JPS6239359B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a heat transfer tube that transfers heat between the inside and outside of the tube by utilizing a phase change of a liquid inside the tube.

Examples of machining a plurality of grooves having one type of helical angle on the inner wall surface of a heat exchanger tube are known (for example, Jikkosho et al.
55-14956).

Heat exchanger tubes are also known in which main grooves and sub grooves are formed with twist angles in opposite directions with respect to the tube axis (for example, see Japanese Utility Model Application No. 55-60089).

When the former is used as a heat transfer tube for an air conditioner, when the former is used as an evaporator using boiling heat transfer of the refrigerant inside the tube,
It is known that there is a difference in the heat transfer coefficient within the tubes between a condenser that uses condensation heat transfer, and a heat pump type air conditioner that uses one heat exchanger as both an evaporator and a condenser. In this case, the heat exchanger must be designed based on the smaller in-tube heat transfer coefficient, that is, the condensing performance, and the heat exchanger itself must be enlarged, which is uneconomical.

Although the latter has better condensation performance than the former, it has the following drawbacks mainly in terms of mass production technology.

In general, internal groove machining involves inserting a plug with a required groove on the outer circumferential surface into the pipe to be machined, then contracting the pipe from outside the pipe by some method to press the pipe wall against the plug, and axially moving the pipe. A method is adopted in which the plug is moved relative to the plug.

One example of an industrially successful tube shrinking method is to rotate multiple rolls in a planetary manner along the outer wall of the tube, but experience has shown that the grooves in the tube that occur as the material moves It is known that processing can be carried out more smoothly if the direction of rotation of the plug is opposite to the direction of rotation of the tube shrinking roll around the tube.

In order for heat exchanger tubes to be used in mass-produced products such as air conditioners, the price must be reasonable, and therefore, if the double groove processing is not done in one process, the cost will be high and its use will become impossible. There is a possibility that it may become possible.

As shown in the example above, when machining grooves with helical angles in opposite directions relative to the tube axis, a tube shrinking device with two sets of planetary rotating rolls rotating in opposite directions is used. However, such equipment has a complicated structure and is difficult to operate.
This ultimately leads to higher product costs.

An object of the present invention is to provide an industrially usable heat transfer tube in which the boiling and condensation heat transfer coefficients of the refrigerant inside the tube are both larger and more balanced than those of a bare tube.

In order to achieve this purpose, this invention:
The double grooves formed on the inner wall surface of the tube were inclined in the same direction with respect to the tube axis and crossed.

In this case, the two types of grooves formed have dimensions of an average depth of about 0.05 to 0.5 mm and a pitch of about 0.1 to 0.5 mm, similar to the grooves of known heat exchanger tubes. The inclination of such grooves with respect to the tube axis is preferably in the range of 0 to 45 degrees.

FIG. 1 shows an example of a conventionally known double-grooved tube. In the figure, the inner wall surface 2 of the tube 1 has a plurality of cross sections V at a helical angle of θ ₁ with respect to the tube axis.
A groove 3 in the shape of a letter is machined, and a plurality of grooves 4 are further machined at a helical angle of θ ₂ in the opposite direction to θ ₁ with respect to the tube axis. The intersection of these two types of grooves 3 and 4 creates a large number of unevenness 5 on the inner wall surface of the tube, which contributes to improving the boiling and condensation heat transfer coefficient of the refrigerant in the tube.

FIG. 2 shows an example of a heat exchanger tube according to the present invention. The fact that two types of grooves 6 and 7 are provided intersectingly on the inner wall surface of the tube 1 is the same as in the case of FIG. 1, but one groove 7 has a helical angle of θ ₃ with respect to the tube axis. The other groove 6 is θ ₄ in the same direction as θ ₃ .
It is machined with a helical angle.

A heat exchanger tube having such a combination of grooves 6 and 7 can be manufactured by using a simplified device in which two types of mandrels and rolls that rotate planetarily in the same direction are arranged in two stages in the processing method described above. Therefore, it can be easily processed.

As a specific example of this invention, two types of narrow grooves (the depth corresponds to θ 3) with helical angles of θ ₃ = 7° and θ ₄ = 25° are formed on the inner wall surface of a thin-walled copper tube with an outer diameter of _{9.53 mm} .
0.07 mm and 0.15 mm corresponding to θ ₄ ), 65 tubes were prepared in each cross section.

Figure 3 shows the boiling and condensation characteristics of the refrigerant (Freon R-22) in the tube in this single tube.

The main measurement conditions at this time are condensation pressure 14.0
Kg/cm ² G (1.5 MPa), refrigerant flow rate 46 Kg/h, and average dryness of the refrigerant in the pipe at the measurement part was 0.65.

In addition, FIG. 3 also shows the results of measurement under the same conditions for a tube with a smooth inner surface and a tube with an inner groove with a helical angle of 7 degrees.

Assuming that the heat flux of a heat exchanger for an air conditioner is 20 KW/ ^m2 , the boiling and condensing heat transfer coefficients in the case of the example of this invention are 1.7 times and 1.9 times, respectively, compared to the smooth inner surface pipe. .

As is clear from this result, according to this invention, since the helical angles of the two types of grooves with respect to the tube axis are in the same direction, mass production is possible in the same way as a tube with one type of groove, and the condensation characteristics and evaporation Since the characteristics are well-balanced, it has the advantage of being immediately applicable to heat pumps, and its industrial value is high. Furthermore, the heat transfer tube according to the present invention is suitable for transferring heat by utilizing the phase change of boiling and condensation of the liquid inside the tube, and therefore can be used not only for air conditioners but also as a container material for heat pumps, for example. For example, it is possible to obtain a heat pipe with excellent performance and low cost.

[Brief explanation of the drawing]

1A and 1B are cross-sectional views showing examples of known internally grooved heat exchanger tubes, FIG. 2 is a partial cross-sectional view showing an example of an internally grooved heat exchanger tube according to the present invention, and FIG. 3 is a cross-sectional view showing an example of a known internally grooved heat exchanger tube. It is a graph which shows the single tube heat transfer characteristic of the example of the internally grooved heat exchanger tube which concerns. 1: pipe, 2: inner wall surface, 3, 4, 6 and 7: groove,
5: Unevenness.

Claims (1)

[Claims] 1. In heat exchanger tubes that have a plurality of thin grooves continuous in the axial direction on the inner wall surface, there are two types of heat exchanger tubes that are not parallel to each other and have an inclination of 0 to 45 degrees in the same direction with respect to the tube axis. An internally grooved heat exchanger tube characterized by having the same number of grooves stacked one on top of the other.