JPH11294899A - Heat exchanger tube for absorber of absorption heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wetting spreadability in a tube peripheral direction and a tube axial direction, and improving absorption heat transfer performance by forming a protruding part in the tube axial direction of an independent boss and providing a recessed part on the outside of the tube. SOLUTION: In a heat exchanger tube 1, a plurality of ribs 2 are formed on the inside thereof spirally extending in a twisting direction in a tube axial direction, and a recessed part 3 is formed on the outside thereof spirally extending in an area matching the rib 2. On the outside of heat exchanger 1 is formed a mutually independent boss 4. The boss 4 forms a quadrangular truncated pyramid, and a protruding part 5 is formed, and both sides thereof parallel in the tube axial direction protrude in an axial direction. Further, the top of the boss 4 is recessed to lower in an area which matches the recessed part 3 (forming the rib 2) on the outside of the tube, forming a recessed part 6. As a result, liquid dropped or sprayed on the outside surface of the heat exchanger tube 1 is made to flow easily in the tube axial direction, and the wetting spreadability of a solution is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an absorber of an absorption heat exchanger such as an absorption refrigerator and an absorption chiller / heater.
The present invention relates to a heat transfer tube for an absorber having an irregular outer surface and improved absorption performance.

[0002]

2. Description of the Related Art Conventionally, in an absorption heat exchanger such as an absorption refrigerator, the inside of the equipment is kept at a vacuum, the refrigerant is evaporated at a low temperature, cold water is taken out by the latent heat of evaporation, and the cold water is used for air conditioning and the like. .

[0003] The absorber and the evaporator are housed in a single body, and in order to obtain continuous evaporation, the refrigerant vapor generated in the evaporator is sprayed on the surface of the heat transfer tube of the absorber. The inside of the body is maintained at a certain degree of vacuum. Therefore, in order to improve the refrigeration capacity of the absorption refrigerator and the absorption chiller / heater, it is necessary to increase the amount of refrigerant vapor generated in the evaporator and increase the absorption amount, that is, the absorption capacity. Regarding the increase in absorption capacity, improving the performance of the heat transfer tube is the most effective means.For this reason, a groove portion and a peak portion extending in the tube axis direction are provided on the outer surface of the tube, and the peak portion has an arcuate curved shape, A heat transfer tube has been proposed in which an independent fin is formed by providing a concave portion in the circumferential direction with respect to the peak portion (Japanese Patent Application Laid-Open No. 9-113066).

[0004]

However, this conventional heat transfer tube has 3 to 25 recesses on the outer surface of the tube / perimeter of the tube. On the other hand, there is a drawback that the wet-spreading property is poor in the axial direction of the tube, and the absorption liquid in the heat transfer tube is separated before the water vapor generated from the evaporator is absorbed by the surface of the heat transfer tube, thereby deteriorating the performance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a heat transfer tube for an absorber of an absorption type heat exchanger having improved wettability and spreadability in the tube axis direction.

[0006]

A heat transfer tube for an absorber of an absorption type heat exchanger according to the present invention is provided in a heat transfer tube for an absorber incorporated in the absorption type heat exchanger so as to extend spirally on the inner surface of the tube. A plurality of spiral ribs, and a plurality of protrusions formed independently of each other on the outer surface of the tube, and the upper surface of the protrusion has an area corresponding to the rib forming portion on the inner surface of the tube. The outer surface of the tube between the protrusions is lower than the region matching the rib non-formed portion, and the region matching the rib formed portion of the tube inner surface is concave to form a spirally extending concave portion, and the protrusion is It is characterized in that the ridge portion projects in the pipe axis direction.

In the present invention, the projections provided independently on the outer surface of the pipe are formed so that the ridges thereof protrude in the pipe axis direction. , And the size of the space interposed between the projections changes. For this reason, the solution dropped or sprayed on the outer surface of the heat transfer tube is less likely to flow in the tube circumferential direction, and is more likely to flow in the tube axis direction, so that the wettability of the solution in the tube axis direction is improved.

The heat transfer tube is usually a copper or copper alloy tube, but an aluminum or aluminum alloy tube, a steel tube or the like can also be used.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a perspective view partially showing a heat transfer tube for an absorber according to an embodiment of the present invention, FIG. 2 is a sectional view taken along a plane including a tube axis, and FIG. 5 is a sectional view orthogonal to the tube axis. The heat transfer tube 1 has a plurality of ribs 2 formed on the inner surface of the heat transfer tube 1 and extending spirally in a direction of twist in the tube axis direction. Is formed. On the outer surface of the heat transfer tube 1, protrusions 4 independent of each other are formed. The projection 4 basically has a truncated pyramid shape as shown in FIG. 4, and both side surfaces parallel to the tube axis direction project from the tube axis direction to form an overhang portion 5. . And
The upper surface of the projection 4 is recessed so as to be lower in a region corresponding to the recess 3 on the outer surface of the tube (and, consequently, the rib 2 on the inner surface of the tube), thereby forming a recess 6.

In the heat transfer tube for an absorber constructed as described above, the projections 4 provided independently of each other on the outer surface of the tube are formed so that their ridges project in the axial direction of the tube.
Is provided, the space sandwiched between the protrusions in the circumferential direction of the tube becomes uneven. Therefore, the solution dropped or sprayed on the outer surface of the heat transfer tube easily flows in the tube axis direction, and the wettability and spreadability of the solution is improved. Conventionally, the wall thickness of this type of heat transfer tube is
Although it was about 1.2 mm or more at 5.88 mm, in the present embodiment, the pipe processing method was improved to reduce the wall thickness to 0.75 m.
m or less. As a result, a helical rib 2 on the inner surface of the tube, that is, an area on the outer surface of the tube that matches the portion of the protrusion protruding into the tube appears as a concave portion 3. Due to the formation of the concave portion 3, the flow of the fluid in the circumferential direction of the pipe on the outer peripheral surface of the pipe becomes slower than that without the concave portion 3, and the wetting and spreading in the axial direction of the pipe are promoted.

In this case, when the area ratio A between the upper surface and the bottom of the independent projection 4 which basically forms a truncated pyramid is less than 0.25, the area of the upper surface of the fin is reduced and the fin is dropped on the heat transfer tube. Alternatively, the sprayed solution easily flows into the space sandwiched between the protrusions, and the Marangoni convection is prevented. On the other hand, when the area ratio A exceeds 0.40, the space between the projections becomes narrow, and the absorbing liquid does not flow into this space, and the heat transfer performance is reduced. Therefore, the area ratio A between the top and bottom of the projection is 0.2
It is preferably set to 5 to 0.40.

As shown in FIG. 5, when the pitch P of the concave portion 6 as the circumferential length on the outer surface of the projection 4 is less than 5.75 mm in the cross section perpendicular to the tube axis, the flow of the solution in the circumferential direction of the tube is reduced. On the other hand, on the other hand, the liquid film on the outer surface of the tube becomes thicker, and the heat transfer performance decreases. On the other hand, the pitch P is 6.75 m
m, the flow of the solution in the circumferential direction of the tube becomes faster,
The wettability and spreadability decrease. Therefore, the pitch P of the recess 6
Is preferably 5.75 to 6.75 mm.

The angle .theta. Formed by the recess 3 on the outer surface of the tube with respect to the tube axis
Is less than 30 °, the flow of the solution in the circumferential direction of the tube is slowed, and the heat transfer performance is reduced. On the other hand, if it exceeds 50 °, the flow in the circumferential direction of the tube becomes faster, and the wettability and spreadability decrease. Therefore, θ is preferably set to 30 to 50 °.

As shown in FIG. 2, if the pitch PF of the projections 4 in the tube axis direction is less than 0.62 mm, the space between the projections 4 becomes narrow, the absorbing liquid does not flow into this space, and the heat transfer performance is reduced. descend. On the other hand, if the pitch PF exceeds 1.33 mm, the space between the projections 4 becomes too wide, and the wet-spreading property in the tube axis direction decreases, and the heat transfer performance decreases. For this reason,
The pitch PF of the projections 4 in the tube axis direction is 0.62 to 1.33.
mm is preferable.

On the other hand, as shown in FIG. 5, when the pitch PR of the projections in the circumferential direction of the tube is less than 0.50 mm, the wet-spreading property in the tube axis direction is reduced, and the heat transfer performance is reduced. Also,
When the pitch PR exceeds 1.20 mm, the solution dropped or sprayed on the heat transfer tube 1 tends to flow in the tube circumferential direction, and the wet-spreading property is reduced.

As shown in FIG. 4, when the ratio AF (= AF1 / AF2) of the area AF1 of the protrusion 5 of the ridge of the projection to the area AF2 of the space between the projections 4 is less than 0.05. The solution dropped or sprayed on the heat transfer tube is likely to flow in the circumferential direction of the tube, and the wet spread is reduced. On the other hand, when the area ratio AF exceeds 0.65, the solution dropped or sprayed on the heat transfer tube does not flow between the protrusions, and the wet spreadability is reduced. Therefore, the area ratio AF is 0.05 to 0.65.
It is preferable that

[0017]

EXAMPLES Next, examples for demonstrating the effects of the above numerical ranges will be shown in comparison with comparative examples which fall outside the scope of claims 2 to 7 of the present invention. Table 1 below
And Table 2 shows the shape and dimensions of the outer and inner surfaces of the tube, Table 1 is an example, and Table 2 is a comparative example.

[0018]

[Table 1]

[0019]

[Table 2]

FIG. 6 shows a test apparatus used for a performance evaluation test of these heat transfer tubes. The interior of the chamber 9 is divided into two chambers of an evaporator and an absorber by a partition 9a, and the same number of heat transfer tubes 10 are arranged horizontally in each chamber and connected in series. In addition, steam can flow through the upper part of the partition 9a. In one evaporator, cold water is introduced into the heat transfer tube 10 from the cold water inlet 11 and discharged from the cold water outlet 12 of the heat transfer tube 10 at the upper end. In addition, these heat transfer tubes 1
0, a refrigerant inlet 13 for introducing the refrigerant into the room is provided.
It is designed to run down. Also, the refrigerant pump 21
Pumps the refrigerant accumulated in the chamber from the refrigerant outlet 14 to the refrigerant inlet 13. On the other hand, in the absorber, the cooling water is introduced from the cooling water inlet 17 to the heat transfer tube 10 at the lower end, and the cooling water is discharged from the heat transfer tube 10 at the upper end via the cooling water outlet 18. Above these heat transfer tubes 10, there is provided a LiBr aqueous solution inlet 15 for introducing the LiBr aqueous solution into the room, and the aqueous solution flows down onto the heat transfer tubes 10 from the aqueous solution inlet 15.
The LiBr aqueous solution collected at the bottom of the chamber 9 is L
The water is discharged from the iBr aqueous solution outlet 16 by the pump 22. The chamber 9 is provided with a digital manometer 20 and a valve 19 for discharging gas from the chamber.

In the evaporator, the refrigerant that has cooled the cold water flowing through the heat transfer tube by evaporating is partially liquefied and accumulated at the bottom of the chamber, and the remainder is formed in the absorber through the upper part of the partition 9a. to go into. Then, the refrigerant is absorbed by the aqueous LiBr solution flowing down on the heat transfer tube 10 in the absorber.

The test conditions are as follows. Internal pressure: 6.0 (mmHg) LiBr solution inlet concentration: 63 (wt /%) LiBr solution inlet temperature: 46 (° C) Cooling water flow rate: 1.50 (m / s) Cooling water inlet temperature: 32.0 (° C) Liquid film flow rate: 0.017 to 0.035 (kg / ms) Surfactant: 2-ethylhexanol added Tube arrangement: 1 row x 6 steps (step pitch 26 mm) Number of passes: 6 passes

However, the flow rate of the cooling water was set based on the sectional area of the pipe end (original pipe). The liquid film flow rate was the amount of absorbing liquid flowing down one side of the tube. The overall heat transfer coefficient K ₀ was calculated from the measured values according to the following formula.

[0024]

K ₀ = Q _a / (ΔT _m · A _o ) Q _a = G _a · C _p · (T _Wout −T _Win ) ΔT _m = (T _Lin −T _Wout ) − (T _Lout −T _Win ) / Ln
_{{(T Lin -T Wout) /} (T Lout -T Win)} A o = π · D o · L · N where, Q _a: absorber heat transfer (kcal / hr) G _a: cooling water flow ( kg / h) C _p : Specific heat of cooling water (kcal / kg · ° C.) T _Win : Cooling water inlet temperature (° C.) T _Wout : Cooling water outlet temperature (° C.) ΔT _m : Logarithmic average temperature difference (° C.) _Ko : Overall heat transfer coefficient (kcal / m ² · h
・ ℃) A _o : Outer diameter of the original pipe Reference surface area of the outer pipe (m ² ) _Do : Outer diameter of the original pipe (m) L: Effective length of the tube (m) N: Number of tubes (number)

FIG. 7 is a graph showing the relationship between the overall heat transfer coefficient obtained from the equation (1) and the angle θ formed with respect to the tube axis of the recess 3 on the outer surface of the tube. FIG. 8 is a graph showing the overall heat transfer coefficient and the protrusion. FIG. 9 is a graph showing the relationship between the area ratio AF of the area AF1 of the ridge portion 5 to the area AF2 of the space sandwiched therebetween and FIG.
Is a graph showing the relationship between the overall heat transfer coefficient and the pitch PR of the projections 4 in the circumferential direction of the tube, and FIG. 10 shows the relationship between the overall heat transfer coefficient and the area ratio A between the top surface and the bottom of the projection 4. Graph diagram,
FIG. 11 is a graph showing the relationship between the overall heat transfer coefficient and the circumferential pitch P of the concave portion 3 on the outer surface of the tube, and FIG. 12 is a graph showing the relationship between the pitch PF of the projections 4 in a cross section orthogonal to the tube axis. As shown in FIGS. 7 to 12 and Tables 1 and 2, Examples 1 to 14 satisfying claims 2 to 7 of the present invention.
Was higher than the overall heat transfer coefficients of Comparative Examples 1 to 17.

[0026]

As described above, according to the present invention,
The ridges of the independent projections protrude in the pipe axis direction to form a protruding part, and by providing a concave part on the pipe outer surface, wetting and spreading in the pipe circumferential direction and pipe axis direction are improved, and absorption heat transfer performance is improved. I do. This makes it possible to reduce the size and performance of the equipment and to reduce the amount of heat transfer tube constituent material used.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a part of an absorption heat transfer tube according to an embodiment of the present invention.

FIG. 2 is a sectional view of a plane including the tube axis.

FIG. 3 is a diagram illustrating an area ratio AF.

FIG. 4 is a plan view of a projection.

FIG. 5 is a cross-sectional view in a direction orthogonal to a tube axis.

FIG. 6 is a diagram showing a test apparatus.

FIG. 7 is a graph showing the relationship between the overall heat transfer coefficient and the angle θ formed by the concave portion 3 of the outer surface of the tube with respect to the tube axis.

FIG. 8 is a graph showing a relationship between an overall heat transfer coefficient and an area ratio AF of an area AF1 of the ridge portion 5 to an area AF2 of a space interposed between protrusions.

FIG. 9 is a graph showing the relationship between the overall heat transfer coefficient and the pitch PR of the projections 4 in the circumferential direction of the tube.

FIG. 10 is a graph showing the relationship between the overall heat transfer coefficient and the area ratio A between the top surface and the bottom of the protrusion 4.

FIG. 11 is a graph showing the relationship between the overall heat transfer coefficient and the circumferential pitch P of the concave portion 3 on the outer surface of the tube.

FIG. 12 is a graph showing the relationship between the overall heat transfer coefficient and the pitch PF of the projections 4 in a cross section orthogonal to the tube axis.

[Explanation of symbols]

 1: heat transfer tube 2: rib 3: concave portion 4: protrusion 5: overhang portion 6: concave portion

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 1, 1998

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] Heat transfer tube for absorber of absorption heat exchanger

Claims (7)

[Claims] 1. A heat transfer tube for an absorber incorporated in an absorption type heat exchanger, wherein a plurality of helical ribs provided to extend helically on the inner surface of the tube and formed independently of each other on the outer surface of the tube. And a plurality of projections, the upper surface of the projections,
The region of the inner surface of the tube that matches the rib forming portion is lower than the region of the inner surface of the tube that matches the non-rib forming portion, and the outer surface of the tube between the protrusions is concave in the region of the inner surface of the tube that matches the rib forming portion and is spiral. A heat transfer tube for an absorber of an absorption type heat exchanger, wherein a concave portion extending to the protrusion is formed, and the protrusion has a ridge portion projecting in a tube axis direction. 2. An area ratio (A) between a top surface and a bottom portion of the projection.
2. The heat transfer tube for an absorber of an absorption heat exchanger according to claim 1, wherein satisfies 0.25 ≦ A ≦ 0.40. 3. A cross section perpendicular to the tube axis, wherein the pitch (P) of the concave portions on the upper surface of the projection is 5.75 mm ≦ P ≦ 6.
The heat transfer tube for an absorber of an absorption heat exchanger according to claim 1 or 2, wherein the heat transfer tube is 75 mm. 4. The tube according to claim 1, wherein an angle (θ) formed by the concave portion of the outer surface of the tube with respect to the tube axis direction is 30 ° ≦ θ ≦ 50 °. Heat transfer tube for absorber of absorption heat exchanger. 5. The absorption type heat exchange according to claim 1, wherein a pitch (PF) of the projections in a tube axis direction is 0.62 mm ≦ PF ≦ 1.33 mm. Tube for absorber of vessel. 6. The absorption type heat exchange according to claim 1, wherein a pitch (PR) of the projections in the circumferential direction of the tube is 0.50 mm ≦ PR ≦ 1.20 mm. Tube for absorber of vessel. 7. A sectional area (A) of a space interposed between the projections.
The ratio (AF) of the area (AF1) of the protrusion of the ridge portion of the projection to F2) is 0.05 ≦ AF ≦ 0.65.
The heat transfer tube for an absorber of an absorption type heat exchanger according to any one of claims 1 to 6, wherein