JPH0723820B2 - Heat transfer tube for absorber - Google Patents

Description

The present invention relates to a heat transfer tube used in an absorber such as an absorption refrigerator and an absorption heat pump.

[Prior Art and Problems Thereof] An absorber in an absorption refrigerator, an absorption heat pump, or the like is configured by arranging a large number of heat transfer tubes horizontally or vertically in a closed container. In this case, an absorbing liquid, for example, a LiBr aqueous solution (concentration of about 60% by mass) is dropped and sprinkled on the outside of the heat transfer tube to absorb the steam generated in the evaporator, and at the same time, heat at the time of absorption is absorbed by the cooling water flowing in the tube. Acts to remove.

Absorption is caused by the pressure difference between the evaporation pressure in the evaporator and the saturated vapor pressure of the absorbing liquid dropped on the surface of the heat transfer tube. If this pressure difference is large, the capacity is improved. Further, the lower the temperature or the higher the concentration of the absorbing liquid, the lower the saturated vapor pressure and the larger the pressure difference, which contributes to the improvement of the absorbing capacity.
Therefore, this type of heat transfer tube is required to improve both the heat transfer and the mass transfer of the condensed water into the absorbing liquid. However, there are many unclear points regarding this absorption mechanism, and smooth tubes have been the mainstream as heat transfer tubes.

On the other hand, in the absorber, the heat transfer tubes are arranged horizontally and the absorption liquid is dripped from above. At this time, the absorbing liquid flowing on the surface of the tube is in the form of a thin film, and further progress is being made toward a thin film in order to reduce the heat transfer resistance and improve the efficiency of the device. However, in absorption, mass transfer is rate limiting rather than heat transfer. Therefore, in the current thin-film flow-through method, it is impossible to expect a dramatic improvement in absorption performance unless the mass transfer is promoted rather than the heat transfer is promoted. Therefore, recently, it has been attempted to use a processing tube such as a low fin tube for the purpose of increasing the heat transfer area and at the same time making the absorption liquid into a thin film. Has not improved.

Since the absorber is an important component that influences the performance of the equipment, it is important to improve the performance of the absorber in order to make the equipment compact and high performance in the future. Therefore,
Improving the performance of heat transfer tubes is an important point, and it is especially necessary to promote mass transfer during the absorption process.

[Object of the Invention] Surfactants such as diethylhexanol are added to the absorption liquid of commercial absorption refrigerators, absorption heat pumps and the like. This is empirically known as a method of improving absorption capacity.

An object of the present invention is to provide a novel heat transfer tube capable of dramatically improving performance even in an absorber using an absorbent containing such a surfactant.

[Summary of the Invention] The inventors have conducted research and experiments on heat transfer performance as well as heat transfer performance, and as a result, when convection occurs in the absorbing liquid film on the surface of the heat transfer tube, heat transfer, particularly mass transfer, is significantly increased. It turned out to be promoted to. The solution on the surface of the heat transfer tube absorbs the water vapor on the surface in contact with the water vapor to have a low concentration, but the movement in the depth direction does not progress much by diffusion alone. If convection occurs there, agitation occurs in the liquid film, and only the surface of the solution becomes low in concentration, and absorption is not suppressed, and the performance is improved.

Further, it is known that convection is generally caused by a difference in surface tension due to the addition of a surfactant, and tends to occur when the thickness of the solution is large.

In the present invention, the shape of the pipe itself is made wider in the dropping direction of the liquid, so that the liquid film is thickly retained at the upper part of the pipe and at the same time, the liquid flow is distributed in the circumferential direction, and the entire pipe surface is covered. It works effectively as a heat transfer surface. As a result, the fin tube is more effectively exerted, and heat and mass transfer are greatly promoted.

[Embodiment of the Invention] FIGS. 1 and 2 show that a copper tube having an outer diameter of 19 mm for a heat transfer tube is provided with independent fins 2 each having a height of 0.9 mm and a longitudinal pitch of 0.7 mm. The case where the heat transfer tube 1 is pressed in one direction to have a track shape of a long axis 24 mm and a short axis 14 mm is shown.

Regarding this heat transfer tube 1, the liquid flow was observed by incorporating the heat transfer tube 1 in multiple stages in an experimental apparatus 3 as shown in FIG.

In the experiment, the absorption liquid 4 (concentration 58 wt% LiBr aqueous solution) at 40 ° C. was dropped, while the cooling water at 28 ° C. was flown into the heat transfer tube 1.

As a result of this experiment, the liquid 4 was retained at the upper part of the pipe and the liquid film thickness was kept thick. The appearance was as shown.

From this, it can be seen that a significant improvement in heat transfer performance of the heat transfer tube can be expected due to the agitation of the liquid due to the generation of convection and the increase in the heat transfer area.

[Effects of the Invention] The heat transfer tube of the present invention has a shape wide in the width direction of the absorbing liquid, and when the liquid is retained at the upper part of the tube to keep the liquid film thickness large and convection is generated. At the same time, the liquid is evenly distributed in the circumferential direction to allow the liquid to flow over almost the entire surface of the tube, greatly increasing the heat transfer area and making the fin tube more effective. Therefore, the performance of an absorber such as an absorption refrigerator or an absorption heat pump using the same is improved, which greatly contributes to downsizing of the equipment.

[Brief description of drawings]

FIG. 1 is a transverse sectional view showing an embodiment of a heat transfer tube according to the present invention, FIG. 2 is a front view thereof, and FIG. 3 is a view showing a state of liquid flow in the heat transfer tube of the embodiment. 1: Heat transfer tube, 2: Needle fin.

Claims (1)

[Claims] Claim: What is claimed is: 1. A heat transfer tube of an absorber which is horizontally arranged in a closed container, in which an absorbing liquid is dripped on the outside, and cooling water flows on the inside, fins are formed on the outer surface, and the heat transferring tube itself is a liquid A heat transfer tube for an absorber, which has an elliptical or elliptical cross section that is wide in the direction of dripping.