U.S. patent application number 12/602329 was filed with the patent office on 2010-07-08 for parallel flow heat exchanger with connectors.
Invention is credited to Satyam Bendapudi, Joseph J. Sangiovanni, Michael F. Taras, Igor B. Vaisman.
Application Number | 20100170664 12/602329 |
Document ID | / |
Family ID | 40075392 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100170664 |
Kind Code |
A1 |
Vaisman; Igor B. ; et
al. |
July 8, 2010 |
PARALLEL FLOW HEAT EXCHANGER WITH CONNECTORS
Abstract
A parallel flow heat exchanger includes a plurality of connector
tubes which fluidly interconnect the individual flat heat exchange
tubes to a refrigerant delivery member such that the refrigerant
flows along the lengths of the connector tubes and then flows in a
direction orthogonal thereto to enter the flat heat exchange tubes
to thereby provide improved refrigerant distribution thereto. The
refrigerant distribution member may be an inlet manifold or an
entrance port or a refrigerant distributor. The connector tubes may
be connected so as to conduct the flow in parallel or in series,
and an orifice may be placed at the entrance end thereof to improve
refrigerant distribution.
Inventors: |
Vaisman; Igor B.; (West
Hartford, CT) ; Taras; Michael F.; (Fayetteville,
NY) ; Sangiovanni; Joseph J.; (West Suffield, CT)
; Bendapudi; Satyam; (Manchester, CT) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Family ID: |
40075392 |
Appl. No.: |
12/602329 |
Filed: |
June 1, 2007 |
PCT Filed: |
June 1, 2007 |
PCT NO: |
PCT/US07/12929 |
371 Date: |
November 30, 2009 |
Current U.S.
Class: |
165/151 ;
165/175 |
Current CPC
Class: |
F28F 1/126 20130101;
F28F 9/02 20130101; F28D 1/05391 20130101; F28D 2021/0071
20130101 |
Class at
Publication: |
165/151 ;
165/175 |
International
Class: |
F28D 1/04 20060101
F28D001/04 |
Claims
1. A parallel flow heat exchanger of the type having a plurality of
flat heat exchange tubes aligned in substantially parallel
relationship, comprising: a plurality of connector tubes, each
connector tube being fluidly connected to at least one of said
plurality of said heat exchange tubes for conducting the flow of
refrigerant therein; and a refrigerant delivery member for
delivering refrigerant to each of said plurality of connector
tubes.
2. A parallel flow heat exchanger as set forth in claim 1 wherein
each of said plurality of connector tubes includes a linear slot
into which a flat heat exchange tube is inserted.
3. A parallel flow heat exchanger as set forth in claim 2 wherein
said flat heat exchange tubes extend inside said respective
connector tubes.
4. A parallel flow heat exchanger as set forth in claim 3 wherein
the protrusion depth of said flat heat exchange tubes into
respective connector tubes is not uniform.
5. A parallel flow heat exchanger as set forth in claim 2 wherein
said flat heat exchange tubes are inserted into said respective
connector tubes such that the respective ends of said flat heat
exchange tubes are substantially flush with the inner walls of said
respective connector tubes.
6. A parallel flow heat exchanger as set forth in claim 1 wherein
said connector tubes are cylindrical in shape and have a diameter
which is larger than the height of said flat heat exchange
tubes.
7. A parallel flow heat exchanger as set forth in claim 1 wherein
said connector tubes have a length which is greater than the width
of said flat heat exchange tubes.
8. A parallel flow heat exchanger as set forth in claim 1 wherein
said refrigerant delivery member comprises an inlet manifold.
9. A parallel flow heat exchanger as set forth in claim 8 wherein
said inlet manifold is connected at one end of said connector
tubes.
10. A parallel flow heat exchanger as set forth in claim 1 wherein
adjacent connector tubes are fluidly interconnected at their ends
such that the refrigerant flows serially through the plurality of
connector tubes.
11. A parallel flow heat exchanger as set forth in claim 1 wherein
said refrigerant delivery member comprises a refrigerant
distributor fluidly connected to the respective connector
tubes.
12. A parallel flow heat exchanger as set forth in claim 1 and
including an orifice disposed in one end of each of the plurality
of connector tubes such that the refrigerant from the refrigeration
delivery member flows first through the orifice and then into the
respective connector tubes.
13. A parallel flow heat exchanger as set forth in claim 1 and
including an outlet manifold fluidly connected at an end of each of
said flat heat exchange tubes.
14. A parallel flow heat exchanger as set forth in claim 1 wherein
at least one dimension of said flat heat exchange tube is not the
same for said plurality of said flat heat exchange tubes.
15. A parallel flow heat exchanger as set forth in claim 14 wherein
said dimension of said heat exchange tube is at least one of the
tube width and the tube height.
16. A method of promoting uniform refrigerant flow into a plurality
of parallel flat heat exchange tubes, comprising the steps of:
providing a plurality of connector tubes, each connector tube being
fluidly connected to at least one of said parallel flat heat
exchanger tubes for conducting the flow of refrigerant therein; and
providing a refrigerant flow delivery apparatus for delivering
refrigerant to each of said of plurality of flat heat exchange
tubes.
17. A method as set forth in claim 16 and including the step of
providing in each of said plurality of connector tubes a linear
slot into which a flat heat exchanger tube is inserted.
18. A method as set forth in claim 17 wherein said flat heat
exchange tubes extend inside said respective connector tubes.
19. A method as set forth in claim 18 and the protrusion depth of
said flat heat exchange tubes into respective connector tubes is
not uniform.
20. A method as set forth in claim 17 wherein said flat heat
exchange tubes are inserted into said respective connector tubes
such that the respective ends of said flat heat exchange tubes are
substantially flush with the inner walls of, said respective
connector tubes
21. A method as set forth in claim 16 wherein said connector tubes
are cylindrical in shape and have a diameter which is larger than
the height of said flat heat exchange tubes.
22. A method as set forth in claim 16 wherein said connector tubes
have a length which is greater than the width of said flat heat
exchange tubes.
23. A method as set forth in claim 16 wherein said refrigerant
delivery member comprises an inlet manifold.
24. A method as set forth in claim 23 and including the step of
connecting said inlet manifold to at one end of said connector
tubes.
25. A method as set forth in claim 16 and including the step of
fluidly interconnecting adjacent connector tubes at their ends such
that the refrigerant flows serially through the plurality of
connector tubes.
26. A method as set forth in claim 16 wherein said refrigerant
delivery member comprises a refrigerant distributor fluidly
connected to the respective connector tubes.
27. A method as set forth in claim 16 and including the step of
providing an orifice in one end of each of the plurality of
connector tubes such that the refrigerant from the refrigeration
delivery member flows first through the orifice and then into the
respective connector tubes.
28. A method as set forth in claim 16 and including the step of
fluidly connecting an outlet manifold to an end of each of said
flat heat exchange tubes.
29. A method as set forth in claim 16 wherein at least one
dimension of said flat heat exchange tube is not the same for said
plurality of said flat heat exchange tubes.
30. A method as set forth in claim 29 wherein said dimension of
said heat exchange tube is at least one of the tube width and the
tube height.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to air conditioning and
refrigeration systems and, more particularly, to parallel flow
evaporators thereof.
[0002] A definition of a so-called parallel flow heat exchanger,
sometimes referred to as a flat tube heat exchanger, is widely used
in the air conditioning and refrigeration industry now and
designates a heat exchanger with a plurality of parallel passages,
among which refrigerant is distributed to flow in an orientation
generally substantially perpendicular to the refrigerant flow
direction in the inlet and outlet manifolds.
[0003] Refrigerant maldistribution in refrigerant system
evaporators is a well-known phenomenon. It causes significant
evaporator and overall system performance degradation over a wide
range of operating conditions. Maldistribution of refrigerant may
occur due to differences in flow impedances within evaporator
channels, non-uniform airflow distribution over external heat
transfer surfaces, improper heat exchanger orientation or poor
manifold and distribution system design. Maldistribution is
particularly pronounced in parallel flow evaporators due to their
specific design with respect to refrigerant routing to each
evaporator circuit. Attempts to eliminate or reduce the effects of
this phenomenon on the performance of parallel flow evaporators
have been made with little or no success. The primary reasons for
such failures have generally been related to complexity and
inefficiency of the proposed technique or prohibitively high cost
of the solution.
[0004] In recent years, parallel flow heat exchangers, and brazed
aluminum heat exchangers in particular, have received much
attention and interest, not just in the automotive field but also
in the heating, ventilation, air conditioning and refrigeration
(HVAC&R) industry. The primary reasons for the employment of
the parallel flow technology are related to its superior
performance, high degree of compactness, good structural rigidity
and enhanced resistance to corrosion. Parallel flow heat exchangers
are now utilized in both condenser and evaporator applications for
multiple products and system designs and configurations. The
evaporator applications, although promising greater benefits and
rewards, are more challenging and problematic. Refrigerant
maldistribution is one of the primary concerns and obstacles for
the implementation of this technology in the evaporator
applications.
[0005] As known, refrigerant maldistribution in parallel flow heat
exchangers occurs because of unequal pressure drop inside the
channels and in the inlet and outlet manifolds, as well as poor
manifold and distribution system design. In the manifolds, the
difference in length of refrigerant paths, phase separation and
gravity are the primary factors responsible for maldistribution.
Inside the heat exchanger channels, variations in the heat transfer
rate, airflow distribution, manufacturing tolerances, and gravity
are the dominant factors. Furthermore, the recent trend of the heat
exchanger performance enhancement promoted miniaturization of its
channels (so-called minichannels and microchannels), which in turn
negatively impacted refrigerant distribution. Since it is extremely
difficult to control all these factors, many of the previous
attempts to manage refrigerant distribution, especially in parallel
flow evaporators, have failed.
[0006] If the two-phase flow enters the inlet manifold at a
relatively high velocity, the liquid phase (droplets of liquid) is
carried by the momentum of the flow further away from the manifold
entrance to the remote portion of the header. Hence, the channels
closest to the manifold entrance receive predominantly the vapor
phase and the channels remote from the manifold entrance receive
mostly the liquid phase. If, on the other hand, the velocity of the
two-phase flow entering the manifold is low, there is not enough
momentum to carry the liquid phase along the header. As a result,
the liquid phase enters the channels closest to the inlet and the
vapor phase proceeds to the most remote ones. Also, the liquid and
vapor phases in the inlet manifold can be separated by the gravity
forces, causing similar maldistribution consequences. In either
case, maldistribution phenomenon quickly surfaces and manifests
itself in evaporator and overall system performance
degradation.
[0007] While traditional round tube heat exchangers have a
potential to feed each tube or circuit individually, flat tubes
have not had such a capability and efforts to improve refrigerant
distribution in such heat exchanger have included, for instance,
the use of inserts and multiple inlet headers, all of which
complicate the design and increase the manufacturing cost. Also,
since large diameter headers are replaced with small diameter
headers and connectors, operating pressures may be substantially
elevated.
SUMMARY OF THE INVENTION
[0008] Briefly, in accordance with one aspect of the invention, the
individual flat heat exchange tubes of an evaporator are
interconnected to a refrigerant delivery member by way of connector
tubes such that the two phase refrigerant flows first from the
refrigerant delivery member into the connector tubes and then into
the individual flat heat exchange tubes to thereby obtain improved
distribution of refrigerant flow.
[0009] In accordance with another aspect of the invention the
connector tubes are connected to a common inlet manifold and extend
generally orthogonally therefrom.
[0010] In accordance with another aspect of the invention, the
connector tubes are cylindrical in shape, and the flat heat
exchange tubes are inserted into longitudinal slots formed in the
connector tubes to form tee joints.
[0011] By yet another aspect of the invention, the connector tubes
have orifices at their one end such that the refrigerant entering
the connector tube is expanded in the process to thereby improve
uniform refrigerant distribution.
[0012] In accordance with another aspect of the invention, each of
the connector tubes is fluidly connected directed to a traditional
refrigerant distributor by way of an inlet tube.
[0013] In the drawings as hereinafter described, preferred and
alternative embodiments are depicted; however, various other
modifications and alternate constructions can be made thereto
without departing from the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic illustration of the present invention
as incorporated into a parallel flow evaporator.
[0015] FIG. 2 is a side view thereof.
[0016] FIG. 3 is an end view thereof.
[0017] FIG. 4 is an enlarged view of a portion thereof.
[0018] FIG. 5 is a sectional view as seen along lines 5-5 of FIG.
4.
[0019] FIGS. 6A and 6B are respective front and top view of a tee
connector.
[0020] FIGS. 7A and 7B are schematic illustrations of an alterative
embodiment thereof.
[0021] FIGS. 8 and 9 are schematic illustrations of another
alternative embodiment thereof.
[0022] FIG. 10 is a schematic illustration of another alternative
embodiment thereof.
[0023] FIG. 11 is a schematic illustration of another alternative
embodiment thereof.
[0024] FIG. 12 is a schematic illustration of another alternative
embodiment thereof.
[0025] FIGS. 13A and 13B are schematic illustrations of another
alternative embodiment thereof.
[0026] FIGS. 14 and 15 are schematic illustrations of another
alterative embodiment thereof.
[0027] FIG. 16 is a schematic illustration of yet another
embodiment thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Referring to FIGS. 1-3, the invention is shown generally at
10 as incorporated into a parallel flow heat exchanger 11 which
includes an inlet manifold 12, a plurality of flat heat exchange
tubes 13 and an outlet manifold 14.
[0029] Each of the flat heat exchange tubes 13 is fluidly connected
to a respective connecting tube as shown at 16, 17, 18 and 19 which
are, in turn, fluidly connected to the inlet manifold 12.
[0030] In operation, two-phase refrigerant flow enters an inlet
port 21 of the inlet manifold 12 and flows toward both ends of the
inner manifold 12. It then flows to the individual connector tubes
16, 17, 18 and 19 and then to the respective flat heat exchange
tubes 13, after which it passes to the outlet manifold 14 and exits
from the outlet port 22.
[0031] Such a design configuration allows for sufficiently small
diameters of the inlet manifold 12 and connecting tubes 16-19,
which are favorable for refrigerant, distribution among the flat
heat exchange tubes 13.
[0032] As is seen in FIGS. 4 and 5, the connector tubes 16, 17 and
18 are cylindrical in a cross-section and have linear slots 23, 24
and 26, respectively formed therein for receiving the respective
flat heat exchange tubes 13 therein. The degree of the penetration
of the flat heat exchange tubes 13 into the respective connector
tubes 16, 17 and 18 is a matter of a design choice and may be
selected to have a significant penetration as shown, or they may
have little or no penetration such that the ends of the heat
exchange tubes 13 are substantially flush with the inner walls of
the connector tubes. Alternatively, the flat heat exchange tubes 13
may have different penetration depths, which may be selected
depending on the position of the inlet port 21 to provide
substantially equal inlet refrigerant flow impedances among the
heat exchange tubes 13. The flat heat exchange tubes 13 are then
fixed in their positions by a process such as welding, furnace
brazing or the like.
[0033] As is seen in FIG. 5, the flat heat exchange tubes 13 may
include a plurality of spaced ports 27 of any suitable cross
section and have an overall height of H and an overall width of W.
One end 28 of each connector tube, e.g. 17, is open and connected
to the inlet manifold 12 as indicated above. The other end 29 can
be sealed as shown in FIG. 5, or it may be interconnected to
another connector tube as will be described hereinafter.
[0034] As should be understood, the relative sizes of the flat heat
exchange tubes 13 and their respective connector tubes 16-19 are
such that the diameter of the connector tubes is sufficient to
allow for the height of the slot 24 to accommodate the height H of
the flat heat exchange tube. Similarly, the length of the connector
tube, i.e. the distance between the two ends 28 and 29, should be
sufficient to accommodate the width W of the heat exchange tube
13.
[0035] FIGS. 4 and 5 show connectors 16, 17, and 18 as tubes with a
cylindrical cross-section. As should be understood, the connectors
may have elliptical, square, rectangular, triangular, or of any
other possible shape. Also, the shape of the cross-section and the
area may be different along the centerline of the connectors.
[0036] FIGS. 4 and 5 imply one connector per one flat heat exchange
tube. As should be understood, a number of adjacent flat heat
exchange tubes may be connected to one connector. In this case,
multiple slots have to be made in the connectors to accommodate
multiple flat heat exchange tubes.
[0037] Further, it may be beneficial to have flat heat exchange
tubes of different sizes. For instance, the height or the width of
the flat heat exchange tube may be varied. The corresponding slot
dimensions of the respective connectors then need to be adjusted
accordingly to accept the flat heat exchange tube of different
sizes. As one example, the parallel flow heat exchanger may include
sections with flat heat exchange tubes of different width to
accommodate substantially different airflow amounts passing over
these sections.
[0038] FIGS. 4 and 5 show connectors 16, 17, and 18 as straight
tubes. Such connectors are called two-end connectors. As should be
understood, the connectors may be fabricated as triple-end
connectors, particularly as a tee connector shown on FIGS. 6A and
6B. The tee connector has a first side end 101, a second side end
102, and a central end 103. As should be also understood, each end
may have a plurality of ends. Such connectors are called
multiple-end connectors. It is obvious that at least one end of the
connectors must be active. All remaining ends, if there are any,
are inactive and sealed.
[0039] FIGS. 6A and 6B show the ends 101, 102, and 103 having their
centerline in one plane and shaped as the letter T. As should be
understood, each end of the two-end, triple-end, and multiple-end
connectors may have any possible shape of their centerlines.
[0040] Although the outlet header 14 has been shown as being
directly connected to the flat tube channels 13, it should be
understood that connector tubes similar to the connector tubes
16-19 may be used to interconnect the flat heat exchange tubes 13
to the outlet manifold 14.
[0041] The embodiment as described above shows the individual
connector tubes 16-19 (which are of the two-end connector type)
being aligned in parallel arrangement and extending orthogonally
from the inlet manifold 12. It also shows them as being connected
such that the flow of refrigerant therein is parallel. It should be
understood that, the connector tubes 16-19 may be interconnected in
serial flow relationship and may be further connected directly to
the inlet port, without the need for an inlet manifold 12. Such an
embodiment is shown in FIGS. 7A and 7B wherein an elbow 28
interconnects the ends of connector tubes 16 and 17, an elbow 32
interconnects the ends of connector tubes 17 and 18, and an elbow
33 interconnects the ends of connector tubes 18 and 19 as
shown.
[0042] The refrigerant flow then enters the inlet port 34, passes
through the connector tube 16, one flat heat exchange tube 13, the
elbow 31, the connector tube 17, another flat heat exchange tube
13, the elbow 32, the connector tube 18, the elbow 33 and the
connector tube 19. Eventually, the refrigerant flows out of the
outlet port 36.
[0043] FIGS. 7A and 7B demonstrate a heat exchanger having tee
connectors 16, 17, 18, and 19 on one end of the heat transfer tubes
13 and tee-connectors 116, 117, 118 and 119 on the other end
thereof. The connectors each have one active end and two inactive
ends. Ultimately, any described connector type is applicable.
[0044] FIGS. 8 and 9 show a heat exchanger having one circuit and
four passes. As should be understood, any number of passes per
circuit is possible, whatever is appropriate for a particular
application. Also, it may be appropriate to have multiple
circuits.
[0045] FIG. 10 shows a heat exchanger having three equal parallel
circuits. Each circuit has its own inlet port 34a, 34b, and 34c and
its own outlet port 36a, 36b, and 36c, respectively. The
refrigerant flow in the FIG. 10 embodiment is generally downward,
as it enters at the top and flows down to the bottom. However, it
is possible to have a reversed generally upward (refrigerant enters
at the bottom and flows up to the top) or a mixed flow arrangement.
The heat exchanger design in FIG. 10 provides two-end connectors,
for the top circuit, 116, 16, 17, 117, 118, 18, 19, and 119, and
each connector has one active end and one inactive end.
[0046] The heat exchanger design in FIG. 11 demonstrates a
three-circuit, four-pass heat exchanger with tee connectors 116,
16, 17, 117, 118, 18, 19, and 119. Each tee connector has one
active end and two inactive ends.
[0047] FIGS. 10 and 11 demonstrate the embodiments having the same
number of passes in each circuit. As should be understood, the
number of passes for each circuit may be different.
[0048] The heat exchangers described above may operate as
condensers and evaporators. Usually, condensers have vapor at the
inlet and liquid at the outlet. Due to the difference in densities
of liquid and vapor phases, the condensers are typically more
efficient if they have more inlets and fewer outlets. FIG. 12 shows
a three-circuit heat exchanger having three inlets 34a, 34b, and
34c; one outlet 36; tee-connectors 116, 16, 17, 117, 118, 18, 119;
and four-end connector 19 with two sealed side ends. FIGS. 13A and
13B show a similar heat exchanger where the four-end connector 19
has one sealed side end.
[0049] The heat exchangers shown on FIGS. 12, 13A and 13B may be
applied as components of a heat pump system and operate as
condensers and evaporators. Evaporators have a two-phase
refrigerant at their inlet and typically vapor at the outlet. Due
to the differences in densities of liquid and vapor phases, the
evaporators may be more efficient if they have fewer inlets and
more outlets. Since the operation as a condenser and the operation
as an evaporator are reversed, with respect to the refrigerant flow
direction, the embodiments in FIGS. 12, 13A and 13B should have an
appropriate number of inlets and outlets for both operational
modes.
[0050] Heat exchangers operating as evaporators should have means
for distribution of the two-phase refrigerant. Another embodiment
which is applicable for evaporators wherein an inlet manifold is
not used is that shown in FIGS. 14 and 15, wherein a traditional
distributor 40 is fluidly connected to the individual connector
tubes 16-19 by way of small diameter distributor tubes 38, 39, 41
and 42 respectively. In this case, an expansion device (not shown)
is provided upstream of the distributor 40 such that the two-phase
refrigerant flow is passed from the distributor 40 to the
individual small diameter distributor tubes 38, 39, 41 and 42. The
two-phase refrigerant flow then passes to the individual connector
tubes 16-19 and is further distributed in the manner described
hereinabove.
[0051] FIGS. 14 and 15 imply that the number of distributor tubes
corresponds to the number of flat heat exchange tubes. It should be
understood that, in general, each circuit may have a number of
passes with the number of distributor tubes corresponding to the
number of circuits. Also, as before with the connector tubes, there
is an option to use one distributor for several circuits.
[0052] A variation of the FIGS. 1-5 embodiment is shown in FIG. 16
wherein, rather than having an open-end connection between the
connector tube 17 and the inlet manifold 12, as shown in FIG. 5,
both ends 28 and 29 of the connector tube 19 are closed, and an
orifice 42 is provided in the end 28 as shown. Thus, as the
refrigerant passes from the inlet manifold 12 through the orifice
42, expansion occurs so as to provide two-phase lower pressure and
temperature refrigerant to the connector tube 19. The flow of
refrigerant from that point is the same as described hereinabove.
It should be understood that the orifice 42 may have a plurality of
orifices arranged in parallel and/or in series.
[0053] FIG. 16 shows that the number of orifices 42 (or their
pluralities) corresponds to the number of flat heat exchange tubes.
It should be understood that, in general, each circuit may have
several passes with the number of the orifices 42 (or their
pluralities) corresponding to the number of circuits. Also, there
is an option to use one orifice 42 (or its plurality) for several
circuits.
[0054] There are two possible designs. One configuration implies
that the manifold 12 operates as a receiver, and the orifices 42
along the manifold 12 operate as expansion devices, providing
isenthalpic expansion from a condenser pressure to the evaporator
pressure. Another arrangement includes an expansion device attached
to the manifold 12. The expansion device provides isenthalpic
expansion from the condenser pressure to a pressure which is higher
than the evaporator pressure and lower than the condenser pressure.
The orifices 42 function as a refrigerant distributor of the
two-phase refrigerant providing single, double, or multiple
expansions from the pressure downstream of the expansion device to
the evaporator pressure.
[0055] In addition to the advantages discussed hereinabove, the
present design features allow for the use of substantially wider
heat exchange tubes, reduced fin density and/or increased fin
height, without comprising performance characteristics and cost of
the heat exchanger.
[0056] It should be understood that the present invention is
intended for use with a heat exchanger that can be oriented
horizontally, vertically, or inclined. That is, although the flat
heat exchange tubes are shown as being horizontally oriented, the
present invention would also be useful with vertically oriented and
inclined flat heat exchange tubes.
[0057] While certain preferred embodiments of the present invention
have been disclosed in detail, it is to be understood that various
modifications in its structure may be adopted without departing
from the spirit of the invention or the scope of the following
claims.
* * * * *