JP2997189B2 - Condensation promoting type heat transfer tube with internal groove - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condensation-promoting heat transfer tube having an inner groove using a non-azeotropic refrigerant, and is used for a heat transfer tube for an air conditioner such as a room air conditioner.

[0002]

2. Description of the Related Art Heat transfer tubes used in heat exchangers for air conditioners such as refrigerators and room air conditioners are filled with freon gas (Freon is a trade name of DuPont for fluorochloro-substituted hydrocarbons). A refrigerant is caused to flow, and the refrigerant is evaporated or condensed to exchange heat with a fluid flowing outside the pipe. In the heat transfer tube, as shown in FIG.
A heat transfer tube with an inner surface groove having a large number of fine spiral grooves 20 formed on the inner surface to improve heat transfer characteristics is frequently used (the groove portion is shown in a developed view in FIG. 6A). In this heat transfer tube 10 with an inner groove,
Various groove shapes have been proposed (JP-A-60-1421).
No. 95), but the lead angle θ between the direction of the groove 20 and the pipe axis is
It is usually designed around 20 degrees. FIG. 6B is a perspective view of the spiral groove. In the figure, 20 is a spiral groove, and 21 is a groove crest. By the way, Freon R22 and R12 have been conventionally used as the refrigerant, but since these destroy the ozone layer, a plan to completely eliminate them from the viewpoint of environmental conservation is being advanced. Freon R
22 and R12 substitutes include Freon R32, R134a, R125, etc. which do not affect the ozone layer. In particular, [R32 / R134a / R125] and [R32
/ R125] has a cooling capacity close to that of the conventional Freon R22 and the like, and is highly evaluated as a substitute because it is nonflammable.

The above-mentioned mixed refrigerants include an azeotropic refrigerant and a non-azeotropic refrigerant, and the above-mentioned [R32 / R134a / R125] and [R32 /
R125] and the like are both non-azeotropic refrigerants. The azeotropic refrigerant has the same liquefaction start temperature (dew point) and liquefaction end temperature (boiling point) and exhibits the same behavior as a single refrigerant, so there is no particular problem. Since the end temperatures are different, in the case of condensation, many high-boiling components are condensed at the gas-liquid interface, and low-boiling components are concentrated on the gas phase side. This concentration difference causes diffusion resistance and thermal resistance, and lowers the condensation heat transfer coefficient. In the case of evaporation, the same phenomenon occurs, and the heat transfer coefficient of evaporation decreases. As a method for reducing the concentration difference, a method is known in which, in the case of evaporation, a notch is provided in a crest of a groove to promote boiling (Japanese Patent Publication No. 1-317637). Also, in the case of condensation, a method has been proposed in which high fins are provided at a constant pitch in the crests of the grooves to disturb the flow of the refrigerant in a region where the dryness is high to promote the condensation (Japanese Patent Laid-Open No. Hei 6 (1994)). -307787).

[0004]

However, in the method of providing condensation by providing the above-mentioned high fins, most of the refrigerant is steam in a region where the dryness is high, and since the steam has a large volume flow velocity, the pressure loss in the pipe is reduced. There is a problem that the power consumption increases as a result. From these facts, the present inventors have studied the condensation heat transfer coefficient of a heat transfer tube with an inner groove using a non-azeotropic refrigerant, and the lead angle of the inner groove has a great effect on the heat transfer coefficient of condensation. Having found that, the present inventors have further studied and completed the present invention. An object of the present invention is to provide a condensation-promoting heat transfer tube with a non-azeotropic refrigerant, which can improve the condensation heat transfer coefficient without increasing the pressure loss.

[0005]

According to the first aspect of the present invention,
In the condensation-promoting heat transfer tube with an inner groove using a non-azeotropic refrigerant as the refrigerant, the lead angle of the inner groove is 25 degrees or more , and the groove depth is
A condensation-promoting heat transfer tube with an inner surface groove having a diameter of 0.15 to 0.35 mm .

In the heat transfer tube with an inner groove according to the present invention, the lead angle θ of the inner groove is set to 25 degrees or more, so that the liquid film in the groove is sufficiently stirred, and the difference in the concentration of the refrigerant in the groove is reduced. It reduces and improves the condensation heat transfer coefficient. Further, in the present invention, since no high fin is provided at the peak of the groove, the pressure loss can be suppressed low, and a high condensing heat transfer coefficient can be obtained with a small amount of power consumption. In the present invention, the reason why the lead angle θ is limited to 25 degrees or more is that when the lead angle is less than 25 degrees, the refrigerant liquid film in the groove is not sufficiently stirred, and the concentration difference in the refrigerant does not decrease. In addition, even if a single refrigerant (azeotropic refrigerant) flows through the inner grooved heat transfer tube of the present invention,
Since a single refrigerant does not cause a concentration difference in the refrigerant liquid film in the groove, the effect of increasing the lead angle of the inner surface groove does not appear.

A heat transfer tube with an inner groove according to the present invention will be described with reference to the drawings. FIG. 1 is a partially cutaway view showing a groove shape of a heat transfer tube with an inner surface groove according to the present invention. In the figure, reference numeral 10 denotes a heat transfer tube having an inner surface groove, in which a spiral groove 20 is formed on the inner surface of the tube 10. The lead angle θ between the direction of the spiral groove 20 and the axial direction is 45 °
(The groove portion is shown in a developed view in FIG. 1). The heat transfer tube with an inner surface groove of the present invention can be manufactured by a normal manufacturing method such as drawing a raw tube with a floating plug. As shown in FIG. 4, a heat transfer tube with an inner surface groove having a special shape in which the direction of the inner surface groove is changed, for example, a groove is formed on one surface of the line, and the line is formed by roll forming with the groove forming surface inside. It can be manufactured by a method of forming into a tube and welding the ends.

[0008] In the present invention, the depth of the inner surface groove may be set to 0.1.
If it is less than 15 mm, the liquid film flows over the groove fins, and the liquid film is not sufficiently stirred. 0.35mm
When the pressure exceeds, the pressure loss tends to increase. Thus the depth of the groove you to 0.15-0.35 mm.

[0009]

The present invention will be described below in detail with reference to examples. (Example 1) A spiral groove was formed on the inner surface of a copper tube having an outer diameter of 7.0 mm by a floating plug method to produce a heat transfer tube with an inner surface groove having an effective length of 4 m. The depth of the spiral groove (height of the peak, H in FIG. 6B) was 0.25 mm, and the number of grooves was 50. The lead angle was varied.

The condensed heat transfer coefficient of each of the thus obtained heat transfer tubes with internal grooves was measured using the apparatus shown in FIG. In the apparatus shown in FIG. 2, the test section is a double tube type of an inner tube and an outer tube, and an inner grooved heat transfer tube 10 is set as an inner tube, and a refrigerant flows through the inner grooved heat transfer tube 10, flowing a predetermined amount of coolant in the annular gap 31 between the outer tube 30 and an inner surface grooved heat transfer tube 10, to measure the tube condensation heat transfer rate from the elevated temperature of the cooling water at this time (T ₂ -T ₁₎ Device. Heat transfer tube with internal groove 10
The average condensed saturation temperature of the refrigerant at the inlet and outlet was controlled at 48 ° C, the superheat at the inlet was controlled at 35 ° C, and the supercooling at the outlet was controlled at 5 ° C. The control is performed by an evaporator 40 provided in the device,
The adjustment was performed by adjusting the compressor 41 and the expansion valve. As the refrigerant, non-azeotropic refrigerant Freon R407C or R22 was used. Freon R407C is Freon R32, R134a, R125
Were mixed in a weight ratio of 23:52:25 [R32 / R134a / R12
5]. Refrigerant flow rate in the inner grooved heat transfer tube is
It was set to 200kg / m ² sec. Normally used for air conditioners. The results are shown in FIG.

As is clear from FIG. 3, when the refrigerant is R22, the condensed heat transfer coefficient in the tube shows a peak value (4.1 kw / m ² k) at a lead angle of 18 °, and then gradually decreases. Refrigerant is R
In the case of 407C, the condensed heat transfer coefficient in the tube is from 20 ° to 30
It rises sharply at ° and gradually increases from around 30 °. The condensation heat transfer coefficient in the pipe of R407C is R at the lead angle of 18 °.
24% lower than the peak value of 22. But at a lead angle of 25 °
10% lower and only 3% lower at 40 ° lead angle. That is, even when the substitute R407C is used, a heat transfer coefficient almost equal to that of the conventional refrigerant of R22 can be obtained by setting the lead angle to 25 ° or more.

Example 2 A spiral groove having a lead angle θ of 25 ° or more was formed on the inner surface of a copper tube having an outer diameter of 7.0 mmφ by a floating plug method to manufacture a heat transfer tube with an inner surface groove. 50 grooves
And The lead angle and groove depth were varied.

Comparative Example 1 A heat transfer tube with an inner surface groove was manufactured in the same manner as in Example 1 except that the lead angle θ was changed to 20 °.

Comparative Example 2 A heat transfer tube with an inner surface groove was manufactured in the same manner as in Comparative Example 1, except that a high fin having a height of 0.3 mm was formed at a predetermined interval in the crest of the groove.

The condensed heat transfer coefficient of the obtained inner grooved heat transfer tube was measured in the same manner as in Example 1. R407C was used as a refrigerant. Table 1 shows the results.

[0016] * A 0.3 mm high hi-fin was formed at the top of the groove.

As is clear from Table 1, the products of the present invention (N
o.1 to 4) all had a high condensation heat transfer coefficient in the tube. This is because the refrigerant liquid film in the groove was sufficiently stirred, and the concentration difference was reduced. In particular, those having a large lead angle and a deep groove (high ridge) showed a high value of the condensed heat transfer coefficient in the tube. On the other hand, in Comparative Examples Nos. 5 and 6 , since the lead angle was small, the in-tube condensation heat transfer rate was reduced. In No. 7 , the condensation heat transfer coefficient in the pipe was improved due to the formation of the high fin at the peak of the groove, but the pressure loss was significantly increased.

(Embodiment 3) The groove shape shown in FIGS.
An inner grooved heat transfer tube with an outer diameter of 6.0 mm was manufactured. The groove shape of the heat transfer tube with an inner surface groove is such that the direction of the groove is changed on the way. This heat transfer tube with internal grooves was manufactured by forming a groove on one surface of a copper strip, forming the copper strip into a tubular shape by roll forming with the groove forming surface inside, and welding the edge. The lead angle was 40 degrees or more, the groove depth was 0.25 mm, and the number of grooves was 50. About the obtained heat transfer tube with an inner surface groove, the condensed heat transfer coefficient in the tube was measured by changing the flow rate of the refrigerant in various manners in the same manner as in Example 1. R407C was used as a refrigerant. For comparison, a heat transfer tube with an inner surface groove having the same groove depth and the same number of grooves and a lead angle of 20 degrees was manufactured (FIG. 4D), and the same measurement was performed. FIG. 5 shows the results.

As apparent from FIG. 5, the lead angle is 40 °.
The above examples A to C of the present invention exhibited higher values of the in-tube condensation heat transfer coefficient than the comparative example D having a lead angle of 20 °. The condensed heat transfer coefficient in the pipe showed a higher value as the lead angle θ was larger and the refrigerant flow velocity was faster. As described above, the heat transfer tube with an inner surface groove according to the present invention can obtain an excellent heat transfer coefficient in the tube in various groove shapes.

[R32 / R134a / R125] (R407C)
Described the mixed refrigerant, the heat transfer tube of the present invention,
The same effect can be obtained by using other mixed refrigerants such as [R32 / R125] if the refrigerant is a non-azeotropic refrigerant.
The heat transfer tube of the present invention can also be used as an evaporative heat transfer tube.

[0021]

As described above, the condensation-promoting heat transfer tube using the non-azeotropic refrigerant according to the present invention has a large inner groove lead angle of 25 degrees or more. The refrigerant liquid film is sufficiently stirred, and the concentration difference of the non-azeotropic refrigerant at the gas-liquid interface is reduced, so that the diffusion resistance and the thermal resistance are reduced, and the condensed heat transfer coefficient in the pipe is improved. Also in the present invention, since no or provided Haifin the crests of the grooves, without incurring increase in pressure loss,
Power consumption can be reduced. Moreover, the groove depth is set to 0.1
Since it is defined as 5 to 0.35 mm, the liquid film is
Is prevented from flowing over
Loss increase is suppressed. Further, a non-azeotropic refrigerant that does not destroy the ozone layer can be used. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway view showing an embodiment of a heat transfer tube with an inner groove according to the present invention.

FIG. 2 is an explanatory diagram of an apparatus for measuring a condensed heat transfer coefficient in a pipe.

FIG. 3 is a diagram showing a relationship between a lead angle of a heat transfer tube having an inner surface groove having a spiral groove and a heat transfer coefficient of condensation in the tube.

FIG. 4 is an explanatory diagram of a shape of an inner surface groove of the heat transfer tube with an inner surface groove.

FIG. 5 is a diagram showing the relationship between the refrigerant flow rate and the condensed heat transfer coefficient in an inner grooved heat transfer tube having an inner groove having the shape shown in FIG.

FIG. 6 is a partially cutaway view of a conventional heat transfer tube with internal grooves.

[Explanation of symbols]

 10 Heat transfer tube with inner groove 20 Spiral groove 21 Groove crest 30 Outer tube 40 Evaporator 41 Compressor 42 Expansion valve

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-144595 (JP, A) JP-A-59-38596 (JP, A) JP-A-9-42880 (JP, A) JP-A-62 98200 (JP, A) JP-A-8-145585 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F28F 1/00-1/44

Claims (1)

(57) [Claims] 1. A condensation-promoting heat transfer tube with an inner groove using a non-azeotropic refrigerant as a refrigerant, wherein the lead angle of the inner groove is 25 degrees or more and the groove depth is 0.15 to 0.35 mm . Condensation promoting type heat transfer tubes with internal grooves.