JPS644118B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plate finch tube heat exchanger used in air conditioners, refrigeration equipment, etc.

In general, a plate finch tube type heat exchanger has a plurality of heat transfer tubes passing through the plate fins arranged in parallel in a direction perpendicular to the heat transfer tubes, and the heat transfer tubes are held in close contact with the fins by means such as tube expansion. I'm letting you do it. A primary fluid such as cold/hot water or a refrigerant is passed through the heat transfer tube, and a secondary fluid such as air is made to flow between the fins to exchange heat between the two fluids.

Incidentally, in the air flow flowing between the fins, a boundary layer of the flow tends to occur along the fins.
The temperature gradient within this boundary layer is extremely large, which means that the boundary layer portion has a large thermal resistance. Further, the boundary layer develops thickly in the flow direction of the secondary fluid, and therefore the heat transfer coefficient is significantly reduced in the trailing portion of the fin in the flow direction.

As described above, the biggest problem with plate fin fin heat exchangers is the low heat transfer coefficient on the secondary fluid side (fin side), and in order to improve this heat transfer coefficient, the formation of the boundary layer described above, It is effective to prevent this growth, and various proposals have been made regarding the processed shape on the plate fin surface.

These proposals can be broadly divided into two types. One way to do this is by bending the fins or forming uneven parts on the fin surface to expand, contract, and change the direction of the air flow path that occurs when the fins are stacked. There are some types that aim to create a repeating effect (part), and typical examples include wave-shaped fins and trapezoidal fins. Another method is to divide the fin surface in the air direction to improve heat transfer by utilizing the so-called leading edge effect, which cuts the boundary layer into pieces and eliminates the thick portions.

In recent years, the latter type of leading edge effect has been mainly used.
It has become popular because it can obtain a relatively high heat transfer coefficient, and there are, for example, those shown in FIGS. 1 and 2. This is a flat fin substrate 2 having a tube insertion hole 1 through which a heat transfer tube (not shown) is inserted.
A large number of cuts are made perpendicular to the direction of the pipe stage of the tube insertion hole 1, and the strips formed by the cuts are extruded to form a large number of bridge-like cut and raised strips 3 (strips). The structure is such that when the fin substrates 2 are stacked, the groups of cut and raised strips 3 are arranged in a parallel array.

In the heat exchanger configured in this manner, the cut and raised strips 3 divide the boundary layer of the air flow and prevent its formation and development, so that the heat transfer coefficient on the fin side is improved. However, since there are many cut and raised strips 3 on the same plane parallel to the flow direction and these are close to each other, the air flow is formed by the cut and raised strips 3 on the upstream side of the air flow. The cut and raised strips 3 on the wake side are affected by the boundary layer, and the leading edge effect of each cut and raised strip 3 is not fully utilized, and the fins are made up of an aggregate of strips. Because of this, the fins had strength problems.

A second example is disclosed in Japanese Utility Model Application No. 56-58184, as shown in FIGS. 3 and 4. In this case, the cut and raised strips 5 are installed so as to be inclined in the air flow direction with the surface of the fin board 4 as the central axis. In this conventional example, if only one fin is used, the problem similar to the first conventional example described above does not occur. However, in order to use it as a heat exchanger, the fins are stacked at a pitch of several millimeters, and in this case, the main direction of the air flow is bent along the slope of the cut and raised strips 5, as shown in FIG. The positional relationship between the cut and raised strips 5a and the cut and raised strips 5b is on the same plane parallel to the flow direction, and as in the first conventional example, the cut and raised strips 5 are Leading edge effects are underutilized. Further, in this example, if the stacking pitch of the fins is made small, the leading edge effect of the cut and raised strips 5 is almost completely lost, so there is a problem that the stacking pitch is limited.

In order to further improve the above-mentioned problems, there is a proposal disclosed in Japanese Utility Model Publication No. 52-35575 as a third conventional example. In this proposal, as shown in FIGS. 5 and 6, the cut and raised strip 3 shown in the first conventional example is attached to a fin board 6 so that its surface faces the air flow direction shown by the arrow. It is installed at an angle.

In this proposal, in order to fully utilize the leading edge effect, the cut and raised strips 7 are inclined with respect to the fin substrate 6, and other cut and raised strips 7 are arranged in the direction of boundary layer development. Although this method attempts to improve heat transfer by creating turbulence in the airflow, it is difficult to obtain a high heat transfer coefficient because no consideration is given to the mainstream direction of the airflow.
This point will be explained with reference to FIG. 7, which schematically shows the air flow.

In such a proposal, a fin substrate 6 parallel to the air flow as shown by an arrow, and an inclined cut and raised strip 7 are used.
For example, as shown in FIG. 4 of the second conventional example, the inclined cut and raised strips 5 are arranged in an orderly manner, and the main flow flows along the cut and raised strips 5. Instead, flow separation occurs on the back side of the cut and raised strip 7. In the area where this separation occurs, the flow velocity near the back surface of the cut and raised strip 7 becomes almost zero, and the heat transfer in that area becomes extremely small, and on the contrary, the wind pressure loss increases significantly. It's put away. In this way, the aforementioned airflow turbulence is actually separation, but when used in laminar flow areas such as air conditioners, this separation increases wind pressure loss and makes it difficult to improve heat transfer. .

In addition to the above-mentioned conventional example, there is one disclosed in, for example, Japanese Utility Model Application Publication No. 56-144988, which is shown in FIGS. 8 and 9 as a fourth conventional example. Further, similar proposals are disclosed in Japanese Patent Application Laid-open Nos. 55-105194 and 57-131995, etc.

These fourth conventional examples can be regarded as having both ends in the width direction of the cut and raised strip 5 shown as the second conventional example bent in the direction of the ends so as to be parallel to the air flow. It can also be said that the fins are obtained by dividing the waveform fins and trapezoidal fins described above. Note that 8 is a fin board. The purpose of this proposal is to improve the drawbacks of the second conventional example, but the upstream part of each of the adjacent cut and raised strips 9 with respect to the air flow (indicated by the arrow) The boundary stratified velocity field formed by the side cut and raised strips 9a influences the downstream cut and raised strips 9b, and the leading edge effect of this cut and raised strips 9b is not fully utilized. The heat transfer coefficient was also lower than that of the second conventional example, and there were also disadvantages such as an increase in wind pressure loss, an increase in blowing power, and an increase in noise.

The present invention has been made in order to eliminate the conventional drawbacks as described above, and an object thereof is to provide a heat exchanger having a large heat transfer coefficient and a small wind pressure loss.

An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 10, 10 is a fin substrate, that is, a plate fin, and this fin substrate 10 is provided with a plurality of heat exchanger tube insertion holes 10a. Further, reference numeral 11 denotes a cut and raised strip formed between each of the heat exchanger tube insertion holes 10a of the fin board 10. This cut and raised strip 1
1, a large number of notches parallel to the longitudinal direction of the fin board 10 are provided, and these are cut and raised leaving flat portions on the front and back sides of the fin board 10, respectively, and both end edges thereof are made approximately parallel to the surface of the fin board 10. It is bent again in the direction opposite to the cut and raised pieces, and is formed so that its cross section becomes step-like in the air flow direction (indicated by the arrow) as shown in Figure 11, and the adjacent cut and raised strips are Planar fin substrate portions 12 are arranged between the fin substrates 11 so as to be parallel to the air flow.

The fin substrate 10 configured in this way is
As shown in the figure, when stacked, the cut and raised strips 11 are formed in a stepped shape, so the cut and raised strips 11
A plurality of bent wave-shaped channels are formed by the cut and raised strips 11 of adjacent fins stacked in parallel. Also,
Because of the stepped shape, the flow path length of each cut and raised strip 11 is small. Since the airflow passing through this wave-shaped flow path changes direction multiple times, the overall boundary layer becomes thinner due to the effect of repeating the run-up section, and the heat transfer coefficient improves.

Furthermore, since the fin substrate portions 12 are present between the cut and raised strips 11, the distance between the cut and raised strips 11 becomes long, and the boundary stratification that affects the front edge of the cut and raised strips 11 becomes longer. Unlike the fourth conventional example, etc., the leading edge effect of the cut and raised strip 11 on the downstream side of the airflow is fully utilized, and a high heat transfer coefficient can be obtained. Further, as shown in FIG. 11, the cut and raised strips 11 of adjacent fins stacked in parallel do not interfere with each other's leading edge effect due to the influence of the boundary layer, unlike in the prior art example.

Each cut and raised strip 11 and fin board part 1
The leading edge portions of No. 2 are all arranged in parallel rows with respect to the flow direction, and the cut and raised strips 11 and the fin substrate portion 12 on the upper and downstream sides are arranged so that the boundary layer growth direction is not on the same plane. Even if they grow in the same direction, the distance between them is far enough that the boundary layer in the front stream almost disappears and has no influence. In addition, the air flow is smooth because it does not have an unreasonable configuration that would cause separation or turbulence in the flow, which would cause a decrease in heat transfer characteristics or an increase in wind pressure loss.

Incidentally, since the edges of the cut and raised strips 11 are bent again, sufficient strength of the fins can be obtained. Next, FIG. 12 shows a performance comparison between the heat exchanger of the embodiment formed by laminating the fin substrates 10 and a fourth conventional example as a comparative example. In the figure, curve A is an example, and curve B is a comparative example. In this way, the example has an average surface heat transfer coefficient of 25% compared to the comparative example.
However, the wind pressure loss is about 30% smaller (front wind speed around 1 m/s), and it is clear that the example is superior in practical terms.

As described above, the present invention provides a large number of cut and raised strips in a direction perpendicular to the airflow direction on the front and back sides of the fin board in the portion between the heat exchanger tubes of the fin board of a heat exchanger, and the cut and raised strips are provided on the front and back sides of the fin board. The edge of the piece is re-bent in the direction opposite to the cut-and-raised direction, so that its cross section has a step-like shape in the air flow direction, and a fin substrate portion exists between adjacent cut-and-raised pieces in parallel to the air flow. I configured it like this,
The growth direction of the boundary layer is no longer on the same plane, the leading edge effect is fully functional, air flows are guided smoothly, no disturbances such as separation occur, wind pressure loss is small, and the heat transfer coefficient is low. This has the effect of providing a very large heat exchanger.

[Brief explanation of drawings]

Fig. 1 is a plate fin surface view of a first conventional heat exchanger, Fig. 2 is a sectional view taken along the line shown in Fig. 1, Fig. 3 is a plate fin plan view of a second conventional heat exchanger, and Fig. 4 3 is a sectional view taken along the line in FIG. 3, FIG. 5 is a plan view of the plate fin according to the third conventional example, and FIG.
The figure is a sectional view taken along the line shown in FIG. 5, FIG. 7 is a diagram schematically showing the air flow in the same fin, FIG. 8 is a plan view of the plate fin according to the fourth conventional example, and FIG. 10 is a plan view of the plate fins of a heat exchanger according to an embodiment of the present invention, FIG. 11 is a sectional view taken along the line XI-XI of FIG.
FIG. 2 is a characteristic diagram of the example and the comparative example (fourth conventional example). DESCRIPTION OF SYMBOLS 10... Plate fin, 10a... Heat exchanger tube insertion hole, 11... Cut and raised strip, 12... Fin substrate portion. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A plate that is composed of plate fins stacked in multiple rows and heat transfer tubes held through the plate fins, and that exchanges heat between the refrigerant flowing inside the heat transfer tubes and the air passing between the plate fins. In the finch-tube heat exchanger, cut and raised strips in a direction perpendicular to the air flow direction are cut and raised on the front and back sides of the plate fins in the direction of the air flow between the heat transfer tubes adjacent to each other in the longitudinal direction of the plate fins. A large number of the cut and raised strips are provided at intervals, and both end edges of the cut and raised strips are re-bent in the anti-cut and raised direction substantially parallel to the plate fin surface, so that the cross section of the cut and raised pieces is centered on the flat part. 1. A heat exchanger characterized by having a stepped shape in the air flow direction, and a fin base plate portion existing parallel to the air flow between adjacent cut and raised strips.