AU2001244740B2

AU2001244740B2 - Heating tube with inner surface grooves

Info

Publication number: AU2001244740B2
Application number: AU2001244740A
Authority: AU
Inventors: Kanji Akai; Hirokazu Fujino; Kazushige Kasai
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2000-04-07
Filing date: 2001-04-06
Publication date: 2005-02-17
Anticipated expiration: 2021-04-06
Also published as: CN1436293A; JP2001289586A; AU4474001A; CN1253686C; EP1271087A4; WO2001077601A1; EP1271087A1

Description

tt 1 CKHEATING TUBE WITH INNER SURFACE GROOVES TECHNICAL FIELD The present invention relates to inner grooved heat transfer tubes for use in heat exchangers.

More specifically, the invention relates to specific structures of the internal groove.

BACKGROUND ART There is a conventional heat exchanger serving as an evaporator or as a condenser in a C refrigerating apparatus such as an air conditioner. Such a heat exchanger employs for example an inner grooved heat transfer tube comprising an inner surface in which are formed a large number of helical line grooves. By virtue of these helical line grooves, the area of heat transfer of the inner grooved heat transfer tube is increased and, besides, the performance of heat transfer is upgraded by causing refrigerant to flow in the tube while forming an even and thin film of liquid.

However, if, when an inner grooved heat transfer tube of the above-described type is used in a condenser, the action of condensation makes progress as refrigerant flows forward from inlet port to outlet port in the tube, the refrigerant becomes an annular flow. This causes a layer of liquid refrigerant flowing along the tube inner surface to become thicker toward the downstream side. This increases thermal resistance, therefore reducing the performance of condensation.

To cope with such a problem, the Applicant made a proposal (see Japanese Patent Kokai No.

H10-153360). The proposal discloses an inner grooved heat transfer tube capable of suppressing the decrement in condensation performance. In the inner grooved heat transfer tube, each line groove comprises a main groove of a first lead angle and a non-aligned portion of a second lead angle different from the first lead angle which are successively formed, and refrigerant is made to flow along the main groove while forming a thin film of liquid. When arriving at the non-aligned portion, the liquid refrigerant comes into collision with a groove side surface of the non-aligned portion and is scattered toward the center of the heat transfer tube. In accordance with such a configuration, since a thick layer of liquid refrigerant is less likely to be formed on the internal surface of the heat transfer tube, this accelerates the liquefaction of gas refrigerant.

m:\specifications\1 00000\112412spcmjca25.doc However, if the ratio of the non-aligned portion to the main groove is too small in the inner grooved heat transfer tube of the above described configuration, then the effect of causing liquid refrigerant to be scattered at the non-aligned portion is hardly obtained. Consequently, there is no improvement in heat transfer performance. On the other hand, if the ratio of the nonaligned portion to the main groove is too large, this produces the problem of increasing the loss of pressure, particularly when used as an evaporator. As described above, in the abovementioned conventional inner grooved heat transfer tube, it is intended to secure the performance of condensation by providing non-aligned portions in a part of the line groove.

However, the performance of heat transfer and the loss of pressure vary greatly, depending on the configuration of a non-aligned portion, therefore producing the problem that it is difficult to stabilize the performance of heat exchange when used as a heat exchanger.

Bearing in mind the above-described problems, the present invention was made. It is therefore desirable that the present invention make it possible to make the performance of heat exchange much steadier than conventional by specifying concrete configurations about the main groove and non-aligned portion of the line groove in the inner grooved heat transfer tube.

SUMMARY OF THE INVENTION According to one aspect, the present invention provides an inner grooved heat transfer tube in which a plurality of line grooves are formed in an inner peripheral surface of an electric welded tube and said line groove is made up of main grooves formed at a first lead angle and nonaligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein a joint portion of said electric welded tube and said non-aligned portion are arranged at respective locations substantially equally dividing the direction of the circumference of said electric welded tube.

In another aspect, the present invention provides an inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and m:\specifications\1 00000\112412spcmjca25.doc said secondary groove is formed centrally in said convexity of said main groove so as to be spaced a predetermined distance apart from said non-aligned portion.

In a further aspect, the present invention provides an inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and said secondary groove is formed to a depth of 0.25 to 0.75 times the depth of said line groove.

In yet a further aspect, the present invention provides an inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and said secondary groove is formed substantially along the tube axis directional line.

In embodiments of the invention a plurality of line grooves are formed in an inner peripheral surface of the heat transfer tube and the line groove comprises main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle differing from the first lead angle which are successively formed, wherein the main groove and the nonaligned portion of the line groove are set to predetermined relationships specified as follows.

Preferably the percentage of the length of the non-aligned portion to the length of a single round of the line groove is so set as to fall in the range of 10 to 35% in the configuration as set forth above.

In embodiments of the invention the length of the non-aligned portion is so set as to fall in the range of five to fifteen times the pitch of the line groove.

m:\specifications\1 00000\1 12412spcmjca25.doc Furthermore, the from five to fifteen non-aligned portions maybe so arranged as to intersect an extension of a single main groove.

Further, in embodiments of the invention, the joint portion of an electric welded tube and the non-aligned portion are arranged at respective locations substantially equally dividing the direction of the circumference of the electric welded tube. By an "electric welded tube" is meant, in general, a tube formed by connecting a long strip-shaped material by electric resistance welding. However, in the Specification such an electric welded tube is taken in the wide sense. Therefore, the electric welded tube includes any type of tube connected along the longitudinal direction by any connecting technique.

Preferably the non-aligned portion is formed at a plurality of positions in a single round of the line groove.

Preferably the first lead angle and the second lead angle is so set as to fall in the range of to 30 degrees in one torsional direction with respect to a tube axis directional line whereas the other of the first lead angle and the second lead angle (13) is so set as to fall in the range of to 30 degrees in the other torsional direction with respect to the tube axis directional line.

Furthermore the first lead angle and the second lead angle (13) are set in such a way that the main groove and the non-aligned portion of the line groove maybe symmetrically directed with respect to the tube axis directional line.

With this embodiment, it is preferable that the first lead angle and the second lead angle (13) are specified. More preferably, the first lead angle and the second lead angle (13) are each set at 18 degrees in opposite directions with respect to the tube axis directional line.

Furthermore, in embodiments of the invention, the secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming the main groove.

With this embodiment, it is preferable that the secondary groove is centrally formed in the convexity of the main groove so that the secondary groove is spaced a predetermined distance apart from the non-aligned portion.

It is preferable with this embodiment that the secondary groove is formed to a depth of 0.25 to 0.75 times the depth of the line groove.

m:\specifications\1 00000\112412spcmjca25.doc Preferably the secondary groove is formed substantially along the tube axis directional line.

Furthermore, in embodiments of the invention in which the plurality of line grooves are formed in an inner peripheral surface of the heat transfer tube and the line groove comprises main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle differing from the first lead angle which are successively formed.

Further, in embodiments of the invention the secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming the main groove and the secondary groove is centrally formed in the convexity of the main groove so as to be separated a predetermined distance apart from the non-aligned portion.

Further, in embodiments of the invention in which a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming the main groove and the secondary groove is formed to a depth which is from 0.25 to 0.75 times the depth of the line groove.

Further, in embodiments of the invention, in which a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming the main groove and the secondary groove is formed substantially along the tube axis directional line.

It is desirable that the present invention is used in a condenser, refrigerant in the heat transfer tube condenses from a gas phase, changes to a thin film of liquid, and flows in the line groove.

Upon arriving at the non-aligned portion, the refrigerant comes into collision with a side surface of the non-aligned portion and is scattered in the direction of the center of the heat transfer tube because the first lead angle of the main groove differs from the second lead angle of the non-aligned portion. Accordingly, thick layers of liquid are less likely to be formed on the inner surface of the heat transfer tube, thereby preventing the occurrence of an annular flow.

Preferably the percentage of the length of the non-aligned portion to the length of a single round of the line groove is so set as to fall in the range of 10 to 35%. If the percentage is less than 10%, liquid refrigerant is not scattered readily even when the non-aligned portion is provided. However, the aforesaid setting provides a sufficient scattering action. On the other hand, if the percentage is greater than 35%, this increases the loss of pressure when used particularly in an evaporator. However, the aforesaid range suppresses the loss of pressure.

m:\specifications\100000\1 12412spcmjca25.doc Preferably the length of each non-aligned portion is so set as to fall in the range of five to fifteen times the pitch of the line groove. As a result of such arrangement, liquid refrigerant flowing in the main groove of the line groove moves forward while climbing over a plurality of non-aligned portions, during which the liquid refrigerant is scattered sufficiently. If the aforesaid value is less than five times the pitch of the line groove, the liquid refrigerant is not scattered readily even when the non-aligned portion is provided. However, the aforesaid setting provides a sufficient scattering action. On the other hand, if the value is greater than fifteen times the pitch of the line groove, this increases the loss of pressure when used particularly in an evaporator. However, the aforesaid setting suppresses the loss of pressure.

In embodiments of the invention the liquid refrigerant flowing in the main groove is sufficiently scattered when climbing over a plurality of non-aligned portions (five to fifteen non-aligned portions). Accordingly, it is possible to secure a refrigerant scattering action when used in a condenser and to suppress the loss of pressure when used in an evaporator.

It is preferable that the joint portion of the electric welded tube and the non-aligned portion are arranged at respective locations substantially equally dividing the direction of the circumference of the electric welded tube. As a result of such arrangement, the liquid refrigerant flowing in the main groove of the line groove is evenly scattered at the joint portion and the non-aligned portion in the heat transfer tube. As described above, the action of scattering liquid refrigerant is obtained throughout the entire inner surface of the heat transfer tube and the arrangement that the non-aligned portion and the joint portion are disposed in a scattering manner suppresses the loss of pressure when used in an evaporator.

In the embodiments where the non-aligned portion is formed at multiple positions in a single round of the line groove the action of scattering liquid refrigerant can be obtained at each non-aligned portion. This further ensures that the liquid layer is prevented from growing thicker.

Furthermore, in the embodiments where the first lead angle and the second lead angle (P) are so set as to fall in the range of 5 to 30 degrees in opposite torsional directions respectively with respect to the tube axis directional line, (particularly if these angles are set at 18 degrees), the refrigerant flows in a helical direction by the main groove and efficiently forms an even and thin layer of liquid and, at the same time, the action of scattering by the non-aligned portion is obtained reliably.

m:\specifications\1 00000\1 12412spcmjca25.doc Further, in the embodiments where the secondary groove is provided in the convexity which forms the main groove, this means that a plurality of spaced recessed portions are defined in the convexity. As a result, the area of heat transfer increases. Further, the provision of the secondary groove reduces the loss of pressure because while producing a helical flow by a main groove a part of the refrigerant is caused to flow into the next main groove by the secondary groove.

Further, if the secondary groove is formed centrally in the convexity of the main groove so that the secondary groove is spaced a predetermined distance apart from the non-aligned portion, this ensures a helical flow action by the main groove. In other words, if the secondary groove is formed in close proximity to the non-aligned portion, this causes refrigerant to escape from the secondary groove, and helical flows are less likely to occur. The above-mentioned configuration is free from such a danger.

Further, if the depth of the secondary groove is less than 0.25 times the depth of the line groove, the area of heat transfer will not increase as expected. On the other hand, if the depth of the secondary groove is more than 0.75 times the depth of the line groove, this will cause the refrigerant to readily escape from the secondary groove thereby preventing a helical flow from being produced. However, if made to fall in the range of 0.25 to 0.75 times the depth of the line groove, this makes it possible to produce a helical flow while increasing the area of heat transfer.

Furthermore, if the secondary groove is formed substantially along the tube axis directional line, this makes it possible to suppress the loss of pressure while increasing the area of heat transfer because the flow of refrigerant becomes relatively less disturbed in the main groove.

Further, in some embodiments the secondary groove is formed in the convexity which forms the main groove. Accordingly, it is possible to reduce the loss of pressure while increasing the area of heat transfer.

In accordance with the embodiments of the invention, the percentage of the length of the nonaligned portion to the length of a single round of the line groove is so set as to fall within the range between 10% and 35%. This provides a sufficient scattering action by the non-aligned portion when used in a condenser and reduces the loss of pressure when used in an evaporator.

In other words, if it is intended to obtain only a refrigerant scattering action in the condenser, it m:\specifications\1 00000\1 12412spcmjca25.doc is sufficient for the inner surface of the heat transfer tube to be formed into an irregular convexconcave shape. In such a case, however, the loss of pressure in the evaporator will increase. On the other hand, if the percentage is so set as to fall within the above-mentioned range, this makes it possible to maintain well-balanced relationships between the action of scattering refrigerant and the loss of pressure.

Further, in embodiments of the invention, the length of a single non-aligned portion is so set as to fall within the range between five times and fifteen times the pitch of the line groove, and liquid refrigerant flowing in a main groove of the line groove moves forward while climbing over a plurality of non-aligned portions, during which the liquid refrigerant is scattered sufficiently. Additionally, the relationship between the length of the non-aligned portion and the pitch of the line groove is not set greater than necessary but within the above-described range, thereby making it possible to suppress the loss of pressure while achieving a sufficient liquid refrigerant scattering action.

Furthermore, in embodiments of the invention, five to fifteen non-aligned portions are so arranged as to intersect a main groove. As a result of such arrangement, liquid refrigerant flowing in the main groove is scattered sufficiently at the time of climbing over a plurality of non-aligned portions and the loss of pressure is suppressed when used in an evaporator.

Further, according to embodiments of the invention, it is arranged in such a way that liquid refrigerant is scattered evenly at the joint portion and the non-aligned portions in the electric welded tube. As a result of such arrangement, it becomes possible to obtain an action of sufficiently scattering refrigerant in the condenser and, in addition, it is possible to suppress the loss of pressure in the evaporator because the non-aligned portions and the joint portion are arranged scatteredly. In such a case, liquid refrigerant and gas refrigerant are dispersed evenly, which has an effect, particularly on a drifted flow of refrigerant.

As described above, in embodiments of the invention it is possible to provide improvement in heat transfer efficiency when used as a condenser by sufficiently scattering liquid refrigerant and to suppress the increase in pressure loss when used as an evaporator. In other words, by the use of the inner grooved heat transfer tubes of the above-mentioned embodiments, it is possible to improved the performance of heat exchangers.

Further, if the first lead angle and the second lead angle are so set as fall in the range of to 30 degrees in opposite torsional directions respectively with respect to the tube axis m:\specifcations\l 00000\1 12412spcmjca25.doc directional line, (particularly if these angles are set at 18 degrees), this makes it possible to maintain well-balanced relationships between the heat transfer efficiency and the loss of pressure while securing the effect of a helical flow.

Furthermore, if the first lead angle and the second lead angle are set in order that the main groove and the non-aligned portion of the line groove may be directed symmetrically with respect to the tube axis directional line, this makes the manufacture of the heat transfer tube relatively easy. In other words, if the heat transfer tube is an electric welded tube, this enables a roll for marking the line grooves in a material of which the heat transfer tube is made to have symmetrical grooves and ridge angles. This facilitates the manufacture of the roll itself and torsion of the material at the time of marking is less likely to occur.

Further, if the secondary groove is formed in the convexity which forms the main groove, this makes it possible to improve heat transfer efficiency by expanding a heat transfer area. Besides, it is possible to reduce the loss of pressure. Particularly, if the position, the depth, and the angle of the secondary groove are set to the foregoing predetermined values, this further ensures the aforesaid effects.

Furthermore, in some embodiments, the secondary groove is formed in the convexity of the main groove, thereby making it possible to provide not only improvement in heat transfer efficiency by heat transfer area expansion but also reduction in pressure loss. More specifically, even when the percentage of the non-aligned portion in the line groove is made relatively large, it is possible to suppress the loss of pressure when used as an evaporator. Further, when used as a condenser, it is possible to obtain an effect of scattering liquid refrigerant without fail.

Accordingly, in embodiments of the present inventionit is possible to improve the performance of heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially broken-out front view of an inner grooved heat transfer tube according to an embodiment of the invention; Figure 2 is a development of a part of the heat transfer tube, showing a shape of the line groove; Figure 3 is an enlarged cross-sectional schematic view taken along the lines HI-Inl of Figure 1; Figure 4 is an enlarged view showing a cross-sectional shape of the line groove; m:\specifications\1 00000\1 12412spcmjca25.doc Figure 5 is a partially enlarged view of Figure 2; Figure 6 is a perspective view roughly showing a shape of the secondary groove; Figure 7 is a graph showing the capability of condensation as the performance of a single heat exchanger; Figure 8 is a graph showing the capability of evaporation as the performance of a single heat exchanger; and Figure 9 is a graph showing the loss of evaporation pressure with respect to the amount of refrigerant circulation.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the invention will be described in detail with reference to the Figures.

Figure 1 is a partially broken-out front view of an inner grooved heat transfer tube (10) of the present embodiment. As shown in the Figure, the heat transfer tube (10) has a U-bent shape, in other words the heat transfer tube (10) is a so-called hairpin tube. Formed in the internal surface of the heat transfer tube (10) are a great number of line grooves (11) oblique to the tube axis directional line. And, a plurality of such heat transfer tubes (10) and a plate fin (not shown) are combined together, and opening ends of the heat transfer tubes (10) are connected appropriately to form a plate-fin coil type heat exchanger.

Figure 2 shows the inner grooved heat transfer tube (10) with a part thereof developed. As shown in the Figure, each of the line grooves (11) formed in the internal surface of the heat transfer tube (10) comprises an alternative series of main grooves (12) formed at a first lead angle and non-aligned portions (13) formed at a second lead angle which is different from the first lead angle The first lead angle and the second lead angle are formed in opposite directions relative to a tube axis directional line. More specifically, the first lead angle and the second lead angle (13) are formed at 18 degrees with respect to the tube axis directional line in opposite directions. Because of such arrangement, the main groove (12) and the non-aligned portion (13) of the line grooves are symmetrically directed with respect to the tube axis directional line.

The non-aligned portion (13) is formed at two positions in a single round of the line groove In other words, in the state in which the heat transfer tube (10) is developed, there are m:\specifications\1 00000\112412spcmjca25.doc t' 11 provided two non-aligned portions (13) in a line groove (11) extending from one Scircumferential end to the other circumferential end. Further, it is set such that the percentage of the total length of the two non-aligned portions (13) to the length of a single round of the line groove (11) is 28%.

It is set such that the length of each non-aligned portion (13) is about 8.5 times the pitch of the line groove And, by virtue of these set values, about twelve non-aligned portions (13) are so arranged as to intersect an extension of a single main groove (12) of the line groove (11).

The heat transfer tube (10) is an electric welded tube, wherein a joint portion (14) and each non-aligned portion (13) of the heat transfer tube (10) are arranged at respective locations substantially equally dividing the direction of the circumference of the heat transfer tube in other words they are spaced about 120 degrees apart from each other, as shown in Figure 3 which is an enlarged cross-sectional schematic view taken along the lines III-III of Figure 1.

On the other hand, Figure 4 is an enlarged view showing a cross section of the line groove (11).

The line groove (11) is defined between adjoining convexities The convexities (15) have the same cross-sectional shape for both the main groove (12) and the non-aligned portion (13).

Referring to Figure 5 which is a partially enlarged view of Figure 2 and to Figure 6 which is a schematic perspective view of the convexity a plurality of spaced recessed portions are formed in the convexity (15) constituting the main groove And, each recessed portion forms a secondary groove As shown in Figure 2, the secondary groove (16) is formed only at a substantially central portion of the convexity (15) of each main groove (12) and is spaced a predetermined distance apart from both ends of each non-aligned portion (13).

Further, the secondary groove (16) is illustrated in Figure 2 in which only the region where it is formed is simplified.

Further, the secondary groove (16) is formed, having a depth of about 0. 5 times the groove depth of the line groove Furthermore, the secondary groove (16) is formed substantially along the tube axis directional line.

Next, the flow of a refrigerant in the heat transfer tube (10) will be described.

When the heat transfer tube (10) is used in a condenser, the refrigerant changes to liquid from a gas phase as it moves forward through the condenser and then flows along the main groove m:\specifications\1 00000\1 12412spcmjca25.doc (12) of the line groove And, since the first lead angle formed between the main groove (12) and the tube axis directional line is set at 18 degrees, this ensures that the refrigerant flows helically and forms a thin film of liquid. Furthermore, in such a setting of angle, the loss of pressure will not increase excessively by the angle of helix becoming too great.

And, when the refrigerant flows in the main groove (12) and reaches the non-aligned portion the refrigerant comes into collision with a side wall of the convexity (15) of the nonaligned portion (13) and is scattered from the inner peripheral surface of the heat transfer tube toward the center because the first lead angle of the main groove (12) differs from the second lead angle of the non-aligned portion The non-aligned portion (13) is formed at a lead angle of 18 degrees in an opposite direction to the main groove The percentage of the total length of the two non-aligned portions (13) to the length of a single round of the line groove (11) is 28%. Further, the length of each non-aligned portion (13) is so set as to be about times the pitch of the line groove As a result of such arrangements, about twelve nonaligned portions (13) are arranged so as to intersect an extension of a single main groove (12) of the line groove And, the refrigerant, which is flowing in the main groove climbs over about twelve non-aligned portions (13) (twelve ridges).

These conditions, such as the percentage of the total length of the non-aligned portions (13) to the length of a single round of the line groove the lead angle of the main groove (12) and the lead angle (13) of the non-aligned portion the relationship between the length of each non-aligned portion (13) and the pitch of the line groove the number of nonaligned portions (13) which intersect an extension of one main groove and other condition, are set as described above. Accordingly, the refrigerant, which flows along the main groove (12) and forms a thin film of liquid, is scattered definitely when climbing over the convexities (15) of the non-aligned portions (13) many times (twelve times in the present embodiment), so that formation of a thick layer of liquid is less likely to take place on the inner surface of the heat transfer tube thereby preventing the occurrence of an annular flow.

As described above, the action of scattering refrigerant can be obtained sufficiently because the percentage of the total length of the non-aligned portions to the length of a single round of the line groove (11) is not set too small the ratio of the length of each non-aligned portion to the pitch of the line groove is not set too small (8.5 times), and the number of non-aligned portion ridges that the refrigerant climbs over is not set too small (12 ridges).

m:\specifications\1 00000\112412spcmjca25.doc Further, the joint portion (14) and the plural non-aligned portions (13) of the heat transfer tube are arranged at respective locations substantially equally dividing the direction of the circumference of the heat transfer tube As a result of such arrangement, liquid refrigerant flowing in the main groove (12) of the line groove (11) is scattered evenly at the joint portion (14) and the non-aligned portions (13) in the heat transfer tube Accordingly, the action of equal scattering of liquid refrigerant can be obtained throughout the entire inner surface of the heat transfer tube Furthermore, when used as an evaporator the loss of pressure can be suppressed because the percentage of the total length of the non-aligned portions (13) to the length of a single round of the line groove (11) is not set too large the ratio of the length of each non-aligned portion (13) to the pitch of the line groove (11) is not set too large (8.5 times), and the number of the convexities of the non-aligned portions (13) that the refrigerant climbs over is not set too many (12 ridges) in the aforesaid configuration.

Further, since the secondary groove (16) is formed in the convexity (15) which forms the main groove this provides an increased heat transfer area and reduces the loss of pressure by causing, while creating a helical flow by a main groove a part of the refrigerant to flow to the next main groove (12) by the secondary groove Further, the location, the depth, and the directionality of the secondary groove (16) are specified. This ensures that the loss of pressure is suppressed while at the same time definitely securing the action of a helical flow.

As described above, in accordance with the present embodiment, it is possible to sufficiently scatter liquid refrigerant when the heat transfer tube (10) is used as a condenser. As a result, the efficiency of heat transfer can be improved. On the other hand, when used as an evaporator, the increase in pressure loss can be suppressed. In other words, it is sufficient for the heat transfer tube (10) to have, as its inner surface, an irregularly rugged surface, when it is intended just to improve the efficiency of heat transfer by upgrading the action of scattering refrigerant.

However, in such a case, there is an increase in pressure loss. On the other hand, by the use of the heat transfer tube (10) of the present embodiment, it is possible to maintain well-balanced relationships between refrigerant scattering action and pressure loss by specifying the structure of the non-aligned portion (13) to the aforesaid structure. Accordingly, it becomes possible to upgrade the performance of heat exchangers.

It is arranged such that liquid refrigerant is scattered evenly at the joint portion (14) and the plural non-aligned portions (13) of the heat transfer tube which effectively contributes to m:\specifications\1 00000\112412spcmjca25.doc reducing the loss of pressure. Further, in such a configuration, there is created an action of evenly dispersing liquid refrigerant and gas refrigerant, which effectively contributes to preventing the occurrence of a drift.

Further, the first lead angle and the second lead angle are each set at 18 degrees in opposite torsional directions relative to the tube axis directional line, which makes it possible to maintain highly well-balanced relationships between heat transfer efficiency and pressure loss by scattering refrigerant while securing a helical flow effect.

Particularly, since the first lead angle and the second lead angle are set in such a way that the main groove (12) and the non-aligned portion (13) of the line groove (11) are symmetrically directed with respect to the tube axis directional line, this makes the manufacture of the heat transfer tube (10) relatively easy. In other words, if the heat transfer tube (10) is an electric welded tube, this enables a roll for marking the line grooves (11) in a material of which the heat transfer tube (10) is made to have symmetrical grooves and ridge angles. This facilitates the manufacture of the roll itself and torsion of the material at the time of marking is less likely to occur.

Further, since the secondary grooves (16) are formed in the convexity (15) forming the main groove this makes it possible to provide improvements in heat transfer efficiency by heat transfer area expansion. Besides, it is possible to reduce the loss of pressure. Especially, setting the location, the depth, and the angle of the secondary groove to the foregoing predetermined values further ensures the effects. The provision of the secondary groove (16) is effective particularly for suppression of the loss of pressure, even when making the size of the nonaligned portion (13) relatively large.

Next, a more concrete exemplary embodiment of the heat transfer tube (10) will be described.

All the values described in the foregoing embodiment are applicable to the heat transfer tube according to the present embodiment. Additionally, the following values are set: the outside diameter 9.52 mm; the wall thickness 0.30 mm; the number of line grooves (11) 60; the depth of the line groove (11) the height of the convexity 0.24 mm; the pitch about 6 degrees, and the ridge angle of the convexity (15) 25 degrees.

With the above-mentioned values, the following heat transfer tubes were prepared, namely a heat transfer tube (a comparative example) in which the line groove (11) comprises only a helical main groove (12) of 18 degrees; a heat transfer tube (the first embodiment) in which the m:\specifications\l 00000\112412spcmjca25.doc line groove (11) comprises a main groove (12) and a non-aligned portion and a heat transfer tube (the second embodiment) which further comprises a secondary groove (16) in the first embodiment. These different heat transfer tubes were used in heat exchangers for comparison. The results are graphically shown in Figures 7-9. In these Figures, the heat transfer tube as a comparative example in which the line groove (11) comprising only a helical main groove (12) is formed is indicated by long dashed short dashed line, the heat transfer tube of the first embodiment in which the line groove (11) comprises a main groove (12) and a non-aligned portion (13) is indicated by broken line, and the heat transfer tube of the second embodiment in which the line groove (11) is provided with a non-aligned portion'(13) and a secondary groove (16) is indicated by solid line.

As can be seen from Figure 7, both the heat transfer tube of the first embodiment and the heat transfer tube of the second embodiment are superior in condensation capability to the comparative example heat transfer tube. More specifically, when the front surface wind velocity of the heat exchanger is relatively slow, the heat transfer tube of the second embodiment is slightly superior in condensation capability to the heat transfer tube of the first embodiment. On the other hand, when the front surface wind velocity of the heat exchanger is relatively fast, the heat transfer tube of the first embodiment is slightly superior in condensation capability to the heat transfer tube of the second embodiment. However, from the results, these numeric values are in the range of error, and it is believed that the provision of the non-aligned portion (13) has a sufficient effect on the improvement in condensation capability, regardless of whether the secondary groove (16) is formed.

Further, as can be seen from Figure 8, the heat transfer tube of the first embodiment is superior in evaporation capability to the comparative example heat transfer tube in every wind velocity range used for measurement, and the heat transfer tube of the second embodiment provides further improved evaporation capabilities. In other words, the provision of the secondary groove (16) has a great effect on reducing the loss of pressure, thereby achieving improvement in evaporation capability.

This is clear from Figure 9 showing variations in evaporation pressure loss with respect to the increase in refrigerant circulation amount. More specifically, the heat transfer tube of the first embodiment undergoes a greater pressure loss in comparison with the comparative example heat transfer tube. However, in the heat transfer tube of the second embodiment in which the line groove (11) is provided with non-aligned portions (13) and secondary grooves the m:\specifications\1 00000\112412spcmjca25.doc loss of pressure is reduced to a smaller value in comparison with the comparative example. The secondary groove (16) plays an extremely important role of reducing the loss of pressure.

Further, the invention is not limited to the foregoing embodiments. The invention may be embodied in various other manners.

For example, in the above-mentioned embodiments, it is set such that the percentage of the length of the non-aligned portion (13) of the line groove (11) to the length of a single round of the line groove (11) is 28%. However, it may be set such that the percentage falls in the range between 10% and 35%. Such setting provides a sufficient scattering action (if the percentage is less than 10%, liquid refrigerant is less likely to be scattered in the condenser even when the non-aligned portion (13) is provided), and suppresses the loss of pressure (if the percentage is more than 35%, this results in an increase in the loss of pressure when used in the evaporator).

Further, the length of each non-aligned portion (13) is not limited to 8.5 times the pitch of the line groove The length of each non-aligned portion (13) may be set so as to fall within the range between five times and fifteen times the pitch of the line groove Such setting provides a sufficient scattering action (if the non-aligned portion length is less than five times the line groove pitch, liquid refrigerant is less likely to be scattered in the condenser even when the non-aligned portion (13) is provided), and suppresses the loss of pressure (if the nonaligned portion length is more than fifteen times the line groove pitch, this results in an increase in the loss of pressure when used in the evaporator).

Further, the number of the convexities (15) of the non-aligned portions (13) intersecting an extension of a single main groove (12) of the line groove (11) is not limited to twelve. If the number is set so as to fall in the range of from five to fifteen, this not only secures an effect of scattering refrigerant when used in a condenser but also effectively suppresses the loss of pressure when used in an evaporator.

Furthermore, the invention is not necessarily required to meet all the above-mentioned conditions. For example, if at least one of the conditions, such as the percentage of the length of the non-aligned portion (13) to the length of a single round of the line groove is satisfied, this makes it possible to achieve better heat exchange performance than conventional heat transfer tubes.

m:\specifications\1 00000\112412spcmjca25.doc Particularly, the provision of the secondary grooves (16) provides a higher effect of preventing the increase in pressure loss. Therefore, as long as the secondary grooves (16) are provided, the conditions, such as the percentage of the length of the non-aligned portion (13) to the length of a single round of the line groove the relationship between the length of each non-aligned portion (13) and the pitch of the line groove and the number of non-aligned portions (13) intersecting a single main groove may fall outside the aforementioned ranges.

Furthermore, in the previous embodiments, it is arranged such that two non-aligned portions (13) are provided in a single round of the line groove However, the number of nonaligned portions (13) may be one or not less than 3. Even in such a case, it is preferable that the joint portion (14) and the non-aligned portion(s) (13) of the heat transfer tube (10) implemented by an electric welded tube are arranged at respective locations substantially equally dividing the direction of the circumference thereof. However, they are not necessarily arranged at equal intervals in cases including a case in which the number of non-aligned portions (13) is two, as in the previous embodiments.

Further, the first lead angle and the second lead angle are each set at 18 degrees in opposite torsional directions relative to the tube axis directional line. However, such a set angle may fall within the range between 5 degrees and 30 degrees. Furthermore, the first lead angle and the second lead angle may not be set in such a way that the main groove (12) and the non-aligned portion (13) are symmetrically directed with respect to the tube axis directional line. Additionally, the first lead angle and the second lead angle may not be set in opposite directions, in other words they may be set in the same direction, having different values.

Further, the depth of the secondary groove (16) is not necessarily 0.5 times larger than the depth of the line groove As long as the secondary groove (16) is formed having a depth of 0.25 to 0.75 times the depth of the line groove it is possible to obtain a helical flow effect while increasing the area of heat transfer. Finally, the secondary groove (16) is not necessarily formed along the tube axis directional line. Even if the secondary groove (16) is formed in such a way that it is inclined about five degrees toward both sides with respect to the tube axis directional line, this still effectively reduces the loss of pressure.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part m:\specifications\1 00000\112412spcmjca25.doc of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

m:\specifications\1 00000\11 2412spcmjca25.doc

Claims

1. An inner grooved heat transfer tube in which a plurality of line grooves are formed in an inner peripheral surface of an electric welded tube and said line groove is made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein a joint portion of said electric welded tube and said non-aligned portion are arranged at respective locations substantially equally dividing the direction of the circumference of said electric welded tube.

2. An inner grooved heat transfer tube according to claim 1, wherein the percentage of the length of said non-aligned portion to the length of a single round of said line groove is so set as to fall in the range of 10 to

3. An inner grooved heat transfer tube according to claim 1 or claim 2 wherein the length of each said non-aligned portion is so set as to fall in the range of five to fifteen times the pitch of said line groove.

4. An inner grooved heat transfer tube according to any one of the preceding claims wherein from five to fifteen non-aligned portions are so arranged as to intersect an extension of a single main groove. The inner grooved heat transfer tube according to any one of claims 1-4, wherein said non-aligned portion is formed at a plurality of positions in a single round of said line groove.

6. The inner grooved heat transfer tube according to any one of claims 1-4, wherein one of the first lead angle and the second lead angle is so set as to fall in the range of 5 to degrees in one torsional direction with respect to a tube axis directional line whereas the other of the first lead angle and the second lead angle is so set as to fall in the range of 5 to degrees in the other torsional direction with respect to the tube axis directional line.

7. The inner grooved heat transfer tube of claim 6, wherein the first lead angle and the second lead angle are set in such a way that said main groove and said non-aligned portion of said line groove are symmetrically directed with respect to the tube axis directional line. m:\specifications\l 00000\112412spcmjca25.doc

8. The inner grooved heat transfer tube of claim 7, wherein the first lead angle and the second lead angle are each set at 18 degrees in opposite directions with respect to the tube axis directional line.

9. The inner grooved heat transfer tube of any one of claims 1-4, wherein a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove. The inner grooved heat transfer tube of claim 9, wherein said secondary groove is formed centrally in said convexity of said main groove so as to be spaced a predetermined distance apart from said non-aligned portion.

11. The inner grooved heat transfer tube of claim 9, wherein said secondary groove is formed to a depth of 0.25 to 0.75 times the depth of said line groove.

12. The inner grooved heat transfer tube of claim 9, wherein said secondary groove is formed substantially along the tube axis directional line.

13. An inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and said secondary groove is formed centrally in said convexity of said main groove so as to be spaced a predetermined distance apart from said non-aligned portion.

14. An inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and said secondary groove is formed to a depth of 0.25 to 0.75 times the depth of said line groove. m:\specifications\1 00000\1 12412spcmjca25.doc An inner grooved heat transfer tube comprising an inner peripheral surface in which are formed a plurality of line grooves, said line groove being made up of main grooves formed at a first lead angle and non-aligned portions formed at a second lead angle different from the first lead angle which are successively formed, wherein: a secondary groove made up of a plurality of spaced recessed portions is formed in a convexity forming said main groove, and said secondary groove is formed substantially along the tube axis directional line.

16. An inner grooved heat transfer tube substantially as hereinbefore described with reference to the drawings and/or the preferred embodiments and excluding, if any, comparative drawings. Dated this twenty-fifth day of January 2005 Daikin Industries, Ltd. Patent Attorneys for the Applicant: F B RICE CO m:\specifications\1 00000\1 12412spcmjca25.doc