JPH11148747A - Heat transfer tube for evaporator of absorption refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent evaporator for an absorption refrigerator in which a refrigerant adhered to its outer surface has excellent wet spreading, a thin temperature boundary layer of fluid on its inner surface, a large surface area, and excellent heat transfer performance. Provide heat transfer tubes. SOLUTION: A fin 1 extending in a direction orthogonal or inclined to a tube axis direction is provided on an outer surface of a heat transfer tube for an evaporator of an absorption refrigerator.
Is provided. The height of this fin 1 is 0.85 mm
The number of fins per meter in the tube axis direction is set to 1339 rows. At the top of the fin 1, a groove 3 is provided along the fin. The angle between the side walls of the groove 3 is set to 50 °. Further, the fin 1 is provided with a notch 2. On the inner surface of the heat transfer tube, there is provided a rib 4 extending in a direction inclined in the tube axis direction. The lead angle of the rib with respect to the tube axis direction is 43 °. Ratio P / D between rib pitch P and maximum inner diameter Di of the portion having fins
i is 0.13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube for an evaporator suitable for being incorporated in an absorption refrigerator for industrial use, air conditioning of a building, and the like, and more particularly to an absorption refrigerator having good evaporation heat transfer characteristics. The present invention relates to a heat transfer tube for an evaporator.

[0002]

2. Description of the Related Art Generally, in a heat transfer tube, a refrigerant flows down the outer peripheral surface of the heat transfer tube to exchange heat between the fluid flowing in the tube and the refrigerant, thereby cooling the fluid in the tube. The refrigerant that has contacted the heat transfer tube spreads on the surface of the heat transfer tube, evaporates at a low pressure, and removes heat from the heat transfer surface of the heat transfer tube, thereby cooling the fluid inside the heat transfer tube. Further, when the refrigerant spread and wet on the surface of the heat transfer tube evaporates, heat of vaporization is taken from the heat transfer surface, so that the fluid in the tube can be efficiently cooled. Therefore, in order to obtain a high-performance heat transfer tube with good heat transfer performance,
It is necessary to increase the contact area between the refrigerant and the heat transfer tube (that is, the area of the heat transfer surface) as much as possible.

In order to increase the contact area between the refrigerant and the cooling pipe, it is conceivable to increase the surface area of the heat transfer pipe and to improve the wetting and spreading of the refrigerant on the surface of the heat transfer pipe.
Conventionally, as a heat transfer tube having an increased surface area, a low fin tube in which spiral fins are formed on the outer peripheral surface of the tube, a low fin tube with internal ribs provided with spiral ribs on the inner peripheral surface of the low fin tube, and the like. Has been proposed. For example, Japanese Patent Application Laid-Open No.
Japanese Patent Publication No. 2-206356 has been proposed. In the conventional heat transfer tube described in this publication, a wet area is increased by providing a crack in a part of the outer fin. Further, for the purpose of improving the heat transfer property of the inner surface of the tube, for example, a heat transfer tube in which the temperature boundary layer is thinned by providing independent protrusions on the inner surface has been proposed (Japanese Patent Laid-Open No. Sho 62-2).
No. 42799).

Further, in the conventional heat transfer tube described in Japanese Patent Application Laid-Open No. 7-71889, a groove is formed in a fin on the outer surface, and a notch is formed in a tip portion of the fin in a tube axial direction, so that the refrigerant is cooled. Improves wet spreading properties and increases heat transfer surface area. Further, by providing a rib on the inner peripheral surface, the fluid in the pipe is disturbed, and the heat transfer performance on the inner surface side of the pipe is improved.

[0005]

However, the above-described heat transfer tubes have the following problems. That is, in the heat transfer tube described in JP-A-62-206356, the evaporative heat transfer characteristics are not sufficient. Further, in the heat transfer tube described in Japanese Patent Application Laid-Open No. 62-242795, although the independent projections provided on the inner surface have the effect of promoting the turbulent flow of the liquid, the temperature boundary layer is thinned. Is not enough. Also, Japanese Patent Application Laid-Open No. 7-718
In the heat transfer tube described in Japanese Patent Publication No. 89, the temperature boundary layer is formed again even if the turbulent flow of the fluid in the tube is promoted due to the large pitch of the ribs on the inner surface of the tube, and there is a limit to the improvement of the heat transfer performance. is there.

Furthermore, in the prior art, since a high overall heat transfer coefficient was not exhibited in a low flow rate range, it was necessary to increase the capacity of the motor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the turbulent flow of a fluid flowing in a pipe is promoted as much as possible, and the formation of a temperature boundary layer is reduced, thereby significantly improving the evaporative heat transfer performance. It is an object of the present invention to provide a heat transfer tube for evaporation of an absorption type refrigerator which is made to perform the heat transfer.

[0008]

A heat transfer tube for an evaporator of an absorption refrigerator according to the present invention comprises: a tube main body; and a fin provided on an outer surface of the tube main body and extending in a direction orthogonal or inclined to the tube axis direction. A groove formed along the top of the fin, a notch extending in a direction intersecting the fin and notching a tip of the fin, and a notch provided on the inner surface of the pipe body and extending in a direction inclined in the pipe axis direction. In the heat transfer tube for an evaporator of an absorption refrigerator having ribs, the fin is 1 m in the tube axis direction.
There are 1142 to 1417 rows per contact, the height of the fins is 0.7 to 1.2 mm, the angle between the wall surfaces of the grooves is 45 to 65 °, and the pitch P of the ribs and the fins are provided. Ratio P / D to the maximum inner diameter Di of the part
i is 0.1 or more and less than 0.4, and the lead angle of the rib with respect to the tube axis direction is 35 to 50 °.

In the present invention, when a refrigerant such as water is dropped on the above-mentioned heat transfer tube, the refrigerant is captured by the fins of the heat transfer tube,
The refrigerant flows down the fin top in the circumferential direction along the groove, and moves in the tube axis direction through the notch.
The refrigerant that has moved in the pipe axis direction finally flows down from the upper part of the pipe toward the lower part of the pipe through between the fins. As described above, in the heat transfer tube according to the present invention, the refrigerant flows in the circumferential direction and the pipe through the groove formed at the top of the fin and the notch that cuts the fin tip at a predetermined pitch in the tube axis direction. Since the refrigerant spreads in both axial directions, the refrigerant flowing down the outer surface of the heat transfer tube does not have a wetting and spreading bias due to the flow. Therefore,
The heat transfer tube for an evaporator according to the present invention has a large contact area between the refrigerant and the heat transfer tube, and can effectively utilize a large tube surface area due to the formation of the fins.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing a side wall and a fin structure of a heat transfer tube for an evaporator of an absorption refrigerator according to an embodiment of the present invention. Fins 1 extending on the outer periphery of the heat transfer tube at right angles or at an angle to the tube axis direction
Is provided. The top of the fin 1 is provided with a groove 3 formed along the fin. Further, notches 2 arranged in the pipe axis direction are provided at the tips of the fins 1.

In the evaporative heat transfer tube of the absorption refrigerator according to this embodiment, the refrigerant dropped from above the heat transfer tube is captured by the upper half of the heat transfer tube. Then, the refrigerant flows down along the groove 3 at the top of the fin, and moves in the pipe axis direction through the notch 2. Since the top of the fin 1 is compressed when the groove 3 is formed on the top, the top is slightly swelled in the tube axis direction. For this reason, the distance between the tips of the adjacent fins is shorter than when there is no groove at the top of the fin 1. Therefore, it is possible to further control the bias of the refrigerant in the tube axis direction as compared with the heat transfer tube in which the notch is simply provided in the fin. Further, in the low fin tube, the fin acts as a barrier, so that the wetting and spreading of the refrigerant in the tube axis direction is small. However, in the heat transfer tube according to the present embodiment, the groove 3 formed along the fin 1 is provided at the top of the fin 1, and the notch 2 arranged in the tube axis direction is provided in the fin 1. For this reason, it is possible to prevent the refrigerant from contracting due to a large wet spread in the tube axis direction and the flow down.

FIG. 2 is a schematic cross-sectional view of a heat transfer tube according to an embodiment of the present invention in a tube axis direction. As shown in FIG. 4, a rib 4 is provided on the inner surface of the tube in a spiral shape around the tube axis. In the heat transfer tube for the evaporator of the absorption refrigerator according to the present embodiment, since the ribs 4 extend in the direction inclined in the tube axis direction, the turbulence effect of the fluid passing through the tube increases, and the heat transfer in the tube increases. Performance is improved. By this. The heat transfer tube for an evaporator of the absorption refrigerator according to the present embodiment has an effect of improving the heat transfer performance as compared with the case where there is no rib on the inner surface.

The method for forming the outer surface and the inner surface is not particularly limited. For example, Japanese Patent Publication No. 52-11670
Is mentioned. In this method, a mandrel having a hollow pin having a spiral groove on the surface is inserted into the inside of the tube, and the outside of the tube is pressed by a group of disks composed of a plurality of disks. The ribs can be molded simultaneously.

Hereinafter, the reasons for limiting the numerical values of the heat transfer tubes for the evaporator of the absorption refrigerator according to the present invention will be described.

The number of fins per meter in the tube axis direction: 1142
When the number of fins per 1 m in the tube axial direction is less than 1142 rows and when the number of fins exceeds 1417 rows, the wet spreadability is reduced, and the heat transfer performance is reduced. Therefore, 1m in the pipe axis direction
The number of fins per hit is preferably 1142 to 1417 rows.

Fin height: 0.7 to 1.2 mm Both when the fin height is less than 0.7 mm and when it exceeds 1.2 mm, the wet spreading property is reduced. Therefore, it is preferable that the height of the fin is 0.7 to 1.2 mm.

The angle between the two wall surfaces of the groove: 45 to 65 ° The angle between the two wall surfaces of the groove provided on the top of the fin is 45 °
If it is less than 65 ° or more than 65 °, the wet spreadability is reduced. Therefore, it is preferable that the angle between the two wall surfaces of the groove provided on the fin top is 45 to 65 °. The angle formed by both wall surfaces of the groove means the angle formed by both wall surfaces forming the groove in a cross section passing through the pipe axis.

The pitch P of the ribs and the maximum
Ratio P / Di to large inner diameter Di: 0.1 or more and less than 0.4 When the ratio P / Di between the pitch P of the rib provided on the inner surface of the pipe and the maximum inner diameter Di of the portion having the fin becomes less than 0.1. In addition, the width of the groove on the inner surface is reduced, so that the turbulence of the fluid flowing in the pipe is not promoted, and the improvement of the heat transfer performance is reduced.
On the other hand, when P / Di is 0.4 or more, the turbulent flow of the fluid flowing in the pipe is promoted because the width of the groove is widened, but the temperature boundary layer is formed again, and the improvement in heat transfer performance is reduced. . Therefore, the ratio P / Di between the pitch P of the ribs and the maximum inner diameter Di of the portion having the fin is preferably 0.1 or more and less than 0.4.

Lead angle of the rib with respect to the tube axis direction: 35 mm
If the lead angle of the rib provided inside the pipe with respect to the pipe axis direction is less than 35 °, the fluid flowing in the pipe flows along the groove in the pipe, so that the temperature boundary layer is easily formed, and Thermal performance improvement is reduced. On the other hand, when the lead angle exceeds 50 °, the pressure loss in the pipe increases significantly before turbulence of the fluid flowing in the pipe is promoted. Therefore,
The lead angle of the rib with respect to the tube axis direction is preferably 35 to 50 °.

[0020]

EXAMPLES Next, examples of the present invention will be described in comparison with comparative examples outside the scope of the claims.

First, the outer diameter of the tube is 15.88 mm,
Phosphorus deoxidized copper tube (C120) having a tube thickness of 1.24 mm
1; JIS H3300), fins were formed on the outer surface thereof, and ribs were formed on the inner peripheral surface thereof by using a rolling device described in Japanese Patent Publication No. 52-11670 described above to form test tubes. At this time, the outer peripheral surfaces of the tubes of Example 1 and Comparative Examples 2 and 3 have shapes as shown in Table 1. The fins on the outer peripheral surface have a height of 1 mm, and are provided in 1339 rows per 1 m in the tube axis direction. Furthermore, after forming a notch in the tube axis direction at the tip of the fin using a gear-shaped disk, the tip of the fin is formed with a disk having a substantially wedge-like shape, and the angle between the two wall surfaces is 5 °.
It was formed in the circumferential direction so as to be 0 °. Comparative Example 4
A heat transfer tube having 1024 rows / m of fins on the outer surface in the tube axis direction was used.

[0022]

[Table 1]

Then, the evaporating performance of the heat transfer tubes for the evaporator of the absorption refrigerators of the examples and comparative examples of the present invention was measured. FIG.
Is a test device used for measuring the evaporation performance. The test tubes were arranged in one row × 4 stages (stage pitch: 24 mm). Evaporation section 1
In the upper part of the test tube group 7, an inlet 7 for the refrigerant is provided, and in the lower part of the test tube group, an outlet 8 for the refrigerant flowing in the evaporator is provided. The refrigerant discharged from the refrigerant outlet 8 is connected to a pipe 19a.
The refrigerant is sent to the refrigerant pump 15 through the refrigerant pump 15, and the refrigerant is further supplied to the refrigerant inlet 7 through the pipe 19b by the refrigerant pump 15.
Transported to The pipe 19b is provided with a refrigerant spray amount control valve 20, and the refrigerant spray amount control valve 20 controls the amount of the refrigerant sprayed to the evaporating section. The lower end of the test tube group is connected to an inlet 5 of cold water flowing into the test tube, and the upper end is connected to an outlet 6 of cold water.
At this time, the number of passes of the cold water passing through the evaporator was four. Further, a digital manometer 14 for measuring the pressure in the measuring device is provided above the evaporating section 17 by a valve 13b.
Is provided via

On the other hand, an inlet 9 for a LiBr aqueous solution flowing in the absorber is provided above the heat transfer tube group of the absorber 18, and an outlet 10 for the LiBr aqueous solution is provided below the heat transfer tube group.
Further, the outlet 10 of the LiBr aqueous solution is connected to a LiBr aqueous solution pump 16 via a pipe 19c,
The Br aqueous solution is discharged out of the system by the LiBr aqueous solution pump 16. The lower end of the heat transfer tube group is connected to an inlet 11 of cooling water flowing into the heat transfer tube, and the upper end is connected to an outlet 12 of cooling water. Further, a valve 13a for evacuating the inside of the measuring device is attached to the upper part of the absorbing section 18, and this piping is connected to a vacuum pump.

The measurement of the evaporation performance was performed as follows. First, from the inlet 5 of the cold water to the heat transfer tube of the evaporating section 17, 1.
6. Flow cold water at a flow rate of 50 m / s, and the outlet temperature of the cold water is 7.
The inlet temperature of the cold water was adjusted to be 0 ° C. In addition, a constant amount of cooling water was flowed from the cooling water inlet 11 to the heat transfer tube of the absorption section 18, and the flow rate of the cooling water was adjusted such that the pressure in the measuring device was 6.0 mmHg. In this way, after the heat transfer amount of the evaporator is in a steady state, the refrigerant is sprayed to the test tube group from the refrigerant inlet 7 at a spraying amount of 0.75 to 1.25 kg / m · min. The temperature and inlet temperature, the flow rate of cold water and the pressure in the measuring instrument were measured.

By the way, the evaporation performance is represented by Q (kcal / hour) as the refrigerating capacity of the evaporator, and ΔT as the logarithmic average temperature difference.
_m (° C.) and A ₀ (m ² )
, The overall heat transfer coefficient K ₀ (kca
1 / hour · ° C. · m ² ).

[0027]

K ₀ = Q / (ΔT _m · A ₀ )

However, the refrigerating capacity Q of the evaporator is defined as G (kg / hour) of the chilled water flow rate and C _p (kcal / kg ·
° C), the cold water inlet temperature is T _in (° C.), and the cold water outlet temperature is T _out (° C.).

[0029]

## EQU2 ## Q = G · C _p · (T _in -T _out )

The logarithmic average temperature difference ΔT _m is expressed by the following equation (3), where T _e (° C.) is the refrigerant evaporation temperature.

[0031]

[Number 3] _{ΔT m = (T in -T out} ) / ln ((T in -
T _e ) / (T _out −T _e ))

Further, the outer surface area A ₀ of the outer diameter of the original pipe portion is determined as follows:
The outer diameter of the original tube is D ₀ (m) and the effective tube length is L (m)
And when the number of tubes is N, it is expressed by the following Equation 4.

[0033]

A ₀ = π · D ₀ · L · N

FIG. 4 is a graph showing the relationship between the amount of refrigerant sprayed on the horizontal axis and the overall heat transfer coefficient on the vertical axis.
As shown in FIG. 4, in the first embodiment, the lead angle, the ratio P / Di of the pitch P of the rib to the maximum inner diameter Di of the portion having the fin, and the height of the rib are defined by the present invention. The evaporation performance was improved about 1.18 times (when the amount of refrigerant sprayed was 1.00 kg / m · min) as compared with the current product, Comparative Example 4.

On the other hand, in Comparative Examples 2 and 3, since the lead angle is different from that specified in the present invention, a temperature boundary layer is formed, and the heat transfer performance is reduced. For 4, the evaporation performance was reduced.

[0036]

As described above in detail, according to the heat transfer tube for an evaporator of an absorption refrigerator according to the present invention, a fin extending on the outer surface of the tube main body in a direction perpendicular or inclined to the tube axis direction is provided. A groove provided along the fin at the top of the fin, a notch extending in a direction intersecting the fin and cutting out a tip of the fin, and a rib extending in a direction inclined in the pipe axis direction on the inner surface of the pipe main body The number and height of the fins, the angle formed by the wall surface of the groove, the ratio P / Di between the pitch P of the ribs and the maximum inner diameter Di of the portion having the fins, and the tube axis of the ribs. Since the lead angle with respect to the direction is specified as appropriate, the contact area between the refrigerant and the heat transfer tube can be increased, and the wet-spreading property of the refrigerant flowing down the outer surface of the tube can be extremely improved. , And on the inner surface of the pipe There, it is possible to very thin thermal boundary layer. Therefore, the heat transfer characteristics of the heat transfer tube for the evaporator of the absorption refrigerator according to the present invention are extremely excellent. Further, since a high overall heat transfer coefficient is exhibited in a low flow rate range, a large-capacity motor is not required and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a heat transfer tube for an evaporator according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a heat transfer tube for an evaporator according to an embodiment of the present invention in a tube axis direction.

FIG. 3 is a schematic view of an apparatus for measuring the heat transfer performance of a heat transfer tube.

FIG. 4 is a graph showing a comparison between heat transfer performances of heat transfer tubes of an example and a comparative example.

[Explanation of symbols]

 1; Fin 2; Notch 3; Groove 4; Rib 5; Cold water inlet 6; Cold water outlet 7; Refrigerant inlet 8; Refrigerant outlet 9; LiBr aqueous solution inlet 10; LiBr aqueous solution outlet 11; Inlet 12; Cooling water outlet 13a, 13b; Valve 14; Digital manometer 15; Refrigerant pump 16; LiBr aqueous solution pump 17; Evaporator 18; Absorber 19a, 19b, 19c;

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroyuki Kijima 65, Hirasawa, Hadano-shi, Kanagawa Prefecture Inside the Hadano Plant, Kobe Steel Co., Ltd. (72) Inventor Mitsugu Kawai 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. (72) Inventor Takatoshi Takigawa 1-1-1, Nishiichitsuya, Settsu-shi, Osaka, Daikin Industries

Claims (1)

[Claims] 1. A tube main body, a fin provided on an outer surface of the tube main body and extending in a direction orthogonal or inclined to a tube axis direction, a groove formed along a top of the fin, and a direction intersecting the fin. A fin extending from the fin, and a rib provided on the inner surface of the pipe main body and extending in a direction inclined in the pipe axis direction, the fin being a pipe. 1339 rows are provided per meter in the axial direction, and the height of the fin is 0.85 m.
m, the angle formed by the wall surface of the groove is 50 °,
The pitch P of the rib and the maximum inner diameter D of the portion having the fin
A ratio P / Di to i is 0.13, and a lead angle of the rib with respect to a tube axis direction is 43 °, wherein the heat transfer tube for an evaporator of an absorption refrigerator is characterized in that: