JPS63306371A - 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 1i3r aqueous solution (concentration of about 60 mass %), is dripped onto the outside of the heat transfer tube to absorb the water vapor generated in the evaporator, and at the same time, the heat from the absorption is transferred to the cooling water that flows into the tube. It acts to remove it.

Absorption occurs due to the pressure difference between the evaporation pressure in the evaporator and the saturated vapor pressure of the absorption liquid dripped 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 the shortened 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 method, it is not possible to expect a drastic improvement in absorption performance unless efforts are made to promote mass transfer rather than heat transfer. Recently, attempts have been made to use cut tubes such as loaf indupes to avoid increasing the heat transfer area and at the same time to make the absorption liquid thinner. Absorptive capacity has not yet improved to the extent that it is commensurate with this.

Since the absorber is an important component that affects the performance of equipment, it is of great benefit to improve the performance of the absorber in order to make equipment more compact and high-performance in the future. Therefore,
Improving the performance of the heat exchanger 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 as well as material heat transfer performance, the inventors found that when convection occurs within the absorption liquid film on the surface of the heat transfer tube, not only heat but also mass transfer is significantly increased. was found to be promoted. When the solution on the surface of the heat exchanger tube comes into contact with water vapor, it absorbs the water vapor and has a low ci degree, but the movement in the depth direction does not progress much due to diffusion. If convection occurs, stirring will occur within the liquid film, and only the surface of the solution will have a low m degree, which will no longer suppress absorption and improve performance.

Further, 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, a plurality of deep grooves extending in the tube axis direction are provided on the surface of the tube to form a thick liquid film for generating convection in the solution, and at the same time, shallow spiral grooves intersect with the grooves. By providing this, the solution is distributed and flows in the circumferential direction, and by changing the film thickness of the liquid flowing in the circumferential direction, stirring of the liquid is promoted and heat and mass transfer are greatly promoted. There is.

Note that the depth of the groove is preferably in the range of about 0.5 to 5 m at the deeper end and about 0.1 to 2.5 a+w at the shallower end.

[Actual PA) Embodiments of the present invention will be described with reference to the drawings.

Figures 1 and 2 show WP12 with a depth of 1 aw extending in the tube axis direction on the surface of a steel pipe for heat exchanger tubes with an outer diameter of 19 s.
The heat exchanger tube is shown in which 20 grooves are equally spaced, and 30 spiral grooves 3 having a depth of 065# and a helical angle of 30 degrees are equally spaced on the circumference.

Regarding this heat exchanger tube 1, 3 pieces of 24 wood with an effective length of 300ag+ were installed in the absorber part 5 of the performance measuring device 4 as shown in FIG.
The performance was measured by installing it in eight rows.

In the experiment, an absorption liquid (temperature: 58 wt% 1-iBr aqueous solution: additive (xL)) 6 was dropped from the nozzle of the dropping tube 7, and cooling water 8 at 28° C. was flowed into the heat transfer tube 1, while the evaporator The refrigerant (water) 12 is introduced into the heat transfer tube 11 in the evaporator section 10 from the nozzle of the drip tube 15 W4T L,', and the flow rate of water 13 is flowed into the heat transfer tube 11 in the evaporator section 10 so that the evaporation temperature is constant at 10°C. was controlled.

In this experimental method, if the performance of the heat exchanger tubes 1 in the absorber section 5 is good, the amount of water vapor 14 absorbed increases, and the ability to cool the water 13 in the evaporator section 10 improves.

Figure 4 shows the measurement results. In addition, liquid film flow on the horizontal axis (1°)
indicates the flow rate per unit length on one side of the pipe.

From the results in FIG. 4, it can be seen that the cooling performance is improved by about 1.4 times compared to the smooth tube at r'-0,015 Ng/m-s. As mentioned above, this is the case with the heat exchanger tube of the present invention.
The heat and mass transfer is greatly improved due to the generation of convection due to the dropped liquid staying in the deep groove 2 and the stirring effect due to the constant change in the film thickness of the liquid flowing in the circumferential direction along the shallow groove 2. This can be expected to be due to the promotion of

Although the illustrated example shows a case where the inner side of the tube is smooth, the inner surface may be machined with grooves or protrusions.

[Effects of the Invention] The heat transfer tube of the present invention maintains a large film thickness of the dropped liquid by providing a deep groove to generate convection, and at the same time, by providing a shallow spiral vortex, the liquid is distributed in the circumferential direction. distribute,
The film thickness of the liquid flowing along the ff/i is changed at any time to promote agitation of the liquid and greatly improve heat and mass transfer, so absorption refrigerators and absorption heat pumps using this It is possible to avoid improving the performance of absorbers such as

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an embodiment of the heat exchanger tube according to the present invention, Fig. 2 is a front view, Fig. 3 is a schematic diagram of the device used to measure the performance of the heat exchanger tube, and Fig. 4 is a It is a graph that does not show the performance measurement results of the heat exchanger tube of the example. 1: heat transfer tube, 2: deep groove, 3: shallow spiral groove. Figure 1 Figure 2 M3

Claims (1)

[Claims] (1) A heat transfer tube of an absorber that is arranged horizontally in a closed container, with absorption liquid dripping on the outside and cooling water flowing inside, with multiple deep grooves extending in the tube axis direction on the outside surface. A heat exchanger tube for an absorber, comprising a plurality of spiral grooves that are shallower than the grooves and intersect with the grooves.