JPS636364A - 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 [Industrial Application Field] 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 such as absorption refrigerators and absorption heat pumps are constructed by arranging a large number of heat transfer tubes in parallel horizontally or vertically within a closed container. In this case, an absorption liquid such as a LiBr aqueous solution (concentration of approximately 60% by 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 transfer the absorbed heat from the cooling water flowing inside the tube. It acts to remove it. Absorption is caused by a 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 lower 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. For example, recently attempts have been made to use processed tubes such as loaf-in tubes for the purpose of increasing the heat transfer area and thinning the absorption liquid at the same time. Absorptive capacity has not improved.

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, it is important to improve the performance of heat transfer tubes, and in particular, it is necessary to promote the movement of materials 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.

The object of the present invention is to provide a novel heat exchanger tube that can dramatically improve the performance of 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 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 occurs. It was found that it was significantly 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, disturbance will occur within the liquid film, and the concentration will be low only on the surface of the solution, which will no longer suppress 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 solution is thicker.

Therefore, in the present invention, by providing a high protrusion on the tube surface and further providing a large number of notches in the protrusion, a thick liquid film of the solution is formed to generate convection in the solution, and at the same time, the notches The solution is also distributed and flowed in the circumferential direction, and as the solution passes over the ridges and moves to the next stage, it is further stirred, greatly promoting heat and mass transfer.

- On the other hand, when the operation of the equipment is stopped, there is a risk that the solution will stagnate between the protrusions and crystallize. Therefore, in the present invention, the notches in each protrusion improve surface wettability and allow liquid to drain. is promoted.

In addition, the height of the protrusion is preferably about 0.5 to 10+ nm,
In addition, the notch has a depth of 0.1~10+no+ and a pitch of 1~
Approximately 10 mm is desirable. Further, the arrangement of the notches in the circumferential direction may be any arrangement such as a staggered arrangement or a lattice arrangement.

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

Figure 1 shows a steel pipe for a heat exchanger tube with an outer diameter of 191 Ill+, in which 12 protrusions 2 with a height of 2 cm are provided parallel to the tube axis, and grooves in the shape opposite to the protrusions 2 appear on the inside of the tube. , a heat exchanger tube 1 is shown in which notches 4 with a pitch of 5III111 and a depth of 0.5 mm are provided in each protrusion 2.

Regarding this heat exchanger tube 1, using the experimental apparatus shown in FIG.
When the flow state was observed using a LiBr aqueous solution (60 mass% a degree) 7 to which n-octyl alcohol was added as a surfactant, the solution 7 flowed preferentially between the protrusions 2 on the outer surface of the tube, and the recesses 3 At the same time, the flow was also distributed in the circumferential direction by the notches 4. In addition, the tube 1 was entirely covered with the solution 7. In FIG. 2, 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.

Next, 48 heat exchanger tubes 1 having an effective length of 300 mm were assembled in 6 rows and 8 stages into a performance measurement apparatus as shown in FIG. 3, and the performance was measured.

In the experiment, 40°C absorption liquid (same as above) 7 was dropped, and cooling water 18 was flowed into the heat exchanger tube 1, while flowing into the heat exchanger tube 13 of the evaporator 16 so that the evaporation temperature was constant at 10°C. water 19
The flow rate was controlled.

In FIG. 3, 14 is a dropping tube, 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 exchanger tubes 1 of the absorber 15 is good, the amount of water vapor 20 absorbed increases, and the cooling capacity of the evaporator 16 improves.

The n1 constant results are shown in FIG. The liquid film flow rate F on the horizontal axis is the flow rate divided by the tube outer circumference. As a result, r'-0,1
The cooling performance was improved by about 1.5 times in kg/m-s compared to the smooth tube. As mentioned above, in the heat transfer tube of the present invention, the heat and mass transfer is greatly improved due to the generation of convection due to the increased thickness of the dropped liquid on the tube surface and the agitation when the liquid passes over the protrusions. It can be expected that this will be promoted.

FIG. 4 shows another example of a heat exchanger tube. In the example in Figure 1, solution 7
Although the part where the water stays was smooth, in this example, fine fins 22 whose height is lower than the protrusion 2 are provided in that part. This effectively works to increase the heat transfer area of the recess 3 and improve wettability.

Such a structure can be obtained, for example, by providing deep unevenness as shown in FIG. 1 on a processed tube, such as a loaf-in tube, in which fine fins are provided in the circumferential direction.

[Effects of the Invention] The heat exchanger tube of the present invention has a plurality of protrusions continuous in the direction of the pitcher's force in the circumferential direction to increase the thickness of the dripped liquid on the tube surface to generate convection. This system distributes the liquid in the circumferential direction and greatly improves heat and mass transfer by stirring the liquid as it passes over the ridges, so absorption refrigerators and absorption heat pumps that use this system This has the effect of improving the performance of absorbers such as

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the heat exchanger tube according to the present invention, Fig. 2 is a schematic diagram of a solution dripping experiment device, Fig. 3 is a schematic diagram of a performance measurement device, and Fig. 4 is an illustration of another heat exchanger tube. FIG. 5 is a graph showing the performance measurement results of the example. DESCRIPTION OF SYMBOLS 1... Heat exchanger tube, 2... Projection, 3... Recessed part, 4... Notch, 22... Fin. Agent Patent Attorney Usui 1) Toshiyuki Figure 1 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) A heat transfer tube of an absorber that is placed horizontally in a closed container, with absorption liquid dripping on the outside and cooling water flowing inside, and the outer surface has longitudinally continuous protrusions in the circumferential direction. 1. A heat exchanger tube for an absorber, characterized in that a plurality of protrusions are provided, and each of the protrusions is provided with a plurality of notches. (2) The heat exchanger tube according to item 1, wherein a groove having a shape opposite to the protrusion on the outer surface is formed on the inside of the tube. (3) The heat exchanger tube according to item 1 or 2, wherein a large number of fins having a height lower than the ridges are provided on the outer surface of the tube.