Abstract:
The fan of a refrigeration machine operatively connected to a container box is operated in one direction during normal operation and is periodically operated in the opposite direction in order to reverse the direction of airflow to and from the container box so as to thereby promote a more uniform temperature distribution within the container box. A door is automatically closed when operating in the reverse direction so as to accelerate the airflow speed into the container box.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/151,016 entitled “Temperature Distribution Improvement in Refrigerated Container,” filed on Feb. 9, 2009. The content of this application is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to refrigerated containers and, more particularly, to a method and apparatus for obtaining a more uniform temperature distribution therein. 
       BACKGROUND OF THE INVENTION 
       [0003]    Refrigerated containers are used to transport perishable cargo that requires very tight temperature control. The industry standard today is to have the refrigeration machine mounted at one end of the container box. The air in the container box is drawn into the refrigeration machine by fans which then blow the warmer air through an evaporator coil, with the cooled air then passing back into the container box to cool the cargo. The common problem with this arrangement is that the cargo&#39;s temperature tends to be higher towards the back door of the container and away from the refrigeration machine. The main reason is due to poor airflow distribution from the front to the back of the container box, with airflow being reduced significantly toward the back door. As a result, the temperature of the cargo is generally higher as it extends toward the rear door. The problem is exacerbated by the fact that the typical perishable cargo gives off heat of its own. 
       DISCLOSURE OF THE INVENTION 
       [0004]    Briefly, in accordance with one aspect of the invention, the direction of the fan rotation is periodically reversed to thereby cause the direction of the airflow from and to the refrigerated container to be reversed to thereby improve the temperature distribution in the container box. 
         [0005]    By another aspect of the invention, a plenum is provided at the top of the container box and is closed during the reverse operation in order to increase the airflow speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a refrigerated container with the present invention incorporated therein. 
           [0007]      FIG. 2  is a schematic illustration thereof showing the airflow therein during normal operation. 
           [0008]      FIG. 3  is a graphic illustration of the temperature distribution therein during normal operation. 
           [0009]      FIG. 4  is a schematic illustration of the airflow pattern which results in a refrigerated container when operated in accordance with the present invention. 
           [0010]      FIGS. 5A and 5B  are perspective views of a door portion thereof during normal and reverse flow operation thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    A refrigerated container is shown generally at  11  as including a container box  12  having bottom and top sides  13  and  14  and front and rear ends  16  and  17 . The container box  12  is designed to temporarily hold perishable cargo as shown at  18 . 
         [0012]    At the front end  16  of the container box  12 , a refrigeration machine  19  is installed in such a manner as to fluidly communicate with the air in the container box  12  in order to cool that air for the purpose of refrigerating the cargo  18 . The refrigeration machine  19  includes a standard refrigeration circuit comprising, in serial flow relationship, a compressor, a condenser, an expansion device and an evaporator. It is by the flow of the return air from the container box  12  and through the evaporator, that the air in the container box  12  is cooled. Circulation of air through the evaporator and into and out of the container box  12  as shown in  FIG. 1  is caused by operation of a fan  21  within the refrigeration machine  19 . 
         [0013]    As will be seen in  FIG. 2 , the fan  21  is located near a top portion  22  of the refrigeration machine  19  which, during normal operation, acts to draw the return air forwardly along a top portion  23  of the container box  12  and through an open door  24 . The warm air is then blown through the evaporator coil  24  where the air is cooled, with the cooled air then being discharged from a lower portion  26  of the refrigeration machine  19 . From there, the cooled air flows rearwardly through a bottom portion  27  of the container box  12  as shown by the arrows. The cooler air rises upwardly through a t-bar floor as indicated by the upwardly extending arrows. 
         [0014]    The cooled air passes upwardly through the cargo  18  with heat being transferred thereto from the cargo  18 . The warmer air then continues upwardly to enter the top portion  23  of the container box  12  to complete the cycle. 
         [0015]    It should be recognized that as the cooled air travels rearwardly, it gradually becomes warmer such that when it reaches the rear end  17  it is at its higher temperature. Further, since the flow of air through the container box  12  relies on the momentum created by the fan  21  and the convection currents within the container box  12 , the velocity of flow will be reduced as its extends toward the rear wall  17 . For that reason, a substantial temperature gradient will exist both in the vertical direction and in the horizontal direction, within the container box  12 . Since the cargo is exposed to this distribution of air for long periods of time such as days or even weeks, the temperature of the cargo  18  within the container box reflects a similar temperature distribution. This cargo temperature distribution is shown in  FIG. 3 . Here it will be seen that the cooler cargo will be in the lower left portion of the container box and the warmer cargo will be at the upper right portion thereof. In fact, at the top and rear of the container box  12  there is a hot spot that may well impact the quality of the cargo. That is, the perishable cargo temperature distribution in a container determines the shelf life of the cargo. Thus, the shelf life of the cargo will be variable as indicated by the temperature distribution in  FIG. 3 . It is thus desirable to eliminate the hot spots and promote a more uniform temperature distribution within the container box  12 . This is accomplished by operation of the system as shown in  FIG. 4 . 
         [0016]    Here, the fan  21  is caused to operate in reverse so as to draw air through the evaporator coil  14  rather than blow air therethrough. This causes an associated reversal of airflow through the container box  12  as shown by the arrows. That is, the cooled air from the evaporator coil  24  passes upwardly through the fan  21  and into the top portion  22  of the refrigeration machine  19 . From there it passes through the opening  30  and into the top portion  23  of the container box  12  to then flow rearwardly and downwardly as indicated by the arrows. The cooled air passes through the cargo  18  and then downwardly into the bottom portion  27  of the container box  12  before returning forwardly to the bottom portion  26  of the refrigeration machine  19  to complete the cycle. This reversal of flow causes mixing of the air within the container box  12  so as to thereby promote a more uniform distribution. 
         [0017]    In order to increase the airflow speed, and thus the “throw”, during reverse flow operation, the door  25  is provided at the front end of the container top portion  23  as shown in  FIGS. 5A and 5B . That is, as shown in  FIG. 5A , during normal operation the return airflow causes the door  25  to open and allow the air to flow freely across the entire cross section of the top portion  23  as shown. However, in reverse flow operation, the flow of air will cause the door  25  to be moved to the closed position such that the opening  30  is of reduced cross section as shown in  FIG. 5B . This will, in turn, cause the velocity of the airflow therethrough to increase, which will provide better “throw” and further promote mixing. 
         [0018]    It is recognized that the blow-through operation of the fan  21  as shown in  FIG. 2  is more efficient then the draw-through approach as shown in  FIG. 4 . However, the time in which the fan  21  is operated in the reverse mode is relatively small compared with the time that it operates in the normal mode as shown in  FIG. 2 . A typical time cycle of normal and periodic reverse operation is shown in  FIG. 6 . 
         [0019]    While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.