Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD OF MECHANICAL COMPRESSION REFRIGERATION
BASED ON TWO-PHASE EJECTOR
FIELD OF THE INVENTION
The invention relates to system and method of mechanical compression
refrigeration. In particular,
the present invention discloses the use of a two-phase ejector to improve
efficiency and stability
of mechanical compression refrigeration system.
BACKGROUND OF THE INVENTION
In recent years, technological advancements in the field of equipment
optimization and controls
have substantially reduced energy consumption. At the same time, the demand
for increased
comfort (for example, heating and air-conditioning) or production of goods
(for example, Agro-
food industry), however, undermines these achievements by giving rise to
demands for additional
energy consumption. As a result, the overall costs relating to energy
consumption increase.
Estimations by research carried out by Natural Resources Canada indicate that
ten percent of total
energy consumption in commercial, institutional and industrial activities
relates to refrigeration.
Refrigeration, or more generally, air conditioning, are no longer an option
but a requirement for
daily consumptions, given the increasing demand from consumers.
Currently, one of the solutions most investigated in improving energy
efficiency in refrigeration
involves the use of an ejector which may be integrated into conventional
refrigeration systems as
internal components in order to form hybrid cycles and improve performance. A
number of these
options are being considered in the current research (for example, cascades,
hybrids, subcooling
agents, ejecto-compression or ejecto-absorption).
Some of these options, such as cascade and hybrid configurations, have a good
potential for
performance improvement and have been studied theoretically and experimentally
at
CanmetENERGY. They are typically suitable for low temperatures and medium to
large capacities.
1
The refrigeration systems most currently used are based on mechanical
compression.
Electrically driven compressors are the main components in such systems.
Decent performance
is generally obtained in such systems, which explains the popularity of this
technology.
However, low temperature refrigeration or heat pumping in cold conditions or
air conditioning in
a hot environment imposes a heavy load on the electrical grid so that
innovative ways of
increasing efficiency and decreasing energy consumption are sought.
Other than ejectors, other technologies based on heat activation (i.e.
absorption, adsorption and
chemical heat pumps) may also be available. However, they are complex, bulky
and are not
suitable alternatives to mechanical compression.
Mechanical based compression refrigeration becomes increasingly complex and
consumes
increasingly more electricity (noble energy) at high and/or low temperature
working conditions.
Therefore, there is the need for an efficient mechanical compression
refrigeration system.
SUMMARY OF THE INVENTION
The objective of the present invention is to enhance the efficiency of the
existing refrigeration
cycles by assisting the compressor in a refrigeration system with a two-phase
ejector activated by
potential energy and available internal heat recovery.
According to one aspect of the invention, there is provided a refrigeration
system, comprising:
a metering device for controlling flow of a refrigerant,
an evaporator,
means for supplying the refrigerant from the metering device into the
evaporator wherein
the refrigerant evaporates into vapor,
a two-phase ejector comprising means defining a liquid chamber having a liquid
inlet,
means defining a vapor chamber having a vapor inlet, and an outlet discharging
a two-phase
vapor-liquid refrigerant stream,
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means for supplying the vapor from the evaporator into the vapor inlet of the
two-phase
ejector,
a flash tank compound separator,
means for supplying the refrigerant from the two-phase ejector into the flash
tank
compound separator wherein the refrigerant separates into two phases,
a compressor,
means for supplying the refrigerant from the flash tank compound separator
into the
compressor wherein the refrigerant compresses,
a condenser,
means for supplying the refrigerant from the compressor into the condenser
wherein the
refrigerant condenses,
a receiver,
means for supplying the refrigerant from the condenser to the receiver,
means for supplying the refrigerant from the receiver to the liquid inlet of
the two-phase
ejector,
means for supplying the refrigerant from the receiver to the metering device
and then into
the evaporator to start another cycle through the system,
means for supplying the refrigerant from the flash tank compound separator
into a pump
where pressure of the refrigerant is regulated,
means for supplying the refrigerant from the pump into the receiver,
wherein the two-phase ejector then draws vapor from the evaporator lifting its
pressure to
an intermediate level when activated a mixture of condensate from the
condenser and subcooled
refrigerant fed by the pump, and
wherein the pressure of the liquid inlet of the two-phase ejector is
controlled by the pump
in accordance with operating conditions of the compressor.
According to another aspect of the invention, there is provided a
refrigeration system,
comprising:
a metering device for controlling flow of a refrigerant,
an evaporator,
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means for supplying the refrigerant from the metering device into the
evaporator wherein
the refrigerant evaporates into vapor,
a two-phase ejector comprising means defining a liquid chamber having a liquid
inlet,
means defining a vapor chamber having a vapor inlet, and an outlet discharging
a two-phase
vapor-liquid refrigerant stream,
means for supplying the vapor from the evaporator into the vapor inlet of the
two-phase
ejector,
a flash tank compound separator,
means for supplying the refrigerant from the two-phase ejector into the flash
tank
compound separator wherein the refrigerant separates into two phases,
a compressor,
means for supplying the refrigerant from the flash tank compound separator
into the
compressor wherein the refrigerant compresses,
a condenser,
means for supplying the refrigerant from the compressor into the condenser
wherein the
refrigerant condenses,
a heat exchanger,
means for supplying the refrigerant from the condenser to the heat exchanger,
means for supplying the refrigerant from the heat exchanger to the liquid
inlet of the two-
phase ejector,
means for supplying the refrigerant from the heat exchanger to the metering
device where
pressure and temperature of the refrigerant decrease and then into the
evaporator to start another
cycle through the system,
wherein the heat exchanger simultaneously increases condensate subcooling at
an inlet of
the metering device and decreases motive liquid subcooling at the liquid inlet
of the two-phase
ejector,
means for supplying the refrigerant from the flash tank compound separator
into a pump
where the pressure of the refrigerant is regulated,
means for supplying the refrigerant from the pump into the heat exchanger,
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wherein the two-phase ejector then draws vapor from the evaporator lifting its
pressure to
an intermediate level when activated a mixture of condensate from the
condenser and subcooled
refrigerant fed by the pump, and
wherein the pressure of the liquid inlet of the two-phase ejector is
controlled by the pump
in accordance with operating conditions of the compressor.
According to a further aspect of the invention, there is provided a
refrigeration system,
comprising:
a metering device for controlling flow of a refrigerant,
an evaporator,
means for supplying the refrigerant from the metering device into the
evaporator wherein
the refrigerant evaporates into vapor,
a two-phase ejector comprising means defining a liquid chamber having a liquid
inlet,
means defining a vapor chamber having a vapor inlet, and an outlet discharging
a two-phase
vapor-liquid refrigerant stream,
means for supplying the vapor from the evaporator into the vapor inlet of the
two-phase
ejector,
a flash tank compound separator,
means for supplying the refrigerant from the two-phase ejector into the flash
tank
compound separator wherein the refrigerant separates into two phases,
a compressor,
means for supplying the refrigerant from the flash tank compound separator
into the
compressor wherein the refrigerant compresses,
a condenser,
means for supplying the refrigerant from the compressor into the condenser
wherein the
refrigerant condenses,
a mixing junction,
means for supplying the refrigerant from the condenser to the mixing junction,
means for supplying the refrigerant from the mixing junction to the liquid
inlet of the
two-phase ejector,
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means for supplying the refrigerant from the flash tank compound separator to
the
metering device where pressure and temperature of the refrigerant decrease and
then into the
evaporator to start another cycle through the system,
means for supplying the refrigerant from the flash tank compound separator
into a pump,
means for supplying the refrigerant from the pump into the mixing junction,
wherein the two-phase ejector then draws vapor from the evaporator lifting its
pressure to
an intermediate level when activated a mixture of condensate from the
condenser and subcooled
refrigerant fed by the pump, and
wherein the pressure of the liquid inlet of the two-phase ejector is
controlled by the pump
in accordance with operating conditions of the compressor.
According to one aspect of the invention, there is provided a refrigeration
system, comprising:
a metering device for controlling flow of a refrigerant,
an evaporator,
means for supplying the refrigerant from the metering device into the
evaporator wherein
the refrigerant evaporates into vapor,
a two-phase ejector comprising means defining a liquid chamber having a liquid
inlet,
means defining a vapor chamber having a vapor inlet, and an outlet discharging
a two-phase
vapor-liquid refrigerant stream,
means for supplying the vapor from the evaporator into the vapor inlet of the
two-phase
ejector,
a flash tank compound separator,
means for supplying the refrigerant from the two-phase ejector into the flash
tank
compound separator wherein the refrigerant separates into two phases,
a compressor,
means for supplying the refrigerant from the flash tank compound separator
into the
compressor wherein the refrigerant compresses,
a condenser,
means for supplying the refrigerant from the compressor into the condenser
wherein the
.. refrigerant condenses,
a heat exchanger,
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means for supplying the refrigerant from the condenser to the heat exchanger,
means for supplying the refrigerant from the compressor to the heat exchanger,
a first valve for controlling the supply of the refrigerant from the
compressor to the
condenser and a second valve for controlling the supply of the refrigerant
from the compressor
to the heat exchanger;
wherein by controlling and adjusting the first and/or the second valve, the
heat exchanger
transfers part of condensation heat of compressed vapor to subcooled
compressed liquid
circulated by pump to the two-phase ejector,
means for supplying the refrigerant from the heat exchanger to the liquid
inlet of the two-
phase ejector,
means for supplying the refrigerant from the heat exchanger to the metering
device where
pressure and temperature of the refrigerant decrease and then into the
evaporator to start another
cycle through the system,
wherein the heat exchanger simultaneously increases condensate subcooling at
the inlet
of metering device and decreases motive liquid subcooling at the liquid inlet
of two-phase
ejector,
means for supplying the refrigerant from the flash tank compound separator
into a pump
where the pressure of the refrigerant is regulated,
means for supplying the refrigerant from the pump into the heat exchanger,
wherein the two-phase ejector then draws vapor from the evaporator lifting its
pressure to
an intermediate level when activated a mixture of condensate from the
condenser and subcooled
refrigerant fed by the pump, and
wherein the pressure of the liquid inlet of the two-phase ejector is
controlled by the pump
in accordance with the operating conditions of the compressor.
According to one aspect of the invention, there is provided a refrigeration
system, comprising:
a metering device for controlling flow of a refrigerant,
an evaporator,
means for supplying the refrigerant from the metering device into the
evaporator wherein
the refrigerant evaporates into vapor,
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a two-phase ejector comprising means defining a liquid chamber having a liquid
inlet,
means defining a vapor chamber having a vapor inlet, and an outlet discharging
a two-phase
vapor-liquid refrigerant stream,
means for supplying the vapor from the evaporator into the vapor inlet of the
two-phase
ejector,
a flash tank compound separator,
means for supplying the refrigerant from the two-phase ejector into the flash
tank
compound separator wherein the refrigerant separates into two phases,
a compressor,
means for supplying the refrigerant from the flash tank compound separator
into the
compressor wherein the refrigerant compresses,
a condenser,
means for supplying the refrigerant from the compressor into the condenser
wherein the
refrigerant condenses,
a direct contact condenser,
means for supplying the refrigerant from the condenser to the direct contact
condenser,
means for supplying the refrigerant from the compressor to the direct contact
condenser,
a first valve for controlling the supply of the refrigerant from the
compressor to the
condenser and a second valve for controlling the supply of the refrigerant
from the compressor to
the direct contact condenser;
wherein by controlling and adjusting the first and/or the second valve, the
direct contact
condenser transfers part of condensation heat of compressed vapor to subcooled
compressed
liquid circulated by pump to the two-phase ejector,
means for supplying the refrigerant from the direct contact condenser to the
liquid inlet of
the two-phase ejector,
means for supplying the refrigerant from the flash tank compound separator to
the
metering device where pressure and temperature of the refrigerant decrease and
then into the
evaporator to start another cycle through the system,
means for supplying the refrigerant from the flash tank compound separator
into a pump
where the pressure of the refrigerant is regulated,
means for supplying the refrigerant from the pump into the direct contact
condenser,
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Date Recue/Date Received 2021-09-29
wherein the two-phase ejector then draws vapor from the evaporator lifting its
pressure to
an intermediate level when activated a mixture of condensate from the
condenser and subcooled
refrigerant fed by the pump, and
wherein the pressure of the liquid inlet of the two-phase ejector is
controlled by the pump
in accordance with operating conditions of the compressor.
Preferably, the metering device is a thermal expansion valve, or a capillary
tube.
Preferably, refrigerant used in the refrigeration system is carbon dioxide.
Other features and advantages of the present invention will become apparent
from the following
detailed description and the accompanying drawings, which illustrate, by way
of example, the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
By way of example only, preferred embodiments of the present invention are
described
hereinafter with reference to the accompanying drawings, wherein:
Figure 1 is a schematic representation of an embodiment of a conventional
refrigeration cycle
(prior art);
Figure 2 is a schematic representation of an embodiment of a two-phase ejector
assisted
mechanical refrigeration cycle according to the present invention;
Figure 3 is a schematic representation of a second embodiment of a two-phase
ejector assisted
mechanical refrigeration cycle according to the present invention;
Figure 4 is a schematic representation of a third embodiment of a two-phase
ejector assisted
mechanical refrigeration cycle according to the present invention;
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Figure 5 is a schematic representation of a fourth embodiment of a two-phase
ejector assisted
mechanical refrigeration cycle according to the present invention; and
Figure 6 is a schematic representation of a fifth embodiment of a two-phase
ejector assisted
mechanical refrigeration cycle according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Mechanical refrigeration is the utilization of mechanical components arranged
in a "refrigeration
system" for the purpose of transferring heat. The refrigeration cycle is based
on the well-known
physical principle that a liquid evaporating into a gas extracts heat from the
surrounding area. The
refrigeration cycle is to remove unwanted heat from one place and discharge it
into another. To
accomplish this, the refrigerant is pumped through a closed refrigeration
system.
Refrigerants are chemical compounds that are alternately compressed and
condensed into a liquid
and then permitted to expand and to evaporate into a vapor or gas as they are
pumped through the
mechanical refrigeration system to cycle. Refrigerants evaporate at much lower
temperatures than
water, which permits them to extract heat at lower temperature than water.
Two different pressures exist in the cycle - the evaporating or low pressure
in the "low side," and
the condensing, or high pressure, in the "high side." These pressure areas are
separated by two
dividing points: one is the metering device where the refrigerant flow is
controlled, and the other
is at the compressor, where vapor is compressed.
Referring to Figure 1, a schematic representation of an embodiment of an
existing conventional
refrigeration cycle system 1, a metering device 5 may be a thermal expansion
valve, a capillary
tube, or any other device to control the flow of refrigerant into an
evaporator 6, or cooling coil, as
a low-pressure, low-temperature refrigerant. The expanding refrigerant
evaporates as it goes
through evaporator 6, where it removes the heat from the substance or space in
which evaporator
6 is located. Heat travels from the warmer substance to evaporator 6 cooled by
the evaporation of
the refrigerant within the system, causing the refrigerant to evaporate to a
vapor. This low-pressure,
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low-temperature vapor is then drawn to a compressor 7 where the low-
temperature vapor is
compressed into a high-temperature, high-pressure vapor. Compressor 7 then
discharges the high-
temperature, high-pressure vapor to a condenser 8. The high-temperature, high-
pressure
refrigerant vapor is at a higher temperature than the air or water passing
across the condenser,
therefore heat is transferred to the cooler air or water. As heat is removed
from the vapor, the
vapor is condensed into a liquid, at a high-pressure. The liquid refrigerant
travels to metering
device 5 where it passes through a small opening or orifice where a drop in
pressure and
temperature occurs, and then it enters into evaporator 6. As the refrigerant
makes its way into the
large opening of the evaporator tubing or coil, it vaporizes, ready to start
another cycle through the
system.
An ejector is a device in which two streams flow in intimate contact at
relatively high velocity
such that the driving stream transfers momentum to the driven stream, thereby
increasing the
stagnation pressure of the driven stream. The two streams are accelerated in
separate nozzles to
approximately the same pressure before being brought together in a mixing
section and the mixed
stream is decelerated in a diffuser. An ejector can be used to generate
isentropic condition in the
throttling process. Because the phase of the working fluid in the diffuser is
a two phase, an ejector
is usually named as two-phase ejector.
In the present invention, two-phase ejector(s) activated by pressurized
refrigerant are used and
strategically located in the cycle of the refrigeration system so as to
provide part of the compression
effect required for the refrigeration load, thereby relieving the conventional
mechanical
compressor from part of its duty, hence increasing the overall cycle
efficiency of the refrigeration
system.
The two-phase ejectors are pressure-activated. In a mechanical refrigeration
cycle, the two-phase
ejectors can recover internal energy otherwise wasted, in order to produce a
modest compression
effect, a pseudo-isentropic expansion and an appreciable refrigerant
circulatory effect. The two-
phase ejectors can be integrated therefore in a mechanical compression system
to produce
improved cooling or refrigeration of the conventional cycle.
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Unlike conventional mechanical compressors, the two-phase ejectors are static
mechanical
components; they are compact, flexible, simple and low cost.
In its function, the two-phase ejector contributes to the overall compression
so that conventional
mechanical compressor's work is reduced, and its efficiency improved,
resulting in overall
improved cycle performance.
Because two-phase ejectors are static and compact components, modification to
the conventional
refrigeration cycle to incorporate the two-phase ejectors introduces no major
and/or costly changes
but results in substantial performance gains.
According to the present invention, the two-phase ejector does not completely
replace the
conventional mechanical compressor but serves to build a new cycle arrangement
in which the
conventional mechanical compressor and the two-phase ejector can fulfill their
respective duties
of fluid circulation and compression without or with minimal interference.
According to the present invention, the two-phase ejector is placed in series
with the conventional
mechanical compressor to the suction of which it feeds refrigerant drawn from
the evaporator, but
it is activated independently from the conventional mechanical compressor.
The two-phase ejector and conventional mechanical compressor assembly forms a
hybrid system
which uses a common refrigerant to both components.
In existing prior art refrigeration systems, either:
(1) the two-phase ejector completely replaces the conventional mechanical
compressor
which is then replaced by a pump; or
(2) the two-phase ejector and the conventional mechanical compressor are
arranged in
series in such a way that the ejector is activated by the conventional
mechanical
compressor via the condensate and in turn the two-phase ejector feeds the
conventional mechanical compressor in vapor via the evaporator.
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In these types of existing setups, it is obvious that both the two-phase
ejector and the conventional
mechanical compressor are strongly coupled, therefore preventing their stable
operation.
In contrast, the refrigeration cycle options described in the present
invention hybrid the two-phase
ejector and conventional mechanical compressor configurations. Their main
features are
summarized below.
In Figure 2, an embodiment of a two-phase ejector assisted mechanical
refrigeration system 10
consists of a cycle in which a two-phase ejector 11 and a flash tank compound
separator (or a
second reservoir) 12 are positioned sequentially between a receiver (or the
first fluid distribution
reservoir) 9 and a compressor 7. Part of the liquid in receiver 9 is expanded
through metering
device 5 to the conditions of evaporator 6. The two-phase ejector 11 draws
vapor from evaporator
6 lifting its pressure to an intermediate level when activated a mixture of
condensate and subcooled
refrigerant fed by a pressure pump 13. Therefore, adequate subcooling of the
two-phase ejector
feed and the evaporator can be adjusted for optimal operation. This
combination minimizes the
detrimental coupling of two-phase ejector 11 and compressor 7 and results in
improved cycle
stability and performance. The two-phase ejector 11 and compressor 7 are in
series and are always
both in operation. The system uses one refrigerant and is suitable for a wide
range of applications
and capacities.
Figure 3 depicts another embodiment of a two-phase ejector assisted mechanical
refrigeration
system 20, which is a variant of system 10 as described in Figure 2.
In Figure 3, receiver (or the first fluid distribution reservoir) 9 in Figure
2 is replaced by a compact
heat exchanger 21, which allows for more operational flexibility. This measure
simultaneously
increases condensate subcooling at the inlet of metering device (expansion
valve) 5 and decreases
motive liquid subcooling at the primary inlet of two-phase ejector 11, which
improve the overall
cycle performance. In addition, the primary inlet pressure of two-phase
ejector 11 is controlled by
pump 13 independently of the pressure of condenser 8.
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Figure 4 depicts another embodiment of a two-phase ejector assisted mechanical
refrigeration
system 30, which is a variant of system 10 and 20 as depicted in Figures 2 and
3, respectively.
In Figure 4, evaporator 6 is fed by the refrigerant from flash tank compound
separator (or a second
reservoir) 12 at intermediate pressure; and receiver (or the first fluid
distribution reservoir) 9 in
Figure 2 is replaced by a mixing junction 31. This configuration simplifies
the cycle of the
refrigeration system further by the removal of a vessel, therefore reducing
expansion losses in
evaporator 6.
Figure 5 represents an additional embodiment of a two-phase ejector assisted
mechanical
refrigeration system 40 wherein the condenser 8 is partially replaced by a
heat exchanger 21,
achieved by controlling valves 42 (valve 42a for controlling the supply of the
refrigerant from
compressor 7 to condenser 8 and/or valve 42b for controlling the supply of the
refrigerant from
compressor 7 to heat exchanger 21) and depend on the expansion extent and
quality in the nozzle
of two-phase ejector 11; the other components remaining unchanged.
In this case, heat exchanger 21 transfers a variable part of the condensation
heat of the compressed
vapor to the highly subcooled compressed liquid circulated by pump 13 to two-
phase ejector 11.
This process has, inter alia, the following advantages:
= By condensing part of the compression vapor, the size of condenser 8 will
be
substantially reduced;
= The two-phase ejector 11 subcooled inlet conditions can be adjusted to
maximize its
efficiency;
= The level of heat rejection can be varied to maximize the efficiency of
compressor 7
and maximize overall performance of the system, particularly when condenser 8
is less
needed; and
= Where condenser 8 is fully used, two-stage compressor and multi-circuit
heat
exchanger may be contemplated to divert only minimal stream to condenser 8 in
order
for the compressor 7 to operate with minimal consumption.
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Figure 6 depicts another embodiment of a two-phase ejector assisted mechanical
refrigeration
system 50, which is a variant of system 40 as described in Figure 5.
In Figure 6, the heat exchanger 21 in Figure 5 is replaced by a more efficient
and direct contact
condenser 55 and an evaporator feed from intermediate pressure flash tank
compound separator
(or a second reservoir) 12 to further reduce expansion losses.
Any of the configurations as described above may use any of the refrigerants
currently available.
Preferably, carbon dioxide (CO2) is more suitable for the intended two-phase
ejector
refrigeration/heat pump operation.
Preferably, the metering device is a thermal expansion valve, or a capillary
tube.
Although the present invention has been described in considerable detail with
reference to certain
preferred embodiments thereof, other embodiments and modifications are
possible. Therefore, the
scope should not be limited by the preferred embodiments set forth in the
afore-mentioned
illustrative examples but should be given the broadest interpretation
consistent with the description
as a whole.
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