Patent Publication Number: US-2016223245-A1

Title: Refrigerator having cooling air circulating structure for preventing frost

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY 
     The present application is related to and claims priority under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2015-0016144, filed on Feb. 2, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates generally to a refrigerator, and more particularly to a refrigerator having a cooling air circulating structure, which prevents frost from being formed in a storage chamber inside a refrigerator main body. 
     BACKGROUND 
     In general, a refrigerator includes a refrigerator main body including a freezing chamber and a refrigerating chamber, doors installed in front of the refrigerator main body to open or close front openings of the freezing chamber and the refrigerating chamber, and a cooling system composed of a compressor, a condenser, and an evaporator. 
     Referring to  FIG. 1 , a refrigerator in the related art includes a cabinet portion  1  that is composed of an inner case and an outer case, and a thermal insulation material fills between the inner case and the outer case. In this case, a heat exchanger  3  is positioned in a space of a storage chamber on a front surface of the inner case of the cabinet, and cooling air is supplied to the storage chamber through an air duct  2  that is connected to the heat exchanger  3 . The heat exchanger  3  is provided with a pipe that is bent in zigzag and a plurality of heat dissipation fins formed on an outside of the pipe. In this case, an air blowing fan  4  is installed adjacent to an upper side of the heat exchanger  3 . 
     A cooling air flow of the refrigerator in the related art as described above is as follows. If the air blowing fan  4  is driven, air in the storage chamber  5  on the inside of the cabinet portion  1  is sucked into an inlet port  6  of the air duct  2 . The air that flows into the air duct  2  comes in contact with the heat exchanger  3  to be cooled, and then flows to the side of the air blowing fan  4 . The air that has passed through the air blowing fan  4  moves to an upper side of the cabinet portion  1  along the air duct  2 , and then is discharged to the storage chamber  5  through a plurality of discharge ports  7  that communicate with the storage chamber. 
     However, in the refrigerator in the related art as described above, since a flow path for air cooling is formed in the air duct  2  with a short distance that corresponds to the height of the heat exchanger  3  arranged on a lower portion of the air duct  2 , it is difficult to effectively cool the storage chamber  5 , and thus it is not easy to prevent frost that is formed on an inner wall of the storage chamber  5 . Accordingly, in the refrigerator in the related art having low cooling efficiency as described above, a defrost heater that is positioned at a lower end of the heat exchanger  3  is operated to prevent the frost from being formed in the storage chamber  5 , and in this case, a large amount of used power (such as about 100 to 200 W) is consumed. 
     Further, in the case of the refrigerator in the related art having a plate type heat exchanger, the heat exchanger is fixedly installed in close contact with one surface of the air duct. In this case, the air that flows from the storage chamber to the air duct is primarily cooled through the heat exchanger and then is discharged again to the storage chamber. Accordingly, in the same manner as the above-described refrigerator in the related art using the fin type heat exchanger, the refrigerator in the related art having the plate type heat exchanger has low heat exchanging efficiency, and thus is unable to meet consumer expectations. 
     SUMMARY 
     To address the above-discussed deficiencies, it is a primary object to provide a refrigerator, which prevents frost from being formed on an inner wall of a storage chamber and minimize power that is used to prevent the frost. 
     A refrigerator is provided that improves cooling efficiency through providing of an air flow path so as to perform cooling at least twice in a heat exchanger. 
     In a first example, a refrigerator is provided. The refrigerator includes a refrigerator main body including a storage chamber and hinge-connected with a door that opens or closes the storage chamber. The refrigerator also includes a heat exchanging chamber arranged on one side of the storage chamber along the storage chamber. The refrigerator includes a heat exchanger having a predetermined thickness that is arranged in the heat exchanging chamber. The refrigerator also includes an air circulating unit configured to circulate cooling air in the storage chamber and the heat exchanging chamber The heat exchanging chamber includes a cooling air discharge flow path formed on a front surface of the heat exchanger, and a cooling air suction flow path formed on a rear surface of the heat exchanger. 
     The cooling air discharge flow path communicates with the storage chamber through at least one cooling air discharge port, and the cooling air suction flow path communicates with the storage chamber through at least one cooling air suction port. The cooling air suction port is set in a position that is lower than the cooling air discharge port. The refrigerator further includes a defrost water draining portion arranged on a lower side of the heat exchanging chamber to collect and discharge defrost water that is generated in the heat exchanging chamber. The cooling air suction flow path communicates with the defrost water draining portion. The heat exchanger can be of a plate type. In this case, the heat exchanger can be partially bent. The storage chamber and the heat exchanging chamber are formed in a cabinet portion that is arranged inside the refrigerator main body. 
     The refrigerator further includes a duct assembly arranged in a rear of the cabinet portion. The duct assembly includes a front panel positioned on the cabinet portion side and a rear panel configured to open the heat exchanging chamber. The heat exchanger is spaced apart from an inner surface of the rear panel by a plurality of spacers. The cooling air discharge flow path is positioned between the front panel and a front surface of the heat exchanger, and the cooling air suction flow path is positioned between a rear surface of the heat exchanger and the rear panel. 
     The refrigerator further includes at least one plate type additional heat exchanger arranged in the heat exchanging chamber. The heat exchanger and the additional heat exchanger are arranged in parallel to be spaced apart from each other. The additional heat exchanger is arranged between the heat exchanger and the rear panel. The air circulation unit is arranged on a boundary between the cooling air discharge flow path and the cooling air suction flow path. The air circulation unit includes an inlet port configured to communicate with the cooling air suction flow path and an injection port configured to communicate with the cooling air discharge flow path. The injection port is smaller than the inlet port. A defrost heater is arranged in front of the heat exchanger in the heat exchanging chamber. 
     In a second example, a refrigerator is provided. The refrigerator includes a storage chamber. The refrigerator also includes a heat exchanging chamber configured to communicate with the storage chamber in a rear of the storage chamber. The refrigerator further includes a plate type heat exchanger arranged in the heat exchanging chamber. The refrigerator includes and an air circulating unit configured to compulsorily circulate cooling air between the storage chamber and the heat exchanging chamber. The heat exchanging chamber includes a cooling air discharge flow path formed on a front side of the heat exchanger and a cooling air suction flow path formed on a rear surface of the heat exchanger, and by means of the air circulating unit, the air that flows into the heat exchanging chamber passes through the cooling air suction flow path to be primarily heat-exchanged, and then passes through the cooling air discharge flow path to be secondarily heat-exchanged. 
     In a third example, a refrigerator is provided. The refrigerator includes a refrigerator main body. The refrigerator also includes a cabinet portion arranged inside the refrigerator main body and provided with a storage chamber and a heat exchanging chamber. The refrigerator further includes a door hinge-connected to the refrigerator main body to open or close the storage chamber. The refrigerator includes a plate type heat exchanger arranged in the heat exchanging chamber and partitioning a cooling air discharge flow path and a cooling air suction flow path configured to communicate with the storage chamber. The refrigerator also includes an air circulating unit configured to receive cooling air from the cooling air suction flow path and to discharge the cooling air to the cooling air discharge flow path. The cooling air suction flow path is formed on a rear side of the heat exchanger to primarily cool the air that is received from the storage chamber. The cooling air discharge flow path is formed on a front side of the heat exchanger to secondarily cool the air that is supplied from the air circulating unit. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  is a side cross-sectional view illustrating an example cooling air flow path formed in a refrigerator according to this disclosure; 
         FIG. 2  is a perspective view illustrating an example interior of a refrigerator according to this disclosure; 
         FIG. 3  is a perspective view illustrating an example front part of a first cabinet portion installed in a main body of a refrigerator according to this disclosure; 
         FIG. 4  is a side cross-sectional view illustrating an example first cabinet portion according to this disclosure; 
         FIG. 5  is a perspective view illustrating an example rear part of the first cabinet portion according to this disclosure; 
         FIG. 6  is an exploded perspective view illustrating example configurations of a heat exchanging chamber of the first cabinet portion and a plate type heat exchanger arranged in the heat exchanging chamber according to this disclosure; 
         FIG. 7  is an exploded perspective view illustrating an example air circulating unit arranged in a first cabinet portion according to this disclosure; and 
         FIG. 8  is a cross-sectional view illustrating an example of a plurality of heat exchangers arranged in a heat exchanging chamber of a first cabinet portion according to this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 8 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged electronic device and refrigeration device. 
     Further, although the present disclosure includes configurations that are normally provided in a refrigerator to form a refrigeration cycle, such as a compressor, a condenser, an expansion valve, and various kinds of control-related configurations for controlling freezing and refrigerating functions. In addition, although it is exemplified that a refrigerator has two storage chambers and two doors for opening/closing the respective storage chambers, the present disclosure is not limited thereto, but is also applied to a refrigerator having one storage chamber and one door. A refrigerator  10  according to an embodiment of the present disclosure includes a refrigerator main body  20 , first and second doors  41  and  42 , first and second cabinet portions  61  and  62 , a duct assembly  70 , a heat exchanger  80 , an air circulating unit  90 , and a defrost heater H. 
     Referring to  FIG. 2 , the refrigerator main body  20  includes first and second storage chambers S 1  and S 2  provided therein to keep food that is wrapped or contained in receptacles frozen or refrigerated. The first storage chamber S 1  is to keep vegetables or food refrigerated with freshness, and the second storage chamber S 2  is set to a temperature that is lower than the temperature of the first storage chamber to keep food frozen. 
     The first and second storage chambers S 1  and S 2  is partitioned by a plurality of shelves  23   a  and  23   b , and a plurality of drawers for accommodating vegetables or fruits therein is provided on lower sides thereof. The drawers  25   a  and  25   b  are made of transparent or semitransparent material, such as plastic or glass, so that stored items inside the drawers are seen. The first and second doors  41  and  42  are hinge-connected to both sides of the refrigerator main body  20  to open/close the first and second storage chambers S 1  and S 2 . A plurality of accommodation portions  44   a  and  44   b  are provided on inner surfaces thereof. 
     The first and second cabinet portions  61  and  62  are arranged inside the refrigerator main body  20 , and the first and second storage chambers S 1  and S 2  as described above are formed therein. Further, each of the first and second cabinet portions  61  and  62  is provided with a heat exchanging chamber and a heat exchanger arranged in the heat exchanging chamber. Since the first and second cabinet portions  61  and  62  have substantially the same structure, only the structure of the first cabinet portion  61  will be hereinafter described with reference to  FIGS. 3 to 7 . 
     Referring to  FIGS. 3 and 4 , the first cabinet portion  61  includes the first storage chamber S 1  of which the front is open, and a heat exchanging chamber  77  arranged on the rear side of the first storage chamber S 1 . Further, the first cabinet portion  61  includes a duct assembly  70  that forms the heat exchanging chamber  77 . In this case, the duct assembly  70  includes a front panel  71  and a rear panel  73 . On both sides of the first storage chamber S 1 , a pair of support projections  23   c  for supporting the shelf  23   a  and a pair of support grooves  23   d  for supporting the drawer  25   a  is formed to project. 
     The front panel  71  partitions the first storage chamber S 1  and the heat exchanging chamber  77 , and includes a plurality of air discharge ports  71   a  formed thereon to supply cooling air that is discharged from the heat exchanging chamber  77  to the first storage chamber S 1  and a plurality of air suction ports  71   b  formed thereon to guide the cooling air that is supplied to the first storage chamber S 1  again to the heat exchanging chamber  77 . The plurality of air discharge ports  71   a  communicate with the first storage chamber S 1  and the heat exchanging chamber  77  (specifically, cooling air discharge flow path P 1  formed in the heat exchanging chamber  77  described here). The plurality of air discharge ports  71   a  are arranged along the front panel  71  at predetermined intervals in upper and lower directions. 
     The plurality of air suction ports  71   b  communicate with the first storage chamber S 1  and the heat exchanging chamber  77  (specifically, cooling air suction flow path P 2  formed in the heat exchanging chamber  77  to be described later). The air suction port  71   b  is positioned on the lower side than the air discharge port arranged on the lowermost side among the plurality of air discharge ports  71   a . The air suction port  71   b  is positioned in consideration of the property of the cooling air that goes down, and naturally guides the cooling air that is gathered after cooling the first storage chamber S 1  into the heat exchanging chamber  77 . In this embodiment, it is described that only one air suction port  71   b  is formed. However, this is merely exemplary, and a plurality of air suction ports is formed. Further, the front panel  71  includes a projection portion  72   a  formed thereon to come in close contact with an upper end of a front surface of the heat exchanger  80 , and a partition  72   a  formed thereon to come in close contact with a lower end of the front surface of the heat exchanger  80 . 
     Referring to  FIG. 7 , the projection portion  72   a  includes an injection port  72   b  formed thereon to inject the cooling air from the air circulating unit  90  to the cooling air discharge flow path P 1 . The partition  72   c  separates the cooling air discharge flow path P 1  and the cooling air suction flow path P 2  from each other. 
     Referring to  FIG. 5 , one end portion of the rear panel  73  of the duct assembly  70  is hinge-engaged with the first cabinet portion  61 , and the other end portion thereof is locked by a plurality of locking portions R. Further, the rear panel  73  is coupled to the first cabinet portion  61  by a plurality of fastening screws. 
     Referring again to  FIG. 4 , the plate type heat exchanger  80  is arranged in the heat exchanging chamber  77  with a length that substantially corresponds to the first storage chamber S 1 . Further, the cooling air discharge flow path P 1  and the cooling air suction flow path P 2  that are partitioned by the heat exchanger  80  are provided in the heat exchanging chamber  77 . The cooling air discharge flow path P 1  and the cooling air suction flow path P 2  communicate with each other in series through the air circulating unit  90 . 
     The cooling air discharge flow path P 1  is formed between the front panel  71  and the front surface of the heat exchanger  80 , and supplies the cooling air to the first storage chamber S 1  through the plurality of air discharge ports  71   a  formed on the front panel  71 . The cooling air suction flow path P 2  is formed between the rear surface of the heat exchanger  80  and the inner surface of the rear panel  73 , and intakes the air of the first storage chamber S 1  through the plurality of air suction ports  71   b  formed on the front panel  71  to guide the air to the air circulating unit  90 . 
     The cooling air suction flow path P 2  has a lower portion  77   a  that is opened to discharge defrost water that is generated by the heat exchanger  80 . In this case, a defrost water draining portion  78  for collecting and discharging the defrost water is formed on the lower portion of the cooling air suction flow path P 2 . The defrost water draining portion  78  forms the lower part of the first cabinet portion  61 , and the inside thereof is in the form of an inverted triangle. A defrost water discharge port  78   a  is formed at the lowermost end of the defrost water draining portion  78 . 
     According to the present disclosure, the heat exchanging flow path for cooling the air in the heat exchanging chamber  77  is formed longer than that of the refrigerator in the related art, and the air that flows from the first storage chamber S 1  to the cooling air suction flow path P 2  flows to the air circulating unit  90 . In this case, the air is primarily cooled by the heat exchanger  80 , and the air then secondarily cooled the heat exchanging chamber passes through the cooling air suction flow path to be primarily heat-exchanged, and the air that flows through the cooling air discharge flow path P 1  is secondarily cooled. Accordingly, the flow path that cool the air using a single heat exchanger is maximized, and thus the cooling efficiency is maximized while minimizing power consumption for the heat exchange. 
     Referring to  FIG. 6 , the heat exchanger  80  is a plate type evaporator. Since the length of the first cabinet portion  61  in front/rear direction is reduced, and thus the front/rear width of the refrigerator  10  is maintained slim as a whole. The heat exchanger  80  as described above is formed of two thin metal plates, and a coolant flow path through which a coolant flows is formed on one side of the heat exchanger  80 . The coolant flow path includes a discharge port formed on one side thereof to intake the coolant and a discharge port formed on the other side thereof to discharge the coolant. Further, the heat exchanger  80  is formed to be partially bent in accordance with the shape of the heat exchanging chamber  77  or the shape of the cabinet portion. 
     In addition, although not illustrated in the drawing, a plurality of heat dissipation fins is formed on the front surface and the rear surface of the heat exchanger  80 , and the coolant flow path is formed through attaching of a pipe to a metal plate. The heat exchanger  80  is fixed to a plurality of first and second spacers  69   a  and  69   b  that are fixed to the inner surface of the rear panel  73 . In this case, the heat exchanger  80  is spaced apart for a predetermined distance from the rear panel  73  by the first and second spacers  69   a  and  69   b.    
     The pair of first spacers  69   a  is coupled to both sides of the rear panel  73  along the length direction of the rear panel  73 . In this case, the pair of first spacers  69   a  forms the cooling air suction flow path P 2  together with the rear panel  73  and the heat exchanger  80 . The pair of second spacers  69   b  is to fix the rear panel  73  more firmly, and is coupled to an upper end and a lower end of the rear panel  73 . The plurality of first and second spacers  69   a  and  69   b  have the same thickness, and through adjustment of this thickness, the volume of the cooling air suction flow path P 2  is set as desired by a user. 
     In this embodiment, it is exemplified that one plate type heat exchanger  80  is provided. However, as illustrated in  FIG. 7 , a plate type additional heat exchanger  180  is further provided in the heat exchanging chamber  77  of the first cabinet portion  161 . In this case, the additional heat exchanger  180  is arranged between the heat exchanger  80  and the rear panel  73  in parallel to the heat exchanger  80 . Since the additional heat exchanger  180  is arranged in the cooling air suction flow path P 2 , primary cooling efficiency of the air that flows in from the first storage chamber S 1  is greatly improved. In the case where the additional heat exchanger  180  is arranged in the heat exchanging chamber  77 , predetermined intervals are maintained between the heat exchanger and the additional heat exchanger  180  and between the additional heat exchanger  180  and the rear panel  73  by the plurality of spacers. 
     Referring to  FIG. 8 , the air circulating unit  90  is arranged in a portion that is a boundary between the cooling air discharge flow path P 1  and the cooling air suction flow path P 2 . Accordingly, the air circulating unit  90  intakes the primarily cooled air through the cooling air suction flow path P 2  and supplies the air to the cooling air discharge flow path P 1 . The air circulating unit  90  as described above includes a fan  91 , a support housing  93 , and a motor  95 . 
     The fan  91  is rotatably arranged on the upper side of the front panel  71 , and is arranged on the side that communicates with the cooling air discharge flow path P 1 . In this case, the fan  91  is replaced by an impeller. The support housing  93  is separably coupled to the upper side of the front panel  71  by a plurality of fastening screws to cover the fan  91 . Further, the support housing  93  includes an inlet port  93   a  through which the air from the cooling air suction flow path P 2  flows. In this case, the inlet port  93   a  has a size that is larger than the size of the injection port  72   b  as described above. Since the injection port  72   b  is formed to be smaller than the inlet port  93   a , the discharge speed becomes high. 
     The motor  95  is connected to the fan  91  through a driving shaft to rotate the fan  91 , and is fixed to the support panel  97  that is coupled to the support housing  93 . In this case, the motor  95  is arranged on an opposite side of the fan  91  on the basis of the support housing  93 . The support panel  97  has a hole  97   a  formed thereon to correspond to the support housing  93 , and includes a support  97   b  arranged in the periphery of the hole  97   a  to fix the motor  95  thereto. The cooling air flow in the refrigerator  10  as configured above according to an embodiment of the present disclosure will be described. 
     First, as the motor  95  is driven, the fan  91  is rotated to form negative pressure in the cooling air suction flow path P 2 . Accordingly, the air of the first storage chamber S 1  flows into the cooling air suction flow path P 2  through the air suction port  71   b . The air that flows into the cooling air suction flow path P 2  comes in contact with the rear surface of the heat exchanger  80  to be primarily cooled in the process in which the air flows to the side of the air circulating unit  90  along the cooling air suction flow path P 2 . The primarily cooled air flows into the air circulating unit  90  through the inlet port  93   a , and then is discharged again to the cooling air discharge flow path P 1  through the injection port  72   b  by the rotation of the fan  91 . 
     The air that flows into the cooling air discharge flow path P 1  comes in contact with the front surface of the heat exchanger  80  to be secondarily cooled as flowing in a lower direction along the cooling air discharge flow path P 1 . As described herein, the air that is twice cooled is discharged to the first storage chamber S 1  through the plurality of air discharge ports  71   a  to cool food accommodated in the first storage chamber S 1 . According to the present disclosure as described herein, by maximizing flow paths (cooling air discharge flow path P 1  and cooling air suction flow path), which cools the air using the single heat exchanger  80 , the cooling efficiency is maximized while minimizing the power consumption for the heat exchange. 
     Further, the refrigerator  10  according to an embodiment of the present disclosure removes frost through cooling air circulation, and in addition, includes a defrost heater H to remove the frost that occurs on the surface of the heat exchanger  80 . The defrost heater H is installed on the rear surface of the front panel  71  of the duct assembly as shown in  FIGS. 7 and 8 . In this case, the defrost heater H is installed even on the partition  72   c  that corresponds to the lower end portion of the front panel  71 . Further, the installation position of the defrost heater H is not limited to the rear surface of the bottom panel  71  as described herein, but is positioned in front of the heat exchange  80  to come in contact with the heat exchange  80  or is arranged in a position that is spaced apart for a predetermine distance from the heat exchanger  80 . 
     As described above, the defrost heater H is a thin pipe type heater so that it is arranged in a narrow space that forms the cooling air discharge flow path P 2  between the front panel  71  and the front surface of the heat exchanger  80 . The refrigerator  10  according to an embodiment of the present disclosure removes the frost that occurs on the heat exchanger  80  together with the defrost heater H and the fan  91  of the air circulating unit  80 . In this case, defrosting is performed in first to third defrost mode using the defrost heater H and the fan  91 . The fan  91  is used for defrosting while cooling air circulation is not performed in the refrigerator  10 . On conditions of the first to third defrost modes, the defrosting is performed by simultaneously or selectively driving at least one of the defrost heater H and the fan  91  as shown in Table 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Mode 
                 Defrost Heater 
                 Fan 
               
               
                   
                   
               
             
            
               
                   
                 First Defrost Mode 
                 ON 
                 ON 
               
               
                   
                 Second Defrost Mode 
                 OFF 
                 ON 
               
               
                   
                 Third Defrost Mode 
                 ON 
                 OFF 
               
               
                   
                   
               
            
           
         
       
     
     In the first defrost mode, in the case where the defrost temperature of the heat exchanger  80  and the inside of the duct assembly  70  is lower than a required fresh room temperature, the defrosting is performed by simultaneously turning on the defrost heater H and the fan  91  to meet all the defrosting states and peripheral conditions. In this case, it is preferable that the operating time of the first defrost mode is about 20 to 30 minutes. 
     In the second defrost mode, in the case where the defrost temperature of the heat exchanger  80  and the inside of the duct assembly  70  is lower than the required fresh room temperature and the defrosting state is not serious (such as a low peripheral temperature and high peripheral temperature are equal to or lower than 5° C. and equal to or higher than 20° C.), the defrosting is performed by turning on only the fan  91  while turning off the defrost heater H. In this case, it is preferable that the operating time of the second defrost mode is about 15 to 30 minutes. 
     In the third defrost mode, in the case where the defrost temperature of the heat exchanger  80  and the inside of the duct assembly  70  is higher than the required fresh room temperature (such as in a case where the defrost heater H comes in direct contact with the heat exchanger  80  or the power of the defrost heater H is high), the defrosting is performed by turning on only the defrost heater H while turning off the fan  91 . In this case, it is preferable that the operating time of the third defrost mode is about 20 to 60 minutes. The operating time of the defrost heater H and the fan  91  in the first to third defrost modes as described herein is variously set in accordance with the capacity of the refrigerator  10  or the size of the heat exchanger  80 . 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.