JPH10176890A - Heat transfer pipe for flowing-down fluid film type evaporator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a substantial heat transfer area and hence improve heat transfer performance by suppressing occurrence of drying-out without increasing the amount of supply of a liquid refrigerant. SOLUTION: The present heat transfer pipe 10 is adapted such that many fins 12 are formed on an outer peripheral surface of a pipe body 11 so as to perpendicularly intersect a pipe axis, and a plurality of grooves 13 are formed in the many fins 12 so as to extend in the direction of the pipe axis. The fin 12 is formed into a fin height H of 0.3 to 1.5mm and a fin pitch Pf of 0.4 to 1.5mm, and the groove 13 is formed into a groove depth D of 0.5 to 2.0mm and a groove interval Pg of 0.3 to 4.0mm. By mounting the many fins 12 on the pipe outer peripheral surface a heat transfer area is increased, and wetting is improved. By providing the plurality of the grooves 13 in the many fins 12 so as to extend in the direction of the pipe axis liquid dispsersion effect in the direction of the pipe axis is increased, and liquid film thickness is made uniform to prevent drying-out from happening and increase the substantial heat transfer area. As a result, heat transfer performance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a seawater desalination apparatus,
The present invention relates to a heat transfer tube for a falling film evaporator applied to a falling film evaporator such as an absorption refrigerator or a chemical process device.

[0002]

2. Description of the Related Art A falling liquid film type evaporator is constituted by arranging a number of heat transfer tubes horizontally in a closed vessel. A heating fluid flows through the heat transfer tubes, and a liquid refrigerant is supplied from above the heat transfer tubes. The liquid refrigerant evaporates while flowing down in a film form along the outer peripheral surface of the heat transfer tube, and the heating fluid is cooled by the latent heat. This falling liquid film type evaporator is suitable for a low temperature heat source evaporator having a low evaporation pressure of the liquid refrigerant, because there is no evaporation suppression by the hydrostatic head of the liquid refrigerant unlike the full liquid type evaporator. Therefore, it has been used as an evaporator for seawater desalination equipment, absorption refrigerators, chemical process equipment, etc.
Recently, it has been widely studied as an evaporator for a low temperature difference power generation plant or a heat pump device using an ocean temperature difference or the like.

As a conventional heat transfer tube for a falling liquid film type evaporator applied to such a falling liquid film type evaporator, an attempt has been made to use a processing tube such as a low fin tube. This processing pipe has a large number of fins arranged in a circumferential direction. Thereby, the heat transfer area can be increased, and the heat transfer performance can be improved.

FIG. 6 shows a conventional falling liquid film type evaporator, in which a dropping pipe 1 as a liquid dispersing device disposed at an upper portion in the evaporator is shown.
And a multi-stage heat transfer tube 2 provided with a large number of fins (not shown) in the circumferential direction. The heat transfer performance is improved based on the increase in the heat area.

[0005]

However, according to the conventional heat transfer tube 2 for a falling liquid film type evaporator using a processing tube such as a low fin tube, the liquid refrigerant 3 is formed by a large number of fins arranged in the circumferential direction. , Obstructs the flow along the pipe axis,
Since the circumferential flow of the pipe 2 becomes dominant, the liquid refrigerant 3
Has a problem that the effect of dispersing the liquid in the direction of the tube axis becomes extremely poor, and the heat transfer performance cannot be improved corresponding to the increase in the heat transfer area.

That is, from the dropping tube 1 to the uppermost heat transfer tube 2
Even if the liquid refrigerant 3 is uniformly distributed in the pipe axis direction, the liquid film thickness of the liquid refrigerant 3 becomes non-uniform as going to the lower stage,
A so-called dryout 4 occurs. This dryout 4
Does not contribute to the heat transfer, and the substantial heat transfer area is reduced. Therefore, if the number of heat transfer tubes 2 is increased to compensate for this, the evaporator becomes large, and if a large amount of liquid refrigerant is supplied, it is possible to suppress the occurrence of dryout 4, but it is impossible to evaporate completely. The required power of the pump used to recirculate the liquid refrigerant 3 accumulated in the lower part of the evaporator also becomes extremely high, so that the inconvenience of reducing the performance count of the device occurs. In addition, since the heat transfer performance of the evaporator largely depends on the size of the area of the dryout 4, there is a disadvantage that the reliability of the apparatus is impaired.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to suppress the occurrence of dryout without increasing the supply amount of the liquid refrigerant, thereby increasing the substantial heat transfer area and improving the heat transfer performance. An object of the present invention is to provide a heat transfer tube for an evaporator.

[0008]

According to the present invention, in order to achieve the above object, a liquid refrigerant flows down an outer peripheral surface of a heat transfer tube to form a liquid film of the liquid refrigerant on the outer peripheral surface. In a falling liquid film evaporator heat transfer tube applied to a falling liquid film evaporator that performs heat transfer through, a large number of fins formed on the outer peripheral surface so as to be orthogonal to a tube axis, and the large number of fins. The fin has a plurality of grooves formed so as to extend in parallel with the direction of the tube axis or at a predetermined angle, and the fin has a fin height of 0.3 to 1.5 mm and a fin pitch of 0.4.
~ 1.5mm, the plurality of grooves,
A heat transfer tube for a falling liquid film type evaporator, characterized in that the groove depth is 0.5 to 2.0 mm and the interval in the circumferential direction of the groove is 0.3 to 4.0 mm. provide.

According to the above configuration, by providing a large number of fins on the outer peripheral surface of the tube, the heat transfer area is increased and the wettability is improved. By providing a plurality of grooves extending in the tube axis direction on a large number of fins, the liquid dispersion effect in the tube axis direction increases, the liquid film thickness becomes uniform, and the occurrence of dryout can be suppressed. Increase. As a result, the heat transfer performance is improved.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a heat transfer tube (hereinafter simply referred to as a “heat transfer tube”) for a falling liquid film type evaporator according to an embodiment of the present invention.
That. (A) is a cross-sectional view, and FIG.
(b) is a longitudinal sectional view, and (c) is a detailed view of a portion A in (a) of FIG. The heat transfer tube 10 has a predetermined size (for example, an outer diameter d).
_o = 14.50 mm, inner diameter d _i = 12.90 mm), for example, a pipe body 11 made of copper, and a large number of fins 12 are formed on the outer peripheral surface of the pipe body 11 so as to be orthogonal to the pipe axis. A plurality of grooves 13 are formed in the fins 12 so as to extend parallel to the tube axis direction or at a predetermined angle.

The fin 12 has a fin height H of 0.3 to
1.5 mm, the fin pitch P _f is formed to be 0.4 to 1.5 mm. The groove 13 has a groove depth (depth from the tip of the fin 12) D of 0.5 to 2.0 mm,
3 is formed so that the interval Pg in the circumferential direction is 0.3 to 4.0 mm, and further, -10 to +1 with respect to the tube axis.
It is formed at an angle of 0 °.

Next, the grounds for setting the fins 12 and the grooves 13 to the above values will be described. The fin pitch _Pf is a parameter that determines the wettability of the liquid. When the fin pitch _Pf is increased, the wettability decreases. On the other hand, if the fin pitch _Pf is reduced, it becomes difficult to form the high fins 12, and the heat transfer area cannot be secured. For this reason,
Fin pitch P _f is suitably 0.4 to 1.5 mm.
Unless the groove depth D is larger than the fin height H, the liquid dispersion effect in the tube axis direction will not be improved. Furthermore, since the heat transfer area increases as the fin height H increases, increasing the fin height H is effective as a means for improving the heat transfer performance. However, when the outer diameter of the heat transfer tube 10 is constant, the higher the fin height H, since the inner diameter d _i of the tube body 11 is decreased, to cause an increase in pressure loss of the fluid flowing within the tube 10 Become. Therefore, in consideration of the above, the fin height H is 0.3 to. 1.5mm,
An appropriate groove depth D is 0.5 to 2 mm.

The number of grooves is closely related to the heat transfer performance.
That is, if the number of grooves is small, the effect of liquid dispersion in the tube axis direction is reduced, but if the number is large, the area of the fin 12 is reduced. Therefore, the groove pitch P _{g in} the circumferential direction of the groove 13 is
1-4 mm is appropriate. In consideration of the fact that the heat transfer tubes 10 are arranged horizontally, it is not preferable that the angle of the groove 13 with respect to the tube axis is large, and it is preferable that the angle be about -10 to + 10 °.

When the above-described heat transfer tube 10 is applied to a falling liquid film type evaporator, a large number of heat transfer tubes 10 are arranged horizontally in a closed vessel, a heating fluid is flowed into the heat transfer tube 10, and the heat transfer tube 1 is heated.
The liquid refrigerant is supplied from above, and the liquid refrigerant evaporates while flowing down in a film form along the outer peripheral surface of the heat transfer tube 10, and the heating fluid is cooled by the latent heat. The liquid refrigerant that could not evaporate in the fins 12 flows through the adjacent grooves 13 in the tube axis direction, then flows down to the adjacent fins 12 and repeats this operation. The liquid refrigerant that could not evaporate on the heat transfer tube 10 flows down to the heat transfer tube 10 arranged at the lower stage, and repeats the above-described operation.

FIG. 2 is a diagram showing an evaporation performance measuring device.
The evaporating performance measuring apparatus 20 includes an evaporator 21 and a condenser 22, and incorporates 24 heat transfer tubes 10 according to the present invention into an evaporator 21 with an effective length of 270 mm in three rows and eight stages. In the measurement, a liquid refrigerant (water) at 15 ° C. was dropped from the dropping tube 23, and cold water at 20 ° C. was flowed into the heat transfer tube 10 at a flow rate of 1 m / tube.
The flow rate and temperature of the cooling water flowing into the condenser heat transfer tube 24 of the condenser 22 were controlled such that the liquid refrigerant evaporated at 15 ° C. while flowing at s.

FIG. 3 is a diagram showing the measurement results obtained by the evaporating performance measuring device 20. As a comparative example, a heat transfer tube 10 according to the present invention and a low fin tube (19 ridges / inch) having a fin outer diameter of 15.88 mm and an outer diameter are shown. The results of performance measurement of a 15.88 mm smooth tube are shown. The liquid film flow rate on the horizontal axis indicates the mass flow rate per unit length flowing on one side of the tube. As is clear from FIG. 3, the heat transfer tube 10 has a significantly improved evaporation performance, approximately twice as large as the smooth tube, and 1.5 times as large as the conventionally used low fin tube.

FIG. 4 is a diagram showing an absorption performance measuring device.
The absorption performance measuring device 30 includes an evaporator 31 and an absorber 32, and the absorber 32 includes eight heat transfer tubes 1 according to the present invention.
0 is incorporated into eight rows in one row with an effective length of 270 mm. The measurement was performed at a concentration of 58 wt% and a temperature of 40 ° C. of the absorbing solution (n
-Octyl alcohol 250 ppm added)
And cooling water at 28 ° C. is flowed into the heat transfer tube 10 at a flow rate of 1 m / s in the tube, and a liquid refrigerant (water) is dropped from the dropping tube 35 to the cooling heat transfer tube 34 of the evaporator 31 so that the evaporation temperature is 10 ° C. The flow rate and the temperature of the cold water flowing into the cooling heat transfer tube 34 of the evaporator 31 were controlled so as to be constant at ° C.

FIG. 5 is a diagram showing the measurement results obtained by the absorption performance measuring device 30, and shows the results of performance measurements on the heat transfer tube 10 according to the present invention and a smooth tube having an outer diameter of 15.88 mm as a comparative example. The liquid film flow rate on the horizontal axis indicates the mass flow rate per unit length flowing on one side of the tube. As is apparent from FIG. 5, even when the heat transfer tube 10 is used as an absorber, the absorption performance is remarkably improved to 1.45 times that of a smooth tube conventionally widely used.

As described above, according to the heat transfer tube 10,
A large number of fins 12 are provided on the outer peripheral surface of the pipe, and a large number of fins 12 are provided.
By providing a plurality of grooves 13 extending in the pipe axis direction,
The liquid dispersion effect of the liquid refrigerant in the tube axis direction is extremely excellent, and the occurrence of dryout can be suppressed even in the lower heat transfer tube 10. Therefore, when the present heat transfer tube 10 is applied to a falling liquid film type evaporator, a dry-out does not occur in all the heat transfer tubes 10 arranged in the evaporator because the liquid dispersion effect in the tube axis direction is excellent. The substantial heat transfer area is improved, and excellent heat transfer performance can be obtained.

For this reason, the evaporation performance of a falling film evaporator such as a seawater desalination device, an absorption refrigerator, and a chemical process device using the heat transfer tube 10 can be improved. Further, since the heat transfer area is substantially large, the number of heat transfer tubes 10 used can be reduced, and the evaporator can be downsized. Further, it is not necessary to supply a large amount of liquid refrigerant in order to suppress the occurrence of dryout.

Further, since the area where dryout occurs is small, the heat transfer performance is stable, and the reliability of the apparatus is improved.

Note that the present invention is not limited to the above embodiment, and various embodiments are possible. For example, in the above embodiment, the case where the groove depth D is larger than the fin height H has been described, but may be smaller than the fin height H. Although the liquid dispersion effect in the tube axis direction is lower than that in the case where the fin height is larger than H, the liquid dispersion effect in the tube axis direction is larger than that of a conventional smooth tube or low fin tube, so that substantial heat transfer is achieved. The heat transfer performance can be improved by increasing the area.

[0023]

As described above, according to the present invention, since a large number of fins are provided on the outer peripheral surface of the tube body, the heat transfer area is increased, and the wettability is improved. Furthermore, since a large number of fins are provided with a plurality of grooves extending in the tube axis direction, the effect of liquid dispersion in the tube axis direction is increased, the liquid film thickness is uniformed, the occurrence of dryout can be suppressed, and substantial The heat transfer area increases. As a result, the heat transfer performance is improved.

Therefore, it is possible to suppress the occurrence of dryout without increasing the supply amount of the liquid refrigerant, to increase the substantial heat transfer area, and to improve the heat transfer performance. This can contribute to the improvement of the evaporation performance of the evaporator.

[Brief description of the drawings]

FIG. 1 shows a heat transfer tube for a falling liquid film type evaporator according to the present invention, wherein FIG. 1 (a) is a cross-sectional view, FIG. 1 (b) is a side view, and FIG.
Is a detailed view of part A of the same figure (a)

FIG. 2 is a diagram showing an evaporation performance measuring device.

FIG. 3 is a diagram showing a measurement result obtained by the evaporation performance measuring device shown in FIG. 2;

FIG. 4 is a diagram showing an absorption performance measuring device.

FIG. 5 is a diagram showing measurement results obtained by the absorption performance measuring device shown in FIG.

FIG. 6 is a view for explaining a problem of a conventional heat transfer tube for a falling film evaporator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Heat transfer tube for falling liquid film type evaporator 11 Tube main body 12 Fin 13 Groove 20 Evaporation performance measuring device 21 Evaporator 22 Condenser 23, 33, 35 Dropping tube 24 Condensing heat transfer tube 30 Absorption performance measuring device 31 Evaporator 32 Absorber 34 intervals in the circumferential direction of the cooling heat transfer pipe d _i the inner diameter d _o outer diameter D depth H fin height P _f fin pitch P _g groove

Continued on the front page (72) Inventor Takashi Sato 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Tsuchiura Plant

Claims (3)

[Claims] The present invention is applied to a falling liquid film type evaporator in which a liquid refrigerant flows down on an outer peripheral surface of a heat transfer tube to form a liquid film of the liquid refrigerant on the outer peripheral surface, and performs heat transfer through the liquid film. In the heat transfer tube for a falling liquid film type evaporator, a plurality of fins formed on the outer peripheral surface so as to be orthogonal to a tube axis, and formed on the plurality of fins so as to extend in parallel with a direction of the tube axis or at a predetermined angle. Wherein the fins are formed such that the fin height is 0.3 to 1.5 mm and the fin pitch is 0.4 to 1.5 mm; A heat transfer tube for a falling liquid film type evaporator, wherein the heat transfer tube is formed so as to have a diameter of 0.5 to 2.0 mm and an interval in a circumferential direction of the groove of 0.3 to 4.0 mm. 2. A heat transfer tube for a falling liquid film type evaporator according to claim 1, wherein said plurality of grooves are formed so as to be deeper than said fin height. 3. The method according to claim 2, wherein the plurality of grooves have a predetermined angle of-
2. The heat transfer tube for a falling liquid film type evaporator according to claim 1, wherein the heat transfer tube is formed at an angle of 10 to +10 [deg.].