Abstract:
A method and apparatus facilitate lowering the temperature of a cooling module positioned in heat exchange relation to a loaded container to be maintained at a low temperature. The module establishes convective air flow in heat exchange relation to the load without the use of forced air circulation. The module is self-contained and externally accessible to supply water and liquid CO 2  to the module interior. Expansion and change in state of the liquid CO 2  lowers the temperature of a water ice and CO 2  snow mixture in the module. By continuing inflow of CO 2  after terminating inflow of water, the mixture can be cooled from about −76° F. to about −117° F. Convective air flow in heat exchange relation to the module walls circulates cooling air, thereby eliminating any direct contact of products with the liquid CO 2  or CO 2  snow formed by the expanding refrigerant.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is directed to a method and apparatus for lowering the temperature of a mixture of water ice and CO 2  snow for cooling storage and transport containers and the like. The present invention controls the mixing of the water and liquid CO 2  in a cooling module in heat exchange relation to air circulating in a container having a load of products therein to maintain a desired temperature of the load during storage or transport of such products without the use of air circulating fans or other devices for assisting air circulation. The cooling module is associated with the interior of the container in a manner to establish convection air flow in heat exchange relation to the cooling module and the load of products in the container. The temperature of the water ice and CO 2  snow is controlled by maintaining the inflow of liquid CO 2  into the mixture beyond cessation of the inflow of water, so as to reduce the temperature of the water ice and CO 2  snow mixture from about −76° F. to about −117° F. 
         [0003]    2. Description of the Related Art 
         [0004]    The use of an expandable liquid refrigerant to cool or freeze products and the like during storage and transport is well known. Liquid carbon dioxide (CO 2 ) has been used successfully for many years in refrigeration by discharging pressurized liquid CO 2  through a nozzle or nozzles and expanding the CO 2  to reach a triple point condition where liquid, gaseous, and solid phases of CO 2  can coexist and flash to a mixture of CO 2  in a gaseous phase and particles of CO 2  snow. My below-listed prior U.S. patents relate to cooling of products in a load receiving container such as a truck body, railroad car, shipping container or the like which utilize liquid CO 2  as an expandable refrigerant that changes state: 
         [0000]    
       
         
               
             
           
               
                   
               
             
             
               
                 4,376,511 
               
               
                 4,381,649 
               
               
                 4,462,423 
               
               
                 4,502,293 
               
               
                 4,640,460 
               
               
                 5,092,133 
               
               
                 5,154,064 
               
               
                 5,259,199 
               
               
                 5,295,368 
               
               
                 5,398,522 
               
               
                 5,505,055 
               
               
                 5,775,111 
               
               
                 6,109,058 
               
               
                 6,182,458 
               
               
                   
               
             
          
         
       
     
         [0005]    While such prior systems have functioned successfully, some concern has arisen regarding the advisability of direct contact between CO 2  snow, liquid CO 2 , and water and the contained products and with loading and unloading personnel, the truck operators, and other personnel that may come into contact with the products. Also, if water and liquid CO 2  are combined to vary the cooling temperature in a container, a residue, such as water, may be left on the products and on the interior of the container when the load is removed. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to overcome the drawbacks of prior systems, the present invention utilizes a cooling module in heat exchange relation to a load receiving container. The cooling module is positioned in a manner to enable convective circulation of air in heat exchange relation to the exterior of the module and the products loaded into the container without the use of air fans or other air circulation devices, and without any direct contact of the coolant within the module with the load located in the container. 
         [0007]    The cooling module is self-contained and provided with externally accessible pipes to supply pressurized liquid refrigerant and water with expansion and change in state of the refrigerant cooling the module and/or forming ice and CO 2  snow within the interior of the module. Convective air flow in heat exchange relation to the surface of the module circulates cooling air in heat exchange contact with the products, thereby eliminating any direct contact of the expanding refrigerant or water ice with the storage products, and without exposing personnel engaged in loading and unloading container loads or transporting such loads from contact with the refrigerant or water ice. However, when using convective air flow to maintain the products at a desired temperature, the air must be cooled to a temperature below that which is normally obtained by convective flow of air in heat exchange relation to a cooling module. 
         [0008]    More specifically, the convective circulation of the air in accordance with the present invention is achieved because of the very cold −117° F. temperature at the cooling module which causes the air to fall to the floor. At the same time, hot air adjacent to the ceiling and above the products being cooled is drawn down for cooling, while the already cooled air is transported along the floor and underneath the products being cooled, away from the cooling module to the opposite end of the container. From there, the air rises to the ceiling and is drawn back along the ceiling, again above the products being cooled, to the cooling module, thus completing the convective air circulation. 
         [0009]    It is therefore an object of the present invention to provide a cooling module in which the time period for the inflow of liquid CO 2  is extended for about 15-25 percent more than the time period for inflow of water. This extended CO 2  inflow unexpectedly results in a reduction in temperature of the water ice and CO 2  snow mixture in the cooling module from about −76° F. to about −117° F., thereby ensuring that air in heat exchange relation to the cooling module will maintain the products at a desired lowered temperature. 
         [0010]    The load receiving container includes air circulation passageways around the exterior surfaces of the module and the interior surfaces of the container. Such passageways enable convective air circulation in heat exchange relation to the exterior surfaces of the module and in heat exchange relation to products within the container. This convective air circulation will maintain a desired low temperature within the interior of the container without any direct contact between the load in the container and the heat extracting coolant within the module, and without the use of air moving fans or other mechanical air circulating devices. 
         [0011]    Another object of the present invention is to provide a cooling module for a container in which the interior of the module is accessible from a position exteriorly of the container. The access from the exterior facilitates the introduction of liquid water and liquid CO 2 . The liquid water and expanding CO 2  initially produce a water ice block in the module and continuation of the liquid CO 2  flow produces CO 2  snow on top of the ice block. Thus, the cooling characteristics of the cooling module can be controlled. 
         [0012]    Yet another object of the present invention is to provide a cooling module for a load receiving container in accordance with the preceding objects which will conform to conventional forms of manufacture, be of simple construction and easy to use so as to provide an apparatus that will be economically feasible, long lasting, and relatively trouble free in operation. 
         [0013]    These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numbers refer to like parts throughout. The drawings are intended to illustrate the invention and are not necessarily to scale. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a transport trailer having a cooling module positioned therein in accordance with the present invention. 
           [0015]      FIG. 2  is an enlarged view of the cooling module shown in  FIG. 1 , showing certain internal components in dashed lines. 
           [0016]      FIG. 3  is a side view of the trailer and cooling module shown in  FIG. 1 , illustrating the load space and air flow passageways according to the present invention. 
           [0017]      FIG. 4  is a vertical sectional view of the trailer taken along section line  4 - 4  of  FIG. 3  illustrating details of the cooling module and the container. 
           [0018]      FIG. 5  is a vertical sectional view of the cooling module taken along section line  5 - 5  of  FIG. 2 . 
           [0019]      FIG. 6  is a vertical sectional view of the cooling module and components thereof taken along section line  6 - 6  of  FIG. 5 . 
           [0020]      FIG. 7  is a vertical sectional view of the trailer and cooling module taken along section line  7 - 7  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Although only one preferred embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the preferred embodiments, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
         [0022]    Referring specifically to the drawings, the present invention is incorporated in a standard insulated trailer  12  having wheels  13 . The trailer  12  includes an insulated bottom wall  14 , an insulated top wall or roof  16 , insulated side walls  18 , an insulated front end wall  20  and a rear end wall  22  usually formed by a pair of pivotal doors or, in some instances, a single pivotal door, a roll up door, or the like. The insulated walls While          connection with a transporting trailer, it will be understood by those skilled in the art that the present invention is applicable to any insulated load receiving container such as a trailer, truck body, railroad car, shipping container, or the like, and the use of “trailer” is intended to encompass all such storage and transporting structures for cooling products. Further, the specific dimensional characteristics of the trailer may vary but should comply with established requirements, regulations and rules when used in an over-the road truck body or trailer truck body and comply with standardized international requirements when used as a shipping container. 
         [0023]    The floor of the trailer  12  includes a plurality of inverted channel-shaped metal deck members  39 , which are anchored in any suitable manner and are typically included in any conventional refrigerated trailer. The deck members  39  cooperate with the bottom of a load positioned in a load space, generally designated by reference numeral  100 , to form longitudinal bottom ducts or lower air passages  40 . As is known by those skilled in the art, air enters the passageways  40  adjacent the front and moves longitudinally from the front of the trailer to the rear of the trailer under the load in the load space. 
         [0024]    In accordance with the present invention, a cooling module, generally designated by reference number  10 , is positioned on the trailer floor adjacent the front end of the trailer  12  and in heat exchange relation to the load space  100 . The module  10  is preferably attached to the trailer front wall  20  by suitable brackets or the like. The positioning of the cooling module  10  adjacent to the front end wall  20  of the trailer  12  and in front of the load space  100  is preferred due to the insulation of the trailer walls and the distance from the trailer doors in the rear wall  22 . Alternatively, the module  10  may be positioned externally of the trailer  12  and provided with insulated air passageways or ducts in convection air flow communication around the load space  100  as hereinafter described. 
         [0025]    The load space  100  for receiving the load is defined by a front partition  32 , a top partition  34 , the floor channels  39 , interior partitions  24  of side walls  18  and an open back  37 . When installed in the front of the trailer  12 , the module  10  is supported on channels  39  in spaced relation between the trailer front wall  20  and the load space front partition  32 , above trailer bottom wall  14 , below the trailer top wall  16  and along each of the trailer side walls  18 , respectively. These spaced relationships provide a top passageway  26  between a top wall  23  of module  10  and the trailer top wall  16  and a vertical passageway  28  between the trailer front wall  20  and module front wall  19 . A vertical passageway  30  is also formed between module back wall  25  and container front partition  32 , vertical passageways  70  are formed on both ends  72  of module  10  spaced from the trailer side walls  18 , and horizontal passageway  42  extends underneath module bottom wall  21 . Preferably, the walls of module  10  are spaced approximately one inch away from their respective opposite walls inside the trailer. 
         [0026]    The load space front partition  32  has its upper end connected to a forward end of the load space horizontal top partition  34 , which is spaced below the inside of trailer top wall  16  to form a longitudinal upper duct or passageway  36 . The front partition  32  and top partition  34  extend completely across the width of the trailer  12 , and top partition  34  extends along the full length of trailer  12 , as illustrated in  FIG. 4 . The top partition  34  is preferably constructed of a sheet metal having a high heat conductivity, such as aluminum, or canvas, with downturned edge flanges  35  fastened to and supported by trailer side walls  18  (see  FIG. 4 ). The front partition  32  is preferably constructed of sheet metal or plywood with flanges or attaching strips  43  fastened to and supported by the trailer side walls  18 . 
         [0027]    As illustrated in  FIGS. 3 ,  4  and  7 , the upper duct or passageway  36  communicates with the passageways  26 ,  28 ,  30  and  70 , as well as the forward end portion  42  of the ducts  40  which extends in underlying relation to the module  10 . Thus, warm air can move toward the front of the trailer  12  through upper passageway  36  with a substantially equal amount of air passing downwardly through the passageways  28 ,  30  and  70  into the lower passageway  42  and along ducts  40  toward the rear of the trailer  12 . At the rear of the trailer  12 , the air then moves upwardly along passageway  44  formed by vertical corrugation  46  usually provided on the inner surface of the door or doors forming end wall  22  for reentry into duct or passageway  36 . 
         [0028]    If the module  10  is to be mounted exteriorly of the trailer, an insulated housing encloses the module. Upper and lower insulated air passageways or ducts connect the insulated housing with air passageway  36  and ducts  40 , respectively, inside the trailer. The convective air flow follows the same flow paths as shown in  FIG. 3 . 
         [0029]    The top partition  34  which forms the upper duct or air passageway  36  and the passageway  36  extend completely across the trailer from one trailer side wall  18  to the other trailer side wall  18  to provide approximately a four inch high longitudinal passageway  36 . The rear of the trailer  12  is provided with conventional access doors  62  which may be a single pivotal door, two pivotal doors, a roll up door, or any other conventional closure structure with the interior surface of the doors being provided with vertical corrugations  46  to provide vertical passageways between a load within the load space  100  and the rearward end wall  22  of the container. 
         [0030]    In accordance with this invention, convective air circulation occurs as air which has been heated by passage in heat exchange relation to the products forming the load in load space  100  moves upwardly in space  44  and forwardly in passageway  36 . The warm air in heat exchange contact with the module  10  is cooled and moves downwardly in the passageways  28 ,  30  and  70  and then rearwardly in the bottom air passageways  42  and  40  with heating and upward movement of the air occurring at the rear end of floor passageways  40  past the load. The heating of the air passing through the load and cooling of the air in contact with the cooling module  10  maintain the above described convective air flow. 
         [0031]    The module  10  includes the necessary pipes  54  and  56  for selectively spraying variable amounts of water and liquid CO 2 , respectively, downwardly from the top of the module  10 . The pipes preferably include a vertical section  82  and a closed end horizontal section  84 . The lower ends of the vertical sections turn with a short horizontal section  86  which extends outside the module and are fitted with externally accessible valves  88 . The valves  88  for the respective water and liquid CO 2  are preferably mounted in the side wall  72  of the module  10  adjacent the front side wall access door  90  typically included in all conventional trailers. 
         [0032]    As shown in  FIGS. 2 and 6 , the horizontal sections  84  of pipes  54  and  56  are mounted side-by-side and suspended from the top  23  of module  10  by suitable brackets  92  or the like. The horizontal sections have downwardly facing holes  94  for spraying the water and CO 2  downwardly toward the bottom of module  10 . The liquid CO 2  expands out of its holes  94  into CO 2  snow and CO 2  gas which mix with the exiting water to form water ice. The water ice and CO 2  snow form as a solid ice block and CO 2  snow inside the module  10  causing all of the wall surfaces of the module  10  to cool to a desired low temperature. The low temperature of the module walls will, in turn, maintain convective air circulation in order to maintain a load in load space  100  at a desired cool temperature. 
         [0033]    A conventional pressure release flap valve  96  is located in a wall of the module  10 , preferably in the side wall opposite the side wall having the water and liquid CO 2  inlets  88  therethrough. The valve  96  relieves any pressure build up inside the module  10  and allows the gases and vapors to escape to the atmosphere surrounding the module  10 . The bottom or floor of the module  10  has holes  88 , preferably two, which serve as outlet drains to allow water from melting ice to drain out of the module when no longer operating to cool. Water draining from the module  10  can drain from the trailer  12  through any of the floor drains typically provided in the trailer floor, usually adjacent each corner (not shown). 
         [0034]    Liquid CO 2 , when expanded, can produce a temperature as low as approximately −117° F. within the trailer  12 . Frequently, ambient outside temperature reaches 100° F., resulting in a temperature differential of 217° F. Even with good insulation, a substantial heat loss can occur. By introducing water into the module along with liquid CO 2 , the water ice and CO 2  snow will mix to form a slush at a temperature of about −46° F. 
         [0035]    In the present invention, after the water ice and CO 2  snow mixture reaches a temperature of −76° F., water inflow is terminated. Unexpectedly, continuing inflow of liquid CO 2  for approximately 15-25 percent of the time period of inflow of water and CO 2  to reach a temperature of −76° F. results in a mixture of water ice and CO 2  snow at a substantially lower temperature. For example, if the time period to reach −76° F. is 1 hour, extending inflow of CO 2  for an additional 15-20 minutes lowers the temperature of the mixture to approximately −117° F., which enables module  10  to maintain the load in load space  100  at a desired low temperature of 0° F., or below, for at least several days. 
         [0036]    A typical insulated trailer  12  for use in accordance with the present invention is approximately 50 feet long, 8 feet wide and 8 feet high. Module  10 , in accordance with the present invention should have approximately a one inch clearance on all sides. Hence, the module would be almost 8 feet high, 8 feet wide and preferably about 2-3 feet thick. 
         [0037]    A typical cooling cycle for a trailer  12  and module  10  having sizes as above described would be the following. Water and liquid CO 2  from external sources would be fed to their respective pipes  54  and  56  through valves  88 , and out of their respective holes  94 , simultaneously for a period of approximately 50 minutes. The mixture of water and liquid CO 2  should form a solid block of ice filling approximately 75% of the module height and reaching a temperature of approximately −76° F. The water to pipe  54  is then discontinued by shutting its respective valve  88 , while liquid CO 2  continues to be fed to the module  10  for a period of approximately 10 or more minutes. During this extended inflow of CO 2 , CO 2  snow is formed on top of the ice block up to about 2 inches below pipes  84 . The temperature of the ice and CO 2  snow reduces to approximately −117° F. With this reduced temperature inside module  10 , the module  10  should be able to maintain a temperature inside the load space  100  of 0° F., or below, for a period of several days. 
         [0038]    The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.