JP2505069B2 - Heat transfer tube for absorption refrigerator regenerator - Google Patents

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 absorption chiller regenerator, and more specifically, it is provided in a regenerator of an absorption refrigeration cycle using water / lithium bromide aqueous solution as a working medium, and spirally formed on an outer peripheral surface of a cylindrical tube. The present invention relates to a heat transfer tube having a fin.

[0002]

2. Description of the Related Art Conventionally, water / lithium bromide aqueous solution (refrigerant / absorbent) has been used as a working medium in absorption refrigerators and absorption heat pumps utilizing absorption refrigeration cycles. In the absorption refrigerator, the absorbent that has absorbed the refrigerant evaporated in the evaporator is sent to the regenerator by the pump and is heated there to separate the absorbed refrigerant. Then, the separated refrigerant vapor is sent to the condenser, condensed and returned to the evaporator, and the absorbent after the refrigerant separation is returned to the absorber.

The regenerator used here is provided with a heat transfer tube below the liquid surface of the working medium in order to heat and concentrate the working medium (diluted solution of lithium bromide which has absorbed the refrigerant).
As the heat transfer tube, a smooth tube which is a cylindrical tube or a tube with a spiral fin having spiral fins formed on the outer peripheral surface is used. Then, the working medium is heated by flowing hot water or heating steam as a heat source in the heat transfer tube. For this reason,
The working medium around the heat transfer tube reaches the boiling point to generate bubbles (refrigerant vapor), and water is expelled and concentrated. In this way, the working medium (absorbent) returned to the predetermined concentration is sent to the absorber again and continues the absorbing action.

Thus, in the regenerator, the working medium that has become a dilute solution due to the absorbing action is heated by the heat transfer tube and returns to a predetermined concentration. The conventional spiral finned tube has a fin height (protruding length from the outer peripheral surface) of 0.7 to
It is formed so that the fin pitch is 1.5 mm and the fin pitch is 0.63 to 1.34 mm.

[0005]

The lithium bromide aqueous solution used as the absorbent is a highly viscous fluid as shown in Table 1. For example, at 60 wt% and 80 ° C., it has a viscosity about 7 times stronger than that of water.

Further, as shown in FIG. 5, under a constant pressure, the boiling point rises as the concentration rises.
Therefore, the conventional heat transfer tube has the following problems.

[0007]

[Table 1]

That is, as shown in FIGS. 2 (a) and 2 (b),
A thin liquid film c of the high-concentration solution is easily formed around the heat transfer tube (smooth tube a or tube with spiral fin b) by heating from the heat transfer surface. Therefore, in this high-concentration solution thin film c, the boiling point rises as the concentration of the solution rises, and the wall surface superheat degree required for boiling rises as much as the boiling point rises. As a result, the boiling heat transfer rate decreases.

Further, since the high concentration solution thin film c has a higher viscosity than that of the surrounding solution, the viscosity increases, so that active generation of bubbles is hindered. For this reason, the boiling heat transfer coefficient also decreases.

In the conventional spiral finned tube b, since the aqueous solution of lithium bromide is highly viscous, the flow resistance is high, which hinders the stirring action due to the generation of bubbles between the fins bf and the boiling heat transfer coefficient. Is reduced.

An object of the heat transfer tube for an absorption refrigerating machine regenerator of the present invention is to solve the above problems and improve boiling heat transfer performance.

[0012]

A heat transfer tube for an absorption chiller regenerator according to the present invention is provided in a regenerator of an absorption refrigeration cycle using water / lithium bromide aqueous solution as a refrigerant / absorbent as a working medium. Do not form a spiral fin on the outer peripheral surface of
In addition, it is placed under the liquid surface of the working medium and heats the inside.
In a heat transfer tube for an absorption refrigerator regenerator in which a fluid serving as a source flows , the spiral fin has a protruding length of 1.8 mm to 3.5 mm from an outer peripheral surface of the cylindrical tube and a fin pitch of 1.8 mm to 2 The gist is that it is formed as 0.8 mm.

[0013]

In the heat transfer tube for the absorption refrigerator regenerator of the present invention having the above-mentioned structure, the protruding length of the spiral fin, that is, the fin height is 1.8 mm to 3.5 mm and the fin pitch is 1.8 m.
It is formed to m-2.8 mm. That is, the fin height is higher and the fin pitch is wider than the conventional spiral finned tube. Therefore, even if a thin liquid film of a high-concentration solution is formed around the heat transfer tube, the height of the fins is high, so that the solution thin film does not fill the recesses between the fins. As a result, a sufficient heat transfer area is secured in the portion not covered with the high-concentration solution thin film, and the degree of wall superheat required for boiling is reduced. Further, since the fin pitch is wide, the flow resistance of the solution flowing between the fins due to the generation of bubbles between the fins becomes small. That is, the solution smoothly flows between the fins as the bubbles are generated. As a result, a sufficient stirring action is obtained and the boiling heat transfer coefficient is improved.

The fin pitch is 1.8 mm to 2.8 m.
When m is less than 1.8 mm, the flow resistance at the time of inflow of the solution accompanying bubble generation increases, and effective heat transfer performance cannot be obtained, and when it is wider than 2.8 mm, This is because the effective heat transfer area cannot be expected to increase. Also,
The fin height is 1.8 mm to 3.5 mm,
If it is less than 1.8, most of the periphery of the heat transfer tube (most of the fins) is covered with the high-concentration solution thin film, and effective heat transfer performance cannot be obtained. This is because production is impossible due to processing restrictions.

[0015]

EXAMPLES In order to further clarify the structure and operation of the present invention described above, preferred examples of the heat transfer tube for an absorption refrigerator regenerator of the present invention will be described below.

FIG. 1A is a cross-sectional view of a spiral finned tube as one embodiment, and FIG. 1B is a partially enlarged view thereof. The spiral finned tube 1 of the present embodiment is provided in a liquid-filled regenerator (not shown) of an absorption refrigerator using water / lithium bromide aqueous solution as a working medium, and has a spiral shape on the outer peripheral surface of the cylindrical tube portion 2. The fin 3 is formed. This spiral finned tube 1
Is provided below the liquid surface of a working medium (hereinafter referred to as a solution) sent into the regenerator, and heated water is passed through the pipe. Therefore, the solution is heated by using the heated water as a heat source to drive out water and concentrate the solution.

Here, the dimensional specifications of the spiral finned tube 1 are
Table 2 shows the dimensions of a conventional pipe with a spiral fin (hereinafter, referred to as a conventional pipe b) in comparison with each other. The reference numerals attached to the items in the table correspond to the distances indicated by the reference numerals in FIG.

[0018]

[Table 2]

As shown in Table 2, in the spiral finned tube 1 of this embodiment, the fin pitch Pf and the fin height H are:
It is characterized in that it is larger than the conventional tube b. That is, the fin height H is set to 1.8 mm to 3.5 mm, and the fin pitch Pf is set to 1.8 mm to 2.8 mm. Therefore, the solution has the following effects.

First, the fin height H is set to 1.8 mm to 3.5.
As shown in FIG. 2C, even if a thin liquid film c of the high-concentration solution is formed around the spiral finned tube 1 by heating the solution, the high-concentration solution thin film The state that c does not completely fill the concave portion 4 between the fins 3 does not occur. That is, the high concentration solution thin film c is not covered except for the root side of the fin 3. Therefore, since the boiling point of the solution is low in the portion not covered with the high-concentration solution thin film c, the wall surface superheat required for boiling can be kept low, and a high boiling heat transfer coefficient can be obtained. Moreover, since the viscosity of the solution is low in the portion not covered with the high-concentration solution thin film c, active generation of bubbles is not hindered.

On the other hand, in the conventional tube b, as shown in FIG.
As shown in, although the heat transfer surface is uneven by the fin bf, the fin height H is 0.7 mm to 1.5 m.
Since it is as low as m, the high-concentration solution thin film c (the boiling point increases due to the high concentration) almost completely fills the concave portions between the fins bf. As a result, the wall surface superheat required for boiling increases by the amount corresponding to the increase in the boiling point, and the boiling heat transfer coefficient decreases. Further, as shown in FIG. 2A, in the smooth tube a, the outer peripheral surface is uniformly covered with the high-concentration solution thin film c, and the boiling heat transfer coefficient is also reduced. Moreover,
Since the high-concentration solution thin film c has a high viscosity, neither of the heat transfer tubes a and b can actively generate bubbles.

Further, the spiral finned tube 1 has a large fin pitch Pf of 1.8 mm to 2.8 mm, so that the flow of the solution flowing between the fins 3 as the bubbles are generated between the fins 3. The resistance is small. That is, FIG. 3 (a)
As shown in FIG. 3, when the solution is heated and bubbles k are generated between the fins 3 and float in the direction of arrow e, the surrounding solution is recessed between the fins 3 as indicated by arrow f as the bubbles k float. It is possible to smoothly flow into 4 and obtain a sufficient stirring action up to the base of the fin 3. As a result, the boiling heat transfer coefficient increases.

On the other hand, in the conventional tube b, since the fin pitch Pf is as small as 0.63 mm to 1.34 mm, the flow resistance of the solution flowing between the fins bf due to the generation of the bubbles k is large. Therefore, as shown in FIG. 3B, even if bubbles k are generated between the fins bf and float in the direction of the arrow g, the surrounding solution may flow to the roots of the fins bf as shown by the arrow h. It is not possible to obtain a sufficient stirring action.

As described above, according to the spiral finned tube 1 of this embodiment, the fin height H is set to 1.8 mm to 3.5 mm,
By setting the fin pitch Pf to 1.8 mm to 2.8 mm, it is possible to suppress the heat transfer inhibition phenomenon due to the increase in boiling point and viscosity of the solution due to heating and the flow resistance of the solution. Further, since the spiral finned tube 1 is formed with such fin height H and fin pitch Pf, the fin root radius R (0.3 mm in this embodiment) is smaller than that of the conventional tube b having the same fin outer diameter. can do. Therefore, the fin root portion becomes a nucleus for bubble generation, and bubbles can be generated more actively. As a result, the boiling heat transfer performance can be significantly improved.

Here, the measurement results of the boiling heat transfer performance test of the spiral finned tube 1 of this embodiment and the conventional tube b and the smooth tube a will be described. The measurement target is a smooth pipe a and two types of conventional pipes b1 and b2 having the dimensions shown in Table 3.
Then, three types of spiral finned pipes 11, 12, and 13 which are the spiral finned pipes of this embodiment are used. These heat transfer tubes had a fin portion outer diameter Df of 19.05 mm (the smooth tube a is the original tube outer diameter).

The performance test conditions are set with reference to the operating conditions of the low temperature regenerator used in the actual double-effect absorption refrigerator, and are shown in Table 4.

[0027]

[Table 3]

[0028]

[Table 4]

The results of the boiling heat transfer performance measurement of these heat transfer tubes are shown in FIG. As shown in the figure, the spiral finned tube 11,
12, 13 are compared with the conventional tubes b1, b2 and the smooth tube a,
It can be seen that the boiling heat transfer coefficient is much higher. In particular, the higher the fin height H is, the higher the boiling heat transfer coefficient is obtained. In the spiral finned tube 11 having the fin height H of 3.2 mm, the smoothing tube a is about 1.5 times larger than the conventional tubes b1 and b2. It is about twice as much as

In this way, the excellent boiling heat transfer performance of the spiral finned tube 1 is also demonstrated by experiments. Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it is needless to say that the present invention can be implemented in various modes without departing from the scope of the present invention.

[0031]

As described above in detail, the heat transfer tube for the absorption refrigerator regenerator of the present invention has the protruding length of the spiral fin, that is,
Since the fins are formed to have a height of 1.8 mm to 3.5 mm and a fin pitch of 1.8 mm to 2.8 mm, the wall surface superheat required for boiling is reduced, and a sufficient stirring action accompanying bubble generation is achieved. can get. As a result, there is an excellent effect that the boiling heat transfer performance can be significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a spiral finned tube as an example.

FIG. 2 is an explanatory view showing a formation state of a high-concentration solution thin film formed around a heat transfer tube.

FIG. 3 is an explanatory diagram showing a flow of a solution accompanying generation of bubbles.

FIG. 4 is a graph showing the results of boiling heat transfer performance measurement of heat transfer tubes.

FIG. 5 is a graph showing characteristics of an aqueous lithium bromide solution.

[Explanation of symbols]

1 ... Tube with spiral fin, 3 ... Fin, H ... Fin height, P
f ... fin pitch

Claims (1)

(57) [Claims] 1. A provided the regenerator of the absorption type refrigerating cycle to the working medium water / lithium bromide solution as refrigerant / absorbent, it forms a helical fin on the outer circumferential surface of the cylindrical tube
In addition, it is placed under the liquid surface of the working medium and heats the inside.
In a heat transfer tube for an absorption refrigerator regenerator in which a fluid serving as a source flows , the spiral fin has a protrusion length of 1.8 mm to 3.5 mm from an outer peripheral surface of the cylindrical tube, and a fin pitch of 1.
A heat transfer tube for an absorption refrigerator regenerator, which is formed to have a thickness of 8 mm to 2.8 mm.