JPH07243784A - Stainless steel heat pipe - Google Patents

Abstract

PURPOSE:To provide a heat pipe made of stainless steel, which is provided with prominent durability capable of being used for a long period of time for the recovery of waste heat of exhaust gas of a boiler or the like. CONSTITUTION:A heat pipe made of stainless steel is constituted of a vessel main body, made of a stainless steel containing 14-27wt.% of Cr, and operating fluid or pure water, sealed into the vessel main body. A surface oxide layer, showing the content of Cr-oxide of 65wt% or more at a position of predetermined depth within the range of 0.002-0.2mum from the uppermost surface, is formed at least on the inner surface of the vessel main body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel heat which is excellent in durability and can recover waste heat contained in, for example, combustion gas of a boiler and exhaust gas of a dust incinerator for a long period of time. It's about pipes.

[0002]

2. Description of the Related Art Generally, for example, pure water is used as a working liquid for waste heat recovery in a boiler, a dust incinerator, etc., and it is sealed in a cupronickel container body and the outer surface of the container body is corrosion resistant. For the purpose of improvement, a heat pipe made of a copper alloy coated with Ni plating or the like is used.

[0003]

The copper alloy heat pipe used for recovering waste heat of exhaust gas from a boiler or the like has excellent performance in terms of heat conduction.
When exposed to exhaust gas such as O _x gas and CO _x gas, there is a problem that the outside is damaged by high temperature corrosion, the heat exchange efficiency is significantly reduced, and the service life is shortened.

Attempts have been made to construct the container body from stainless steel for the purpose of improving the high temperature corrosion resistance.
The pure water enclosed in the stainless steel container gradually reacts with Ni contained in the container to generate hydrogen gas, which causes a problem that the heat exchange rate of the heat pipe is significantly reduced when used for a long time. It was

[0005]

SUMMARY OF THE INVENTION From the above viewpoints, the inventors of the present invention focused on a stainless steel heat pipe for waste heat recovery and showing high temperature corrosion resistance to exhaust gas far superior to that of a copper alloy, and As a result of earnest research aimed at prolonging the life, the Cr content of the container body of the heat pipe is 14-
After being composed of 27% by weight of stainless steel, (a): anodize the inner surface of the container body in an electrolytic solution mainly containing sulfuric acid, (b): container with an oxidizing acid (for example, 20% or more nitric acid) Treating the inner surface of the main body, (c): in an atmosphere containing oxygen in the air (oxygen partial pressure: 10 ⁻¹ to 10 ⁻⁴ torr) or an atmosphere containing water vapor (H ₂ O: 10000 ppm or less),
The container body is heated and held at 400 to 700 ° C.

By performing any one of the oxidation treatments (a) to (c) above, the surface of the container body is measured at a predetermined depth position within the range of 0.002 to 0.2 μm from the outermost surface. When a surface oxide layer having a Cr oxide content of 65% by weight or more is formed, in the resulting stainless steel heat pipe, the reaction with pure water is suppressed by the surface oxide layer, and the heat pipe is used for a long time. Even so, we have obtained the knowledge that the reduction of heat exchange efficiency is prevented.

The present invention has been made on the basis of the above results, wherein pure water is enclosed as a working fluid in a stainless steel container body containing Cr: 14 to 27% by weight, and the container is 65 at a predetermined depth position within the range of 0.002 to 0.2 μm from the outermost surface on at least the inner surface of the main body.
It is characterized by a stainless steel heat pipe formed by forming a surface oxide layer having a Cr oxide content of not less than wt%.

Next, the Cr content of the stainless steel of the stainless steel heat pipe of the present invention and the C of the inner surface of the pipe.
The reason for limiting the Cr content of the r oxide layer as described above will be described. (A) Cr The Cr component has the function of forming a surface oxide layer to improve the corrosion resistance, but if the content is less than 14% by weight, the desired effect cannot be obtained for the above-mentioned action, while the content thereof is Is 2
If it exceeds 7% by weight, the toughness will be deteriorated and pipe processing will be difficult, so the content was set to 14 to 27% by weight.

(B) Cr oxide The inner surface of the Cr oxide is measured at a predetermined depth within the range of 0.002 to 0.2 μm from the outermost surface. Since the desired effect on the reaction suppressing action cannot be obtained, the Cr oxide content is set to 65% by weight or more.

[0010]

EXAMPLES Next, the heat pipe of the present invention will be described by way of examples. From stainless steel pipes specified in various JIS standards, outer diameter: 25.4 mm, thickness: 1.2 mm, length: 3000
It was cut into a size of mm, and end plates made of the same material were attached to both ends thereof by TIG welding, and an injection port was attached to one end plate and processed to obtain a container body material.

In the container body material adjusted in this way,
(A) Treatment of injecting 65% nitric acid at room temperature and standing for 10 minutes (hereinafter referred to as nitric acid treatment), (b) 500 mV. vs. 10 in SCE
Treatment for anodizing for a minute (hereinafter referred to as anodizing treatment),
(C) A process of heating to 400 to 700 ° C. in the atmosphere, holding for 10 minutes, and then air cooling (hereinafter referred to as atmospheric oxidation process),
(D) Oxygen partial pressure: a process of heating at 500 ° C. for 1 hour under a low oxygen partial pressure of 10 −3 torr (hereinafter referred to as low oxygen process), (e) 500 ppm heated to 520 ° C.
By holding for 10 minutes in the atmosphere containing H2O, and then subjecting it to a furnace (hereinafter referred to as steam oxidation treatment),
A surface oxide layer having a Cr oxide content shown in Table 1 measured at a depth of 0.1 μm from the surface is formed on the inner surface of the container body material to form a container body, and then the inner surface of the container body is pure. After washing with water, drying, baking at 150 ° C., vacuuming the inside to 10 torr, then injecting deaerated pure water to 20% of the internal volume of the pipe, crimping the sealing port and welding The present invention heat pipes 1 to 30
Was produced.

For comparison, comparative heat pipes 1-10 without Cr oxide layers or with Cr oxide layers outside the scope of the present invention were made.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

As shown in FIG. 1, the heat pipes 1 to 30 of the present invention and the comparative heat pipes 1 to 10 each have a total length of the heat pipe 1 such that the axial direction of the heat pipe 1 is inclined 6 ° with respect to the horizontal. Insert 1/2 into the constant temperature bath 1 heated to 100 ° C, and
2 is exposed to the atmosphere outside the thermostat 1 and kept at room temperature, and a thermocouple thermometer 3 is attached 10 cm from the tip of the heat pipe 1 (hereinafter referred to as the condensation tip 2) that is exposed to the atmosphere. ,
After holding for 3 hours, the temperature T ₀ at this point was measured.

After that, in order to evaluate the efficiency of the heat pipe, the temperature T was held for 1000 hours under the above conditions, the temperature T after 1000 hours was measured, and the temperature of the condensation tip 2 after being held for 3 hours and 1000 hours were held. A heat pipe deterioration test for measuring the temperature difference ΔT (= T ₀ −T) (° C.) of the subsequent condensation tip portion 2 was performed, and the obtained ΔT (° C.) measurement results are shown in Tables 1 to 4.
It was shown to.

When hydrogen gas is generated inside the heat pipe, the hydrogen gas is lighter than water vapor, and is also affected by separation and purification due to repeated evaporation and condensation of the working liquid. As a reflection of the rate decline, Δ
The value of T (° C) becomes large.

[0020]

From the results shown in Tables 1 to 4, it can be seen that the heat pipes 1 to 30 of the present invention have a small temperature drop due to the heat exchange rate drop due to the generation of hydrogen gas inside. However, it can be seen that the heat exchange rates of the comparative heat pipes 1 to 10 are significantly reduced after long-term use. As mentioned above,
The heat pipe of the present invention can efficiently recover heat from exhaust gas from a boiler or the like for a long period of time, and can greatly contribute to effective use of energy.

[Brief description of drawings]

FIG. 1 is a schematic view showing a heat pipe deterioration test method.

[Explanation of symbols]

 1. Constant temperature bath 2. Condensation tip 3. Thermocouple thermometer 4. Tilt angle

Claims (1)

[Claims] 1. A stainless steel container body containing 14 to 27% by weight of Cr containing pure water as a working fluid, and 0.002 to 0 from the outermost surface to at least the inner surface of the container body. 65 at a predetermined depth within the range of 0.2 μm
A heat pipe made of stainless steel, wherein a surface oxide layer having a Cr oxide content of not less than wt% is formed.