JP2000213876A - Heat exchanger for cooling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent channelling from occurring by arranging at least two inner tubes where a fluid to be cooled flows between the inside of an outer tube and the outside of a cylindrical object while the cylindrical object that forms a concentric circle with the central position of a sectional circle in a vertical direction for the flow direction of the outer tube is in parallel with a flow direction. SOLUTION: A cylindrical object 1-3 that does not have a space part where a fluid passes are provided on a concentric circle with the central position of the sectional circle of an outer tube, and an inner tube, namely a heat transfer pipe, is arranged only between the outer tube and the cylindrical objects, thus preventing the difference in resistance from being generated. A mixing element 1-4 is filled into each heat transfer pipe to increase heat transfer efficiency by agitating passing fluid, and a conical projection 1-7 is mounted to plates 1-2 for connection so that it can be nearly in parallel with the inclination of a reducer 1-6, thus preventing channelling from occurring and hence performing efficient cooling for the cooling of a high-temperature, high-viscosity fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling heat exchanger which is installed immediately after an extruder in order to obtain a foam molded article having excellent mechanical properties in a molding process of expanded polystyrene.

[0002]

2. Description of the Related Art One of the most common methods of forming a plastic film is to melt a plastic by heat and then extrude it from a T-die to form a flat film. That is, a plastic raw material is supplied from a hopper to a screw groove, and the screw is rotated by an electric motor to extrude the plastic raw material. Here, while being transported along the screw groove, the plastic raw material is heated and melted by the barrel heater.
The molten plastic is extruded from a die through a screen breaker plate and an adapter to form a film. The molten plastic extruded from the die is hot-drawn to a thickness of, for example, 1/10 to 1/100 of the die lip width, and then forcibly cooled and cured to form a film.

Similarly, in the case of producing a plastic foam, a compound (decomposition type foaming agent) which is decomposed by heating to generate a gas (decomposition type foaming agent) is put into an extruder together with a plastic raw material, and the resin is melted in the extruder. A method is used in which the blowing agent is heated to a temperature higher than the decomposition temperature and then extruded. In the above method,
There are various problems when molding a foamed sheet. That is, when the plastic material containing the foaming agent that has entered the die from the extruder has entered the die, even after heating, the internal pressure is high, so that foaming has not yet occurred. However, when the plastic material is extruded into the atmosphere from the exit of the die, the plastic material foams and expands three-dimensionally. Because this foaming phenomenon is rapid, it may cause irregular wavy or thickness fluctuation due to shape distortion,
Excessive expansion may cause a reduction in the strength of the film material. The reason why such a problem occurs is that the plastic material containing the foaming gas after the outlet of the extruder is rapidly foamed by being discharged from the die in a state of high temperature and high pressure while being opened to the atmosphere. It is very effective to cool before sending to the die. However, in practice, there is no means to efficiently cool high-viscosity, high-temperature plastic materials during transfer, and the film discharged from the die is cooled by forced air cooling using a cooling water tank, cooling rolls, or a fan. It was the current situation.

As a means for cooling a high-viscosity, high-temperature plastic material during transfer, a refrigerant (water, air, etc.) is made to flow through an outer tube using a double-tube heat exchanger or a multi-tube heat exchanger. There is a way to cool. Usually, a double-tube heat exchanger or a method of installing a water tank immediately before a die as disclosed in JP-A-53-8668 is used. This is because cooling a high-viscosity fluid using a multi-tube heat exchanger is not suitable for use because of the problem of drift described later. However, the double-pipe heat exchanger is very large to perform the necessary heat exchange because the effective heat transfer area is limited, and there is a major problem in use.

[0005] The multi-tube heat exchanger has a feature that a large effective heat transfer area can be obtained in a small space. However, when cooling a highly viscous fluid such as molten plastics used in the present application, there is a problem of drifting and it cannot be used. Absent. The drift refers to a phenomenon in which the fluid to be cooled flows only through a certain inner pipe without the same flow rate flowing through all of the two or more inner pipes. The drift that occurs when using a multitubular heat exchanger occurs for the following reasons.

First, a high-temperature, high-viscosity fluid flows equally into each inner tube of the multi-tube heat exchanger, but the respective flow rates are slightly different from each other. Conversely, the amount of cooling provided by the refrigerant from the heat exchanger is the same for each inner tube. Under the same cooling condition, the inner pipe having a small flow rate is easy to cool by the small flow rate, and the passage time (cooling time) is long because the flow velocity is low. For this reason, the temperature drops faster than other inner tubes. As the temperature decreases, the viscosity of the fluid increases accordingly, and the flow becomes less difficult. Accordingly, the high-temperature fluid that has flowed later flows naturally into the easily flowable (low resistance) pipe, so that the flow rate flowing through the inner pipe is further reduced. Due to this repetition, the inner tube is finally closed. Therefore, unless this problem is solved, the use of the shell-and-tube type heat exchanger in this step was practically impossible.

[0007] One way to avoid this problem is to use a double tube heat exchanger.
In the case of the same volume, the effective area for performing heat exchange becomes extremely small, and sufficient cooling cannot be performed. Conversely, if a sufficient cooling performance is to be ensured, the size of the heat exchanger becomes much larger than that of the multi-tube heat exchanger, and it becomes impractical for reasons such as cost and installation space. As a method for preventing the knitting flow of the multi-tubular heat exchanger, a method of moving the fluid in the heat exchanger in two passes or four passes, various baffles for mixing in the reducer, etc. However, it has been considered that a sufficient effect cannot be obtained in addition to a problem such as an increase in pressure loss.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a structure of a multitubular heat exchanger which does not cause a current drift in cooling a high-temperature high-viscosity fluid. It is.

[0009]

As a means for achieving the above object, a multi-tube heat exchanger comprising an outer tube and two or more inner tubes disposed with a gap in the outer tube includes a multi-tube heat exchanger. A cylindrical object that forms a concentric circle with the center position of the cross-section circle perpendicular to the flow direction is disposed in the outer tube in parallel with the flow direction,
Two or more inner pipes through which the fluid to be cooled flows are arranged between the inner side of the outer pipe and the outer side of the columnar object. Further, the inlet of the fluid to be heated in the heat exchanger is smaller than the cross-sectional circle of the outer pipe having the inner pipe through which the fluid to be heated flows, and the cross-sectional area thereof is the same as the outer pipe cross-section at the mounting portion of the outer pipe in the flow direction. The reducer is composed of a substantially conical pipe that spreads in a shape, and a conical protrusion attached substantially parallel to the inside of the pipe. In this way, the fluid is forced through the gap between the conical projection and the substantially conical pipe. Further, the mounting portion of the inner tube and the connection plate is formed in a reverse taper shape with respect to the flow direction. This can prevent stagnation when the fluid flows into the inner tube.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. First, one of the preferable production steps according to the present invention is a film production step of a foamed polystyrene film. In the expanded polystyrene industry, Low-sta
ck), that is, a movement to reduce the height at the time of loading to about 2/3 of the conventional height has started, and quality improvement such as "thinning the thickness of the sheet and maintaining the strength as before" is required. The point of improvement is the control of the bubble diameter of the foam, which requires temperature control. That is, accurate cooling is required while the polystyrene stock solution extruded from the extrusion is fed to the die. However, there is no appropriate method for cooling in this state for the reasons described above. In the present invention, in order to achieve the above object, a heat exchanger having good heat transfer performance, a reducer having a knitting prevention function, and a mixer for improving the heat history generated by passing through the heat exchanger It is composed of

FIG. 1 is a sectional view of a heat exchanger used in the present invention. As the heat exchanger, a multi-tube heat exchanger is used. The mounting position of the plate (1-2) for connecting the heat transfer tubes (1-1) of the ordinary multi-tube heat exchanger is, for example, a triangular arrangement with respect to a cross section perpendicular to the traveling direction of the viscous fluid of the heat exchanger (FIG. Although they are arranged so as to be uniform on the cross section as in 2), in the present application, a cylindrical object (1-3) having no space through which the fluid passes concentrically with the center position of the cross section circle of the outer tube. )
An inner tube, that is, a heat transfer tube is arranged only between the outer tube and the columnar object (FIG. 3). As a result, it is possible to minimize the difference in resistance between the heat transfer tubes. The inside of each heat transfer tube is filled with a mixing element (1-4) for the purpose of increasing the heat transfer efficiency by imparting a stirring action to the passing fluid. This mixing element is disclosed in, for example,
The 180 ° twisting swivel element disclosed in 592
A so-called static mixer (FIG. 4) alternately connected in the opposite direction with a connection angle of 0 °, or a low-resistance type mixing element in which the above-mentioned 180 ° twisting swivel element is connected in the opposite direction or the same direction with a connection angle of 0 ° ( FIG. 5) is used. An ordinary mixing element has a twist degree, ie, L / D (L:
Length of mixing element in flow direction, D: inner diameter of heat transfer tube)
2 is suitable from the viewpoint of heat exchange performance, but in this application, the resistance (pressure loss) caused by flowing a highly viscous fluid
The degree of twist is designed to be 2 to 3 in order to minimize the increase of the resistance and the variation in the resistance value of each heat transfer tube. Reducers to be installed before and after the heat exchanger (1-6)
Are the respective heat transfer tubes (1--1) arranged in the heat exchanger.
3) The viscous fluid is designed to flow efficiently. That is, the conical projection (1-7) is attached to the connection plate (1-2) so as to be substantially parallel to the inclination of the reducer (1-6). As a result, the viscous fluid flowing in the reducer spreads toward the outer tube (1-8) along the inclination angle of the reducer as it progresses.

[0012] As described above, it is required that the flow rate and the pressure of the viscous fluid at this time when it spreads circumferentially be uniform. These are, of course, due to differences in resistance in the flowing direction, but the initial cause is the non-uniform properties of the viscous fluid. One of the major factors is a velocity change in the flow direction of the viscous fluid. Generally, the volume at each passing position is given by the product AU of the cross-sectional area A and the velocity U. Since the viscous fluid handled here is an incompressible fluid, no volume change occurs. Therefore, in order to prevent a speed change at each passing point, it is necessary to make the passing cross section constant at each passing point. For that purpose, the height H of the cross section passing through in the reducer (1-6) must decrease as it progresses. That is, the gradient θ2 of the reducer (1-6)
On the other hand, the gradient θ1 of the conical projection (1-7) must be steep. Empirically, θ2
Suitably, 1 is increased by 5 ° to 10 °. Also, the mounting section of the cross section plate of the heat exchanger and the heat transfer tube is machined into a tapered shape (FIG. 6). Thereby, the stagnation of the viscous fluid in the cross section plate portion can be prevented as much as possible.

[0013]

An embodiment of the present invention will be described below. FIG. 7 is a schematic view of forming a foamed polystyrene film according to one embodiment of the present invention. Plastic raw material in hopper (7-
The raw material is supplied from 1) to the screw groove (7-2), and the plastic material is extruded by rotating the screw (7-3) by an electric motor. Here, while being transported along the screw groove, the plastic raw material is supplied to the barrel heater (7).
It is heated and melted by -8). This molten plastics is homogenized in a mixer (7-4) and then heat-exchanged (7-4).
-5) and cooled. After the molten plastics coming out of the heat exchanger is homogenized again by the mixer (7-6),
The film is extruded from the die (7-7) through a screen breaker plate and an adapter to form a film.

(Production Example) Hereinafter, a production example of the present invention will be described in detail. The present invention is a method of foaming and molding a styrene-based resin, and the styrene-based resin to be applied is not particularly limited. For example, a styrene homopolymer and propylene and ethylene and / or having 4 to 4 carbon atoms are used. 1
Examples include a random copolymer with two α-olefins and a block copolymer.

These styrenic resins may be produced by a widely known production method. For example, a transition metal compound such as a titanium compound or a transition metal compound supported on a carrier such as a magnesium compound may be used. Compounds that polymerize in the presence of a catalyst system obtained from an organic metal compound such as a compound can be used.

In the present invention, although it is not particularly necessary to enhance the foaming moldability, one or two or more kinds of thermoplastic resins can be blended with styrene. For example, polyethylene, polyvinyl chloride,
A polymer or a copolymer such as an ethylene-vinyl acetate copolymer can be used. In addition, pigments, antioxidants, lubricants, antistatic agents, weatherability improvers, fillers, and the like can be appropriately added within a known amount. In order to improve the dispersibility of the foaming agent and the additive in the resin, an additive such as liquid paraffin can be added and used.

In the present invention, such a polystyrene resin is mixed with a foaming agent using a general blender, a mixer, or the like, and charged into an extruder. The blowing agent used in the present invention is a decomposition type blowing agent that decomposes upon heating to generate gas. The heat-decomposable foaming agent is one or a mixture of two or more of various organic and inorganic heat-decomposable foaming agents. Examples of the organic foaming agent include azodicarbonamide and N, N'-dinitrosopenta. Methylenetetramine,
And PP′-oxybisbenzenesulfonyl hydrazide. Examples of the inorganic foaming agent include sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide and the like. The decomposition-type foaming agent preferably has a decomposition temperature of 150 ° C to 210 ° C, but needs to decompose at the temperature in the extruder. An appropriate amount of the foaming agent is 0.1 to 6 parts by weight, preferably 0.3 to 5 parts by weight, based on 100 parts by weight of the resin. When the amount is less than 0.3 parts by weight, the expansion ratio does not increase, and when the amount is more than 6 parts by weight, the resin cannot retain the air bubbles and the air bubbles are crushed, so that the expansion ratio decreases.

In the present invention, in order to produce a uniform and high-magnification foam, the temperature of the molten resin from the material input port of the molding extruder to the die outlet is determined by the melting end temperature of the resin + 15 ° C. It is necessary to be within the following range, and it is more preferable that the melting end temperature is + 10 ° C or lower, and it is even more preferable that the melting end temperature is + 6 ° C or lower. The melting end temperature varies depending on the type of resin material used for molding, but in the present invention, the molding temperature is preferably maintained at 175 to 185 ° C for a polystyrene homopolymer or a block copolymer. In addition, also about the above-mentioned decomposition type foaming agent, the thing whose decomposition temperature is in this range is applied.

Conventionally, regarding the temperature at the time of extrusion molding of the foam, it has been important to melt and knead the resin and decompose the foaming agent. In an extruder, the temperature must be raised within a range in which gas does not escape from the hopper. It is said that it is better to lower the resin temperature only near the die. In the present invention, the temperature of the molten plastic is controlled at 110 ° C. by installing a cooling heat exchanger at the outlet of the extruder.

The temperature of the resin at the time of molding is not always equal to the set temperature of the cylinder or the die of the extruder, but depends on the kneading conditions of the resin. In addition, in many molding machines, the resin temperature in the extruder cannot be measured. Therefore, it is desirable to grasp the resin temperature and the extrusion conditions by inserting a thermometer in a cylinder portion in advance.

In the present invention, as a means for making the resin temperature more uniform, a method of providing a static mixer (7-6) between a cooler after the extruder and a die as shown in FIG. 7 is effective. The static mixer used here is used as a means for making the temperature of the resin more uniform.

The static mixer to be applied may be a generally known one. As shown in FIG. 8, a plurality of baffle plates having a predetermined angle twisted baffle plate are formed in a cylindrical tubular housing (8-1). Spiral elements (8-
2) is arranged and schematically constituted, and one rear end and the other front end of adjacent spiral elements are usually 9
It is arranged to be twisted by 0 ° and has no movable parts.
The resin flows along the plurality of helical elements in the tubular housing of the static mixer under the pressure from the extruder, during which the temperature is made uniform.

If the temperature of the resin extruded from the cooler is not uniform in both the width and thickness directions, a foam in a uniform foaming state cannot be obtained, and the foaming state deteriorates and the foaming ratio decreases. The reason why the temperature of the resin extruded from the cooler is non-uniform is mainly due to the non-uniform temperature of the resin when flowing into the die from the extruder and the difference due to each heat transfer tube in cooling. Static mixer (8-
The mounting of 1) is effective.

The expansion ratio of the foam according to the present invention is as follows.
It is eight times or more and the bubble diameter is 1.2 mm or less. Such a material has high strength and excellent elasticity. The foam of the present invention is formed into various shapes such as a plate, a sheet, a bar, and a tube, and is used as a heat insulating material, a packaging material, a soundproofing material, a buoyancy material, and the like. For example, it is used for applications such as a cover of a binder, a protective material for walls and floors, a returnable box, a partition plate, a food container, a building material, and a heat insulating pipe.

[0025]

[Effect] By using the heat exchanger having the above-described structure, it is possible to prevent the occurrence of a drift in cooling a high-temperature, high-viscosity fluid, and to perform efficient cooling.

[Brief description of the drawings]

FIG. 1 is a sectional view of a heat exchanger for cooling.

FIG. 2 is a conventional heat transfer tube layout.

FIG. 3 is a layout diagram of the heat transfer tubes of the present application.

FIG. 4 Static mixer

FIG. 5: Mixed element

FIG. 6 is a sectional plate

FIG. 7 is a schematic view of forming a film of expanded polystyrene.

FIG. 8 is a schematic view of a conventional foamed polystyrene film forming.

[Brief description of reference numerals]

 (1-1) Heat transfer tube (1-2) Connection plate (1-3) Column having no space (1-4) Mixing element (1-5) Refrigerant inlet (1-6) Reducer ( 1-7) Conical projection (1-8) Outer tube (7-1) Hopper (7-2) Screw groove (7-3) Screw (7-4) Mixer (7-5) Heat exchanger (7-6) Mixer (7-7) Die (7-8) Barrel heater

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takahiro Oguri 3-36 Noritake Shinmachi, Nishi-ku, Nagoya City, Aichi Prefecture Inside Noritake Company Limited (72) Inventor Akira Matsubara 3-1-1 Noritake Shinmachi, Nishi-ku, Nagoya City, Aichi Prefecture No. 36 Noritake Co., Ltd. F-term (reference) 3L103 BB26 DD08 DD33 DD38 DD42 DD62 4F207 AA13 AB02 AG01 AG20 AK02 KA01 KA11 KK45 KK63 KL55 KL83

Claims (4)

[Claims] 1. A multi-tube heat exchanger comprising an outer tube and two or more inner tubes disposed with a gap in the outer tube, wherein a center position of a cross-sectional circle in a direction perpendicular to a flow direction of the outer tube is determined. A concentric cylinder is disposed in the outer tube in parallel with the flow direction,
A cooling heat exchanger comprising two or more inner pipes through which a fluid to be cooled flows is disposed between the inner side of the outer pipe and the outer side of the columnar object. 2. The inlet of the fluid to be cooled in the heat exchanger is smaller than the cross-sectional circle of the outer pipe having the inner pipe through which the fluid to be cooled flows. 2. A reducer comprising a substantially conical pipe extending so as to have the same shape as a cross-sectional circle and a conical protrusion mounted substantially parallel to the inside of the pipe. Heat exchanger for cooling. 3. The cooling heat exchanger according to claim 1, wherein an attachment portion between the inner tube and the connection plate is formed in a reverse taper shape with respect to a flow direction. 4. A method for producing a polystyrene film, comprising using the heat exchanger for cooling according to claim 1.