JPS59167695A - Heat exchanger - Google Patents

Abstract

PURPOSE:To increase the heat transmitting rate of a heat exchanger by sufficiently utilizing the front edge effect by not directing the growing direction of boundary layers to the same plane, by constituting a fin base board in such a manner that the edges of many raised pieces provided to the surface and the back side of a fin base board are bent in twice to the opposite side of the raised direction, and the sections of the raised pieces form steps to the direction of air flow, while the fin base board is positioned in parallel with the air flow between neighboring raised pieces. CONSTITUTION:The raised pieces 11 are formed by raising a number of raisings in parallel with the longitudinal direction of a fin base board 10 on the surface and the back side of a fin base board 10, and by bending both edges in twice on the opposite side of the raised direction, nearly in parallel with the flat fin base board 10, so that their sections are made stepwise to the direction of air flow as shown by arrows in the figure. A flat fin base plate 12 is arranged between neighboring raised pieces 11 so as to be in parallel with the air flow, respectively. Accordingly a raised piece 11 forms a waved air flow path having a plurality of bent parts together with a neighboring raised piece 11 which is arranged in parallel with it. The air flow, passing through these wave-formed flow paths, repeats turning of directions several times. Then the boundary layers are made thin as a whole by the repeated effect of approach run, as a result, the heat transmitting rate of a heat exchanger can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plate-fin tube type heat exchanger used in air conditioning, refrigeration equipment, etc.

Generally, a plate-fin tube type heat exchanger has a plurality of heat exchanger tubes passing through a plurality of plate fins arranged in parallel in a direction perpendicular to the heat exchanger tubes, and holding the heat exchanger tubes in close contact with the fins by means such as tube expansion. There is. 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 passed between the fins to exchange heat between the two fluids.

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

In this way, the biggest problem with plate-fin tube heat exchangers is the low heat transfer coefficient on the secondary fluid side (fin side), and in order to improve this heat transfer coefficient, it is necessary to form a boundary layer as described above. It is effective to prevent the development of fins, 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 of doing 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 fins are stacked. There are some types of fins that aim to create a repeating effect (part), and typical examples include wave-shaped fins and trapezoidal fins. Another method is to improve heat transfer by dividing the fin surface in the air flow direction, thereby making use of the so-called leading edge effect, which cuts the boundary layer into small pieces and eliminates thick portions.

In recent years, devices that mainly utilize the latter leading edge effect have become popular because they can obtain relatively high heat transfer coefficients, such as those shown in FIGS. 1 and 2, for example. This is a flat fin board 2 having a tube insertion hole 1 through which a heat exchanger tube (not shown) is passed, and a large number of cuts perpendicular to the direction of the tube stages of the tube insertion hole 1. Extrude the pieces to create a number of bridge-like cut and raised strips 3 (stripe 1).
This structure is such that when the fin substrates 2 are stacked, the groups of cut and raised strips 30 are arranged in parallel rows.

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 they are close to each other, the boundary layer formed by the cut and raised strips 3 on the upstream side of the air flow The cut and raised strips 3 on the downstream side are affected by this, and the leading edge effect of each cut and raised strip 3 is not fully utilized, and the fin is composed of an aggregate of strips. Therefore, the fin had a strength problem.

A second example is disclosed in Japanese Utility Model Application No. 56-58'184, as shown in FIGS. 3 and 4. In this case, each of the cut and raised strips 5 is installed so as to be inclined in the airflow direction with the 4th surface of the fin board as the middle JIL% axis. This conventional example does not have the same problem as the first conventional example described above if only one fin is used. 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 Figure 4. Since the positional relationship between the cut and raised strips 5a and 5b is on the same plane parallel to the flow direction, similarly to the first conventional example, the cut and raised strips 5 The leading edge effect of is 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 strips 3 shown in the first conventional example are attached to a fin board 6 such that the surface thereof faces in one direction of the air flow 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 this proposal, the fin substrates 6 and 9 parallel to the air flow as shown by the arrows and the slanted cut and raised strips 7 are alternately mixed, for example, as shown in FIG. 4 of the second conventional example. As shown in , the inclined cut and raised strips 5 are arranged in an orderly manner and the main flow does not flow along the cut and raised strips 5, but rather the cut and raised strips 7
Separation of flow occurs on the back side. 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. be. In this way, the turbulence in the ρ airflow mentioned above is actually separation, but when used in laminar flow areas such as air conditioners, this separation increases wind pressure loss, but it is hoped that heat transfer will improve. It is difficult.

In addition to the above-mentioned conventional example, there is one disclosed in, for example, Japanese Utility Model Application Laid-Open No. 56-144988, which is shown in FIGS. 8 and 9 as a fourth conventional example. A similar proposal is published in Japanese Unexamined Patent Application Publication No. 1983. There are those disclosed in No. 105194, No. 57-131995, and the like.

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 aforementioned waveform fins and trapezoidal fins. 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) Side cut and raised strip 9a
The boundary stratified velocity field formed by this affects the cut and raised strip 9b on the downstream side, and the leading edge effect of this cut and raised strip 9b is not fully utilized, and the heat transfer coefficient is also lower than that of the second conventional example. On the contrary, it is lower than that, and wind pressure loss increases and the blowing power increases.
There were drawbacks such as 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 the fin board, i.e. Goo? - This fin board 10 has a plurality of heat exchanger tube insertion holes 10.
A is provided. 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 11 is formed by providing a large number of cuts parallel to the longitudinal direction of the fin board 10, and
The front and back sides of the fin board 10 are cut and raised, and both edges thereof are re-bent in the direction opposite to the cut and raised approximately parallel to the surface of the fin board 10, and as shown in FIG. It is formed to have a step-like cross section, and flat fin substrate parts 12 are arranged between adjacent cut and raised strips 11 so as to be parallel to the air flow. .

When the fin substrates 10 configured in this way are stacked as shown in FIG. The cut and raised strips 11 of the fins form a plurality of bent wave-shaped channels. Since the air flow passing through this wave-shaped flow path changes direction multiple times, the overall boundary layer becomes thinner due to the steering effect of 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. Fourth
Unlike conventional examples, etc., the leading edge effect of the cut and raised strip on the downstream side of the airflow is fully utilized and a high thermal conductivity 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.

The front edges of each of the cut and raised strips 11 and the fin substrate portion 12 are all arranged in a parallel row 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 in a boundary layer. The growth directions are arranged so that they are not on the same plane, and even if the growth directions are the same, they are far apart and the boundary layer in the front stream almost disappears, so that there is no influence. It's getting summer. In addition, the air flow is smooth because the structure is not forced to cause separation or turbulence in the flow, which is a cause of deterioration of heat transfer characteristics and increase of wind pressure loss. Since the fins are re-bent, sufficient strength can be obtained from the fins.

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. As described above, the average surface heat transfer coefficient of the example is more than 25% higher than the comparative example, and the wind pressure loss is about 30 coefficient lower (front wind speed around 1 m/s), so the example is practically superior. That is clear.

As described above, the present invention provides a large number of cut and raised strips in a direction perpendicular to the air flow 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 also provides the cut and raised strips on the front and back sides of the fin board. The end edge of the piece is bent again in the direction opposite to the cut and raised strips, so that the cross section is step-like in the air flow direction, and a fin board part exists between adjacent cut and raised strips in parallel to the air flow. Since the growth direction of the boundary layer is not on the same plane9, the leading edge effect functions sufficiently, and the air flow is guided smoothly, preventing disturbances such as separation, and reducing wind pressure loss. This has the effect of providing a heat exchanger with a small coefficient of heat transfer and a very large heat transfer coefficient.

[Brief explanation of the drawing]

Fig. 1 is a plate fin side view of the first conventional heat exchanger, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 is a plate fin plan view of the second conventional heat exchanger. Figure 4 is the same figure 3 I.
5 is a plan view of the plate fin according to the third conventional example, FIG. 6 is a sectional view taken along the Vl-Vl line in FIG. 5, and FIG. 7 schematically shows the air flow in the fin. The figure shown in FIG. 8 is a plan view of a plate fin according to the fourth conventional example,
FIG. 9 is a sectional view taken along line IX-TX in FIG. 8, and FIG. 10 is a plan view of 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 in FIG. 10, and FIG. 12 is a characteristic diagram of the embodiment and a comparative example (fourth conventional example). DESCRIPTION OF SYMBOLS 10... Plate fin, 10a... Heat exchanger tube insertion hole, 11... Cut and raised strip, 12... Fin board part.・
Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Makoto Kuzuno - Figure 1 Figure 2 Figure 3 Figure 4 - Saichi 1- 1"th Figure 5 Figure 8 Figure 9 Figure 10 Figure 11 Figure 11 1? Figure 12 Wind number m/S

Claims (1)

[Claims] Plate fins are composed of plate fins stacked in multiple rows and heat transfer tubes held through the plate fins, and exchange heat between the refrigerant flowing inside the heat transfer tubes and the air passing between the plate fins. In the tube type heat exchanger, cut and raised strips in a direction perpendicular to the air flow direction are cut and raised in the air flow direction on the front and back of the plate fins between the heat transfer tubes adjacent to each other in the longitudinal direction of the plate fins. A large number of 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 approximately parallel to the plate fin surface, so that the cross section of the cut and raised pieces is stepped in the air flow direction. What is claimed is: 1. A heat exchanger characterized in that the heat exchanger has a fin base portion parallel to the airflow between adjacent cut and raised strips.