JPH04316991A - Manufacture of fin-and-tube type heat exchanger - Google Patents

Abstract

PURPOSE:To expand a metallic tube by utilizing steam pressure and the like to contact the tube with heat radiating fins closely and obtain a product of high quality inexpensively by a method wherein the metallic tubes, which are inserted into the heat radiating fins, are connected to form a refrigerant flow passage to seal water thereinto and, therafter, the assembled product is heated. CONSTITUTION:Inserting holes 2 are bored on a copper fin 1 and a copper tube 3 is inserted into the copper fin 1. U-bents 4 are brazed to the terminals of the copper tubes 3 while a plurality of these copper tubes are combined to form a refrigerant flow passage 5. Water 6 is poured into the refrigerant flow passage 5 while the terminals 7 of respective flow passages are sealed by valves 8 or the like. Such assemblies are heated in a heating furnace 9 whereby water 6 is evaporated to obtain a predetermined steam pressure while the copper tubes 3 are expanded thermally and are contacted closely with the inner surfaces of the inserting holes 2. Thereafter, the assemblies are cooled and the valves 8 are opened to eject water, which has become steam, to the outside of the assemblies. According to this method, the manufacturing cost of the heat exchanger is reduced and the deterioration of an inner surface heat conductivity with respect to refrigerant is eliminated.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] A so-called fin-and-tube heat exchanger composed of fins and metal tubes, especially copper fins and copper tubes, has a plurality of copper fins arranged in parallel to each other and a heat exchanger formed on these copper fins. It consists of a copper tube that passes through a hole. A tube expansion method is generally used to fix the copper fins and the copper tube. The tube expansion method is a method in which a copper tube is inserted into a hole with an inner diameter slightly larger than the outer diameter of the copper tube provided in a copper fin, and then the copper tube is expanded so that it comes into close contact with the copper fin.Mandrel tube expansion method, hydraulic tube expansion method, There are methods such as ball expansion method.

In the mandrel tube expansion method shown in FIG. 3, a tube expansion 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. This is to tightly fix the tube 3. The hydraulic pipe expansion method shown in FIG. 4 is a method in which one end of the copper pipe 3 is closed and high-pressure liquid is injected from the other end to expand the copper pipe 3. The ball expansion method shown in FIG. 5 expands the copper tube 3 by pushing a tube expansion ball 12 such as a steel ball into the copper tube 3 using the hydraulic pressure of the high-pressure liquid 11.

[0004] In addition to the above-mentioned pipe expansion method, a press-fitting method is also used in which the copper pipe is forcibly inserted using a press or the like. In this method, as shown in FIG. 6, a fin press-fitting pressing jig 13 is used to forcibly push a copper fin 1 having a copper tube insertion hole 2 with approximately the same diameter as the outer diameter of the copper tube 3 into the copper tube 3. This is the way to put it.

[0005]

[Problems to be Solved by the Invention] However, the conventional manufacturing method of the fin-and-tube heat exchanger as described above is
There were problems as shown below. First, the mandrel tube expansion method, which has been most commonly used in the past, requires the use of lubricating oil to reduce the friction between the tube expansion mandrel and the inner wall surface of the copper tube. Its occurrence was inevitable. Therefore, it was necessary to perform cleaning with an organic solvent after the pipe expansion work was completed.

[0006] In recent years, copper tubes with grooves formed on their inner surfaces have come into widespread use in order to improve the internal evaporative heat transfer coefficient to the refrigerant (fluorocarbon) circulating within the tubes. FIG. 7 shows the inner evaporative heat transfer coefficients of a smooth tube without grooves on the inner surface and a copper tube with inner grooves before and after expansion. From Figure 7, it can be seen that the inner surface evaporative heat transfer coefficient of the inner grooved copper tube is higher than that of the smooth tube, but this type of copper tube has many fine spiral fins (protrusions) formed on the inner wall surface. When using internally grooved copper tubes, wear particles are more likely to be generated than when using smooth tubes. Furthermore, the tips of the fins on the inner wall surface are crushed by the tube expansion mandrel, reducing the fin height (groove depth). As a result, as shown in FIG. 7, a problem has arisen in that the internal evaporative heat transfer coefficient is lower after pipe expansion than before pipe expansion. In addition, the shrinkage margin of copper pipes that occurs during pipe expansion changes due to subtle variations in the pipe expansion conditions, so more uniform copper pipe characteristics are required.
This led to an increase in the manufacturing cost of copper pipes.

On the other hand, the hydraulic pipe expansion method, ball pipe expansion method, press-fitting method, etc. are used when the above-mentioned mandrel pipe expansion method cannot be adopted, but all of them have the problem of relatively high manufacturing costs. There was a point.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a fin-and-tube heat exchanger that reduces manufacturing costs and does not cause a decrease in the internal heat transfer coefficient to the refrigerant.

[0009]

[Means for Solving the Problems] The present invention involves inserting metal tubes into holes provided in a plurality of radiation fins, connecting the metal tubes to each other to form a refrigerant flow path, and injecting water into the refrigerant flow path. After injecting the refrigerant, both ends of the refrigerant flow path are sealed, the assembly including the metal tube and the radiator fin is heated to a predetermined temperature, and then the assembly is cooled and the water in the refrigerant flow path is removed. and a metal tube are closely fixed. here,
The metal tube and the radiation fins are heated to a temperature at which the water injected into the refrigerant flow path has a predetermined vapor pressure. Further, the amount of water to be injected is desirably equal to or less than the amount at which saturated water just ceases to exist at a temperature where the predetermined vapor pressure is equal to the bursting pressure due to the internal pressure of the metal tube. Furthermore, if a low melting point metal is interposed at the interface between the metal tube and the heat dissipation fin, and the low melting point metal is melted by the heat generated when both members are heated, the metal tube and the heat dissipation fin are metallically joined. The fixation between the metal tube and the radiation fin becomes more reliable.

0010

[Operation] In the present invention, after a predetermined amount of water is injected into the refrigerant flow path constituted by a metal tube, both ends of the tube are sealed and the whole is heated to a predetermined temperature. is vaporized and has a predetermined vapor pressure. Due to the synergistic effect of this increase in vapor pressure and the softening and creep of the metal tube caused by heating, the metal tube expands at a relatively low temperature.

The predetermined vapor pressure must be lower than the pressure at which the copper tube bursts due to internal pressure. Figure 2 shows the saturated vapor pressure of water at various temperatures, and the outer diameter of 9.52 mm and wall thickness of 0.34 mm, which is often used as a heat transfer tube for air conditioners.
The figures show actual measured values such as bursting pressure due to internal pressure of copper pipes at high temperatures. In the figure, it can be seen that the saturated vapor pressure and the bursting pressure match at about 304° C., and the pressure is about 9 MPa.

[0012] When a large amount of water is sealed, the rate of change in saturated vapor pressure near 304°C is as large as about 0.13 MPa/°C, making temperature control difficult in practical use. Therefore, the amount of water enclosed should be as small as possible, and preferably, the amount should be selected so that no saturated liquid (water) exists at a temperature slightly lower than the temperature at which the saturation pressure corresponding to the bursting pressure is exhibited. For example, the specific weight of saturated steam at 300°C is approximately 4
6.2 g/1 tr, and if the amount of water sealed is kept below the amount equivalent to this value, the rate of change in vapor pressure due to temperature will be reduced by an order of magnitude to 0.016 MPa/℃, making industrial handling easier. It becomes easier.

[0013] If water is injected into the pipe and then the pipe is sealed without removing air, the inner surface will be slightly oxidized by residual oxygen. However, the amount of residual oxygen is determined by the above-mentioned outer diameter 9.
In the case of a copper tube with a diameter of 52 mm and a wall thickness of 0.34 mm, it is as small as about 0.6 cc per 1 m, and the effect of oxidation is practically negligible. If internal oxidation is extremely objectionable, air may be removed in advance by purging with an inert gas or vacuuming when filling water.

[0014] After heating and expanding the tube, the entire tube is cooled, and the end of the flow path is opened to the atmosphere while the temperature is lowered to a point where oxidation of the copper tube in the atmosphere does not pose a practical problem and the temperature exceeds 100°C. The water sealed inside will gush out on its own due to residual heat. Furthermore, by subsequently purging with inert gas, water is almost completely eliminated.

[0015] Furthermore, when a low melting point metal such as solder for bonding is interposed at the interface between the radiation fin and the metal tube and heated to over 300°C, this low melting point metal melts and the interface is joined metallically. Ru. As a result, the thermal resistance at the interface is significantly reduced.

[0016]

[Examples] Examples of the present invention will be described in detail below. FIG. 1 shows a partially cutaway front view of a fin-and-tube heat exchanger during heating and tube expansion, manufactured by a method according to an embodiment of the present invention. In the figure, a copper tube insertion hole 2 is formed in a copper fin 1 by means such as pressing, and a copper tube 3 is inserted into this copper tube insertion hole 2. Further, a U-bend 4 is hard-soldered to the end portion 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 end portion 7 is hermetically sealed with a closing jig, for example, a valve 8 or the like.

By heating this assembly to a predetermined temperature in a protective atmosphere in a heating furnace 9 such as a batch or continuous tunnel furnace, the copper tube 3 expands and the inner surface of the copper tube insertion hole 2 of the copper fin 1 is heated. In close contact. At this time, if a low melting point metal such as solder is added to the surface of either or both of the copper fins 1 and the copper tube 3 by plating or other means in advance,
By heating, the interface is joined metallically, and the close fixation between the copper fin 1 and the copper tube 3 is strengthened.

After heating and expanding the tube, the entire assembly is cooled and when the valve 8 is opened while the temperature exceeds 100° C., the water becomes steam and is blown out by itself. Thereafter, by further purging with an inert gas through the valve 8, the inner surface is dried without being oxidized with the help of residual heat.

The amount of water to be injected for pipe expansion is calculated as follows. For example, if the aforementioned copper tube with 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 will be approximately 1.231 tr, so
As mentioned above, when the temperature is 300°C, the specific weight of saturated steam is about 4.2g/1tr, so the amount of saturated steam at 300°C is about 56g, and the amount of water to be injected is less than this. It turns out that only a very small amount is required. In addition, the heating temperature is 3
The temperature may be set at 05 to 310°C.

[0020] In this embodiment, there is no need to lubricate the copper pipe during expansion as in the mandrel expansion method.
Moreover, since no copper powder is generated, a cleaning process after assembly is unnecessary. Therefore, it helps prevent pollution and also contributes to cost reduction. In addition, when using internally grooved copper tubes, the internal fins do not collapse as in the case of pipe expansion using the mandrel expansion method, so the internal heat transfer coefficient does not decrease, improving the performance of the heat exchanger. can be achieved. Furthermore, the problem of variations in the shrinkage margin of the copper pipe due to pipe expansion such as the mandrel pipe expansion method is also solved.

Another advantage of the method of this embodiment is that it can be applied to a heat exchanger mass production line by simply adding a heating furnace and auxiliary equipment without significantly changing the conventional process.

Note that when straight copper tubes are connected by U-bends as in this embodiment, there is no need to perform hairpin bending, so the thickness of the copper tubes can be made thinner. This is also an advantage in reducing the cost of the entire heat exchanger. In this case, the end of a U-bend using a bare copper tube is expanded with a bell mouth and a copper tube end is inserted, so it is much better than the case where the end of an internally grooved copper tube is expanded with a bell mouth and a U-bend end is inserted. The amount of soldering material used can be reduced because the occurrence of cracks at the terminals is reduced and the soldering material does not flow along the inner grooves.

[0023]

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

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing saturated water vapor pressure, bursting pressure of a copper tube, saturated steam specific volume, amount of increase in outer diameter of a copper tube, etc.

FIG. 3 is an explanatory diagram showing a method of expanding a metal tube by the mandrel expansion method to bring the heat radiation fin and the metal tube into close contact.

FIG. 4 is an explanatory diagram illustrating a method of expanding a metal tube using a hydraulic expansion method to bring the radiation fins and the metal tube into close contact with each other.

FIG. 5 is an explanatory diagram illustrating a method of expanding a metal tube using a ball expansion method to bring the radiation fins and the metal tube into close contact with each other.

FIG. 6 is an explanatory diagram showing a method of closely contacting a heat dissipation fin and a metal tube by a press-fitting method.

FIG. 7 is a diagram showing the internal evaporative heat transfer coefficient of a copper tube.

[Explanation 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 Mandrel for tube expansion 11 High pressure liquid 12 Tube expansion ball 13　Press jig for fin press-fitting

Claims (4)

[Claims] 1. A fin-and-tube heat exchanger comprising a plurality of radiation fins arranged parallel to each other and a metal tube passing through holes provided in the plurality of radiation fins, the metal tube forming a refrigerant flow path. In the manufacturing method, a step of inserting the metal tube into a hole provided in the plurality of radiation fins, a step of connecting the metal tubes to each other to form a refrigerant flow path, a step of injecting water into the refrigerant flow path, a step of sealing both ends of the refrigerant flow path; a step of heating an assembly including the metal tube and the radiation fins to a temperature at which the inside of the metal tube has a predetermined vapor pressure by the injected water; and a step of cooling an assembly including the radiation fins, and a step of removing the injected water from the refrigerant flow path, expanding the metal tube with the predetermined vapor pressure and forming the metal tube. A method for manufacturing a fin-and-tube heat exchanger, characterized in that the heat radiation fins are closely fixed. 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 internal pressure. 3. The amount of water in the water injection step is:
2. The method for manufacturing a fin-and-tube heat exchanger according to claim 1, wherein the amount is just below the amount at which saturated water ceases to exist at a temperature where the predetermined vapor pressure and the bursting pressure due to the internal pressure of the metal tube are equal. 4. In the heating step, a low melting point metal is interposed at the interface between the heat dissipation fin and the metal tube, and the low melting point metal is melted by the heat during the heating step, so that the heat dissipation fin and the metal tube are bonded together. to join them metallically,
A method for manufacturing a fin-and-tube heat exchanger according to claim 1.