Finned tube heat exchanger

A finned tube heat exchanger is disclosed in which the structure thereof is simple, and the heat exchanging performance is increased. The heat exchanger has a plurality of fin plates spaced at regular intervals and arranged in parallel with one another, and a plurality of heat exchanger tubes extending through the fin plates and including a refrigerant fluid therein. Each of the fin plates has a plurality of strips projected from the surface thereof, and the strips include first to fifth rows of strips arranged between openings, which are disposed adjacent to one another, in a parallel relationship. The first row of strips is located near a leading edge of the fin plates and formed of two louverlike strips in a form of a trapezoid having a long side located on the upper stream of the air flow. Each of the second to fourth rows of strips is formed of one bridgelike strip in a form of a rectangle. The fifth row of strips is formed of two louverlike strips in a form of a trapezoid having a short side located on the upper stream of the air flow.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a heat exchanger, and more particularly, 
to a finned tube heat exchanger for use in an air conditioner, a 
refrigerator or the like. 
2. Description of the Prior Art 
The typical air conditioning system is a combination of electromechanical 
elements that operate to circulate a refrigerant fluid, e.g., one of the 
Freon compounds, according to a refrigeration cycle. Typically, the Freon 
vapor is compressed by an electrically driven compressor and the 
compressed vapor is cooled by being passed through a heat exchanger, 
commonly known as a condenser. Then the Freon vapor is passed through a 
second heat exchanger where it picks up heat from air within the building. 
The refrigerant is then returned to the compressor to undergo the cycle 
once again. 
Generally, a conventional heat exchanger is formed of a plurality of tubes 
made of a highly thermal conductive metal like copper and numerous thin 
metallic fins attached to the tubes which conduct away heat from the tubes 
to transfer it to air-flow directed between and over the fins. A motor 
driven fan generates air-flow passing through the fins surrounding the 
tubes. To reduce both the cost of the structure and the power requirements 
of the fan directing the air-flow through the heat exchanger, it is 
important to maximize the rate at which the refrigerant fluid flowing 
through the tubes transfers heat to the air flowing past the tubes and 
between the fins, while keeping the air flow pressure drop through the 
heat exchanger low. 
One solution is to increase the total area of the fins by increasing the 
number of fins to obtain increased transfer of heat to the air flowing 
therebetween. This, however, diminishes the size of the passages between 
the fins through which the air flows and will require a more powerful fan 
to provide the pressure difference to force the desired amount of air flow 
through the fins. An alternative is to provide the fins having a 
wafflelike or undulation configuration to increase the area exposed to the 
air flow. Unfortunately, with the latter solution, a problem arises in 
heat transfer boundary layers which very soon diminish the amount of heat 
transfer that can take place between the flowing air and the fin surfaces. 
In recognition of this problem, designers of heat exchangers have focused 
on techniques to inhibit the growth of heat transfer boundary layers while 
increasing flow mixing and turbulence without significantly increasing the 
overall pressure difference required to obtain the desired flow of air 
through the tubes and fin assembly. 
Heat transfer by conduction must first occur between the surface of the 
tubes and the fins, and thereafter, by convection from the fin surfaces to 
the air flowing between the fins. There is also a direct transfer of heat 
from the surface of the tubes by convection to the air flowing past the 
tubes, but this generally amounts to a relatively small fraction of the 
overall heat transfer. 
FIG. 1 shows a conventional finned tube heat exchanger. As shown in FIG. 1, 
a heat exchanger 1 is provided with a plurality of fin plates 2 of 
aluminum spaced at regular intervals and a plurality of heat exchanger 
tubes 3 extending through fin plates 2. Heat exchanger tubes 3 are 
securely held in openings formed in fin plates 2 by any suitable means. 
Each fin plate 2 has a plurality of cut-out strips extending across the 
direction of air flow indicated by arrow A. These strips are for raising 
the heat exchanging performance and project upwardly from the surface of 
fin plates 2. 
FIGS. 2A and 2B show the structure of a conventional fin plate. A plurality 
of louverlike strips 4 parallel with one another extend in a direction 
perpendicular to the direction of air flow indicated by an arrow A. Strips 
4, as shown in FIG. 2B, are formed on the same side of each fin plate 2. 
In the conventional fin plate, there are problems that the manufacture is 
not easy and foreign materials such as dust included in the air flowing 
through strips 4 become easily attached to reduce the heat exchanging 
performance, since each strip 4 has a narrow width. 
Additionally, in the case of strips 4 as shown in FIG. 2B, water drops tend 
to stay between adjacent strips 4, since strips 4 are spaced at narrow 
intervals. Thus, water drops stay on fin plates 2 until they grow into a 
considerable size, so that the heat exchanging performance is lowered and 
the corrosion of the heat exchanger is promoted. 
SUMMARY OF THE INVENTION 
To solve the above problems, an object of the present invention is to 
provide an improved finned tube heat exchanger in which the structure 
thereof is simple and the heat exchanging performance is raised. 
To achieve the object of the present invention, there is provided a heat 
exchanger comprising: 
a plurality of fin plates spaced at regular intervals, arranged in parallel 
with one another and adapted to allow air to flow therebetween, each fin 
plate having openings arranged in a longitudinal direction thereof and a 
leading edge arranged perpendicularly to the air flow; and 
a plurality of heat exchanger tubes extending through the openings of the 
fin plates in a direction perpendicular to the planes in which the fin 
plates lie and being adapted to allow a refrigerant fluid to pass therein. 
Each of the fin plates has a plurality of strips projected from the surface 
of the fin plates and extends perpendicularly to a direction in which air 
is to flow between the fin plates. 
The strips comprise first to fifth rows of strips arranged between the 
openings, which are disposed adjacent to one another, along the 
longitudinal direction of the fin plates in a parallel relationship. 
The first row of strips is located near the leading edge of the fin plates 
and is formed of two louverlike strips in a form of a trapezoid having a 
long side located on the upper stream of the air flow, each of the second 
to fourth rows of strips is formed of one bridgelike strip in a form of a 
rectangle, and the fifth row of strips is formed of two louverlike strips 
in a form of a trapezoid having a short side located on the upper stream 
of the air flow. 
Each of the first and fifth rows of strips has the long side cut to be 
projected upwardly, and each of the second to fourth rows of strips has 
four sides, two opposing sides, facing the air flow, being opened by 
cutting and the other two sides being provided with leg portions for 
connecting the second to fourth rows of strips with the fin plates. 
The first, second, fourth and fifth rows of strips are formed on the same 
side of the fin plates, and the third row of strips is formed on the other 
side of the fin plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, the preferred embodiment of a finned tube heat exchanger 
according to the present invention will be described in detail with 
reference to FIGS. 3 and 4. 
Similar to the conventional finned tube heat exchanger, a heat exchanger of 
the present invention is provided with a plurality of fin plates 10 spaced 
at regular intervals and a plurality of heat exchanger tubes 12 extending 
through fin plates 10. Heat exchanger tubes 12 are securely held in 
openings 14 formed in fin plates 10. Each fin plate 10 has a plurality of 
cut-out strips extending along a direction perpendicular to the direction 
of air flow indicated by arrow A. These strips are for raising the heat 
exchanging performance and project upwardly from the surface of fin plates 
10. 
FIG. 3 shows a fin plate 10 mounted in a finned tube heat exchanger 
according to the preferred embodiment of the present invention. 
Fin plate 10 is made of aluminum and preferably, has a thickness of 0.12 
mm. As shown in FIG. 3, strips 16a-16b, 17, 18, 19 and 20a-20b extend in a 
direction perpendicular to the direction of air flow indicated by arrow A 
and project upwardly from the surface of fin plate 10 to have a height of, 
preferably, 1.0 mm. Strips 16a-16b, 17, 18, 19 and 20a-20b have a width 
of, preferably, 1.0 mm. Strips 17 to 19 are bridgelike, and each of them 
has two leg portions for connecting it with fin plate 10. 
The first row of strips located near a leading edge of fin plate 10 in the 
direction of air flow between two adjacent heat exchanger tubes 14 
consists of two louverlike strips 16a and 16b in a form of a trapezoid 
having a long side located on the upper stream of the air flow. The long 
side of respective strips 16a and 16b is cut, and strips 16a and 16b bend 
at a predetermined angle, preferably 35.degree., with respect to the 
surface of fin plate 10. 
The second row of strips consists of a bridgelike strip 17 in a form of a 
rectangle having four sides and projecting up. Two opposing sides, facing 
the air flow, are opened by cutting and the other two sides are provided 
with leg portions for connecting strip 17 with fin plate 10. The third and 
fourth rows of strips have the same shape as the second row of strips and 
consist of bridgelike strips 18 and 19 in a form of a rectangle having 
four sides and projecting up. Strip 18 is located substantially on a line 
between the centers of adjacent openings formed in fin plate 10. 
The fifth row of strips consists of two louverlike strips 20a and 20b in a 
form of a trapezoid having a short side located on the upper stream of the 
air flow. A long side of respective strips 20a and 20b is cut, and strips 
20a and 20b bend by a predetermined angle, preferably 35.degree., with 
respect to the surface of fin plate 10. 
Accordingly, the first and second rows of strips are disposed in a 
symmetric relationship with the fourth and fifth rows of strips with 
respect to the center line of the third row of strips. 
As shown in FIG. 4, strips 16a-16b, 17, 19 and 20a-20b are formed on the 
same side of fin plate 10, whereas strip 18 is formed on the other side of 
fin plate 10. 
As clearly described in the above, the effects of the heat exchanger 
according to the present invention are as follows: 
(1) Since strips of the heat exchanger according to the present invention 
have a wide width and are spaced at wide intervals in comparison with 
those of the conventional heat exchanger, the manufacture is easy and 
foreign materials such as dust are less likely to become attached to 
maintain the constant heat exchanging performance. 
(2) Since flow mixing is increased by means of projected strips, the growth 
of heat transfer boundary layers is inhibited to increase the heat 
exchanging performance. Thus, the size of the heat exchanger may be 
reduced. 
(3) Since the interval between the strips becomes relatively wide, water 
drops on the fin plates drop readily. Thus, there is no case that the heat 
exchanging performance is lowered, and the corrosion of the heat exchanger 
is prevented. 
While the present invention has been particularly shown and described with 
reference to preferred embodiment thereof, it will be understood by those 
skilled in the art that various changes in form and details may be 
effected therein without departing from the spirit and scope of the 
invention as defined by the appended claims.