Refrigeration – Cryogenic treatment of gas or gas mixture – Solidification
Reexamination Certificate
2002-04-16
2003-07-01
Tapolcai, William E. (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Solidification
C062S384000
Reexamination Certificate
active
06584802
ABSTRACT:
TECHNICAL FIELD
The invention relates to a cooling apparatus and method that uses carbon dioxide (CO
2
) to cool, refrigerate or freeze; and more particularly to a portable device preferably embodied in a selfcontained refrigeration system that cools indirectly with liquid carbon dioxide, utilizing the sublimation of CO
2
“dry-snow” to self-regulate the flow of the CO
2
refrigerant in the system.
BACKGROUND OF THE INVENTION
Carbon dioxide (CO
2
), in its liquid and solid forms is employed in many commercial, industrial and to some extent residential refrigeration, freezing and cooling applications. Under normal, atmospheric pressure, CO
2
can only exist as a gas at ambient temperatures or a chilled solid that sublimates into the gas at minus 109.3 degrees, Fahrenheit. However, if pressurized, gaseous CO
2
forms a liquid with a water-like viscosity. CO
2
is a desirable refrigerant because it is colorless and typically odorless. It is also chemically inert under ordinary conditions.
Because CO
2
is inexpensive to manufacture and has little potential for adverse environmental impact in small quantities, it is often employed as a disposable refrigerant. Several U.S. patent references utilize the unique properties of CO
2
in re-chargeable types of refrigeration, freezing and cooling systems.
U.S. Pat. No. 3,561,226 Rubin describes a refrigeration system for vehicles that includes a minimum of moving parts. Rubin '226 employs a liquid reservoir of carbon dioxide to fill a set of containers with densely packed “snow.” The filling of the container with carbon dioxide is activated by a timed solenoid valve, or alternatively a manual valve. CO
2
vapor passes out of each container, while CO
2
snow is trapped by a screen, backing up the snow into the container. A portable refrigeration system is needed that better utilizes liquid CO
2
to more evenly generate a self regulated refrigeration effect, rather than the expansion of liquid CO
2
into a trough or bin container.
Similarly, to Rubin '226, U.S. Pat. No. 4,704,876 to Hill shows a cryogenic refrigeration system that uses carbon dioxide snow formed by spraying CO
2
through a series of nozzles within a snow collection compartment. The compartment is open to a refrigerated space, below. This feature is undesirable because the cargo is directly exposed to the frigid CO
2
snow, which can result in damage to the cargo, especially if it is perishable fruits or vegetables. Control is achieved with temperature sensors in the refrigerated compartment that opens a valve to deliver more liquid CO
2
to the nozzles, or alternatively by manual valving. Hill '876 also requires that the nozzles remain “free and open” of solid CO
2
.
U.S. Pat. No. 4,381,649 to Franklin discloses a CO
2
snow producer that includes spray nozzles for directing jets of liquid carbon dioxide onto a surface of a heat exchanger. The pressure at the nozzles of Franklin '649 is approximately 75 psi and the temperature in the supply line to the nozzle is maintained near minus 69° F., as a goal. From the Franklin disclosure, control of the system is achieved through what appears to be a manual control valve at the tank of liquid CO
2
.
Several problems are encountered in Ruben '226, Franklin '649 and Hill '876 when the temperature feedback is disabled or malfunctions, the timer is set incorrectly, or the operator fails to activate or deactivate the system as needed. Direct, on/off control by an operator is especially unreliable in that the system can over-cool, with an over production of CO
2
snow risking damage to the refrigerated contents or to the operators. Under cooling can also cause undesirable effects in the unwanted thawing or spoiling of refrigerated articles. A CO
2
refrigeration system is needed that employs a simple design but eliminates the need for an on/off CO
2
control valve that directly meters the release of CO
2
into a refrigerated space.
REFERENCES:
patent: 1997151 (1935-04-01), Maiuri
patent: 2096255 (1937-10-01), MclIrath
patent: 3757367 (1973-09-01), Campbell
patent: 4111671 (1978-09-01), Williamson
patent: 4145894 (1979-03-01), Frank et al.
patent: 4399658 (1983-08-01), Nielsen
patent: 5566553 (1996-10-01), Gibot et al.
patent: 5924181 (1999-07-01), Takasugi
patent: 6023941 (2000-02-01), Rhoades
patent: 6109058 (2000-08-01), Franklin, Jr.
Cofield Monty J.
Wheeler Scott B.
Stratton Ballew PLLC
Tapolcai William E.
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