JPS6266099A - Graphite heat transfer tube - Google Patents

Abstract

PURPOSE:To hold the excellent heat transfer property, promote the heat transfer and the thermal efficiency of the heat transfer tube by forming the heat transfer tube into a liquid-tight tube the outer part of which is made of a heat curing resin and graphite, and holding at its inner part a porosity possessed by a graphite tube. CONSTITUTION:The tube wall of a tubular body 6 made of a porous graphite is divided into two, inner and outer, parts. The inner part 3 at least the inner wall surface of the tube, is held by a structure of porous graphite 2, and the outer part 4, at least the outer peripheral surface of the tube, is constituted of a tubular body 6 of a liquid-tight structure. That is, the heat transfer tube is a tubular body having a so-called dual layer structure. A layer 51 of a heat curing synthetic resin is applied to the outer peripheral surface of the graphite pipe 2 and thereafter dried and cured or application, drying and curing are repeated. Alternatively, a heat curing synthetic resin is applied to the outer peripheral surface of the tubular body 6 both ends of which are blocked, and thereafter an atmospheric pressure is applied thereto, and is impregnated in the front surface portion of the tube, and then a heat cured liquid-tight layer 52 is formed via drying means including heating. Accordingly, this tube can be used as a tube for transporting the fluid, and since it has its porous inner part 3, at least inner surface, it has an improved heat transfer function as a heat transfer tube by the promotion of nuclear boiling.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heat exchanger tube made of graphite used in a heat exchanger consisting of a shell and a heat exchanger tube, and particularly to a heat exchanger tube with improved heat transfer characteristics.

Conventional technology Graphite is a stable substance in terms of its properties, and in terms of chemical properties it has excellent corrosion resistance, and in terms of thermal properties, it does not have a high melting point, but has a small coefficient of thermal expansion and little deformation at high temperatures. Benefits such as: In addition, graphite is suitable for use as a heat exchanger tube because it can be freely molded from the manufacturing process and can be easily formed into a tube body, and has excellent thermal conductivity. On the other hand, regarding metal tubes, which have conventionally been widely used as heat transfer tubes, techniques such as powder metallurgy have been developed to form a sintered radius of metal or alloy to significantly improve the heat transfer coefficient.

Graphite is known to have excellent 5Nl properties, but as an industrially available material, it is obtained as a porous body from a carbon-containing material such as coke through several rounds of calcination. Therefore, it is permeable to fluids even when formed as a tube material. Therefore, in order to use this as a pipe material, it is impregnated with a thermosetting synthetic resin such as a phenolic resin, epoxy thread, or furan resin, and then thermosetted to form an impermeable graphite pipe. However, this only utilizes the thermal properties of graphite as is or under the constraints of the properties of the synthetic resin, and its properties as a porous body are lost. On the other hand, the porosity of sintered bodies such as metals is known to have a remarkable effect on the heat transfer promotion mechanism due to nucleate boiling on the surface, and can also ensure impermeability when made into a tube. Its stability against corrosion is incomparable to lateral graphite, and its uses are limited.

Means for Solving the Problems The present invention was developed in view of the above-mentioned circumstances with the aim of obtaining a graphite tube that could be used to promote heat transfer in heat exchangers. The wall of a graphite pipe body is divided into two parts, the inner and outer parts, and the inner part, at least the inner wall surface of the pipe, maintains a porous graphite structure, and the outer part, at least The main idea is to create a pipe with a so-called double-layer structure in which the outer peripheral surface of the pipe is liquid-tight.In actual pipes, thermosetting resin is applied to the outer surface of the pipe. Or impregnation from the outside, inside the cord trunk part left unimpregnated or after impregnation 8! A is characterized in that it is formed into a rough surface that is exposed on the surface of graphite containing impregnated synthetic resin by machining means, and furthermore, such a tube is used as a heat exchanger tube for a heat exchanger, and furthermore, it is used. It can be used as a heat transfer promoting tube for an evaporator.

Function The present invention will be explained in detail based on the drawings. FIG. 1 is a schematic cross-sectional view of the heat exchanger tube of the present invention.

1 shows the entire heat exchanger tube, 2 is a porous graphite tube which is the main body 65, and as shown in the cutaway diagram, it is divided into two layers, inner and outer parts, an inner part 3 and an outer part 4, The inner part 3 includes only the inner surface of the tube, and the outer part 4 includes only the outer circumferential surface of the tube. Reference numeral 5 denotes a thermosetting synthetic resin layer impregnated or coated on the outer part 4 according to the above definition, and is shown by hatching. Reference numeral 6 indicates the entire tubular body with its full thickness when both the inner part 3 and outer part 4 are viewed as one body.

Each figure in FIG. 2 illustrates various changes in the method of applying the synthetic resin 5 to the graphite portion 2, and shows various aspects of the heat exchanger tube.

In FIG. 2 (8), 51 is a layer of thermosetting synthetic resin, which is applied to the outer peripheral surface of the graphite tube 2 and then dried and hardened.
Or, it is a liquid-tight layer obtained by repeating coating, drying and curing.

In this case, the inner part 3 has a total wall thickness of 6 and the outer part 4 has a wall thickness of 0.
The synthetic resin 5 exists only on the outside of the tube. This tube is the simplest to manufacture, but the configuration of the inner part 3 and outer part 4 is an extreme example.

In Fig. 2 et al.), 52 is a method of applying a thermosetting synthetic resin to the outer circumferential surface of the tube body 6 with both ends closed, impregnating it into the surface layer of the tube by applying external pressure, and then drying means including heating. It is a liquid-tight layer that is heat-cured through a process. Such a layer of impregnating resin 52 also includes natural impregnation into the surface layer due to simple coating in the holes.

FIG. 2 (The synthetic resin 53 of the outer part 4 in Q is
This is an example in which graphite 2 is impregnated with a thermosetting resin that remains as a raw material. For this impregnation, both ends of the tube are closed in the same manner as above, and the tube is immersed in the impregnating liquid to reduce the pressure in the inner space.
This is done by applying pressure from the outer periphery or by using a combination of both.1. The thickness of the outer portion 4 changes depending on changes in impregnation conditions such as the viscosity of the impregnating resin, relative pressure difference, impregnation time, or repetition of the impregnation process.

In FIG. 2 (II), the impregnation of the thermosetting resin resin layer 54 is carried out within the total wall thickness 6 ((casting), and thus the thickness of the inner part 3. is 0, which is only the inner surface of the tube.In this example, the graphite 2 portion of the inner part 3 is formed of graphite exposed by mechanical processing from the inner surface of the tube, and the impregnated resin is processed into this. A rough surface will also be added to the tube body 6, which consists of a thick inner part 3 and an outer part 4 including a coating layer, which is liquid-tight on the outside and porous on the inside. It has a two-layer structure.Therefore,
This tube can be used as a tube for fluid transport and has a porous inner part, at least an inner surface, which promotes nuclear AM and has an improved heat transfer function as a heat transfer tube. The mechanism of nucleate boiling on a porous heat transfer surface is known, for example, from Mr. Nakayama's ``Introduction to Heat Exchange Technology'' (published by Ohmsha), but the present invention applies this principle and is outside the scope of this invention. Therefore, I will omit the review.

Example (1) An impermeable graphite heat transfer tube impregnated with phenolic resin and heat-cured for use in a heat exchanger, with an outer diameter of 32 fins, an inner diameter of 22 fins, and a length of 4 m, with a wheel-shaped wire brush installed inside the tube. It was inserted and operated in the axial direction and the inner circumferential direction of the tube to perform grinding-type machining on the inner surface of the tube. As a result, all of the resin layer on the inner surface of the tube was removed, and the graphite inner layer containing the impregnated resin was also removed to form a rough surface having lattice-like grooves in the circumferential direction and the axial direction. The rough surface is a hybrid surface consisting of a porous surface where the graphite itself is exposed and a ground surface of the impregnated resin, and forms four parts of 0.1 to 0.51111.

(2) After sealing both ends of an unimpregnated black ship tube with an outer diameter of 3211 and an inner diameter of 22 mm and a length of 4 m, it was immersed in an epoxy resin solution,
Impregnation is carried out by relative pressure under a vacuum of 10 Torr. After about 20 minutes, the tube is taken out and the tube is heated to 80 Torr.
The resin was cured by drying at <0>C and this operation was repeated twice. The thickness of the resin impregnation on the outer part of the cut surface of the sample was 3 to 47 mm.

(3) A liquid film descending heat exchanger was constructed using the unprocessed impermeable graphite heat exchanger tube used in Example (1) and the one whose inner surface was machined to form a rough surface. We manufactured them, conducted evaporation tests, and compared their heat transfer efficiency. The heat exchanger tube has an outer diameter of 3
There are two pieces each with 2-× inner diameter of 22 mm and length of 4 m, and the heat transfer area is −1.36 m' (average). Evaporation degree 7
0°C, operating pressure 205 Thrr.

The overall heat transfer coefficient (
UM) was measured and compared, and it was found that the value of the inner surface treated one was about twice that of the untreated one.

Inc and 1. The graphite heat exchanger tube of the present invention has an outer part made of a thermosetting resin and graphite that is liquid-tight, an inner part which retains the porous texture of a graphite pipe, and an inner and outer part. Since the pipe is made of composite layers with different compositions, it is possible to make the porous pipe suitable for fluid transport, while at the same time retaining its original excellent heat conductivity and having a unique perforated rough surface on the inner surface. A heat exchanger tube that promotes heat transfer was obtained. In particular, the porosity on the inner surface significantly improves the nucleate boiling function and greatly contributes to improving the thermal efficiency of the heat exchanger and, by extension, the evaporator incorporating this, and the present invention is groundbreaking. You can say that.

[Brief explanation of drawings]

The drawings are schematic diagrams for explaining the heat transfer and tube of the present invention, and FIG. 1 is a schematic diagram for explaining the inner and outer parts, and FIG.
2 is a sectional view showing each side of the application of synthetic resin in the outer part; FIG. DESCRIPTION OF SYMBOLS 1... Heat exchanger tube, 2... Graphite, 3... Inner part, 4...
...Outer part, 5...Thermosetting synthetic resin, 6...Pipe body, thick wall agent Masao Miyake and 1 other person Figure 1 Figure 2

Claims (2)

[Claims] (1) A porous graphite tube body obtained by molding from a material containing carbonaceous material, the inner part of which is made of graphite material or has an exposed graphite surface, and the outer part in contact with it is made of graphite material or has an exposed graphite surface. 1. A heat exchanger tube for a heat exchanger, characterized in that it is an impermeable layer whose inner part is coated or impregnated with a thermosetting synthetic resin and cured. (2) The exposed surface of graphite is a rough surface formed by machining the inner surface of an impermeable graphite tube to form a porous surface where graphite itself is exposed and a ground surface of the impregnated resin. The heat exchanger tube according to item 1.