Background of the Invention
[0001] This invention relates generally to air conditioning systems and, more particularly,
to a refrigerant metering apparatus for multicircuit evaporator coils.
[0002] It is a common feature in evaporator coils to provide a plurality of refrigeration
circuits, with refrigerant flowing simultaneously in parallel relationship through
such circuits. The refrigerant is commonly delivered to those parallel circuits from
a liquid line by way of a distributor which receives refrigerant from the liquid line
and distributes it to the individual circuits by way of capillary tubes, with the
capillary tubes performing the refrigerant expansion and metering functions in a well-known
manner.
[0003] Several problems have been recognized with the use of capillary tubes as described
above. For example, where a plurality of capillary tubes are nested together, which
is generally the case, they tend to rub against each other and wear, which, in turn,
can lead to failure and loss of refrigerant charge.
[0004] Another problem with capillary tubes is that it is difficult to obtain consistent
flow characteristics for a given capillary tube length, since the inside diameter
thereof tends to vary, even though they may be of the same nominal diameter. These
inconsistencies, in turn, create inefficiency in the system.
[0005] Another disadvantage with such capillary tubes is that they are not particularly
conducive to automated brazing processes. That is, in the interest of quality and
productivity, it is now becoming common practice to solder return bends and header
assemblies into a coil by way of an autobrazing process. However, because of their
relatively small mass, when compared to header assemblies and return bends, capillary
tubes cannot, as a practical matter, be attached by that process. Accordingly, they
are generally installed by way of a hand brazing process, which is more labor intensive
and less consistent in quality.
[0006] Finally, the use of capillary tubes in a system adds considerable cost thereto, primarily
due to their labor intensive nature, but more significantly, by installation cost.
[0007] In evaporator coils having a single circuit, it has become common practice to provide
a so called "accurater" in a circuit to perform the refrigerant metering function.
Such a device is described in U.S. Patent 3,877,248 issued on April 15, 1975 and assigned
to the assignee of the present invention. Such a use of a single metering device at
a point upstream of the distributor in a multicircuit system has generally not been
done because it is difficult to obtain proper distribution of the vaporized refrigerant
to the multiple refrigeration circuits. Further, it was recognized by the Applicant
that the use of such "accurater" devices in each of the refrigeration circuits would
be prohibitively expensive.
[0008] It is therefore an object of the present invention to provide an improved refrigerant
metering apparatus for a multicircuit evaporator coil.
[0009] Another object of the present invention is the provision in a multicircuit evaporator
coil for a refrigerant metering apparatus which is conducive to automated brazing
techniques.
[0010] Yet, another object of the present invention is the provision in a multicircuit evaporator
coil for a refrigerant metering apparatus which is not susceptible to loss of refrigerant
charge.
[0011] Still, another object of the present invention is the provision in a multicircuit
evaporator coil for a refrigerant metering apparatus which is economical to manufacture
and effective and efficient in use.
[0012] These objects and other features and advantages become more readily apparent upon
reference to the following description when taken in conjunction with the appended
drawings.
Summary of the Invention
[0013] Briefly, in accordance with one aspect of the invention, a multicircuit evaporator
coil is provided with a header to receive liquid refrigerant from the liquid line
and for distributing refrigerant to a plurality of feeder tubes which are in turn
connected to respective refrigerant circuits in the coil. Disposed within each of
the feeder tubes is an expansion device for metering the flow of refrigerant therethrough.
[0014] By another aspect of the invention, each of the expansion devices includes an orifice
having a length-to-diameter, L/D ratio in the range of 3-50, with such structure causing
refrigerant expansion primarily by way of its sharp edged orifice, but also by way
of friction in its bore.
[0015] In accordance with another aspect of the invention, the individual orifices are tailored
in size to match the cooling requirements of the respective circuits, with those requirements,
in turn, being related to the characteristics of the air flow through those respective
circuits.
[0016] By yet another aspect of the invention, the expansion device comprises a cylinder
with a central bore, and said cylinder is secured within said feeder line by a brazing
process or by a mechanical fastening method.
[0017] By still another aspect of the invention, the expansion device comprises a short
contracted portion of the feeder tubes, with such portion being formed by swaging
or the like.
[0018] In the drawings as hereinafter described, a preferred embodiment is depicted; however,
various other modifications and alternate constructions can be made thereto without
departing from the true spirit and scope of the invention.
Brief Description of the Drawings
[0019]
Figure 1 is a side view of a liquid refrigerant header apparatus in accordance with
a preferred embodiment of the present invention.
Figure 2 is a perspective view of the extension device portion thereof.
Figure 3 is an axial, sectional view of the feeder tube and metering device portion
of the invention.
Figure 4 is longitudinal, sectional view thereof.
Figures 5 and 5a are longitudinal and sectional views of an alternative embodiment
of the present invention.
Figures 6 and 6a are longitudinal and axial sectional views of another alternative
embodiment thereof.
Description of the Preferred Embodiment
[0020] Referring now to Figure 1, the invention is shown generally at 10 as applied to a
multicircuit evaporator coil which is not shown but which is represented by the Figure
11 outlined in phantom lines. Typical of such multicircuit evaporator coils is the
one shown in U.S. Patent 4,057,976 issued on November 13, 1977, and assigned to the
assignee of the present invention. In such a coil, refrigerant vapor is introduced
into the individual parallel circuits, and then the circuits function to absorb heat
from the flow of air thereover. While the refrigerant is caused to flow simultaneously
in the various parallel circuits with the volume flow to each being substantially
equal, in order to optimize the performance of the coil, it is desirable that each
of the circuits be tailored to a specific volume flow rate to thereby match the requirements
of the respective circuits, such that the overall performance of the coil is optimized.
Heretofore, this could only be accomplished by the use of capillary tubes of varying
lengths, a solution that was not considered practical. With the present system, this
is accomplished in a manner which is simple and effective.
[0021] Leading to each of the evaporator coil circuits is a distribution line 12 having
a belled end 13 to facilitate the easy and effective attachment to the individual
coils by way of an automated brazing process of the like. The other ends of the distribution
lines 12 are integrally connected to a liquid header 14 by way of brazing or the like.
As will be seen, the distribution lines 12 extend substantially normally from the
common liquid header 14. On the other side of the liquid header 14 is a liquid line
16 which functions to bring liquid refrigerant into the liquid header 14 for distribution
to the individual distribution lines 12.
[0022] As mentioned hereinabove, in order for the evaporator coils to function in the heat
absorbing mode, it is necessary that refrigerant flowing therethrough be in the vaporized
form. This is accomplished in the present invention by way of an expansion device
17 which is installed in each of the distribution lines 12 as will now be described.
[0023] As will be seen in Figure 2, expansion device 17 comprises a cylindrical billet having
a flat face 18 on either end thereof and an axial bore 19 formed therein. The outer
diameter of the cylinder is slightly smaller than the inner diameter of the distributor
line 12 such that it can be securely mounted therein in a manner to be described hereinafter.
The sizing of the axial bore 19 is more critical in that it is this size which determines
the manner and degree to which the refrigerant is expanded prior to entering the individual
evaporator circuits. Generally, the dimensions of the axial bore 19 will be determined
in accordance with the guidelines set forth in the above-mentioned U.S. Patent 3,877,248;
however, it should be recognized that strict adherence to the L/D relationship at
5-12 is not necessary, and that an L/D relationship of 3-50 is possible while remaining
within the scope of the present invention.
[0024] Referring now to Figures 3 and 4, the expansion device 17 is shown in its installed
position within the distributor line 12. Although each of the expansion devices 17
are shown in substantially the same longitudinal position within the distribution
line 12, the position is not critical, and it should be understood that the expansion
device 17 can be placed at almost any location along the length of the distribution
line 12. It is necessary, however, that the expansion device 17 be securely fixed
within the distribution lines 12 and that there be no leakage of refrigerant between
the outer wall of the expansion device 17 and the inner wall of the distribution line
12. This is accomplished by a brazing process wherein the first step is to place a
ring of brazing material 21 within the distribution line 12, with the outer diameter
thereof being substantially equal to the inner diameter of the distribution line 12.
The expansion device 17 is then placed in the distribution line 12 with its one end
thereof abutting the ring of brazing material 21. Another ring of brazing material
22 is then placed in the distribution line 12 and moved against the other end of the
expansion device 17 such that there is a ring on either end thereof. The assembly
is then exposed to heating process which is suitable for brazing. As a result, the
expansion device 17 is securely fastened within the distribution line 12 by way of
brazed rings 21 and 22 around the periphery of the flat faces 18 of the expansion
device 17. In order to optimize the efficiency of the coil as mentioned above, it
is desirable that the diameter of each of the expansion devices be selected to meet
the flow requirements of their respective circuits. Thus, it should be understood
that the bore diameter of the expansion device in the distribution line serving a
coil circuit with a larger volume of air flowing thereover may be greater than that
in the expansion devices installed in the distribution line serving a coil with a
smaller volume of air flowing thereover. In this way, the coil performance can be
optimized with an apparatus which is easy to manufacture and which overcomes the problems
associated with the use of capillary tubes.
[0025] Referring now to Figure 5 and 5a, the refrigerant metering portion of the invention
is shown in an alternative form as an integral part of the distribution line 12. In
this case, rather than installing an insert within the distribution line 12, a portion
23 of the distribution line is reduced in diameter such that its internal flow passage
24 has substantially the same L/D characteristics as the bore of the embodiment described
hereinabove. The reduced diameter portion 23 can be formed by an appropriate crimping
or swaging process.
[0026] Since it is difficult to obtain an abrupt radial contraction to the reduced diameter
portion 23 in the distribution line 12, such that an angled face 26 is likely to result
at the entrance to the internal flow passage 24 rather than a flat face as shown in
the embodiment described hereinabove, the flow characteristics of the metering device
may be affected and therefore require some modifications to the design. For example,
since the resistance of the angled face would be less than that of the flat face,
the bore dimensions would most likely need to be varied accordingly. That is, the
bore for an angled face device would most likely need to be of a smaller diameter
and/or longer in length than that for a flat faced device.
[0027] However, it is intended that the reduced diameter portion 23 functions in substantially
the same way as the orifice 19 in the embodiment described hereinabove and therefore
will have substantially the same L/D parameter relationships.
[0028] Referring now to Figures 6 and 6a, another embodiment of the present invention is
shown wherein the distribution line is formed of male and female portions 26 and 27,
respectively. The diameters of the male 26 and female 27 portions are substantially
the same except that the male portion has an engagement section 28 of a smaller diameter
such that its outer diameter is substantially the same as the inner diameter of the
female portion 27. In this way, the male portion 26 may be installed into the female
portion 27 by way of a force fit, with the two portions being connected in a secure
manner by way of a braze bead 29 at one end of the female section 27 as shown. As
will be seen in Figure 6 and 6a, the male portion engagement section 28 is further
reduced in diameter at 31 to finally form a metering portion 32 with a central passage
33 whose L/D characteristics are substantially the same as those of the orifice described
hereinabove. In this case, since the refrigerant would flow from left to right in
Figure 6, the flow characteristics would be substantially the same as those of the
Figure 5 design (i.e. with an angled face) discussed hereinabove.
[0029] While the present invention has been disclosed with particular reference to a preferred
embodiment, the concepts of this invention are readily adaptable to other embodiments,
and those skilled in the art may vary the structure thereof without departing from
the essential spirit of the present invention. For example, although the present invention
has been described in terms of particular structures in accordance with a preferred
and alternative embodiment, it should be understood that other types of expansion
devices and methods of mounting may be employed while remaining within the scope of
the present invention.
1. In a heat exchanger coil of the type having a plurality of parallel circuits for
receiving a gaseous refrigerant therein for the absorption of heat, an improved refrigerant
metering apparatus comprising:
a header for receiving liquid refrigerant from the supply line for distribution to
said plurality of parallel circuits;
a plurality of distribution lines fluidly interconnecting said header to said parallel
circuits; and
an expansion device disposed in each of said distribution lines for metering the flow
of refrigerant therethrough by way of an orifice.
2. An improved refrigerant metering apparatus of the type as set forth in claim 1
wherein said expansion device comprises a cylinder with a central bore, said cylinder
being secured within said distribution line by a braze material on at least one end
thereof.
3. An improved refrigerant metering apparatus as set forth in claim 1 wherein said
expansion device comprises a portion of said distribution line which is reduced in
diameter.
4. An improved refrigerant metering apparatus as set forth in claim 3 wherein said
reduced diameter portion is integral with the remaining portion of said distribution
line.
5. An improved refrigerant metering apparatus as set forth in claim 3 wherein said
reduced diameter portion is coaxially located within a non-reduced diameter portion
of said distribution line.
6. A refrigerant metering apparatus as set forth in claim 1 wherein said orifice has
a length to diameter ratio in the range of 3-50.
7. An improved refrigerant expansion apparatus of the type interconnecting a liquid
line to a plurality of evaporator coil circuits comprising:
a plurality of feeder tubes with each being fluidly connected to one of said plurality
of evaporator coil circuits;
a header which is attachable to receive a liquid refrigerant from the liquid line
and to deliver the refrigerant to said plurality of feeder tubes; and
an expansion device disposed in each of said feeder tubes for transforming the refrigerant
flow from a liquid to a gaseous state by way of an orifice.
8. An improved refrigerant expansion apparatus as set forth in claim 7 wherein said
expansion device is secured within said feeder tube by way of a braze material on
at least one end thereof.
9. A refrigerant expansion apparatus as set forth in claim 7 wherein said orifice
has a length-to-diameter ratio in the range of 3-50.
10. An improved refrigerant metering apparatus as set forth in claim 7 wherein said
expansion device comprises a reduced diameter portion of said feeder tube.
11. An improved refrigerant expansion apparatus as set forth in claim 10 wherein said
reduced diameter portion is integral with a non-reduced diameter portion of said feeder
tube.
12. An improved refrigerant expansion apparatus as set forth in claim 10 wherein said
reduced diameter portion is coaxially disposed within a non-reduced diameter portion
of said feeder line.