JP2773459B2 - Manufacturing method of fin and tube heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a fin-and-tube heat exchanger, and more particularly to a method of fixing a fin to a tube.

[0002]

2. Description of the Related Art A so-called fin-and-tube heat exchanger composed of fins and metal tubes, in particular, copper fins and copper tubes, has a plurality of copper fins provided in parallel with each other and formed on these copper fins. And a copper tube passing through the hole. As a method of fixing the copper fin and the copper tube, an expansion method is generally employed. The pipe expansion method is a method in which a copper pipe is inserted into a hole having an inner diameter slightly larger than the outer diameter of the copper pipe provided on the copper fin, and then the copper pipe is expanded and brought into close contact with the copper fin, and a mandrel expansion method, a hydraulic expansion method, There is a ball expansion method and the like.

In the mandrel expansion method shown in FIG. 3, a copper mandrel 10 is inserted into a copper tube 3 inserted into a copper tube insertion hole 2 of a copper fin 1 to expand the copper tube 3, and the copper fin 1 and copper This is for tightly fixing the tube 3. 4 expands the copper pipe 3 by closing one end of the copper pipe 3 and injecting a high-pressure liquid from the other end. In the ball expanding method shown in FIG. 5, the expanding tube 12 such as a steel ball is pushed into the copper tube 3 by the liquid pressure of the high-pressure liquid 11 to expand the copper tube 3.

[0004] As a method other than the above-described tube expansion method, a press-fitting method in which a copper tube is forcibly inserted by a press or the like is also used. In this method, as shown in FIG. 6, a copper fin 1 having a copper tube insertion hole 2 having substantially the same diameter as the outer diameter of the copper tube 3 is forcibly pressed against the copper tube 3 by a fin press-fitting jig 13. How to put.

[0005]

However, the conventional method for manufacturing a fin-and-tube heat exchanger as described above involves:
There were the following problems. First, the most commonly used mandrel expansion method in the past requires the use of lubricating oil to reduce friction between the expansion mandrel and the inner wall of the copper pipe. The occurrence was inevitable. Therefore, it was necessary to perform cleaning with an organic solvent after the completion of the pipe expansion operation.

In recent years, copper tubes having grooves on the inner surface have been frequently used in order to improve the heat transfer coefficient of the inner surface to the refrigerant (fluorocarbon) circulating in the tube. FIG. 7 shows the internal heat transfer coefficient of the inner surface of the smooth tube having no groove on the inner surface and the inner grooved copper tube before and after the expansion. From FIG. 7, it can be seen that the inner grooved copper tube has a higher inner surface heat transfer coefficient than the smooth tube, but such a copper tube has a large number of fine spiral fins (projections) formed on the inner wall surface. When the inner grooved copper tube is used, abrasion powder is more easily generated than in the case of a smooth tube. Further, the tip of the fin on the inner wall surface is crushed by the pipe expanding mandrel, and the fin height (groove depth) is reduced. As a result, as shown in FIG. 7, there has been a problem that the inner surface heat transfer coefficient is lower after expansion than before expansion. In addition, since the shrinkage allowance of the copper pipe caused by the expansion of the pipe changes due to subtle variations in the expansion conditions, more uniform copper pipe characteristics are required.
This has led to an increase in copper tube manufacturing costs.

On the other hand, the hydraulic expansion method, the ball expansion method, the press-fitting method and the like are used when the above-mentioned mandrel expansion method cannot be adopted, but all of them have a problem that the production cost is relatively high. There was a point.

Accordingly, it is an object of the present invention to provide a method of manufacturing a fin-and-tube heat exchanger which reduces the manufacturing cost and does not cause a decrease in the internal heat transfer coefficient to the refrigerant.

[0009]

According to the present invention, a metal pipe is inserted into holes provided in a plurality of radiating fins, and the metal pipes are connected to each other to form a refrigerant flow path. After the injection, the both ends of the refrigerant flow path are sealed, the assembly including the metal tube and the heat radiation fin is heated to a predetermined temperature, and then the assembly is cooled, and the water in the refrigerant flow path is eliminated to thereby release the heat radiation fin. And the metal tube in close contact with each other. here,
The metal tube and the radiating fins are heated to a temperature at which water injected into the coolant channel has a predetermined vapor pressure. The amount of water to be injected is desirably equal to or less than the amount at which saturated water does not exist at a temperature at which the predetermined vapor pressure and the burst pressure due to the internal pressure of the metal tube become equal. Furthermore, if a low-melting-point metal is interposed at the interface between the metal tube and the radiating fins, the low-melting-point metal is melted by heat generated when both members are heated, and the metal tube and the radiating fins are joined metallically. The fixing between the metal tube and the radiation fins is more reliable.

[0010]

According to the present invention, a predetermined amount of water is injected into a refrigerant flow path constituted by a metal pipe, and then both ends of the pipe are sealed and the whole is heated to a predetermined temperature, whereby the water injected into the pipe is formed. Is vaporized and has a predetermined vapor pressure.
Along with this increase in vapor pressure, the metal pipe expands at a relatively low temperature due to a synergistic effect with softening and creep of the metal pipe caused by heating.

The predetermined vapor pressure needs to be lower than the pressure at which the copper tube bursts due to the internal pressure. FIG.
Is the saturated vapor pressure at each temperature of water, the outer diameter is 9.52 mm and the wall thickness is 0.34 m, which is frequently used as a heat transfer tube for air conditioners.
4 shows actual measured values such as a burst pressure due to an internal pressure at a high temperature of a copper pipe of m. In the figure, the saturated vapor pressure and burst pressure match at about 304 ° C., it can be seen that the pressure is about 9 MPa.

When the amount of water is large, the rate of change of the saturated vapor pressure around 304 ° C. becomes a large value of about 0.13 MPa / ° C., and it is difficult to control the temperature in practical use.
Therefore, the amount of filled water is made as small as possible, and preferably, an amount is selected in which the saturated liquid (water) does not exist at a temperature slightly lower than the temperature showing the saturation pressure corresponding to the burst pressure. For example, the specific weight of the saturated steam at 300 ° C. is about 46.2 g / tr, and if the amount of filled water is set to an amount corresponding to this value or less, the rate of change of the steam pressure with temperature is 0.016 MPa / ° C, which is an order of magnitude lower, making industrial handling easier.

When water is injected into the tube and the tube is sealed without removing air, the inner surface is slightly oxidized by residual oxygen. However, the amount of residual oxygen depends on the above-mentioned outer diameter of 9.
In the case of a copper tube having a thickness of 52 mm and a wall thickness of 0.34 mm, it is as small as about 0.6 cc per m, and the effect of oxidation is practically negligible. If the inner surface oxidation is extremely disliked, air may be removed in advance by purging with an inert gas or vacuuming when filling in water.

After the completion of the heat expansion, the whole is cooled, and the end of the flow channel is opened to the atmosphere in a state where the temperature is lowered to a level where oxidation of the copper tube in the atmosphere does not pose a practical problem and exceeds 100 ° C. The water sealed inside gushes on its own by the residual heat. Further, the water is almost completely eliminated by purging with an inert gas thereafter.

When the interface between the radiating fin and the metal tube is heated to a little over 300 ° C. with a low melting point metal such as solder interposed therebetween, the low melting point metal is melted and the interface is metallically joined. You. As a result, the thermal resistance at the interface is significantly reduced.

[0016]

Embodiments of the present invention will be described below in detail. FIG. 1 is a partially cutaway front view of a fin-and-tube heat exchanger that is manufactured by a method according to an embodiment of the present invention and that is being heated and expanded. In FIG.
Is formed with a copper tube insertion hole 2 by means such as a press, and a copper tube 3 is inserted into the copper tube insertion hole 2.
A U-bend 4 is hard brazed to the end of the copper tube 3. A refrigerant flow path 5 is formed by a plurality of combinations of the copper tube 3 and the U-bend 4. Water 6 is injected into the refrigerant flow path 5, and each flow path terminal portion 7 is sealed by means of a closing jig, for example, a valve 8.

When this assembly is heated to a predetermined temperature in a protective atmosphere by a heating furnace 9 such as a batch or tunnel type continuous furnace, the copper tube 3 expands, and the copper fin 1 is inserted into the inner surface of the copper tube insertion hole 2. In close contact. At this time, if one or both surfaces of the copper fin 1 and the copper tube 3 are previously added with a low-melting metal for bonding such as solder by means of plating or the like,
The interface is metallically joined by the heating, and the tight fixing between the copper fin 1 and the copper tube 3 is strengthened.

After the completion of the heat expansion, the entire assembly is cooled, and when the valve 8 is opened in a state where the temperature exceeds 100 ° C., the water is spouted to the outside by itself as steam. Thereafter, by purging with an inert gas through the valve 8, the inner surface is dried without being oxidized due to the residual heat.

The injection amount of water used for expanding the pipe is calculated as follows. For example, if the above-mentioned copper tube having an outer diameter of 9.52 mm and a wall thickness of 0.34 mm is used and the total length of the flow path is 20 m, the internal volume is about 1.231 tr,
As described above, when the temperature is 300 ° C., since the specific weight of the saturated steam is about 4.2 g / 1 tr, the saturated steam amount at 300 ° C. is about 56 g, and the amount of water to be injected is less than this. It can be seen that only a very small amount is required. The heating temperature is 3
What is necessary is just to set to 05-310 degreeC.

In the present embodiment, there is no need to perform lubrication accompanying the expansion of the copper tube as in the mandrel expansion method.
In addition, since no copper powder is generated, a cleaning step after assembly is not required. Therefore, it contributes to pollution prevention and cost reduction. In addition, when copper pipes with internal grooves are used, the internal fins do not collapse as in the case of pipe expansion by the mandrel expansion method, so the internal heat transfer coefficient does not decrease and the performance of the heat exchanger improves. Can be achieved.
Further, the problem of the variation in the shrinkage of the copper pipe due to the pipe expansion such as the mandrel expansion method is solved.

Further, the method of the present embodiment has an advantage that it can be applied to a mass production line of heat exchangers by simply adding a heating furnace and ancillary equipment without largely changing the conventional process.

When the straight copper pipes are connected by U-bends as in this embodiment, the thickness of the copper pipes can be reduced because it is not necessary to perform the hairpin bending. This is also an advantage in reducing the cost of the entire heat exchanger. In this case, the terminal of the U-bend using the bare copper tube is bell-mouth expanded and the copper tube terminal is inserted. In addition, the number of cracks in the end is reduced, and the brazing material does not flow along the inner surface groove, so that the amount of the brazing material used can be reduced.

[0023]

As described above, according to the present invention, it is possible to provide a method of manufacturing a fin-and-tube heat exchanger which reduces the manufacturing cost and does not cause a decrease in the internal heat transfer coefficient to the refrigerant.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view of a heat exchanger manufactured by a manufacturing method according to an embodiment.

FIG. 2 is a diagram showing a saturated steam pressure, a rupture pressure of a copper tube, a saturated steam specific volume, an outer diameter increase amount of the copper tube, and the like.

FIG. 3 is an explanatory view showing a method of expanding a metal pipe by a mandrel expansion method and bringing a radiation fin and a metal pipe into close contact with each other.

FIG. 4 is an explanatory view showing a method of expanding a metal pipe by a hydraulic expansion method and bringing a radiation fin and a metal pipe into close contact with each other.

FIG. 5 is an explanatory view showing a method of expanding a metal pipe by using a ball expanding method and bringing a heat radiation fin and the metal pipe into close contact with each other.

FIG. 6 is an explanatory view showing a method of bringing a heat radiation fin and a metal tube into close contact by a press-fitting method.

FIG. 7 is a diagram showing the heat transfer coefficient of evaporation of the inner surface of a copper tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper fin 2 Copper pipe insertion hole 3 Copper pipe 4 U bend 5 Refrigerant flow path 6 Water 7 Refrigerant flow path terminal 8 Valve 9 Heating furnace 10 Expansion mandrel 11 High pressure liquid 12 Expansion ball 13 Pressing jig for fin press-fitting

Claims (3)

(57) [Claims] 1. A fin-and-tube heat exchanger comprising: a plurality of radiating fins provided in parallel with each other; and a metal tube penetrating holes provided in the plurality of fins. In the manufacturing method, a step of inserting the metal pipe into a hole provided in the plurality of radiating fins, a step of connecting the metal pipes to each other to form a coolant channel, a step of injecting water into the coolant channel, A step of sealing both ends of the refrigerant flow path, a step of heating an assembly including the metal pipe and the heat radiation fins to a temperature at which the inside of the metal pipe has a predetermined vapor pressure by the injected water,
A step of cooling an assembly including the metal tube and the radiation fins, and a step of removing the injected water from the inside of the coolant flow path ;
The amount is ruptured due to the predetermined vapor pressure and the internal pressure of the metal tube
Just at the temperature where the pressure equals, there is no saturated water
A method for producing a fin-and-tube heat exchanger, wherein the metal pipe is expanded by the predetermined vapor pressure to tightly fix the metal pipe and the radiation fin. 2. The method for manufacturing a fin-and-tube heat exchanger according to claim 1, wherein the predetermined vapor pressure in the heating step is lower than a pressure at which the metal tube bursts due to an internal pressure. 3. In the heating step, the radiating fins and the fins
A low melting point metal is interposed at the interface with the metal pipe,
Melting the low melting point metal by the heat at the time
The heat radiation fin and the metal tube are metallically joined.
Item 1. Manufacturing method of fin and tube heat exchanger according to item 1.
Law.