JPS6153640B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a heat exchange device for passing a heating or cooling fluid through a plastic tube to heat or cool another fluid in contact with the outside of the tube.

Traditionally, plastic tubes, such as polytetrafluoroethylene, polytrifluorochloroethylene, polyvinyl fluoride, copolymers of tetrafluoroethylene and hexafluoropropylene, or copolymers of vinylidene fluoride and hexafluoropropylene, have traditionally been used. Tubes made of corrosion-resistant plastics, such as 1.0-2.0 mm, are widely used for heating and cooling corrosive fluids such as metal pickling solutions.

In such a heat exchange device, heat is of course transferred through the tube wall of the tube, but
The thermal conductivity of plastics is inferior to that of metals, so in order to ensure high heat transfer efficiency, the outside diameter of the tube must be made small to increase the heat transfer area, and the tube walls must also be made thin to reduce heat transfer resistance. Must.
Practically speaking, it is said that the outer diameter should be 13 mm or less and the tube wall thickness 0.8 mm or less (see Japanese Patent Publication No. 3851/1983).

Conventionally, saturated steam has been used as the heating fluid supplied to these plastic tubes with a narrow outer diameter and thin walls, but the superheated steam sent out from the steam generation boiler is sufficiently depressurized during transfer. If superheated steam is supplied to the tube without being heated or converted into saturated steam, microscopic cracks of less than 1 millimeter in size will occur on the tube wall, and the steam will leak from these cracks and leak to the outside. The heated fluid may be diluted, the heated fluid may enter the tube and be discharged outside the machine when the steam supply is stopped, or the corrosive heated fluid may reach the boiler and corrode the piping. There was a risk of destroying the boiler.

In the present invention, the cracks that occur on the wall of the tube were stained with a colorant and then magnified and observed using a microscope. As a result, the shape of the cracks was found to be similar to dendritic treeing that occurs in the insulation coating of the power transmission cable. They found that it closely resembled deterioration, and by analogy, they found that the cause of cracks was local destruction of the tube wall due to partial discharge of static electricity.

Based on this new knowledge, the present invention aims to prevent the occurrence of cracks by inserting a grounding conductor into the hollow of a plastic tube and dissipating the static electricity charged in the tube to the outside, thereby eliminating the drawbacks of the conventional method. With the goal.

To explain the embodiment of the present invention shown in the drawings, 1 is a tube or hollow cylindrical body made of the above-mentioned corrosion-resistant plastic, left and right parallel support rods 2,
The tube 1 is inserted into a through hole in a frame plate 3 connected between the tubes 2 and 2, the tube 1 is wound in a concentric vortex, and the tube 1 is sunk along the inner wall of the liquid tank 4 and installed in the liquid tank 4 by means of support frames 2, 2. The support rods 2, 2 and the liquid contact parts of the frame plate 3 are also made of the same material as the tube 1 or a relatively inexpensive corrosion-resistant plastic such as polypropylene, or their outer peripheries are covered with a coating of corrosion-resistant plastic.

A conductive wire 5 is inserted into the tube 1 and its both ends are extended to the outside of the openings at both ends of the tube 1. Since the tube 1 is elongated, the conducting wire 5 winds gently inside the tube 1 and comes into contact with the tube wall.

Then, both ends of the tube 1 are connected to the iron steam supply pipe 6 and liquid return pipe 7, respectively, and the tip of the conductor 5 is inserted into each pipe 6, 7.
are bent freely and come into contact with the inner walls of the tubes 6 and 7.

8 and 9 are known pipe joints, and when they are screwed together, a stop ring 10 interposed between them is deformed inward to tighten the outer circumference of the end of the tube 1, and the tube 1 is connected to the supply pipe 6 or liquid Securely connect to the return pipe 7.

However, when superheated steam is supplied to the tube 1 from a boiler (not shown) via the steam supply pipe 6,
The superheated steam releases heat through the pipe wall of the tube 1 to the heated fluid in the liquid tank 4, such as the metal pickling liquid, and gradually condenses to become hot water, which is sent from the other end of the tube 1 via the liquid return pipe 7 to the boiler. Return to

At this time, the superheated steam rubs against the wall of the tube 1 and static electricity is generated in the tube 1, but the static electricity immediately escapes from the conductor 5 to the steam supply pipe 6 and the liquid return pipe 7, and the tube 1 is not charged.

For example, a tube made of fluororesin, a copolymer of tetrafluoroethylene and hexafluoropropylene, has an outer diameter of 6 mm and a wall thickness of 6 mm.
For a 0.5 mm tube, if this tube is submerged in a bath of potassium gold cyanide solution and superheated steam is supplied, a 40 micron diameter crack will appear at about 1 meter from the supply side as early as 30 minutes after the start of supply. One crack occurred at one point, but when a stainless steel conductor wire with a diameter of 0.5 mm was inserted into the same tube, no cracks occurred.

When steam is used as the heating fluid in this way, the superheated steam sent out from the boiler can be directly supplied to the tube 1 as it is without any trouble, so compared to supplying saturated steam, heat loss during steam transfer can be reduced. Additionally, installation of a decompression and temperature reduction device can also be omitted.

In addition to the embodiment shown in the drawings, in a heat exchanger in which a large number of tubes with an outer diameter of several millimeters or less are bundled and their open ends are tied together and arranged in a honeycomb, it is possible to insert one conductor into each tube. By grounding the terminals via the common terminal, it is possible to prevent cracks caused by static electricity discharge.

Note that the length of the conducting wire 5 may be shorter than the entire length of the tube 1, but the conducting wire 5 must be at least long from the steam supply side end of the tube 1 to the hot water generation point. In this case, the static electricity in tube 1 is
and the hot water in the tube 1 and are grounded by the tube 6 or 7.

When the tube 1 is sufficiently long or is bent in a spiral shape as in the embodiment shown in the drawings, the conductor 5 contacts the wall of the tube 1 over a sufficient length and receives frictional resistance. Even if the tip of the conductor 5 is not fixed to the tubes 6 and 7 and left as a free end, the conductor 5
There is no risk of movement due to the delivery pressure of heated fluid such as steam.

The conducting wire 5 may be inserted into the tube at the same time as the tube is extruded when the tube is manufactured, or may be inserted after the tube is manufactured.

In the heat exchange device of the present invention, in addition to superheated steam, heat transfer oil heated to 130°C to 150°C can be used as a heating fluid, and tap water or ethylene glycol can be used as a cooling fluid. Needless to say, any antifreeze solution can be used.

In short, in the present invention, tube 1
Through the simple technical means of inserting the conductor 5 through the plastic tube, static electricity generated in the plastic tube is grounded and cracking due to static electricity discharge is completely prevented. is protected by tube 1 and does not come into contact with the corrosive fluid in the liquid tank, so there is no risk of corrosion, and since the material of the tube itself is not changed in any way, it has excellent chemical and physical properties such as corrosion resistance and non-adhesion. The effect is that the characteristics are not impaired at all.

[Brief explanation of the drawing]

FIG. 1 is an overall front view of a heat exchange device embodying the present invention, and FIG. 2 is an enlarged sectional view of the main parts thereof. 1 indicates a tube, and 5 indicates a conductor.

Claims (1)

[Claims] 1. A plastic heat exchange device in which a conductor is inserted into a corrosion-resistant plastic tube and the tube wall is grounded.