Patent Application
20050160754
The present invention generally relates to ultra low temperature upright freezers which are particularly useful in laboratories and other scientific environments.
Several types of upright, ultra low temperature freezers are available, for example, for cooling various scientific products to very low temperatures. One such upright freezer has been available since prior to this invention from Thermo Electron Corp., located in Marietta, Ohio, under its “8600” and “900” series of freezers. These upright freezers use various controls but each traditionally include a single inner chamber cooled by a surrounding “cold wall” type refrigeration system operated by an ultra low temperature refrigeration unit disposed in the base of the freezer. Evaporation or cooling coils run up and down the side walls and back wall of the freezer as well as through the top and bottom walls. No fans are used for cooling the freezer chamber. Cooling is only accomplished by conduction and convection from the freezer walls into the chamber. A single full length upright door is mounted by hinges in a conventional fashion to the front of the freezer to provide access to the chamber. This particular freezer is capable of cooling the chamber to temperatures within the range of about −50 degrees Celsius to −86 degrees Celsius.
A problem which has arisen with such ultra low temperature freezers is that when the front door is opened, the extremely cold and heavy air within the chamber tends to spill out of the bottom of the chamber through the front opening of the freezer. Often, these freezers are used for containing items which must be maintained at a low temperature and which must be accessible in a repeated fashion throughout the day. The extremely cold and relatively heavy air sinks to the bottom of the freezer and spills or falls out the bottom of the front door opening resulting in a substantial loss of cold air every time the door is opened. The cold air that spills from the chamber is replaced by warm, moist ambient air. Due to the low temperatures maintained within the chamber, when the front door is closed, the moisture in the air quickly condenses to a solid, usually in the form of a frosting layer along the cold walls of the chamber. Moreover, removing the moisture from the air causes the pressure within the chamber to decrease creating a partial vacuum within the chamber. This pressure differential between the chamber and the ambient makes it difficult to reopen the freezer door without the application of excessive force.
Several previous ultra low temperature freezer designs provide for vacuum relief by including a vacuum relief port that draws air into the chamber when a pressure difference develops between the chamber and the ambient. The vacuum relief port generally includes some type of valve mechanism that opens when a vacuum is created within the chamber. Previous vacuum relief ports, however, have some drawbacks, such as becoming blocked with solid condensate and therefore requiring regular maintenance for proper operation. To this end, as the ambient air is pulled through the vacuum relief port, the moisture in the air quickly condenses and forms frost or ice within the relief port. Over a relatively short period of time, sometimes less than a day, depending on the usage of the ultra low temperature freezer, the frost or ice will accumulate so as to substantially occlude the port thereby preventing the relief of the vacuum within the chamber. To prevent the frost from occluding the port, the port must be cleared of any frost or ice on a regular basis.
It would therefore be desirable to provide an ultra low temperature freezer which allows repeated access to items contained therein without the application of excessive force and without the regular maintenance required for previous vacuum relief ports.
The present invention provides an improved ultra low temperature freezer that includes a vacuum relief assembly that relieves a vacuum created within the freezer chamber upon opening and closing the freezer door. An ultra low temperature freezer has a freezer chamber surrounded by an external environment and contained by insulated peripheral walls including a pair of side walls, a top wall, a bottom wall, a rear wall, and an insulated door hingedly secured to one of the side walls. The vacuum relief assembly comprises tubing having an inlet port open to the external environment and an outlet port open to the freezer chamber. The inlet port and exit port are in fluid communication with each other. The vacuum relief assembly further includes a first valve coupled to the tubing having an open and closed position. In the open position, the external environment and the freezer chamber are in fluid communication and fluid may flow through the valve. In the closed position, fluid is prevented from flowing through the valve. The vacuum relief assembly further includes a heating element coupled to the tubing and operable to apply heat thereto so as to prevent condensation from occluding the tubing.
The vacuum relief assembly may further include an activation switch operatively coupled to the heating element and operable to cause the heating element to produce heat. The activation switch may be further operatively coupled to freezer operations, such as opening or closing the freezer door or moving a latching handle on the freezer door. Moreover, the vacuum relief assembly may further include a timing circuit operatively coupled to the heating element and operable to cause the heating element to stop producing heat after a predetermined period of time. Alternatively, or in addition to the timing circuit, the vacuum relief assembly may include a thermal switch operatively coupled to the heating element and operable to cause the heating element to stop producing heat when at least a portion of the tubing reaches a specified temperature.
In one embodiment, the vacuum relief assembly is carried by the freezer door and includes a latching handle mounted to the freezer door and moveable between a first and second position. When the latching handle is in the first position, fluid is prevented from flowing between the external environment and the freezer chamber. When the latching handle is in the second position, fluid is permitted to flow between the external environment and the freezer chamber. The activation switch causes the heating element to produce heat when the latching handle is placed in the second position.
To relieve a vacuum in the freezer chamber, a user moves the latching handle from the first position to the second position thereby exposing the inlet port to ambient pressure. If a vacuum exists within the freezer chamber, fluid flows through the inlet port, through the exit port and into the freezer chamber. This equalizes the pressure between the freezer chamber and the external environment such that the freezer door may be opened without excessive force. Moreover, moving the latching handle to the second position energizes the heating element. The application of heat removes any condensation that may occlude the tubing such that when the freezer door is subsequently reopened, the tubing is free of condensation and vacuum relief may occur. A user then closes the freezer door and moves the latching handle from the second position to the first position, thereby preventing fluid communication between the external environment and the freezer chamber.
In another embodiment of the invention, the vacuum relief assembly includes tubing comprising a housing having a first and second end. The first end of the housing is configured as the inlet port open to the external environment. The tubing further includes a porting tube having a first end coupled to the second end of the housing. The second end of the porting tube is configured as the exit port open to the freezer chamber. A first valve, configured as a check valve, is coupled to the housing and has a open and closed position. When a vacuum is created within the freezer chamber, the check valve opens to allow fluid to flow into the chamber and relieve the vacuum. A heater, configured as a positive temperature coefficient heater is thermally coupled to the porting tube and operable to apply heat thereto so as to prevent condensation from occluding the tubing.
By virtue of the foregoing, an ultra low temperature freezer includes a vacuum relief assembly to relieve a vacuum often created upon opening and closing the freezer door. These and other objects and advantages of the invention shall be made apparent from the accompanying drawings and the description thereof.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description of the invention given above and the detailed description of the embodiments given below, serve to explain the present invention.
With reference to
In reference to
As shown in the exemplary embodiment of
Because a goal of the ultra low temperature freezer 10 is to keep the contents (not shown) of the freezer chamber 12 at a low temperature, it can be counter productive and potentially harmful to the freezer contents to provide a heat source, such as heater 38, near the freezer chamber 12. In order to minimize the effects of heater 38, or other heat source, on freezer operation and freezer contents, the vacuum relief assembly 28 may further include an activation switch 40 that energizes heater 38 and causes heater 38 to produce heat along at least a portion of tubing 36. In this way, heater 38 does not operate in a continuous manner, so as to, for example, keep exit port 34 at a constant temperature above the dew point temperature, but may be operated in a selective manner so that heater 38 may be energized on the happening of a certain event, such as for example the opening or closing of door 24. The activation switch 40 may be a manual type of switch wherein a user positions the switch in a first position that activates heater 38. Alternatively, activation switch 40 may be tied to a user's normal operation of the freezer. For example, activation switch 40 may be a magnetic switch that detects the opening or closing of freezer door 24. In this way, when door 24 is placed in the open position after having been in the closed position, the activation switch 40 energizes heater 38 and causes heater 38 to produce heat. Activation switch 40 may also activate heater 38 by placing door 24 in the closed position after having been in the open position.
To keep heater 38 from continuously operating after having been energized by activation switch 40, vacuum relief assembly 28 may further include a timing circuit 42 that causes heater 38 to stop producing heat after a predetermined period of time. Thus after having been energized by activation switch 40, such as by opening the freezer door 24, timing circuit 42 provides power to heater 38 so as to produce and apply heat to tubing 36 to defrost the exit port 34 or a portion of tubing 36. After the predetermined period of time, timing circuit 42 cuts power to heater 38 so that heater 38 stops producing heat. In this way, the exit port 34 and tubing 36 may be cleared of any frost or other condensation so that a vacuum in freezer chamber 12 may be relieved without significantly affecting freezer operation or harming freezer contents. The amount of time required to clear the exit port 34 and/or tubing 36 depends on several factors, including the temperature inside the freezer chamber 12 and the amount of frost or condensation formed in the exit port 34 or tubing 36. It is contemplated that under most circumstances, energizing heater 38 for between approximately three to five minutes will clear the condensation without adversely affecting the freezer contents. The invention, however, is not so limited and timing circuit 42 may provide for adjusting the amount of time heater 38 remains energized.
Alternatively, to prevent heater 38 from operating in a continuous manner, vacuum relief assembly 28 may further include a thermal switch 44, such as for example a thermostat, in conjunction with heater 38. Thermal switch 44 may be adapted to monitor the temperature of the exit port 34 or a portion of tubing 36 and cause heater 38 to stop producing heat when the exit port 34 or portion of tubing 36 reaches a specified temperature. Thus after having been energized by activation switch 40, such as by opening the freezer door 24, the thermal switch 44 provides power to heater 38 so as to produce heat and apply it to tubing 36 to defrost the exit port 34 or a portion of tubing 36. When the exit port 34 or portion of tubing 36 reaches the specified temperature, thermal switch 44 cuts power to heater 38 so that heater 38 stops producing heat. The exit port 34 and tubing 36 may be cleared of any condensation so that a vacuum in freezer chamber 12 may be relieved without significantly affecting freezer operation or harming freezer contents. The specified temperature at which heater 38 stops producing heat may be set at, for example, 10° C. The invention, however, is not so limited and thermal switch 44 may provide for adjusting the temperature at which the heater 38 stops producing heat. It should also be realized that timing circuit 42 and thermal switch 44 may be used in combination with each other to prevent the exit port 34 or portion of tubing 36 from reaching, for example, a maximum specified temperature during the predetermined period of time. In this way, thermal switch 44 acts as a safety switch in the event timing circuit 42 fails or power is not cut to heater 38.
In further reference to
In continued reference to
As shown in
When latching handle 26 is in the first position, as shown in
In addition, latching handle 26 may activate heater 38. Activation switch 40 may be configured such that when freezer door 24 is to be opened and latching handle 26 is moved to the second position, activation switch 40 energizes heater 38 and causes heater 38 to produce heat. It should be recognized, however, that activation switch 40 can activate heater 38 by placing latching handle 26 in the first position, such as when closing the freezer door 24.
As shown in
In
Check valves are well known in the art and may, for example, be commercially obtained through Neoperl Inc. located in Waterbury, Conn. Check valve 72 has an open and closed position and permits fluid communication between the external environment 32 and freezer chamber 12 when in the open position and prevents fluid communication when in the closed position. When the pressure at the inlet port 62 is greater than the pressure at the exit port 64, such as when a vacuum is created within freezer chamber 12, the check valve automatically opens and fluid may flow from the inlet port 62 to exit port 64. As the pressure between the freezer chamber 12 and external environment 32 equalizes, the check valve 72 moves toward the closed position to seal the fluid communication path.
As shown in the embodiment in
The operation of the ultra low temperature freezer 10 having the vacuum relief assembly 60 incorporated therein works in a manner similar to that shown and described above. In particular, vacuum relief assembly 60 includes an activation switch 40 that energizes heater 74 and causes heater 74 to produce heat along at least a portion of porting tube 70. Activation switch 40 may be a manual type of switch, but is preferably tied to the normal operation of the freezer, such as by opening or closing the freezer door 24. In this way, when door 24 is placed in the open position after having been in the closed position, the activation switch energizes heater 74 and causes heater 74 to produce heat. Activation switch 40 may alternately activate heater 74 by placing door 24 in the closed position after having been in the open position.
Vacuum relief assembly 60 may further include a timing circuit 42 that causes heater 74 to stop producing heat after a predetermined period of time. Thus, after having been energized by activation switch 40, such as by opening freezer door 24, timing circuit 42 provides power to heater 74 so as to produce and apply heat to porting tube 70 to defrost the exit port 64 or a portion of porting tube 70. After the predetermined period of time, timing circuit 42 cuts power to heater 74 so that heater 74 stops producing heat. In this way, the exit port 64 may be cleared of any frost or other condensation so that a vacuum in freezer chamber 12 may be relieved without significantly affecting freezer operation or harming freezer contents. As with the previous embodiment, it is contemplated that under most circumstances, energizing heater 74 for between approximately three to five minutes will clear the condensation without adversely affecting the freezer contents. The invention, however, is not so limited as timing circuit 42 may provide for adjusting the amount of time heater 74 remains energized.
The heater 74 is preferably a PTC thermistor heater. This type of heater is inherently self-regulating so as to prevent an overheating or a run away heating condition that would adversely affect the contents in freezer chamber 12. To this end, the PTC heater advantageously contains a ceramic heating element having an electrical resistance that depends on the temperature of the ceramic heating element. This characteristic allows the PTC heater to be effectively self-regulating so as to operate at an equilibrium temperature, called the switch temperature, as will now be explained. When a constant voltage source is applied across the heating element and the heating element is, for example, at its equilibrium point, the resistance of the heating element and the current flowing through the heater are such that the generated resistance heating, defined by I2R, is equal to the heat loss from the heating element, thus maintaining equilibrium. If the heat loss from the heating element decreases, the temperature of the heating element increases. As the temperature of the heating element increases, so does its electrical resistance causing the current flowing through the heating element to decrease. This in turn causes the generated resistance heating to decrease, thus decreasing the temperature of the heating element toward the switch temperature.
Conversely, if the heat loss from the heating element increases, the temperature of the heating element decreases. As the temperature of the heating element decreases, so does its electrical resistance causing the current flowing through the heating element to increase. This in turn causes the generated resistance heating to increase, thus increasing the temperature of the heating element toward the switch temperature. In this way, the PTC heater is thus self regulating so as to have a temperature approximately equal to its switch temperature. Moreover, by varying the materials of the ceramic heating element, the switch temperature may be selectively chosen for a particular application. For example, a PTC heater having a switch temperature of approximately 40° C. may be used in the invention and is commercially available through DBK, Inc. located in Cincinnati, Ohio. PCT heaters are advantageous because the self-regulating feature allows for the elimination of a thermal switch 44, such as a thermostat, or other circuitry designed to cut power to heater 72 in the event activation switch 40 fails.
While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept.
This claims the benefit of U.S. Provisional Application Ser. No. 60/538,813, filed Jan. 23, 2004 and herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60538813 | Jan 2004 | US |
