JPH11270980A - Heat transfer pipe for evaporator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer pipe for an evaporator that can thinly retain a refrigerant between fins and can obtain high heat transfer performance with a small amount of refrigerant. SOLUTION: A single fin part consisting of a fin 10 with a twisting angle of θ1 and a cross fin part consisting of the fin 10 with the twisting angle of θ1 and a fin 11 with a twisting angle of θ2 are formed alternately in the direction of a pipe axis on the outer surface of the heat transfer pipe. As a result, since a refrigerant falls at the cross fin part, the refrigerant is retained thinly between fins, thus obtaining a high heat transfer rate outside the pipe and achieving improved heat transfer performance. Also, since the amount of refrigerant storage can be reduced, a refrigerator can be miniaturized and the circulation load of the refrigerant can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporator which is used in an evaporator such as an absorption refrigerator for producing a cooling fluid such as cold water or an absorption heat pump for air conditioning and which can obtain high heat transfer performance with a small amount of refrigerant. Regarding heat transfer tubes.

[0002]

2. Description of the Related Art In an evaporator such as an absorption refrigerator, heat transfer tubes are horizontally disposed in a multi-row, multi-stage or the like, and a refrigerant is dropped on the outer surface of the heat transfer tube under reduced pressure to evaporate the refrigerant. Fluid such as water flowing in the heat transfer tube is cooled by the latent heat of evaporation. As the heat transfer tube, a heat transfer tube having spiral fins formed on the outer surface to increase the surface area and enhance the heat exchange efficiency is used. This heat transfer tube with a spiral fin is also used for a heat exchange tube of a turbo refrigerator or various heat exchangers. In order to enhance the heat transfer performance of the heat transfer tube with the spiral fins, it is necessary to prevent the refrigerant from spreading over the spiral fins and spreading in a film form so that a dry surface is not formed on the surface of the heat transfer tube. A heat transfer tube has been developed in which the coolant is reduced to about 0.3 to 0.7 mm so that the refrigerant gets over the spiral fins and spreads in a film form.

[0003]

The fin heat transfer tube having a low fin height can obtain relatively high heat transfer performance. However, the present inventors aimed at further improving the heat transfer performance. Various investigations were made on the fin heat transfer tubes. As a result, the refrigerant is held thick between the fins (gap) of the heat transfer tube, and it has been found that this thickly held refrigerant lowers the heat transfer coefficient outside the tube. Thus, the present invention has been completed. An object of the present invention is to provide a heat transfer tube for an evaporator in which a refrigerant is held thin between fins and high heat transfer performance can be obtained with a small amount of refrigerant.

[0004]

According to the first aspect of the present invention,
The outer surface of the heat transfer tube, a single fin portion comprising a fin helix angle theta _1, alternating with cross fin portion in the tube axis direction of the heat transfer tube comprising a fin helix angle theta ₁ between the fin and the twist angle theta ₂ A heat transfer tube for an evaporator, which is formed.

The invention according to claim 2 is the heat transfer tube for an evaporator according to claim 1, wherein the cross fin portion is formed in a ring shape in a circumferential direction of the heat transfer tube.

According to a third aspect of the present invention, there is provided the heat transfer tube for an evaporator according to the first aspect, wherein the cross fin portion is formed in a spiral shape in the tube axis direction of the heat transfer tube.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A heat transfer tube according to the present invention is provided with cross fin portions where fins cross each other at a plurality of locations of a fin heat transfer tube.
The coolant held thick between the fins is dropped at the cross fin portion so that the coolant is held thin between the fins. Thereby, the heat transfer coefficient outside the tube is improved, and higher heat transfer performance can be obtained. The reason why the refrigerant drops at the crossed fin portion is that the refrigerant flowing through the single fin portion is blocked by the crossed fins formed in the crossed fin portion and stays in a large amount in the crossed fin portion. .

Hereinafter, the heat transfer tube of the present invention will be specifically described with reference to the drawings. FIG. 1 is a side view (a) and a partially enlarged explanatory view (b) and (c) showing a first example of a heat transfer tube of the present invention. The outer surface of the heat transfer tube 32, a single fin portion comprising a fin 10 of the helix angle theta _1, the helix angle theta ₁ of the fin 10 and the helix angle theta ₂ of the fins 11
Are formed alternately in the tube axis direction on the surface of the heat transfer tube 32. The cross fin portion is formed in a ring shape in the circumferential direction of the heat transfer tube 32. The angle θ ₃ between the direction of the cross fin portion and the pipe axis is 90 °,
The angle α between the direction of the cross fin portion and the direction of the fin 10 is approximately 45 °.

FIG. 2 is a side view showing a second example of the heat transfer tube of the present invention. The heat transfer tube 32 has a cross fin portion formed spirally in the tube axis direction. Here, the angle between the direction of the intersection fin and the tube axis is counterclockwise θ ₃ (θ ₃
<90 °), and the angle α between the direction of the cross fin portion and the direction of the fin 10 is substantially 90 °.

FIG. 3 is a side view showing a third example of the heat transfer tube of the present invention. The heat transfer tube 32 has a cross fin portion formed spirally in the tube axis direction. Here, the angle between the direction of the cross fin and the tube axis is clockwise θ ₃ (θ ₃ <
90 °), and the angle α between the direction of the cross fin portion and the direction of the fin 10 is approximately 15 degrees. The heat transfer tubes shown in FIGS. 1 to 3 have different cross fin portions,
The effect of the difference on the heat transfer performance is small. In the present invention,
Since the refrigerant is kept thin between the fins, the amount of refrigerant stored in the refrigerator becomes small, so that the refrigerator can be downsized and the load of refrigerant circulation can be reduced.

Next, a method of manufacturing a heat transfer tube according to the present invention will be described. Heat transfer pipe 32 shown in FIG. 1, the outer surface of the smooth tube running to the base tube to form fins 10 of the rotary tool a the knurled grooves are formed in the theta ₁ of inclination against press, then the element knurls a predetermined position of the tube outer surface is produced by forming a fin 11 in a ring shape in the circumferential direction of the mother tube outer surface against press rotary tool b formed in theta ₂ gradient. Here, the rotating tool b is caused to run in the tube axis direction together with the raw tube while rotating the planetary gear around the raw tube to form the fins 11, and thereafter, the rotating tool b
The fin 11 can be formed without stopping the running of the raw tube by repeating the operation of returning the fin 11 to the original position.

The heat transfer tube 32 shown in FIGS. 2 and 3 is formed into a base tube by forming a fin 10 by pressing a rotating tool a having a knurl groove formed at an inclination of θ ₁ against the outer surface of a running smooth tube. It is then produced the fins 11 of the rotary tool b a devoted press helix angle theta ₂ which knurls are formed by theta ₂ of inclination to the base pipe outer surface and formed in a spiral shape. Here, the contact length of the rotary tool b with the raw pipe is usually about ２〜 to ６ of the contact length of the rotary tool a with the smooth tube. The rotating tool b rotates the planet around the raw tube while fixing the position in the tube axis direction.

In the present invention, the height of the fin is 0.2
If it is less than 0.1 mm, the surface area of the outer surface of the tube cannot be sufficiently increased.
If it exceeds 7 mm, the refrigerant liquid film between the fins becomes thick, and the heat transfer coefficient outside the tube decreases. Therefore, the height of the fin is desirably 0.2 to 0.7 mm, particularly desirably 0.2 to 0.5 mm. Since the single fin portion is a portion where the refrigerant liquid film is spread in the tube axis direction and heat exchange is performed efficiently, its length L ₁ (see FIGS. 1 to 3) is increased. Since the cross fin portion is a portion where the flowing refrigerant on the single fin portion falls, the length L ₂ (see FIGS. 1 to 3) may be short. The length L ₁ of the single fin portion is 20
About ～30Mm, the length L ₂ of the cross fin portion 5~10m
About m is appropriate.

[0014]

The present invention will be described below in detail with reference to examples. (Example 1) Various heat transfer tubes shown in FIGS. 1 to 3 were manufactured by the above-described method. A phosphorus deoxidized copper tube was used as the smooth tube before the fin formation, and had an outer diameter of 19.05 mm and a wall thickness of 0.75.
mm heat transfer tube. Fin height, number of fins, torsion angle θ _1, θ _{2 of} heat transfer tube, lengths L ₁ , L _{2 of} single fin portion and cross fin portion, angle θ ₃ between tube axis in direction of cross fin portion Was varied.

Each of the heat transfer tubes obtained in Example 1 was used as a heat transfer tube for an evaporator of an absorption refrigerator, and the heat transfer coefficient α ₀ outside the tube was measured. For comparison, the same measurement was performed on a heat transfer tube having only a single fin portion and a heat transfer tube made of phosphor deoxidized copper having a smooth surface. The results are shown in Tables 1 and 2. The heat transfer coefficient α ₀ outside the tube of each heat transfer tube is represented by a ratio when the heat transfer coefficient α ₀ outside the tube of the heat transfer tube including only a single fin portion is set to 100.

FIG. 4 shows the absorption refrigerator used for the measurement. This absorption refrigerator comprises an evaporator 31 and an absorber 41,
Two evaporator heat transfer tubes 32 each having a length of 500 mm are provided in the evaporator 31.
The heat transfer tubes 32 are arranged in five rows at a shaft center interval of 35 mm, and the heat transfer tubes 32 are connected in series so that cold water is passed inside. The pressure inside the evaporator 31 is reduced, and the refrigerant (pure water) sprayed from the spray pipe 33 evaporates on the surface of the heat transfer tube 32, and the cold water inside the heat transfer tube 32 is cooled by the latent heat of evaporation at that time. The heat transfer tube of the present invention and a comparative example were used for the heat transfer tube 32 of the evaporator 31.

In the absorber 41, ordinary heat transfer tubes 42 for the absorber are arranged in five rows in one row, and the heat transfer tubes 42 are connected to each other in series so that the cooling water flows therein. The evaporator 31 and the absorber 41 are in communication with each other.
The water is condensed on the surface of the heat transfer pipe 42 in the inside, and is absorbed by the absorbing liquid (LiBr) sprayed from the spray pipe 43. In FIG. 4, 44 is a storage tank for the diluted absorption liquid, 45 is a concentration adjusting tank, 46 is a circulation pump, and 47 is a pipe.

The conditions in the evaporator of the absorption refrigerator are as follows. (1) Refrigerant (water) Inlet temperature: 15 ± 1 ° C. Flow rate: 1.0 liter / m · min. (2) Refrigerant spraying device Hole diameter: 1.5 mm, spacing 12 mm (3) Cold water in the heat transfer tube Inlet temperature: 28 ± 0.3 ° C, flow rate: 2.0 m / sec (4) Pressure in the evaporator 1.6 ± 0.07 kPa (12 ± 0.5 mmHg)

Out-of-tube heat transfer coefficient α ₀ (unit: KW / m ² ·
K) was calculated by the following equation. α ₀ = (1 / U) − [D ₀ / (D _i · α _i )] where U is the heat transfer rate determined by the equation U = Q / (ΔT · S) (where Q is the cold water in the pipe) heat exchange amount, logarithmic mean temperature difference ΔT and the pipe cold water temperature and the refrigerant evaporation temperature, the surface area of the maximum outer diameter criterion S is the tube), D ₀ is the maximum outer diameter of the heat transfer tube, D _i is the inner diameter of the heat transfer tube, α _i is calculated by the equation α _i = 0.023 (K /
D _i) R _e ^0.8 P tract heat transfer coefficient obtained by _r ^0.4 (wherein K is cold thermal conductivity, R _e is cold water Reynolds number, P
_r is the number of _plandles in cold water).

[0020]

[Table 1] (Note) No. 1 is the heat transfer tube shown in Fig. 1, and No. 2 to 9 are the heat transfer tubes shown in Fig. 2. Single fin fin, cross fin cross fin. θ ₁ , θ ₂ , θ ₃ : Units: The angle from the tube axis clockwise is +, and the counterclockwise angle is-. Height: fin height mm. Number of fins: Number of fins per round in the pipe circumferential direction.

[0021]

[Table 2] (Note) Nos. 10 and 11 are the heat transfer tubes shown in Fig. 2, and Nos. 12 and 13 are the heat transfer tubes shown in Fig. 3. Single fin fin, cross fin cross fin. θ ₁ , θ ₂ , θ ₃ : Units: The angle from the tube axis clockwise is +, and the counterclockwise angle is-. Height: fin height mm. Number of fins: Number of fins per round in the pipe circumferential direction.

As is clear from Tables 1 and 2,
Nos. 1 to 13 all had an out-of-tube heat transfer coefficient ratio of 104 to
135, a heat transfer tube consisting of only a single fin (No. 1
4,15) and smooth heat transfer tubes (No.16). The length of the length L ₁ intersecting the fin portion of a single fin unit L ₂
When compared for the No.4,5,6 the effect on extravascular heat transfer coefficient α _0, L ₁ is longer, L ₂ is shorter is extravascular heat transfer coefficient alpha
₀ becomes large, and the length L ₂ of the cross fin portion is 6 mm
It turns out enough. The shape of the cross fin portion is compared for No.1,4,13 the effect on extravascular heat transfer coefficient alpha _0, the degree the influence is small, as shown in FIG. 2 (No.4) is slightly better It is. The influence of the fin height of the single fin portion is less than 0.2 mm (No. 10) or more than 0.7 mm (No. 10).
Is extravascular heat transfer coefficient alpha ₀ slightly decreased at No.11), but others showed a high value, the height of the fin it can be seen that no problem if 0.2 to 0.7 mm. Effect of twist angle theta ₁ of the fins of a single fin unit is on extravascular heat transfer coefficient alpha ₀ is twist angle theta ₁ it can be seen that no significant difference in the 40 to 60 ° (provided that the height of the fins 0. Range from 2 to 0.7 mm).

(Example 2) No. 4 (Example of the present invention) used in Example 1, No. 14 (a heat transfer tube having only a single fin portion),
No.16 The extravascular heat transfer coefficient alpha ₀ of (smooth heat transfer tube) were measured by variously changing the refrigerant flow rate. The measurement conditions other than the refrigerant flow rate were the same as in Example 1. FIG. 5 shows the results.

[0024] Figure 5 As is evident, the heat transfer tube of the present invention example, the highest is the extravascular heat transfer coefficient alpha ₀ in the region with less refrigerant flow rate, different heat transfer tubes and tends to be only a single fin unit To This is because the heat transfer tube of the present invention has crossed fins,
This is because the refrigerant drops at the cross fin portions and the refrigerant is kept thin between the fins. When the behavior of the refrigerant was observed during the measurement, as shown in FIG. 6, it was recognized that the refrigerant 20 spread in a film shape over the entire single fin portion and dropped at the cross fin portion. The illustration of the film-like spread is omitted. Refrigerant
20 at a flow rate of 1.0 liter / m · min. No dry surface was produced even when squeezed below. Heat transfer tube consisting of only a single fin
(No. 14) produced a dry surface at the same refrigerant flow rate.

[0025]

As described above, in the heat transfer tube for an evaporator according to the present invention, since the refrigerant falls at the intersection fin portion, the refrigerant is kept thin between the fins and a high heat transfer coefficient outside the tube is obtained. Excellent heat transfer performance. Further, since the amount of stored refrigerant can be reduced, the size of the refrigerator can be reduced, and the circulation load of the refrigerant can be reduced. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

FIG. 1 is a side view (a) and a partially enlarged explanatory view (b) and (c) showing a first example of a heat transfer tube of the present invention.

FIG. 2 is a side view showing a second example of the heat transfer tube of the present invention.

FIG. 3 is a side view showing a third example of the heat transfer tube of the present invention.

FIG. 4 is an explanatory view of a main part of the absorption refrigerator.

FIG. 5 is an explanatory diagram showing an influence of a refrigerant flow rate on an extra-tube heat transfer coefficient α ₀ .

FIG. 6 is an explanatory diagram showing behavior of a refrigerant in the heat transfer tube of the present invention.

[Explanation of symbols]

10 Fin with torsion angle θ ₁ 11 Fin with torsion angle θ ₂ 20 Refrigerant (water) 31 Evaporator 32 Heat transfer tube for evaporator 33 Evaporator scatter pipe 41 Absorber 42 Heat transfer tube for absorber 43 Scatter pipe for absorber 44 Storage tank 45 Concentration adjustment tank 46 Circulation pump 47 Piping

Claims (3)

[Claims] The outer surface of 1. A heat transfer tube, a single fin portion comprising a fin helix angle theta _1, tube and crossing the fin portion is the heat transfer tube comprising a helix angle theta ₁ between the fin and the twist angle theta ₂ of the fin A heat transfer tube for an evaporator, which is formed alternately in the axial direction. 2. The heat transfer tube for an evaporator according to claim 1, wherein the cross fin portion is formed in a ring shape in a circumferential direction of the heat transfer tube. 3. The heat transfer tube for an evaporator according to claim 1, wherein the cross fin portion is spirally formed in a tube axis direction of the heat transfer tube.