U.S. patent application number 10/534447 was filed with the patent office on 2007-04-05 for refrigeration system with bypass subcooling and component size de-optimization.
Invention is credited to Cheolho Bai.
Application Number | 20070074536 10/534447 |
Document ID | / |
Family ID | 32313105 |
Filed Date | 2007-04-05 |
United States Patent
Application |
20070074536 |
Kind Code |
A1 |
Bai; Cheolho |
April 5, 2007 |
Refrigeration system with bypass subcooling and component size
de-optimization
Abstract
A refrigeration system having a primary refrigerant path
including a compressor, a condenser, a primary expansion device,
and an evaporator connected together to form a closed loop system
with a refrigerant circulating therein; and a bypass path coupled
to an outlet of the condenser. The bypass path includes a secondary
expansion device; and a heat exchanger thermally coupled to the
primary refrigerant path between the condenser outlet and the
primary expansion device inlet to remove heat from the refrigerant
discharged from the condenser. The condenser is downsized such that
lacks the heat transfer capacity to provide some or all of the
required subcooling as provided according to conventional practice,
and the heat exchanger provides some or all the required subcooling
according to the capacity of the condenser. A pressure differential
accommodating device operative to mix two vapors at different
pressures may also be provided to connect the outlets of the
evaporator and the heat exchanger to an inlet of the compressor. A
method of operating a refrigeration system with a downsized
condenser and an a bypass path including a heat exchanger to
provide subcooling is also described.
Inventors: |
Bai; Cheolho; (Taegu,
KR) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
US
|
Family ID: |
32313105 |
Appl. No.: |
10/534447 |
Filed: |
November 12, 2003 |
PCT Filed: |
November 12, 2003 |
PCT NO: |
PCT/US03/36424 |
371 Date: |
March 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60426073 |
Nov 11, 2002 |
|
|
|
Current U.S.
Class: |
62/513 ;
62/5 |
Current CPC
Class: |
F25B 5/02 20130101; F25B
2500/01 20130101; F25B 2400/23 20130101; F25B 2400/13 20130101;
F25B 2700/21151 20130101; F25B 2341/0011 20130101; F25B 40/00
20130101; F25B 43/00 20130101; F25B 9/006 20130101; F25B 6/04
20130101; F25B 41/00 20130101 |
Class at
Publication: |
062/513 ;
062/005 |
International
Class: |
F25B 41/00 20060101
F25B041/00; F25B 9/02 20060101 F25B009/02 |
Claims
1-80. (canceled)
81. A refrigeration system comprising: a primary refrigerant path
including a compressor, a condenser, a primary expansion device,
and an evaporator connected together to form a closed loop system
with a refrigerant circulating therein; and a bypass path attached
between the outlet of the condenser and the inlet of the
compressor, the bypass path including: a secondary expansion
device; and a heat exchanger thermally coupled to the primary
refrigerant path between the condenser outlet and the primary
expansion device inlet which provides subcooling of the refrigerant
discharged from the condenser, the heat transfer capacity of the
condenser being insufficient to provide the required
subcooling.
82. A refrigeration system according to claim 81, wherein the heat
exchanger and the condenser are so constructed that the required
subcooling is provided substantially entirely by the heat
exchanger.
83. A refrigeration system according to claim 81, wherein the heat
exchanger and the condenser are so constructed that a majority of
the subcooling of the refrigerant is provided by the heat
exchanger.
84. A refrigeration system according to claim 81, wherein: the
vapor pressure of the refrigerant exiting the heat exchanger is
higher than that of the refrigerant exiting the evaporator, and the
system further includes a pressure differential accommodating
device connecting the outlets of the evaporator and the heat
exchanger to an inlet of the compressor.
85. A refrigeration system according to claim 84, further including
a valve in the bypass path, the valve being operable to divert
about 5% to about 15% of the refrigerant to the bypass path when
maximum cooling capacity is required due to high thermal load, and
to divert up to about 60% of the refrigerant to the bypass path
according to reductions in thermal load.
86. A refrigeration system according to claim 84, wherein the
pressure differential accommodating device is a vacuum generating
device having inlets connected to outlets of the evaporator and the
heat exchanger and an outlet connected to the inlet of the
compressor, or a pressure reducing device connected to the outlet
of the heat exchanger, and a mixing device connecting the pressure
reducing device and the outlet of the evaporator to the inlet of
the compressor.
87. A refrigeration system according to claim 86, wherein the
vacuum generating device is a vortex tube or a venturi tube, and
the pressure reducing device is a capillary tube, a restricted
orifice, a valve, or a porous plug.
88. A refrigeration system according to claim 81, wherein the
bypass path is connected to the outlet of the condenser downstream
of the heat exchanger.
89. A refrigeration system according to claim 81, wherein: the
evaporator is comprised of a plurality of parallel-connected
evaporator elements located in respective portions of the space
being cooled by the system; and the system further includes a
plurality of on-off valves respectively connecting the primary
expansion device to the evaporator elements, the on-off valves
being operable to idle respective evaporator elements by shutting
of the flow of refrigerant thereto when cooling of a particular
location is not required at given time; and an adjustable valve in
the bypass path, the adjustable valve being operative to control
the flow of refrigerant in the bypass path such that refrigerant
mass flow which is not required in the primary refrigerant path
when a particular evaporator element is idle flows to the bypass
path.
90. A refrigeration system according to claim 89, wherein the
compressor is configured and controlled to run continuously when
the system is in operation, independent of changes in thermal
load.
91. A refrigeration system according to claim 89, wherein the
condenser is downsized from that conventionally required for an
evaporator selected to achieve a desired cooling capacity.
92. A refrigeration system according to claim 91, wherein the
evaporator is oversized from that conventionally required to
increase cooling capacity without increasing compressor work
93. A refrigeration system according to claim 89, further including
a pressure differential accommodating device having a low pressure
inlet connected in common to outlets of the evaporator elements, a
high pressure input connected to the bypass path, and an outlet
connected to an inlet of the compressor.
94. A refrigeration system according to claim 89, wherein the valve
in the bypass path is operable to divert about 5% to about 15% of
the refrigerant to the bypass path when maximum cooling capacity is
required due to operation of all the evaporator elements, and to
divert up to about 60% of the refrigerant to the bypass path
according to reductions in thermal load due to deactivation of
particular evaporator elements.
95. A refrigeration system according to claim 81, further including
a valve in the bypass path, the valve being operable to divert
about 5% to about 15% of the refrigerant to the bypass path when
maximum cooling capacity is required due to high thermal load, and
to divert up to about 60% of the refrigerant to the bypass path
according to reductions in thermal load.
96. A refrigeration system according to claim 81, wherein the
compressor is configured and controlled to run continuously when
the system is in operation, independent of changes in thermal
load.
97. A refrigeration system according to claim 81, wherein the
expansion device in the primary refrigeration path is
thermostatically operated in response to a temperature sensor
thermally coupled to the inlet of the compressor to maintain a
constant superheat in the evaporator.
98. A refrigeration system according to claim 81, wherein the
condenser is downsized from that conventionally required for an
evaporator selected to achieve a desired cooling capacity.
99. A refrigeration system according to claim 98, wherein the
compressor is configured and controlled to run continuously when
the system is in operation, independent of changes in thermal
load.
100. A refrigeration system according to claim 98, wherein the
evaporator is oversized from that conventionally required to
increase cooling capacity without increasing compressor work
101. A refrigeration system according to claim 81, wherein the heat
exchanger is connected to provide counter-flow of refrigerant in
the heat exchanger and the thermally coupled refrigerant in the
primary refrigerant path.
102. A refrigeration system according to claim 81, wherein the
refrigerant circulated in the system consists of a single
component.
103. A refrigeration system according to claim 81, wherein the
refrigerant circulated in the system is a mixed-refrigerant
comprising a plurality of components selected to provide a desired
combination of thermal and flammability characteristics.
104. A refrigeration system according to claim 103, further
including a liquid-vapor separator operable to selectively divert
at least one component of the mixed refrigerant to the bypass path
to increase the percentage of liquid in the refrigerant as it
enters the evaporator, thereby improving evaporator efficiency.
105. A refrigeration system according to claim 104, wherein the
diverted refrigerant component has a higher condensation
temperature and boiling temperature than the remainder of the
refrigerant components.
106. A method of increasing the efficiency of a refrigeration
system comprising the steps of: passing refrigerant through a
primary refrigerant path which includes a compressor, a condenser,
a primary expansion device, and an evaporator connected together to
form a closed loop system wherein the heat transfer capacity of the
condenser is insufficient to provide required subcooling for the
circulating refrigerant; diverting a portion of the refrigerant
exiting the condenser into a secondary refrigerant path which
includes a secondary expansion device and a heat exchanger
thermally coupled to the primary refrigerant path between the
condenser outlet and the primary expansion device inlet; and
passing the diverted refrigerant through the heat exchanger to
provide subcooling for refrigerant flowing in the primary
refrigerant path.
107. A method according to claim 106, further including the steps
of: passing the refrigerant exiting the heat exchanger and the
refrigerant exiting the evaporator through a pressure differential
accommodating device that mixes two vapors at different pressures;
and delivering the refrigerant exiting the pressure differential
accommodating device to an inlet of the compressor.
108. A method according to claim 106, wherein the refrigerant is
diverted to the bypass path at a location downstream of the heat
exchanger.
109. A method according to claim 106, wherein substantially all of
the subcooling required is provided by heat transfer in the heat
exchanger.
110. A method according to claim 106, wherein a majority of the
subcooling required is provided by heat transfer in the heat
exchanger.
111. A method according to claim 106, wherein between about 5% and
about 15% of the liquid refrigerant outflow from the condenser is
diverted to the bypass path.
112. A method according to claim 106, further including the step
of: controlling the quantity of refrigerant outflow from the
condenser which is diverted to the bypass path to adjust the
cooling capacity of the system according to the thermal load.
113. A method according to claim 112, further including the step of
running the compressor continuously independent of the required
cooling capacity when the system is in operation.
114. A method according to claim 106, wherein: the primary
refrigeration path includes a plurality of evaporators located in
respective locations to be separately cooled; and the method
further includes the steps of: diverting a predetermined minimum
quantity of refrigerant to the bypass path when maximum cooling
capacity is required to cool all of the locations; and diverting
increasing quantities of refrigerant to the bypass path as thermal
load decreases.
115. A method according to claim 114, further including the step of
running the compressor continuously independent of the required
cooling capacity when the system is in operation.
116. A method according to claim 114, wherein the condenser is
downsized from that conventionally required for an evaporator
selected to achieve a desired cooling capacity.
117. A method according to claim 116, wherein the evaporator is
oversized from that conventionally required to increase cooling
capacity without increasing compressor work.
118. A method according to claim 114, further including the steps
of: idling particular evaporators in locations which do not require
cooling at a given time by blocking the flow of refrigerant
thereto; diverting the refrigerant normally delivered to a
particular evaporator to the bypass path what that evaporator is
idle.
119. A method according to claim 106, wherein the refrigerant
circulated in the system consists of a single component.
120. A method according to claim 106, wherein the refrigerant
circulated in the system is a mixed-refrigerant comprising a
plurality of components selected to provide a desired combination
of thermal and flammability characteristics.
121. A method according to claim 120, further including the step of
selectively diverting at least one component of the mixed
refrigerant to the bypass path to increase the percentage of liquid
in the refrigerant as it enters the evaporator, thereby improving
evaporator efficiency.
122. A method according to claim 121, wherein the diverted
refrigerant has a high condensation temperature and a high boiling
temperature relative to the remainder of the refrigerant.
123. A method according to claim 106, further including the steps
of: sensing the temperature of the refrigerant at the inlet of the
compressor; and controlling the mass flow rate of refrigerant
through the expansion device in the primary refrigeration path
according to the sensed temperature to maintain the superheat of
the refrigerant exiting the evaporator at a constant level.
124. A method according to claim 106, wherein the condenser is
downsized from that conventionally required for an evaporator
selected to achieve a desired cooling capacity.
125. A method according to claim 124, wherein the evaporator is
oversized from that conventionally required to increase cooling
capacity without increasing compressor work.
126. A method according to claim 106, further including the step of
running the compressor continuously independent of the required
cooling capacity when the system is in operation.
Description
CROSS-REFERENCE TO PRIOR APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 60/426,073, filed Nov. 11, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a high efficiency
refrigeration system and more specifically, to a refrigeration
system utilizing a bypass path for subcooling, in combination with
selection of the sizes of the condenser, compressor and evaporator,
to achieve increased overall system efficiency.
[0004] 2. Relevant Art
[0005] FIG. 1 is a block diagram of a conventional refrigeration
system, generally denoted at 10. The system includes a compressor
12, a condenser 14, an expansion device 16 and an evaporator 18.
These components are connected together, typically by copper tubing
such as indicated at 19 to form a closed loop system through which
a refrigerant such as R-12, R-22, R-134a, R-407c, R-410a, ammonia,
carbon dioxide or natural gas is cycled.
[0006] The main steps in the refrigeration cycle are compression of
the refrigerant by compressor 12, heat extraction from the
refrigerant to the environment by condenser 14, throttling of the
refrigerant in the expansion device 16, and heat absorption by the
refrigerant from the space being cooled in evaporator 18. This
process, sometimes referred to as a vapor-compression refrigeration
cycle, is used in air-conditioning systems, which cool and
dehumidify air in residential, commercial and industrial
environments, in a moving vehicle (e.g., automobile, airplane,
train, etc.), in refrigeration equipment, in heat pumps and in
other applications.
[0007] In the condenser 14, heat is removed from the refrigerant so
that the superheated refrigerant vapor from the compressor 12
becomes liquid refrigerant by the time it reaches the exit of the
condenser. In FIG. 1, the condenser 14 is divided into two parts,
14a and 14b. In the first portion, 14a, superheated refrigerant
vapor becomes saturated vapor, a process called desuperheating, and
the saturated vapor undergoes phase change from vapor to liquid
refrigerant. In the second portion, 14b, the liquid refrigerant is
further cooled below the saturation temperature at the condenser
pressure, a process known as subcooling.
[0008] FIG. 2 shows the temperature profiles inside the condenser.
During the desuperheating process (from point A to point B), there
is a rapid temperature drop. During the vapor-to-liquid phase
change (from point B to point C), the temperature of the
refrigerant remains constant. At the end of the condensation
process (point C), 100 percent liquid refrigerant is present. The
temperature of the liquid refrigerant is further decreased during
the subcooling process (point C to point D) in the second portion
of the condenser 14b. In the subcooling process, the temperature
difference between the refrigerant and cooling medium (e.g., air or
water) decreases such that subcooling becomes an increasingly
inefficient heat transfer process. Hence, for a given cooling
capacity, one needs to have a relatively large-sized condenser to
counteract the inefficient heat transfer which results from the
small temperature difference.
[0009] As is known, the required cooling capacity dictates the size
of the evaporator, and this dictates the compressor capacity. While
a larger compressor gives better cooling performance, cost and
energy consumption must also be taken into account. Moreover, since
the heat removal capacity of the condenser must equal the heat
input due to the operation of the evaporator and the compressor,
increasing the size of the compressor for a given cooling capacity
means the condenser must be larger and more costly.
[0010] Thus, a compromise is necessary, and according to
conventional practice, in a a so-called optimized or balanced
system, there is an accepted relationship between system cooling
capacity (evaporator size) and compressor capacity. For example, in
a conventional 1 ton system, the evaporator is designed to remove
12 KBTU/Hr. and the matched compressor size is 4 KBTU/Hr. The
condenser must therefore be sized to handle 16 KBTU/Hr.
[0011] Much effort has been directed find ways to improve the
efficiency, size and cost of refrigeration systems. Because of the
inefficiency of heat transfer during subcooling, this aspect of the
refrigeration cycle has received considerable attention, but up to
now, no suitably cost effective technique has been found to reduce
the size of the subcooling section in the condenser or to eliminate
it altogether.
[0012] For example, it has been proposed to divert a portion of the
high-pressure refrigerant exiting the condenser to expand through a
secondary expansion device into a bypass circuit, and to employ the
resulting cold refrigerant in a heat exchanger to subcool the main
stream of the high-pressure refrigerant. The pressure at the bypass
circuit is maintained to be the same as the pressure at the
evaporator. Such an arrangement is shown in Kita et al. U.S. Pat.
No. 6,164,086. FIG. 3 shows a schematic diagram of a system of this
kind.
[0013] Kita et al. also propose an arrangement in which all the
refrigerant is diverted to the bypass path, and when the
refrigerant flows through the bypass, the main expansion valve in
the main refrigeration path is shut off. The purpose of diverting
the refrigerant to the bypass line is to produce ice in a heat
storage container so that the ice can be used for subcooling the
refrigerant. (Kita et al. use the term "supercooling" for the
subcooling process.) To meet the normal subcooling operational
requirements in Kita et al., the bypass line is shut off, and the
main expansion valve is opened. Then, all of the refrigerant flows
through the container filled with ice, and as the ice removes heat
from the refrigerant, the refrigerant is subcooled. The subcooled
refrigerant then flows to through the main expansion device and
eventually to the evaporator.
[0014] Kita et al., however, appear to suggest that their bypass
methods are beneficial only for mixed (nonazetropic) refrigerant
systems such as R-32/134a or R-407c due to the temperature gradient
in the dual-phase region. For a single refrigerant (azeotripic)
system such as R-22 or R-134a, the bypass method does not produce a
temperature reduction at the inlet of the evaporator.
[0015] Kim and Domanski, in Intracycle Evaporative Cooling in a
Vapor Compression Cycle (NISTIR 5873), also investigated the first
of the bypass methods described above, which they referred to as
their "Method 2". In addition, they also considered another method,
referred to by them as "Method 1", which is similar to a
conventional liquid-line/suction line heat exchange where
superheated vapor is used to subcool the high-pressure liquid, but
which uses a liquid-vapor mixture from the evaporator instead of
superheated vapor. This is shown schematically in FIG. 4
herein.
[0016] In neither instance, did they find beneficial results for a
single refrigerant system, but with their first method, they did
find some improvement for nonazetropic refrigerants. For their
second method (the first method of the Kita et al. patent),
however, they found no improvement with mixed or single refrigerant
systems.
[0017] Moreover, the reported improvements with mixed refrigerants
are small, and in any case, are of limited current practical
interest because mixed refrigerants are not in commercial use, and
can not be used in current systems because they require higher
pressure capability than systems using single refrigerants.
[0018] An approach similar to the second method taught by Kita et
al. appears to have been used in very large systems (e.g., 2,000
tons) but is of questionable use in small and intermediate size
systems (less than about 1,000 tons).
[0019] Cho and Bai, in U.S. Pat. No. 6,449,964, demonstrate a
method and use of mixed refrigerant systems with higher bypass
circuit pressure. They have also shown the use of a pressure
differential accommodating device to mix the two vapors at two
different pressures.
[0020] Therefore, a need clearly still exists for a cost-effective
way to achieve the subcooling without having a large subcooling
section in the condenser, especially using current single
refrigerants, and in systems having both small and large cooling
capacities. The present invention seeks to meet this need.
SUMMARY OF THE INVENTION
[0021] According to the present invention, it has been found that
significant improvements can be obtained using a bypass circuit for
subcooling in a system in which the conventional balanced or
optimized relationship between the evaporator, compressor and
condenser is abandoned, and in which a condenser is used which
would not provide sufficient heat removal capacity according to
normal practice. In other words, in an optimized system, the
required capacity determines the evaporator size which then
dictates the compressor size, and the heat input of these together
dictate the condenser size. In contrast, according to the present
invention, after the evaporator size has been determined, the
condenser size is "de-optimized" by reducing or eliminating the
subcooling capacity, and providing the lost subcooling through use
of a heat exchanger driven by refrigerant diverted into a bypass
circuit, e.g., from the main expansion valve. This allows use of
smaller compressor, with consequent improved EER and system cost.
The smaller condenser also reduces space requirements for the
system.
[0022] This surprising ability to achieve improved performance
beyond that thought possible using bypass technology comes about
because in a balanced system, the condenser is already large
enough, and the system cannot utilize the additional subcooling.
However, in a refrigeration system like the present invention where
the condenser is substantially smaller than the optimum-sized
condenser, the bypass method is able to show significant benefit as
the increased subcooling makes the small condenser behave like an
optimum-sized condenser or an oversized condenser. This increases
both the cooling capacity and EER significantly.
[0023] Similarly, the invention allows the evaporator to be made
substantially larger than the optimum-sized evaporator, and the
heat absorption is increased accordingly. Then, the bypass method
is able to demonstrate significant benefit as the increased
subcooling makes the proportionally smaller condenser behave like
an optimum-sized condenser or an oversized condenser. In such an
embodiment of the present invention, the condenser pressure is
maintained constant despite the increased heat absorption at the
evaporator, thus increasing both the cooling capacity and EER
without increasing compressor work.
[0024] Broadly stated, according to this invention, a portion of
the liquid refrigerant exiting the condenser is diverted into a
bypass line from which it is re-injected into the primary
refrigerant path at a location between the evaporator outlet and
compressor inlet. In the bypass line, a secondary expansion valve
is used to throttle the liquid refrigerant that was diverted from
the condenser, thus decreasing its temperature substantially below
the condenser outlet temperature.
[0025] The cooled refrigerant exiting the secondary expansion valve
then passes through the heat exchanger which is thermally coupled
to the primary refrigerant line between the condenser outlet and
the primary expansion device inlet. The heat exchanger removes heat
from the refrigerant vapor exiting the condenser, thus reducing its
temperature. As a result, the refrigerant enters the primary
expansion device at a substantially lower temperature than its
saturation temperature. In other words, the level of subcooling is
increased significantly, by 10-15 degree Celsius for example.
Moreover this is achieved without devoting any portion of the
condenser to subcooling.
[0026] Because the refrigerant pressure in the bypass line at the
outlet of the heat exchanger is greater than the pressure at the
evaporator outlet, a pressure differential accommodating device is
used at the intersection of bypass line outlet and the primary
refrigerant line. A pressure differential accommodating device can
be either a vacuum generating device or a pressure reducing
device.
[0027] According to a first aspect of the invention, there is
provided a refrigeration system including refrigerant compressing
means, refrigerant condensing means, expansion means and
evaporation means connected together to form a closed-loop system
with a refrigerant circulating therein, and a bypass line attached
between the outlet of the condensing means and the inlet of the
expansion means, the bypass line including a secondary expansion
means, heat exchanging means to remove heat from the discharge
liquid refrigerant from the condenser between the outlet of the
condensing means and an inlet of the expansion means, and a
pressure differential accommodating means for mixing two vapors at
different pressures connecting the outlets of the evaporation means
and the heat exchanging means to an inlet of the compressing
means.
[0028] According to a second aspect of the invention, there is
provided a refrigeration system comprised of a primary refrigerant
path including a compressor, a condenser, a primary expansion
device, and an evaporator connected together to form a closed loop
system with a refrigerant circulating therein, and a bypass line
attached between the outlet of the condenser and the inlet of the
compressor, the bypass line including a heat exchanger thermally
coupled to the primary refrigerant path between the condenser
outlet and the primary expansion device inlet to remove heat from
the discharge vapor from the compressor, and a pressure
differential accommodating device for mixing two vapors at two
different pressures connecting the outlets of the evaporator and
the heat exchanger to an inlet of the compressor.
[0029] Further according to the second aspect of the invention, the
pressure differential accommodating device may be a vacuum
generating device with no moving parts such as a venturi tube, or a
so-called "vortex tube" which is conventionally used to create two
fluid steams of differing temperature from a single high pressure
input stream.
[0030] Also according to the second aspect of the invention, the
pressure differential accommodating device may be a pressure
reducing device with no moving parts such as a capillary tube, a
restricted orifice, a valve, or a porous plug. The pressure
reducing device is used in the bypass line which is maintained at a
higher pressure than the evaporator. The pressure reducing device
equalizes the pressure between the bypass line and the evaporator
outlet, and includes suitable tubing connections to permit mixing
of the pressure-equalized vapors before return to the compressor
inlet.
[0031] According to a third aspect of the invention, there is
provided a method of increasing the efficiency of a refrigeration
system comprised of a primary refrigerant path including a
compressor, a condenser, a primary expansion device, and an
evaporator connected together to form a closed loop system with a
refrigerant circulating therein, the method comprising the steps of
bypassing a portion of the refrigerant exiting the condenser into a
secondary refrigerant line, passing the bypassed refrigerant
through a heat exchanger thermally coupled to the primary
refrigerant path between the condenser outlet and the primary
expansion device inlet to remove heat from the discharge liquid
refrigerant from the condenser, and passing the refrigerant exiting
the heat exchanger and the refrigerant exiting the evaporator
through a pressure differential accommodating device that mixes two
vapors at different pressures and feeding the refrigerant exiting
the pressure differential accommodating device to an inlet of the
compressor.
[0032] Providing a bypass path for performing subcooling makes the
condenser more efficient, thereby reducing the condenser pressure,
a phenomenon which decreases the pressure lift at compressor, and
thus reduces the compressor work. Correspondingly, because
subcooling does not have to be done inside the condenser, the
condenser can be substantially smaller and becomes materially more
efficient and cost-effective. The increased subcooling increases
the amount of liquid refrigerant after the throttling process
through the primary expansion valve. Thus, the heat absorption at
the evaporator (often referred as the cooling capacity)
increases.
[0033] The above-described benefits of the subcooling bypass are
achieved with diversion of 5-15% of the liquid refrigerant outflow
from the condenser. At this level, reduced compressor work and
increased cooling capacity are achieved. Since the EER (energy
efficiency ratio) is defined as the ratio of the cooling capacity
to compressor work, this increases the EER.
[0034] According to a fourth aspect of the invention, when more
than 15%, for example, 30%, of the liquid refrigerant from the
condenser is diverted to the bypass path, the cooling capacity is
reduced due to the substantial decrease in the refrigerant mass
flow rate circulating through the evaporator. By use of an
adjustable valve in the bypass path, the bypass mass flow rate, and
thus, the cooling capacity, can be varied according to the thermal
load, whereby it is possible to operate an air conditioning or
refrigeration system without frequent, highly energy-inefficient,
ON-OFF operations of the compressor. This results in an improved
long-term seasonal energy efficiency ratio (SEER).
[0035] According to a fifth aspect of the invention, multiple
evaporators can be employed, e.g., in a zoned cooling system. Thus,
several small evaporators could be provided for separate rooms,
with one condenser and one compressor. When all the rooms require
cooling, the system can be operated with a 5% bypass rate to
provide the maximum cooling capacity and the maximum efficiency. If
the thermal load decreases, as when fewer rooms need to be cooled,
the bypass rate can be increased to reduce the cooling capacity
without the need to cycle the compressor on and off. This is quite
beneficial because the repeated ON-OFF cycling of the compressor is
a very energy-inefficient process.
[0036] In further contrast to conventional techniques, the concepts
of this invention are applicable to conventional single-refrigerant
systems, and also to mixed-refrigerant systems using a combination
of refrigerants selected to provide the desired combination of
thermal and flammability characteristics. Such mixed-refrigerant
systems may also include regenerative features which provide higher
evaporator efficiency by increasing the percentage of liquid in the
refrigerant as it enters the evaporator. Regenerative mixed
refrigerant systems are disclosed, for example, in U.S. Pat. Nos.
6,250,086 and 6,293,108, the contents of which are hereby
incorporated by reference.
[0037] According to a further aspect of the invention, even further
reduction of condenser size can be achieved by employing the bypass
circuit for de-superheating, as well as for subcooling. Use of
de-superheating bypass is disclosed in my pending U.S. patent
application Ser. No. 10/253,000, filed Sep. 23, 2002 (Atty Docket
3474-21), the contents of which are hereby incorporated by
reference.
[0038] It is accordingly an object of this invention to provide an
apparatus and method that eliminates the subcooling section in the
condenser of a refrigeration system.
[0039] It is also an object of the invention to increase the
efficiency of known refrigeration systems by providing a more
cost-effective way of providing subcooling of the refrigerant in a
refrigeration system.
[0040] It is another object of the invention to increase the
cooling capacity and EER of known refrigeration systems by
providing a cost-effective way of providing subcooling of the
refrigerant.
[0041] A further object of the invention is to provide a system in
increased cooling capacity and EER are achieved by use of bypass
subcooling technology in combination with de-optimizing the size of
the condenser used according to conventional practice for a given
cooling capacity.
[0042] A related object of the invention to allow use of smaller
condensers in known refrigeration systems by providing a
cost-effective way of providing subcooling of the refrigerant.
[0043] It is another object of the invention to enable the use,
without a degradation of EER or cooling capacity, of a condenser
and a compressor of smaller sizes than the current optimum sizes
and size ratios of components of known refrigeration systems
without bypass subcooling technology.
[0044] An additional object of the invention is to provide a method
and apparatus for subcooling of the refrigerant, which may be used
in single-refrigerant systems and also in mixed-refrigerant
systems, with and without regenerative features.
[0045] An additional object of the invention is to provide an
improved refrigeration system with substantially lower evaporator
pressure by use of a vacuum-generating device thereby boosting the
evaporator capacity.
[0046] An additional object of the invention is to provide an
improved refrigeration system in which the mixing of refrigerant
streams having two different pressures using a vacuum generating
device increases the suction pressure of the compressor, whereby
the required pressure rise over the compressor is reduced, and
which, in turn, reduces the compressor work and increases the
EER.
[0047] An additional object of the invention is to provide an
improved refrigeration system in which the mixing of two different
pressure vapors is carried out using a vacuum generating device so
that the pressure at the bypass line can be maintained at a higher
pressure than the evaporator pressure.
[0048] An additional object of the invention is to provide an
improved refrigeration system in which the mixing of two different
pressure vapors is carried out using a pressure-reducing device so
that the pressure at the bypass line can be maintained at a higher
pressure than the evaporator pressure.
[0049] Yet another object of the invention is to provide an
improved refrigeration system in which subcooling is performed
outside the condenser in a bypass path to which refrigerant from
the condenser outlet is diverted, into a bypass path, and in which
the quantity of refrigerant diverted is controlled such that the
cooling capacity can be adjusted to meet varying thermal
requirements, whereby the system can be operated without the need
for energy-inefficient repeated on and off cycling of the
compressor.
[0050] An additional object of the invention is to provide a method
and apparatus for improving the cooling capacity and EER of a
conventional refrigeration system by employing bypass technology in
combination with de-optimizing condenser size both for subcooling
and for de-superheating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 shows a block diagram of a conventional refrigeration
system.
[0052] FIG. 2 shows an example of the temperature variation inside
a condenser for the conventional refrigeration system of FIG.
1.
[0053] FIG. 3 shows another prior art refrigeration system where a
part of the high-pressure refrigerant expands through a secondary
expansion device in a bypass line which is at the same pressure as
that at the evaporator outlet.
[0054] FIG. 4 shows an example of a bypass device using a
conventional liquid-line/suction line heat exchanger.
[0055] FIG. 5 shows a block diagram of an embodiment of the present
invention in which subcooling bypass technology is used in
combination with de-optimization of the condenser size, as dictated
by conventional practice, and a pressure differential accommodating
device is used to mix two refrigerant streams at two different
pressures.
[0056] FIG. 6 shows a block diagram of an embodiment of the present
invention in which the evaporator is enlarged to take advantage of
the additional subcooling.
[0057] FIG. 7 shows a block diagram of an embodiment of the present
invention using a vortex generator as a pressure differential
accommodating device.
[0058] FIG. 8 shows a block diagram of an embodiment of the present
invention where the liquid refrigerant is diverted downstream of
the secondary heat exchanger.
[0059] FIG. 9 shows a block diagram of an embodiment of the present
invention in which a thermostatic expansion valve (TXV) is used to
maintain a constant suction temperature.
[0060] FIGS. 10A and 10B illustrate the construction of a vortex
generator which may be used as a pressure differential
accommodating device according to the invention.
[0061] FIG. 11 is a block diagram showing application of the
present invention to a zoned cooling system.
[0062] FIG. 12 is a block diagram showing application of the
present invention to a mixed-refrigerant system.
[0063] FIG. 13 shows a block diagram of an embodiment of the
present invention in which a small condenser and a large evaporator
are used in combination with a TXV to take advantage of the
additional subcooling in which the heat exchanger is driven by
refrigerant exiting the evaporator.
[0064] FIG. 14 shows a block diagram of an embodiment of the
present invention in which a small condenser and a large evaporator
are shown to take advantage of the additional subcooling in which
the heat exchanger is driven by refrigerant diverted from the main
expansion device.
[0065] Throughout the drawings, like parts are given the same
reference numerals.
DETAILED DESCRIPTION OF THE INVENTION
[0066] FIG. 5 shows a bypass technology concept, where a portion of
liquid refrigerant is bypassed through a bypass line or path 27.
The refrigerant in the bypass path goes through a secondary
expansion device 23, thus lowering its pressure and temperature.
The cold refrigerant mixture after the secondary expansion device
receives heat energy from the hot liquid refrigerant that has
exited the condenser and is flowing through the primary refrigerant
line, producing additional subcooling in the liquid refrigerant.
The additional subcooling produced from this bypass method makes
the subcooling process in the condenser unnecessary. Thus, FIG. 5
shows a smaller condenser 14b, where the subcooling section has
been removed and is identified as a dotted rectangular box.
[0067] FIG. 6 shows that the bypass technology enables the use of a
larger evaporator than the evaporator in an optimized system
without the bypass technology. The use of the larger evaporator is
possible because of the increased subcooling produced by the bypass
technology. The increased subcooling means more liquid refrigerant
after the main expansion device is produced at a lower temperature
thereby increasing the heat absorption at the evaporator. The
increased size of the evaporator is indicated by a dotted
rectangular box 18a. The increased evaporator is identified as 28
in FIG. 6. The size of an evaporator directly reflects on the
capacity of a refrigeration system. The use of an evaporator in
this embodiment of the present invention that is larger than that
of an optimized system without the bypass is very significant
because it means that with the present bypass technology one can
increase the capacity of a system without increasing the sizes of
the condenser and compressor. An increase in evaporator size, with
all other component sizes held equal, would represent a direct
increase in cooling capacity, or from another perspective, by
adding the bypass, the condenser and compressor sizes can be
reduced and still meet the needs of a given evaporator capacity.
For example, one can build a refrigeration system with a smaller
condenser and a smaller compressor than the sizes in the optimized
system, while maintaining evaporator size and cooling capacity.
Since the cost of the compressor is currently about half of the
total cost of a refrigeration system, the size reduction in the
compressor is a particularly attractive option.
[0068] FIG. 7 shows the bypass technology with a condenser 24 that
is smaller and an evaporator 28 that is larger than those without
the bypass. For example, in a 1 ton air-conditioning system without
the bypass, one needs a condenser 14 corresponding to 1 ton (i.e.,
15 KBtu/hr), an evaporator 18 corresponding to 1 ton (i.e., 12
KBtu/hr), as well as a compressor 12 designed for the 1 ton
application as shown in FIG. 1. In a 1 ton air-conditioning system
with the bypass, one needs a smaller condenser 24 (i.e., 10
KBtu/hr), a larger evaporator 28 (i.e., 15 KBtu/hr), and the same
compressor 12 designed for 1 ton application as shown in FIG.
6.
[0069] FIG. 6 shows the bypass technology using a pressure
differential accommodating device 38. The pressure at the bypass
path 27 is greater than the pressure at the evaporator. Hence, one
needs to have a pressure differential accommodating device to
account for the vapors at two different pressures after the
evaporator. The pressure differential accommodating device can be
either a vacuum-generating device such as a vortex generator or a
venturi tube or a pressure reducing device such as a capillary
tube, a restricted orifice, a valve, or a porous plug. In the case
of the pressure reducing device, friction reduces the pressure of
the refrigerant stream coming from the bypass path to match the
evaporator pressure. The pressure reducing device may also include
suitable tubing or the like to permit mixing of the
pressure-equalized vapors before return to the compressor
inlet.
[0070] FIG. 7 shows the bypass technology where a vortex generator
29 is used as a pressure differential accommodating device to
generate a vacuum and achieve mixing for the two refrigerant
streams at different pressures.
[0071] In the implementations illustrated in FIGS. 5-7, the
refrigerant is diverted to the secondary path before the primary
refrigerant flow is subjected to subcooling in heat exchanger 22.
FIG. 8 shows an alternative embodiment in which the diversion takes
place after subcooling. Again, a pressure differential
accommodating device 38 is used between the evaporator and the
compressor to combine two vapors at different pressures.
[0072] FIG. 9 shows an embodiment of the present invention which
employs a thermostatic expansion valve (TXV) 16a together with the
bypass technology. The TXV 16a meters the refrigerant flow to
evaporator 28 using a thermal sensing element 41 to monitor the
superheat. The TXV 16a opens or closes in response to the thermal
element 41. The TXV 16a maintains a constant superheat in the
evaporator 28. The use of the TXV 16a together with the bypass
technology allows the use of a smaller evaporator than otherwise.
When the heat absorption at the evaporator 28 increases, the
superheat increases. Accordingly, the TXV 16a opens, increasing the
circulating refrigerant mass flow rate so that the superheat
remains constant. When one uses a larger evaporator with the TXV
16a, the heat absorption at the evaporator can significantly
increase as the TXV 16a can increase the circulating refrigerant
mass flow rate.
[0073] Without the bypass, the increased heat absorption resulting
from use of a larger evaporator also increases the condenser
pressure, thus increasing compressor work. Often the increase in
the compressor work is greater than the increase in the heat
absorption thereby decreasing the energy efficiency ratio (EER).
However, in the present invention, the bypass technology creates
enough subcooling at and after the condenser 24 so that the
increased heat absorption at the evaporator 28 does not increase
the condenser pressure, because the bypass enables the condenser 24
to behave as if it were oversized. Hence, the EER increases in the
case with the bypass.
[0074] The construction of a vortex generator is shown
schematically in FIGS. 10A and 10B. The design of the vortex
generator, generally denoted at 40, is derived from the so-called
vortex tube, a known device which converts an incoming flow of
compressed gas into two outlet streams-one stream hotter than and
the other stream colder than the temperature of the gas supplied to
the vortex tube. A vortex tube does not contain any moving parts.
Such a device is illustrated in U.S. Pat. No. 6,250,086, which is
incorporated herein for reference.
[0075] As illustrated in FIGS. 10A and 10B, vortex generator 40 is
used to mix two vapors at different pressures into one stream. The
present invention uses the vortex generator 40 as a mixing means.
It is comprised of a tubular body 60, with an axial inlet 52 and a
tangential inlet 54 at an inlet end 62, and an outlet 58 at an
opposite outlet end 64. The interior construction of tube 60 at the
inlet end is such that a high-pressure gas stream entering
tangential inlet 54 travels along a helical path toward the outlet
58. This produces a strong vortex flow in tube 60, and a radial
pressure differential due to the centrifugal force created by the
vortex flow forces the vapor radially outward and produces high
pressure at the periphery and low pressure at the axis. The low
pressure allows fluid drawn in through axial inlet 52 to mix with
the high-pressure helical stream and to exit with it through outlet
58.
[0076] With reference to the system shown in FIG. 7 and the
construction of the vortex generator 40 as illustrated in FIGS. 10A
and 10B, the high-pressure tangential flow is provided through tube
54 from secondary heat exchanger 22 and the bypass path 27, whereas
the incoming stream at axial inlet 52 is provided from the outlet
of evaporator 28. Using a vacuum-generating device based on the
vortex generator makes it possible to combine the refrigerant
exiting from evaporator 28 and the higher pressure refrigerant
exiting from the secondary heat exchanger 22 without the need for a
costly pump having moving parts.
[0077] Other devices which rely on geometry and fluid dynamics may
also be used to generate a vacuum which permits mixing the
refrigerant streams exiting from evaporator 18 and heat exchanger
22. For example, a device operating on the principle of a venturi
tube may also be used.
[0078] Referring again to FIG. 7, in operation, a portion of the
liquid refrigerant exiting from condenser 24 is diverted into
bypass path 27, for example, by a suitable valve (not shown). The
diverted refrigerant passes through secondary expansion device 23
and then through heat exchanger 22 which performs the subcooling
function conventionally performed by the downstream portion of the
condenser. By proper selection of system parameters, in particular,
the mass flow rate of refrigerant diverted to the bypass path, the
refrigerant can be made to leave condenser 24 at or close to the
saturation temperature, and the entire flow path through the
condenser can be devoted to the phase-change operation by transfer
of heat to the environment, whereby maximum condenser efficiency
can be achieved. It has been found that this requires diversion of
5-15% of the liquid refrigerant outflow from the condenser to the
bypass path.
[0079] More particularly, providing a bypass path for subcooling
makes the condenser 24 more efficient thereby reducing the
condenser pressure, which, in turn, decreases the pressure lift at
the compressor 12, thus reducing the compressor work. The
coefficient of performance ("COP") of a refrigeration system,
sometimes termed the energy-efficiency ratio (EER), is defined as
Qv/Wc, where Qv is the heat absorption by the evaporator of the
system and Wc is the work done by the compressor. As will be
appreciated, a decrease in Wc increases the COP and the EER.
[0080] Correspondingly, because subcooling does not have to be done
inside condenser 24, the condenser becomes more efficient, and
subcooling prior to the main expansion device 16 is increased. This
increases the amount of liquid refrigerant after the throttling
process through the main expansion valve 16. Thus, the heat
absorption at evaporator 28 (often referred as the cooling
capacity) increases.
[0081] Referring still to FIG. 7, by proper design of the vacuum
generating device such as vortex generator 40 illustrated in FIGS.
10A and 10B, or venturi tube, the pressure at the low pressure
inlet 52 can be made lower than the inlet pressure at main
evaporator 28. As a consequence, a pressure drop may be imposed
across the evaporator 28. This is advantageous in that the lower
evaporator outlet pressure means that the evaporator temperature
differential is greater, resulting in enhanced evaporator
capacity.
[0082] Of even more significance, after the mixing of the two vapor
streams from heat exchanger 22 and evaporator 28, the pressure of
the combined stream can have a higher pressure than the evaporator
inlet pressure. This means that the suction pressure at the
compressor inlet is increased, which reduces the required pressure
lift across the compressor 12. The reduced compressor work can
provide a beneficial increase in the EER.
[0083] FIG. 11 illustrates a zoned air conditioning system
embodying the principles of this invention, generally denoted at
110. This differs from system 50 illustrated in FIG. 5 in that
bypass path 92 includes an adjustable control valve 94, and the
evaporator 96 is formed of several parallel-connected evaporator
units 98a and 98b located to serve different rooms, and
respectively connected to the primary expansion device 16 by ON-OFF
valves 100a and 100b. System 110 is thus configured to provide two
separate cooling zones, but as will be appreciated, more zones can
be provided if desired.
[0084] The outlets of evaporator units 98a and 98b are at the same
pressure, and are therefore connected in common to the input of
pressure differential accommodating device 38.
[0085] In operation, when cooling in both zones is required, valves
100a and 100b are opened, and refrigerant flows through both
evaporators 98a and 98b. Valve 94 is adjusted to divert between 10
and 60 percent of the refrigerant from condenser 24 into bypass
path 92 to achieve maximum cooling and efficiency. Thus, all of the
benefits of the subcooling bypass described in connection with
FIGS. 5, 6 and 7 are also realized in system 110.
[0086] As an additional feature of system 110, however, if cooling
is required, e.g., only in the zone served by evaporator unit 98a,
valve 100a is opened, valve 100b is closed, and valve 94 is
adjusted to divert the refrigerant which would otherwise flow
through evaporator 98b into bypass path 92, along with the
refrigerant required for subcooling.
[0087] To vary the bypass mass flow rate, valve 94 in bypass path
92 should be continuously adjustable or adjustable in steps, to
provide the desired number of different flow rates. For example, 5%
to 15% diversion could be provided for maximum performance, with
20%, 30%, 40%, 50%, and 60% diversion for reduced cooling capacity.
Valves providing the above-described capability are commercially
available, and any suitable or desired valve of this type may be
employed.
[0088] As previously indicated, maximum efficiency and cooling
capacity are achieved by diversion of 5-15% of the refrigerant mass
flow to bypass path 92. As the amount of refrigerant diverted is
increased beyond 15%, for example, up to 30% or more, the cooling
capacity is reduced due to the substantial decrease in the
refrigerant mass flow rate circulating through evaporator 96. Thus,
by diverting the refrigerant not needed in the idle evaporator, the
cooling capacity can be made to vary according to the thermal load,
without the need for repeated on-off cycling of the compressor or
resort to costly variable speed compressors.
[0089] This is particularly advantageous in that cycling the
compressor on and off consumes a large quantity of energy.
Eliminating this inefficiency results in significantly improved
long-term energy efficiency, a parameter sometimes measured in
terms of seasonal energy-efficiency ratio (SEER), which takes
account of the ON/OFF operation of the compressor on the efficiency
of the system. SEER is defined as the ratio of the sum of Qv (heat
absorbed by the evaporator) times the hours of operation on one
hand, to the sum of Wc (compressor work) times the hours of
operation on the other.
[0090] As will also be appreciated, a variable cooling capacity can
be provided in single-zone systems such as illustrated in FIGS.
5-9. Here, additional refrigerant would be diverted to bypass path
27 through a suitable adjustable valve (not shown) to accommodate a
decrease in required cooling capacity, and the system could operate
without the need for frequent compressor on-off cycling.
[0091] In the constructions described above, it has been assumed
that a single refrigerant circulates through the system. Subcooling
bypass can also be used in conjunction with mixed refrigerants in
regenerative systems to achieve highly beneficial results.
[0092] FIG. 12 illustrates an embodiment of the invention as
applied to a simple mixed-refrigerant system, employing, for
example, a mixture of refrigerants R-32, R-125, and R-134a. This is
a commonly used beneficial combination, as the R-32 component is
flammable but possesses excellent thermal characteristics, whereas
the R-125 and R-134a components exhibit less desirable thermal
characteristics than R-32 but are non-flammable and therefore
safer. In the interest of simplicity, variations in the
regenerative paths as illustrated in U.S. Pat. Nos. 6,293,108 and
6,449,964 have been omitted from the illustrative system of FIG.
12.
[0093] The system, generally denoted at 120, comprises of a
compressor 12, an expansion device 16a, an evaporator 28, a heat
exchanger 22, and a pressure differential accommodating device 38
in a bypass path 27 just as in system 50 (see FIG. 5). The
condenser in system 120 of FIG. 12, however, is split into two
stages 24a and 24b, and a liquid-vapor (LV) separator 108 of any
suitable or desired type is provided between the two condenser
stages.
[0094] The LV separator 108 separates the incoming vapor stream
exiting from condenser stage 24a into a first vapor component which
passes to the inlet of condenser stage 24b, and a second lower
temperature liquid component a portion of which passes into the
bypass path 27 through a valve 112 to the inlet of heat exchanger
22.
[0095] The second component exiting from LV separator 108 through
the valve 112 is rich in R-134a refrigerant due to its high
condensation and boiling point relative to the other refrigerant
components. Aside from the advantages of performing the
desuperheating step outside condenser stage 24a as described above,
the R-134a-rich composition of the refrigerant allocated to the
bypass path in liquid form has the added benefit of reducing the
condenser pressure.
[0096] As indicated above, the system illustrated in FIG. 12 is
representative of the application of the principles of this
invention to mixed-refrigerant regenerative systems. It should be
understood, however, that the bypass is applicable to other
mixed-refrigerant regenerative system configurations as well.
[0097] FIG. 13 illustrates the present invention as applied to the
conventional liquid-line/suction line heat exchange where
superheated vapor or liquid-vapor mixture exiting the evaporator is
used to subcool the high-pressure liquid exiting the condenser
combined with de-optimization of condenser size as dictated by
conventional practice. As the suction temperature increases prior
to the compressor 212, the present invention increases the
circulating mass flow rate of the refrigerant by using a
thermostatic expansion device 216 together with a thermostatic bulb
241, which monitors the suction temperature. The thermostatic
expansion device 216 increases the mass flow rate of circulating
refrigerant so that the suction temperature is maintained constant
in the present invention. The present invention uses a condenser
214 whose size is much smaller than the condenser in an optimized
system. Furthermore, the present invention uses an evaporator 218
whose size is much larger than the evaporator in an optimized
system. In an optimized system, the conventional
liquid-line/suction line heat exchange does not improve the
efficiency of the system. The present invention using a large
evaporator 218 allows a refrigeration system to be built with a
smaller condenser and a smaller compressor than the sizes in an
optimized system without the bypass method.
[0098] FIG. 14 illustrates the present invention applied to a
system configuration similar to the system shown in FIG. 4, again
in combination with de-optimization of condenser size as dictated
by conventional practice. Here, a portion of liquid refrigerant is
bypassed through a secondary expansion device 223 and a heat
exchanger 222 to subcool the high-pressure liquid exiting the
condenser. The present invention uses a condenser 224 whose size is
much smaller than the condenser in an optimized system.
Furthermore, the present invention uses an evaporator 228 whose
size is much larger than the evaporator in an optimized system.
[0099] In describing the invention, specific terminology has been
employed for the sake of clarity. However, the invention is not
intended to be limited to the specific descriptive terms, and it is
to be understood that each specific term includes all technical
equivalents that operate in a similar manner to accomplish a
similar purpose.
[0100] Similarly, the embodiments described and illustrated are
also intended to be exemplary, and various changes and
modifications, and other embodiments within the scope of the
invention will be apparent to those skilled in the art in light of
the disclosure. The scope of the invention is therefore intended to
be defined and limited only by the appended claims, and not by the
description herein.
* * * * *