EP2224198A1

EP2224198A1 - Fin and tube type heat exchanger

Info

Publication number: EP2224198A1
Application number: EP08866432A
Authority: EP
Inventors: Akira Yoshikoshi; Yuuzi Okada; Hironobu Kuwayama; Yoshinori Watanabe
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2007-12-28
Filing date: 2008-11-26
Publication date: 2010-09-01
Also published as: EP2224198A4; WO2009084347A1; JP5185611B2; JP2009162406A

Abstract

A fin-and-tube type heat exchanger having a higher performance is provided by further improving the fin-side heat-transfer coefficient, without increasing the air-side circulation resistance (pressure loss). In a fin-and-tube type heat exchanger including multiple plate fins (2) that are arranged in parallel at a predetermined pitch and allow airflow to circulate therebetween, and a heat transfer tube (4) that is tightly inserted into tube holes (3) provided in the plate fins (2) at predetermined row and column pitches and allow fluid to circulate therethrough, the plate fins (2) each have a column-direction peak portion (6) provided in a column direction, between adjacent tube holes (3) in the column direction, and a flat portion (7) provided at an apex of the column-direction peak portion (6).

Description

Technical Field

The present invention relates to heat exchangers that exchange heat between fluid (refrigerant) circulating in a heat transfer tube and airflow (air) circulating between multiple plate fins provided outside the heat transfer tube, and, more specifically, it relates to fin-and-tube type heat exchangers suitable for use as air heat exchangers of air conditioners and refrigerators.

Background Art

In a fin-and-tube type heat exchanger used as an air heat exchanger of an air conditioner, a refrigerator, or the like, various improvements have been made to a fin side to increase its heat transfer area. This has improved a fin-side (air-side) heat-transfer coefficient and has achieved a higher performance. On the other hand, in order to reduce the input to a blower fan for circulating air in the heat exchanger to save energy, it is desirable that fin-side circulation resistance (air-side pressure loss) be reduced to the utmost. However, a reduction in fin-side circulation resistance and an improvement in heat-transfer coefficient are contradictory.
Furthermore, in an air heat exchanger, frost on the fins clogs the air flow path, leading to a possible decrease in heat exchange capacity. Thus, frost prevention needs to be considered in the design of the fins.
In such circumstances, Patent Citation 1 proposes a heat exchanger that has a plurality of peak portions extending in an air circulation direction and corresponding to each row of tube holes provided in plate fins. The heat exchanger also has washers in the form of a plane surface around the tube holes, the lower ends of which have an acute angle such that the apexes thereof conform to ridge lines of the peak portions.
Furthermore, Patent Citation 2 proposes a heat exchanger that has a plurality of triangular or trapezoidal (i.e., having a flat apex) peak portions extending in an air circulation direction and corresponding to each row of tube holes provided in plate fins. One of the peak portions is higher than adjacent peak portions. In addition, peak portions concentric with the tube holes are provided around the tube holes.

Patent Citation 1: Japanese Unexamined Patent Application, Publication No. Hei 8-178573
Patent Citation 2: Japanese Unexamined Patent Application, Publication No. Hei 10-141880

Disclosure of Invention

The heat exchanger disclosed in Patent Citation 1 causes the peak portion to generate turbulence that destroys a thermal boundary layer of air over the entire fin area and causes walls provided along the ridge lines of the washers to guide the airflow behind the heat transfer tube to reduce the dead region. Thus, the heat exchanger can improve the heat-transfer coefficient. In addition, the heat exchanger can discharge water droplets deposited on the surfaces of the fins toward the downstream side as quickly as possible. However, because the structure of the peak portions is monotonic repetition of uniform peaks arranged in the row direction of the tube holes, the improvement of the heat-transfer coefficient is limited, and sufficient advantages cannot be expected. Moreover, although the walls provided along the ridge lines of the washers help reduce the dead region (non-effective heat transfer region), they serve as walls against the airflow in a region having a high airflow rate near the heat transfer tube. This leads to a problem in that circulation resistance increases pressure loss.
Furthermore, the heat exchanger disclosed in Patent Citation 2 can improve the heat transfer performance while reducing the circulation resistance of the airflow, because various heights of the peak portions can meander the airflow flowing between the plate fins. In addition, because the peak portions provided concentrically with and around the tube holes can guide the airflow behind the heat transfer tube, the dead region can be reduced to improve the heat transfer performance. However, because the peak portions extend only in one direction along the row direction of the tube holes, a sufficient improvement of the heat-transfer coefficient resulting from a turbulence promoting effect cannot be expected. In addition, an increase in fin-side circulation resistance around the tube holes (increase in pressure loss) is inevitable, raising a concern about an increase in the input to the blower fan.
As has been described, the conventional fin-and-tube type heat exchangers still have room for improvement with respect to the fin-side heat-transfer coefficient and the circulation resistance (pressure loss).
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fin-and-tube type heat exchanger having a higher performance by further improving the fin-side heat-transfer coefficient, without increasing the air-side circulation resistance (pressure loss).
To solve the above-described problems, the fin-and-tube type heat exchanger of the present invention employs the following solutions.
Namely, a fin-and-tube type heat exchanger of the present invention includes multiple plate fins that are arranged in parallel at a predetermined pitch and allow airflow to circulate therebetween, and a heat transfer tube that is tightly inserted into tube holes provided in the plate fins at predetermined row and column pitches and allow fluid to circulate therethrough. The plate fins each have a column-direction peak portion provided in a column direction between adjacent tube holes in the column direction, and a flat portion provided at an apex of the column-direction peak portion.
According to the present invention, the plate fin has the column-direction peak portion provided in the column direction between the adjacent tube holes in the column direction, and the flat portion provided at the apex of the column-direction peak portion. Therefore, a turbulence promoting effect caused by the column-direction peak portion can improve the heat-transfer coefficient. Furthermore, downward slopes of the column-direction peak portion leading to the tube holes can cause the airflow circulating between the plate fins to smoothly flow behind the heat transfer tube. In addition, the flat portion at the apex of the column-direction peak portion can increase a region having a high local air-side heat-transfer coefficient. Thus, not only can the dead region of the plate fins be reduced to increase the effective heat transfer area and improve the heat-transfer coefficient, but also the region having a high local air-side heat-transfer coefficient can be increased to improve the average heat-transfer coefficient. Accordingly, the heat transfer performance can be improved without increasing the airflow-side circulation resistance (pressure loss). In addition, because this makes it possible to secure sufficient heat exchange capacity while increasing the fin pitch, the number of fins and the costs can be reduced.
Furthermore, a fin-and-tube type heat exchanger of the present invention includes multiple plate fins that are arranged in parallel at a predetermined pitch and allow airflow to circulate therebetween, and a heat transfer tube that is tightly inserted into tube holes provided in the plate fins at predetermined row and column pitches and allow fluid to circulate therethrough. The plate fins each have at least three row-direction peak portions provided in a row direction with respect to each row of the tube holes, a column-direction peak portion provided in a column direction between adjacent tube holes in the column direction, and a flat portion provided at an apex of the column-direction peak portion.
According to the present invention, the plate fin has at least three row-direction peak portions provided in the row direction with respect to each row of the tube holes, the column-direction peak portion provided in the column direction between the adjacent tube holes in the column direction, and the flat portion provided at the apex of the column-direction peak portion. Therefore, a synergistic turbulence promoting effect caused by the row-direction and column-direction peak portions can produce turbulence sufficient to destroy the thermal boundary layer of the airflow circulating between the plate fins. Thus, the heat-transfer coefficient can be further increased. Furthermore, downward slopes of the column-direction peak portion leading to the tube holes can cause the airflow circulating between the plate fins to smoothly flow toward the immediate wake of the heat transfer tube. In addition, the flat portion at the apex of the column-direction peak portion can increase the size of the region having a high local air-side heat-transfer coefficient. Thus, not only can the dead region of the plate fins be reduced to increase the effective heat transfer area and improve the heat-transfer coefficient, but also the region having a high local air-side heat-transfer coefficient can be increased to improve the average heat-transfer coefficient. Accordingly, the heat transfer performance can be improved without increasing the airflow-side circulation resistance (pressure loss). In addition, because this makes it possible to secure sufficient heat exchange capacity while increasing the fin pitch, the number of fins and the costs can be reduced.
Furthermore, in the fin-and-tube type heat exchanger of the present invention, in the above-described fin-and-tube type heat exchanger, both-end peak portions of the row-direction peak portions, formed at both ends in the row direction, may be lower than a central peak portion formed therebetween.
With this structure, because the both-end peak portions formed at both ends, in the row direction, of the row-direction peak portions are lower than the central peak portion formed therebetween, the airflow alternately repeats collision and separation at the row-direction peak portions. In general, the heat-transfer coefficient is high at the collision surfaces and is low at the separation surfaces. Therefore, by increasing the region having a high heat-transfer coefficient, the average heat-transfer coefficient can be improved. At this time, by making the both-end peak portions, which intrinsically have a high heat-transfer coefficient, low, and by making the central peak portion higher than the both-end peak portions, the average local heat-transfer coefficient at the peak portions can be made a constant high value. Accordingly, the heat transfer performance can be improved to a constant high value without increasing the airflow-side circulation resistance (pressure loss). In addition, by making the peak portion at the rear end of the plate fin in the airflow circulation direction low, the airflow is made to flow toward the wake of the heat transfer tube, promoting heat exchange in that region. This recovers the heat-transfer coefficient at an airflow outlet in the wake of the heat transfer tube, which also improves the heat transfer performance. Furthermore, by making the peak portion at the front end of the plate fin in the airflow circulation direction low, clogging of an airflow path due to frost on the fins can be suppressed. Thus, decreases in airflow and heat exchange capacity can be suppressed.
Furthermore, in the fin-and-tube type heat exchanger of the present invention, in any one of the above-described fin-and-tube type heat exchangers, four row-direction peak portions may be formed, and the both-end peak portions formed at both ends in the row direction may be lower than two central peak portions formed therebetween.
With this structure, four row-direction peak portions provided in the row direction are formed, and, the both-end peak portions of the row-direction peak portions, formed at both ends in the row direction, are lower than two central peak portions formed therebetween. Therefore, a turbulence promoting effect caused by the peak portions and a local-heat-transfer-coefficient improving effect caused by an increase in the collision surfaces can be provided. At the same time, the balance of resistance against the airflow in the row direction can be improved. Accordingly, not only does the airflow flow through the central region between the tube holes, but also multiple flows are formed around the heat transfer tube. Thus, the effective heat transfer area can be increased in the immediate wake region of the heat transfer tube, further increasing the heat-transfer-coefficient improving effect.
Furthermore, in the fin-and-tube type heat exchanger of the present invention, in any one of the above-described fin-and-tube type heat exchangers, the column-direction peak portion may be a three-dimensional peak portion projecting both in the row and column directions.
With this structure, because the column-direction peak portion is a three-dimensional peak portion projecting both in the row and column directions, downward slopes, leading to the tube holes, of the peak portion projecting in the three-dimensional directions can cause the airflow circulating between the plate fins to smoothly flow toward the immediate wake of the heat transfer tube. Accordingly, the dead region of the plate fins can be reduced to increase the effective heat transfer area, without increasing the airflow-side circulation resistance (pressure loss). Thus, a heat-transfer-coefficient improving effect corresponding to the increase in the effective heat transfer area can be obtained.
Furthermore, in the fin-and-tube type heat exchanger of the present invention, in any one of the above-described fin-and-tube type heat exchangers, the proportion of the length of the flat portion in the column direction to the column pitch may be one-third or less.
With this structure, because the proportion of the length of the flat portion in the column direction to the column pitch is one-third or less, the region having a high local air-side heat-transfer coefficient can be increased, and a high heat-transfer coefficient can be secured, without increasing the airflow-side circulation resistance (pressure loss). If the length of the flat portion is too large, the pressure loss in the region around the heat transfer tube, where the airflow rate is high, tends to increase. However, by making the proportion of the length to the column pitch one-third or less, a high heat-transfer coefficient can be maintained.
Furthermore, in the fin-and-tube type heat exchanger of the present invention, in any one of the above-described fin-and-tube type heat exchangers, the proportion of the length of the flat portion in the column direction to a pitch between tube sections of the heat transfer tube may be 0.5 or less.
With this structure, because the proportion of the length of the flat portion in the column direction to the pitch between tube sections of the heat transfer tube is 0.5 or less, the region having a high local air-side heat-transfer coefficient can be increased, and a high heat-transfer coefficient can be secured, without increasing the airflow-side circulation resistance (pressure loss). If the length of the flat portion is too large, the pressure loss in the region in the vicinity of the heat transfer tube, where the airflow rate is high, tends to increase. However, by making the proportion of the length to the pitch between tube sections of the heat transfer tube 0.5 or less, a high heat-transfer coefficient can be maintained.
With the present invention, the heat-transfer coefficient can be improved with a turbulence promoting effect caused by the column-direction peak portions. Furthermore, the downward slopes of the column-direction peak portion leading to the tube holes can cause the airflow circulating between the plate fins to smoothly flow toward the immediate wake of the heat transfer tube. Moreover, the flat portion provided at the apex of the column-direction peak portion can increase the size of the region having a high local air-side heat-transfer coefficient. Thus, not only can the dead region of the plate fins be reduced to increase the effective heat transfer area and improve the heat-transfer coefficient, but also the region having a high local air-side heat-transfer coefficient can be increased to improve the average heat-transfer coefficient. Accordingly, the heat transfer performance can be improved without increasing the airflow-side circulation resistance (pressure loss).
In addition, with the present invention, because the synergistic turbulence promoting effect caused by the row-direction and column-direction peak portions can produce turbulence sufficient to destroy the thermal boundary layer of the airflow circulating between the plate fins, the heat-transfer coefficient can be further increased. Furthermore, the downward slopes of the column-direction peak portion leading to the tube holes can cause the airflow circulating between the plate fins to smoothly flow toward the immediate wake of the heat transfer tube. In addition, the flat portion at the apex of the column-direction peak portion can increase the size of the region having a high local air-side heat-transfer coefficient. Thus, not only can the dead region of the plate fins be reduced to increase the effective heat transfer area and improve the heat-transfer coefficient, but also the region having a high local air-side heat-transfer coefficient can be increased to improve the average heat-transfer coefficient. Accordingly, the heat transfer performance can be improved without increasing the airflow-side circulation resistance (pressure loss).

Brief Description of Drawings

[FIG. 1] FIG. 1 is a perspective view of a fin-and-tube type heat exchanger according to an embodiment of the present invention.
[FIG. 2] FIG. 2 is a side view of a plate fin of the fin-and-tube type heat exchanger shown in FIG. 1.
[FIG. 3] FIG. 3 is a perspective view of a segment of the plate fin shown in FIG. 2, divided into four equal segments in the row and column directions from the tube hole.
[FIG. 4] FIG. 4 is a sectional view of the plate fin segment shown in FIG. 3, taken along line A-A in FIG. 2.
[FIG. 5] FIG. 5 is a sectional view of the plate fin segment shown in FIG. 3, taken along line B-B in FIG. 2.
[FIG. 6] FIG. 6 is a graph showing the relationship between the length, F, of a flat portion of a column-direction peak portion of the plate fin shown in FIG. 2 and an air-side heat-transfer coefficient, αa.

Explanation of Reference:

1: fin-and-tube type heat exchanger
2: plate fin
3: tube hole
4: heat transfer tube
5: row-direction peak portion
5A, 5D: both-end peak portion
5B, 5C: central peak portion
6: column-direction peak portion
7: flat portion (plane portion)
F: length of flat portion
m: row pitch
n: column pitch
Pt: pitch between tube sections of tube

Best Mode for Carrying Out the Invention

Referring to FIGS. 1 to 6, an embodiment of the present invention will be described.
FIG. 1 shows a perspective view of a fin-and-tube type heat exchanger 1 according to this embodiment. The fin-and-tube type heat exchanger 1 includes multiple plate fins 2 that are arranged in parallel at a predetermined pitch and allow airflow (air) to circulate therebetween, and a heat transfer tube 4 that is tightly inserted into tube holes 3 provided in the plate fins 2 at predetermined row and column pitches and allow fluid (refrigerant) to circulate therethrough. The heat transfer tube 4 is formed of multiple hairpin tubes 4A that are tightly inserted into the tube holes 3 in the plate fins 2 and U-bends 4B that connect the ends of the adjacent hairpin tubes 4A, and forms at least one path of a refrigerant circulation path at the core of the heat exchanger 1. Typically, a copper tube is used as the heat transfer tube 4.
FIG. 2 shows a side view of the plate fin 2. In general, the plate fin 2 is produced by stamping a thin aluminum plate (having a thickness of, for example, 0.1 mm) into a rectangular shape using a press. As shown in FIG. 2, the plate fin 2 has a rectangular shape having a dimension in the width direction of M and a dimension in the top-bottom direction of N, and, in this embodiment, has one or two rows (in the figure, two rows) of the tube holes 3 arranged at a predetermined row pitch m (for example, 18 mm) in the width direction. The distance of the tube holes 3 on both sides in the width direction from the left and right edges of the plate fin is 1/2 m (m = row pitch). In addition, an arbitrary number of columns of the tube holes 3 are provided within a dimension N1, at a predetermined column pitch n (for example, 21 mm) in the top-bottom direction. Note that the tube holes 3 positioned at the top and bottom of each row are either 3/4 n (n = column pitch) or 1/4 n away from the upper edge and lower edge of the plate fin. Thus, the tube holes 3 in adjacent rows are staggered.
FIG. 3 shows a segment of the plate fin 2 divided into four equal segments in the row and column directions from the tube holes 3, FIG. 4 shows a sectional view of the same taken along line A-A in FIG. 2, and FIG. 5 shows a sectional view of the same taken along line B-B in FIG. 2. The tube hole 3 has a collar 3A formed by burring around the hole. The tube hole 3 is bored such that the diameter thereof, Φ, is slightly larger than the narrowed diameter of the heat transfer tube 4 (for example, 6.35 mm). By expanding the heat transfer tube 4 after insertion, the collar 3A comes into tight contact with the heat transfer tube 4. The collar 3A has a height of, for example, 1.2 mm, and the height of the collar 3A defines the fin pitch, Pf, of the multilayered plate fins 2.
As shown in FIG. 4, the plate fin 2 has at least three row-direction peak portions 5 provided in the row direction (width direction) with respect to each row of the tube holes 3 (four row-direction peak portions 5 are provided in this embodiment, and FIG. 4 shows two of them). In the plurality of row-direction peak portions 5, the height, h2 (for example, 0.7 mm), of central peak portions 5B and 5C provided at the central portion in the row direction is greater than the height, h1 (for example, 0.4 mm), of two both- end peak portions 5A and 5D provided at both ends in the row direction.
Regarding the widths of these row-direction peak portions 5 in the row direction, the length, p, in the width direction from the lowest position to the highest position of the both- end peak portions 5A and 5D is, for example, 1.4 mm, whereas the length, q, in the width direction from the lowest position to the highest position of the central peak portions 5B and 5C is, for example, 2.8 mm. Thus, the row-direction peak portions 5 have substantially the same gradients. In addition, the plate fin 2 has plane portions 5E and 5F having a length in the width direction of r at both widthwise ends. Note that the apex and base of the peak portions 5A to 5D are rounded with an arbitrary curvature.
In addition, as shown in FIG. 5, in the plate fin 2, with respect to the central peak portions 5B and 5C provided in the row direction, two column-direction peak portions 6 are provided in the column direction, between the adjacent tube holes 3 in the column direction. The column-direction peak portions 6 have the same height as the height, h1 (for example, 0.4 mm), of the both- end peak portions 5A and 5D provided in the row direction and have a flat portion (plane portion) 7 at the apex thereof. The length, F, of the flat portion 7 (FIG. 5 shows 1/2 F) is set to be one-third or less of the column pitch n or 0.5 or less of the pitch, Pt, between tube sections of the heat transfer tube 4 (see FIG. 2), i.e., in the range of about 2 mm to 6 mm.
Thus, by providing the column-direction peak portions 6 having the flat portion 7 at the apex between the adjacent tube holes 3 in the column direction, three-dimensional peak portions projecting both of them in the row and column directions (three-dimensional directions) are formed between the adjacent tube holes 3 in the column direction.
In this embodiment, because two central peak portions, 5B and 5C, arranged in the row direction are disposed between the adjacent tube holes 3 in the column direction, two column-direction peak portions 6 are provided corresponding thereto. However, when there is one central peak portion in the row direction (when three row-direction peak portions 5 are provided), one column-direction peak portion 6 is provided corresponding thereto.
The above-described structure of this embodiment provides the following advantages.
As shown by arrow I in FIG. 1, a blower fan (not shown) blows air to the fin-and-tube type heat exchanger 1, in the width direction of the plate fins 2. The air circulating between the multiple plate fins 2 exchanges heat with the refrigerant circulating in the heat transfer tube 4. The air flowing between the plate fins 2 is guided to the plane portion 5E, having a width r and provided at the front end in the width direction, and flows smoothly between the plate fins 2. While circulating between the plate fins 2, the air is guided by the row-direction peak portions 5 and the column-direction peak portions 6, repeats collision and separation at the peak surfaces, generates turbulence sufficient to destroy the thermal boundary layer, and is directed toward the immediate wake region of the heat transfer tube 4 mainly by the effect of the column-direction peak portions 6. Then, the air having flowed between the plate fins 2 is discharged from the rear end thereof.
As shown in FIGS. 2 to 5, in this embodiment, four row-direction peak portions 5 are provided in the row direction of the plate fin 2. The both- end peak portions 5A and 5D are low, and the central peak portions 5B and 5C are higher than the both- end peak portions 5A and 5D. Furthermore, because the column-direction peak portions 6 corresponding to the central peak portions 5B and 5C are provided in the column direction, the effect of the peak portions 5 and 6 can make the average local heat-transfer coefficient at an air inlet a substantially constant high value.
That is, in the plate fin 2 of a type having a plurality of row-direction peak portions 5 arranged in the row direction, the heat-transfer coefficient is high at the collision surfaces and is low at the separation surfaces. Therefore, by increasing a region having a high heat-transfer coefficient in the collision surfaces, the average heat-transfer coefficient can be improved. Furthermore, the peak portions 5 can increase the heat transfer area, which also improves the heat transfer performance. If only an improvement of the fin-side heat-transfer coefficient is intended, the heights of all the row-direction peak portions 5 may be increased. However, this increases the fin-side circulation resistance (increases the air-side pressure loss) and increases the input to the blower fan, which is undesirable from the standpoint of energy saving. Accordingly, as described above, by making the both- end peak portions 5A and 5D at the end surfaces of the fin low and by making the central peak portions 5B and 5C higher than the both- end peak portions 5A and 5D, the average local heat-transfer coefficient can be made a high value without increasing the circulation resistance.
In addition, because the peak portion 5D at the rear end of the plate fin 2 is low, the heat-transfer coefficient at the airflow outlet behind the heat transfer tube 4 fitted to the tube holes 3 can be recovered. This may be because the low peak portion 5D at the rear end of the fin forms an airflow flowing in the wake region of the heat transfer tube 4, promoting heat exchange between the fins and the airflow. Furthermore, in the row-direction peak portions 5 of the plate fin 2, because the length, q, in the width direction, of the central peak portions 5B and 5C provided in the row direction is larger than (twice the length of) the length, p, in the width direction, of the both- end peak portions 5A and 5D, the gradients of all these peak portions 5A to 5D can be made substantially the same. This makes it possible to increase the height of the row-direction peak portions 5 to further increase the local heat-transfer coefficient at the row-direction peak portions 5, while suppressing an increase in circulation resistance against the airflow (airflow-side pressure loss) and reducing the input to the blower fan.
Another reason to make the peak portion 5A at the front end of the of the plate fin 2 low is to suppress frost on the fins. For example, in general, in the case where the fin-and-tube type heat exchanger 1 is used as an outdoor heat exchanger of an air conditioner, frost tends to accumulate at the front edges of the plate fins 2 during heating, where the heat-transfer coefficient is high. If the front-end peak portion 5A of the plate fin 2 is high, the space between the fins is narrow. As a result, frost clogs the air flow path, or an increase in flow path resistance due to the frost decreases the quantity of air, accelerating a decrease in heat exchange capacity and making the frost more likely to accumulate. By making the peak portion 5A at the front end of the plate fins 2 low, frosting on the fins is suppressed. Thus, these problems can be solved.
On the other hand, the plate fin 2 has column-direction peak portions 6 provided in the column direction, between the adjacent tube holes 3 in the column direction. Thus, the heat-transfer coefficient can also be improved by the turbulence promoting effect caused by the column-direction peak portions 6. Furthermore, because the column-direction peak portions 6 can form downward slopes (inclined surfaces) leading to the tube holes 3, between the adjacent tube holes 3 in the column direction, the airflow circulating between the plate fins 2, along the slopes, can be made to flow behind the heat transfer tube 4 fitted to the tube holes 3. This can reduce the dead region (non-effective heat transfer region) behind the heat transfer tube 4 (the tube holes 3) of the plate fins 2 to increase the effective heat transfer area of the fins, which improves the heat-transfer coefficient corresponding thereto.
In particular, four row-direction peak portions 5 are provided, and the column-direction peak portions 6 corresponding to two central peak portions 5B and 5C, which are large in height, are provided. This provides a structure in which three-dimensional peak portions projecting both in the row and column directions (three-dimensional directions) are provided between the adjacent tube holes 3 in the column direction, improving the balance of resistance against the airflow. Therefore, not only does the airflow flow in the central region between the adjacent heat transfer tube 4 in the column direction of the plate fin 2, but also sufficient airflow is formed around the heat transfer tube 4. Accordingly, it is possible to further increase the effective heat transfer area and further improve the heat-transfer coefficient in the immediate wake region of the heat transfer tube 4.
In addition, in this embodiment, the flat portion (plane portion) 7 is formed at the apex of the column-direction peak portion 6. The flat portion 7 can increase the size of the region having a high local air-side heat-transfer coefficient, which can improve the average heat-transfer coefficient. Furthermore, the length, F, of the flat portion 7 in the column direction is set to be one-third or less of the column pitch n, or 0.5 or less of the pitch, Pt, between tube sections of the heat transfer tube 4, i.e., in the range of about 2 mm to 6 mm. Thus, as shown in FIG. 6, the air-side heat-transfer coefficient, αa, can be further increased by several percent compared with a case where the flat length, F, is 0. Note that, if the length, F, of the flat portion 7 is larger than the above-mentioned range, the pressure loss in the region around the heat transfer tube 4, where the airflow rate is high, tends to increase. Therefore, in order to improve the heat transfer performance while suppressing the air-side circulation resistance (pressure loss), the above-mentioned range is appropriate.
As has been described above, in this embodiment, because the synergistic effect of the row-direction peak portions 5 and the column-direction peak portions 6 provided in the plate fins 2 can produce turbulence sufficient to destroy the thermal boundary layer of the airflow, the heat-transfer coefficient can be improved. Furthermore, by forming four row-direction peak portions 5, of which the peak portions 5A and 5D at both ends are low and the two central peak portions 5B and 5C formed therebetween are high, the size of the airflow collision surfaces, having a high heat-transfer coefficient, is increased. Because this can make the average local heat-transfer coefficient at the row-direction peak portions 5 a constant high value, the heat transfer performance can be improved to a constant high value.
In addition, because the peak portion 5D at the rear end of the row-direction peak portions 5 is made low so that the peak portion 5D forms an airflow flowing in the wake region of the heat transfer tube 4, it is possible to promote heat exchange between the fins and the airflow in that region. Thus, the heat-transfer coefficient in the wake region of the heat transfer tube 4 can be improved. Moreover, because the peak portion 5A at the front end of the row-direction peak portions 5 is made low so as to provide a large space between the fins at the front ends of the fins having a high heat-transfer coefficient, frosting on the fins can be suppressed.
In addition, the both- end peak portions 5A and 5D of the row-direction peak portions 5, which are low in height, have a small width, and the two central peak portions 5B and 5C formed therebetween, which are large in height, have a large width such that their gradients are substantially the same. This makes it possible to increase the height of the row-direction peak portions 5 to make the average local heat-transfer coefficient at the row-direction peak portions 5 a constant high value, while suppressing an increase in the circulation resistance (airflow-side pressure loss) against the airflow and reducing the input to the blower fan. Furthermore, because the plane portions 5E and 5F are provided at both widthwise ends of the plate fin 2 to guide the inflow of the air to reduce the inflow resistance (airflow-side pressure loss), it is possible to reduce the input to the blower fan and save energy.
In addition, the provision of the downward inclined surfaces, leading to the tube holes 3, of the three-dimensional peak portions projecting both in the row and column directions and provided between the adjacent tube holes 3 in the column direction allows the airflow circulating between the plate fins 2 to flow toward the immediate wake of the heat transfer tube 4. Because this can reduce the dead region of the plate fins 2 and can increase the effective heat transfer area, the heat transfer performance can be improved corresponding thereto. In particular, two column-direction peak portions 6 corresponding to the two central peak portions 5B and 5C of the row-direction peak portions 5, which are large in height, are provided to form the peak portions projecting in the three-dimensional directions. This improves the balance of resistance against the airflow and allows sufficient airflow to be formed not only in the central region between the adjacent heat transfer tube 4 in the column direction, but also around the heat transfer tube 4. This further increases the effective heat transfer area in the immediate wake region of the heat transfer tube 4, making further improvement of the heat-transfer coefficient possible.
In addition, by forming the flat portion (plane portion) 7 at the apex of the column-direction peak portion 6, the region having a high local air-side heat-transfer coefficient is increased. This can improve the average heat-transfer coefficient. At this time, the length, F, of the flat portion 7 in the column direction is set to be one-third or less of the column pitch n, or 0.4 or less of the pitch, Pt, between tube sections of the heat transfer tube 4, i.e., in the range of about 2 mm to 6 mm. Thus, the air-side heat-transfer coefficient, αa, can be further increased by several percent compared with a case where the flat length, F, is 0, while suppressing the air-side circulation resistance (pressure loss). Thus, the heat transfer performance can be improved. Furthermore, an improvement of the heat-transfer coefficient and an enhancement of the heat transfer performance achieved by improving the structure of the fins make it possible to secure sufficient heat exchange capacity while increasing the fin pitch. This can reduce the number of plate fins 2 and can reduce the material cost accompanied by a reduction in diameter of the heat transfer tube 4 (for example, a tube diameter Φ of 6.35 mm). Accordingly, the costs can be reduced.
Note that the present invention is not limited to the invention according to the above-described embodiment, and it can be arbitrarily modified within a scope not departing from the spirit thereof. For example, although the dimensions of the parts of the plate fins are specified in the above-described embodiment, they are merely examples, and the present invention is not limited thereto. The numbers of rows and columns of the tube holes 3 can of course be arbitrarily modified corresponding to the capacity of the heat exchanger.

Claims

A fin-and-tube type heat exchanger comprising:
multiple plate fins that are arranged in parallel at a predetermined pitch and allow airflow to circulate therebetween; and

a heat transfer tube that is tightly inserted into tube holes provided in the plate fins at predetermined row and column pitches and allow fluid to circulate therethrough,

wherein the plate fins each have a column-direction peak portion provided in a column direction between adjacent tube holes in the column direction, and a flat portion provided at an apex of the column-direction peak portion.
A fin-and-tube type heat exchanger comprising:
multiple plate fins that are arranged in parallel at a predetermined pitch and allow airflow to circulate therebetween; and

a heat transfer tube that is tightly inserted into tube holes provided in the plate fins at predetermined row and column pitches and allow fluid to circulate therethrough,

wherein the plate fins each have at least three row-direction peak portions provided in a row direction with respect to each row of the tube holes, a column-direction peak portion provided in a column direction between adjacent tube holes in the column direction, and a flat portion provided at an apex of the column-direction peak portion.
The fin-and-tube type heat exchanger according to claim 2,
wherein both-end peak portions of the row-direction peak portions, formed at both ends in the row direction, are lower than a central peak portion formed therebetween.
The fin-and-tube type heat exchanger according to claim 2 or 3,
wherein four row-direction peak portions are formed, and the both-end peak portions formed at both ends in the row direction are lower than two central peak portions formed therebetween.
The fin-and-tube type heat exchanger according to any one of claims 1 to 4,
wherein the column-direction peak portion is a three-dimensional peak portion projecting both in the row and column directions.
The fin-and-tube type heat exchanger according to any one of claims 1 to 5,
wherein the proportion of the length of the flat portion in the column direction to the column pitch is one-third or less.
The fin-and-tube type heat exchanger according to any one of claims 1 to 5,
wherein the proportion of the length of the flat portion in the column direction to a pitch between tube sections of the heat transfer tube is 0.5 or less.