JPH0621744B2 - 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 its Problems] Absorbers such as absorption refrigerators and absorption heat pumps are configured by arranging a large number of heat transfer tubes in parallel in a sealed container in a horizontal or vertical direction. In this case, in the heat transfer tube, an absorbing liquid, for example, a LiBr aqueous solution (concentration of about 60 mass%) is dropped and sprinkled on the outer side of the tube to absorb the steam generated in the evaporator, and at the same time, absorb the absorbed heat at the time of cooling water flowing in the tube Acts to remove by. 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 lower 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 in 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. For example, recently, as this heat transfer tube, 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 thinning the absorbing liquid. The absorption capacity has not been 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 the heat transfer tube is an important point, and it is particularly necessary to promote the movement of goods 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] As a result of repeated research and experiments on heat transfer performance as well as heat transfer performance of the material, the inventors have found that when convection occurs in the absorbing liquid film on the surface of the heat transfer tube, heat transfer, especially mass transfer, is significantly increased. It turned out to be promoted. The solution on the surface of the heat transfer tube absorbs the water vapor at 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. Therefore, if convection occurs, disturbance occurs in the liquid film, the concentration of only the solution surface becomes low, and absorption is not suppressed, so that the performance is improved. In addition, it is known that convection is generally caused by a difference in surface tension due to the addition of a surfactant, and is likely to occur when the solution is thick. Therefore, in the present invention, in order to generate convection in the solution, deep recesses that allow the solution to be kept thick to some extent are provided intermittently in the tube axial direction on the tube surface. Convection occurs in the solution retained therein by the recesses, and fine fins having a height smaller than the depth of the recesses are provided to distribute the flow in the circumferential direction. Then, the solution is agitated when flowing down to the recess of the next stage, and heat and mass transfer are greatly promoted. On the other hand, when the operation of the equipment is stopped, there is a concern that the solution may remain in the recess and crystallize. Therefore, in the present invention, the fineness of the fins having a height smaller than the depth of the recesses is additionally used to improve the wettability of the surface and accelerate the drainage of the liquid.

Embodiments Embodiments of the present invention will be described with reference to the drawings.

Fig. 1 shows a low fin tube with an outer diameter of 19.05 mm (1
9 mm / inch) outer surface, depth 2 mm, length 10 mm, width 3 mm
Shows the case where the concave portions 3 are formed in parallel with the tube axis at a pitch of 12 threads in the axial direction of 14 mm to form the heat transfer tube 1, and the minute fins 2 remain on the outer surface excluding the concave portions 3 and on the inner side of the outer portion. Protrusions 26 are intermittently formed facing the recess 3.

Such a heat transfer tube 1 can be easily formed, for example, by pushing a gear-shaped disk 22 into a tube 25 such as a low fin tube and rotating the disk 22 while moving the tube 25, as shown in FIG. You can In FIG. 2, reference numeral 23 is a holding disk and 24 is a three-way chuck.

With respect to this heat transfer tube 1, the flowing state of the absorbing liquid was observed by the experimental apparatus shown in FIG.

In the experiment, a LiBr aqueous solution (concentration 60 mass%) 7 to which n-octyl alcohol was added as a surfactant was dropped onto the heat transfer tube 1 arranged in two stages. In addition, in FIG.
5 is a drip tube, 6 is a transparent casing, 8 is a drop, 9 is a valve, 10
Is a solution tank, 11 is a pump, and 12 is a flow meter.

As a result, the solution 7 flowed down in the circumferential direction on the outer surface of the tube, but the flow-down was blocked by the recess 3 and stayed there. The entire tube 1 was covered with the solution 7.

Next, 48 heat transfer tubes 1 having an effective length of 300 mm were assembled in 6 rows and 8 stages in a performance measuring device as shown in FIG. 4 to measure the performance.

In the experiment, the absorbing liquid (same as above) 7 at 40 ° C. is dropped, and the cooling water 18 is flown into the heat transfer pipe 1, while it is flown into the heat transfer pipe 13 of the evaporator 16 so that the evaporation temperature becomes constant at 10 ° C. Water 19
Was controlled. In FIG. 3, 14 is a dropping pipe, 15 is an absorber, 17 is a refrigerant (water), 20 is water vapor, and 21 is a low-concentration LiBr aqueous solution.

In this experimental method, if the performance of the heat transfer tube 1 of the absorber 15 is good, the absorption amount of the steam 20 is large, and the cooling capacity of the evaporator 16 is improved.

The measurement results are shown in FIG. The liquid film flow rate Γ on the horizontal axis is the flow rate divided by the pipe outer circumference. This result Γ = 0.1 kg / m
In s, the cooling performance of the heat transfer tube 1 of the example was improved about 1.6 times that of the smooth tube. This is, as mentioned above,
In the heat transfer tube 1 of the present invention, the dropped solution 7 spreads over the whole, the liquid thickness in the recess 3 was large, and convective retention was likely to occur. Further, the solution in the recess 3 moved to the next recess. It can be expected that the heat / mass transfer is greatly promoted by the stirring effect at the time, and further the heat transfer performance on the cooling water side is improved by the projections 26 in the pipe.

The fins 2 do not have to be continuous in the circumferential direction and may be independent.

[Effects of the Invention] In the heat transfer tube of the present invention, a plurality of recesses intermittently provided in the longitudinal direction are provided in the circumferential direction to increase the thickness of the dropped liquid on the surface of the pipe to generate convection, and Since the heat and mass transfer is greatly improved by the stirring effect when moving to the next recess, it is possible to improve the performance of absorbers such as absorption refrigerators and heat pumps that use this. There is.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the heat transfer tube according to the present invention, FIG. 2 is a schematic view showing an example of a method for manufacturing the heat transfer tube, FIG. 3 is a schematic view of a solution dropping experimental apparatus, and FIG. FIG. 5 is a schematic diagram of the performance measuring device, and FIG. 5 is a graph showing the performance measuring results of the examples. 1 ... Heat transfer tube, 2 ... Fin, 3 ... Recess, 26 ... Protrusion.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noriyuki Nishiyama 1-5-20 Kaigan, Minato-ku, Tokyo Within Tokyo Gas Co., Ltd. Inside the EBARA MFG. (72) Inventor Gen Habashi No. 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Inside the EBARA MFG. Co., Ltd. (72) Osamu Kawamata 3550, Kidayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. 72) Inventor Tadao Otani 3550, Kitayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. (72) Inventor Atsushi Sawada 3550, Kida-yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd., Tsuchiura Plant (72) Inventor Yoshihiro Shinohara 3550 Kitayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. Tsuchiura factory (72) Inventor Tokuo Miyauchi 3550 Kida-yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. Tsuchiura Factory (56) Reference JP 54-159754 (JP, A) JP 61-243288 (JP, A)

Claims (3)

[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 is made to flow on the inside, and a concave portion which is interrupted in a longitudinal direction is formed on the outer surface of the absorber. A plurality of heat transfer tubes for an absorber, which are provided in a plurality of directions, and have a plurality of minute fins on at least an outer surface thereof except for the recess. 2. The heat transfer tube according to claim 1, wherein a projection having a shape facing the recess of the outer surface is formed inside the tube. 3. The first fin, wherein the fin extends in a circumferential direction.
The heat transfer tube according to item 2 or item 2.