This invention relates to ultra low temperature freezer units, in particular, ultra low temperature (ULT) freezers that have an improved evaporator with an improved capillary feed system on the low stage compressor assembly.
Ultra low temperature (ULT) freezers are typically designed to store and protect critical biological materials. Minus 86° C. freezers are a common product produced by several manufacturers. This type of freezer as well as other ULT freezers operating at even colder temperatures is used for the storage of blood component additives, bone marrow, insect cell culture, mammalian cell culture, nucleic acids (DNA/RNA), sperm, fertilized ova, tissues and viruses.
Referring to
This single length of capillary tube 22 causes the suction pressure of the low stage compressor to run in a substantial vacuum. This vacuum can cause accelerated wear and tear on the crankshaft and connecting rod. In turn, this will drive up the compression ratio of the compressor. Thus, a higher compression ratio can result in the compressor to be running at a pressure exceeding the compressor manufacturer's recommended operating envelope. Of course, operating in such a manner is likely to adversely affect the reliability of the compressor. Further, the flow rate of the refrigerant is reduced in a negative manner. Consequently, longer “pull down” times (the time required for the unit to reach the desired temperature) are experienced. This requires the compressor to run longer as well thus reducing the lifespan of the unit and also increasing operating costs.
As shown in
There is no ULT freezer unit presently available that solves the problems noted above.
It is an aspect of the invention to provide an ULT freezer evaporator apparatus that has a triple feed capillary tube system.
It is another aspect of the invention to provide an ULT freezer evaporator apparatus that prevents a low stage compressor from running in a vacuum.
Another aspect of the invention is to provide an ULT freezer evaporator apparatus that significantly reduces the “pull down” time.
Finally, it is still another aspect of the invention is to provide an ULT freezer evaporator apparatus that significantly increases the transfer area between the evaporator tubing and the contact surface on the unit to assist the transfer of heat from the refrigerated unit through the condenser to the surrounding room.
Referring now to
When the freezer sensor units call for cooling, high stage compressor 40 runs by itself until heat exchanger 42 reaches a temperature of −34 degrees Centigrade. At that time, the controller will start low stage compressor 50 to run with the high stage. The low stage refrigerant will begin to circulate through oil separator 56, downstream to heat exchanger 42 and through filter dryer 60 then to distributor 32 where the refrigerant will be dispersed evenly into three equal length sections 13, 14 and 15 of evaporator invention 10 with each section having capillary tubes 22A, 22B, and 22C inside copper tubing 20A, 20B, and 20C, respectively.
The capillary tubes 22A, 22B, and 22C are of a predetermined diameter and length to cause a predetermined temperature/pressure drop of the refrigerant as it reaches the ⅜ copper tubing 20A, 20B, and 20C that is attached to freezer liner 12. In the example shown in
The three-piece evaporator invention 10 is attached to freezer liner walls 12 with aluminum tape (not shown) to provide better heat transfer. Care must be taken to attach evaporator 10 either level or slightly sloping downhill to aid in refrigerant/oil to return to low stage compressor 50. Refrigerant is fed at the top of the freezer cabinet providing a down feed design, thus letting gravity assist the refrigerant/oil back to compressor 50.
Two sections of evaporator invention 10 are mirror images of each other.
The back section 14 is adjusted by reducing the radius of the turns to achieve the same length as the other two sections 13 and 15. The three-evaporator sections tees into a manifold 34, then back to the compressor 50 as shown
As shown in
As shown in
The use of evaporator invention 10 provides an accelerated “pull down” by providing increased contact area. In fact, when the inventor tested a similar freezer model without evaporator invention 10, it was found that runtime was approximately 40% less to go from ambient temperature to −80 degrees Centigrade.
The high capacity air-cooled condenser 49 features rifled tubing. Having rifled tubing will spin the refrigerant to keep more liquid against the tubing walls for improved heat rejection to the surrounding environment.
Again, referencing
The low stage compressor 50 will start once heat exchanger temperature reaches −34° c. The refrigerant passes through oil separator 56 where the oil is retained through a coalescing filter and falls to the bottom of oil separator 56. The filtered refrigerant exits and enters heat exchanger 42 where heat is rejected to the high stage circuit. The refrigerant exits and enters filter drier 60 where particles and moisture are filtered from the refrigerant. The refrigerant now enters distributor 32 where the pressure evenly disperses the refrigerant into capillary tubes 22A, 22B and 22C to achieve the right temperature/pressure drop and then onward to evaporator sections 13, 14 and 15. Here the refrigerant will absorb heat from conditioned area 12. The refrigerant enters manifold 34 and returns to low stage compressor 50 where the refrigerant is drawn into the combustion chamber. Heat of compression will add heat and raise the pressure of the refrigerant where it exits through the discharge line and the cycle will start again. Both compressors will run until the cabinet sensor is satisfied.
Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the preferred embodiments contained herein.
This application claims benefit of U.S. Provisional Application Ser. No. 61/581,234 filed Dec. 29, 2011, pursuant to 35 USC §119(e).
Number | Date | Country | |
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61581234 | Dec 2011 | US |