JPH02143094A - Heat exchanger equipped with heat transfer tube - Google Patents

Abstract

PURPOSE:To improve both of evaporation performance and condensation performance by a method wherein a flat tube is connected lengthwisely to a grooved tube and refrigerant is made to flow from the side of the flat tube in the case of an evaporator while refrigerant is made to flow from the side of the grooved pipe in the case of a condenser. CONSTITUTION:A heat transfer tube is constituted by combining a flat tube 1 with a grooved tube 2 and refrigerant is made to flow from the side of the flat tube 1 when a heat exchanger, equipped with this heat transfer tube, is used as an evaporator. The tube is filled with liquid refrigerant upon the early period of evaporation and, therefore, heat transfer performance, same as the heat transfer performance obtained when the grooved tube 2 is used, may be obtained when the flat tube 1 is used. On the other hand, gaseous refrigerant is produced in the tube at the later period of evaporation and, therefore, the refrigerant is made to flow through the grooved tube 2, in which the heat transfer of the gaseous refrigerant is effected highly efficiently. According to this method, highly efficient evaporating performance and condensing performance, same as the performances obtained when the total length of the tube is made by the grooved tube, may be obtained while the pressure loss and the manufacturing cost of said combined tube may be reduced as compared a unit grooved tube.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger equipped with heat exchanger tubes that exchange heat by evaporating or condensing a refrigerant within the heat exchanger tubes.

[Prior art] Heat transfer tubes used in conventional heat exchangers such as plate-fin heat exchangers or double-tube heat exchangers include smooth tubes with a smooth inner surface and spiral grooves formed on the inner surface. There are internally grooved pipes and internally porous pipes with a porous structure. These internally grooved tubes and internally perforated tubes are heat transfer tubes developed to improve heat transfer performance. Internally grooved tubes have superior condensation characteristics, while internally porous tubes have better evaporation characteristics than internally grooved tubes. This is approximately 185% of the case. In addition, in terms of pressure loss, the internally porous tube is superior to the internally grooved tube in both evaporation and condensation.

On the other hand, smooth tubes have the advantage of low manufacturing cost and minimal pressure loss.

[Problems to be Solved by the Invention] However, as a heat transfer tube for a heat exchanger, it is desirable that both evaporation characteristics and condensation characteristics are excellent for boat fishing. In particular, a heat exchanger used as a heat pump type must have excellent evaporation characteristics and condensation characteristics since evaporation and condensation alternate.

However, although internally porous tubes have excellent evaporation characteristics, their condensation characteristics are as low as 72% of internally grooved tubes, making them unsuitable as heat exchanger tubes for heat pump type heat exchangers.

On the other hand, although smooth tubes are the least expensive, when they are used as evaporators, particularly when the outer diameter is 101 or less, a phenomenon occurs in which the heat transfer performance deteriorates when the refrigerant flow rate is increased.

Furthermore, although internally grooved tubes are often used in plate-fin or double-tube heat exchangers, they are significantly more expensive than smooth tubes, which significantly increases the manufacturing cost of the heat exchanger. It ends up.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a heat exchanger equipped with heat exchanger tubes that has excellent both evaporation characteristics and condensation characteristics and is inexpensive to manufacture.

[Means for Solving the Problems] A heat exchanger equipped with a heat transfer tube according to the present invention connects a smooth tube with a smooth inner surface and a grooved tube with grooves formed on the inner surface in the longitudinal direction, When used as an evaporator, the refrigerant is passed through the smooth tube side, and when used as a condenser, the refrigerant is passed through the grooved tube side.

A heat exchanger equipped with a heat transfer tube according to the present invention connects a grooved tube with grooves formed on the inner surface and a perforated tube with a porous inner surface in the longitudinal direction, and when used as an evaporator, The refrigerant is allowed to flow through the porous tube side, and when used as a condenser, the refrigerant is allowed to flow through the grooved tube side.

[Function] In the present invention, when a heat exchanger tube is formed by combining a smooth tube and a grooved tube to form an oval heat exchanger tube and a heat exchanger equipped with this heat exchanger tube is used as an evaporator, the refrigerant is passed from the smooth tube side. Let it flow.

In the early stage of evaporation, the inside of the tube is filled with liquid refrigerant, so in this state, whether or not the inner surface of the tube is grooved has no significant effect on heat transfer performance. Therefore, even if a smooth tube is used, it has the same heat transfer performance as a grooved tube. On the other hand, in the latter stage of evaporation, a gaseous refrigerant is generated within the tube, so a grooved tube is used in order to conduct heat transfer with this gaseous refrigerant with high efficiency. As a result, a heat exchanger tube having the same heat transfer performance as a case where the entire length is composed of a grooved tube can be obtained at a low cost.

On the other hand, when this heat exchanger is used as a condenser, the refrigerant is passed through from the grooved tube side. In the early stage of condensation, the inside of the pipe is filled with gaseous refrigerant, so it is necessary to use grooved pipes to improve heat transfer performance, but in the latter stage of condensation, the inside of the pipe is filled with liquid refrigerant, so the above-mentioned As in the case of evaporation, the presence or absence of grooves on the inner surface does not affect heat transfer performance, so a smooth tube is used.

In addition, when a heat exchanger tube is configured by combining a grooved tube and a perforated tube, when using a heat exchanger equipped with this heat exchanger tube as an evaporator, the perforated tube side is the refrigerant inlet side, and the condenser When used as a refrigerant, the grooved tube side should be the refrigerant inlet side.

The flow form of the refrigerant in the pipe is a gas-liquid two-phase flow, but internally grooved pipes give a swirling flow to the refrigerant flow, making it easier for the gas-liquid two-phase boundary layer to separate, so the more gas phase the better. It is effective in terms of heat transfer effect. On the other hand, in an internally porous tube, a large number of small pores serve as nuclei, and nucleate boiling is likely to occur, so the more liquid phase there is, the more effective the heat transfer effect will be. Therefore, the internally grooved tube is used on the refrigerant outlet side of the evaporator and the refrigerant inlet side of the condenser, and the internally porous tube is used on the refrigerant inlet side of the evaporator and the refrigerant outlet side of the condenser. As a result, a heat exchanger having both excellent evaporation performance and condensation performance can be obtained.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

First, as shown in Fig. 1, a smooth tube l with a smooth inner surface,
A heat exchanger using a heat exchanger tube in which a grooved tube 2 having a spiral groove formed on the inner surface is connected in the longitudinal direction will be described.

In the embodiment shown in FIG. 1, 3/4 of the total length of the tube is a smooth tube 1, and the remaining 1/4 is a grooved tube 2, which are joined in a straight line. The total length of these smooth tubes 1 and grooved tubes 2 is, for example, 4 m, and the outer diameter is 6.35 m.
It is m.

When a heat exchanger using heat transfer tubes configured as described above is used in an evaporator, liquid refrigerant is first passed through the smooth tubes 1 and then through the grooved tubes 2. While flowing through the smooth tube 1, the liquid refrigerant undergoes heat exchange (heating) and evaporates, becoming two phases: a gas phase and a liquid phase. This two-phase refrigerant then flows through the internally grooved tube 2 and undergoes heat exchange (heating) with high efficiency.On the other hand, in the condenser, the gaseous refrigerant first flows through the grooved tube 2.
After passing through the fluid, the smooth tube 1 is passed through. While flowing through the grooved pipe 2, the gaseous refrigerant undergoes heat exchange (cooling) with high efficiency and is condensed into two phases: a gas phase and a liquid phase. And this 2
The phase refrigerant then flows through the smooth tube 1 to undergo further heat exchange (cooling).

As described above, in this embodiment, the refrigerant undergoes heat exchange by heat transfer from the smooth tube 1 during the early stage of evaporation or the late stage of condensation when the inside of the pipe is filled with liquid refrigerant, and the refrigerant undergoes heat exchange during the late stage of evaporation or condensation when the inside of the pipe is filled with liquid refrigerant. In the first period, the refrigerant is heated by heat transfer from the grooved tube 2. In this case, for liquid refrigerant, there is no big difference in heat transfer performance between smooth tubes and grooved tubes, so the combined tube of this example has the same heat transfer efficiency as when using a single grooved tube. is obtained. Furthermore, since 3/4 of the total length is a smooth tube, the pressure loss is small, and in this respect it is superior to the case of a single grooved tube. Furthermore, since 3/4 of the total length is a smooth tube, the manufacturing cost is extremely low compared to a case where the entire length is composed of a grooved tube.

On the other hand, for a refrigerant with a large amount of gas phase, a swirling flow is given by the internally grooved tube 2, and the gas-liquid two-phase boundary layer is separated, resulting in highly efficient heat exchange.

That is, when a fluid flows along a wall surface whose temperature is different from that of the wall surface, a boundary layer appears near the wall surface where the temperature and velocity of the fluid suddenly change. The manner in which this boundary layer is generated differs depending on the velocity of the fluid and the temperature difference between the fluid and the wall surface, but this boundary layer acts as a thermal resistance and inhibits heat exchange between the main flow part of the fluid and the wall surface.

In the case of a smooth tube, most of the inner wall of the tube is covered by a well-developed boundary layer, resulting in poor heat transfer performance.In contrast, in a tube with internal grooves, the fluid flow becomes a swirling flow due to the grooves on the inner surface, and at the same time,
Since turbulence is generated in the groove, the boundary layer generated in the internally grooved tube due to this flow is thin and intermittent. Therefore, in the gas-liquid two-layer region, the turbulent flow generated inside the internally grooved tube entrains fine air bubbles, and these air bubbles separate and destroy the aforementioned boundary layer, making it difficult to form a boundary layer. Good heat transfer is always possible between the fluid and the inner surface of the tube wall.

Next, the results of actually measuring the heat transfer performance and pressure loss of the combined tube of this example will be explained.

Figure 2 shows the refrigerant flow rate on the horizontal axis and the heat transfer performance on the vertical axis.
FIG. 2 is a graph showing the evaporation performance of a smooth tube + an internally grooved tube. Note that the outer diameter of the container tube is 6.35 m+n. Furthermore, in the tube of this example, the refrigerant was introduced from the smooth tube side. As is clear from FIG. 2, the heat transfer performance of the smooth tube is low, and the heat transfer performance is significantly reduced when the refrigerant flow rate is low or high. On the other hand, in the case of the combined tube of this embodiment, excellent heat transfer performance can be obtained similar to that of the single tube with internal grooves.

Moreover, FIG. 3 is a graph showing the pressure loss of the container tube, with the refrigerant flow I plotted on the horizontal axis and the pressure loss plotted on the vertical axis. As is clear from FIG. 3, the internally grooved pipe has the largest pressure loss, and the smooth pipe has the smallest pressure loss. The combined pipe of this example exhibits a pressure loss intermediate between these single pipes.

As mentioned above, the combined tube of this example has the same heat transfer performance as the case where the entire length is composed of internally grooved tubes, but
The pressure loss is smaller than that of an internally grooved tube. FIG. 4 is a schematic diagram showing an embodiment in which the present invention is applied to a plate-fin type heat exchanger. A plurality of plate-shaped aluminum fins 5 are arranged in parallel at appropriate length intervals, and three smooth tubes 3 curved in a hairpin shape and one tube 4 with an inner groove in the shape of a hairpin are formed into a fin. 5 perpendicularly to that surface and fixed to each other. Adjacent smooth tubes 3 or adjacent smooth tubes 3 and inner grooved tubes 4 are interconnected by U-bend tubes 6. This constitutes one refrigerant circuit in which 3/4 of the total length is the smooth tube 3 and the remaining 1/4 is the grooved tube 4.

In this embodiment as well, when used as an evaporator, the refrigerant is introduced from the smooth pipe 3 side, and when used as a condenser, the refrigerant is introduced from the grooved pipe 4 (ll!I). The same effect as that of the embodiment shown in Fig. 1 is achieved.Although each of the above embodiments is a case where the smooth tube occupies 3/4 of the total length, the present invention is not limited to this, and the present invention is not limited to this. It is of course possible to combine tubes.

Next, a case will be described in which a heat exchanger tube is constructed by combining an internally grooved tube in which a spiral groove is formed on the internal surface and an internally porous tube in which a large number of small holes that do not penetrate are formed in the internal surface.

FIG. 5 is a schematic diagram showing a so-called finted coil type heat exchanger incorporating this combination of heat exchanger tubes. Five hairpin-shaped or U-shaped internally grooved tubes 11 (NlLL~5
) and five hairpin-shaped or U-shaped internally porous tubes 12 (N[L6-10) are made of aluminum fins 13.
However, it is inserted perpendicularly to that surface and is tightly fixed.

Then, the adjacent pipes (the internally grooved pipe 11 and the internally porous pipe 1
2) One refrigerant circuit is constructed by connecting them with each other through a U-bend pipe 14. This constitutes a fin-type heat exchanger in which 20 stages of heat transfer tubes are arranged in the negative row.

When this heat exchanger is used as an evaporator, the refrigerant is passed through the tubes so that the tube end B on the internally porous tube 12 side serves as the refrigerant inlet, and the tube end A on the internally grooved tube 11 side serves as the refrigerant outlet. Let it flow. Then, the liquid refrigerant first enters the internally porous pipe 12.
A flow passes through it, heat is received, and a gas phase is generated, resulting in a two-phase flow of a liquid phase and a gas phase. In the internally porous tube 12, the liquid refrigerant undergoes nucleate boiling with the large number of small pores on the internal surface serving as nuclei. For this reason,
It is more effective to use the internally porous tube 12 for heat transfer of a refrigerant with a large liquid phase.

Next, the two-phase refrigerant flows through the internally grooved tube 11 and receives heat, further progressing evaporation of the refrigerant. In the internally grooved tube 11, swirling flow is given to the refrigerant flow, separation of the boundary layer progresses, and heat exchange becomes difficult, so it is more effective to use the refrigerant for heat transfer with a large gas phase. be.

In this way, during the early stage of evaporation when there is a large amount of liquid phase, the inner porous tube 12
In the latter stage of evaporation when there is a large amount of gas phase, heat is exchanged with high efficiency by the internally grooved tube 11.

On the other hand, when the heat exchanger is used as a condenser, the tube end A on the internally grooved tube 11 side becomes the refrigerant inlet, and the internally porous tube 12
The refrigerant is made to flow through the tube so that the side tube end B becomes the refrigerant outlet. Then, in the early condensation stage where there is a lot of gas phase,
The refrigerant receives highly efficient heat transfer through heat exchange accompanied by a swirling flow through the internally grooved tube 11 .

Therefore, in this example, both the evaporation characteristics and the condensation characteristics are excellent. FIG. 6 is a graph showing the relationship between evaporation characteristics, condensation characteristics, and distribution ratio, with the horizontal axis representing the distribution ratio of the internally porous tube 12 and the internally grooved tube 11, and the vertical axis representing the heat transfer characteristic. . As shown in FIG. 6, if the internally porous tube accounts for less than 20%, the evaporation characteristics will be significantly reduced, and conversely, if the internally grooved tube accounts for less than 20%, the condensing characteristics will decrease significantly.

This is because a tube with internal holes has better evaporation characteristics, and a tube with grooves on the inside has better condensation characteristics.

Figure 7 shows the refrigerant flow rate on the horizontal axis and the internal heat transfer coefficient on the vertical axis. It is a graph diagram showing the evaporation characteristics of the tube (D). As is clear from Fig. 7, the perforated pipe (D) has the best evaporation characteristics, and the perforated pipe (D) has a heat transfer coefficient of 1.85 times that of the triangular grooved pipe (B). has.

On the other hand, FIG. 8 is a graph showing the condensation characteristics of the above-mentioned container tube, with the refrigerant flow rate plotted on the horizontal axis and the heat transfer coefficient within the tube plotted on the 1i1 axis. As is clear from Fig. 8, the grooved tubes (C, B) have the best condensation characteristics, and the triangular grooved tubes (C, B) have the best condensation characteristics.
If the condensation characteristic of B) is 100, the condensation characteristic of the porous pipe (D) is 72.

Therefore, as in this embodiment, when the internally grooved tube 11 and the internally porous tube 12 are combined, the internally porous tube side is used as the refrigerant inlet when the objective is to evaporate within the tube, and the internally grooved tube is used when the objective is to condense within the tube. By using the attached tube side as the refrigerant inlet, it is possible to obtain a heat exchanger tube that has both the features of an internally porous tube and an internally grooved tube and has excellent evaporation characteristics and condensation characteristics.

In this case, as shown in FIG. 6, if the distribution ratio of both the internally porous tube and the internally grooved tube is less than 20%, either the evaporation characteristics or the condensation characteristics will be extremely degraded. For this reason, it is preferable that the distribution ratio of the internally porous tube or the internally grooved tube be 20 to 80%.

As shown in FIG. 9, the heat transfer characteristics during evaporation of the combined tube constructed in this way are superior to those of a single tube with internal grooves. The same is true when condensing,
Furthermore, the combination tube of this embodiment can similarly provide excellent heat transfer performance with respect to a single tube with internally porous tubes.

This heat exchanger is installed indoors and outdoors, and the indoor unit is used as a condenser,
It can be assembled as a heating device by using the outdoor unit as an evaporator and forcing refrigerant to flow through the side heat exchanger while heating the outdoor unit.

Conversely, by using the indoor unit as an evaporator and the outdoor unit as a condenser, and forcing the outdoor unit to cool down while allowing the refrigerant to flow through the side heat exchanger, it is possible to assemble this heat exchanger as a cooling device. can.

FIG. 11 is a schematic diagram showing an embodiment in which the present invention is applied to a shell-and-type heat exchanger.

A heat transfer tube is constructed by connecting a straight inner grooved tube 15 and a straight inner porous tube 16 in the longitudinal direction. In this heat exchanger tube, 1/2 of its length is an internally grooved tube 15, and the remaining 1/2 is an internally porous tube 16.

The plurality of heat transfer tubes are fixed in an air-tight and liquid-tight manner by inserting a pair of tube plates 17 at their tube ends. The heat exchanger tubes assembled in this manner are inserted into the shell 18, and three spaces are partitioned within the shell 18 by the tube plate 17. At both ends of the shell 18, refrigerant flow ports 19a and 19b are provided which communicate with the spaces at both ends. The refrigerant introduced into the shell 18 through this refrigerant flow port 19a (or one b) is transferred to the inner grooved pipe 15.
and the other refrigerant flow port 19b (or 19a).
It is discharged to the outside of the shell 18 through the. On the other hand, shell 18
When using the heat exchanger as an evaporator, other refrigerant flows through the space in the center of the tube and contacts the outer surface of the heat transfer tube to exchange heat with the heat transfer tube. The refrigerant flow port 19b on the 16 side is used as a refrigerant inlet, and when used as a condenser, the refrigerant flow port 19a on the inner grooved tube 15 side is used as a refrigerant inlet. This embodiment configured in this manner also provides the same effects as the embodiment shown in FIG. 5.

[Effects of the Invention] According to the present invention, since a heat transfer tube that is a combination of a smooth tube and a grooved tube is used, it is possible to obtain the same evaporation performance and condensation performance as when the entire length is composed of an internally grooved tube. On the other hand, the pressure drop and manufacturing cost are lower than in the case of a single tube with internal grooves.

Further, since the other invention of the present application uses a heat exchanger tube that is a combination of a grooved tube and a perforated tube, it has excellent evaporation characteristics and condensation characteristics, and is extremely useful as a heat pump type heat exchanger.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a heat exchanger tube used in a heat exchanger according to the first embodiment of the present invention, Fig. 2 is a graph showing its evaporation performance, and Fig. 3 is a graph showing its pressure loss. figure,
Fig. 4 is a schematic diagram showing a second embodiment of the present invention, Fig. 5 is a schematic diagram showing a third embodiment of the invention, and Fig. 6 shows the relationship between the distribution ratio and heat transfer characteristics. Graph diagram, Figure 7 is a graph diagram showing the evaporation characteristics of the container tube, Figure 8 is a graph diagram showing the condensation characteristics of the container tube, Figure 9 is a graph diagram showing heat transfer performance, and Figure 10 is a graph diagram showing the pressure loss. FIG. 11 is a schematic diagram showing a fourth embodiment of the present invention. 1.3; Smooth pipe, 2, 4, 11, 15: Internally grooved pipe, 1
2, 16; Internally porous tube, 6.14; U-bend tube, 18;
shell

Claims (3)

[Claims] (1) A smooth tube with a smooth inner surface and a grooved tube with grooves formed on the inner surface are connected in the longitudinal direction, and when used as an evaporator, a refrigerant is passed from the smooth tube side to form a condenser. A heat exchanger equipped with a heat transfer tube, characterized in that when used as a heat exchanger, a refrigerant is caused to flow from the grooved tube side. (2) A grooved tube with grooves formed on the inner surface and a porous tube with a porous structure on the inner surface are connected in the longitudinal direction, and when used as an evaporator, a refrigerant is caused to flow from the porous tube side, A heat exchanger equipped with a heat transfer tube, characterized in that when used as a condenser, a refrigerant is passed through the grooved tube side. (3) The heat exchanger equipped with a heat transfer tube according to claim 2, wherein the perforated tube occupies 20 to 80% of the total length of the tube.