阅读说明：本技术 一种高效液氮换热器的换热管及换热器 (Heat exchange tube of high-efficiency liquid nitrogen heat exchanger and heat exchanger ) 是由 徐维泰 张鹏 程诚 于 2020-07-28 设计创作，主要内容包括：本发明涉及一种高效液氮换热器的换热管及换热器,所述换热管本体的外表面设置疏水层,所述换热管本体的内表面设置薄热阻层,本发明将换热管的内外表面进行了特殊加工,提供了具有疏水外表面和薄热阻层的内表面的换热管,疏水外表面能够有效减缓表面结霜,内表面的薄热阻层可以显著提升内部的沸腾传热效率。本发明具有以下优点和效果：换热效果好,可实现快速冷却,液氮的使用效率高,液氮汽化后冷氮气的大量冷量也可进行回收利用。(The invention relates to a heat exchange tube of a high-efficiency liquid nitrogen heat exchanger and the heat exchanger, wherein the outer surface of a heat exchange tube body is provided with a hydrophobic layer, and the inner surface of the heat exchange tube body is provided with a thin heat resistance layer. The invention has the following advantages and effects: the heat exchange effect is good, quick cooling can be realized, the use efficiency of the liquid nitrogen is high, and a large amount of cold energy of the cold nitrogen after the liquid nitrogen is vaporized can be recycled.)

1. The heat exchange tube of the high-efficiency liquid nitrogen heat exchanger comprises a heat exchange tube body and is characterized in that a hydrophobic layer is arranged on the outer surface of the heat exchange tube body, and a thin thermal resistance layer is arranged on the inner surface of the heat exchange tube body.

2. The heat exchange tube of a high efficiency liquid nitrogen heat exchanger as claimed in claim 1, wherein the thin thermal resistance layer is a Teflon coating layer, and the thickness of the thin thermal resistance layer is in the micron order.

3. The heat exchange tube of a high efficiency liquid nitrogen heat exchanger as claimed in claim 2, wherein the thin thermal resistance layer is coated on the inner surface of the heat exchange tube body by the following method:

(1) polishing the inner surface of the heat exchange tube, then ultrasonically cleaning the heat exchange tube by acetone, absolute ethyl alcohol and distilled water in sequence to remove oil stains, and drying the heat exchange tube by nitrogen for later use;

(2) pouring Teflon into the heat exchange tube and rotating until the coating is uniform;

(3) baking, and naturally cooling to room temperature to finish the preparation of the internal coating.

4. The heat exchange tube of the high-efficiency liquid nitrogen heat exchanger as claimed in claim 3, wherein the baking process in the step (3) is specifically as follows: heating to 150 deg.C at a heating rate of 10 deg.C/min, keeping the temperature constant for 10min, heating to 200 deg.C, keeping for 15min, and keeping for 15min to 340 deg.C, and stopping.

5. The heat exchange tube of a high efficiency liquid nitrogen heat exchanger as claimed in claim 1, wherein the hydrophobic layer is an anodic oxide film.

6. The heat exchange tube of a high efficiency liquid nitrogen heat exchanger as claimed in claim 5, wherein the hydrophobic layer is coated on the outer surface of the heat exchange tube body by the following method:

(1) preparing a sulfuric acid and phosphoric acid mixed acid solution for electropolishing, and subjecting an electrolyte system consisting of ammonium fluoride, water and ethylene glycol to anodic oxidation;

(2) mechanically polishing the outer surface of the heat exchange tube, then ultrasonically cleaning the outer surface of the heat exchange tube by using acetone, absolute ethyl alcohol and distilled water in sequence to remove oil stains, and drying the outer surface of the heat exchange tube by using nitrogen for later use;

(3) vertically immersing a heat exchange tube into the acidic solution prepared in the step (1), taking the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, performing electropolishing treatment, then washing with distilled water, and drying with nitrogen;

(4) and (2) vertically inserting a heat exchange tube into the electrolyte system configured in the step (1), taking the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, keeping the surface temperature of the sample uniform through magnetic stirring, carrying out anodic oxidation treatment, washing with distilled water, and drying with nitrogen, thus completing the preparation of the anodic oxide film.

7. The heat exchange tube of the high-efficiency liquid nitrogen heat exchanger as claimed in claim 6, wherein in the mixed acid solution of sulfuric acid and phosphoric acid in the step (1), the mass fraction of phosphoric acid is 85%, the mass fraction of sulfuric acid is 98%, the mass fraction of ammonium fluoride in the electrolyte system is 0.125-0.250 mol/L, and the water concentration is 0.05-0.80 mol/L.

8. The heat exchange tube of the high-efficiency liquid nitrogen heat exchanger as claimed in claim 6, wherein the electropolishing in step (3) is performed under the following conditions: the temperature is kept at 50 ℃, and the current is 0.25A/cm²The polishing time is 20 min; the anodic oxidation working condition in the step (4) is as follows: the temperature is kept at 20 ℃, the oxidation voltage is 50V, and the oxidation time is 60 min.

9. A high-efficiency liquid nitrogen heat exchanger comprises a shell (1), a pipe box flange (2), a pipe connection flange (3), a heat exchange pipe (4), a convex seal head (6), a seal head pipe box (7) and a movable saddle (8), wherein the pipe connection flange (3) is arranged at the upper part or the lower part of the shell (1), and the heat exchange pipe (4) is arranged in the shell (1); the convex end socket (6) is arranged at the end part of the end socket channel box (7), the end socket channel box (7) is connected to the two ends of the shell (1) through the channel box flange (2), and the heat exchange tube (4) is the heat exchange tube according to any one of claims 1 to 8.

10. The high efficiency liquid nitrogen heat exchanger according to claim 9,

the heat exchange tube (4) and the shell (1) are both made of 316L stainless steel;

the pipe connecting flange at the upper part of the shell (1) is a liquid nitrogen inlet, the pipe connecting flange at the lower part of the shell is a nitrogen outlet, and the liquid nitrogen inlet and the nitrogen outlet are positioned at the same side of the shell;

a range partition plate (10) is arranged in the middle of the shell (1) and is used for carrying out range division on liquid nitrogen;

a baffle plate (5) is arranged in the shell and used for baffling gas entering the shell;

the heat exchanger is also provided with a gas or liquid discharge opening (9) for discharging condensed liquid or excess gas in the housing.

Technical Field

The invention relates to the technical field of heat exchangers, in particular to a heat exchange tube of a high-efficiency liquid nitrogen heat exchanger and the heat exchanger.

Background

Cryogenic gases and cryogenic liquids are increasingly used in engineering applications. In high temperature areas or seasons, the density of the air is reduced, which has many adverse effects on the operational performance of the gas turbine, and therefore, cooling of the intake air of the unit is often required. In addition, in the case where air contains a small amount of a low boiling point solvent such as methanol or the like, recovery by condensation is required. The cooling interval that common cooling unit can realize is less and the start-up time is longer, and the unit is also comparatively huge, is difficult to realize quick precooling and cryogenic cooling.

With the more mature preparation technology of liquid nitrogen, wide sources and low cost, the liquid nitrogen is applied more and more in engineering. The saturation temperature of liquid nitrogen is-196 ℃ under normal pressure, a large amount of heat can be absorbed during vaporization, and low-temperature rapid cooling can be realized by adopting the liquid nitrogen phase change process. However, the liquid nitrogen is used as a cooling working medium, so that two problems exist, the temperature of the heat exchange tube is lower than the freezing point of common liquid such as water, the frost and ice are easily formed on the surface of the heat exchange tube, and the generated additional thermal resistance weakens the heat transfer performance. In the pipeline, the temperature of liquid nitrogen on stainless steel is about-148.15 ℃, so that the liquid nitrogen in the pipeline is subjected to film boiling within a long period of time just after the liquid nitrogen is introduced, the temperature of the pipeline wall is reduced slowly, the rapid cooling is difficult to realize, and the waste of the liquid nitrogen is caused.

Disclosure of Invention

The invention aims to solve the problems of surface frosting of a heat exchange tube and low boiling heat exchange efficiency in the heat exchange tube, and provides the heat exchange tube of the high-efficiency liquid nitrogen heat exchanger, the manufacturing method of the heat exchange tube and the heat exchanger with the heat exchange tube, so that the heat exchange capacity is further improved.

The purpose of the invention is realized by the following technical scheme:

the heat exchange tube of the high-efficiency liquid nitrogen heat exchanger comprises a heat exchange tube body, wherein a hydrophobic layer is arranged on the outer surface of the heat exchange tube body, and a thin thermal resistance layer is arranged on the inner surface of the heat exchange tube body. The invention specially processes the inner surface and the outer surface of the heat exchange tube, provides the heat exchange tube with the hydrophobic outer surface and the inner surface of the thin heat resistance layer, the hydrophobic outer surface can effectively slow down surface frosting, and the thin heat resistance layer on the inner surface can obviously improve the boiling heat transfer efficiency inside.

Further, the thin thermal resistance layer is a Teflon coating, and the thickness of the thin thermal resistance layer is in the micron level.

Further, the thin thermal resistance layer is coated on the inner surface of the heat exchange tube body by the following method:

(1) polishing the inner surface of the heat exchange tube, then ultrasonically cleaning the heat exchange tube by acetone, absolute ethyl alcohol and distilled water in sequence to remove oil stains, and drying the heat exchange tube by nitrogen for later use;

(2) pouring Teflon into the heat exchange tube and rotating until the coating is uniform;

(3) baking, and naturally cooling to room temperature to finish the preparation of the internal coating.

Further, the baking process in the step (3) specifically comprises: heating to 150 deg.C at a heating rate of 10 deg.C/min, keeping the temperature constant for 10min, heating to 200 deg.C, keeping for 15min, and keeping for 15min to 340 deg.C, and stopping.

Further, the hydrophobic layer is an anodic oxide film.

Further, the hydrophobic layer is coated on the outer surface of the heat exchange tube body by the following method:

(1) preparing a sulfuric acid and phosphoric acid mixed acid solution for electropolishing, and subjecting an electrolyte system consisting of ammonium fluoride, water and ethylene glycol to anodic oxidation;

(2) mechanically polishing the outer surface of the heat exchange tube, then ultrasonically cleaning the outer surface of the heat exchange tube by using acetone, absolute ethyl alcohol and distilled water in sequence to remove oil stains, and drying the outer surface of the heat exchange tube by using nitrogen for later use;

(3) vertically immersing a heat exchange tube into the acidic solution prepared in the step (1), taking the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, performing electropolishing treatment, then washing with distilled water, and drying with nitrogen;

(4) and (2) vertically inserting a heat exchange tube into the electrolyte system configured in the step (1), taking the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, keeping the surface temperature of the sample uniform through magnetic stirring, carrying out anodic oxidation treatment, washing with distilled water, and drying with nitrogen, thus completing the preparation of the anodic oxide film.

Further, in the mixed acid solution of sulfuric acid and phosphoric acid in the step (1), the mass fraction of phosphoric acid is 85%, the mass fraction of sulfuric acid is 98%, the mass fraction of ammonium fluoride in an electrolyte system is 0.125-0.250 mol/L, and the water concentration is 0.05-0.80 mol/L.

Further, the working conditions of the electropolishing in step (3) are as follows: the temperature is kept at 50 ℃, and the current is 0.25A/cm²The polishing time is 20 min; the anodic oxidation working condition in the step (4) is as follows: the temperature is kept at 20 ℃, the oxidation voltage is 50V, and the oxidation time is 60 min.

A high-efficiency liquid nitrogen heat exchanger comprises a shell, a pipe box flange, a pipe connecting flange, a heat exchange pipe, a convex end socket, an end socket pipe box and a movable saddle, wherein the pipe connecting flange is arranged at the upper part or the lower part of the shell, and the heat exchange pipe is arranged in the shell; the convex end socket is arranged at the end part of the end socket pipe box, the end socket pipe box is connected to the two ends of the shell through the pipe box flange, and the heat exchange pipe adopts the heat exchange pipe.

Furthermore, the heat exchange tube and the shell are both made of 316L stainless steel;

the pipe connecting flange at the upper part of the shell is a liquid nitrogen inlet, the pipe connecting flange at the lower part of the shell is a nitrogen outlet, and the liquid nitrogen inlet and the nitrogen outlet are positioned at the same side of the shell;

a pass partition plate is arranged in the middle of the shell and is used for passing liquid nitrogen, so that the nitrogen vaporized by the first pass still has large cold quantity, and the shell pass gas can be continuously cooled by the second pass;

the shell is internally provided with a baffle plate for baffling gas entering the shell, the gas enters from the shell side pipe connecting flange and is baffled by the baffle plate, and the gas is discharged from the other end of the shell side pipe connecting flange and is cooled gas;

the heat exchanger is also provided with a gas relief port or a liquid drain port for draining condensed liquid or excess gas in the shell.

In the practical use process of the liquid nitrogen heat exchanger, the gas is not required to be cooled to the saturation temperature of liquid nitrogen, but is rapidly cooled above-148.15 ℃, the efficiency of the process is low due to film boiling in the tube and frosting outside the tube, a thick frost layer is difficult to form on the hydrophobic surface compared with the hydrophilic surface, and the heat transfer efficiency of transition boiling and nucleate boiling in the tube is far higher than that of film boiling. In order to achieve different heat exchange purposes inside and outside the tube, the invention respectively carries out the preparation of Teflon coatings and the preparation of anodic oxidation hydrophobic membranes on the inner surface and the outer surface of the heat exchange tube.

The heat exchange tube for the liquid nitrogen heat exchanger provided by the invention has a hydrophobic outer surface and an inner surface of a thin thermal resistance layer. The surface is more difficult to frost compared with the common surface due to the hydrophobicity of the outer surface, the film boiling time is shortened due to the thermal resistance layer of the inner surface, and the overall heat exchange capacity of the heat exchange tube is improved, so the heat exchange tube provided by the invention has a greater application prospect, and has the following advantages:

compared with the conventional heat exchange tube, when the outer surface of the heat exchange tube cools gas, due to the fact that hydrophobic property can form bead condensation, liquid drops are difficult to form a liquid film on the outer surface and easy to fall off under the action of gravity, frosting is difficult to occur, a cooling surface is provided for the following gas, and the heat exchange capacity of the outer surface is improved; compared with the conventional heat exchange tube, when liquid nitrogen is introduced into the heat exchange tube, the surface temperature is quickly reduced to be lower than the Laden Floes characteristic temperature due to the effect of the internal thermal resistance layer, so that the internal boiling enters the transition and nucleation boiling stages from the film boiling stage in advance. The heat exchange capacity of the inner surface is further improved because the heat exchange capacity in the transition boiling and nucleate boiling stages is much stronger than that in the film boiling stage.

Compared with the prior art, the invention has the following beneficial effects:

1. the outer surface of the heat exchange tube is provided with a hydrophobic surface, so that the frosting is slowed down, and the cooling and heat exchange capacity of the outer surface is improved;

2. the thin thermal resistance layer is prepared on the inner surface of the heat exchange tube, so that the boiling time of the inner film state is shortened, and the boiling heat exchange capability of the inner surface is obviously improved;

3. the heat exchange capacity of the heat exchange tube is enhanced, and meanwhile, the heat exchange tube has better durability.

Drawings

FIG. 1 is a structural view of a shell-and-tube heat exchanger according to a preferred embodiment of the present invention;

FIG. 2 is a schematic structural diagram of the coating layer prepared on the inner and outer surfaces of the heat exchange tube according to the preferred embodiment of the present invention;

FIG. 3 is a graph comparing the cooling of the surface of a pipe prepared as above with that of a general stainless steel pipe;

fig. 4 shows the results of 3 repetitive experiments.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

As shown in fig. 1, the present invention provides a shell-and-tube heat exchanger including: the device comprises a shell 1, a pipe box flange 2, a pipe connecting flange 3, a heat exchange pipe 4, a baffle plate 5, a convex seal head 6, a seal head pipe box 7, a movable saddle part 8, an air release port/liquid discharge port 9 and a pass partition plate 10, wherein liquid nitrogen is introduced into a pipe pass, and a cooling medium is introduced into a shell pass. Wherein the inner surface of the heat exchange tube 4 has a thin thermal resistance layer, and the outer surface has a hydrophobic anodic oxide film, as shown in fig. 2.

The hydrophobic surface of the heat exchange tube in the embodiment has the characteristics that liquid drops are difficult to spread on the surface, but form bead-shaped condensation and fall off rapidly, so that a thicker frost layer is not easy to form; the thin thermal resistance layer on the inner surface has the characteristic that the surface temperature can be rapidly reduced to be lower than the Laden Floes characteristic temperature, so that liquid nitrogen enters transition boiling or nucleate boiling from film boiling in advance, and the overall heat exchange capacity of the heat exchange tube is improved.

The outer surface can be prepared by other methods, only a hydrophobic layer needs to be formed, and the inner surface can be made of other materials, only the thickness is thin and the heat conductivity coefficient is small.

The invention has good heat exchange effect, can realize quick cooling, has high use efficiency of liquid nitrogen, and can recycle a large amount of cold energy of cold nitrogen gas after the liquid nitrogen is vaporized.

The heat exchange tube can be made of stainless steel, and the thin thermal resistance layer and the hydrophobic surface are respectively prepared on the inner surface and the outer surface of the stainless steel tube.

The preparation method of the Teflon coating on the inner surface of the heat exchange tube comprises the following steps:

(1) polishing the surface of the heat exchange tube, then ultrasonically cleaning the heat exchange tube for 15min by using acetone, absolute ethyl alcohol and distilled water in sequence to remove oil stains, and drying the heat exchange tube by using nitrogen for later use;

(2) pouring Teflon into the tube and rotating the tube until the coating is uniform;

(3) and baking the sample, heating to 150 ℃ at a heating rate of 10 ℃/min, keeping the temperature constant for 10min, heating to 200 ℃ and keeping for 15min, and finally, keeping for 15min after the temperature reaches 340 ℃, and then naturally cooling to room temperature to finish the preparation of the internal coating.

The preparation method of the anodic oxide film on the outer surface of the heat exchange tube comprises the following steps:

(1) preparing a sulfuric acid and phosphoric acid mixed acid solution for electro-polishing, wherein the mass fraction of phosphoric acid is 85%, the mass fraction of sulfuric acid is 98% (national drug group), and the volume ratio of the phosphoric acid to the sulfuric acid is 2: 3. 0.125-0.250 mol/L ammonium fluoride and 0.05-0.80 mol/L water concentration in the electrolyte system. Preparing an electrolyte system consisting of ammonium fluoride, water and glycol for use in anodic oxidation, wherein the ammonium fluoride is 0.125-0.250 mol/L, and the water concentration is 0.05-0.80 mol/L;

(2) vertically immersing a heat exchange tube in an electropolishing acidic solution, using the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, performing electropolishing treatment, keeping the reaction temperature at 50 ℃ and the current at 0.25A/cm²Continuing for 20min, then washing with distilled water, and drying with nitrogen;

(3) vertically immersing a heat exchange tube into an electrolyte system, taking the heat exchange tube as an anode and a carbon cylinder as a cathode, sleeving the carbon cylinder outside the heat exchange tube, keeping the surface temperature of a sample at about 20 ℃ through magnetic stirring, keeping the voltage at 50V for 60min, washing with distilled water, and drying with nitrogen gas, thus finishing the preparation of the anodic oxide film.

The preparation flows of the inner surface and the outer surface cannot be reversed, the inner surface thermal resistance layer should be prepared firstly, and the Teflon coating has better chemical property stability and insulativity, so that the inner surface can be protected when the anodic oxidation process is carried out on the outer surface.

As shown in FIG. 3, the cooling speed of the surface of the stainless steel pipe prepared by the invention is much higher than that of a common stainless steel pipe, and the heat exchange capability is greatly improved; after the surface is subjected to multiple experiments, the test result is shown in fig. 4 (inevitable errors exist due to the fact that the inlet pressure of liquid nitrogen is difficult to guarantee to be completely equal in each experiment), and the experimental data is consistent within an acceptable range, so that the durability of the surface is better.

Table 1 shows the contact angle results of the hydrophobic surface, and the larger the contact angle, the better the hydrophobicity, and it can be seen that the hydrophobic surface of the present invention has better hydrophobicity.

TABLE 1 hydrophobic surface contact Angle results

Group of	Contact Angle/°
		Hydrophobic surfaces	135～140
Polishing stainless steel surfaces	80～84

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.