Patent Application
20110146302
The present apparatus and methods are related to heat exchangers and refrigeration systems used with for example with food products.
In known thermoacoustic refrigeration systems, warm and cold temperatures may be formed at opposed ends of a heat exchanger stack for the system. Heat exchangers are usually disposed at either end of the stack to transfer heat away from the process and to distribute cooling to a system which requires refrigeration and hence there is provided a “warm end” and a “cold end” of the stack. A temperature differential in the stack or the ability of the refrigeration system to achieve colder temperatures is dictated by the ability of the heat exchanger at the warm end to remove system heat. Known systems use at the warm end air and water for example as a means of cooling to remove heat from the stack.
For a more complete understanding of the present embodiments, reference may be had to the following drawings taken in connection with the description of the embodiments, of which:
In
In the present embodiments, a liquid or gaseous cryogen, such as for example carbon dioxide, nitrogen, argon or liquid air, is introduced at an inlet of a pipe or conduit 22 and passed through the warm end heat exchanger 18 to cool the cool end 20 of the stack 14. The cryogen used with the heat exchanger 18 cools the warm end of the stack 14 which has been heated from the acoustic waves of the wave generator 12. Such cryogen provides temperatures much colder than that which can be realized in heat exchange of known systems. The warming and expansion of the cryogenic fluid in the heat exchanger 18 results in a cryogenic gas being emitted at an outlet pipe 24 of the heat exchanger 18.
At the cold end heat exchanger 20, a cooling fluid which can be cryogen but can also be air, helium, glycol, argon, oxygen or other fluid used for cooling, is introduced in liquid or gaseous phase at inlet pipe 26 so that the fluid is cooled at the heat exchanger 20 and removed at outlet 28 of the heat exchanger 20 to be used for a refrigeration process for example. In effect, the cryogen introduced at the inlet pipe 22 is used to remove heat from the stack 14, while at the same time substantially cooling the fluid introduced at inlet 26 so that same can be used in subsequent refrigeration or cooling processes after it has been emitted from the heat exchanger 20 through the outlet pipe 28. The cryogenic liquid being used at least at the heat exchanger 18 provides for substantially cooling fluid at the heat exchanger 20 for such refrigeration processes. The temperature of the fluid in the outlet pipe 28 can be 100°-150° F. colder than the temperature of the cryogen at the heat exchanger 18.
The temperature differential in the stack 14 or the ability of the device 10 to reach colder temperatures is realized by the use of the cryogenic fluid introduced at the pipe 22. Sound waves generated by the acoustic wave generator 12 are always moving in the stack 14 and therefore, such movement provides an increase in heat which must accordingly be controlled and reduced by use of the heat exchanger 18. To accommodate at least the reduced temperatures of the cryogenic fluid, the heat exchanger 18 is constructed from a highly conductive material such as monocrystalline synthetic diamond, which material has the highest thermal conductivity of any known solid at room temperature, i.e. 2,000-2,500 W m/m2 K (200-250 W mm/cm2 K). At these lower temperatures, conductivity becomes more effective and more efficient as Fermi electrons can match the phononic normal transport mode near the Debye point, and transport heat more swiftly, to overcome the drop of specific heat with the fewer quantal microstates, to reach 41,000 W m/m2 K at 104° K (Kelvin). This is only one example of possible heat exchanger materials. Any highly conductive material can be used. However, the greater the thermal conductivity of the material the more effective the process. Copper or copper-nickel alloys can also be used for at least the heat exchanger 18.
Two other exemplary embodiments of the present apparatus and methods are illustrated in
Referring now to
In the embodiment of
Referring to
A drive shaft 68 is constructed and arranged for rotational movement as indicated by arrows 70, and is coupled at one end to the piston assembly 62 and, at an opposed end to an electric motor 72. The electric motor is connected to and obtains power from a power source 74.
Interposed between the generator 60 and the electric motor 72 is a gas motor 76 into which the exhaust from the pipe 324 is introduced. The gas motor 76 is also connected to the drive shaft 68. The high pressure nitrogen gas is used to power the gas motor and provide mechanical energy for the process. The gas motor 76 is also mechanically connected to the drive shaft 68 to rotate same. That is, electric motor 72 and the gas motor 76 coact to rotate the shaft 68. In effect, use of the gas motor 76 reduces the power demand of the electric motor 72 in order to rotate the shaft 68, thereby reducing the cost to operate the electric motor 72 and to generate the sound waves 61. As shown in
For all embodiments discussed above, the cryogenic fluid can be selected from carbon dioxide, nitrogen, argon and liquid air. The coolant fluid or medium introduced to the cool end of the heat exchanger can be a cryogen as well, or can be selected from any type of coolant fluid, such as for example air, helium, glycol, argon, oxygen. The heat exchangers 218, 318 at least may also be constructed from the same materials as the heat exchanger 18.
The present embodiments provide for colder operating temperatures at heat exchangers and refrigeration systems to which they are connected. As a result, the overall efficiency of the freezing process is realized.
It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the embodiments. All such variations and modifications are intended to be included within the scope of the embodiments as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments may be combined to provide the desired result.
