JP2010203670A - Cross fin tube type heat exchanger for evaporator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cross fin tube type heat exchanger for an evaporator, using a refrigerant mainly composed of carbon dioxide as a refrigerant and having excellent evaporation heat transfer characteristics. <P>SOLUTION: The cross fin tube type heat exchanger for the evaporator includes an aluminum fin and an inner helically grooved heat transfer pipe installed in the aluminum fin, and uses the refrigerant mainly composed of carbon dioxide. When the bottom thickness of the inner helically grooved heat transfer pipe is represented as t (mm) and the pipe outer diameter as D (mm), a formula (1) of 0.055≤t/D≤0.09 is satisfied. In the bottom of an inner groove of the inner helically grooved heat transfer pipe, pores are formed in the longitudinal direction of the inner groove. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cross-fin tube type heat exchanger for an evaporator such as a refrigerator, an air conditioner, or a hot water heater using a refrigerant mainly composed of carbon dioxide as a refrigerant.

  From the viewpoint of suppressing the discharge of refrigerant gas, which is a global warming gas, the use of natural refrigerants typified by carbon dioxide refrigerants as a refrigerant for heat exchangers has been studied in place of CFC refrigerants.

  Among the heat exchangers using such carbon dioxide refrigerant, as a heat exchanger for an evaporator, a cross fin tube type heat exchanger in which aluminum fins and copper heat transfer tubes are assembled as in the case of conventional chlorofluorocarbons. As the copper heat transfer tube, an internally grooved heat transfer tube has been used.

For example, Japanese Patent Application Laid-Open No. 2003-343492 (Patent Document 1) discloses an evaporator that evaporates carbon dioxide flowing in a tube, and the cross-sectional shape of the passage of the tube is circular, and the inner wall of the tube Is provided with a plurality of protrusions protruding to the center side,
Formula 1: 0.5 × d ^1.2682 ≦ L ≦ 2.09 × d ^1.2682
An evaporator is disclosed in which the passage length (L) of the tube and the average inner diameter (d) of the tube have the relationship shown in the above formula 1.

  However, in the evaporator shown in Patent Document 1, an internally grooved heat transfer tube is used. However, although the heat transfer coefficient in the tube is higher than that using a smooth tube, the inner surface is simply grooved. The heat transfer coefficient in the pipe was insufficient.

As an example of improving the heat transfer coefficient in a tube of an internally grooved heat transfer tube, for example, Japanese Patent Laid-Open No. 2006-162100 (Patent Document 2) discloses a heat transfer tube constituting a cross fin tube heat exchanger using a high-pressure refrigerant. In addition, a large number of grooves are formed on the inner surface of the tube so as to extend in the tube circumferential direction or with a predetermined lead angle with respect to the tube axis, and inner surface fins having a predetermined height are formed between the grooves. In an internally grooved heat transfer tube made of copper or copper alloy, the tube outer diameter D (mm), the bottom wall thickness to be the tube wall thickness at the groove formation site is t (mm), and the groove depth of the groove is d ( mm) and t / D is 0.041 or more and 0.146 or less, and d ² / A, where A (mm ² ) is the cross-sectional area per groove in the cross section perpendicular to the tube axis. Is not less than 0.75 and not more than 1.5, and N is a groove of the groove. The inner surface for high-pressure refrigerant, wherein N / Di is 8 or more and 24 or less, where Di is the maximum inner diameter corresponding to the inner diameter of the pipe formed by connecting the groove bottoms of the grooves. A grooved heat transfer tube is disclosed.

Japanese Patent Laid-Open No. 2002-90086 (Patent Document 3) discloses that an inner fin on the inner surface of a tube is deformed when a heat transfer tube with an inner groove is assembled on an aluminum fin to manufacture a cross fin tube heat exchanger. As an internally grooved heat transfer tube that can be suppressed, a large number of grooves are formed on the inner surface of the tube so as to extend in the circumferential direction of the tube or with a predetermined lead angle with respect to the tube axis. And an inner grooved heat transfer tube formed with inner fins of a predetermined height, the outer diameter of the tube being 4 mm to 10 mm, and the groove depth of the groove being 0.10 mm to 0.30 mm. The bottom wall thickness (t), which is the tube wall thickness at the groove forming site, satisfies the following formula: t ≦ 0.1248 × D ^0.32782 (where D represents the ^outer diameter of the ^tube ), Inner surface characterized by being constructed A grooved heat transfer tube is disclosed.

JP 2003-343492 A (Claims) JP 2006-162100 A (Claims) JP 2002-90086 (Claims)

  In the heat transfer tube with an inner surface groove of Patent Document 2, the evaporation heat transfer characteristic is improved, but still further improvement of the evaporation heat transfer characteristic is required. Similarly, the inner surface grooved heat transfer tube of Patent Document 3 is also required to further improve the evaporation heat transfer characteristics.

  Therefore, the present invention provides a cross-fin tube type heat exchanger for an evaporator using a refrigerant mainly composed of carbon dioxide as a refrigerant, the cross-fin tube type heat exchanger for an evaporator having excellent evaporative heat transfer characteristics. It is to provide.

  As a result of intensive studies to solve the problems in the prior art, the present inventors have formed fine grooves in the longitudinal direction of the inner surface groove at the bottom of the inner surface groove of the inner surface grooved heat transfer tube. Since the nucleate boiling is promoted by the fine grooves, it has been found that a cross fin tube type heat exchanger having excellent evaporative heat transfer characteristics can be obtained, and the present invention has been completed.

That is, the present invention is a cross fin tube type heat exchanger for an evaporator having an aluminum fin and an internally grooved heat transfer tube assembled to the aluminum fin and using a refrigerant mainly composed of carbon dioxide. And
When the bottom wall thickness of the internally grooved heat transfer tube is t (mm) and the tube outer diameter is D (mm), the following formula (1):
0.055 ≦ t / D ≦ 0.09 (1)
The filling,
A fine groove is formed in the longitudinal direction of the inner surface groove at the bottom of the inner surface groove of the inner surface grooved heat transfer tube;
A cross fin tube type heat exchanger for an evaporator is provided.

  According to the present invention, there is provided a cross fin tube type heat exchanger for an evaporator using a refrigerant mainly composed of carbon dioxide as a refrigerant, the cross fin tube type heat exchanger for an evaporator having excellent evaporative heat transfer characteristics. Can be provided.

It is a schematic diagram of the form example of the cross fin tube type heat exchanger for evaporators of this invention. FIG. 2 is a cross-sectional view of the internally grooved heat transfer tube assembled to the cross fin tube heat exchanger shown in FIG. 1 when cut along a plane perpendicular to the tube axis direction. It is the figure which expanded a part of inner surface fin among the cross sections of the heat exchanger tube with an inner surface groove | channel shown in FIG. It is a figure of a part of inner surface fin and inner surface groove | channel seen from the direction of the code | symbol 14 in FIG. FIG. 4 is a perspective view of the internally grooved heat transfer tube shown in FIG. 3. FIG. 6 is an enlarged view of a portion indicated by reference numeral 13 in FIGS. 4 and 5. It is the figure which expanded a part of inner surface fin among the cross sections of the heat exchanger tube with an inner surface groove | channel shown in FIG. It is the figure which expanded a part of inner surface fin among the cross sections of the heat exchanger tube with an inner surface groove | channel shown in FIG. It is sectional drawing which shows the cross fin tube type heat exchanger for evaluation manufactured by the Example and the comparative example. It is a figure which shows the heat-transfer coefficient performance evaluation method in a pipe | tube.

The cross fin tube type heat exchanger for an evaporator of the present invention has an aluminum fin and an internally grooved heat transfer tube assembled to the aluminum fin, and is used for an evaporator using a refrigerant mainly composed of carbon dioxide. A cross fin tube heat exchanger,
When the bottom wall thickness of the internally grooved heat transfer tube is t (mm) and the tube outer diameter is D (mm), the following formula (1):
0.055 ≦ t / D ≦ 0.09 (1)
The filling,
It is a cross fin tube type heat exchanger for an evaporator in which a fine groove is formed in the longitudinal direction of the inner surface groove at the bottom of the inner surface groove of the inner surface grooved heat transfer tube.

  The cross fin tube type heat exchanger for an evaporator of the present invention will be described with reference to FIGS. FIG. 1 is a schematic view of an embodiment of a cross fin tube heat exchanger for an evaporator according to the present invention, and FIG. 2 is an internally grooved transmission assembled to the cross fin tube heat exchanger shown in FIG. FIG. 3 is a cross-sectional view of the heat tube when cut along a plane perpendicular to the tube axis direction, and FIG. 3 is an enlarged view of a part of the inner fin in the cross section of the inner-surface grooved heat transfer tube shown in FIG. .

  In FIG. 1, a cross fin tube type heat exchanger 1 for an evaporator includes an aluminum fin 2 and an internally grooved heat transfer tube 3. The internally grooved heat transfer tube 3 is hairpin processed at the hairpin processing portion 4 and processed into a U shape, and is inserted into the plurality of aluminum fins 2 and assembled. A plurality of the internally grooved heat transfer tubes 3 are inserted into the aluminum fins 2, and the inner grooved heat transfer tube 3 is provided with a U bend tube 5 on one side of the internally grooved heat transfer tube 3 opposite to the hairpin processed portion 4. The tube end of the heat transfer tube 3 and the tube end of the other internally grooved heat transfer tube 3 are connected. As a result, a flow path for the carbon dioxide refrigerant 6 is formed in the cross fin tube type heat exchanger 1 for the evaporator.

  As shown in FIG. 2, in the cross section obtained by cutting the inner surface grooved heat transfer tube 3 along a plane perpendicular to the tube axis direction, the inner surface grooved heat transfer tube 3 has a large number of pipe circumferential directions 17 in the tube circumferential direction 17. The inner surface groove 12 is formed in a spiral shape with a constant spiral angle θ (°) with respect to the tube axis direction, and a plurality of inner surface fins 11 are formed in a spiral shape. The tube outer diameter D (mm) refers to the outer diameter of the internally grooved heat transfer tube 3. The inner surface grooved heat transfer tube 3 is formed with the inner surface grooves 12 and the inner surface fins 11 in the tube circumferential direction 17. For convenience of drawing, in FIG. A part of the inner fin 11 is described, and other description is omitted.

  As shown in FIG. 3, the inner surface groove 12 and the inner surface fin 11 are processed on the tube inner surface of the inner surface grooved heat transfer tube 3. The shape of the inner fin 11 is a substantially isosceles trapezoid that is narrowed toward the center of the tube.

  A fine groove is formed in the bottom 29 of the inner surface groove 12 in the longitudinal direction of the inner surface groove 12. The fine groove formed in the bottom 29 of the inner surface groove 12 will be described. FIG. 4 shows a view of the inner surface groove 12 and the inner surface fin 11 in FIG. 3 when viewed from the reference numeral 14 side, that is, the inner surface of the tube from the center of the inner surface grooved heat transfer tube 3. FIG. 5 is a perspective view of the internally grooved heat transfer tube 3 in FIG. 4 and 5, a portion surrounded by a dotted line (reference numeral 13) is a part of the bottom 29 of the inner surface groove 12. An enlarged view of the portion indicated by reference numeral 13 is shown in FIG. The longitudinal direction 18 of the inner surface groove 12 is a direction in which the inner surface groove 12 continues in a spiral shape with a constant helical angle θ (°) with respect to the tube axis direction.

  As shown in FIG. 6, fine grooves 15 (15 a, 15 b, 15 c) are formed at the bottom 29 of the inner surface groove 12. The direction in which the fine grooves 15 are formed is the longitudinal direction 18 of the inner surface grooves 12. Here, in the present invention, the fact that the fine grooves are formed in the longitudinal direction of the inner surface groove means that each fine groove 15 has the same helical angle as the inner surface groove 12 over the entire range. It does not mean that it is formed, that is, it is not formed in a straight line with the same spiral angle as the inner surface groove 12, but may be formed meandering like the fine groove 15b, for example. . In other words, in the present invention, the fact that the fine groove is formed in the longitudinal direction of the inner groove means that when the formation direction of the fine groove 15 is locally observed over the entire range, at each observation point, The groove forming direction may be within ± 30 ° with respect to the longitudinal direction 18 of the inner surface groove 12. When the formation direction of the fine groove 15 is observed over the entire range locally, the formation direction of the groove is within ± 30 ° with respect to the longitudinal direction 18 of the inner surface groove 12 at each observation point. If there is, the fine groove that exhibits the nucleate boiling promoting action is present so as to substantially follow the flow direction of the refrigerant. Therefore, the fine groove acts as a boiling nucleus of the refrigerant, and the evaporation heat transfer characteristic is Get higher.

  Each fine groove 15 may not have a constant groove width 19 over the entire range, and the groove width may be changed like the fine groove 15a. Further, even if the groove width 19 is very narrow like the fine groove 15c, if it is about 1 μm, the nucleate boiling promoting action can be exhibited. The groove width of the fine groove 15 is not particularly limited as long as it can exhibit a nucleate boiling promoting effect, but is preferably 1 to 30 μm, particularly preferably 3 to 20 μm, in view of increasing the nucleate boiling promoting effect. It is. The groove width of the fine groove is observed as the width of the opening of the fine groove.

  The length 20 of the fine groove 15 is not particularly limited, and having a certain length has an effect of increasing the possibility of becoming a nucleus of nucleate boiling.

  The fine groove 15 is not a gentle recess, but has a narrow groove width and a deep depth with respect to the groove width, and exhibits a nucleate boiling promoting action. On the other hand, the gentle dent does not sufficiently exhibit the effect of promoting nucleate boiling.

  7 and 8 are enlarged views of a part of the inner fin in the cross section of the inner grooved heat transfer tube shown in FIG. In FIG. 7, the bottom wall thickness t (mm) indicates the wall thickness of the inner surface grooved heat transfer tube 3 at the deepest portion 23 of the inner surface groove 12 of the inner surface grooved heat transfer tube 3. Hereinafter, a circle drawn so that the deepest portion 23 of each inner surface groove 12 overlaps the circumference, that is, a circle that is concentric with an outer circumference circle of the inner surface grooved heat transfer tube 3 and the radius is the bottom wall thickness t. A circle that is smaller by an amount is called a bottom thick line 25 (a chain line indicated by reference numeral 25 in FIG. 7). The inner fin height h (mm) refers to the height of the apex 26 of the inner fin 11 and refers to the length of the portion protruding from the bottom thickness line 25 toward the center of the tube. Here, the inner fin height h is the height of the central portion of the inner fin 11 in the width direction, that is, the length of the center line of the inner fin 11. The inner surface fin pitch p (mm) refers to a linear distance between adjacent inner surface fins 11 between the points where the center line of the inner surface fins 11 intersects the bottom wall thickness line 25. The fin apex angle α (°) indicates the crossing angle when the side surface of the inner fin is extended. The inner fin width Wf (mm) refers to the width of the inner fin 11 at a position half the inner fin height h. The shape of the tip of the inner fin 11 is an arc in FIGS. 3, 7 and 8, but is not limited to this, and the tip may be a flat shape or a triangular shape with a sharp tip. Good.

  In the internally grooved heat transfer tube according to the present invention, t / D is 0.055 to 0.09. Since the refrigerant having carbon dioxide as a main component has a high operating pressure of 3.5 to 16 MPa, it is necessary to improve the pressure resistance of the heat transfer tube. Therefore, it is necessary to increase the bottom wall thickness t. The thickness of the bottom wall thickness t is appropriately determined in consideration of the safety factor depending on the outer diameter D of the tube and the tensile strength σB of the heat transfer tube material. Phosphorus deoxidation generally used as a heat transfer tube material In a soft alloy material such as copper or low alloy copper in which an additive component of about 2% by mass at maximum is added to pure copper, t / D needs to be 0.055 or more. On the other hand, if t / D exceeds 0.09, the unit weight increases, resulting in an increase in cost, heat transferability is deteriorated, and the inner fin height h has to be lowered. Heat exchange performance cannot be obtained. Therefore, t / D needs to be 0.09 or less. In the present invention, the value of t / D is a value calculated from the average value of the bottom wall thickness t of all inner surface grooves in the pipe circumferential direction in a cross section perpendicular to the pipe axis direction. The tube outer diameter D is 4 to 12.7 mm, preferably 7 to 12.7 mm.

  Since the fine groove is formed at the bottom of the inner surface groove, the following effects can be obtained.

  Forming the inner surface groove in the heat transfer tube has an effect of thinning the liquid refrigerant as compared with the smooth tube. When this inner surface grooved heat transfer tube is assembled in a cross fin tube heat exchanger and carbon dioxide refrigerant is circulated inside the heat transfer tube to exchange heat as an evaporator (when heat is absorbed from the air side by evaporation of liquid refrigerant) The quality (dryness) changes from the refrigerant inlet to the refrigerant outlet, and the quality increases toward the refrigerant outlet.

  In the inner surface grooved heat transfer tube according to the cross fin tube type heat exchanger for an evaporator of the present invention, the part contributing to nucleate boiling differs depending on the quality. First, in the low quality region where the liquid film near the refrigerant inlet is thick, the inner groove itself (the inner groove indicated by reference numeral 12 in FIG. 2) functions as an open cavity and promotes nucleate boiling. As a preferable form of the inner surface groove functioning as an open cavity for promoting such nucleate boiling, Wg is 0.07 to 0.15 mm and Wg / d is 0.5 to 0.8 (Wg And d will be described later).

  Next, the quality increases from the refrigerant inlet to the refrigerant outlet, but as the liquid film becomes thinner with this increase, the fine groove formed at the bottom of the inner groove also nucleates. It comes to function as an open cavity that promotes. In such a region, both the inner groove and the fine groove contribute to promotion of nucleate boiling.

  Further toward the refrigerant outlet, the quality further increases and the liquid film becomes very thin. In such a high quality region, the effect of promoting nucleate boiling by the fine groove formed at the bottom of the inner groove becomes dominant.

  Therefore, in the cross fin tube heat exchanger for an evaporator according to the present invention, the promotion of nucleate boiling is exhibited over the entire region from the low quality region to the high quality region, and the evaporation heat transfer coefficient is improved. Has the effect of making

  In FIG. 8, the inner surface groove depth d (mm) is a distance from the inner surface fin apex line 27 to the deepest portion 23 of the inner surface groove 12. Note that a circle drawn so that the apex 26 of the inner surface fin 11 of the inner surface grooved heat transfer tube 3 overlaps the circumference, that is, a circle that is concentric with an outer periphery circle of the inner surface grooved heat transfer tube 3 and has a radius A circle smaller by the sum of the bottom wall thickness t and the inner fin height h is referred to as the inner fin apex line 27 (a chain line indicated by reference numeral 27 in FIG. 8). The inner surface groove width Wg (mm) indicates the width of the inner surface groove 12 at a position half the inner surface groove depth d.

  In the present invention, the bottom portion of the inner surface groove is a portion indicated by reference numeral 29 in FIG. That is, it is the wall surface of the inner surface groove 12 from the deepest portion 23 of the inner surface groove 12 to the upper position 28 by the length of one fifth of the inner surface groove depth d. In other words, the position closer to the center of the inner surface grooved heat transfer tube 3 from the deepest portion 23 of the inner surface groove 12 by the length of one fifth of the inner surface groove depth d (dotted line indicated by reference numeral 28). This is the wall surface of the inner surface groove 12. The inner surface groove 12 has a wall surface extending from the deepest portion 23 of the inner surface groove 12 to an upper position 28 by a length of one fifth of the inner surface groove depth d. By forming the fine groove 15 at the bottom, the nucleate boiling promoting action is exhibited and the evaporation heat transfer characteristic is enhanced.

  In the present invention, it is preferable that the fine grooves 15 are formed in all of the individual inner surface grooves 12, but at least one of the inner surface grooves 12 formed in the heat transfer tube 3 with the inner surface grooves, If the fine groove 15 is formed, the portion exhibits a nucleate boiling promoting action, so that the evaporation heat transfer characteristic is improved as compared with the case where the fine groove 15 is not formed at all. Further, it is preferable that the fine groove 15 is formed over the entire area in the longitudinal direction of the inner surface groove 12, but the fine groove 15 is formed in at least a part of the longitudinal direction of the inner surface groove 12. If this is done, the portion exhibits a nucleate boiling promoting action, so that the evaporation heat transfer characteristic is improved as compared with the case where the fine groove 15 is not formed at all.

  h is 0.10 to 0.25 mm, p is 0.18 to 0.45 mm, Wf is 0.05 to 0.15 mm, and Wg is 0.05 to 0.15 mm.

  α is 0 <α ≦ 30, and preferably 15 ≦ α ≦ 30. By setting α within the above range, the evaporation heat transfer characteristics are improved. In the inner surface grooved heat transfer tube according to the present invention, α is larger than 0 °, so that the inner surface fin 11 has a shape in which the width of the inner surface fin becomes narrower as it goes upward. In FIG. 7, when α is 0 °, the side surfaces on both sides of the inner fin are parallel to each other, and when the angle is larger than 0 ° (positive number), the shape of the inner fin increases toward the top (tube The width becomes narrower as it goes to the center.

  The helical angle θ of the internally grooved heat transfer tube 3 is 5 ° or more, preferably 10 to 30 °. The greater the helix angle, the greater the effect of raising the liquid refrigerant to the top of the heat transfer tube and the thinner the liquid film on the entire inner surface of the tube. As the liquid film becomes thinner, the evaporation heat transfer is promoted and the evaporation heat transfer performance is improved. The helical angle θ refers to the angle of the inner groove with respect to the tube axis.

  The material of the internally grooved heat transfer tube 3 is not particularly limited, but is preferably pure copper or low-alloy copper obtained by adding an additive component of up to about 2% to pure copper, which has good workability and thermal conductivity. .

  The material of the aluminum fin according to the cross fin tube type heat exchanger for an evaporator of the present invention is not particularly limited, but pure aluminum such as JIS A 1050 is used in terms of high workability and thermal conductivity. preferable.

  The cross fin tube type heat exchanger for an evaporator of the present invention is used for an evaporator using a refrigerant mainly composed of carbon dioxide. The refrigerant mainly composed of carbon dioxide used in the cross fin tube type heat exchanger for an evaporator of the present invention is carbon dioxide alone or a carbon dioxide refrigerant containing 0 to 15% by mass of refrigerating machine oil.

  An example of a method for producing a cross fin tube heat exchanger for an evaporator according to the present invention will be described. In addition, the following manufacture examples are illustrations, Comprising: The cross fin tube type heat exchanger for evaporators of this invention is not limited to what was manufactured by this method.

  First, a grooved plug is inserted into one continuous original pipe by a known rolling process method, and between the grooved plug and a circular die arranged outside the original pipe, By pressing the original tube, the diameter of the original tube is reduced, and a groove is formed on the inner surface of the tube. Next, an empty drawing drawing process is performed, and the inner surface grooved heat transfer tube before assembling the aluminum fin (before expansion) obtain.

  Next, the obtained inner-grooved heat transfer tube before the tube expansion is inserted into the aluminum fin, and the inner-grooved heat transfer tube before the tube expansion is expanded and fixed, so that the cross fin tube type heat for the evaporator of the present invention is obtained. Manufacture exchangers.

  EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.

(Example 1 and Comparative Example 1)
<Preparation of heat transfer tube with inner groove before tube expansion>
Using an original pipe made of phosphorous deoxidized copper, an inner-grooved heat transfer pipe (before pipe expansion) having a pipe outer diameter of 7 mm was produced by rolling and empty drawing (Example 1). Moreover, the inner surface grooved heat transfer tube (before tube expansion) having a tube outer diameter of 7 mm was produced by rolling using an original tube made of phosphorous deoxidized copper (Comparative Example 1). Table 1 shows the dimensions of the obtained internally grooved heat transfer tube (before tube expansion).

<Manufacture of cross fin tube type heat exchanger>
The internally grooved heat transfer tube obtained before the expansion was expanded by mechanical expansion under the following conditions and assembled to an aluminum fin to produce a cross fin tube heat exchanger for evaluation shown in FIG. Table 2 shows the specifications.
(Conditions for tube expansion)
Mechanical pipe expansion was performed using a pipe expansion plug having an outer diameter of φ6.09 mm.

<Extraction of heat transfer tube with inner groove after expansion>
From the cross fin tube type heat exchanger for evaluation manufactured as described above, the heat transfer tube with the inner surface groove after tube expansion (after tube expansion) was extracted. Table 3 shows the dimension specifications of the obtained heat-transfer tube with an inner groove after expansion (after expansion).

<Form observation of heat transfer tube with inner groove after tube expansion>
The tube at the x position in FIG. 9 was sampled. There are a total of four observation points, one at the left and one at a position where the distance x from the first fin on the anti-U bend side is 100 mm and 200 mm.
About each observation location, the surface of the bottom part of the inner surface groove | channel of four positions was observed by scanning electron microscope observation (SEM) at 90 degree intervals of the tube periphery. Therefore, SEM observation of 4 positions × 4 places = 16 fields of view was performed. The results are shown in Table 3. The size of each visual field was 125 μm × 90 μm.

１）視野中に、溝幅１μｍ以上で長さ２０μｍ以上の微細溝が１個でも観察された場合、微細溝が観察されたとする。
２）１６視野分の合計である。

1) In the field of view, when even one fine groove having a groove width of 1 μm or more and a length of 20 μm or more is observed, it is assumed that the fine groove is observed.
2) Total for 16 fields of view.

<In-tube heat transfer coefficient performance evaluation of the internally grooved heat transfer tube after expansion>
The following two types of heat transfer tube pieces (1) and (2) were selected from the inner grooved heat transfer tube after tube expansion (after tube expansion) extracted from the cross fin tube type heat exchanger for evaluation in Example 1. Connected and evaluated. Moreover, the inner surface grooved heat transfer tube after tube expansion (after tube expansion) extracted from the cross fin tube type heat exchanger for evaluation of Comparative Example 1 was joined and evaluated as the following (3).
(1) Among the internally grooved heat transfer tubes expanded in Example 1, fine grooves were observed at three positions among four positions at 90 ° intervals around the tube circumference. (2) Expanded tubes in Example 1 Of the inner grooved heat transfer tubes thus formed, the fine groove was observed at one of the four positions at 90 ° intervals around the tube circumference. (3) The inner grooved heat transfer tube expanded in Comparative Example 1; That is, no micro-groove was observed at any of the four positions at 90 ° intervals on the tube circumference

Next, as shown in FIG. 10, each inner surface grooved heat transfer tube (after tube expansion) 30 of (1) to (3) above was used as an inner tube, and the inner tube was inserted into the outer tube 31 to control the following conditions. The carbon dioxide refrigerant was allowed to flow into the inner grooved heat transfer tube 30 after the expansion, and heat exchange was performed with the water flowing through the annular portion 32, and the heat transfer coefficient was determined from the inlet and outlet temperatures and flow rates of the water and the refrigerant. As conditions, the heat transfer tube outlet pressure was 4.07 MPa, the saturation temperature was 7.0 ° C., the outlet superheat degree was 3.0 ° C., the inlet dryness was 0.1, and the mass refrigerant speed was 300 or 500 kg / m ² · s. . The results are shown in Table 4.

１）内面溝付伝熱管（拡管後）の（３）の熱伝達率を１００としたときの、各内面溝付伝熱管（拡管後）の熱伝達率

1) Heat transfer coefficient of each internally grooved heat transfer tube (after tube expansion) when the heat transfer coefficient of (3) of the internally grooved heat transfer tube (after tube expansion) is 100

  According to the present invention, an evaporator having excellent heat exchange performance can be manufactured.

DESCRIPTION OF SYMBOLS 1 Cross fin tube type exchanger 2 for evaporator 2 Aluminum fin 3 Heat transfer tube 4 with inner surface groove Hairpin processing part 5 U bend tube 11 Inner surface fin 12 Inner surface groove 15 (15a, 15b, 15c) Fine groove 17 Pipe circumferential direction 18 Inner surface groove Longitudinal direction 19 Width 20 Length 23 Groove deepest portion 25 Bottom wall thickness line 26 Inner surface fin apex 27 Inner surface fin apex line 29 Inner surface groove bottom 30 Extruded heat transfer tube with inner surface groove (after tube expansion)
31 Outer tube 32 Annular portion D Tube outer diameter t Bottom thickness d Inner groove depth h Inner fin height p Inner fin pitch Wf Inner fin width Wg Inner groove width α Inner fin apex angle

Claims (2)

A cross fin tube type heat exchanger for an evaporator having an aluminum fin and an internally grooved heat transfer tube assembled to the aluminum fin and using a refrigerant mainly composed of carbon dioxide,
When the bottom wall thickness of the internally grooved heat transfer tube is t (mm) and the tube outer diameter is D (mm), the following formula (1):
0.055 ≦ t / D ≦ 0.09 (1)
The filling,
A fine groove is formed in the longitudinal direction of the inner surface groove at the bottom of the inner surface groove of the inner surface grooved heat transfer tube;
A cross-fin tube heat exchanger for evaporators.   2. The cross fin tube heat exchanger for an evaporator according to claim 1, wherein the width of the fine groove is 1 to 30 [mu] m.

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