JPH0723818B2 - 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 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. 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 sometimes 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, by providing a plurality of parallel grooves having a large depth in the longitudinal direction on the tube surface, a thick liquid film for generating convection in the solution is formed, and at the same time, the liquid flows in the circumferential direction. Agitates vigorously when moving multiple stages. Further, by providing a large number of fins between the parallel grooves, the heat transfer area is increased to promote heat and mass transfer.

The depth of the parallel groove is preferably in the range of 0.5 to 5 mm.

[Embodiment of the Invention] FIGS. 1 and 2 show that 20 grooves 1 having a depth of 1 mm are provided on the surface of a copper tube for a heat transfer tube having an outer diameter of 19 mm evenly on the circumference, and further between the grooves. Fins 3 with a height of 0.9 mm and a pitch of 0.7 mm on the surface of the
Is shown to provide the heat transfer tube 1.

The performance of the heat transfer tube 1 was measured by incorporating 24 pieces in a performance measuring device 4 imitating an absorber as shown in FIG. 3 in 3 rows and 8 stages with an effective length of 300 mm.

In the experiment, 40 ° C. absorption liquid 6 (58 wt% concentration LiBr aqueous solution) was dropped from the nozzle of the drip pipe 7, while cooling water 8 at 28 ° C. was flown into the heat transfer pipe 1, while the heat transfer pipe inside the evaporator section 10 was flown. Refrigerant (water) to 11
12 is dropped and the evaporator part is adjusted so that the evaporation temperature becomes constant at 10 ° C.
The flow rate of water 13 flowing into the heat transfer tubes 11 of 10 was controlled.
In FIG. 3, 9 indicates a low-concentration absorption liquid, and 15 indicates a dropping pipe with a nozzle.

In this experimental method, if the heat transfer performance of the absorber section 5 is good, the amount of water vapor 14 absorbed will increase and the cooling capacity of the water 13 in the evaporator section 10 will improve.

FIG. 4 shows the measurement results in comparison with the smooth tube. The liquid film flow rate (Γ) on the horizontal axis represents the flow rate per unit length flowing on one side of the tube.

As a result of FIG. 4, in the heat transfer tube 1 according to the present invention, the cooling performance was improved by about 1.8 times at Γ = 0.015 kg / m · s with respect to the smooth tube.

As described above, this is because convection occurs when the dropped liquid stays in the groove 2, and when the liquid flows in the circumferential direction, the liquid is agitated at each stage and the heat transfer area on the surface between the grooves increases. It can be expected that this is due to the fact that heat and mass transfer were greatly promoted.

In the embodiment, the case where the needle-like fins are provided on the inter-groove surface is shown, but this is for the purpose of increasing the heat transfer area, so any fin shape may be used. Further, as for the inner surface structure of the tube, it is not necessary to provide a machined surface having grooves or protrusions as shown in FIG.

EFFECTS OF THE INVENTION The heat transfer tube of the present invention is provided with a plurality of parallel grooves having a large depth in the longitudinal direction to hold the liquid film of the dropped liquid thickly to generate convection there, and at the same time, in the circumferential direction. The flowing liquid changes the liquid film thickness at each stage to promote the stirring of the liquid, and the fins between the grooves increase the heat transfer area, greatly improving heat and mass transfer. It is effective in improving the performance of absorbers such as absorption refrigerators and absorption heat pumps using the same, and making the devices compact.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the heat transfer tube according to the present invention, FIG. 2 is a front view thereof, FIG. 3 is a schematic view of a heat transfer tube performance measuring device of the embodiment, and FIG. It is a graph which shows the performance measurement result of the heat transfer tube of an example. 1: Heat transfer tube, 2: Groove, 3: Needle fin.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Sawada 3550 Kidayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable Electric Co., Ltd. Tsuchiura factory (72) Inventor Kiyoshi Oizumi 3550 Kida-yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. Tsuchiura Plant (56) References JP-A-55-14425 (JP, A) JP-A-62-186179 (JP, A)

Claims (1)

[Claims] 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 caused to flow on the inside, and a plurality of grooves extending parallel to a longitudinal direction on an outer surface thereof. ,
A heat transfer tube for an absorber, characterized in that it has a large number of fins provided at a fine pitch in the groove portions.