigerant path 10: nearly 1.06 mm Hydraulic diameter of the refrigerant path ll: nearly 1.14 mm Apex angle 9 of each projection 12 (refer to Fig. 2): approximately 540 The condenser tube in this preferred embodiment is defined as Sample No. 1 in Performance Test 1, which will be described later.

In accordance with the condenser tube in the preferred embodiment, when used by incorporating the condenser tube into the condenser as shown in Fig. 18, the refrigerant vapor flown in a certain direction within the refrigerant paths 10 and 11 is brought into contact with the surface of each projection 12 and condensed efficiently as shown in Fig. 2. A condensate 4 promptly moves along each groove 13 in a certain direction in such a condition as shown in Fig. 2. Embodiment 2 A condenser tube 1 as a second preferred embodiment shown in Figs. 3 and 4 in prepared by using the same material and process with those of the condenser tube in Embodiment 1. The top portion of each internal projection 12a in each of the refrigerant paths 10 and 11 is formed in a circular arch shape having a radius R of 0.1 mm as shown in Fig. 4.

Each dimension of this condenser tube is in the following, and each dimension of the portion not described in the following is same with that of the condenser tube in Embodiment 1. Width w2 of each projection 12a: 0. 25 mm Pitch p of each projection 12a: 1.03 mm Width w3 of the smooth bottom of each groove 13: 0.78 mm Hydraulic diameter of each of the refrigerant paths 10 and ll: nearly 1.21 mm The condenser tube of this preferred embodiment is defined as Sample No. 2 in Performance Test 1, which will be described later. Embodiment 3 Instead of each projection 12a of the condenser tube 1 shown in Fig. 3, a condenser tube having a projection 12b in a square form in cross section (height h2: 0.15 mm and width w2: 0.25 mm) within the refrigerant paths as shown in Fig. 5 is prepared.

This condenser tube is defined as Sample No. 3 in Performance Test 1, which will be described later.

In the condenser tube of Sample No. 3, the hydraulic diameter of the refrigerant path is 1.24 mm and each dimension of other portions in this condenser tube is same with that of the condenser tube in Embodiment 2. Embodiment 4 Instead of each projection 12a of the condenser tube 1 shown in Fig. 3, a condenser tube having a projection 12 in a triangular shape in cross section (height h2: 0.15 mm and width w2: 0. 15 mm) within the refrigerant path as shown in Fig. 2 is prepared. This condenser tube is defined as Sample No. 4 in Performance Test 1, which will be described later.

In the condenser tube of Sample No. 4, the hydraulic diameter of the refrigerant path is 1.28 mm and each dimension of other portions in this condenser tube is same with that of the condenser tube in Embodiment 2. Embodiment 5 A condenser tube 1 as a fifth preferred embodiment shown in Fig. 6 is made by forming each projection 12a in the same shape in cross section as that in Fig. 4 only on one width surface (the width surface of the upper portion when in use) of each of the refrigerant paths 10 and 11. The other width surface of each of the refrigerant paths 10 and 11 is smooth.

The condenser tube 1 in this preferred embodiment is prepared by using the same material and process with those of the condenser tube in Embodiment 1. The hydraulic diameter of each of the refrigerant paths 10 and 11 is nearly 1.33 mm and each dimension of other portions is same with that of the condenser tube in Embodiment 2.

The condenser tube in this preferred embodiment is defined as Sample No. 5 in Performance Test, which will be described later. Embodiment 6 A condenser tube 1 as a sixth preferred embodiment shown in Fig. 7 is prepared by forming eight parallel refrigerant paths 10 and 11 through spacers 14. Each projection 12a in a sectional form in similar to that in Fig. 4 is formed at the center of both width surface of each of the refrigerant paths 10 and 11. This condenser tube 1 has a structure in which every other spacer 14 of a condenser tube 3, which will be described later in Fig. 13, is substituted with each projection 12a.

The condenser tube 1 in this preferred embodiment is prepared by using the same material"and process as those in the condenser tube in Embodiment 1. Each dimension of the condenser tube is in the following, and each dimension of the portions not described in the following is same with that of the condenser tube in Embodiment 2. Width wl of each of the refrigerant paths 10 and ll: 1.81 Hydraulic diameter of each of the refrigerant paths 10 and 11: nearly 1. 07 Ratio of path width wl to internal height hl: nearly 2.0 The condenser tube in this preferred embodiment is defined as Sample No. 6 in Performance Test, which will be described later. Comparative 1 A condenser tube 2 shown in Fig. 12 is a condenser tube as a comparative for comparing it with the condenser tube 1 in each preferred embodiment described above. This condenser tube 2 is defined as Sample No. 7 in Performance Test 1, which will be described later.

In this condenser tube 2, eight refrigerant paths 20 are formed through vertical spacers 14 so as to extend in parallel in the width direction, and any projection is not formed in each refrigerant path 20. In each refrigerant path 20, the hydraulic diameter is nearly equal to 1.20 mm, and each dimension of other portions in this condenser tube 2 is same with that in the condenser tube shown in Fig. 7. Comparative 2 A condenser tube 3 shown in Fig. 13 is a condenser tube as a comparative for comparing it with the condenser tube 1 in each preferred embodiment described above. This condenser tube 3 is defined as Sample No. 8 in Performance Test 1, which will be described later.

In this condenser tube 3, sixteen refrigerant paths 30 are formed through spacers 14 so as to extend in parallel in the width direction, and any projection is not formed in each refrigerant pati 30. In this condenser tube 3, the width wl of each refrigerant path 30 is 0.78, the hydraulic diameter of each refrigerant path 30 is 0.84 mm (this value is within the range of the condenser tube disclosed in Japanese Pat. Laid-open No. 62175588), and the ratio of the path width wl to the internal height hl is nearly equal to 0.87. Each dimension of other portions in this condenser tube 3 is same with that in the condenser tube shown in Fig. 7. Performance Test 1 The following Samples Nos. 1: to 8 of flat, porous condenser tubes were prepared by using an aluminum alloy and following the process of conformal hot extrusion. The average inside heat transfer rate and the pressure loss were measured with respect to Sample Nos. 1 to 8 under the condition that the vapor inflow temperature and the outside temperature are kept at 40C and 3CC, respectively. The results thus obtained are shown in Figs. 14 and 15.

Fig. 10 shows the pressure loss ratio in case where the pressure loss of the condenser tube 3 as Sample No. 8 is assumed to be unity.

According to the results from Fig. 14, the condenser tube of Sample No. 8 prepared by the similar process to that of the prior art condenser tube is much more excellent than the condenser tube of Sample No. 7, in which the hydraulic diameter of the refrigerant path is approximately 1.20 mm, from the viewpoint of its heat transfer performance.

The condenser tube 3 of Sample No. 8 is, however, inferior in heat transfer performance to that of Sample No. 6 (Embodiment 6), in which every other spacer 14 of all the spacers 14 of this condenser tube 3 is substituted with each projection 12a. Further, the difference in heat transfer performance of the condenser tube of Sample No. 8 from the condenser tubes of Sample Nos. 1 through 5 is far larger.

According to the results from Fig. 15, the condenser tube of Sample No. 6 is slightly inferior in pressure loss to that of Sample No. 7, but it is far more excellent than that of Sample No. 8. In particular, the pressure loss in each of the condenser tubes of Sample Nos. 1 to 5 is far smaller than that of the condenser tube of Sample No. 8.

According to the results from Performance Test 1, it has become clear that the object for further improving the thermal performance without increasing the pressure loss can be attained much more by forming small projections on the internal wall surface of each refrigerant path having the width larger than the internal height like the condenser tube in the preferred embodiments of the present invention as described above, but not by decreasing the hydraulic diameter of the refrigerant path in the condenser tube.

In particular, the condenser tube of Sample No. 1 is far more excellent than that of Sample No. 8 in both pressure loss and heat transfer rate. Performance Test 2 A condenser tube made of an aluminum alloy was prepared by means of conformed hot extrusion. In this condenser tube,-the width w, the length, the external height h, and the internal height hl and width wl of each of the refrigerant paths 10 and 11 are all same with those of the condenser tube in Embodiment 1 (refer to Fig. 1), the sectional shape and dimension of each projection are all same with those show in Figs. 2, 4 and 5, and the projection pitch p is within in the range of 0.2 to 1.94 mm. With respect to the resulting sample products, their average inside heat transfer - 20 rates were measured in the similar manner to that in Performance Test 1.

The results thus obtained are shown in Fig. 16. In Fig. 16, the condenser tube having each projection in a triangle shape in cross section (refer to Fig. 2) is shown by solid lines, the condenser tube having each projection in a square shape in cross section (refer to Fig. 5) is shown by one-dotted chain lines, and the condenser tube having each projection in a circular arc in cross section at its top portion (refer to Fig. 4) is shown by two-dotted chain lines, respectively.

Incidentally, in each of these condenser tubes, any of the hydraulic diameter of the refrigerant path is within the range of 0.7 to 1.5.

Furthermore, any of the pressure loss of each of these condenser tubes is within the range of 0.55 to 0.6, in case where the pressure loss of the condenser tube of Sample No. 8 described above is defined as unity.

According to this Performance Test 2, it has become clear that the condenser tube having each projection pitch p within the range of approximately 0.25 to 0.6 mm has a relatively small pressure loss in the refrigerant path and exerts a heat transfer performance at a high level.

According to experiments, it is most preferable that each projection within the refrigerant path in the condenser tube has the apex angle of 300 to 600 Performance Test 3 A condenser tube made of an aluminum alloy was operated by means of conformal hot extrusion. In this condenser tube, the width w, the length, the external height h, and the internal height hl and width wl of each of the refrigerant paths 10 and 11 are all same with those of the condenser tube in Embodiment 1 (refer to Fig. 1), the cross-sectional shape and dimension of each projection are all same with those shown in Fig. 2 (the cross section of each projection is a triangle, the height of the triangle is same with its base), and the projection height is zero or within the range of 0.05 to 0.3 mm (the ratio of the projection height h2 to the internal height hl of the refrigerant path is equal to zero or within the range of 0.055 to 0.33).

With respect to these sample products, the average inside that transfer rate was measured in the similar manner to that in the case of Performance Test 1.

The results thus obtained are shown in Fig. 17.

In each of these condenser tubes, any of the hydraulic diameter of each refrigerant path is within the range of 0.7 to 1.5.

According to this Performance Test 3, it has become clear that any condenser tube having the ratio of the projection height h2 to the internal height hl of the refrigerant path within the range of 0.055 to 0.25 has a relatively small pressure loss and exerts its heat transfer performance at a higher level.

Furthermore, the pressure loss of the condenser tube, in which the ratio of the internal height hl of the refrigerant path to each projection height h2 is within the range of 0.055 to 0.25, was within the range of 0.55 to- 0.7 in case of assuming the pressure loss of the condenser tube of Sample No. 8 described above is unity.

Other Preferred Embodiments In the condenser tubes according to the present invention, the projections 12 (12a and 12b) of the upper and lower width surfaces of the refrigerant path 10 (11) can be constituted so as to be located alternally in the horizontal direction. In other words, the condenser tube 1 in Embodiment 7 is in such a condition that each projection 12 formed on the upper width surface of the refrigerant path 10(11) and each projection 12 formed on the lower width surface of the refrigerant path 10(11) do not face to each other on the same horizontal plane.

In the condenser tube 1 in Embodiment 7, the number of projections on the upper width surface of the refrigerant path 10(11) is different from that of projection on the lower width surface thereof. However, the number of projections on the upper width surface of the refrigerant path 10(11) when in use is preferably more than the number projections on lower the width surface thereof.

In the condenser tube of the present invention, the projections 12 (12a and 12b) are formed on the upper and lower width surface within each of the refrigerant paths 10 and 11 of the condenser tube 1, and otherwise, the projections 12 (12a and 12b) can be formed on the internal wall surface of the spacer 14 or the side portion, similarly to the condenser tube 1 in Embodiment 8 shown in Fig. 9.

Furthermore, similarly to the condenser tube in Embodiment 9 shown in Fig. 10, the condenser tube of the present invention can be constituted so that the groove 13 adjacent to the spacer 14 is formed in an inverse trapezoid in cross section by molding each projection 12 within the condenser tube 1 in a triangle in cross section and also molding the base of the spacer 14 in a form of taper.

In the condenser tube 1 of each preferred embodiment described above, each projection 12c may be formed in a trapezoid in cross section, as shown in Fig. 11 as well.

Claims

Claims: A flat, porous condenser tube, comprising: a plurality of discrete

refrigerant paths (10, 11) extending in parallel in the width direction and continuing in the length direction; wherein the external height (h) of said condenser tube (1) is set to be not more than 2 mm; the internal height (hl) of each of said refrigerant paths (10, 11) is set to be not more than 1.2 mm; the ratio of the width (wl) of each of said refrigerant paths to the internal height (M) thereof is set to be within the range of 1.8 to 6.0; a plurality of projections (12; 12a; 12b; 12c) continuously extending in the length direction are provided in each of said refrigerant paths (10, 11); a groove (13) adjacent to said projections has a smooth bottom; and the ratio of the height (h2) of each of said projections (12; 12a; 12b; 12c) to the internal height (hl) of each of said refrigerant paths is within the range from 0.055 to 0.25.
2. A flat, porous condenser tube according to claim 1, wherein the pitch (p) of said projections is within the range_ from 0.25 to 0.6 mm.
3. A flat, porous condenser tube according to claim 1 or 2, wherein the sectional shape of the groove (13) between said projections (12; 12a; 12b; 12c) is an inverse trapezoid.
4. A flat, porous condenser tube according to claim 3, wherein the sectional shape of each of said projections (12; 12a; 12b; 12c) is an approximate triangle.
5. A flat, porous condenser tube according to any one of claims 1 to 4, wherein the hydraulic diameter of each of said refrigerant paths is within the rangefrom 0.7 to 1.5 mm.
6. A flat, porous condenser tube substantially as described with reference to any of the embodiments illustrated in Figures 1 to 11 of the accompanying drawings-
7. A heat exchanger including a plurality of condehser tubes in accordance with any preceding claim.