U.S. patent number 3,796,258 [Application Number 05/293,892] was granted by the patent office on 1974-03-12 for high capacity finned tube heat exchanger.
This patent grant is currently assigned to Dunham-Bush, Inc.. Invention is credited to Anthony M. Castello, Ravi K. Malhotra.
United States Patent |
3,796,258 |
Malhotra , et al. |
March 12, 1974 |
HIGH CAPACITY FINNED TUBE HEAT EXCHANGER
Abstract
The fins of a finned tube heat exchanger extend in spaced
parallel fashion across a plurality of fluid carrying tubes. The
fins are bent into shallow angulated convolutions in the direction
of flow of an external fluid passing between the fins and around
the tubes. The fins carry a plurality of aligned openings within
each convolution wall to increase heat transfer capacity with
little increase in the fluid pressure drop of the external fluid
flowing through the exchanger.
Inventors: |
Malhotra; Ravi K.
(Harrisonburg, VA), Castello; Anthony M. (Harrisonburg,
VA) |
Assignee: |
Dunham-Bush, Inc.
(Harrisonburg, VA)
|
Family
ID: |
23131012 |
Appl.
No.: |
05/293,892 |
Filed: |
October 2, 1972 |
Current U.S.
Class: |
165/151;
165/DIG.504; 29/890.047 |
Current CPC
Class: |
F28F
1/325 (20130101); Y10T 29/4938 (20150115); Y10S
165/504 (20130101) |
Current International
Class: |
F28F
1/32 (20060101); F28d 007/00 () |
Field of
Search: |
;165/151-153 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Streule, Jr.; Theophil W.
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn &
Macpeak
Claims
What is claimed is:
1. In a finned tube heat exchanger wherein a plurality of fluid
carrying tubes extend through a plurality of closely spaced,
generally parallel fins formed of metal sheet stock and wherein
heat transfer is facilitated by passing a second exterior fluid
across the surfaces of said fins and generally at right angles to
the axis of the tubes passing through the fins, the improvement
wherein:
said fins are convoluted in the direction of flow of said external
fluid and carry a plurality of holes therein to permit said second
exterior fluid to pass through the convolutions from side to side
for improved heat exchange efficiency,
said fins are accordion pleated to define shallow, angulated
convolutions, said heat exchange fluid carrying tubes are arranged
in multiple, laterally spaced rows with the tubes of adjacent rows
being longitudinally offset with respect to each other, and
said fluid passage holes for respective rows are aligned with the
tubes within said rows and lie intermediate of the tubes in terms
of the direction of flow of the external fluid.
2. The finned tube heat exchanger as claimed in claim 1, wherein
said heat exchange fluid carrying tubes are arranged in multiple
laterally spaced rows with the tubes of adjacent rows being
longitudinally offset with respect to each other and wherein said
external fluid passage holes for respective rows are aligned with
the tubes within said rows and lie intermediate of the same in
terms of the direction of flow of the external fluid.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to finned tube heat exchangers, and more
particularly to a fin construction and configuration for increasing
the heat transfer efficiency of the heat exchanger.
2. Description of the Prior Art
Finned tube heat exchangers consist essentially of a plurality of
closely spaced sheet metal fins with a plurality of refrigerant
carrying tubes passing through the fins generally at right angles
thereto. A high degree of heat transfer occurs between the exterior
fluid such as air which generally is in forced flow across the
surface of the fins and at right angles to the axis of the tubes
and the fluid within the tubes by way of the fins. Such heat
exchangers employ various tube arrangements and fin shapes in an
attempt to achieve maximum heat transfer. Basically, the fin
surfaces are designed to break the boundary layer formed on the
surface of the fin and to create turbulence in the air and thus
increase heat transfer between the refrigerant within the tubes and
the exterior fluid passing over the fin surfaces. Unfortunately,
the heat transfer capacity of the heat exchanger increases at the
expense in air pressure drop to the heat exchanger. One attempt at
providing an increased heat transfer capacity by modification of
the fin structure is set forth in U.S. Pat. No. 3,631,922, wherein
openings are provided within the fin by striking a plurality of
tangs outwardly from the fins from one side thereof and towards the
adjacent fin, the tangs projecting through the air flow and
creating a desired turbulence to air flow through the heat
exchanger and at right angles to the multiple refrigerant carrying
tubes. The presence of the tangs constitutes a lint trap and
accelerates clogging of the coil. Further, the presence of the
tangs actually inhibit passage of the air through the holes
resulting from the struck away tangs and their presence, while
substantially increasing the turbulence of the air stream passing
therethrough for increased heat transfer capacity, materially
increase the pressure drop of the air stream across the heat
exchanger.
SUMMARY OF THE INVENTION
The improved fin structure and configuration of the fin and tube
heat exchanger of the present invention has for its object a
provision of a fin surface which has higher outside film
coefficient with little increase in air pressure drop through the
heat exchanger by diffusing and mixing the air as it flows through
the heat exchanger. The fin is constructed such that the air
flowing through the exchanger changes direction to remove more heat
from the fin surface. The length of the flow path for the air
flowing through the heat exchanger is increased to increase heat
transfer between the fluids. It permits higher face velocities
without condensate blow off problems where the heat exchanger is
used within a dehumidifying application, while further providing a
fin which is lighter in weight which acts to reduce the weight of
the heat exchanger as a whole.
These objects are met in a preferred embodiment of a fin and tube
heat exchanger in which a plurality of fluid carrying tubes pass
through aligned holes within a plurality of closely spaced,
generally parallel fins formed of conventional thin metal sheet
stock. Specifically, the fins are bent into convoluted form in the
flow direction of the external fluid and carry a plurality of
openings or holes within respective convolution walls which are in
flow aligned to permit the air flow to change direction and to pass
alternately along its flow path in contact with respective opposite
surfaces of the same fin as it moves across and through the
convolutions. Preferably, the fins are bent or folded in accordion
pleated fashion in terms of shallow, angulated convolutions with
each convolution wall carrying a plurality of holes elongated in a
direction at right angles to the flow path of the air stream. Where
the fluid carrying tubes are arranged in rows in offset fashion,
the air passage holes within the fins lie intermediate of the tubes
for each row to create air turbulence in line with the tube
row.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary elevational view of a finned tube heat
exchanger utilizing the improved fin construction of the present
invention.
FIG. 2 is a plan view of a portion of one of the fins of the heat
exchanger of FIG. 1.
FIG. 3 is an enlarged, sectional view of a portion of the fin
illustrated in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, there is illustrated in FIG. 1 a
vertically oriented heat exchanger 10 such as that forming an
evaporator coil or a condenser coil for an air conditioning system
humidifier, or the like, in which case, a plurality of elongated
refrigerant carrying tubes 12 are connected in serpentine fashion
by means of return bend tube portions 14 into a vertically oriented
assembly and held in place by frame members at the top and bottom
such as frame member 16 and constituting a relatively rigid
structural array. Only a fragmentary portion of the heat exchanger
is illustrated, the heat exchanger 10 being coupled by conventional
means to a source of refrigerant which passes through the
refrigerant carrying tubes in series or parallel flow paths to
effect heat exchange with a secondary external fluid which in this
case is air, passing at right angles to the axis of the tubes 12
and to the plane of the paper illustrating the same, FIG. 1. In
this respect, the frame member 16 may be provided with annular
flanges 18 through which the individual tubes pass and in the
illustrated portion of the heat exchanger, the return bends 14 may
be integral with or joined to straight tubes 12 approximately at
the location of the flared flanges 18.
The invention is particularly directed to the employment of a
plurality of elongated, thin sheet metal fins 20 which extend
longitudinally from one end of the heat exchanger 10 to the other
in close, vertically spaced fashion to define a vertical array and
through which the refrigerant carrying tubes 12 project to effect
high efficiency heat transfer between the refrigerant within tubes
12 and forced air passing at right angles thereto, through the
spaces between the fins 20. Each fin is formed of a generally
rectangular strip of a high heat conducting metal by being stamped,
for instance, from aluminum sheet stock or the like. Important to
the completion of a low impedance heat conducting path between the
refrigerant carrying tubes, which also may be formed of aluminum,
and the fins 20, is the provision of circular holes 22 for each
tube, the holes 22 being created by punching material from the
desired location to permit forming, as illustrated in FIG. 2, a
number of rows of tubes as A, B, C and D to carry the fins, the
holes 22 of the rows of openings being alternately offset both
laterally and longitudinally in the illustrated embodiment to
achieve maximum heat transfer between the air flowing in the
direction of arrows 24, FIG. 2, at right angles to the axis of the
holes, and the refrigerant or other confined fluid within the tubes
12. Further, in order to effect the conductivity between the fins
and the tubes, which are received thereby, in the illustrated
embodiment, preferably each tube receiving hole 22, is formed by an
annular integral ring 26 formed during stamping, including a flange
portion 28 at bend point 30 with the central tubular portion 32
receiving its tube 12 and forming a low impedance, heat conducting
path between the ring 26 and the fin carrying the same. These
tubular portions and rings are formed by extruding the base sheet
metal (fin stock). Intimate contact is then provided between the
fin and the tube by expanding the tube about twenty thousandths
inch (0.020 inch). The free edge 36 of the tubular portion 32 of
ring 26 is flared outwardly to permit the fins to readily receive
the tubes and be stacked on the tubes during assembly of the heat
exchanger.
An important aspect of the present invention resides in the
provision of accordion pleats or angulated convolutions to the
individual fins 20 by bending the fins along fold lines 38, at
right angles to the air flow path, indicated by arrow 24, to effect
shallow angulated convolutions in which the adjacent convolution
walls 40 extend obliquely in opposite directions as best seen in
FIG. 3. Further, as illustrated in FIG. 3, convolution walls 40 are
provided with air passage openings or holes 42 intermediate of the
fold lines which are generally in flow direction alignment and
permit the air to pass from one side of the fin to the other at
each convolution for increasing turbulence and heat transfer
without materially increasing the pressure drop for the air stream
passing through the heat exchanger 10. As illustrated in FIG. 2,
the air passage openings or holes 42 within the fins are elongated
in a direction at right angles to the air flow path and are
illustrated as being flattened in configuration, although of course
the size and configuration as well as the number of holes for each
convolution wall may readily vary depending upon the design
parameters for the particular heat exchanger application. Further,
as illustrated in FIG. 2, the air passage openings or holes 42 form
a series intermediate of tube openings 22 for a given tube row at
all of the four tube location rows A, B, C, or D. As such, air flow
impinging against a heat exchange refrigerant carrying tube 20
passes about the tube on each side thereof and prior to impacting
the tube downstream therefrom and in line therewith, passes through
the four aligned air passage holes or openings 42 and thrice
changes position relative to the surfaces of the fins to break the
boundary layer formed on the surface of the fin and create
turbulence in the air passing through the heat exchanger. This
causes the air to diffuse and mix for maximum heat transfer with
the refrigerant carried within the individual tubes 20. While the
fin structure preferably carries the rings 36 surrounding the tubes
20 and effects excellent heat transfer between the tubes and the
fins 20, such members may be eliminated, in which case the edge of
the fin defining the opening 20 in each case directly contacts the
tube walls to achieve a high thermal conductivity joint
therebetween.
From the above construction, it is noted that a substantial portion
of the fin surface between adjacent tubes 20 carry the punched
holes 42 to cause the air flowing through the exchanger to follow a
long route relative to the surface of the fins over which the air
passes and thereby increase the heat transfer therebetween. Where
the heat exchanger of the present invention is employed in a
dehumidifying function, the water removed from the air has a
tendency to adhere to the fin surfaces and may accumulate within
the punched holes 42. The punched holes 42 prevent the water blow
out and thus the air passing therethrough may be driven at high
face velocities without condensate blow off problems. Where the
heat exchanger is employed in an environment in which weight is a
material factor, since a substantial portion of the fin material is
punched out to form the holes 42, simultaneously with bending the
fins about fold lines 38 in accordion pleated fashion, the net
result is the creation of a heat exchanger whose overall weight is
reduced and permitting it to be used under high heat exchange
efficiency in vehicle environments and other environments where
weight is an important factor.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *