JPH0961082A - Heat transfer tube for air-cooled absorber - Google Patents

Abstract

(57) Abstract: In a heat transfer tube for an air-cooled absorber, the holding power and stirring power of an absorbing liquid are improved especially in a low flow rate range, thereby improving heat transfer and mass transfer, and an air-cooled absorber. Improve the performance of. SOLUTION: LiBr (lithium bromide) is formed along the inner wall.
A heat transfer tube for an absorber that allows an absorbing solution such as a solution to flow down, allows water vapor to pass through the tube, has fins attached to the outside of the tube, and cools this with a cooling medium such as air to absorb the water vapor into the absorbing solution. In, the groove formed in the pipe has a left-right asymmetrical shape in a cross section perpendicular to the groove forming direction, and the angles θ ₁ and θ formed by the groove bottom plane and both side surfaces of the groove are
_{One of 2} has a smaller angle in the range of 70 ° to 110 ° than the other, the helix angle of the spiral groove is 15 ° to 45 °, the groove pitch is P = 0.4 to 4.0 (mm), and the groove is Groove depth (H)
Is H = 0.3 to 0.7 mm. Heat transfer tube with inner groove.

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 air-cooled absorber used in an absorption refrigerator, an absorption heat pump, etc., and particularly to improve the stirring force and holding force of an absorbing solution flowing down in the form of a liquid film, In addition, the present invention relates to a heat transfer tube for an air-cooled absorber, in which the contact time between the absorbing liquid and steam is significantly increased, and the heat transfer performance and the steam absorbing efficiency of the absorbing liquid are improved.

[0002]

2. Description of the Related Art Absorbers in absorption refrigerators and absorption heat pumps absorb water vapor generated in an evaporator into an absorbing liquid such as high-concentration lithium bromide (LiBr), and generate absorption heat by a heat transfer tube. Is configured to be removed through. For example, in the case of an air-cooled absorber, the absorbing liquid is made to flow down inside the vertically arranged heat transfer tube (inner wall) to bring it into contact with water vapor, and the radiating fins adhered to the outer surface of the heat transfer tube are cooled by using a cooling medium such as air. By cooling, the absorption heat of the absorbing liquid flowing down in the form of a liquid film in the pipe is removed, and the absorbing liquid absorbs the water content of the water vapor.

Known examples of heat transfer tubes used in such air-cooled absorbers include JP-A-64-3474 and JP-A-64-3475. Japanese Unexamined Patent Publication No. Sho 64-3474 discloses a large number of grooves perpendicular to the pipe axis formed in the pipe to improve the stirring ability of the absorbing liquid.
In the gazette, a fin perpendicular to the tube axis is formed in the tube, and a notch is provided in the fin to distribute the absorbing liquid in the circumferential direction and the direction along the tube axis to improve the mass transfer rate of the absorbing liquid. It is intended.

[0004]

A conventional heat-transfer tube for air-cooled absorber has a shape in which an annular fin or groove is formed in the tube in a direction perpendicular to the tube axis. The focus was on ability. However, since these heat transfer tubes form grooves or fins in a direction perpendicular to or close to the tube axis, even if the absorber tilts even slightly, dryout of the absorbing liquid occurs inside the tubes, resulting in extreme heat transfer tube performance. descend.

Further, such an annular groove generates a sufficient absorption liquid stirring ability when the flow amount of the absorption liquid is high to some extent, but in reality, the flow amount of the absorption liquid per heat transfer tube is very small ( (Approximately 0.07 kg / m · s) The flow rate of the absorbing liquid on the fin becomes slow and the stirring ability of the absorbing liquid decreases.

Further, in order to form such an annular groove or fin in the heat transfer tube, the inside of the tube is cut or
Alternatively, if there is no method other than forming a tubular shape by welding after grooving the strip, and processing by cutting, the chips generated during manufacturing and fins formed are high (1 to 3).
mm), it is difficult to clean the cutting oil, and the inner surface is cut, so that the processing speed cannot be improved and the cost increases. Also, when forming a groove that has been grooved by welding into a pipe, there is no problem in terms of processing speed, but the bead (welding trace) that occurs parallel to the pipe axis during manufacturing causes the absorbing liquid to flow along the bead and However, there is a problem that the effect hardly appears even when forming the.

[0007]

As a result of various studies for solving the above-mentioned problems, the present invention provides an outer diameter which has both absorbing liquid stirring ability and absorbing liquid holding ability at a low flow rate and is excellent in workability. It provides a heat transfer tube of 15 to 31 mm.

That is, in the heat transfer tube with inner groove of the present invention, the absorbing liquid is made to flow down along the inner wall, and the steam is passed through the tube.
In a heat exchanger tube for an absorber in which fins are attached to the outside of the pipe and which is cooled by a cooling medium such as air, the absorbing liquid absorbs water vapor, the groove formed inside the pipe is Right angle cross section (hereinafter referred to as groove right angle cross section)
Is asymmetrical in the horizontal direction, and _one of the angles θ ₁ and θ ₂ formed by the groove bottom plane and both side surfaces of the groove is 70 ° to 110 °.
Has a smaller angle than the other one in the range of, and the helix angle of the spiral groove is 15 ° to 45 °, and the groove pitch is P = 0.4 to 4.0 (m
m) and the groove depth (H) of the groove is H = 0.3 to 0.7 mm. At this time, the outer diameter (Do) of the heat transfer tube having grooves formed on the inner surface of the tube is 15 mm to 31 mm. Is effective. The absorbing liquid in the present invention is, for example, LiBr.
A (lithium bromide) solution or the like can be used.

FIG. 1 is a partial cross-sectional view showing a groove shape of a heat transfer tube having a right-left asymmetric groove right-angle cross section according to the present invention.
By making the cross section of the groove perpendicular to the left and right as described above, the angle θ ₁ formed by one side surface (MR) of the groove and the groove bottom plane can be raised up to about 70 ° as shown in FIG. Normally, in the case of a symmetrical groove shape, this angle of θ ₁ is
The limit is 110 ° to 115 °, and if θ ₁ is smaller than this, there are problems such as breakage of the grooved plug and deformation of the groove shape during pipe expansion.

[0010] However groove shape according to the present invention the ₂ even theta caused to around 70 ° the theta ₁ in order to be asymmetrical
By setting the angle to 140 ° or more, it is possible to set the value of the substantial peak angle α to 30 ° or more, and it is possible to solve the processing problem that has occurred conventionally.

Further, by raising the angle of θ ₁ up to about 70 °, the holding force of the absorbing liquid on one side surface (MR) of the groove is dramatically increased in the low flow rate region, and in the high flow rate region. Since the angle θ ₁ is raised up to nearly 70 °, it is possible to provide a heat transfer tube having a liquid film stirring ability superior to that of the conventional shape.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. Outer diameter 15, 1 by rolling using a grooved plug
Grooved tubes of 9, 25 and 31 mm were made. The groove shape of this heat transfer tube is as shown in FIG. 1, and each dimension value of the groove formed on the inner surface is within the scope of the present invention.

FIG. 2 shows a heat transfer tube according to the present invention and a conventional heat transfer tube having a symmetrical groove formed at θ ₁ = θ ₂ = 115 ° in the tube. The result is shown. The liquid film flow rate on the horizontal axis in the figure was calculated by the following equation.

The dimensions of the heat transfer tube prototyped for measurement are as follows: the conventional triangular mountain heat transfer tube has an outer diameter of 19 mm, a mountain height H = 0.3 mm, a groove pitch P = 0.6 mm, a groove helix angle of 15 °, and θ ₁ = θ ₂ = 115
The heat transfer tube of the present invention has an outer diameter of 19 mm and a mountain height H = 0.3 mm.
, Groove pitch P = 0.6mm, groove twist angle 15 °
The angle between both sides of the groove and the groove bottom plane is θ ₁ = 70
°, θ ₂ = 140 °; θ ₁ = 80 °, θ ₂ = 130 °; θ ₁ =
90 °, θ ₂ = 120 °; θ ₁ = 100 °, θ ₂ = 110 °.

As shown in FIG. 2, the performance of the heat transfer tube according to the present invention is improved in the entire flow rate region, as compared with the conventional grooved heat transfer tube, and particularly in the low flow rate region. That is, the heat transfer tube according to the present invention has stable performance especially in a low flow rate region. This is because, in the present invention, the groove formed on the inner surface of the heat transfer tube has a laterally asymmetric shape in a cross section perpendicular to the groove.

Here, this point will be described with reference to FIG. FIG. 3 shows a cross section perpendicular to the groove in the present invention, that is, a cross section parallel to the tube axis of the heat transfer tube.
_Since the angle between ₁ ) and the bottom plane of the groove is up to about 90 °, especially when the flow rate of the absorbing solution is low, the holding force of the absorbing solution on the side surface (ML ₁ ) of this groove is It becomes larger than that of other shapes larger than 90 °, and the performance sequentially improves along the groove where the absorbing liquid is formed, and the performance improves as the effective heat transfer area increases.

Similar to FIG. 3, FIG. 4 shows a cross section parallel to the tube axis of the heat transfer tube according to the present invention. The angle between one side surface (ML ₂ ) of the groove and the groove bottom plane is up to about 70 °. As a result, the holding force of the absorbing solution is dramatically increased, and the flow path of the absorbing solution can be almost completely controlled at a small flow rate. Therefore, stirring of the absorbing liquid on the side surface (ML ₂ ) of the groove is promoted, and the heat transfer coefficient and the mass transfer coefficient are improved.

FIG. 5 shows a cross section taken along the tube axis of a conventional heat transfer tube. The angle formed between one side surface (ML ₃ ) of the groove and the groove bottom plane is 110 ° or more for processing reasons. Therefore, the holding force of the absorbing liquid in the low flow rate range becomes small, and the side surface of the groove (ML
₃ ) It becomes difficult to keep the liquid film above. Therefore, the occurrence of liquid film breakage of the absorbing liquid reduces the effective heat transfer area, resulting in deterioration of performance.

Table 1 shows, for each inner grooved pipe having an outer diameter of 15, 19, 25 and 31 mm, a peak height H = 0.3 mm, a groove pitch P = 0.6 mm,
The angle between both sides of the groove and the groove bottom plane is θ ₁ =
Keep 90 °, θ ₂ = 130 ° constant, and set the groove helix angle to 10 ° to 50
It shows the performance value when it is changed to °. For all tubes, the mass transfer rate at a twist angle of 10 ° is shown as a relative value with the performance value as 100. From Table 1, it can be seen that the performance of each grooved tube maintains good performance between 15 ° and 45 °.

[0020]

[Table 1]

Table 2 shows that in each inner grooved pipe having an outer diameter of 15, 19, 25 and 31 mm, the groove pitch P is 0.6 mm, the angles formed by both side surfaces of the groove and the groove bottom plane are θ ₁ = 90 °, respectively. θ ₂ = 130
The groove height (H) is 0.1-
It shows the performance value when it is changed to 0.9 mm.
For all tubes, the mass transfer rate at a peak height of 0.1 mm is shown as a relative value with the performance value as 100. If the peak height according to Table 2 is less than 0.3 mm, it will be lower than the film thickness of the absorbing solution, and the groove will be filled with the absorbing solution, so that the contact area between water vapor and the absorbing solution will decrease, leading to a decrease in heat transfer performance. .
Further, when the height is higher than 0.7 mm, the peaks become too high than the film thickness of the absorbing solution, and it becomes difficult to wet the entire peak with the absorbing solution, so that the performance is deteriorated.

[0022]

[Table 2]

Table 3 shows that for each inner grooved pipe having an outer diameter of 15, 19, 25, 31 mm, the angles formed by both side surfaces of the groove and the groove bottom plane are θ ₁ = 90 °, θ ₂ = 130 °, and The performance values are shown when the groove pitch is changed from 0.2 to 4.2 mm while the twist angle is 15 ° and the peak height H is 0.3 mm. For all tubes, the mass transfer rate performance value was set to 100 when the groove pitch was 0.2 mm. According to Table 3, if the groove pitch is smaller than 0.4 mm, the film thickness of the absorbing solution in the groove becomes thick and the performance deteriorates with the increase of thermal resistance. The liquid film breaks down, and the performance decreases as the effective heat transfer area decreases.

[0024]

[Table 3]

From the above results, it has been found that the heat transfer tube with internal groove of the present invention has excellent absorption liquid holding power and liquid film stirring ability, and exhibits superior performance to the conventional product in each flow rate of the absorption liquid. did.

[0026]

According to the heat transfer tube with the inner surface groove of the present invention, a plurality of continuous grooves are provided on the inner wall surface thereof, and the shape of the groove is left-right asymmetrical in the cross section perpendicular to the groove, and one side surface of the groove and the groove bottom are formed. By installing so as to hold the flow of the absorbing liquid on the side surface of the groove whose angle with the plane is smaller than the other one, it has an excellent retaining force and stirring force of the absorbing liquid especially in the low flow rate range, As a result, heat transfer and mass transfer are improved, so that the performance of the air-cooled absorber can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a left-right asymmetric main part groove according to the present invention.

FIG. 2 is a diagram showing mass transfer rates of a conventional product and a heat transfer tube according to the present invention at respective flow rates of absorbing liquid.

FIG. 3 is a partial cross-sectional view parallel to the tube axis of the heat transfer tube according to the present invention.

FIG. 4 is a partial sectional view parallel to the tube axis of another heat transfer tube according to the present invention.

FIG. 5 is a partial cross-sectional view parallel to the tube axis of the conventional product.

[Explanation of symbols]

α Crest angle P Groove pitch H Crest height MR, ML ₁ , ML ₂ , ML ₃ One side of groove θ ₁ Angle between one side of groove and groove bottom plane θ ₂ Another side of groove and groove bottom plane Angle

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Gen Habashi 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Ebara Corporation (72) Inventor Osamu Osa-ku 11-1 Haneda-Asahi-cho, Tokyo In EBARA CORPORATION (72) Inventor Akiyoshi Suzuki 11-1 Haneda-Asahi-cho, Ota-ku, Tokyo Inside EBARA CORPORATION

Claims (2)

[Claims] 1. The absorption liquid is allowed to flow down along the inner wall thereof, the water vapor is passed through the pipe, the fins are attached to the outside of the pipe, and the fin is cooled by a cooling medium such as air so that the water vapor is absorbed in the absorption liquid. In the absorber heat transfer tube to be absorbed, the groove formed inside the tube has a left-right asymmetric shape in a cross section perpendicular to the groove forming direction, and the angles θ ₁ and θ ₂ formed by the groove bottom plane and both side surfaces of the groove Either 70 ° to 110 °
Has a smaller angle than the other one in the range of, and the helix angle of the spiral groove is 15 ° to 45 °, and the groove pitch is P = 0.4 to 4.0 (m
m), the groove depth (H) of the groove is H = 0.3 to 0.7 mm, an inner grooved heat transfer tube. 2. The outer diameter (D) of a heat transfer tube having a groove formed on the inner surface of the tube.
o) is 15 mm to 31 mm, the heat transfer tube with an inner groove according to claim 1.