JPS61119697A - Heat exchanger - Google Patents

Abstract

PURPOSE:To improve durability and to prevent the decrease of thermal efficiency by plating heat transmitting members made of copper of a heat exchanger with an alloy of Bi-Sb and coating the latent heat recovering part of said members with an org. resin thereby preventing the corrosion by a waste combustion gas. CONSTITUTION:The heat exchanger 3 of the constitution united with the main heat exchange part A consisting of the heat transmitting members made of copper which are endothermic fins 4 and water tubs 5 and the heat exchange part B for recovering latent heat in the lower part of a burner 1 and a combustion chamber 2 is disposed in a gas water heater provided with said burner 1 and the plating layer consisting of the alloy such as Bi-Sb or Bi-Sb-Sn is formed on the surfaces of the above-mentioned heat transmitting members made of copper. The coating layer consisting of the org. resin binder is further formed on the above-mentioned plating layer of the heat exchange part for recovering the latent heat. The above-mentioned Bi-Sb alloy is composed of 4-14wt% Sb and the balance Bi and any of an epoxy resin, polyamide resin, melamine resin or acrylic resin is preferably used for the above-mentioned resin binder.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a highly efficient heat exchanger used in combustion devices such as gas water heaters.

Conventional technology Recently, there has been a strong trend toward higher performance in combustion equipment such as gas water heaters from the perspective of energy conservation, and in order to improve thermal efficiency, a function that actively condenses water vapor in the combustion exhaust gas and recovers the latent heat of water vapor has been introduced. The development of additional heat exchangers is actively underway.

Combustion exhaust gas contains large amounts of nitrogen oxides, carbon dioxide gas, water vapor, and small amounts of sulfur oxides, and as mentioned above, when the water vapor is condensed to recover latent heat, the combustion gas components mentioned above dissolve. , a large amount of highly corrosive acidic condensed water with a pH of around 3 is produced.

Conventionally, the surface of this type of heat exchanger has generally been plated with lead-based alloy, for example, a lead-tin alloy.

Problems to be Solved by the Invention When this lead-tin alloy plating is applied to a heat exchanger with a latent heat recovery function, it will corrode in an extremely short period of time as the lead itself has no resistance to the acidic condensed water mentioned above. ,
This has the problem of corroding the copper that is the material of the heat exchanger, reducing the performance of the heat exchanger, and creating holes that can cause water leaks, significantly impairing durability and reliability.

In addition, the acidic condensed water is discharged from the equipment, but the drainage standards for sewerage systems stipulate that lead is 1 ppm or less and copper is 3 ppm or less.If the aforementioned corrosion occurs, a large amount of lead and copper will be released in the acidic condensed water. There was a problem that the above-mentioned drainage standards could not be satisfied because of the dissolution.

On the other hand, in the parts that exchange sensible heat, corrosion occurs due to steam oxidation at high temperatures and partial dew condensation during cooling when combustion is stopped, and corrosion products accumulate between the heat-absorbing fins. There were problems such as the flow of exhaust gas being obstructed, resulting in incomplete combustion, and poor heat conduction, resulting in a decrease in thermal efficiency.

The present invention solves such conventional problems, and improves the durability of the heat exchanger by preventing corrosion caused by acidic condensed water in which the combustion exhaust gas of the heat exchanger is dissolved and corrosion caused by high-temperature oxidation. The purpose is to prevent deterioration in combustion and thermal efficiency and improve reliability as a combustion device.

Means for Solving the Problems The present invention provides a main heat exchange section and a latent heat recovery heat exchange section which are disposed at the lower part of the burner and the combustion chamber and are made of copper heat transfer members of heat absorption fins and water tubes. A plating layer made of an alloy of bismuth-antimony or bismuth-antimony-tin, and a coating layer made of an organic resin binder are formed on the plating layer of the heat exchange section for latent heat recovery.

Effect: With this configuration, even if a large amount of acidic condensed water is generated in the heat exchange section for latent heat recovery during combustion, the plating layer and coating layer formed on the copper heat transfer member prevent the invasion of corrosive factors and have excellent corrosion resistance. Therefore, corrosion of the copper heat transfer member is significantly suppressed. Further, in the main heat exchange section, the plating layer formed on the copper heat transfer member has excellent heat resistance and corrosion resistance, so that corrosion due to high temperature oxidation and dew condensation phenomenon that occurs when combustion is stopped can be prevented.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view of a combustion apparatus equipped with a heat exchanger according to the present invention, in which 1 is a burner, 2 is a combustion chamber, 3 is a heat exchanger, 4 is an endothermic fin, and 5 is a water tube. The heat exchanger 3 is arranged at the lower part of the combustion chamber 2, and includes a main heat exchange section A and a latent heat recovery heat exchange section B.
It has an integrated structure. FIG. 2 is a sectional view of the main parts of a heat exchanger showing an embodiment, and a in the same figure is a main heat exchange part A.
, the same figure shows the configuration of the heat exchange section B for latent heat recovery. 6 is a heat-absorbing fin, a copper heat transfer member constituting a water tube, 7 is a plating layer made of bismuth-antimony or bismuth-antimony-tin alloy, and 8 is an organic binder such as polyamide-imide resin, epoxy resin, melamine/acrylic resin, etc. It is a coating layer consisting of.

The plating layer 7 has a main heat exchange section A and a latent heat recovery heat exchange section B.
The coating layer 8 is formed on the surface of the plating layer 7 of the heat exchange section B for latent heat recovery.

As a means of forming the plating layer 7, a method is applied in which the above-mentioned alloy is melted, a copper heat transfer member is immersed in the melt, and the copper heat transfer member is pulled up, that is, a hot-dip plating method so that a uniform film thickness can be obtained even in a complicated shape.

In addition, the processing temperature for hot-dip plating must be 400°C or less, since a complex-shaped heat exchanger such as the heat exchanger of the present invention will be thermally deformed at high temperatures. When immersed in water, the alloy is cooled, so the melting point of the alloy used for hot dip plating is 55% lower than the plating temperature.
It is necessary to lower the temperature by 0 to 100°C.

On the other hand, the heat exchanger of this example has an angle of approximately 270 degrees at its highest point.
Since the temperature is C, the heat resistance of the plating layer 7 must be higher than that. Therefore, considering the durability of the plating layer 7 due to the plating temperature, the melting point of the alloy used in this example is required to be in the range of 290 to 350°C, and the alloy that satisfies this requirement is bismuth- Preferably, a binary alloy of antimony is produced, with a composition range of 4% to 14% by weight antimony and the balance bismuth.

Further, in order to improve the wettability with copper, a ternary alloy in which 1 to 4% by weight of tin is added to the bismuth-antimony alloy is also used.

On the other hand, the coating layer 8 is required to have acid resistance and to have extremely few pinholes. Organic resin binders with complex and dense molecular structures are used to satisfy this requirement, and epoxy resins, polyamideimide resins, melamine, and acrylic resins are particularly good. Further, the coating layer 8 is formed by adding a solvent to these organic resin binders to adjust the viscosity to an appropriate level, applying the coating by either a spray method or a dipping method, and then curing by heating.

In this configuration, when combustion is performed using the combustion apparatus shown in Fig. 1, the main heat exchange section A is heated by the combustion heat from the burner 1 and reaches a high temperature of 270°C at the highest point. When the engine is attacked by water vapor and combustion exhaust gas and combustion is stopped, a small amount of acidic condensed water is generated at the contact area between the endothermic fins 4 and the water pipes 5 due to cooling. However, since a plating layer 7 of bismuth-antimony or bismuth-antimony-tin alloy, which has excellent heat resistance and corrosion resistance, is formed on the copper heat transfer member 6 that constitutes the heat absorption fins 4 and water pipes 5, deterioration due to heat can be prevented. At the same time, corrosion caused by high-temperature oxidation and dew condensation can be prevented, and the accumulation of corrosion products on the heat-absorbing fins 4 and the water pipes 5 can be significantly suppressed.

On the other hand, due to the design of the heat exchanger, the heat exchange section B for latent heat recovery is an environment where the temperature is always below the dew point during combustion, where water vapor condenses, combustion exhaust gas melts into it, and a large amount of acidic condensed water with a pH of about 3 is generated. However, the copper heat transfer member 6 of the heat exchange part B for latent heat recovery
Two layers are provided on the surface: a plating layer 7 made of an alloy having excellent corrosion resistance and a coating layer 8 made of an organic resin binder. The organic resin binders applied to this coating layer 8 include epoxy resins, polyamide resins, and melamine/acrylic resins, which have excellent acid resistance and have complex and dense molecular structures after curing. There are very few pinholes in No. 8, and it is possible to suppress the intrusion of corrosive factors such as nitrate ions and water, which are components of the acidic condensed water.

Furthermore, since a plating layer 7 made of bismuth-antimony or bismuth-antimony-tin alloy, which has excellent corrosion resistance, is provided below the coating layer 8, the corrosion factors Corrosion of the copper heat transfer member 6 is prevented even if
Copper will no longer be leached into acidic condensate water.

As described below, by forming the plating layer 7 and the coachib layer 8 on the surface of the copper heat transfer member 6, excellent corrosion resistance and heat resistance can be achieved, so that corrosion products on the copper heat transfer member 6 are prevented. This eliminates the accumulation of copper ions, prevents incomplete combustion, decreases in thermal efficiency, and contaminates the surrounding area.In addition, copper ions do not elute into acidic condensed water, so even if discharged to the sewer, the copper ion wastewater standard value is fully satisfied. This allows the durability and reliability of the heat exchanger to be significantly improved.

Next, experimental results showing specific effects of the present invention will be explained.

Experimental Example 1 A copper plate with dimensions of 30 x 30 x 0.4 zm was used as a heat transfer member, and this copper plate was pretreated in the following order.

Solvent degreasing - Immersion in 70'C1o% sulfuric acid for 15 minutes - Washing with water → Immersion in 10% hydrochloric acid at room temperature → Washing with water → Drying Next, this copper plate was treated with ammonium chloride, zinc chloride, hydrochloric acid,
After being immersed in a flux containing water as a main component and dried at 140°C, it was subjected to hot-dip plating using the alloys listed in Table 1.

(From No. 1) Table 1: Alloy composition of plating layer The hot-dip plating temperature was 400''C, and the film thickness after plating was 10-20 μm.

Experimental Example 2 Using the sample ridge 3 prepared in Experimental Example 1, each organic resin binder listed in Table 2 was adjusted to an appropriate viscosity with an appropriate solvent on the plated layer, and then applied by dipping and heated. It was cured to form a coating layer 8.

Table 2 Types of resin in coating layer The thickness of all coating layers is 10 to 20 μm.
It was m.

Regarding the test piece prepared as above, nitric acid 11
6 using a solution of 00pp (pH=2.7~2°9)
A corrosion test was conducted by immersion at 0'C for 100 hours, and corrosion resistance was evaluated based on corrosion weight loss. For comparison of corrosion resistance,
A similar test was conducted on a conventional lead-plated one.

The results are shown in Table 3.

(ptT table 3 Corrosion resistance evaluation using nitric acid aqueous solution (mg)) As is clear from Table 3, samples N [17 to 9, in which plating layer 7 and coating layer 8 were provided on the copper plate, were confirmed to exhibit good corrosion resistance. In addition, sample collections 1 to 6 in which only the plating layer 7 was provided also showed good corrosion resistance when compared with conventional lead plating, so that corrosion resistance in the main heat exchange section A can be expected to be sufficient.

Further, when the test liquid after the corrosion test was analyzed for copper ions using an atomic absorption spectrophotometer, no copper ions were detected in all of sample holes 1 to 9.

Experimental Example 3 Next, using the combustion apparatus and heat exchanger shown in FIG. 1, a 50,000-cycle durability test was conducted in which the combustion device was burned for 1 minute and extinguished for 1 minute. This heat exchanger has a coating layer 7 made of a bismuth (90 parts by weight)-antimony (1 part by weight) alloy and a coating layer made of melamine O acrylic resin on the plating layer 7 of the heat exchange section B for latent heat recovery. 8. As a result, although corrosion products were observed in the plating layer 7, there was no incomplete combustion or a decrease in thermal efficiency.
Furthermore, no copper ions were detected in the condensed water discharged, confirming that it satisfies sewerage drainage standards.

Effects of the Invention As described above, the heat exchanger of the present invention provides the following effects.

(1) Corrosion of the heat transfer member can be significantly suppressed, so there is no accumulation of corrosion products between the heat absorbing fins, and the flow of combustion exhaust gas is not inhibited, so incomplete combustion can be prevented.

(2) No more holes or falling off due to corrosion of heat transfer members.
Its durability as a heat exchanger is greatly improved, and its reliability as a combustion device is improved.

(3) Since corrosion can be significantly prevented, the initial excellent thermal efficiency can be maintained over a long period of time.

(b) Even if acidic condensed water is discharged to the sewer, it does not contain copper ions, so it can meet the sewer drainage standards.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a combustion apparatus to which the present invention is applied, and FIGS. 2a and 2b are sectional views of essential parts of a heat exchanger according to an embodiment of the present invention. 3... Heat exchanger, 4... Endothermic fin,
5... Water pipe, 6... Copper heat transfer member, 7
...... Plating layer, 8-... Coating layer, A... Main heat exchange section, B... Heat exchange section for latent heat recovery. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (3)

[Claims] (1) The main heat exchange section and the latent heat recovery heat exchange section are arranged in the lower part of the burner and the combustion chamber, and are made of copper heat transfer members such as heat absorption fins and water tubes. A plating layer made of an alloy of bismuth-antimony or bismuth-antimony-tin is formed on the surface of the copper heat transfer member of the heat exchanger for latent heat recovery, and an organic resin binder is formed on the plating layer of the heat exchanger for latent heat recovery. A heat exchanger with a coating layer. (2) The heat exchanger according to claim 1, wherein the bismuth-antimony alloy plating has a composition of 4% to 14% by weight of antimony and the remainder bismuth. (3) The heat exchanger according to claim 1, wherein the organic resin binder coating layer is made of any one of epoxy resin, polyamideimide resin, melamine, and acrylic resin.