JPS63306372A - Heat transfer tube for absorber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat transfer tube used in an absorber such as an absorption refrigerator or an absorption heat pump.

[Prior art and its problems] Absorbers in absorption refrigerators, absorption heat pumps, etc. are constructed by arranging a large number of heat transfer tubes horizontally or vertically within a closed container. In this case, an absorption liquid such as a LiBr aqueous solution (concentration of about 60% by mass) is dripped and sprayed on the outside of the heat transfer tube to absorb the water vapor generated in the evaporator and at the same time transfer the heat from the absorption to the cooling water flowing inside the tube. It acts to remove.

Absorption occurs due to the pressure difference between the evaporation pressure in the evaporator and the saturated vapor pressure of the absorption liquid dropped onto the surface of the heat transfer tube, and the larger this pressure difference, the better the capacity.

In addition, the lower the temperature or the higher the concentration of the absorption liquid, the lower the saturated vapor pressure, and the greater the pressure difference, which contributes to improving the absorption capacity. Therefore, this type of heat transfer tube is required to improve both heat transfer and mass transfer in which condensed water diffuses into the absorption liquid. However, until now there are many unknowns about this absorption mechanism, and smooth tubes have become the mainstream for heat transfer tubes.

On the other hand, in absorbers, heat transfer tubes are generally arranged horizontally, and the absorption liquid is dripped from above. At this time, the absorption liquid flowing on the tube surface becomes a thin film, and the trend is toward thinner films in order to further reduce heat transfer resistance and improve equipment efficiency. However, in absorption, mass transfer is more rate-determining than heat transfer. Therefore, with the current thin film flow system, a dramatic improvement in absorption performance cannot be expected unless efforts are made to promote mass transfer rather than heat transfer. Therefore, attempts have been made recently to use processed tubes such as loaf-in tubes in order to increase the heat transfer area and at the same time make the absorption liquid thinner. The ability has not improved yet.

Since the absorber is an important component that affects the performance of equipment, improving the performance of the absorber will be of great significance in the future when trying to make equipment more compact and improve its performance. Therefore,
Improving the mold performance of the heat transfer tube is an important point, and in particular it is necessary to promote mass transfer during the absorption process.

[Object of the Invention] A surfactant such as diethylhexanol is added to the absorption liquid of commercial absorption refrigerators, absorption heat pumps, etc. This is empirically known as a method of improving absorption capacity.

An object of the present invention is to provide a novel heat exchanger tube that can dramatically improve performance even in an absorber using an absorption liquid containing such a surfactant.

[Summary of the Invention] As a result of repeated research and experiments on heat transfer performance and mass heat transfer performance, the inventors have discovered that when convection occurs within the absorption liquid film on the surface of the heat exchanger tube, not only heat but also mass transfer is significantly increased. was found to be promoted. The solution on the surface of the heat exchanger tube absorbs water vapor on the surface where it comes in contact with water vapor, resulting in a low concentration, but the movement in the depth direction does not progress much by diffusion alone. If convection occurs, stirring will occur within the liquid film, and only the surface of the solution will have a low concentration, which will no longer inhibit absorption and improve performance.

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

In the present invention, by making the shape of the pipe opening wider in the direction of liquid dripping, a thick liquid film is 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 to effectively act as a heat transfer surface. This makes the fin tube more effective and greatly promotes heat and mass transfer.

[Embodiment of the Invention] Figs. 1 and 2 show a steel pipe for a heat exchanger tube having an outer diameter of 19 am, a height of 0.9 mm, and a pitch of 0.9 mm in the longitudinal direction. Separate needle-like fins 2 are provided at 71, and the heat exchanger tube 1 is pressed in one direction, and the long axis 241. This shows the case where the short axis is in a track shape.

This heat exchanger tube 1 was installed in multiple stages in an experimental apparatus 3 as shown in FIG. 2 with its short axis oriented vertically, and the flow of liquid was observed.

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

As a result of this experiment, the liquid 4 stagnates at the top of the tube and maintains a thick liquid film, and at the same time, the liquid 4 is distributed circumferentially and flows uniformly over almost the entire tube surface, as shown in Figure 3. It appeared as shown.

From this, it can be seen that the heat transfer performance of the heat transfer tube can be expected to be significantly improved due to the stirring 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 wide shape in the direction in which the absorption liquid drips, and when the liquid is retained at the top of the tube to maintain a large liquid film thickness and generate convection. At the same time, the liquid is evenly distributed in the circumferential direction, allowing the liquid to flow over almost the entire tube surface, greatly increasing the heat transfer area and making the fin tube more effective. Because of this, it improves the performance of absorption refrigerators, absorption heat pumps, and other absorbers that use it, and greatly contributes to making devices more compact.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the heat exchanger tube according to the present invention, FIG. 2 is a front view thereof, and FIG. 3 is a diagram showing the state of liquid flow in the heat exchanger tube of the embodiment. 1: heat transfer tube, 2: needle fin.

Claims (1)

[Claims] A heat transfer tube for an absorber that is placed horizontally in a closed container, with an absorbing liquid dripping on the outside and cooling water flowing inside, with fins formed on the outside surface and the heat transfer tube itself facing in the direction of the liquid dripping. A heat exchanger tube for an absorber characterized by having a wide elliptical or oval cross section.