Refrigeration – Processes – Employing diverse materials or particular material in...
Reexamination Certificate
2002-07-03
2004-01-06
Bennett, Henry (Department: 3744)
Refrigeration
Processes
Employing diverse materials or particular material in...
C062S502000
Reexamination Certificate
active
06672084
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to refrigeration apparatus and a refrigeration process and a process employing a mixture of different refrigerants.
BACKGROUND OF THE INVENTION
Refrigeration systems are well known which employ a single refrigerant, for example, CFC refrigerants such as R-12 and HCFC refrigerants such as R-22. These refrigerants, however, have serious environmental drawbacks and are being replaced by refrigerants of the HFC type such as R-32, R-125 and R-134a in different combinations.
The individual HFC refrigerants have diverse characteristics, as shown in the following table:
LATENT
HEAT
BOILING
HEAT
CONDENSER
EVAPORATOR
TRANSFER
FLAM-
DENSITY
POINT
(h
fg
)
PRESSURE
PRESSURE
CHARACT.
ABILITY
R-32
Light
Low
Large
High
High
Good
Yes
R-125
Heavy
Low
Small
High
High
Medium
No
R-134a
Medium
High
Medium
Low
Low
Poor
No
In many refrigeration systems, the following characteristics are preferred:
Density—heavy
Boiling Point—low at evaporator and high at condenser
Latent Heat—large
Condenser Pressure—low
Evaporator Pressure—high
Heat Transfer—good
Flammability—no
In the above, h
fg
is the enthalpy difference between 100% vapor and 100% liquid.
R-32 is a preferred refrigerant because of its high latent heat and high evaporator pressure, which reduces the compressor work and thus the compressor size. That is, the compressor work W
COMPRESSOR
is defined as:
W
COMPRESSOR
=∫vdP
where v=specific volume=1/density; and P=pressure.
The compressor work in a typical refrigeration system can be simplified for an isentropic process as:
W
=
kRT
1
k
-
1
[
(
P
2
P
1
)
(
k
-
1
)
/
k
-
1
]
where k is a specific heat ratio, R is a gas constant, and T is temperature. As depicted in the above equation, the compressor work can be reduced by reducing the pressure differential, P
2
−P
1
or compression ratio, P
2
/P
1
. As the compressor work is reduced, the EER (energy-efficiency ratio) increases because EER is defined as the ratio of the heat absorption at the evaporator to compressor work.
EER
=
Heat
absorption
from
evaporator
Work
done
by
compressor
In a typical system, as evaporator pressure increases, the pressure change in the compressor is reduced, thus reducing the compressor work.
While R-32 has the best thermal characteristics, it is more flammable than the others, and carries with it the danger of fire. Consequently, R-32 is commonly mixed with non-flammable fluids such as R-125 and R-134a to reduce the fire danger.
Currently available mixture refrigerants include R-407c and R-410a. The former (R-407c) is one of the R-407 series refrigerants, which include R-407a, R-407b, R-407c, etc. The R-407 series is made of three refrigerants R-32, R-125 and R-134a. The last letter in the designation of R-407 indicates different composition ratios of R-32, R-125 and R-134a. For example, R-407c is made of R-32, R-125 and R-134a at a ratio of 23:25:52 based on mass. Similarly, R-410a is one of the R-410 series refrigerants, which are made of two refrigerants R-32 and R-125. The last letter “a” in R-410a indicates that a composition ratio of R-32 and R-125 is 50:50 by mass. Depending on the composition ratio, the last letter can vary.
Several new HFC type refrigerants such as R-134a, R-407c and R-410a have been developed as attempts to optimize the trade-off of flammability versus thermal efficiency. The first R-134a has replaced R-12 for automotive air conditioners, refrigerators and large chillers. This refrigerant has relatively poor heat transfer characteristics but in a typical system produces a pressure of about 8 atm at the evaporator and 16 atm at the condenser. Thus, the relatively small &Dgr;P at the compressor produces excellent efficiency. Therefore, this refrigerant has replaced R-12 for many applications, despite its poor heat transfer characteristics.
A second HFC type refrigerant is R-407c, which is a mixture of R-32, R-125 and R-134a in proportions of 23:25:52 respectively. This mixture, however, produces only about 6 atm at the evaporator and 20 atm at the condenser (like R-22) and has poor heat transfer characteristics due to the high proportion of R-134a.
A third HFC type refrigerant is R-410a, which is a mixture of R-32 and R-125 in a ratio of 50:50 respectively. This mixture, however, produces about 12 atm at the evaporator, but 30 atm at the condenser and requires a large compressor and compressor work.
It would be very desirable to provide a novel refrigeration system, which would permit the use of an non-flammable mixture of refrigerants, a reduced condenser pressure and an increased evaporator pressure; and which takes the best advantage of the properties of the individual fluids of the mixture.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the invention, a novel system and refrigeration process is provided in which the composition of the refrigerants is controlled as the thermal load of the refrigeration system changes with the help of a vortex generator and a storage tank. For example, for the case of R-407c, the density of R-32 is substantially smaller than those of R-125 and R-134a such that R-32 is separated from the R-125 and R-134a using the centrifugal force in the vortex generator. Once R-32 is separated, it can be stored in a storage tank for the low-thermal load operation. In the low thermal load operation, one can take benefits of the preponderance of R-134a, which is low condenser pressure and high EER (energy-efficiency ratio). For the case of a high thermal load operation, R-125 and R-134a, instead of R-32, can be stored in the storage tank such that one can take benefits from the preponderance of R-32 in the system, which is a high cooling capacity.
Co-pending application Ser. No. 09/608,656 filed Jun. 30, 2000 (P/3746-2) describes a novel system and refrigeration process in which a first component (for example, R-134a) is recirculated in the condenser while the other component or components (for example, R-32 and R-125) are directed, without recirculation, to the evaporator to increase evaporator pressure and heat capacity. The component of the circulating refrigerant may be controlled, as by a valve, in the recirculation path to effectively control thermal load variation.
According to a first aspect of the present invention, there is provided a refrigeration system comprising a compressor, a plurality of condensers, positioned in parallel, each having an input and an output, an expansion device, an evaporator, said compressor, said condensers, said expansion device, and said evaporator being connected in a closed circuit and being operative to circulate a refrigerant fluid comprised of a first component having a first density and a second component having a second density, a separator having an input connected to an output of said compressor and outputs connected to the inputs of said condensers, a storage tank, a plurality of first valves selectively connecting the outputs of the condensers as inputs to the storage tank, and a second valve operative to selectively feed the contents of the storage tank into the closed circuit.
According to a second aspect of the invention, there is provided a refrigeration system comprising fluid compressor means, a plurality of fluid condenser means, positioned in parallel, each having an input and an output, fluid expansion means, evaporator means, said compressor means, said condenser means, said expansion means, and said evaporator means being connected in a closed circuit and being operative to circulate a refrigerant fluid comprised of a first component having a first density and a second component having a second density, fluid separator means having an input connected to an output of said compressor means and outputs connected to the inputs of said condenser means, fluid storage means, a plurality of first valve means selectively connecting the outputs of the condenser means as inputs to the storage means, and second valve means operative to
Bai Cheolho
Cho Young I.
Bennett Henry
Drake Malik N.
Ostrolenk Faber Gerb & Soffen, LLP
Vai Holdings, LLC
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