LIQUID CO2 PASSIVE SUBCOOLER
A heat exchanger associated with a duct for a first fluid including: a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; upper and lower duct portions in fluid communication with the central duct portion including stationary upper and lower duct portions and movable upper and lower duct portions having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion and enclosing the coiled conduit; and, a refrigeration apparatus and process including the same.
The present embodiments relate to utilizing energy contained in the gaseous refrigerant exhaust of a refrigeration chamber to pre-cool the liquid refrigerant entering the refrigeration chamber, resulting in a more efficient use of refrigerant.
Conventional refrigeration processes take various structural forms and utilize various cooling processes. One such process utilizes pressurized liquid refrigerants, such as CO2, which are flashed upon entering the refrigeration chamber. When CO2 is utilized, the flash typically results in about 48% solid CO2 and about 52% gaseous CO2, at a temperature of about −109° F. (−78.3° C.). The solid CO2 contacts the items which are to be frozen and sublimates, thereby extracting heat from the item to be frozen. Other refrigerants, such as N2, act in a similar manner, except that the phase change usually results in a mixture of liquid and gas, and the cooling effect is provided by the liquid refrigerant evaporating upon contact with the item to be frozen.
Regardless of the refrigerant used, gaseous refrigerant must be exhausted from the refrigeration chamber. Such gaseous refrigerant typically exits the refrigeration chamber at temperatures which are much lower than the temperature at which the pressurized liquid refrigerant enters the refrigeration chamber. The gaseous refrigerant thus expels into the outside environment much of the energy used to produce the pressurized liquid refrigerant. Therefore, in order to increase the efficiency of such refrigeration chambers, it is desirable to harness the energy of the gaseous exhaust in order to pre-cool the liquid refrigerant before it enters the refrigeration chamber.
A refrigeration process embodiment is provided which includes supplying liquid CO2 into a refrigeration chamber, flashing the liquid CO2 into gaseous CO2 and solid CO2 to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO2 from the refrigeration chamber, wherein the liquid CO2 passes through a tube-side of a shell-and-tube heat exchanger prior to entering the refrigeration chamber, and the gaseous CO2 passes through a shell-side of the shell-and-tube heat exchanger after exiting the refrigeration chamber, thereby pre-cooling the liquid CO2 prior to entering the refrigeration chamber.
A refrigeration apparatus embodiment is provided, which includes a refrigeration chamber; a liquid CO2 storage apparatus for providing liquid CO2 at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO2 and CO2 snow; and a heat exchanger disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO2 prior to said flashing; wherein the heat exchanger is a shell-and-tube heat exchanger adapted to receive the liquid CO2 through a tube-side inlet of the heat exchanger and to receive the gaseous CO2 through a shell-side inlet of the heat exchanger after the gaseous CO2 exits the refrigeration chamber, thereby pre-cooling the liquid CO2 prior to the liquid CO2 exiting a tube-side outlet of the heat exchanger and entering the refrigeration chamber.
In certain embodiments, the heat exchanger associated with a duct, such as an exhaust duct, may comprise a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions; a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.
In certain embodiments, the liquid CO2 enters the tube side of the shell-and-tube heat exchanger at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the tube side of the shell-and-tube heat exchanger at about −25° F. (−31.7° C.) to about −5° F. (−20.6° C.). The pressure of the liquid CO2 is substantially the same at entry and exit of the tube side of the shell-and-tube heat exchanger, in certain embodiments the pressure being from about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).
In a further embodiment, the gaseous CO2 enters the shell side of the shell-and-tube heat exchanger at about −80° F. (−62.2° C.) and about atmospheric pressure and exits the shell side of the shell-and-tube heat exchanger at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.
In certain embodiments, the liquid CO2 enters the at least one coiled tube of the heat exchanger at about −10° F. (−23.3° C.) to about 2° F. (−16.7° C.) and exits the at least one coiled tube of the heat exchanger at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.).
In a further embodiment, the gaseous CO2 enters the shell of the heat exchanger at about −90° F. (−67.8° C.) and exits the shell of the heat exchanger at about −31° F. (−35.0° C.) to about −20° F. (−28.9° C.).
Greater than about 48%, and, in certain embodiments, at least about 55% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber.
In certain embodiments, the shell-and-tube heat exchanger is a one pass tube-side straight-tube heat exchanger, a two pass tube-side straight-tube heat exchanger, or a U-tube heat exchanger.
For a more complete understanding of the present embodiments, reference may be made to the following description taken in conjunction with the following drawings, of which:
A process is provided for utilizing the energy contained in the gaseous refrigerant exhaust of a refrigeration chamber in order to pre-cool the liquid refrigerant entering the refrigeration chamber, resulting in a more efficient use of refrigerant.
Provided is a refrigeration process comprising supplying liquid CO2 into a refrigeration chamber, flashing the liquid CO2 into gaseous CO2 and solid CO2 within the refrigeration chamber in order to create a cooling effect, and exhausting gaseous CO2 from the refrigeration chamber, wherein the liquid CO2 passes through a tube-side of a shell-and-tube heat exchanger prior to entering the refrigeration chamber, and the gaseous CO2 passes through a shell-side of the shell-and-tube heat exchanger after exiting the refrigeration chamber, thereby pre-cooling the liquid CO2 in the heat exchanger prior to entering the refrigeration chamber.
Heat exchangers are well known in the art of refrigeration, and any suitable type of heat exchanger may be used for the purposes of the present process, as determined by one of skill in the art, and may include various types of shell-and-tube heat exchangers.
The heat transfer resulting in the cooling or freezing which takes place within the refrigeration process results generally from sublimation of the solid CO2 which contacts the items which are disposed within the refrigeration chamber. Thus, an increased amount of solid CO2 will result in a more efficient cooling process. By pre-cooling the liquid CO2 entering the refrigeration chamber, a greater percentage of the liquid CO2 is converted into solid CO2 via the flash, that is, having conversion to greater than 48% solid CO2 (or “snow”).
In certain embodiments, the liquid CO2 enters the tube side of the shell-and-tube heat exchanger at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the tube side of the shell-and-tube heat exchanger at about −25° F. (−31.7° C.) to about −5° F. (−20.6° C.). The pressure of the liquid CO2 is substantially the same at entry and exit of the tube side of the shell-and-tube heat exchanger, in certain embodiments the pressure being from about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).
It is desirable that the pressure through the tube-side of the shell and tube heat exchanger remain substantially the same because a pressure drop through the tube-side may result in instability of the liquid stream, creating undesirable results such as solid CO2 buildup within the tube-side of the heat exchanger.
In certain embodiments, the gaseous CO2 enters the shell side of the shell-and-tube heat exchanger at about −80° F. (−62.2° C.) and about atmospheric pressure and exits the shell side of the shell-and-tube heat exchanger at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.
Greater than about 48%, and, in certain embodiments, at least about 55% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber, and the temperature of said resulting gaseous CO2 and solid CO2 is less than about −109° F. (−78.3° C.). This results in a more efficient use of CO2, resulting in cost savings due to a reduction in the amount of CO2 required to achieve a desired refrigeration temperature.
Referring now to
Referring now to
In further embodiments, the shell-and-tube heat exchanger may comprise at least one of a one pass tube-side straight-tube heat exchanger, a two pass tube-side straight-tube heat exchanger, or a U-tube heat exchanger.
By a “coiled tube” or “coiled conduit”, what is meant is any conduit which is oriented and/or constructed in such a manner as to allow the exhaust gas to move between and around multiple passes of the tubes or conduits as it travels through the shell, providing a heat-exchange relationship between the liquid within the tube or conduit and the gas moving through the shell.
For example, the exhaust CO2 gas 214 may contain any or all of the following contaminants, without limitation: entrained water in the form of ice crystals or water vapor as a result of mixing with environmental air within the refrigeration process/apparatus; entrained water from the products which are being cooled and/or frozen within the refrigeration process/apparatus; and/or food particles from the products which are being cooled and/or frozen within the refrigeration process/apparatus. If these or other contaminants are allowed to build-up on the heat exchange surfaces, such as the surfaces of the coiled tube 212, the heat exchange efficiency may be greatly reduced. By utilizing a shell which is at least partially movable and/or removable, such as the shell 210, the coiled tube 212 may be accessed to at least partially remove some or all of the contaminants, thereby restoring the heat exchange efficiency.
For example, in certain embodiments, latches may be utilized on multiple portions of the shell in order to only partially, or perhaps completely, remove the shell from the heat exchanger so that the tube and/or conduits may be easily accessed for cleaning and/or maintenance. In another embodiment, such as that shown in
The present refrigeration apparatus and process utilizes cold exhaust CO2 gas (typically at about −90° F. (−67.8° C.)) flowing over the outside of a spiral-wound heat exchanger coil, such as that depicted in
Liquid CO2 is provided to the tube-side of the heat exchanger at 1.7° F. (−16.8° C.) and 300 psig (2,068 kPa). The specific enthalpy of the saturated liquid stream before entering the heat exchanger is 19.6 BTU/lb (45.6 kJ/kg). Exhaust CO2 in gaseous form exiting the refrigeration chamber is provided to the shell-side of the heat exchanger at −80° F. (−62.2° C.) and about atmospheric pressure. The enthalpy of the gaseous stream before entering the heat exchanger is 139.1 BTU/lb (323.5 kJ/kg). The exhaust comprises 80% of the liquid CO2 which enters the refrigeration chamber. This process warms the exhaust gas by 30° F. (−1.1° C.), therefore, the enthalpy of the gaseous stream exiting the heat exchanger would be 145 BTU/lb (337.3 kJ/kg) at a temperature of −50° F. (−45.6° C.).
The calculation to determine the subcooling achieved is: mass flow of the liquid stream times the change in enthalpy of the liquid stream is equal to mass flow of the gaseous stream times the change in enthalpy of the gaseous stream. Thus, where X will be the enthalpy of the liquid stream exiting the heat exchanger:
100×(19.6 BTU/lb−X)=80×(150.9 BTU/lb−145 BTU/lb)
Therefore, X is equal to 14.9 BTU/lb (34.7 kJ/kg), which corresponds to a liquid CO2 temperature of approximately −8° F. (−22.2° C.) at 300 psig (2,068 kPa).
Without precooling, the heat of vaporization of saturated liquid CO2 at 1.7° F. (−16.8° C.) and 300 psig (2,068 kPa) is 119.3 BTU/lb (277.5 kJ/kg). Utilizing the subcooler process according to the exemplified embodiment will result in a new heat of vaporization of 119.3 BTU/lb+change in enthalpy of the liquid CO2 stream (19.6 BTU/lb−14.9 BTU/lb, or 4.7 BTU/lb). The new heat of vaporization of the now subcooled liquid stream will be 124.0 BTU/lb.
The increase in efficiency provided by the present process, utilizing a liquid CO2 subcooler process can be determined by the following formula:
This results in an efficiency increase of 3.8%, which shows that less CO2 can be utilized in the refrigeration process.
The foregoing is just one non-limiting example illustrating a potential freezing efficiency increase obtained with one embodiment of the subject process. The gains in freezing efficiency increase with the increase in the temperature differential of the exhaust gas through the heat exchanger.
A first embodiment of the subject apparatus and/or process includes a heat exchanger associated with a duct for a first fluid comprising: a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions; a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.
A second embodiment of the subject apparatus and/or process comprises a refrigeration apparatus comprising: a refrigeration chamber; a liquid CO2 storage apparatus for providing liquid CO2 at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO2 and CO2 snow; and the heat exchanger of the first embodiment, wherein the at least one conduit is disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO2 prior to said flashing; the second fluid is liquid CO2 flowing through the at least one conduit and the first fluid is gaseous CO2 flowing through the shell after the gaseous CO2 exits the refrigeration chamber, thereby pre-cooling the liquid CO2 prior to the liquid CO2 exiting the at least one conduit of the heat exchanger and entering the refrigeration chamber.
A third embodiment of the apparatus and/or process comprises a refrigeration process, comprising supplying liquid CO2 into a refrigeration chamber, flashing the liquid CO2 into gaseous CO2 and solid CO2 to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO2 from the refrigeration chamber, wherein the liquid CO2 is the second fluid passing through the at least one conduit of the heat exchanger of the first embodiment prior to entering the refrigeration chamber and the gaseous CO2 is the first fluid passing through the shell of the heat exchanger after exiting the refrigeration chamber when the valve is in the closed position and the movable upper duct portion and lower duct portion are in their open positions, thereby pre-cooling the liquid CO2 prior to entering the refrigeration chamber.
Any or all of the first, second or third embodiments may further include that, when the valve is in the open position, and the movable upper duct portion and the movable lower duct portion are in the closed positions, the first fluid passing through the duct passes substantially through the central duct portion.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that when the valve is in the closed position, and the movable upper duct portion and the movable lower duct portion are in their opened positions, the first fluid passing through the duct passes within the shell and around the at least one coiled conduit, thereby allowing heat to be transferred between the first fluid passing within the shell and the second fluid passing through the at least one conduit.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the valve is a quarter-turn valve.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the shell comprises at least two portions which are movably and/or removably engaged on at least one side of the heat exchanger, allowing the shell to be opened such that the at least one conduit can be accessed from exterior to the shell, and wherein the at least two portions are removably engaged on another side of the heat exchanger.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the liquid CO2 enters the at least one conduit at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the at least one conduit at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.), wherein the pressure of the liquid CO2 is substantially the same at entry and exit of the at least one conduit of the heat exchanger.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the pressure of the liquid CO2 as it passes through the heat exchanger is about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the gaseous CO2 enters the shell of the heat exchanger at about −90° F. (−67.8° C.) and about atmospheric pressure and exits the shell at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that greater than about 48% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, that at least about 55% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber.
Any or all of the preceding embodiments may further include, in addition to or in the alternative, opening the valve and closing the movable upper duct portion and the movable lower duct portion, whereby the gaseous CO2 flows substantially through the central duct portion.
The preceding embodiment may further include opening the shell to access the at least one conduit.
The preceding embodiment may further include cleaning, sanitizing, and/or maintaining at least a portion of the at least one conduit.
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 invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.
Claims
1. A heat exchanger associated with a duct for a first fluid comprising:
- a central duct portion in fluid communication with the duct having an interior space and an exterior surface;
- a valve having opened and closed positions engageable within the interior space of the central duct portion;
- at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion;
- an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions;
- a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and
- an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.
2. The heat exchanger of claim 1, wherein when the valve is in the open position, and the movable upper duct portion and the movable lower duct portion are in their closed positions, the first fluid passing through the duct passes substantially through the central duct portion.
3. The heat exchanger of claim 1, wherein when the valve is in the closed position, and the movable upper duct portion and the movable lower duct portion are in their opened positions, the first fluid passing through the duct passes within the shell and around the at least one coiled conduit, thereby allowing heat to be transferred between the first fluid passing within the shell and the second fluid passing through the at least one conduit.
4. The heat exchanger of claim 1, wherein the valve is a quarter-turn valve.
5. The heat exchanger of claim 1, wherein the shell comprises at least two pieces which are movably and/or removably engaged on at least one side of the heat exchanger, allowing the shell to be opened such that the at least one conduit can be accessed from exterior to the shell, and wherein the at least two portions are removably engaged on another side of the heat exchanger.
6. A refrigeration apparatus comprising: a refrigeration chamber; a liquid CO2 storage apparatus for providing liquid CO2 at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO2 and CO2 snow; and the heat exchanger of claim 1, wherein the at least one conduit is disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO2 prior to said flashing; the second fluid is liquid CO2 flowing through the at least one conduit and the first fluid is gaseous CO2 flowing through the shell after the gaseous CO2 exits the refrigeration chamber, thereby pre-cooling the liquid CO2 prior to the liquid CO2 exiting the at least one conduit of the heat exchanger and entering the refrigeration chamber.
7. A refrigeration process, comprising supplying liquid CO2 into a refrigeration chamber, flashing the liquid CO2 into gaseous CO2 and solid CO2 to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO2 from the refrigeration chamber, wherein the liquid CO2 is the second fluid passing through the at least one conduit of the heat exchanger of claim 1 prior to entering the refrigeration chamber and the gaseous CO2 is the first fluid passing through the shell of the heat exchanger after exiting the refrigeration chamber when the valve is in the closed position and the movable upper duct portion and lower duct portion are in their open positions, thereby pre-cooling the liquid CO2 prior to entering the refrigeration chamber.
8. The process of claim 7, wherein the liquid CO2 enters the at least one conduit at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the at least one conduit at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.), wherein pressure of the liquid CO2 is substantially the same at entry and exit of the at least one conduit of the heat exchanger.
9. The process of claim 8, wherein the pressure of the liquid CO2 as it passes through the heat exchanger is about 239 psig to about 300 psig.
10. The process of claim 7, wherein the gaseous CO2 enters the shell of the heat exchanger at about −90° F. and about atmospheric pressure and exits the shell at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.
11. The process of claim 7, wherein greater than about 48% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber.
12. The process of claim 7, wherein at least about 55% of the liquid CO2 is converted into solid CO2 upon flashing within the refrigeration chamber.
13. The process of claim 7, further comprising opening the valve and closing the movable upper duct portion and the movable lower duct portion, whereby the gaseous CO2 flows substantially through the central duct portion.
14. The process of claim 13, further comprising opening the shell to access the at least one conduit.
15. The process of claim 14, further comprising at least one of cleaning, sanitizing or maintaining at least a portion of the at least one conduit.
Type: Application
Filed: May 25, 2010
Publication Date: Jun 2, 2011
Inventors: Stephen A. McCormick (Warrington, PA), Michael D. Newman (Hillsborough, NJ)
Application Number: 12/786,859
International Classification: F25J 1/02 (20060101); F28D 7/02 (20060101); F25J 1/00 (20060101);