JPH0723821B2 - Heat transfer tube for vertical absorber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat transfer tube in an in-tube absorption type vertical absorber in which a large number of heat transfer tubes are arranged vertically, and more particularly to the internal structure thereof. is there.

[Prior art]

An absorber in an absorption refrigerator or absorption heat pump is constructed by arranging a number of heat transfer tubes horizontally or vertically in a closed container. Usually, in this absorber, an absorbing liquid such as a LiBr aqueous solution having a concentration of about 60% by weight is dropped or sprayed on the outside of the heat transfer tube to absorb the water vapor generated in the evaporator and at the same time to transfer the heat at the time of the heat transfer tube. A water-cooled absorber is used in which the water is removed by cooling water flowing through the inside. However, recently, in general, "air cooling of equipment"
Therefore, the appearance of air-cooled absorbers is desired in the absorbers. In that case, since the absorption heat is removed by cooling air, the absorption liquid is made to flow into the heat transfer pipe from above, and at the same time, the steam from the evaporator is supplied into the pipe to be absorbed by the absorption liquid, while the heat transfer pipe Air-cooling fins are attached to the outside of the, and heat is exchanged by applying cooling air to remove absorbed heat generated in the tube. However, in the case of the air cooling type, the temperature of the cooling air becomes higher than the temperature of the cooling water, so the temperature of the cooling cycle rises and the absorbed heat
Higher temperature and higher concentration than water-cooled absorption cooling cycle,
It becomes impractical, and the pressure of the high-temperature regenerator exceeds atmospheric pressure, making it impossible to take advantage of the characteristics of the vacuum container. Therefore, in order to realize air cooling, it is necessary to improve heat transfer on the air side in the absorber, heat transfer on the solution side and diffusion of absorbed water (steam), and improve the function of the absorption liquid circulation cycle. Especially, the improvement of the heat transfer on the solution side and the diffusion of absorbed water is particularly important.

Absorption in the absorber occurs due to the pressure difference between the vapor pressure from the evaporator and the saturated vapor pressure of the absorbing liquid flowing down the surface of the heat transfer tube. If this pressure difference is large, the absorption capacity will improve.
Further, the lower the temperature or the higher the concentration of the absorbing liquid, the larger the pressure difference becomes, and the absorbing ability is improved. Therefore, this type of heat transfer tube is required to improve both heat transfer and “mass transfer” in which absorbed water (steam) diffuses throughout the absorption liquid.

[Problems to be solved by the invention]

However, there are many unclear points regarding the absorption mechanism in these absorbers, and in conventional water-cooled absorbers, the heat transfer tubes were still smooth tubes. Therefore, even for air-cooled absorbers, smooth tubes will be used as heat transfer tubes as well, but it is necessary to clarify the absorption mechanism here and develop high-performance heat transfer tubes with excellent heat transfer and mass transfer. .

[Means and Actions for Solving Problems]

The present invention has been made to solve the above-mentioned problems in the prior art, and an object of the present invention is to provide a novel heat transfer tube with dramatically improved performance, particularly for an air-cooled absorber. Is.

The inventors of the present invention have conducted extensive research on the heat transfer performance as well as the mass transfer performance in the heat transfer tube of the in-tube absorption type vertical absorber, and as a result, when convection occurs in the absorbing liquid film on the inner surface of the heat transfer tube, heat transfer In particular, they have found that mass transfer is greatly promoted. That is, according to the present invention, in a heat transfer tube of an in-tube absorption type vertical absorber in which the absorption liquid flows inside the pipe, the outside of the pipe is air-cooled or water-cooled, and many of them are arranged vertically, A heat transfer tube for an in-pipe absorption type vertical absorber characterized in that a large number of grooves are provided in different directions.

According to the research conducted by the present inventors, a portion of the solution film on the inner surface of the heat transfer tube, which is in contact with the water vapor, absorbs the water vapor to have a gradually lower concentration, and the ability to absorb the water vapor is gradually weakened. In the depth direction, the diffusion does not proceed so much, but if convection occurs in the solution film, agitation occurs in the absorption liquid film, and only the solution surface has a low concentration and the water vapor absorption capacity weakens. It was found that the absorption capacity of the entire absorbent liquid film was improved. In the present invention, a plurality of deep grooves are provided in the longitudinal direction on the inner surface of the tube in a direction different from the flowing direction of the absorbing liquid, and a thick liquid film preferable for generating convection is formed in the solution, and at the same time, the solution forms grooves. It was well agitated when flowing down, and both heat transfer and mass transfer could be greatly promoted.

In the present invention, the cross-sectional shape of the groove provided on the inner wall of the heat transfer tube may be any desired desired shape, for example, a trapezoid as shown in FIG.
It may be a quadrangle or a semicircle. Further, "a direction different from the direction in which the absorbing liquid flows down on the inner surface of the tube" means a direction which is not the longitudinal direction of the tube, and preferably a direction around the tube. The groove may be annular or spiral. In addition, in the case shown in FIG. 1, there is a smooth surface between the grooves, but as shown in FIG. 3, fine grooves shallower than the grooves, fins or uneven surfaces or porous surfaces are formed on the surface. The heat transfer area is increased, especially the heat transfer is improved,
The performance of the heat transfer tube can be improved.

Hereinafter, the present invention will be described more specifically and in detail with reference to Examples.

〔Example〕

FIG. 1 is a sectional view of a part of a heat transfer tube used in an in-tube absorption type vertical absorber according to an embodiment of the present invention. 1 in the figure
Is a tube body of the heat transfer tube, 2 is an inner wall of the tube body 1, 21 is an inner wall 2
It is a groove provided in. In this example, the heat transfer tube consists of a tube body 1 with an outer diameter of 15.88 mm and an inner diameter of 14.5 mm, and its inner wall 2
A trapezoidal groove 21 having a depth of 0.5 mm is annularly provided at a pitch of 2 mm in the longitudinal direction. One of the heat transfer tubes was used as an effective length of 1,000 mm, and the performance measurement test was conducted by incorporating it into the absorber of the "performance measuring device" having the mechanism shown in FIG. In FIG. 2, P is a heat transfer tube used for performance measurement, 3 is an absorption liquid tank (LiBr aqueous solution is contained in the tank as absorption liquid), 4 is an outer tube 41 and a heat transfer tube P. Constituting absorber, 42 absorbs water vapor, flow path of diluted absorption liquid, 5 is evaporator (water is contained in the container), 51 is heater for evaporation,
52 is a water vapor flow path, 6 is a solution tank that absorbs water vapor and stores a diluted absorption liquid, 61 is a temperature adjusting heater, 62 is a concentrated regenerated absorption liquid flow path, 7 is a flow meter,
8 (81, 82) is a densitometer. In the performance measuring apparatus, cooling water is passed through the absorber 4 through the cooling water supply passage 43 and the drainage passage 44 to cool the absorber 4 from the outer periphery. In the evaporator 5, water contained in the container is evaporated by the evaporation heater 51, and steam is supplied to the heat transfer tube P through the flow path 51. On the other hand, the absorbing liquid is supplied from above the heat transfer tube P from the absorbing liquid tank 3. In the heat transfer tube P, the supplied water vapor is absorbed by the absorbing liquid and flows into the solution tank 6 through the flow path 42. In the flow path 42, the density of the diluted absorption liquid is measured by the densitometer 81. The solution tank 6 is equipped with a temperature adjustment heater 61, which concentrates the diluted absorption liquid,
In addition to the absorption liquid having a predetermined concentration, it is refluxed to the absorption liquid tank 3 as a regenerated absorption liquid. The flow path 62 has a flow meter 7 and a density meter 82.
Are installed and each is measured.

In this example, the absorption liquid at a temperature of 40 ° C (concentration of 58 wt% LiBr
Does not contain aqueous solution or surfactant. ) Is supplied from above the absorber 4 so that it flows down along the inner wall of the absorber, and the
From 43, cooling water with a temperature of 28 ° C was flowed in countercurrent. At the same time, water vapor was supplied from the evaporator 5. At this time, the evaporation temperature is 10 ℃
The evaporation heater 51 was adjusted to be constant at. In this measuring method, the heat transfer tube P arranged in the absorber 4
If the performance is good, the amount of water vapor absorbed increases, the input of the evaporation heater 51 in the evaporator 5 increases, and at the same time, the heat exchange amount of the cooling water also increases.

As a result of the above measurement experiment, in the case of the heat transfer tube P of the present embodiment,
Compared with the case of heat transfer tube P'as a reference material for smooth inner wall, the input of the evaporation heater 51 (refrigerating capacity in the actual case) was improved about 1.5 times at liquid film flow rate Γ = 0.1 kg / m · s. . The liquid film flow rate Γ is a value obtained by dividing the absorbed liquid mass flow rate per heat transfer tube by the tube inner peripheral length.

As a result, as described above, in the heat transfer tube of the present invention, the absorbing liquid is stirred well because the absorbing liquid stays in the deep groove and the groove is provided orthogonally to the flow along with the promotion of Marangoni convection. It is considered that both heat transfer and mass transfer were significantly promoted.

〔The invention's effect〕

According to the present invention, in a heat transfer tube for an in-pipe absorption type vertical absorber, a large depth value is provided on the inner wall of the heat transfer tube to maintain a large film thickness of the absorbing liquid flowing down in the tube to generate convection and at the same time Since the grooves are provided in different directions, the absorption liquid is sufficiently agitated, the heat transfer area is further increased, and both heat transfer and mass transfer are greatly improved. It is possible to improve the performance of the absorber such as the absorption refrigerator and the absorption heat pump.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an embodiment of a heat transfer tube according to the present invention, FIG. 2 is a view showing a mutual relation of functions of main parts in a manufactured heat transfer tube performance measuring apparatus, and FIG. 3 is according to the present invention. It is a partial cross section figure of other examples of a heat transfer tube. In the figure, 1: tube (of heat transfer tube), 2: inner wall (of tube 1), 3: absorbing liquid tank, 4: absorber, 41: outer tube, P: heat transfer tube (sample), 5: evaporation Vessel, 6: solution tank, 7: flow meter, 8 (81, 82): density meter.

Claims (1)

[Claims] 1. In a heat transfer tube of an in-tube absorption type vertical absorber in which an absorbing liquid flows inside the pipe, the outside of the pipe is air-cooled or water-cooled, and a large number of them are arranged vertically, the flowing direction of the absorbing liquid on the inner surface thereof. A heat transfer tube for an in-pipe absorption type vertical absorber characterized in that a large number of grooves are provided in different directions.